Powered by Blogger.

Exceptionally deep view of strange galaxy

Monday, February 23, 2009

Exceptionally deep view of strange galaxy (2/5/09)
A spectacular new image of an unusual spiral galaxy in the Coma Galaxy Cluster has been created from data taken by the Advanced Camera for Surveys on the NASA/ESA Hubble Space Telescope. It reveals fine details of the galaxy, NGC 4921, as well as an extraordinary rich background of more remote galaxies stretching back to the early Universe.

The Coma Galaxy Cluster, in the northern constellation of Coma Berenices, the hair of Queen Berenice, is one of the closest very rich collections of galaxies in the nearby Universe. The cluster, also known as Abell 1656, is about 320 million light-years from Earth and contains more than 1000 members. The brightest galaxies, including NGC 4921 shown here, were discovered back in the late 18th century by William Herschel.

The galaxies in rich clusters undergo many interactions and mergers that tend to gradually turn gas-rich spirals into elliptical systems without much active star formation. As a result there are far more ellipticals and fewer spirals in the Coma Cluster than are found in quieter corners of the Universe.

NGC 4921 is one of the rare spirals in Coma, and a rather unusual one — it is an example of an "anaemic spiral" where the normal vigorous star formation that creates a spiral galaxy’s familiar bright arms is much less intense. As a result there is just a delicate swirl of dust in a ring around the galaxy, accompanied by some bright young blue stars that are clearly separated out by Hubble’s sharp vision. Much of the pale spiral structure in the outer parts of the galaxy is unusually smooth and gives the whole galaxy the ghostly look of a vast translucent jellyfish.

NGC 4921 – click for 1280×1309 image

What are mirror neurons good for?

Last week I noted that there have been some serious questions raised in a paper by Gregory Hickok about the "mirror neuron theory of action understanding".

I've now read the paper, and there's a lot that could be said on the topic.

But first, what's the discussion about to begin with?

"Mirror neurons" have received a lot of speculative attention in the popular science media. I've done some of that myself. (See here, here, here, here.)

So what is a "mirror neuron"? According to Wikipedia (which is as good a source as any for popular usage of a term), "A mirror neuron is a neuron which fires both when an animal acts and when the animal observes the same action performed by another (especially conspecific) animal. Thus, the neuron "mirrors" the behavior of another animal, as though the observer were itself acting."

That definition needs to be unpacked a little, for the sake of being specific about what's under discussion, even if we have to deviate from what is popularly understood. So, more specifically, a mirror neuron is one that's found in a motor control area of an animal's brain. It's not the only type of neuron there, but it does activate when the animal performs specific motor actions (different ones for different neurons).

The other characteristic that a mirror neuron is presumed to have is that it also activates when the animal perceives another animal performing the same action that causes activation of the neuron in the observing animal.

Notice what's not being defined as a mirror neuron. We aren't talking about just any neuron which activates when an animal perceives another animal performing some action. If that were the definition, it would be somewhat tautologous to assert that such a neuron helps the observing animal to "understand" the actions of another animal. Clearly, any animal that is capable of "understanding" the actions of other animals (of the same or even different species) must have some action-specific neurons that activate when observing actions of other animals.

It would not be pointless to discuss such things, but we would be more into the area of what it means for an animal to "understand" actions of another and how that might happen. That's a much broader issue, even applied to particular species, especially humans.

However, as soon as we agree that we're talking about certain neurons only in the limited sense mentioned above, the question arises of whether such neurons exist at all. And the interesting thing is that there are generally accepted research findings that such neurons do exist – in one particular species: macaque monkeys. These are one particular species of old world monkeys that happen to be used frequently in neurobiological research, because (being primates) they're a lot closer to humans than, say, rats, but also a lot more convenient and less expensive to work with than humans.

But note that, again according to Wikipedia, "The only animal in which mirror neurons have been studied individually is the macaque monkey. In these monkeys, mirror neurons are found in the inferior frontal gyrus (region F5) and the inferior parietal lobule." Apparently, evidence that mirror neurons even exist in other species, especially humans, is sparse to non-existent.

That's one of the main points made in the Hickok paper I've been referring to (Eight Problems for the Mirror Neuron Theory of Action Understanding in Monkeys and Humans). Specifically:
there have been a host of studies aimed at investigating the ‘‘mirror system’’ in humans, but much of this work has investigated behaviors that mirror neurons could not possibly support given their response properties in monkeys, and therefore, the connection between these behaviors and mirror neurons is tenuously based on a chain of assumptions: Mirror neurons exist in humans (there are individual cells that respond both during action execution and action perception), mirror neurons have evolved to support functions in humans that they do not support in monkeys, this evolution has conserved the functional properties found in monkeys, and mirror neurons are responsible for the behavior in question.

