Monday
Oct082012

One Fish, Two Fish, Red Fish, Black Holes

by Sarah Scoles

 

Where astronomers expected to find at most one black hole, they found two, which is a bigger deal than it sounds like.

Strader, Chomiuk, Maccarone, Miller-Jones, and Seth used the VLA to look at the center of globular cluster M22 to determine whether an intermediate-mass black hole lived at the center. While they did not detect a central object, they did see two bright radio sources. These two radio sources, the recent Nature paper posits, are stellar-mass black holes.

If these sources do turn out to be black holes, not only will they be unexpected, but they will also be the first black holes discovered in a globular cluster and the first stellar-mass black holes discovered using radio waves. Like, ever.

Why did astronomers expect to find a single black hole at the center?

Globular clusters are crowded and geriatric--essentially cosmic nursing homes. Because their stars are so old, the most massive ones have already imploded into black holes. Because these black holes are more massive than the other stars in the cluster (which are still living their regular lives, since the less mass a star has, the longer it lives), they "sink" toward the center.

The theory goes that after the black holes sink to the center, they all get in a big gravitational territory fight in which there can be at most one winner. The winner gets to stay in the nursing home, at the center (the cafeteria?). The other black holes are, theoretically, kicked out of the nursing home and back into the real world (the galaxy)

But that fight obviously doesn't take place exactly the way astronomers thought, given these two black hole tenants.

But how do we know they're really black holes?

Well, we don't "know," per se, but it is, according to the paper, "the most likely explanation" for two reasons:

  1. They are in the core of the globular cluster, which means they must have sunk there, which means they must have a lot of mass.
  2. The ratio of their brightness in radio waves compared to their brightness in X-rays is similar to the radio/X-ray ratio seen in black holes inside the galaxy. These sources were easily detectable in radio waves but were not detected at all in X-rays, which does not mean they are not emitting X-rays, but means they must be below a certain brightness.


    The red M22 represents the properties of the two new black holes. The connected arrow goes to the left because their X-ray luminosities could be 2x10^30 erg/s or lower). Black holes tend to lie along the black line, neutron stars along the blue lines, and white dwarfs not higher than the green line.

In the plot to the right, the x-axis is X-ray luminosity, and the y-axis is radio luminosity. This plot shows the relationship described in #2. If something is emitting lots of X-rays and lots of radio waves, it shows up in the top right. If something is not emitting very much of either sort of radiation, it shows up in the bottom left. 

The red M22, representing both new sources, clearly shares a radio-X-ray relationship more similar to black holes than to neutron stars or white dwarfs--the next heaviest things in the universe. (Note: in the paper, the authors give several reasons that M22 is not on the black hole line; I won't go into them here, but the paper is very readable and the rationalizations come just after Figure 2).

Okay, so these objects are massive, and they emit radiation in the same way that black holes do. Wait, how are we seeing radiation from them if they're black holes? Isn't the point of black holes that they're dark?

As described in the first "So your friend asks..." post, we can only detect black holes if material is in the process of falling into them and/or if other stars are orbiting them.

As the material swirls into the black hole's mouth, like water and your hair down a bathtub drain (yum), it heats up, and this heat causes radiation. The infall also causes huge jets to shoot out of the "top" and "bottom" of the black hole.

For us to see these two globular black holes, they must be actively feeding.

To find out which stars may be the black holes' companions, astronomers compare the locations of the purported black holes to Hubble Space Telescope images of the area. Anything in those two circles could be the stellar companions. Luckily, that looks like only one source for VLA1, and only 1.23 sources for VLA2.On what?

Presumably, on a binary companion star. So these hungry black holes are hanging out in the nursing home, tired from gravitational bouts that were not quite as predicted, and then they decide to eat their long-time partners. Not all at once, but little by little.

To find these unfortunately companions, the team looked at Hubble Space Telescope images to see if any visible stars were very close in location to the black holes' locations. One of the sources is near a red dwarf, and the other is near an orange dwarf (a star somewhere between a red dwarf and the sun. Neither of those is a definite companion, but both are candidates.

How is the research team explaining their result, since it didn't agree with the predictions?

For these two black holes to be here, it must mean that gravitational interactions between black holes that migrate to the center of globular clusters must not always lead to a winner-take-all scenario. Multiple black holes can, it appears, exist in the core of one globular cluster. Strader, et al., say this means that the black holes must not have received a large velocity 'kick' when they were born. It also means that these two are probably not the only ones: if we can only see the black holes that are eating their friends, it stands to reason that there are many more black holes that are not eating their friends, and thus that we can't see. After all, for every person who is eating their friends, there are many more who are not.

