Science Shorts — July 2, 2011

Matter-antimatter asymmetry

When the universe was very young – less than a millionth of a second after the big bang – it was also very hot (around 1013K to be more precise). At that time, there were no “ordinary” particles as we know them today, only quarks and photons. These were in approximate equilibrium, with quarks and antiquarks annihilating each other to make photons, and the photons spontaneously changing back to quark-antiquark pairs (“pair production“).

As the universe cooled, photons no longer had enough energy for pair production to occur, and the existing quarks and antiquarks mostly then annihilated each other – but not entirely, since (obviously) some quarks (but hardly any antiquarks) remained, eventually to form the protons and neutrons of ordinary matter. Two consequences of this process are observable today. There are far more photons than quarks in the universe, by a very large ratio of more than a billion to 1. And there are far more quarks than antiquarks (bound up in protons and neutrons), by a similarly large ratio.

The only conceivable way this could have happened is for some asymmetry in the laws of particle physics to favor quarks over antiquarks. This imbalance need not have been large at all to account for the results – an excess of quarks over antiquarks of only 3 in a billion would have been enough. However, the existing Standard Model of particle physics has no explanation for this asymmetry, and therefore it can’t predict the imbalance between matter and antimatter. Experiments, however, can actually measure imbalances in some cases. Such imbalances will be quantities that any successful theory refining the Standard Model must predict.

Experiments at Fermilab that measure the results of decay of B mesons into muons have found an excess of muons over antimuons of about 1%. As more data is collected, the probability that this excess is not a statistical fluke has risen, and the latest results, just reported, place the odds of a meaningless fluke at about 1 part in 20,000.

arXiv: Measurement of the anomalous like-sign dimuon charge asymmetry with 9 fb^-1 of p pbar collisions

Quantum graininess of space

Einstein’s General Theory of Relativity says nothing about the properties of spacetime on a small scale, and that’s why it is both generally compatible with, yet completely independent of, quantum mechanics. The latter theory, however, suggests that spacetime could have a discrete “grainy” structure at very small dimensions.

Often the Planck length of 1.616×10-35 m is suggested as the proper scale for the graininess to appear. But this length is physically rather arbitrary, and recent astrophysical observations impose much more stringent limits on the scale at which graininess appears – if it even occurs at all.

The most recently published astrophysical results are from ESA’s Integral gamma-ray observatory. The gamma-ray burst GRB 041219A was detected on December 19, 2004. It was extremely bright, in the top 1% of all gamma-ray bursts. In part this is because its source was “only” about 300 million light years away. This brightness made it possible to deduce sufficiently precise values for the amount of polarization of its gamma-ray emissions at different wavelengths. Together with a recent good determination of the distance of GRB 041219A, this has made it possible to deduce that any quantum graininess must be at a length of less than 10-48 m – more than 10 trillion times smaller than the Planck length.

This is not the first use of astrophysical observations to constrain spacetime graininess. A result reported in November 2009, and discussed in detail here, placed limits on the length scale below the Planck length – but not nearly so small as the latest results.

Physical Review D DOI: Constraints on Lorentz Invariance Violation using integral/IBIS observations of GRB041219A

Masturbation as mating call?

Perhaps because the study was done by Europeans or (more likely?) because the findings might be too upsetting to delicate American sensibilities, some rather interesting entomological research hasn’t received the notice it deserves on the U. S. side of the Atlantic. To put it bluntly, a somewhat obscure aquatic bug, the lesser water boatman, serenades its hoped-for romatic conquests by… masturbating. And not only that, but in so doing the bug makes the loudest noise, in proportion to its size, of any animal on the planet. (Including human rock vocalists.) At least, if electronic amplification isn’t a factor.