Unfortunately, the existence of mirror neurons in humans is still just an assumption. And further, assumptions about what aspects of human cognition mirror neurons (if they exist) might take part in significantly exceed what is known about the function of mirror neurons in monkeys. Hickok provides a partial list of human capabilities sometimes assumed to involve mirror neurons: "speech perception, music perception, empathy, altruism, emotion, theory of mind, imitation, autism spectrum disorder, among others".

Clearly, that list far surpasses merely "action understanding". And it goes far beyond the data, because macaque monkeys are not known to exhibit most of those capabilities. Indeed, they are known not to have (e. g.) much ability for imitation. So to assume that mirror neurons can be used to explain all of those things requires the assumptions that humans have analogues of macaque mirror neurons, and that such analogues play a significant role in those varied capabilities.

Such assumptions may well provide fruitful hypotheses for future research. But the research to adequately justify such ideas has scarcely begun.

On top of all that, it's not clear how important mirror neurons are for "action understanding" even in macaques. I find two main points in Hickok's paper, and this is one of them. The other is to call into question the importance of a "mirror system" (of neurons in motor-related brain areas) in humans, should such even exist, for "action understanding". Unfortunately, I don't have time in this note to go into more detail on his arguments regarding these points.

I think one has to question what exactly is meant by "action understanding" in the first place. It's certainly a valid question for macaques. We can't even be sure of what it means for a macaque to "understand" anything – since we have no introspective knowledge of the macaque mind. But here's a possible way to operationalize the notion. We might say that "understanding" means an ability to predict what might follow the observation of a specific action in another individual. For example, certain facial expressions might predict further actions, such as overt aggression or attempts at mating behavior.

Many animals certainly have such abilities. Dogs, for instance, obviously know what it means when another dog is seen baring its teeth. But does that mean dogs have analogues of mirror neurons that contribute to this understanding? Do we know whether mirror neurons, even in macaques, assist in predicting future behavior of other individuals? Since I'm hardly an expert in animal behavior, I can't answer those questions.

What all of these questions mean to me is not that we have to give up hope of understanding human characteristics, such as empathy, altruism, imitation, theory of mind, and so forth. Instead, the take-away is that a vast amount of further research work needs to be done in order to establish a sound scientific understanding of the neurobiology of such abilities. The hypothesis that humans have some sort of "mirror system" of neurons that plays a role in empathy, altruism, imitation, etc. is at least a plausible one, inspired by a rough analogy with macaque mirror neurons.

But almost all the research remains to be done that would (1) identify parts of the human brain that comprise a "mirror system", and (2) show that such subsystems underlie each specific case of what we might call "empathetic behavior" in humans. This would appear to be a task similar in difficulty to that of achieving a neurobiological understanding of almost any type of "higher-level" human capability, from abstraction to complex language to long-range planning.

And yet there are good evolutionary reasons for expecting that one or more "mirror systems", in some broader sense, may exist in humans. Very generally, humans have highly developed capabilities for social organization. Such capabilities are needed to enable specific aspects of human social behavior, e. g. the ability to construct elaborate social hierarchies, build complex, enduring social coalitions, and detect covert violators of important social norms. Such capabilities would be evolutionarily favored in selecting for groups that are more cohesive and unified in competition with rivals. (At least if one thinks that group selection is possible.)

If you don't happen to believe in group selection, there are other reasons that individuals possessing good "empathic skills" would have an adaptive advantage and higher fitness compared to other individuals.

For example, consider hand-to-hand combat. Humans have always fought bloodily against others of their species, especially members of unrelated tribes. The ability to rapidly and accurately predict the next hostile moves of an opponent bent on one's destruction would have to be ranked as very valuable. Obviously, some individuals are able to become very skilled in "martial arts", which rely on highly sensitive observance of the detailed behavior of others.

More generally, beyond the level of physical combat, the admonition to "know your enemy" has always been excellent advice. Sensitive understanding of the subtleties of body language is an extremely useful skill in many competitive situations, as good poker players and canny negotiators will attest. Being able to understand the goals and intentions of an opponent certainly has evolutionary survival value. And the same ability regarding others in general is just as useful for achieving cooperation.

Understanding the neurobiology of such skills is an excellent, albeit very long-range, research goal. I'm not necessarily skeptical of the possibility of such a reductionistic goal, but I don't expect it to be achieved very soon, either....

One may reasonably ask why, if the actual evidence for a mirror neuron system in humans is so questionable, the idea is also so popular and widely discussed. The answer seems to be that, if valid, the idea provides important support for the philosophy of "embodied cognition", which holds that the nature of human thinking and emotion is closely tied to the physical body. But that's far too large of an issue to start addressing here.