 

ResearchBlogging.org Strader J, Chomiuk L, Maccarone TJ, Miller-Jones JC, & Seth AC (2012). Two stellar-mass black holes in the globular cluster M22. Nature, 490 (7418), 71-3 PMID: 23038466

Wednesday
Oct032012

Learning while you sleep

By Brooke Napier

A paper came out this week in Nature Neuroscience with the conclusion: Humans can learn new information during sleep. 

This is not the plot of a Saved By the Bell episode where Zach Morris listens to books on tape before his big test the next day and remembers everything; scoring an “A” and the hottest babe in class – but, these new data show that like Pavlov’s dog, we too can learn without being conscious.

In fact, the experiments used to show this phenomenon are a little too close to Pavlov’s methods for comfort.

Since sleep is defined as “a loss of consciousness and reduced responsiveness to external stimuli”, these researchers had to be sly about how they went about testing learning.

Anat Arzi, et al. knew that the inherent nature of the olfactory response provided an easy read out for learning while unconscious - or sleeping, eureka!

How exactly did they measure learning using odors while people slept?

Simply, bad odors drive weak sniffs and pleasant odors drive stronger sniffs. So they paired pleasant and unpleasant odors with different tones during sleep. Next, they measured the sniff response to the tones alone during the same nights’ sleep and while they were next awake.

In the paper they call this, “partial-reinforcement trace conditioning”.

This sounds trivial, but there is never an experiment on humans that is simple.

Their first hurdle was to make sure that the odors they chose did not wake any of the subjects. A sleep technician used standard polysomnography (diagnostic tool used to study sleep by measuring biophysical changes that occur during sleep) standards for “awake” and “asleep”. Additionally, they characterized the changes in the brain when subjected to the odors using an electroencephalogram (EEG).

I'd like to think my dogs are this smart.

Next, they needed to know that their “pleasant” odor was actually pleasant to everyone (because I know some people who like the smell of Windex, and that’s just wrong) and that it is processed as pleasant while the subject is sleeping. You’ll be happy to know that they chose deodorant and shampoo as pleasant odors and that these were perceived so by the subjects while awake (by verbally agreeing to pleasantness) and while asleep (a measured increase in sniffing while asleep after the pleasant odor).

Ok, now they needed to pair the odor and tone. Since there was a notable increase in concentration of sniffing after exposure to the pleasant odor while sleeping, this was an easy read-out for learning while sleeping.

 

The studied followed as listed below:

1. Pair tones with odors during sleep.

2. Measure sniffs following tones alone on the same night or during their next arousal, or wake, state.

3. Analyze data. 

3 1/2 . Repeat experiments.

4. Get Nature paper.

 

Hey, look at this sweet data:

The sniff response revealed learning during sleep. (a) The averaged normalized sniff trace and (inset) sniff volume during sleep following a pleasant (blue) or unpleasant (brown) odor (n = 28). (b) The averaged normalized sniff volume during sleep following a tone (alone) previously paired during sleep with a pleasant odor (blue outline) and a tone (alone) previously paired during sleep with an unpleasant odor (brown outline) (n = 20). (c) The average learning curve across five continuous repetitions of tones (alone) previously paired with a pleasant odor (blue outline), or five continuous repetitions of tones (alone) previously paired with an unpleasant (brown outline) odor (total = 10 trials). (d) The averaged normalized sniff volume awake following a tone (alone) previously paired during sleep with a pleasant odor (blue outline) and a tone (alone) previously paired during sleep with an unpleasant odor (brown outline) (n = 6). (e) The averaged wake nasal inhalation volume following tones (400 and 12,00 Hz) in a control group that was not conditioned during sleep (n = 10). Statistical analysis was conducted using two-tailed t test (a,b,d,e) and one-tailed t test (c).

 

They also showed that conditioning (or learning) was possible during rapid eye movement (REM) sleep – but was lost when the subject was woken up. They mention that the stronger transfer from non-REM learning to wake may be linked to the previously observed notion that there is increased functional connectivity between olfactory and neocortical areas during slow-wave activity. Interestingly, they then mention that stronger transfer from non-REM may be consistent with previous data showing that humans have rapid loss of memory for REM-related memories (called dream amnesia).

One final interesting tid-bit, they asked the subjects if they remember any of the smells or tones they heard/smelled while sleeping and they have no recollection.

Freaky-deaky.  

In all good Nature paper ediquette they end with a very provocative statement, “[Our study] implies that, beyond the general health advantages associated with good sleep, humans may be able to utilize toward learning new information a state in which they spend about a third of their lives.”

