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The Ring Nebula - Calar Alto Astronomical Observatory

Sunday, December 27, 2009

The Ring Nebula - Calar Alto Astronomical Observatory
The diversity of colours, shapes, and sizes of planetary nebulae make them fascinating objects. In this photo release Calar Alto presents a rather unique view combining both optical and near-infrared data of the Ring Nebula (M57). ...

Planetary nebulae represent the final stage in the evolution of stars whose masses are smaller than eight times that of the Sun. The approach of the final energy crisis that marks stellar old age transforms the star into a red giant whose stellar winds fill their surroundings with a thin envelope composed mainly from hydrogen gas.




Ring Nebula (M57) – click for 1600×1169 image


More: here, here

Selected readings 12/25/09

Friday, December 25, 2009

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


The Psychology of Climate Change Denial
Even as the science of global warming gets stronger, fewer Americans believe it’s real. In some ways, it’s nearly as jarring a disconnect as enduring disbelief in evolution or carbon dating. And according to Kari Marie Norgaard, a Whitman College sociologist who’s studied public attitudes towards climate science, we’re in denial. “Our response to disturbing information is very complex. We negotiate it. We don’t just take it in and respond in a rational way,” said Norgaard. [Wired.com, 12/9/09]

Immune System vs. Cancer
The comeback of an old idea in immunology prompts a rethink of cancer progression and approaches to treatment. [The Scientist, 11/1/09]

How epigenetics is changing our fight with disease
Sequencing the human genome was supposed to answer our questions about the genetic origins of disease but the burgeoning science of epigenetics is telling us it's a whole lot more complicated. [ABC Science, 10/1/09]

Accelerators and Light Sources of Tomorrow (Part 1: From Linacs to Lasers)
From their humble beginnings as offshoots of the ordinary electric light bulb, particle accelerators have evolved in surprising directions. Among the most productive and promising developments have been light sources, first in the form of electron storage rings -- of which the Advanced Light Source is the world's premier source of soft x-rays -- and increasingly as versatile and sophisticated free electron lasers, the next generation of light sources now being studied at Berkeley Lab. [Physorg.com, 12/22/09]

Accelerators and Light Sources of Tomorrow (Part 2: Accelerating with Light)
Accelerators are far from achieving the highest energies their builders aspire to, but size and cost may limit the kinds of facilities funding agencies can support. In the future, new kinds of machines will be needed to make further progress. Perhaps the most promising is the laser plasma accelerator. [Physorg.com, 12/22/09]

Stars Fueled by Dark Matter Could Hold Secrets to the Universe
The first stars in the universe may have been very different from the stars we see today, yet they may hold clues to understanding some of the mysterious features of the universe. These "dark stars," first theorized in 2007, could grow to be much larger than modern stars, and would be powered by dark matter particles that annihilate inside them, rather than by nuclear fusion. [Physorg.com, 11/3/09]

Like built-in GPS, brain maps help you find your way home
Scientists have long known that a small, seahorse-shaped region in the brain, the hippocampus, contains neurons called "place cells" that specialize in geography. In recent years, working mostly with laboratory rats, they've discovered additional types of neurons in or near the hippocampus known as "grid cells," "head-direction cells" and "border cells." Taken together, "these cells form a map of the environment," said Edvard Moser, a leading expert on brain mapping. [McClatchy, 10/30/09]

Herschel Space Observatory sees stars being born
Peering into the heart of a dust-covered stellar nursery, a new infrared observatory has spied some 700 stars in the making. At the moment, the soon-to-be stars are just clumps of dust and gas. But about 100 of the clumps are protostars, embryonic bodies about to initiate nuclear fusion at their cores and become bona fide stars. The other 600 objects are less mature but will ultimately develop into new stars. [Science News, 12/21/09]

Building a Search Engine of the Brain, Slice by Slice
Brain dissection is a craft that goes back centuries and has helped scientists to understand where functions like language processing and vision are clustered, to compare gray and white matter and cell concentrations across different populations and to understand the damage done in ailments like Alzheimer’s disease and stroke. [New York Times, 12/21/09]

Search for extraterrestrial life gains momentum around the world
The instruments, the initial phase of the planned 350-dish Allen Telescope Array, are designed to systematically scan the skies for radio signals sent by advanced civilizations from distant star systems and planets. Fifty years after it began -- and 18 years since Congress voted to strip taxpayer money from the effort -- the nation's search for extraterrestrial intelligence is alive and growing. [Washington Post, 12/22/09]

Starring Intelligent Aliens
When scientists search the heavens for habitable worlds beyond Earth, they don't necessarily know what to look for. A new study has found that the most probable place to find intelligent life in the galaxy is around stars with roughly the mass of the sun, and surface temperatures between 5,300 and 6,000 Kelvin (9,100 and 10,300 degrees Fahrenheit) - in fact, stars very similar to our own sun. [Physorg.com, 11/5/09]

Old discovery could bring new cancer therapies
The reason for cancer cells’ peculiar metabolism - and the question of whether it plays a key role in driving cancer - remained largely mysterious to scientists. Over the past few years, however, biochemistry research has led to a resurgence of interest in cancer cell metabolism - the ways in which cancer cells generate energy to function and grow. [Boston Globe, 12/21/09]

At a Mine’s Bottom, Hints of Dark Matter
An international team of physicists working in the bottom of an old iron mine in Minnesota said Thursday that they might have registered the first faint hints of a ghostly sea of subatomic particles known as dark matter long thought to permeate the cosmos. [New York Times, 12/17/09]

Two events hint at impact of dark matter particles
Two talks from members of the CDMS consortium, which runs a detector designed to spot the presence of a likely dark matter candidate, have indicated that they've spotted two events that bear the signatures of something called a neutralino, a hypothesized particle that has many of the properties of dark matter. With only two of these detections, however, there's still a 23 percent chance that random background events produced the signals. [Ars technica, 12/17/09]

Researchers show off functional single-molecule transistor
As semiconductor manufacturers continue to push down the size of their products' wiring, a number of research labs have started looking into whether they can simply take the process to its logical conclusion: a transistor made from a single molecule. A number of these items have been demonstrated, and they do manage to control the current flow through the molecular transistor, but they do so through a variety of tricks that have nothing in common with the methods used for the semiconductors in our electronics. In today's issue of Nature, an international team reports producing the first voltage-gated molecular transistors. [Ars technica, 12/23/09]


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Hubble Image Showcases Star Birth in M83, the Southern Pinwheel

Monday, December 21, 2009

Hubble Image Showcases Star Birth in M83, the Southern Pinwheel
The spectacular new camera installed on NASA's Hubble Space Telescope during Servicing Mission 4 in May has delivered the most detailed view of star birth in the graceful, curving arms of the nearby spiral galaxy M83.

Nicknamed the Southern Pinwheel, M83 is undergoing more rapid star formation than our own Milky Way galaxy, especially in its nucleus. The sharp "eye" of the Wide Field Camera 3 (WFC3) has captured hundreds of young star clusters, ancient swarms of globular star clusters, and hundreds of thousands of individual stars, mostly blue supergiants and red supergiants.