Tags: , ,

Gut feelings may actually reflect reliable memories

Monday, February 16, 2009

We've had a bit of discussion of "gut feelings" recently. See here, here.

I've thought for a long time that one explanation of "intuition" and "gut feelings" when applied to dealing with a particular issue or problem is that we have dealt with a similar issue or problem before, but we do not have a clear memory of having done so. Or else we have read or otherwise learned some information related to the issue or problem. But when confronted with the issue or problem again, we "intuitively" sense how to deal with it, even though we aren't conscious of remembering the previous experience or information.

Actually, this happens a lot with experts in many areas, such as law, medicine, or business. For example, a young physician examining a patient with a certain set of symptoms may recall having learned in school that the symptoms might indicate any of several different problems. And that to distinguish among the possible causes of the symptoms it is necessary to carefully examine the particulars of the situation.

An older, more experienced physician, on the other hand, may quickly settle on one specific diagnosis without consciously going over the detailed checklist of distinguishing indicators. In this latter case, the "intuition" may simply be unconscious recollection of past experience where some specific feature in the symptoms correctly tipped the balance between one diagnosis or another.

This is not an original observation (though I can't quite recall where I first saw it), but there is new research that does support it:

Gut Feelings May Actually Reflect Reliable Memories (2/8/09)
You know the feeling. You make a decision you're certain is merely a "lucky guess."

A new study from Northwestern University offers precise electrophysiological evidence that such decisions may sometimes not be guesswork after all.

The research utilizes the latest brain-reading technology to point to the surprising accuracy of memories that can't be consciously accessed.

During a special recognition test, guesses turned out to be as accurate or more accurate than when study participants thought they consciously remembered.

"We may actually know more than we think we know in everyday situations, too," said Ken Paller, professor of psychology at Northwestern.

Actually, this is so well known that psychologists have names for it: "implicit memory" or "recognition memory". It's closely related to another effect called "priming".

So when we are, sometimes, urged to go with our intuition or "gut feelings" in making a decision, it's not necessarily bad advice. We may in fact be making well-informed decisions even when we think we are using our "intuition". But the problem is that our memory, whether explicit or implicity, can be unreliable or downright wrong. So "intuition" can just as easily get us into trouble.

In particular, we may be remembering "information" that is simply untrue. As Satchel Paige is reported to have said, "It's not what you don't know that hurts you. It's what you know that just ain't so."

When faced with important decisions, and enough time to consider them, perhaps it's not a bad idea to go consult reliable sources of information, just to be sure...

The blog Neurophilosophy has a good discussion of this research and implicit memory:

The neurological basis of intuition (2/9/09)
Most of us have experienced the vague feeling of knowing something without having any memory of learning it. This phenomenon is commonly known as a "gut feeling" or "intuition"; more accurately though, it is described as implicit or unconscious recognition memory, to reflect the fact that it arises from information that was not attended to, but which is processed, and can subsequently be retrieved, without ever entering into conscious awareness.

Further reading:

Study Suggests Why Gut Instincts Work (2/8/09) – Livescience.com

Hidden memories guide choices (2/9/09) – Nature.com

Subliminal messages really do affect your decisions (2/14/09) – NewScientist.com

Tags: ,

Problems for the mirror neuron theory of action understanding

This is a heads-up for people who have been assuming that mirror neurons – which have been most thoroughly studied in monkeys rather than humans – play an important role in the ability of humans to "understand" the actions of others. (It's kind of hard to determine whether monkeys understand, in the human sense, the actions of other monkeys.)

There is increasing skepticism from some in the neuroscience community that mirror neurons – if they even exist in humans in a form analogous to those in monkeys – live up to the high expectations.

Greg Hickok, Professor of Cognitive Sciences, and Director of the Center for Cognitive Neuroscience at UC Irvine, has been expressing concerns in this area at his blog, Talking Brains. Now a paper of his that discusses these concerns has been published at the Journal of Cognitive Neuroscience.

Here's the announcement from his blog:

Eight problems for the mirror neuron theory of action understanding (2/10/09)
The basic conclusion is that there is little or no evidence to support the mirror neuron=action understanding hypothesis and instead there is substantial evidence against it.

The announcement is also here.

Unfortunately, the journal isn't open access, and I haven't yet seen the paper. If and when I have a chance to read it, I'll very likely try to report a lot more. I've already written about the subject of mirror neurons, based on various earlier accounts, e. g. here, here, here, here.

Pending more information, Hickok has some posts on his blog that provide a few details. Especially this from last August:

Eight Problems for the Mirror Neuron Theory of Action Understanding (8/6/08)
Regular readers (and perhaps even occasional readers) of Talking Brains are well aware that I have been rather critical of the interpretation of mirror neurons that dominates the literature, namely, that they are the basis of action understanding. I've finally synthesized all of these critical comments into a critical review titled "Eight Problems for the Mirror Neuron Theory of Action Understanding in Monkeys and Humans."