 

 

ResearchBlogging.org Arzi A, Shedlesky L, Ben-Shaul M, Nasser K, Oksenberg A, Hairston IS, & Sobel N (2012). Humans can learn new information during sleep. Nature neuroscience, 15 (10), 1460-5 PMID: 22922782

Friday
Sep282012

Non Sequitur Science Shorts

by Sarah Scoles

Genetics in your hands (and not just in their cells)A screen shot of what I am referring to as "slick."

Nature has a new tool that allows you (all of you) to access research about which genes do what, biochemically. The ENCODE Explorer (where "ENCODE" stands for "Encyclopedia of DNA Elements") is graphically slick and visually organized, dividing the research up into 13 topics and showing both how those topics ("threads") connect to each other and to the papers that the ENCODE collaborators have published. You can read the thread, which brings together information that relates to the thread topic, regardless of which paper in which it originally appeared. You can also read the full papers, if that's the kind of thing you would rather do. Best of all, it's publicly free.

What I like about this project is that it is trying, on purpose, to make the science more accessible--you don't have to read all the papers and find all the times "intergenic regions" are discussed; you don't have to have a Nature subscription; you don't even have to know what the unifying themes of genomic research are. But you can find out.

http://www.nature.com/encode/

 

Galaxies are Deep

The Hubble Space Telescope has given us yet another beautiful image to make us feel small and insignificant and less pretty than astronomical phenomena. In the early 2000s, NASA produced the Hubble Ultra-Deep Field (UDF) image by pointing its camera at the same spot for a long time, integrating long enough to find thousands of distant galaxies lurking in a tiny piece of sky. Now the eXtreme Deep Field (XDF) has taken that image one step further toward the beginningo f the universe, showing galaxies up to 13.2 billion light-years away, their light only thus 13.2 billion years old, or almost as old as the universe itself. It took ten years' worth of data to produce this image.The XDF: Billions and billions (credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team)

 

Here is NASA's official page on the matter: http://www.nasa.gov/mission_pages/hubble/science/xdf.html

 

M87 is Going Wild

Astronomers using the Event Horizon Telescope, a huge interferometer, were able to resolve the base of a relativistic jet shooting out of the galaxy M87. So we know galaxies with central black holes that are actively eating material have these gigantic jets, but we don't exactly know why because we have never been able to observe the stuff that's swirling around and then falling into the black hole--unable to do so, that is, until the Event Horizon Telescope, whose goal is to be large enough to be able to observe just that: the interface between material falling in and the place it fell in to. A new paper, linked below, gives the details of what these jet observations found, but the summary is that "the black hole must be spinning and that the material orbiting must also be swirling in the same direction."

Here is a link to the Wired summary.

Here is a link to the actual paper (Doeleman, et al., 2012).

 

 Whalesong: The Note of Aloneness

I think you should read the actual article on this one. It's an older news article (from May), but it's about a whale that is the only whale that speaks at the frequency 52 Hz. "Not only does 52 Hertz sing at a much higher frequency, but his calls are also shorter and more frequent than those of other whales. It's as if he speaks his own language-- a language of one. Even stranger, 52 Hertz does not follow the known migration route of any extant baleen whale species. He sings alone and travels alone."

The Loneliest Whale in the World, via Discover.

 

Qubits for Everybody

If you have ever wondered what, really, is up with quantum computing, check out Joel Taylor's explanation at Scientific American. He makes an extended juice analogy, and what is more understandable than juice?

 

Don't be that guy (credit: VisitHawaii).

The Brightest Comet You've Never Seen (Yet)

A new comet--called ISON after the instrument that discovered it--was found by Nevski (Belarus) and Novichonok (Russia). Starting at approximately the end of October 2013, ISON will be visible with the naked eye, potentially outshining the moon. From now until then, and from then until it gets closest to the Sun, it will increase in brightness over time. Keep an eye out for it; try to stop yourself from starting a cult. 

For more details, check out Astronomy's article.

Tuesday
Sep182012

Infiltrating the blood brain barrier (BBB)

By Brooke Napier

Infection of the brain by bacteria is fascinating, mostly because it is not suppose to happen but (of course) bacteria find a way around the rules. The brain is thought to be an “immune privileged” site in your body (along with the spinal cord, eyes, placenta, fetus, and testicles), this means that the brain should be able to tolerate foreign invaders without an inflammatory response. This is a desirable trait because it protects the vital organs from dangerous inflammatory responses. 