M83 – click for 995×1000 image


More: here, here

Selected readings 12/20/09

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


Mammogram Math
The panel of scientists advised that routine screening for asymptomatic women in their 40s was not warranted and that mammograms for women 50 or over should be given biennially rather than annually. The response was furious. Fortunately, both the panel’s concerns and the public’s reaction to its recommendations may be better understood by delving into the murky area between mathematics and psychology. [New York Times, 12/10/09]

Introns: A mystery renewed
The sequences of nonsense DNA that interrupt genes could be far more important to the evolution of genomes than previously thought. ... Scientists say introns are inserted into the genome far more frequently than current models predict. The scientists also found what appear to be "hot spots" for intron insertion -- areas of the genome where repeated insertions are more likely to occur. And surprisingly, the vast majority of intron DNA sequences the scientists examined were of unknown origin. [Indiana University, 12/10/09]

Science at the petascale: Roadrunner supercomputer results unveiled
The world's fastest supercomputer, Roadrunner, at Los Alamos National Laboratory has completed its initial "shakedown" phase doing accelerated petascale computer modeling and simulations of a variety of unclassified, fundamental science projects. [Physorg.com, 10/26/09]

Scientists use world's fastest supercomputer to model origins of the unseen universe
Understanding dark energy is the number one issue in explaining the universe, according to Salman Habib, of the Laboratory's Nuclear and Particle Physics, Astrophysics and Cosmology group. ... The model is one of the largest simulations of the distribution of matter in the universe, and aims to look at galaxy-scale mass concentrations above and beyond quantities seen in state-of-the-art sky surveys. [Physorg.com, 10/26/09]

A Delicate Balance of Sexual Identity
The difference between male and female is smaller than one might think--at least on a cellular level. Researchers have found that they can change ovary cells into testicular cells in mice by turning off a single gene. The discovery provides new insights into the evolution of sex differences. [ScienceNOW, 12/10/09]

One gene keeps ovaries female
Knocking down a single gene in an adult mouse makes ovaries develop the characteristics of a male gonad and produce testosterone, according to a study published today (December 10th) in Cell. The study suggests that the signal is required to maintain the female phenotype throughout adulthood. [The Scientist, 12/10/09]

How a new muon experiment can advance physics
In recent years, particle physicists have increasingly turned their attention to finding physics beyond the Standard Model description of the building blocks of matter and how they interact. ... Many theories exist to explain the origins of suspected “new physics” and extensions to the Standard Model, the current theoretical framework.A new Fermilab-based experiment, the Muon-to-Electron Conversion experiment, or Mu2e, could shine light on those gray areas. [Symmetry Breaking, 12/9/09]

New evidence links sirtuins and life extension
Ever since he first discovered the lifespan-extending effects of proteins called sirtuins 15 years ago, MIT Professor Leonard Guarente has been accumulating evidence to demonstrate a link between sirtuins and the effects of calorie restriction on lifespan. [MIT News, 12/15/09]

Higgs in space: Orbiting telescope could beat the LHC
Evidence for the Higgs boson could be pouring down upon us from deep space. If so, an orbiting space telescope could upstage the Large Hadron Collider in the search for the elusive particle. [New Scientist, 12/14/09]

P vs. NP -- The most notorious problem in theoretical computer science remains open
In a 2002 poll, 61 mathematicians and computer scientists said that they thought P probably didn’t equal NP, to only nine who thought it did — and of those nine, several told the pollster that they took the position just to be contrary. But so far, no one’s been able to decisively answer the question one way or the other. Frequently called the most important outstanding question in theoretical computer science, the equivalency of P and NP is one of the seven problems that the Clay Mathematics Institute will give you a million dollars for proving — or disproving. [Physorg.com, 10/29/09]

Study: Earth's polar ice sheets vulnerable to even moderate global warming
A new analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities and published in the Dec. 16 issue of Nature, employs a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level. [Physorg.com, 12/16/09]

High testosterone linked to miserly behaviour
If you're looking to haggle, steer clear of big, beefy salesmen. The same hormone responsible for their brawn may also reduce their generosity, new research suggests. "Our broad conclusion is that testosterone causes men essentially to be stingy," says Karen Redwine, a neuro-economist at Whittier College in California. [New Scientist, 10/26/09]

A Molecule of Motivation, Dopamine Excels at Its Task
People talk of getting their “dopamine rush” from chocolate, music, the stock market, the BlackBerry buzz on the thigh — anything that imparts a small, pleasurable thrill. Familiar agents of vice like cocaine, methamphetamine, alcohol and nicotine are known to stimulate the brain’s dopamine circuits, as do increasingly popular stimulants like Adderall and Ritalin. [New York Times, 10/26/09]


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Hubble's Deepest View of Universe Unveils Never-Before-Seen Galaxies

Sunday, December 20, 2009

Hubble's Deepest View of Universe Unveils Never-Before-Seen Galaxies
NASA's Hubble Space Telescope has made the deepest image of the universe ever taken in near-infrared light. The faintest and reddest objects in the image are galaxies that formed 600 million years after the Big Bang. No galaxies have been seen before at such early times. The new deep view also provides insights into how galaxies grew in their formative years early in the universe's history.

The image was taken in the same region as the Hubble Ultra Deep Field (HUDF), which was taken in 2004 and is the deepest visible-light image of the universe. Hubble's newly installed Wide Field Camera 3 (WFC3) collects light from near-infrared wavelengths and therefore looks even deeper into the universe, because the light from very distant galaxies is stretched out of the ultraviolet and visible regions of the spectrum into near-infrared wavelengths by the expansion of the universe.




Very early galaxies – click for 1280×1113 image


More: here

Selected readings 12/13/09

Monday, December 14, 2009

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


Massively collaborative mathematics
The 'Polymath Project' proved that many minds can work together to solve difficult mathematical problems. Timothy Gowers and Michael Nielsen reflect on the lessons learned for open-source science. [Nature, 10/15/09]

What Comes After Hard Drives?
The ability to store and retrieve data is an important component of today's computers, as well as other modern electronic devices such as cell phones, video game consoles, and camcorders. Since their invention in the 1950s, magnetic-based hard disk drives (HDDs) have been the primary method of nonvolatile storage. However, researchers are currently developing several new and promising nonvolatile memory (NVM) technologies, but for one of them to replace HDDs within the next decade, it will be a challenge. [Physorg.com, 10/23/09]

Why antidepressants don't work for so many
More than half the people who take antidepressants for depression never get relief. Why? Because the cause of depression has been oversimplified and drugs designed to treat it aim at the wrong target, according to new research from the Northwestern University Feinberg School of Medicine. The medications are like arrows shot at the outer rings of a bull's eye instead of the center. [Physorg.com, 10/23/09]

Out of LSD? Just 15 Minutes of Sensory Deprivation Triggers Hallucinations
You don’t need psychedelic drugs to start seeing colors and objects that aren’t really there. Just 15 minutes of near-total sensory deprivation can bring on hallucinations in many otherwise sane individuals. Psychologists stuck 19 healthy volunteers into a sensory-deprivation room, completely devoid of light and sound, for 15 minutes. Without the normal barrage of sensory information flooding their brains, many people reported experiencing visual hallucinations, paranoia and a depressed mood. [Wired, 10/21/09]

It's natural to behave irrationally
Psychologists studying the issue say that the now-familiar warnings about climate change kick at emotional dead spots in all human brains -- but especially in American brains. Researchers have only theories to explain why people in the United States have done less than those in such places as Europe and Japan. ... No matter where the public's complacency springs from, psychologists have seen this kind of thing before, Ariely said: "That's why we don't exercise, and we overeat, and we bite our fingernails. . . . It's not something where we're going to overcome human nature." [Washington Post, 12/8/09]

Was our oldest ancestor a proton-powered rock?
Peter Mitchell was an eccentric figure. For much of his career he worked in his own lab in a restored manor house in Cornwall in the UK, his research funded in part by a herd of dairy cows. His ideas about the most basic process of life - how it gets energy - seemed ridiculous to his fellow biologists. [New Scientist, 10/19/09]