Here are other posts by Hickok since that one that discuss mirror neurons:

Mirror neurons, hubs, and puppet masters (8/21/08)
How much can a motor representation contribute to action word meaning? (8/26/08)
Mirror neurons in the inferior parietal lobe: Are they really "goal" selective? (10/24/08)
Rock-Paper-Scissors and mirror neurons: Executed and observed movements have different distributed representations in human aIPS (10/31/08)
Ventral premotor cortex and action processing: Urgesi, et al. (11/3/08)
Mirror neurons in humans revealed by fMRI adaptation (11/4/08)

There are many earlier posts. Just search the blog for "mirror neuron".

One last piece of information – the PubMed abstract for Hickok's paper:

Eight Problems for the Mirror Neuron Theory of Action Understanding in Monkeys and Humans
The discovery of mirror neurons in macaque frontal cortex has sparked a resurgence of interest in motor/embodied theories of cognition. This critical review examines the evidence in support of one of these theories, namely, that the mirror neurons provide the basis of action understanding. It is argued that there is no evidence from monkey data that directly tests this theory, and evidence from humans makes a strong case against the position.

Stay tuned.


Thinking with the gut or the head

Sunday, February 8, 2009

I wrote a longish reply to a comment on this. Since I summarized various other things in that comment, perhaps it will be useful to elevate it to a separate post, so here it is, with minor enhancements:

This strongly echoes an article from mid-2006 in The Guardian, by Johnjoe McFadden. He's at least a reputable molecular biologist and cognitive theoretician.

This is actually a very deep and interesting issue. There are (at least) two sides to it, and a whole lot of oversimplifications.

McFadden makes some good points in his article that you cite. However, I bridle at his subtitle: "The evidence seems to be that the conscious mind isn't much use in making hard decisions".

We have all seen the chaos that results when too many people go with their "intuition" to make hard decisions. Out of that "stupidity of crowds" we get results like the financial catastrophe that we are in the middle of. We also get the election of very bad public officials, sometimes, when the crowd listens only to the emotional appeals of the candidates.

Another example of bad decisions typically made by "intuition" is in mate choice. About 50% of marriages end in divorce, due to bad judgment regarding long-term compatibility and listening only to the "heart" instead of the "head". And who knows how many of those 50% of marriages that don't end in divorce are actually unhappy for both parties?

Caveat emptor!

There seem to be a lot of "popular" writers these days who produce books appealing to the public's frustration with the difficulty of making rational choices.

An example is Gladwell's Blink: The Power of Thinking Without Thinking. Another is Surowiecki's The Wisdom of Crowds.

A writer with somewhat more intellectual respectability is Gigerenzer, who's written a number of the books on this subject, including Gut Feelings: The Intelligence of the Unconscious.

One theme in all these writings is that human consciousness isn't really aware of much that's going on in the brain.

I have discussed, with approval, that exact theme myself, here. There is also a very good blog post that links to mine here.

Just yesterday, in another context, I wrote a bit about why we should expect that evolution has made our brains in such a way that leaves a lot of room for unconscious "reasoning". I'll try to work that into a post here when time permits.

And yet, I have to keep coming back to point out the significant problems caused by relying only on "gut feelings". We simply cannot afford to give up on rational thinking in making our most important decisions. It's just too risky.

My opinions on this shouldn't come as a surprise. Just look at the title of this blog.

Trust Your Gut: Too Much Thinking Leads To Bad Choices?

Saturday, February 7, 2009

Well, this is obviously what sales/marketing droids want people to believe. After all, thinking and rational deliberation is usually somewhat reality based. It tends to take into account at least some facts about the real world. Whereas "going with the gut" can just as easily as not ignore important facts that are known or obvious. Especially when propagandistic or marketing pitches are directed at the person being sold to.

Trust Your Gut: Too Much Thinking Leads To Bad Choices (1/26/09)
Don't think too much before purchasing that new car or television. According to a new study in the Journal of Consumer Research, people who deliberate about decisions make less accurate judgments than people who trust their instincts. ...

In five separate studies, the researchers found that better judgments can often be made without deliberation. In the first study, participants rated Chinese ideograms for attractiveness. In a following study, participants were asked to judge paintings that were widely considered high- or low-quality. Subsequent groups of participants rated jellybeans and apartments. In all the studies, some participants were encouraged to deliberate and others to go with their gut.

The more complex the decision, the less useful deliberation became. For example, when participants rated apartments on just three primary characteristics (location, price, and size) deliberation proved useful. But when the decision became more complex (with nine characteristics) the participants who deliberated made worse decisions.

