# Extracts from the Internet

## Ultracold helium ions

S. Schiller and his colleagues from Germany have developed a new method for cooling helium ions to very low temperatures. Ultracold ions are necessary for experimentally verifying the predictions of quantum electrodynamics and are also needed in the search for new effects. Schiller's team first cooled a gas of beryllium-9 ions to the Coulomb crystal' state in a trap using an ultraviolet laser and then introduced ions of helium into the trap. As a result of the interaction between the ions, a core of ultracold helium ions formed in the center of the cloud of beryllium ions. In this way, about 150 helium ions were cooled to a temperature of 20 mK. Source: physics/0412053

## The effect of gas on nanotube properties

H.E. Romaro and his colleagues from the US and Sweden have experimentally shown that single-wall carbon nanotubes change their electrical resistance when blown by a gas flow, the amount of the change depending on the mass of the gas molecules. The USSweden experiment was conducted at atmospheric pressure and involved nanotubes 1-1.6 nm in diameter and a few microns in length, and the blowing gases used were monatomic inert gases as well as (molecular) methane and nitrogen. The molecular mass dependence of resistance change was approximately m1/3, and the effect itself is due to the very small deformations nanotube walls experience when colliding with molecules. This property, the authors believe, may lead to new high-sensitivity gas analyzers in the future. Source: Science 307 89 (2005)

## A silicon laser

A compact all-silicon laser has been created at an Intel lab. A prototype of such a laser was earlier tested at the University of California, USA. The operation of new laser is based on the Raman effect. The laser generates light pulses for about 100 ns, and then ceases to lase due to two-photon absorption. The solution of this problem may open up a wide range of applications for silicon lasers. Source: http://physicsweb.org/articles/news/9/1/1/1

## Black hole radiation correlations

J.M. Miller and J. Homan have observed a dependence of the iron line intensity on the phase of quasiperiodic X-ray oscillations in the radiation from the X-ray source GRS 1915, presumably an accreting black hole with a mass of 14.4+-4.4 solar masses. The source is 40,000 light years from Earth. The astronomers used data from the Rossi orbital X-ray telescope in their work. The origin of the observed quasiperiodic oscillations with frequencies of 1 and 2 Hz have not yet been reliably established. If the oscillations have to do with a circular Keplerian motion around the black hole, then the radiation should be emitted at a distance of no more then 100 Schwarzshild radii. An alternative answer may be the general relativistic Lense-Thirring precession, in which case the generation should occur much closer to the black hole, in the region of strong spacetime curvature. Although the observed broadening of the lines is associated with reflection from the inner accretion disk, the assumption was often made that the lines are generated in jet regions far from the disk. The observed dependence of the intensity of the lines on the phase of quasiperiodic oscillations provides evidence in favor of another hypotheses, according to which the lines also are generated in the inner accretion disk. Source: astro-ph/0501371

## Giant cavities in a gas halo

Two giant cavities (i. e., low-gas-density regions), 200 kpc in diameter each, were investigated in the halo of the galaxy cluster MS0735.6+7421 using the Chandra X-Ray Space Telescope. At the center of the cluster is a giant elliptic cD galaxy with a black hole 3x108 times solar masses at its core. The plasma in the cavity is a powerful radio source, and cavity boundaries are set by elliptic-shaped shock waves. The cavities were formed at the ends of relativistic jets that emerged from the black hole but are no longer active. According to estimates, the total cavity formation energy is 6x1061erg, which is a record high for other known systems of this kind. If this energy was released into the jets during the accretion process, then the black hole must have taken as little as 100 million years to build up most of its mass. The study of the giant cavities is also important for understanding the structure of cooling gas flows' onto the center of the cluster. Source: astro-ph/0411553

The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

It is compiled from a multitude of Internet sources.

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