Six diseases you never knew you could catch
Twentieth century medicine was phenomenally successful at developing vaccines and antibiotics to fight infectious diseases, taming ancient scourges such as smallpox, tuberculosis and typhoid. In the 1960s and 70s, the prevailing view was that all diseases caused by microorganisms would soon be conquered, leaving only those caused by genetics, unhealthy lifestyles or ageing. That idea now seems naive, not least because of the rise in antibiotic resistance. And there's another reason that no one even considered back then. A growing number of diseases that were thought to be down to genetics or lifestyle turn out to have an infectious origin. [New Scientist, 10/20/09]

Rethinking relativity: Is time out of joint?
It is still not clear how well general relativity holds up over cosmic scales, at distances much larger than the span of single galaxies. Now the first, tentative hint of a deviation from general relativity has been found. While the evidence is far from watertight, if confirmed by bigger surveys, it may indicate either that Einstein's theory is incomplete, or else that dark energy, the stuff thought to be accelerating the expansion of the universe, is much weirder than we thought. [New Scientist, 10/21/09]

Timewarp: How your brain creates the fourth dimension
Perhaps the most fundamental question neuroscientists are investigating is whether our perception of the world is continuous or a series of discrete snapshots like frames on a film strip. Understand this, and maybe we can explain how the healthy brain works out the chronological order of the myriad events bombarding our senses, and how this can become warped to alter our perception of time. [New Scientist, 10/21/09]

Seven questions that keep physicists up at night
It's not your average confession show: a panel of leading physicists spilling the beans about what keeps them tossing and turning in the wee hours. That was the scene a few days ago in front of a packed auditorium at the Perimeter Institute, in Waterloo, Canada, when a panel of physicists was asked to respond to a single question: "What keeps you awake at night?" [New Scientist, 10/23/09]

The complex psychology of climate denial
If the evidence is overwhelming that man-made climate change is already upon us and set to wreak planetary havoc, why do so many people refuse to believe it? ... Experts see several explanations for the eagerness with which so many dismiss climate change as overblown or a hoax. [Cosmos Magazine, 12/1//09]

New Model of the Universe Says Past Crystallizes out of the Future
What do you get when the past crystallizes out of the future? According to a new model of the universe that combines relativity and quantum mechanics, the answer is: the present. [Technology Review arXiv blog, 12/8/09]

Rethinking artificial intelligence
The field of artificial-intelligence research (AI), founded more than 50 years ago, seems to many researchers to have spent much of that time wandering in the wilderness, swapping hugely ambitious goals for a relatively modest set of actual accomplishments. Now, some of the pioneers of the field, joined by later generations of thinkers, are gearing up for a massive “do-over” of the whole idea. [MIT, 12/7/09]

Gremlin Fireworks
Why spend billions of euros to smash subatomic particles together? The physicist Frank Wilczek (a colleague of mine at MIT, though we haven’t worked together directly) shared the 2004 Nobel Prize for his contribution to the reigning theory of high-energy physics; his new book gives non-specialist readers a tour of the conceptual landscape. [London Review of Books, 12/17/09]

Secrets of a cancer-free rodent
Researchers have shed light on an unusual resistance to cancer displayed by the naked mole rat, a burrowing, long-lived desert-dwelling rodent. In these animals, a cell growth switch absent in more cancer-prone organisms turns off cell division before cells get too dense, as they would in a tumor. [The Scientist, 10/26/09]

Choosing Sex
The gonad is an amazingly labile organ where male and female signals vie for dominance in the developing embryo. [The Scientist, 10/1/09]

A Little Fellatio Goes a Long Way
Oral sex is surprisingly rare in the animal kingdom. Humans do it, of course. As do bonobos, our close relatives. But now researchers have observed the practice for the first time in a non-primate. During intercourse, female short-nosed fruit bats lick the genitals of their partner, a possible ploy to increase copulation time. The discovery suggests there may be a biological advantage to fellatio. [ScienceNOW, 10/30/09]


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Selected readings 12/8/09

Tuesday, December 8, 2009

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


How epigenetics is changing our fight with disease
Sequencing the human genome was supposed to answer our questions about the genetic origins of disease but the burgeoning science of epigenetics is telling us it's a whole lot more complicated. [ABC Science, 10/1/09]

Humans wonder, anybody home?
Many people (some scientists among them) would like to believe that consciousness sets the human mind apart from the rest of the animal kingdom. But whether in humans or other creatures, behavioral signs of cognizance all arise from the tangled interactions of neurons in the brain. So a growing number of scientists contend that animals with brain structures and neural circuitry similar to humans’ might experience something like human awareness, even if a bit less sophisticated. [Science News, 10/20/09]

Discovery of Higgs at Large Hadron Collider might not make all physicists happy
Discovery of the Higgs at the LHC would not necessarily be a cause for unrestrained celebration, though. “Many of us are terrified that the LHC will discover a Higgs particle and nothing more,” Weinberg said. That would just confirm the standard model, which everybody believes already. It would not point the way to further progress in solving a deeper problem that physics faces — how to add gravity to the unified theory of the other forces. [Science News, 12/19/09]

Better living through plasmonics
First named in 2001, the field of plasmonics has become popular among physicists and engineers only recently, as scientists have developed tools to create nanosized structures that can guide and shape these light-and-electron waves. Now the field of plasmonics is taking off, possibly leading to new kinds of miniature lasers, better cancer treatments and faster computers. [Science News, 11/7/09]

Windows on the Universe
Already, the year-old Fermi Gamma-ray Space Telescope has extended the range and sensitivity with which scientists can scan the high-energy universe for violent interactions and signs of dark matter. In the infrared, NASA’s Spitzer Space Telescope has given astronomers a more complete picture of galaxy and star formation, much of which happens behind a veil of dust. And new radio telescopes will soon probe the cosmic dark ages—the era just before the very first stars and galaxies illuminated the universe. [Science News, 10/10/09]

It seems biology (not religion) equals morality
Where I intend to be divisive is with respect to the argument that religion, and moral education more generally, represent the only — or perhaps even the ultimate — source of moral reasoning. If anything, moral education is often motivated by self-interest, to do what's best for those within a moral community, preaching singularity, not plurality. Blame nurture, not nature, for our moral atrocities against humanity. And blame educated partiality more generally, as this allows us to lump into one category all those who fail to acknowledge our shared humanity and fail to use secular reasoning to practise compassion. [Edge, 12/4/09]

Measuring (almost) zero
The electron's electric dipole moment is unimaginably tiny – and may not even exist. But as Chad Orzel explains, that has not stopped experimentalists from trying to measure it, since a non-zero result could imply the existence of new physics. [Physicsworld.com, 12/1/09]

Recipes for planet formation
Observations of extrasolar planets are shaping our ideas about how planetary systems form and evolve. Michael R Meyer describes what's cooking elsewhere in our galaxy – and beyond. [Physicsworld.com, 11/2/09]

Mysterious "strange" stars may rival black holes for weirdness
Think black holes are strange? ... But maybe they're not "strange" enough, suggest some astrophysicists. "Stellar" black holes, ones only a few times heavier than the sun, may actually be something even weirder called a quark star, or "strange" star. [USA Today, 12/4/09]

Big Hope for Tiny Particles
Nanotechnology-based drug delivery offers new treatment options for deadly pancreatic cancers. [Technology Review, 11/30/09]