One has to wonder exactly how these "researchers" define "better" or "worse" decisions. Better or worse for whom? The salesperson? Especially in view of the following, it almost seems as though outright deception and manipulation is being advocated:
"For example, if a car boasts one particularly good feature (for example, safety) but has a number of other negative features (for example, expensive, bad gas mileage, poor handling), a car salesman might encourage a potential car buyer to deliberate over the pros and cons of the car, while at the same time emphasizing the importance of safety. In this way, the disturbed weighting of attributes created by deliberation might be used to highlight the one sellable feature and draw attention away from the unattractive features," write the authors.

For example, decisions about home mortgages are obviously complex, yet require careful deliberation. What's advocated in this "research" is what made it possible for so many objectively bad decisions about home mortgages to be sold to buyers in recent years, with eventual disastrous results.

One wonders whether political scientists have investigated to what extent such "consumer research" studies are taught to and studied by political operative, and to what extent they adversely affect political choice about candidates and issues.

Materialism And Death Anxiety Lead To Brand Loyalty

Materialism And Death Anxiety Lead To Brand Loyalty (1/26/09)
Materialistic people tend to form strong connections to particular product brands when their level of anxiety about death is high, according to a new study in the Journal of Consumer Research. ...

While conventional wisdom holds that materialistic individuals are weakly connected to brands and use them as superficial status badges, the new research proves that brands hold more meaning for materialistic consumers than previously thought. When those individuals are also worried about death, their brand attachment grows.

"We propose that materialistic individuals form strong connections to their brands when death anxiety is high but not when death anxiety is low," write the authors. "Materialistic individuals are strongly connected to their brands and employ them as an important source of meaning in their lives."

Sounds like a good description of committed followers of certain ideologies, such as Republicans (the U. S. political party).

Earlier discussion on this theme: here.

Black Hole Outflows From Centaurus A

Friday, February 6, 2009

Black Hole Outflows From Centaurus A
This image of Centaurus A shows a spectacular new view of a supermassive black hole's power. Jets and lobes powered by the central black hole in this nearby galaxy are shown by submillimeter data (colored orange) from the Atacama Pathfinder Experiment (APEX) telescope in Chile and X-ray data (colored blue) from the Chandra X-ray Observatory. Visible light data from the Wide Field Imager on the Max-Planck/ESO 2.2 m telescope, also located in Chile, shows the dust lane in the galaxy and background stars. The X-ray jet in the upper left extends for about 13,000 light years away from the black hole. The APEX data shows that material in the jet is travelling at about half the speed of light.

Centaurus A – click for 665×505 image

Additional information:

Black Hole Outflows From Centaurus A (1/28/09)

Wall Divides East and West Sides of NGC 604

Wall Divides East and West Sides of NGC 604 (1/27/09)
A new study unveils NGC 604, the largest region of star formation in the nearby galaxy M33, in its first deep, high-resolution view in X-rays. This composite image from Chandra X-ray Observatory data (colored blue), combined with optical light data from the Hubble Space Telescope (red and green), shows a divided neighborhood where some 200 hot, young, massive stars reside.

Throughout the cosmic metropolis, giant bubbles in the cool dust and warm gas are filled with diffuse, multi-million degree gas that emits X-rays. Scientists think these bubbles are generated and heated to X-ray temperatures when powerful stellar winds from the young massive stars collide and push aside the surrounding gas and dust. So, the vacated areas are immediately repopulated with the hotter material seen by Chandra.

NGC 604 – click for 720×762 image

Cancer Research Blog Carnival #18

I confess. I like to categorize things. There's something about neat little pigeonholes that I find simply irresistible. So, especially for this carnival, I've done the category thing.

But first, I want to take this opportunity to raise a question that readers here may be able to offer some insight on. Actually, I already raised it: Where are the books on cancer for general readers? If anyone can shed some light on that, please leave a comment to that post.

Cancer research

There's more about "alternative" medicine further down, but there's also some relevant research to discuss. Namely, herbal supplements can occasionally be helpful. However, as Kamel at Bayblab explains, it can also happen that an Anti-cancer supplement interferes with [a] cancer drug. In this case, it's something as seemingly innocuous as green tea.

Animal cells have many remarkable mechanisms for protecting an organism against cancer, including mechanisms for detecting damage to DNA, trying to repair damaged DNA if possible, or inducing cell senescence or death if repair fails. Unsurprisingly, damage to genes associated with these mechanisms is one of the main biological reasons for an animal to develop cancer. Yours truly discusses several recent research papers about this: DNA repair genes and cancer and DNA repair and cancer II.

