Archive for October 3rd, 2011

October 3, 2011

Space Telescopes Reveal Secrets of Turbulent Black Hole

An active galactic nucleus (AGN) is among the most dramatic and complex astrophysical objects in the universe. Extensive new research of a particular AGN in the galaxy Markarian 509 has provided a wealth of new details on the complex internal structure and dynamics of a medium size AGN.

A supermassive black hole at the center of a galaxy drives all the activity of an AGN. The mass of the black hole may be as much as 10 billion solar masses, or more. Quasars represent the most spectacular and active AGNs. They are visible at distances of over 13 billion light-years. Very recent research has connected the intrinsic brightness of an AGN with more detailed physical characteristics, making possible the use of AGNs as “standard candles” for measuring the universe out to very large distances. The largest AGN near Earth is in the giant elliptical galaxy M87, at a distance of about 53 million light-years. The mass of its black hole is about 6.5 billion solar masses.

Somewhat less spectacular AGNs were initially detected as galaxies with unusual properties, such as very bright central cores and broad emission lines in their spectra. These are termed Seyfert galaxies, after the astronomer who identified them. Markarian 509, located about 500 million light-years from Earth, is in the not precisely defined space between Seyfert galaxies and quasars. The mass of its central black hole is estimated at 300 million solar masses. Markarian 509 was selected for detailed study, in part, because earlier observations gave indications of considerable internal turbulence in the gas, plasma, and dust, in the vicinity of the black hole, that comprise the AGN.

All of the seven papers that make up the initial set of analyses of the results are open access, for anyone really curious about the details.

ESA spacecraft reveal new anatomy around a black hole

The black hole was monitored for 100 days. “XMM-Newton really led these observations because it has such a wide X-ray coverage, as well as an optical monitoring camera,” says Jelle Kaastra, SRON Netherlands Institute for Space Research, who coordinated an international team of 26 astronomers from 21 institutes on four continents to make these observations.

During the campaign, the galaxy surpassed itself; instead of the usual 25 percent fluctuations in its brightness, it leapt up in the soft X-ray band by 60 percent, indicating that a major disturbance occurred in the gas flow to the black hole’s deadly clutches.

The resulting observations have shown that the outflow consists of giant bullets propelled at millions of kilometres per hour. The bullets are stripped away from a dusty reservoir of matter waiting to fall into the black hole. The surprise is that the reservoir is situated more than 15 light years away from the black hole. This is further than some astronomers thought was possible for the wind to originate.

Further reading:

Space telescopes reveal secrets of turbulent black hole

Dissecting a Black Hole’s Surroundings: Major study includes observations with NASA/ESA Hubble Space Telescope

Space Telescopes Reveal Secrets of Turbulent Black Hole

Astronomers reveal new findings from ‘monster’ black hole

The environment of a supermassive black hole revealed

Scientists zero in on black hole

Astronomy Cmarchesin: Space Telescopes Reveal Secrets of Turbulent Black Hole

Space telescopes reveal secrets of turbulent black hole (has links to the technical papers – more details here)

Correlated X-Ray and Optical Variability in Markarian 509 (earlier 2008 paper on Markarian 509)

October 3, 2011

Epigenetic clue to schizophrenia and bipolar disorder

Schizophrenia and bipolar disorder are known to occur significantly more often in some families than in others, so some genetic component is rather likely. Particular genes that seem to be involved have even been identified. But at the same time, it often happens that in pairs of identical twins, having identical DNA, one twin may have the disorder while the other does not. So there must be other factors besides strict genetics involved – diet, lifestyle, stress, or infectious diseases, for example.

The task would then be to determine the mechanisms through which such environmental factors act. The mechanisms could still be genetic, if an environmental factor has epigenetic effects, as many do. One of the most studied epigenetic mechanisms is DNA methylation, in which a methyl group is added added at specific places within the DNA. In particular, if a spot in the promoter region for some gene is methylated, expression of the gene is inhibited. But if the methylation is removed, expression of the gene (which might be in a mutated form) is enabled.

The research reported here studied pairs of identical twins in which only one of the pair had schizophrenia or bipolar disorder (or both). Scans of the genomes of each twin found significant differences in methylation patterns occurring in the promoter regions of genes that had already been linked to the psychiatric disorder that was present.

Although that provides very strong indications of genes that might be targeted to relieve the disorder, the question of what environmental factors caused the differences in methylation still remains. This is especially of interest, since it’s known that methylation patterns can be inherited.

Epigenetic clue to schizophrenia and bipolar disorder – New Scientist

Regardless of which condition the twin had, the most significant differences, with variations of up to 20 per cent in the amount of methylation, were in the promoter “switch” for a gene called ST6GALNAC1, which has been linked with schizophrenia. Although the function of the gene isn’t fully established, it is thought to add sugars to proteins, which could alter the speed or specificity of their usual function.

The findings tallied with another study which involved screening post-mortem brain tissue from people who had had some form of psychosis. The researchers found differences of up to 25 per cent in methylation of the same gene compared with controls.

Further reading:

Disease-associated epigenetic changes in monozygotic twins discordant for schizophrenia and bipolar disorder