Psychological Science: Measurement, Uncertainty, and Determinism – Part 1
In the minds of many, including scientists from the more successful sciences, the field of psychology is not a science and may never be a science. The Nobel Laureate, Richard Feynman, was kind in his criticism of psychology as a science when he said that we have the form [of science] down, but we are not producing any laws of nature. In my view, psychology as a science has made some important contributions to describing mental life and behavior in animals and humans, but, on the whole, I tend to agree with Feynman. [3quarksdaily, 12/7/09]

Thanksgiving
This year we give thanks for one of the bedrock principles of classical mechanics: conservation of momentum. ... There are analogous notions once we include relativity or quantum mechanics, but for our present purposes the version that Galileo and Newton would have recognized is good enough: in any interaction between bodies, the total momentum (mass times velocity of each body, added together vectorially) remains conserved. [Cosmic Variance, 11/26/09]

Lose Genes, Gain Weight
Obesity is a disease of excess, but a new study suggests that a few obese patients are actually lacking something--a piece of one of their chromosomes. The loss might remove a gene that helps the body manage blood sugar and appetite. [ScienceNOW, 12/7/09]


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Selected reading 12/5/09

Saturday, December 5, 2009

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


Fuelling fears
There is an awesome amount of energy tied up in an atom of uranium. Because of that, projections of the price of nuclear power tend to focus on the cost of building the plant rather than that of fuelling it. But proponents of nuclear energy—who argue, correctly, that such plants emit little carbon dioxide—would do well to remember that, like coal and oil, uranium is a finite resource. [The Economist, 11/30/09]

The Coming Nuclear Crisis
The perception is that nuclear power is a carbon-free technology, that it breaks our reliance on oil and that it gives governments control over their own energy supply. That looks dangerously overoptimistic, says Michael Dittmar, from the Swiss Federal Institute of Technology in Zurich who publishes the final chapter of an impressive four-part analysis of the global nuclear industry on the arXiv today. [Technology Review: the physics asXiv blog, 11/17/09]

Henry Markram Calls the IBM Cat Scale Brain Simulation a Hoax
This is a mega public relations stunt - a clear case of scientific deception of the public. These simulations do not even come close to the complexity of an ant, let alone that of a cat. IBM allows Mohda to mislead the public into believing that they have simulated a brain with the complexity of a cat - sheer nonsense. [Next Big Future, 11/24/09]

I have a long post on the subject: here

Immune System vs. Cancer
The comeback of an old idea in immunology prompts a rethink of cancer progression and approaches to treatment. [The Scientist, 11/1/09]

There’s No Such Thing as a ‘Simple’ Organism
What may be the most thorough study ever of a single organism has produced a beta code for life’s essential subroutines, and shown that even the simplest creatures are more complex than scientists suspected. [Wired Science, 11/30/09]

Americans' Eating Habits More Wasteful Than Ever
After their biggest meal of the year, Americans might reflect on the fate of those moldering Thanksgiving leftovers. Nearly 40% of the food supply in the United States goes to waste, according to a new study, and the problem has been getting worse. [ScienceNOW, 11/25/09]

A New Spin on Electronics
Some physicists aim to develop a whole new technology called "spintronics" that would encode information in the directions in which electrons spin as well. Those efforts could lead to ultra-low-power electronics and even futuristic quantum computers. Now, such technologies may be an important step closer to reality thanks to a group of researchers that has managed to polarize the spinning electrons in silicon, the most common commercial semiconductor. [ScienceNOW, 11/25/09]

First programmable quantum computer created
Using a few ultracold ions, intense lasers and some electrodes, researchers have built the first programmable quantum computer. The new system, described in a paper to be published in Nature Physics, flexed its versatility by performing 160 randomly chosen processing routines. [Science News, 11/23/09]

Membrane Awakening
The boundary of a living, metabolizing cell is surprisingly similar to that hedge. The cellular membrane, once thought to be an inert barrier, is one of the most dynamic parts of the cell. The membrane and the plethora of proteins that stud its surface direct the exchange of information between cells, tightly control the flow of materials from inside to outside the cell, and provide surfaces for some of life's most vital chemical reactions. [HHMI Bulletin, 11/1/09]

Superior Super Earths
Astronomers have discovered hundreds of Jupiter-like planets in our galaxy. However, a handful of the planets found orbiting distant stars are more Earth-sized. This gives hope to astrobiologists, who think we are more likely to find life on rocky planets with liquid water. The rocky planets found so far are actually more massive than our own. Dimitar Sasselov, professor of astronomy at Harvard University, coined the term “Super-Earths” to reflect their mass rather than any superior qualities. But Sasselov says that these planets – which range from about 2 to 10 Earth masses – could be superior to the Earth when it comes to sustaining life. [Astrobiology Magazine, 11/30/09]

Nanoparticles for gene therapy improve
Nanoparticles, made of biodegradable polymers, offer a chance to overcome one of the biggest obstacles to realizing the promise of gene therapy: The viruses often used to carry genes into the body can endanger patients. Furthermore, the particles created at MIT now rival viruses’ efficiency at delivering their DNA payload. [MIT News, 11/6/09]

Cancer research gets into the groove
The out-of-control cell growth that defines cancer results from runaway growth genes activated by regulator proteins, known as transcription factors, that sit on DNA and turn genes on and off. Transcription factors are often mutated in cancer, but scientists have been largely unable to design or find drugs capable of blocking the proteins. A creative method of targeting these gene regulators has recently been applied to cancer by a multi-institutional collaboration of researchers. [Broad Institute, 11/12/09]

Building a second sun: Take $10 billion, add coconuts
The balmy south of France has always been a magnet for sun worshippers. So it is perhaps fitting that here, not far from the Côte d'Azur, an international team of researchers is building a machine to recreate the sun. ... [An] eclectic mix of ingredients will be turned into ITER, the International Thermonuclear Experimental Reactor - the next big thing in nuclear fusion research. [New Scientist, 10/12/09]

Out of your head: Leaving the body behind
In the 15 years since that dramatic incident, Brugger and others have come a long way towards understanding out-of-body experiences. They have narrowed down the cause to malfunctions in a specific brain area and are now working out how these lead to the almost supernatural experience of leaving your own body and observing it from afar. They are also using out-of-body experiences to tackle a long-standing problem: how we create and maintain a sense of self. [New Scientist, 10/13/09]

Researchers unravel brain's wiring to understand memory
These are a few of the cutting-edge experiments that neuroscientists are performing in the latest efforts to understand the mysteries of how the brain learns, remembers and forgets. The work is shedding new light on how the brain handles memory storage, loss, fear, addiction and aging. Some explore the role of sleep — even a brief nap — in consolidating long-term memories. Others are building colorful wiring diagrams, nicknamed "Brainbows," that use different shades to show which neurons connect with which. [McClatchy, 9/22/09]

Scientists seek to manage dopamine's good and bad sides
Dopamine [is] a natural brain chemical that's linked to pleasure, addiction and disease. This little molecule -- it consists of only 22 atoms -- is essential to life but can be a curse sometimes. Too much or too little of it can lead to drug abuse, reckless thrill-seeking, obesity, the tremors of Parkinson's disease, even restless leg syndrome, an irresistible urge to move your legs. [McClatchy, 10/6/09]


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Selected reading 12/2/09

Wednesday, December 2, 2009

Interesting reading and news items.

These items are also bookmarked at my Diigo account.