Personalized medicine

Erin Cline at 23andMe, a start-up company in the business of providing customers with information on their personal genetic makeup, and what it means, discusses a study that identified More than 100 Genetic Variations Associated with Leukemia Treatment Response. The study is said to be important because it could identify genetic variations (SNPs) in normal cells that might positively or negatively affect treatment outcomes, rather than genetic abnormalities only in the cancerous cells.

In a detailed and informative comment to a post about personalized medicine at Discovering Biology in a Digital World, Gregory Pawelski explains how Personalized Cancer Medicine Is Here, Now.

Exposés of "alternative" medicine

Frank Swain of SciencePunk pens a droll review of an expensively produced film on a quack "diet-based cure for cancer": Stupidity caught on celluloid: The Beautiful Truth. Executive summary: "Is it possible to pack a DVD with idiocy so dense that light bends around it?"

Is it true that advocates of "alternative" medicine will stoop to "abuse" of celebrities in order to promote their delusions? Orac at Respectful Insolence thinks so: Abusing celebrities with cancer in order to promote quackery. I'd say he makes a good case.

Orac also, in an atypically succinct post, tells us about An even more typical than typical "alternative medicine" breast cancer testimonial. How alternative medicine can cure a cancer that isn't even there! That's powerful indeed.

Good health advice

Surfer Sam offers what looks like generally sound advice on how to Prevent and Cure Colon Cancer. Well, at least how to lower the risk. If a cancer at a sufficiently early stage is found during a colonoscopy, removal of it during the procedure may be a cure – if you're lucky.

General information

Jessica Merritt at U. S. PharmD (a portal of information for prospective pharmacists) offers her selection of Top 50 Genetics Blogs. It's not all about cancer, but most of the choices look sound, and there are a few familiar names on the list.


That's it for this month. The next Cancer Research Blog Carnival is scheduled for March 6. Watch the carnival home page for details, or better yet, volunteer to host the carnival yourself.

Which came first - the galaxy or the black hole?

Sunday, February 1, 2009

This news isn't exactly fresh, having been announced several weeks ago, and it's been reported in many places. However, it's quite important (if correct), because it suggests that the supermassive black holes that seem to exist at the centers of most galaxies formed much faster, initially, than the rest of the galaxy.

We've already discussed a little about galaxy formation: here.

The study for present discussion was done using radio telescopes, which could detect spectral sequences due to carbon monoxide gas in order to make estimates of mass in galaxies' central regions. The galaxies studied were all observed as they existed less than two billion years after the big bang (redshift ≳ 3). At that age, all galaxies that can be observed in enough detail with optical telescopes are quasars, in which so much light comes from the hyperactive central black hole that almost nothing can be inferred about the rest of the galaxy. Use of radio telescopes circumvented that problem.

In most sufficiently regular galaxies closer to us, most of the mass of stars and gas is concentrated in a central bulge. In such galaxies, representing the large majority of the universe's age of 13.7 billion years, the ratio of mass in the central bulges to the mass of the central black hole is remarkably predictable and averages about 700:1. But in the four early galaxies studied, the ratio was only about 30:1. Although the mass of the central black holes studied was nearly as large as that of galaxies closer to us, the galaxies themselves appeared to be much less massive.

This anomaly in the ratios does not necessarily imply the black holes formed before the rest of the galaxy, but it does suggest they at least grew more quickly in the early stages. There are not yet good theories for why this might happen, or at what point growth of the rest of the galaxy accelerates compared to growth of the black hole.

The internal workings of quasars are not well understood. It may be that quasars can form only when the ratio of central mass to black hole mass is low, as in the observed examples. Or maybe gas in the neighborhood of a very active quasar is dispersed by the intense radiation, so that it can collapse further only when the activity dies down somewhat. Conversely, perhaps, in cases where the mass ratio is higher, radiation from the black hole has diminished, or never was as strong, so that we have not been able to detect those cases.

Good reasons exist to think that very active black holes should generally disrupt formation of stars in the surrounding gas. But there are also reasons they might at some point assist in star formation. We'll need much more observational evidence, and theoretical calculations, before the picture gets clearer.

There are other problems, too. For instance, the mass of the galactic bulges were estimated from the motion of gas rather than stars (which could not be observed). Magnetic fields could have affected gas flow, resulting in an underestimate of total mass. It's also not clear how supermassive black holes could have formed by themselves, without the gas they presumably grew from also collapsing to form individual stars.

While it's interesting to have a little evidence that the black holes formed first, a claim based on observations of only four early galaxies is less than fully convincing. Many more data points are needed.

And assuming the relationship holds up, even tougher questions remain. How and why did the black holes themselves form? How did they grow so big so quickly? What is the relationship over time between the size of the black hole and the galaxy that forms around it? How do they affect each other's growth?