It doesn’t seem to be known whether the insect finds the activity pleasurable in itself, let alone whether it can lead to orgasm. However, the research did determine that the sound is produced by rubbing of the bug’s genital equipment against its abdomen. And at a sound level peaking at 99.2 decibels (as measured by sound pressure level), the output in proportion to body size exceeds that of any other animal. Evidently it has the desired effect on female water boatmen – the researchers describe it as the outcome of runaway sexual selection. That makes some sense – the ability to make a lot of noise with one’s genitalia is evidence of good reproductive health, or horniness (or both).

PLoS ONE article: So Small, So Loud: Extremely High Sound Pressure Level from a Pygmy Aquatic Insect (Corixidae, Micronectinae)

Telomeres and cancer

The link between cancer and teleomeres gets quite a lot of attention among researchers, as evidenced by the award of a Nobel Prize in 2009 for foundational work on telomeres. Since telomeres are segments of DNA that protect the ends of chromosomes from damage during the DNA replication that occurs during cell division, and cancer is a result of uncontrolled cell division, the connection is apparent.

In non-cancerous cells, the telomeres gradually erode with each cell division. The enzyme telomerase, which is generally present in normal cells only during embryonic development, is able to rebuild telomeres, and so it is, not surprisingly, often present in cancerous cells. However, not all cancerous cells contain telomerase, yet their telomeres are still maintained to allow uncontrolled cell division. The mechanism that enables this is not understood, but it has been given a name: “Alternative Lengthening of Telomeres” (ALT). One possibility is that ALT enables homologous recombination of telomere segments, which is normally prevented.

There is new research that gives some clues about the ALT mechanism. Detailed examination of the proteins expressed in pancreatic neuroendocrine tumors and various other tumor types has identified two genes, ATRX and DAXX, as being of special interest. In particular, in tumor cells with ALT (i. e., no evidence of telomerase), one or both of the genes are either mutated or not expressed at all. This doesn’t directly elucidate the ALT mechanism, but it does help because it implies that the protein products of these genes inhibit ALT somehow – and therefore raises hopes for therapeutics in cancers where ALT is a factor.

Science DOI: Altered Telomeres in Tumors with ATRX and DAXX Mutations

Neuronal plaques and Alzheimer’s disease

There is a long-noticed connection between Alzheimer’s disease and accumulation of amyloid-β peptide in plaques around neurons in the brains of disease victims. The connection isn’t perfect – such plaques are also found (on autopsy) in the brains of people without Alzheimer’s disease symptoms. But the hypothesis that such plaques contribute to neuronal death (through an unknown mechanism), and hence Alzheimer’s disease, is still taken pretty seriously.

It’s also well-known that there’s a correlation between having a particular version (ε4) of the APOE gene and risk for developing Alzheimer’s disease. In fact, having one copy of the APOE4 allele increases the risk by a factor of 3, and two copies multiplies the risk another 5-fold. So the question is: what’s APOE4 doing (or not doing) to raise the risk so dramatically?

New research suggests that amyloid-β plaques are strongly implicated as a disease factor. There are (at least) two ways that APOE4 might play an important role. It might cause increased production of amyloid-β plaques, or it could hinder normal clearance of such plaques from the brain. The research now shows that (at least in mice) APOE4 does not do the latter – but it does do the latter.

What is still not known is how APOE4 hinders plaque clearance. Having that knowledge ought to suggest how to overcome the hindrance, or at least how to speed up the clearance in other ways.

Science Translational Medicine abstract: Human apoE Isoforms Differentially Regulate Brain Amyloid-β Peptide Clearance

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Science Shorts — June 30, 2011

Topics for this edition: galaxy morphology, quasars, pain perception, gene therapy, and cancer.

Galaxy classification

For decades astronomers have classified galaxies into agreed-upon types based on their visible shapes. One broad type consists of spiral galaxies, and the other of elliptical and lenticular galaxies. Spiral galaxies have the familiar pinwheel appearance, while the others lack distinctive features such as arms and instead simply diminish in brightness gradually outward from the center. It has been the prevailing belief that spiral galaxies are generally younger, while the others are older and have gradually lost their spiral structure.