In the Brain, Seven Is A Magic Number
Countless psychological experiments have shown that, on average, the longest sequence a normal person can recall on the fly contains about seven items. This limit, which psychologists dubbed the "magical number seven" when they discovered it in the 1950s, is the typical capacity of what's called the brain's working memory. Now physicists have come up with a model of brain activity that seems to explain the reason behind the magical memory number. [Inside Science News Service, 11/23/09]
Computers Faster Only for 75 More Years? Physicists determine nature's limit to making faster processors
A pair of physicists has shown that computers have a speed limit as unbreakable as the speed of light. If processors continue to accelerate as they have in the past, we'll hit the wall of faster processing in less than a century. [Physorg.com, 10/14/09]
Black Hole Caught Zapping Galaxy into Existence?
Which come first, the supermassive black holes that frantically devour matter or the enormous galaxies where they reside? A brand new scenario has emerged from a recent set of outstanding observations of a black hole without a home: black holes may be “building” their own host galaxy. This could be the long-sought missing link to understanding why the masses of black holes are larger in galaxies that contain more stars. [European Southern Observatory, 11/30/09]
Cosmic "Dig" Reveals Vestiges of the Milky Way's Building Blocks
A team of astronomers has unveiled an unusual mix of stars in the stellar grouping known as Terzan 5. Never observed anywhere in the bulge before, this peculiar "cocktail" of stars suggests that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of a proto-galaxy that merged with the Milky Way during its very early days. [European Southern Observatory, 11/25/09]
Watching a Cannibal Galaxy Dine
A new technique using near-infrared images, obtained with ESO’s 3.58-metre New Technology Telescope (NTT), allows astronomers to see through the opaque dust lanes of the giant cannibal galaxy Centaurus A, unveiling its “last meal” in unprecedented detail — a smaller spiral galaxy, currently twisted and warped. [European Southern Observatory, 11/20/09]
Ticking Stellar Time Bomb Identified
Astronomers have made the first time-lapse movie of a rather unusual shell ejected by a “vampire star”, which in November 2000 underwent an outburst after gulping down part of its companion’s matter. This enabled astronomers to determine the distance and intrinsic brightness of the outbursting object. It appears that this double star system is a prime candidate to be one of the long-sought progenitors of the exploding stars known as Type Ia supernovae, critical for studies of dark energy. [European Southern Observatory, 11/17/09]
Astronomers seek to explore the cosmic Dark Ages
Astronomers call it the Dark Ages, and now they're building huge new radio telescopes with thousands of detectors that they hope will let them peer back into the period, when the first stars and galaxies began turning on their lights. [Physorg.com, 10/15/09]
Intergalactic Controversy
New observations of galactic clusters have revealed a controversial phenomenon called “dark flow,” which could be a sign of parallel universes. [Seed Magazine, 12/2/09]


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Opening up a Colourful Cosmic Jewel Box

Tuesday, December 1, 2009

Opening up a Colourful Cosmic Jewel Box (10/29/09)
The combination of images taken by three exceptional telescopes, the ESO Very Large Telescope on Cerro Paranal , the MPG/ESO 2.2-metre telescope at ESO’s La Silla observatory and the NASA/ESA Hubble Space Telescope, has allowed the stunning Jewel Box star cluster to be seen in a whole new light. ...

The Kappa Crucis Cluster, also known as NGC 4755 or simply the “Jewel Box” is just bright enough to be seen with the unaided eye. It was given its nickname by the English astronomer John Herschel in the 1830s because the striking colour contrasts of its pale blue and orange stars seen through a telescope reminded Herschel of a piece of exotic jewellery.

Open clusters [1] such as NGC 4755 typically contain anything from a few to thousands of stars that are loosely bound together by gravity. Because the stars all formed together from the same cloud of gas and dust their ages and chemical makeup are similar, which makes them ideal laboratories for studying how stars evolve.




NGC 4755 – click for 1280×1283 image


More: here, here

Inflammation, cancer, and NF-κB

Sunday, November 29, 2009

Cancer isn't a single disease, and there are many possible things that can "cause" even a single type of cancer. However, a lot of things basically work in the same general way to promote cancer. One way that's been long suspected though poorly understood is tangled up in the process of inflammation.

At the very center of this story is a transcription factor called NF-κB. It's perhaps best known for its role in inflammation. But we discussed it in connection with cancer over two years ago, here. Since NF-κB is a transcription factor it affects the expression of many genes. Consequently, it's involved in many other biological phenomena, a few of which have been discussed here, here, and here.

Let's review some of the characteristics shared by most forms of cancer. One frequently cited summary, due to Douglas Hanahan and Robert Weinberg, names six "hallmarks of cancer" – self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, and tissue invasion and metastasis. It turns out that inflammation and NF-κB can affect most of these hallmarks, but we'll eventually focus on the role NF-κB plays in inhibition of apoptosis (programmed cell death).

Before we get into details, let's go over the way that cancer typically develops. Each of the hallmarks represents a failure in one or more parts of the machinery of cells to properly regulate the cell's life cycle. The bad thing about cancer, of course, is that a certain group of cells – which might all be descendants of a single aberrant cell – begins to grow and proliferate in an unregulated way. Eventually large numbers of unregulated cells will cease to function as required in the organ where they reside – the brain, the liver, breast tissue, or whatever. Instead they will acquire the ability to migrate and take up residence in places where they continue to proliferate and then disrupt the proper function of whatever organ they wind up in. This is metastasis, and it is usually fatal to the animal in which it occurs.

The cell's machinery is ultimately controlled by the way specific genes of the cell's DNA are expressed to produce proteins. So the reason a cell initially becomes improperly regulated is usually the occurrence of fresh damage to the cell's DNA. It's true that problematic DNA mutations can be inherited from parents, such as the well-known breast cancer genes BRCA1 and BRCA2. Signifcantly, the normal function of both these genes, when not mutated, is to produce proteins whose job is to detect and/or repair DNA damage or to arrest cell proliferation if DNA damage is detected but can't be repaired. So mutated versions of these genes do not exactly "cause" cancer themselves, since some mutation to other genes that actively induce excessive cell proliferation is also required. The potential for cancer may simply remains latent for awhile in cells with mutated genes, regardless of whether the mutation was inherited or occurred much later in life.

But eventually uncorrected DNA damage will occur and affect genes that do induce excessive proliferation. Metastatic cancer eventually results, regardless of whether the first harmful mutations occur in genes that induce proliferation or genes that help regulate proliferation. Cells that contain such mutations divide more frequently and outcompete for resources cells that are functioning properly. So a Darwinian evolutionary scenario arises in which cells that are working "correctly" lose out to cells that become better "adapted" to the job of simply replicating themselves.

The point of this general discussion about cancer is to help clarify what it means to say that something "causes" cancer. In reality, there's never a single event that is the "cause". A number of things have to go wrong before some population of cells with similar defects is numerous enough to outcompete properly functioning cells and to go on to acquire further defects when the mechanisms that normally protect against damage themselves begin to fail.

There appear to be several ways in which NF-κB can contribute to the development of cancer, but one of the least surprising ways is the fact that NF-κB is able to inhibit apoptosis. This ability is not accidental. Most likely it is properly there to enable proliferation of immune system cells in the presence of an infection, as indicated by inflammatory signals.

To return to our main topic, inflammation is a thoroughly normal part of the immune system's operation. NF-κB plays an important part in the inflammatory process. But in simply doing their jobs, these things can, under the right conditions when other cellular mechanisms befome defective, also contribute to the development and progress of cancer.

Normally, the ability of NF-κB to inhibit apoptosis doesn't present a risk of cancer because NF-κB is regulated by other proteins, as we'll discuss later. However, if there are gene mutations that affect NF-κB regulatory proteins, the "safety catch" mechanism may be compromised, and apoptosis may be inhibited when it shouldn't be. Such a problem is more likely to occur when inflammation is present, since then the "safety catch" is already partly disabled.