Black Holes Lead Galaxy Growth (1/6/09)
Earlier studies of galaxies and their central black holes in the nearby Universe revealed an intriguing linkage between the masses of the black holes and of the central "bulges" of stars and gas in the galaxies. The ratio of the black hole and the bulge mass is nearly the same for a wide range of galactic sizes and ages. For central black holes from a few million to many billions of times the mass of our Sun, the black hole's mass is about one one-thousandth of the mass of the surrounding galactic bulge.

"This constant ratio indicates that the black hole and the bulge affect each others' growth in some sort of interactive relationship," said Dominik Riechers, of Caltech. "The big question has been whether one grows before the other or if they grow together, maintaining their mass ratio throughout the entire process." ...

"We finally have been able to measure black-hole and bulge masses in several galaxies seen as they were in the first billion years after the Big Bang, and the evidence suggests that the constant ratio seen nearby may not hold in the early Universe. The black holes in these young galaxies are much more massive compared to the bulges than those seen in the nearby Universe," said Fabian Walter of the Max-Planck Institute for Radioastronomy (MPIfR) in Germany.

"The implication is that the black holes started growing first."

The next challenge is to figure out how the black hole and the bulge affect each others' growth. "We don't know what mechanism is at work here, and why, at some point in the process, the 'standard' ratio between the masses is established," Riechers said.

However, another report quoting one of the researchers points out that only four very early galaxies were included in the radio telescope study:

In the Young Universe, Black Holes May Have Formed First (1/7/09)
“These very distant black holes are already about as massive as they will ever get — about 1 billion solar masses — so the only thing left is for the galaxy to form around them,” says Carilli. One implication, he says, is that the turbulent activity associated with accretion onto these black holes “may have a profound effect on the formation of the host galaxy very early in the universe.” But Carilli emphasizes that his team has examined only four galaxies from these early times. It’s possible, he says, that this handful of galaxies may have unusually heavy supermassive black holes.

“We really need to generalize to more galaxies that are less extreme,” he adds.

Martin Rees lays out the case for skepticism of the results:
“The results are interesting, and an important clue to the growth and evolution of galaxies,” comments Martin Rees of the University of Cambridge in England. However, he adds, “I think it is over-interpreting the data to say that ‘black holes come first.’ Even at [early times] the bulge mass could typically be about 100 times larger than the mass of the hole.”

Rees suggests that the bulges and holes form concurrently throughout cosmic history, but that in the early universe “it may be easier for infalling gas to go all the way to the center of a galaxy, forming a black hole rather than condensing into stars on the way in.”

A key question that’s still unanswered, he adds, is whether galaxies must have a minimum mass in order to possess a central black hole. “This is relevant to the issue of how the 'seed' black holes form, and to the role of mergers … in building up galaxies,” says Rees.

Other news reports:

Tags: ,

18th Cancer Research Blog Carnival

... will be right here on Friday, February 6.

Go check the carnival home page for general information and access to all previous editions. Then go here to send in your recommendation for inclusion in the carnival.

The carnival's looking for your special gem dealing with cancer research. There may be (if I feel like it) prizes awarded for the best submissions, so make 'em good.

What sort of prizes? Oh, maybe the URL of a web site promoting Matthias Rath for the next Nobel Prize in medicine... if I can find one. Or how about the URL of the best internet pharmacy based in Pyongyang, for all your laetrile needs?

In any case, the deadline for submissions is 11:59 PM EST (UTC-5) on Thursday, February 5. So don't delay....