New research based on an observational survey known as ATLAS3D has incorporated measurements of galaxies’ rotational velocities, and it suggests that a more complex classification scheme may be appropriate. While all spiral galaxies rotate relatively rapidly, it has been found that many elliptical and lenticular galaxies do also – about 66% of them, and they may actually have a flattened disk shape like spirals, lacking only discrete arms.

arXiv: The Atlas3D project – VII. A new look at the morphology of nearby galaxies: the kinematic morphology-density relation

Very early quasar

Quasars are a type of active galaxy, in which a supermassive black hole at the center stimulates the radiation of enormous quantities of energy from clouds of matter heated to high temperatures due to a high velocity of rotation around the black hole. Quasars in the nearby universe are quite rare, since the peak production of energy lasts only on the order of 100 million years, before all the infalling matter has been consumed by the black hole.

However, quasars were much more numerous in the early universe, up to several billion years after the big bang. Because of a quasar’s high luminosity, the brightest of them can still be observed even if their peak of energy production occurred less than a billion years after the big bang. Astronomers continue to detect even earlier and more distant quasars, and the latest, known as ULAS J1120+0641, has just been described. It is estimated to be observed as it was only 770 million years after the big bang, implying that its light has taken about 12.9 billion years to reach us. The distance can also be specified through the amount of redshift (7.085) of the quasar’s light. The mass of the central black hole is estimated to be about 2 billion solar masses. That is quite surprising for such an early object, as it is comparable to the mass of quasar black holes that have had a much longer time to grow.

Nature article: A luminous quasar at a redshift of z = 7.085

Love eases pain

Nobody considers it surprising that people suffering physical pain find the presence and attention of loved ones to be comforting. However, research just published in PNAS indicates that merely the sight of a loved one can alter brain activity so as to lower pain. It also identifies some details of this activity.

Female experimental subjects in committed relationships were asked to view a series of images (their partner, a stranger, and a chair) while being subjected to a painful stimulus on their arm. On average, subjects reported feeling less pain when viewing their partner but more pain (in about the same degree) when viewing the stranger or the chair.

At the same time, fMRI scans of the subjects showed higher activity in the ventromedial prefrontal cortex (VMPFC) when viewing their partners than when viewing the neutral stimuli, and less activity in the dorsal anterior cingulate cortex and anterior insula. This is consistent with other research indicating inhibitory effects of VMPFC activity, and heightened response of the the other areas when experiencing pain. There was a positive correlation betwee the degree of VMPFC activity and the length of time subjects had been in their relationship.

PNAS DOI: Attachment figures activate a safety signal-related neural region and reduce pain experience

Gene therapy

The basic idea of gene therapy has been around for a long time, but it’s been very hard to make it work in practice. The idea is that if a particular disease condition is the result of a defect in a specific gene (or maybe a small number of genes), then replacing or supplementing the defective gene or genes with fully functional copies should help alleviate the disease.

However, the devil’s in the details. There are ways to replace defective genes of cells in vitro, but the DNA may be damaged, and getting the modified cells back into the proper locations in the body of a complex organism (like a human) is usually very hard. There are also techniques for more safely introducing fully functional genes into certain types of body cells in vivo – but the new genes do not get copied during cell replication.

What’s needed is a means of safely replacing defective genes with good ones within the actual cellular DNA so that they persist through replication. One technique using special enzymes – zinc finger nucleases (ZFNs) – has been developed, but efforts to demonstrate the efficacy and safety of this technique are still in early stages.

Hemophilia is a well-known heritable disease resulting from a defect in one particular gene (F9). Now there is research showing that a combination of appropriate ZFNs and a functional copy of F9 can be introduced (using viral vectors) into the livers of mice with defective F9 – and the blood clotting deficiency characteristic of hemophilia is substantially alleviated.