One trait of the brain that makes it “immune privileged” is the presence a thin layer of brain microvascular endothelial cells (hBMECs) that separate the circulating blood from the brain, also known as the blood-brain barrier (BBB). This barrier is very important for keeping bacteria (and other molecules) out of the very precious central nervous system (CNS; the brain and spinal cord).

However, like most human immune functions, bacterial species have evolved to overcome this barrier.

How do bacteria disrupt the BBB?

In order to traverse the BBB, bacteria first must cause mayhem by doing exactly what your body does not want them to do – trigger an inflammatory immune response in the BBB.

They accomplish this by calling on a few friends – the human neutrophil.

Neutrophils (purple) migrating into the epithelium (yellow) from the blood (red) to eat and destroy bacterium (orange).

Neutrophils are immune cells that are recruited to sites of inflammation to induce more inflammation. They migrate through blood vessels to the site of inflammation during microbial infection and when they arrive they are dedicated to ingesting the microbes (phagocytosis), releasing of anti-microbial peptides, and generating neutrophil extracellular traps (NETs), which are highly antimicrobial – but will not be discussed here!

It’s known that when neutrophils are recruited to the site of a group B streptococcus infection of hBMECs at the BBB, the integrity of the BBB is severely compromised.

Group B streptococcus is the causative agent of bacterial meningitis, a critical infection of the CNS, and a major health threat in human newborns (mortality rates of 25-50%). Those newborns that survive the infection can suffer permanent neuro-developmental issues, including cerebral palsy, seizure activity, deafness and/or blindness.

So compromising the BBB is detrimental for neural development and is caused by inflammation driven by GBS infection of the BBB, a place there should not be inflammation… 

How does GBS use to trigger this immune response?

Kelly Doran’s group at UCSD has found that the bacterial pilin, found on the surface of GBS, are responsible for promotion of the neutrophilic inflammatory response during infection. Interestingly, all clinical isolates of GBS carry at least one copy of pilus-encoding genes.

Bacterial pili on the outer surface (in green is the structure).

They knew from previous literature that pili are flexible appendages on the surface of bacteria that are required for establishment of infection in multiple pathogenic bacterial species. Specifically, pili have been shown to play an important role in adhesion of GBS to brain endothelium.

Their old information told them that pili are important for adhesion to the BBB cells and now their new information tells them that pili are responsible for the neutrophil-dependent inflammation of the brain during GBS infection – but how does the pilin lead to the neutrophil influx at the site of infection?

Using a global gene expression profile (of wild-type GBS vs. pilA mutant), they found that the GBS PilA protein (a protein found at the tip of the pilus structure) promotes gene expression in the host genes characteristic of a neutrophil-dependent inflammatory response during acute bacterial meningitis.

One of the characteristic genes that were being induced by bacterial PilA encoded for interleukin-8 (IL-8), a signaling molecule produced by the endothelium that works as a chemotactic factor to attract neutrophils. Ah ha!

Therefore, an increase of neutrophils at the BBB, increases BBB permeability and higher levels of GBS can then infiltrate the CNS.

They show that PilA does this by directly binding collagen on the outer membrane of endothelial cells to engage release of proinflammatory molecules. For more detailed information this follow the model below.

Model of GBS PilA-mediated CNS infection. 1) PilA binds the extracellular matrix component collagen, which then engages alpha-2/beta-1 integrins on the brain endothelium. 2) This leads to FAK activation and subsequent intracellular signaling. 3) Signalling pathway involving PI3K results in actin rearrangment and bacterial uptake. 4) A parallel singalling pathway involving MEK1/2 and Erk1/2 activation leads to IL-8 secretion. 5) This further results in functional neutrophil chemotaxis and activation. 6) Increased neutrophilic infiltrate damages the BBB resulting in increased BBB permeability, which likely facilitates further bacterial passage from the blood stream to the CNS.

So for the host: mo pilin, mo problems.


ResearchBlogging.org Banerjee A, Kim BJ, Carmona EM, Cutting AS, Gurney MA, Carlos C, Feuer R, Prasadarao NV, & Doran KS (2011). Bacterial Pili exploit integrin machinery to promote immune activation and efficient blood-brain barrier penetration. Nature communications, 2 PMID: 21897373

Monday
Sep102012

Where is all the Lithium, you guys?

by Sarah Scoles 

 

BBN -- Boy Band Network? Baby Back News? Big Bad Notepad? Barometer-Based Neuroticism?

Gong.