Knowledge Link Suggest

Free Mobile Games Free Online Slots Games Game Mania Shooting Simulator Best Restaurants Online Educational Games Play Free Online Slot Machine Games Chep Holiday Cheap Hotel Chinese Restaurants Play Boat Games Online Free Mobile Games Download Free Games Best games for Android Free Online Slots Games Game Mania Shooting Simulator Shooting Simulator Game Online Educational Games Free Online Slot Online Games For Kids Free Online Learning Games and Apps Free Online Games Play Boat Games Online Free Mobile Games Health Category Best games for Android Hotel and Travel Top free games Play Games Free‎ Game Mania Shooting Simulator Shooting Simulator Game Online Educational Games Free Online Slot Online Games For Kids Free Online Learning Games and Apps Free Online Games Play Boat Games Online Free Mobile Games Download Free Games Best games for Android Shooting Simulator Game Top free games Travel Category Travel Deals Travel guides Travel Information Travel Tips Vegetarian Restaurants Play Games Free‎ ashandtayboe.usa.cc bang-bagsboe.usa.cc bluestindigoboe.usa.cc briwgnboe.usa.cc clwerboe.usa.cc cofwsundayboe.usa.cc criwinboe.usa.cc dabaloghboe.usa.cc film-foodboe.usa.cc highmwippyboe.usa.cc interprofessionals.usa.cc inthedreamingroom.usa.cc investincentralspain.usa.cc jacrancottageboe.usa.cc jerewecurtisboe.usa.cc johwknudsenboe.usa.cc joomlasiterescue.usa.cc jordwyboe.usa.cc judypatoooteboe.usa.cc kawboe.usa.cc keyfoodstores.usa.cc lromneyboe.usa.cc lukeareallboe.usa.cc madridpanoramic.usa.cc medicinegrandrounds.usa.cc medschoolandbeyond.usa.cc mid-east-law.usa.cc monosno-toyboe.usa.cc mylwsboe.usa.cc nowvningboe.usa.cc onlyonawindydayboe.usa.cc pediatricsnow.usa.cc quiwdyboe.usa.cc realrertsboe.usa.cc shelleysscrapbookboe.usa.cc simmarnceboe.usa.cc simpwblymoreboe.usa.cc statetalesboe.usa.cc stevrtoriesboe.usa.cc stjowqboe.usa.cc swewboe.usa.cc thegildedmooseboe.usa.cc thesundahlsboe.usa.cc tuerpecrewboe.usa.cc twohomesboe.usa.cc txstephensboe.usa.cc uglybike.usa.cc unwspoonboe.usa.cc vestlifeboe.usa.cc vintwldtasboe.usa.cc whatsrtsboe.usa.cc decoratedlifeboe.usa.cc fromaloftboe.usa.cc labohemmeboe.usa.cc ofestherleeboe.usa.cc crewchannelboe.usa.cc hiewmaiboe.usa.cc all-too-common-dissent.usa.cc pooflingers.usa.cc moralpanicsandthecopyrightwars.usa.cc burketokirk.usa.cc dialectik.usa.cc overactiveimagination.usa.cc smallcatalogueboe.usa.cc ambulancemommy.usa.cc politicsamongnations.usa.cc design-undercoverboe.usa.cc medievalladyboe.usa.cc cclimpundit.usa.cc sowssentes.usa.cc ooawurootes.usa.cc maiwasttes.usa.cc cowdiarytes.usa.cc hiewmaites.usa.cc lacowdepilytes.usa.cc bakewscratchtes.usa.cc coowkestes.usa.cc cowstowtes.usa.cc devwldtes.usa.cc viowlestes.usa.cc bakwitytes.usa.cc thedwousa.usa.cc ccewifetes.usa.cc unwspoontes.usa.cc simpwblymoretes.usa.cc monosno-toytes.usa.cc nowvningtes.usa.cc smallcataloguetes.usa.cc highmwippytes.usa.cc stjowqtes.usa.cc cofwsundaytes.usa.cc kawtes.usa.cc mylwstes.usa.cc myownmousa.usa.cc ccetes.usa.cc vintwldtastes.usa.cc quiwdytes.usa.cc statetalestes.usa.cc briwgntes.usa.cc criwintes.usa.cc clwertes.usa.cc jerewecurtistes.usa.cc jordwytes.usa.cc johwknudsentes.usa.cc simmarncetes.usa.cc realrertstes.usa.cc stevrtoriestes.usa.cc thesundahlstes.usa.cc vestlifetes.usa.cc whatsrtstes.usa.cc txstephenstes.usa.cc ashandtaytes.usa.cc lromneytes.usa.cc tuerpecrewtes.usa.cc bang-bagstes.usa.cc onlyonawindydaytes.usa.cc akissisjusa.usa.cc cctakisstes.usa.cc bluestindigotes.usa.cc dabaloghtes.usa.cc jacrancottagetes.usa.cc judypatoootetes.usa.cc medievalladytes.usa.cc prettylady21tes.usa.cc shelleysscrapbooktes.usa.cc thegildedmoosetes.usa.cc twohomestes.usa.cc kristiwmpbelltes.usa.cc gatochytes.usa.cc pixfeedtes.usa.cc subjectifytes.usa.cc lizarwshoetes.usa.cc alihewakestes.usa.cc suwingtes.usa.cc elinaminntes.usa.cc kurawkoretes.usa.cc tellyoutodaytes.usa.cc ured8yutes.usa.cc hintoninteriorstes.usa.cc amanwreamingtes.usa.cc thetrwelblogtes.usa.cc craftcitymelbournetes.usa.cc theshopbugtes.usa.cc ciaotaydesignstes.usa.cc decoratedlifetes.usa.cc fromalofttes.usa.cc labohemmetes.usa.cc ofestherleetes.usa.cc crewchanneltes.usa.cc micwarchtes.usa.cc miwaniesuetes.usa.cc

Blog Archive