Nature DOI: In vivo genome editing restores haemostasis in a mouse model of haemophilia

Mutations leading to cancer

The basic “cause” of cancer is mutations of a cell’s DNA that prevent detection and repair of DNA damage that can occur for many other reasons, such as infections, radioactivity, carcinogens, too much ultraviolet light – or even chance errors occurring in the normal process of cell division. The transcription factor p53 plays a key role in detecting mutations and causing an appropriate cellular response. So when both normal copies of the TP53 gene that is the template for p53 itself become mutated the cell may be on an irreversible path to cancer.

Mutations of TP53 are found in more than half of advanced cancers, but it has often been supposed that this damage happens at a relatively late stage. However, it has been difficult to determine the order in which cancerous gene mutations actually occur. New research has developed a statistical technique that involve counting the number of extraneous copies of certain genes, including TP53. And one of the main findings is that mutations of TP53 often seem to occur sooner in the process than previously supposed.

Cancer Discovery DOI: Temporal Dissection of Tumorigenesis in Primary Cancers

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Frazil ice

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Supermassive black hole in a dwarf galaxy

There’s a new study just published, about the existence of a supermassive black hole in a type of galaxy where nobody expected to find one. This story is getting a bizarre amount of attention. I detect a whiff of hype.

But let’s start with the facts. Henize 2-10 is a small, mostly unremarkable compact dwarf galaxy. Its estimated dynamical mass is about 1010 M, only a few percent of our galaxy’s mass, and its distance from us is about 30 million light years. It is irregular in shape and does not fit in any category of the standard Hubble sequence.

The only respect in which Henize 2-10 has attracted attention – for several decades – before now is an extremely high rate of star formation in comparison to its size. The rate is 10 times that of the Large Magellanic Cloud, a satellite galaxy of the Milky Way that is also irregular in form and has approximately the mass of Henize 2-10.

This research – An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 – published 3 days ago in Nature, now offers good evidence that at the center of Henize 2-10 is an active black hole of substantial but somewhat uncertain mass between 2×105 M and 2×107 M. That’s a lot – it could exceed the mass of the Milky Way’s black hole, ~4.2× 106 M.

The evidence presented that Henize 2-10 contains an actively accreting massive black hole is pretty good. It includes detection of radio emissions with a substantial non-thermal component. In other words, much of the radio emissions is due to something besides black body radiation – perhaps synchrotron radiation typical in active black hole jets. There is also a point source of high-energy X-ray emissions coming from the same location as the radio emissions. The evidence that these emissions are due to an active black hole isn’t perfect. In particular, long-baseline interferometry shows gaps in the radio source, and the radio spectrum does not have the shape of a typical radio galaxy’s. But consideration of other possible explanations indicates that the alternatives are rather improbable.

However, the paper concludes “the massive black hole in Henize 2-10 does not appear to be associated with a bulge, a nuclear star cluster or any other well-defined nucleus. This unusual property may reflect an early phase of black-hole growth and galaxy evolution that has not been previously observed. If so, this implies that primordial seed black holes could have pre-dated their eventual dwellings.”

The authors are implying that this black hole could have existed before Henize 2-10 itself. And further, since galaxies in the very early universe (z≥7) have many similarities to Henize 2-10 (as well as certain differences), that many of these very early galaxies could also have formed around pre-existing massive black holes.

These concluding observations should, on the basis of the evidence provided, be regarded as rather speculative. There are substantial logical gaps in the reasoning.

For one thing, Henize 2-10 is pretty unusual based on its high rate of star formation. This implies an unusual and probably chaotic recent history. And so there really isn’t much solid reason to think that the central black hole predated the galaxy.

How closely Henize 2-10 resembles very early galaxies is also open to question. The earliest stars, which made up the earliest galaxies, had very low metallicity and therefore tended to be much larger, brighter, and short-lived than stars forming in the present era. The assumption that galaxy evolution would be pretty similar between now and then is hard to make.