Another mechanism that keeps NF-κB inhibition of apoptosis in check is the existence of pro-apoptotic proteins such as p53. (We've discussed p53 a number of times before, most recently here, where new research about the anti-cancer properties of p53 is described.) Such proteins are normally subject to regulation themselves, and they become available and active only when needed, such as when DNA damage is detected. However, when one of these proteins has itself been compromised by a gene mutation, inflammation and resultant NF-κB activity can inappropriately inhibit apoptosis, because pro-apoptotic factors are weakened or sidelined.

As it turns out, according to recent research, among the ways that p53 promotes apoptosis is by direct interference with NF-κB's ability to inhibit apoptosis. Further, certain mutations of the p53 gene can remove p53's pro-apoptotic ability, allowing inflammation and NF-κB to contribute to development of cancer. (See here. We'll discuss that in a separate article.)

The high-level view of all this is that cells exist continually in a state of balance between opposing possibilities. Pro-apoptotic and anti-apoptotic mechanisms are not only regulated independently, but they also keep each other in check. But when mutations in any number of possible genes upset the balance, otherwise normal and useful mechanisms can lead to cancer.

Now let's go a little deeper into the subject of various factors that actively contribute to cancer, starting with DNA damage – mutations. The class of things that cause mutations comprises factors such as carcinogenic chemicals, reactive oxygen species ("free radicals"), ultraviolet light, ionizing radiation (e. g. x-rays, radon gas), and some types of viruses. DNA is also at risk of damage every time a cell divides, because mechanisms that copy DNA and verify the copy during division aren't perfect. So old age alone, when DNA has been damaged in various types of cells that have divided too often, can also be a cause of cancer. Dangerous gene mutations can also be inherited, as already noted.

Mutations in genes that code for proteins that directly or indirectly promote cell division are, logically enough, one source of increased cancer risk. A mutation in some gene affecting a constituent of NF-κB would be an example here if, say, the mutation rendered NF-κB less subject to regulation by the proteins that normally regulate it. And as noted, mutations in genes for proteins that detect or repair DNA damage, or simply inhibit cell division when DNA damage exists, would also raise cancer risk. In both cases, the amount of risk also depends on environmental conditions, such as any that could cause inflammation. Mutations in many other genes can also affect cancer risk, when such genes are involved in angiogenesis or cell motility, for example.

Although a wide variety of DNA mutations can raise cancer risk, they may not be sufficient by themselves to actually initiate the development of cancer, because nature has provided cells with many defensive safety mechanisms. On the other hand, mutations aren't always necessary either. There are various external factors that might initiate cancer development even in the absence of DNA damage.

Frequently, it could be an infectious agent like a virus that stimulates excessive cell division. It's quite natural to expect some types of viruses to do this, because such viruses depend on a cell's normal DNA replication machinery to replicate virus DNA as well as cellular DNA. A virus that can easily co-opt the replication machinery has an evolutionary advantage. Especially if the virus can also override normal protective mechanisms, by inhibiting tumor-suppressing proteins like p53. All viruses bring along their own DNA or RNA, which may have evolved specifically because they disable anti-cancer mechanisms. Although virus genetic material is imported from outside, it acts like harmful gene mutations.

Viral replication strategies differ widely among different types of viruses, and certain of these strategies are especially conducive to cancer development. HPV, the human papilloma virus, which is responsible for cervical and anal cancers (among others) is an especially good example. Among the proteins that make up HPV are two, called E6 and E7, each of which promotes cell proliferation in its own way.

E6 is able to suppress the important anti-proliferation protein p53, which manages signals of DNA damage to take appropriate action, such as apoptosis or suspension of the cell cycle. E7 affects the protein pRb, which normally suppresses the cell cycle by binding to a transcription factor known as E2F. When E7 binds to pRb, E2F is released and can go on to advance the cell cycle, which then causes replication of HPV as well as unwanted cell division.

However, what HPV does isn't the only way that an infectious agent such as a virus can promote cancer. Infectious agents also activate the body's immune system to produce an inflammatory response. This inflammation itself can be a cause of cancer. Briefly stated, inflammation causes NF-κB to be activated in order to cause expression of genes that help invoke other immune system components to fight the infection. But NF-κB also has a side-effect of suppressing apoptosis, and as noted above, that is one of the "hallmarks" of cancer.

A connection between inflammation and cancer was suspected over 100 years ago by scientists like Rudolf Virchow. But only rather recently has solid evidence for the connection been found. A good example is Helicobacter pylori bacterial infections associated with stomach cancer (as well as stomach ulcers). A more recent example is an apparent link between inflammation, due to infection caused by the protozoan Trichomonas vaginalis, and prostate cancer. (See here.) Epidemiological evidence suggests that underlying infections and inflammation are associated with 15-20% of all cancer deaths.

There seem to be a number of factors that explain the connection. NF-κB seems to be one of the most important factors, though not the only one. It doesn't work only by suppression of apoptosis either. Promotion of angiogenesis, among other things, also seems to be involved. But most likely we still don't have a very complete understanding of the connection.

It's especially important to understand the connection, because infections aren't the only cause of inflammation. Other suspected causes of inflammation include stress and obesity. Understanding how obesity might promote cancer is obviously of no small importance. There is even evidence that depression may cause inflammation (see here), so that it could also lead to cancer.

In what follows, we're going to encounter various proteins and protein complexes that interact with each other in cell signaling pathways. Often this interaction takes the form that protein A inhibits the activity of protein B; while protein B inhibits the activity of protein C. The net effect is that protein A enhances the activity of protein C, and hence promotes any process that protein C assists in. Or if protein C inhibits some process, protein A will probably do likewise. This complexity can be very confusing, but it's also pretty common, so we just have to deal with it. In fact, the complexity of processes associated with cancer (and much other biology as well) is an important lesson in all of this.

Let's first consider the process of inflammation that occurs "upstream" from NF-κB and activates it. Inflammation refers to the whole process that occurs in a state of hightened immune system activity, due to physiological stress, oxidative stress, infection, or whatever. The outwards signs of inflammation include redness and swelling. There is a beneficial effect of inflammatory activity, of course, in (hopefully) destroying pathogens. But there are harmful side effects as well, including cardiovascular disease, diabetes, a variety of autoimmune diseases, and... cancer.

Many environmental stimuli lead to inflammation and so can cause NF-κB to be activated. Among these stimuli are stress, free radicals, ultraviolet irradiation, oxidized LDL (cholesterol), products of necrotic cell death, and bacterial or viral antigens.

Infectious agents such as bacteria and viruses contain proteins that act as antigens. These antigens are recognized by various cell-surface receptors, especially the kind known as Toll-like receptors (TLRs). Binding by appropriate proteins or antigens ("ligands") to such receptors is sufficient to activate NF-κB, in a manner we'll describe in a moment.

Antigens also bind to and stimulate cells of the immune system to produce various chemical signals such as cytokines, chemokines, and other proteins in order to regulate the immune system response to infection. Among the types of immune system cells that do this are mast cells, dendritic cells, neutrophils, eosinophils, macrophages, and various other lymphocytes. Inflammatory cytokines can also cause activation of NF-κB.

The crucial effect of inflammation for our purposes now is the fact that it activates NF-κB. It's worth noting how this process works. NF-κB is a protein complex consisting of five protein subunits, not a single protein. These subunits are RelA (also known as p65), c-Rel, RelB, p50, and p52. Complexes of these subunits normally circulate outside the cell nucleus, but they are bound to other proteins called IκBs ("inhibitors of NF-κBs") that prevent the complexes from entering the cell nucleus where they could act as transcription factors.