Big Bang Nucleosynthesis. Big Bang nucleosynthesis is what it sounds like: it refers to the first formationThis is a great periodic table, by Google, showing pictures of each element. I recommend making it bigger rather than squinting (Credit: Google/Joey Devilla). of nuclei, which started about 3 minutes after the Big Bang. Hydrogen, deuterium, helium-3, helium-4, lithium-6, lithium-7, and beryllium all formed between 3 minutes and 20 minutes after the universe's beginning, after the temperature was low enough to allow quarks to join up and become protons and neutrons, and protons and neutrons to join up into nuceli.

Now, 13.7ish billion years later, we have developed science and can figure out both what we think the relative abundances of those first elements were, and what they actually appear to be. Any discrepancies between the two will help us learn more about the rights and wrongs of our models of the early universe.

One "wrong" that we know of is that, so far, our measurements of the amount of primordial lithium in the universe are about 4 times lower than they "should" be. A new paper by Midwestern astronomers Howk, Lehner, Fields, and Mathews, however, says, "Maybe not. Maybe we've just been measuring the wrong thing."

So, first, let's ask this: How do astronomers measure the amount of lithium formed when the universe was young if the universe has been progressing and producing, you know, lithium ever since?

Second, let's ask, "On what do astronomers base their predictions of light element abundances?"

They only need one piece of information: the number of photons versus the number of baryons (regular matter, like protons and neutrons--atom stuff).

In other words, how much radiation was there compared to how much stuff there was?

With modern equipment, we don't have to guess about that any more: the WMAP satellite, which makes measurements of the cosmic microwave background, can actually measure the photon-baryon ratio.

Its measurements largely satisfy us in their agreement with our ideas. The experimental photon-baryon ratio, when used to predict the abundances of light elements, made predicitions that mostly matched the experimental abundances. Helium-4? Awesome. We were right. Helium-3? Even better. Go us. But lithium? Nope.

Let's step back and ask where these experimental abundances came from.

Astronomers want to find objects whose compositions will reflect the composition of the early universe, and since they are unlikely to find any objects whose compositions have been completely unaffected by processes that have occurred since the Big Bang, they need to be able to figure out how, and how much, those processes would have changed the abundances.

Historically, they have chosen old dwarf stars in the Milky Way's halo, as these stars presumably preserved the primordial chemical state of the universe fairly well. But this abundance was lower than predicted, and that led to the informative term "The Lithium Problem." Either BBN was kind of wrong, or we misunderstood the processes that destory lithium inside stars, and more gets destroyed each year than we think.Dwarfs: Preserving primordial abundances since forever (Credit: Garden and Pond De

Howk and colleagues, however, looked somewhere else: the Small Magellanic Cloud, a small galaxy orbiting the Milky Way. And not at dwarf stars, but at the gas between stars.

After taking into account things like how much lithium is ionized and how much is trapped inside dust grains, they determined how much lithium there was in the Small Magellanic Cloud's interstellar gas, compared to how much other stuff there was.

This abundance matched BBN's predictions, meaning that our ideas about the Big Bang, the moments after the Big Bang, the formation of the first subatomic particles, and the formation of the first atomic particles is (or could be) true.

Yay. Right?

Well, if the lithium abundance is "right" in the gas of some other galaxy, why is it so "wrong" in the old stars in our own galaxy? And how do we know that just because the other galaxy's contents matched what we expected that that answer is "right" and our previous answer was "wrong"?

Well, the authors admit that they can't know that. They say in the paper that maybe the lithium abundance in the SMC gas is no more primordial than in the dwarf stars, and that it is still possible that we don't have BBN, or our conception of the early universe, quite right. It is also possible that we don't exactly get what processes affect lithium in stars. It is also possible that we don't understand, in general, how and why lithium may have been produced or depleted in general.

Small Magellanic Cloud: so much potential truth in its gassy regions (Credit: National Geographic).So not exactly "yay."

But still. What's interesting is that the photon-baryon ratio was directly measured and is pretty well nailed down, and we think we understand BBN pretty well because it didn't happen right after the Big Bang (when we have a lot of speculation and also equations but also speculation) about the conditions and the way that the laws of the universe manifested themselves.

Why care?

The early universe is an interesting place, because it is so foreign and hot, like a tiny island nation. While we can never go back and witness what happened, the conditions of way-back-then are the ones that still determine the way the universe is today. If there were more photons, if there were fewer baryons, if the universe had expanded faster or slower, etc. Had nucleosynthesis produced different amounts of light elements, the universe may have evolved quite differently, and may be quite different now. We know how it is now. We want to know how it was back then, so we can see how we got here. It's like asking your parents to tell you stories about the time before you could form permanent memories.

 

 

ResearchBlogging.org Howk JC, Lehner N, Fields BD, & Mathews GJ (2012). Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud. Nature, 489 (7414), 121-3 PMID: 22955622

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