Some of the popular media accounts go even further and suggest that “most” galaxies probably formed around pre-existing black holes. Even if that were true for Henize 2-10, all that can legitimately be inferred is the possibility, not the necessity, of that circumstance in most cases.

There have been reports of the existence of supermassive black holes in galaxies without central bulges (not just irregular galaxies) – here, for example. There have even been studies of active black holes in the early universe that may have predated their galaxies, one of which I wrote about in this article: Which came first – the galaxy or the black hole?. There are also cases of fairly normal galaxies, such as M33, that seem to have at most a very small central black hole – see here.

So it’s certainly a very real issue whether, at least in some cases, central black holes form before their galaxies, but the present study is just another interesting data point, not the last word on the subject.

Further reading:

Dwarf Galaxy Harbors Supermassive Black Hole – 1/9/11

Ginormous Black Hole May Solve Longstanding Mystery – 1/9/11

Baby Galaxy Hosts Monster Black Hole – 1/10/11

Astronomers Discover Supermassive Black Hole in Center of Tiny Galaxy – 1/9/11

Supermassive Black Hole Peeks From Behind The Skirt Of A Dwarf Galaxy – 1/10/11

Huge Black Hole Found in Dwarf Galaxy – 1/10/11

Henize 2-10: A Surprisingly Close Look at the Early Cosmos – 1/10/11

A Black Hole “Too Big” For Its Galaxy – 1/12/11

Supersized Black Hole Seen in Small Galaxy – 1/11/11

Dwarf galaxy solves supermassive mystery – 1/10/11

Dwarf galaxy hides a cosmic ‘Little Big Man’ – 1/10/11

New Evidence Shows Black Hole Growth Preceding Galactic Formation – 1/9/11

A tiny galaxy that hides a big secret – 1/11/11

Itty Bitty Galaxy Home to Gargantuan Supermassive Black Hole – 1/11/11

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When did humans start wearing clothes?

It’s a question everyone has probably wondered about at some point – some people more than others. Perhaps you recall reading about studies of the molecular genetics of lice indicating a date for the earliest wearing of clothes by humans somewhere between 83,000 and 170,000 years ago. If so, that’s because this idea has been batted around for eight years or more.

The latest research paper on the subject was published this month in Molecular Biology and Evolution

So where does this conclusion come from? Well, it turns out that there are actually two different types of lice that like to call humans their home – head lice and body lice. The former prefer the environment of head hair, while the latter prefer to live in human clothing. So the natural assumption (though it’s only an assumption) is that body lice weren’t around before clothes. If so, on another assumption, body lice separated from head lice by speciation near the time humans began wearing clothes.

The standard techniques of molecular genetics make it possible to estimate when the divergence occurred – by measuring the difference in the genomes of the two species and applying an estimate of the rate of change in the genomes. This relies on the observation that gene mutations occur at a fairly predictable rate.

So far there is no physical evidence of clothing older than about 30,000 years – and it’s pretty unlikely that such evidence could even survive much longer. However, it’s conceivable that something like a crude, ancient sewing needle made of bone might turn up some day.

This lice study isn’t exactly new news. Already in 2003 there was a study (read PDF) in Current Biology that placed the date of species divergence at 72,000 ± 42,000 years ago, so the latest result pushes the earliest possible date back by about 60,000 years.

Further information:

UF study of lice DNA shows humans first wore clothes 170,000 years ago – 1/6/11

Humans First Wore Clothing 170,000 Years Ago – 1/6/11

We were all naked until 170,000 years ago – 1/7/11

Humans Got Lice When We Clothed Our Naked, Hairless Bodies – 1/7/11

Lice DNA Reveals When Humans First Clothed Their Nakedness – 1/10/11

Lice hang ancient date on first clothes – 5/8/10

Human body lice reveal the birthdate of fashion – 9/2/03

Lice genes date first human clothes – 8/20/03

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