When an inflammatory signal binds to an appropriate cell surface receptor, signals are sent that activate kinases of a family called IKK (IκB kinase). An IKK protein phosphorylates IκBs, which in turn causes them to become unbound from NF-κB and then be destroyed by cellular proteasomes. This frees up NF-κB complexes so that they can enter the cell nucleus and affect the transcription of many genes.

The benefit of an inhibited form of NF-κB existing in the cytoplasm outside the nucleus is that it can be quickly enabled to enter the nucleus and start gene transcription when the need arises. This allows NF-κB to function as a "rapid-acting" transcription factor, without any delays caused by having to wait for the constituent proteins to be synthesized. Here's a diagram that summarizes this process. (Similar considerations apply to p53. The protein is produced and is found in the cytoplasm before it's needed, but kept from activity while bound to another protein, Mdm2.)

The next issue is what happens downstream from the inflammation-initiated activity of NF-κB in the nucleus. Since NF-κB can assist in the transcription of many different genes, the effect of its activation strongly depends on what type of cell it occurs in. Undoubtedly, there's a whole lot we don't yet know about all the affected genes and resulting downstream effects. As far as the immune response – in which NF-κB plays such an important role – is concerned, one effect involves production of cytokines for signaling to other immune system cells.

A second effect is stimulation of cell proliferation. That's generally a good thing if the cell is, for example, a B cell that mediates the part of the immune respose by manufacturing antibodies. But it can also be a bad thing when excessive proliferation of B cells leads to autoimmune diseases, leukemias, or lymphomas. NF-κB stimulates proliferation by enhancing expression of cell cycle proteins like cyclin D1.

However, there's also a third type of effect of NF-κB activity – inhibition of apoptosis. This is especially significant for cancer, because apoptosis is crucial for many natural anti-cancer cellular defenses. In particular, apoptosis is the normal response to severe, uncorrectable DNA damage. It's also the typical way that chemotherapy is able to kill tumor cells. Interference with normal apoptosis makes cancer both more likely to occur, and more difficult to treat.

Exactly how does NF-κB activity inhibit apoptosis? This has been studied, and the answer seems to be that NF-κB inhibits certain enzymes called caspases that are central to apoptosis.

There are even further suspected side effects of NF-κB activity which can play a big role in cancer. One of these is promotion of angiogenesis – production of blood vessels that can supply nutrients to solid tumors. Another is elevated expression of enzymes that promote metastasis.

Observe that the discussion here has been largely theoretical. We haven't described actual experimental research that supports the generalizations. There is some recent research already mentioned that fills this gap. It's especially interesting in the way it exposes a direct connection between NF-κB and p53. But we must leave description of that research for another article, coming very soon.

Further reading:

Nuclear factor-κB in cancer development and progression – May 2006 Nature review article

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Most Distant Known Object In The Universe

Sunday, November 1, 2009

On April 23 of this year the Swift Gamma-Ray Burst Telescope detected, just as it was designed to do, a gamma-ray burst (GRB). Within less than a day two of the most powerful Earth-based telescopes had begun studying the quickly fading light of the object, known as GRB 090423. (There were other observatories investigating it as well.)

Because the light from GRBs fades so rapidly, most such objects are detected from space-based instruments that are especially designed for the purpose, like Swift. On average about 1 GRB is detected every 2 or 3 days. But GRB 090423 turned out to be, perhaps, the most interesting one yet observed.

I've written about GRBs a couple of times before, such as here and here.

You can refer to those articles for more details, but the most widely accepted hypothesis concerning the nature of GRBs is that they result from either the core collapse supernova explosion of a massive star or the merger of neutron stars in a binary system. Both processes most likely occur. In the former case, the emission of light lasts somewhat longer than in the latter, so the corresponding types of GRBs are called either "long" or "short".

The long type lasts for more than 2 seconds and tends to be brighter than the short type (whose emissions last less than 2 seconds). Since short GRBs typically appear in locations where new star formation is not occurring, they must result from some cause other than the explosion of a very massive star, which is necessarily quite young. In both cases, there is a prolonged, but much dimmer "afterglow", which is the only part of the event that can be observed except from satellites such as Swift.

Not just any supernova or neutron star collision will result in a detectable GRB. Most of the energy from the event must also be directed in two very narrow and oppositely directed beams, and the Earth must be in the path of one of those. It is because the energy is so narrowly concentrated that a GRB can appear to be far brighter than an entire galaxy or quasar. For such narrowly focused beams to be produced, the progenitor star (or binary system) must have a great deal of angular momentum, due to rapid rotation.

The afterglow is thought to result from the interaction between the matter and energy contained in the beam and the interstellar medium at the location of the GRB. Although it's a secondary effect, there is a wealth of information that can be deduced from this afterglow.

However, the information concerns more than just details about the nature of GRBs – events that occur much closer to us are much more useful for that. There are two other things of far greater interest about which we can learn from very distant GRBs, such as 090423 and subsequent examples we are likely to observe.

Since this event had a redshift of z ≈ 8.2 it actually occurred very long ago, a comparatively short time after the big bang. About 630 million years after, to be more exact. GRB 090423 is farther and earlier than any other object or event we've actually observed, except for the cosmic microwave background (CMB). It is more distant in time and space than even any galaxy or quasar we've ever seen. (See here if you want to review how redshift works.)

GRBs, directly or indirectly, tell us about the nature of the largest stars at that time, which is one thing that's presently very difficult to study with other observations. There's simply no way to observe individual stars 13 billion light-years away. The other thing astronomers are very curious about regarding that time period is the nature of the intergalactic medium (IGM) then.

Let's start with the second of these things. 630 million years after the big bang is somewhere in the middle of what astronomers call the "cosmic dark ages". Precisely where it falls is what we don't know. I wrote about that subject here, last March.

We do know pretty closely when the "dark ages" began – about 380 thousand years after the big bang. That's when the CMB appeared. The time is equivalent to a redshift of z ≈ 1100. The CMB was, and still is, "blackbody" radiation, so wavelengths are distributed around a peak. At the peak of the distribution now, CMB photons have a wavelength of 1.9 mm, in the short microwave part of the spectrum. (That's a lot shorter, so more energetic, than in your microwave oven, where microwaves are about 12 cm.) But when the CMB actually appeared, its photons had a wavelength 1100 times shorter, around 2200 nm – in the infrared part of the spectrum. That's still much cooler and "darker" than human eyes can see.

Effectively, then, there wasn't much light in the universe, certainly not human-visible light, until the first stars showed up. So the time after the CMB appeared but before the first stars is known as the "dark ages". However, we don't know very closely when those first stars appeared – they're far too faint to observe, and even the first galaxies and quasars are too dim to be detected by our present instruments. GRBs seem to be our best observational hope, and GRB 090423 is the earliest we've seen yet.

Since existing GRB models presuppose an origin that involves massive stars, at least indirectly, we now know there were such stars 630 million years after the big bang. There is evidence in the GRB 090423 observations that the progenitor of this object was not one of the first population of stars to form. (Astronomers call such stars "Population III".) Also, GRB 090423 doesn't seem to have been one of the most powerful GRBs ever, so astronomers now figure that with current technology we may be able to find GRBs back to z ≈ 20. That would correspond to 250 million years after the big bang.

Theoretical models suggest that the first stars may have appeared even earlier than that, at perhaps 150 million years after the big bang. When they formed, these first stars did not contain elements heavier than helium, as such elements were first created (in other than trace quantities) only in the earliest generation of stars. (See here for a discussion of the earliest stars.)

The observations of GRB 090423 give some evidence that the galaxy in which it occurred did have small amounts of elements heavier than helium. Further, the afterglow that occurs following the peak brightness of any GRB is generally similar between both GRB 090423 and much closer GRBs. These facts are hints that the progenitor of GRB wasn't one of the Population III stars.

How does a GRB give us information about the intergalactic medium at z ≈ 8.2? That turns out to be closely related to the way that the redshift was estimated in the first place. Normally this is done by identifying known emission or absorption lines in a spectrum and simply calculating the amount of shift directly. However, GRB 090423 is so faint, and declined in brightness so quickly, that it wasn't possible in the time available to obtain a detailed spectrum.

Instead, an important feature of the IGM at that time comes to the rescue. The feature is that there is at that time a substantial, though not precisely known, quantity of un-ionized hydrogen atoms in the IGM. This hydrogen is left over from the period of "recombination" in which the CMB appeared. CMB photons are far too weak to "scatter" from hydrogen atoms, because quantum mechanics requires that a photon must have a certain minimal amount of energy to raise an electron bound in a hydrogen atom out of its "ground state" of lowest energy.

The minimum amount of energy required is that possessed by a 10.2 eV photon of wavelength 121.6 nm, which is in the ultraviolet part of the spectrum. This spectral point is known as "Lyman-α". (We covered this concept in detail here.) Ordinary stars like the Sun in the universe at present emit little light at this wavelength, but much larger, hotter, and brighter stars emit quite a bit of this ultraviolet light.

Consequently, as soon as such hot stars began to shine, the atomic hydrogen in the IGM began to reionize. There was a price to be paid for this, of course: all the photons with enough energy lost some of their energy in the process of reionizing the hydrogen. And so, most of the light whose photons had enough energy was absorbed or "scattered" in this reionization period.

Eventually most of the hydrogen in the IGM of the early universe would become fully ionized, so that very energetic photons could again pass unimpeded. That stage marks the end of the reionization period. The whole period may have lasted from 150 million years to a 900 million years after the big bang, but we are quite unsure of the actual endpoints.

GRBs may be able to tell us. To begin with, it's easy to derive the redshift of a GRB that flared during the reionization period. If the redshift is z, then in the "rest frame" of the GRB, the light will start to be absorbed strongly at 121.6 nm. But we will observe this drop-off to occur at a wavelength of (z+1)×121.6 nm. For example, if z = 8.2, we see the drop-off at 1120 nm, which is in the infrared. Reasoning backwards, we can compute z from the observed drop off.

If we have enough GRB observations with sufficiently good spectra available, we can infer the amount of reionization that has occurred from the rate of drop-off. Further, if we find GRBs where there is no drop-off, we can infer that reionization is complete. Unfortunately, GRB 090423 tells us little by itself, and only two other GRBs have been observed with z > 6, corresponding to somewhat less than 950 million years after the big bang.

Why do we care about the rate of reionization? Because it tells us indirectly about the rate of formation of very large, hot stars in the early universe. So it turns out that the two things that astronomers want to know about the early universe – the nature of the IGM and the rates at which stars were forming – are pretty closely related. On top of that, the distribution in time of early GRBs gives us an independent estimate of the rate of star formation, since the progenitors of GRBs are exactly the sort of large, hot stars that cause reionization.



ResearchBlogging.org
Tanvir, N., Fox, D., Levan, A., Berger, E., Wiersema, K., Fynbo, J., Cucchiara, A., Krühler, T., Gehrels, N., Bloom, J., Greiner, J., Evans, P., Rol, E., Olivares, F., Hjorth, J., Jakobsson, P., Farihi, J., Willingale, R., Starling, R., Cenko, S., Perley, D., Maund, J., Duke, J., Wijers, R., Adamson, A., Allan, A., Bremer, M., Burrows, D., Castro-Tirado, A., Cavanagh, B., de Ugarte Postigo, A., Dopita, M., Fatkhullin, T., Fruchter, A., Foley, R., Gorosabel, J., Kennea, J., Kerr, T., Klose, S., Krimm, H., Komarova, V., Kulkarni, S., Moskvitin, A., Mundell, C., Naylor, T., Page, K., Penprase, B., Perri, M., Podsiadlowski, P., Roth, K., Rutledge, R., Sakamoto, T., Schady, P., Schmidt, B., Soderberg, A., Sollerman, J., Stephens, A., Stratta, G., Ukwatta, T., Watson, D., Westra, E., Wold, T., & Wolf, C. (2009). A γ-ray burst at a redshift of z ≈ 8.2 Nature, 461 (7268), 1254-1257 DOI: 10.1038/nature08459




ResearchBlogging.org
Salvaterra, R., Valle, M., Campana, S., Chincarini, G., Covino, S., D’Avanzo, P., Fernández-Soto, A., Guidorzi, C., Mannucci, F., Margutti, R., Thöne, C., Antonelli, L., Barthelmy, S., De Pasquale, M., D’Elia, V., Fiore, F., Fugazza, D., Hunt, L., Maiorano, E., Marinoni, S., Marshall, F., Molinari, E., Nousek, J., Pian, E., Racusin, J., Stella, L., Amati, L., Andreuzzi, G., Cusumano, G., Fenimore, E., Ferrero, P., Giommi, P., Guetta, D., Holland, S., Hurley, K., Israel, G., Mao, J., Markwardt, C., Masetti, N., Pagani, C., Palazzi, E., Palmer, D., Piranomonte, S., Tagliaferri, G., & Testa, V. (2009). GRB 090423 at a redshift of z ≈ 8.1 Nature, 461 (7268), 1258-1260 DOI: 10.1038/nature08445


Other blog posts

Beyond the Farthest Star (12/14/09)

Reports on the newly-published research on GRB 090423

Most distant gamma-ray burst spotted (10/28/09)

A Blast From the Deep, Dark Past (10/28/09)

Astronomers explore 'last blank space' on map of the Universe (10/28/09)

Blast from the Past Gives Clues About Early Universe (10/28/09)

Blast from the Very Far Past (10/28/09)

Astrophysics: Most distant cosmic blast seen (10/29/09)

A big gamma-ray burst at a redshift of z ≈ 8.2 (10/29/09)

GRB 090423 at a redshift of z ≈ 8.1 (10/29/09)

Discovery of Radio Afterglow from the Most Distant Cosmic Explosion


Reports on the initial observation of GRB 090423

Scrambling to Read the Meaning Of the Sky's Most Ancient Flare (9/18/09)

Earliest astrophysical object yet seen (7/2/09)

Most Distant Known Object In The Universe / Science News (4/28/09)

The Farthest Thing Ever Seen (4/28/09)

Most distant object in the universe spotted (4/27/09)

The Most Distant Object Yet Discovered in the Universe (4/28/09)

Farthest Known Object: New Gamma-Ray Burst Smashes Cosmic Distance Record (4/28/09)

New Gamma-Ray Burst Smashes Cosmic Distance Record (4/28/09)

Ancient gamma-ray burst is most distant object ever seen (4/29/09)

Space Explosion Is Farthest Thing Ever Seen (4/28/09)

Telescope snaps most distant object (4/28/09)

Exploding star is oldest object seen in universe (4/29/09)

Cosmic blast sets distance mark (4/28/09)

Astronomers see oldest object in universe yet (4/28/09)

A glimpse of the end of the dark ages: the gamma-ray burst of 23 April 2009 at redshift 8.3

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