Explode the myth on blackholes

Dear folks,
of late a lot theories are floated involving blackholes based on myths such as being made up of special particles (neutrinos etc.) or a pass through medium and so on. Systematic calculations reveal that a blackhole can be made of ANY material - solid, liquid or gas, any element or a mixture or compound. All it needs is a critical (minimum) size. Wanna have a blackhole of water ball or air or stone or gold or diamond? It is possible. To know more, visit this blog on 'understanding universe' at www.bsrinivasan.blogspot.com

bye

srini
astronomy

Discovery of an exoplanet - an earth-like planet

Astronomers have discovered the most earthlike planet outside our solar system to date, an exoplanet with a radius only 50% larger than the Earth and possibly having liquid water on its surface. Using the ESO 3.6m telescope, a team of Swiss, French, and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbor a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses. This exoplanet — as astronomers call planets around a star other than the Sun — is the smallest ever found up to now and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581, is smaller and colder than the Sun — and thus less luminous — the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! "We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stephane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky — like our Earth — or covered with oceans," he adds. "Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X." The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are at least 50 times intrinsically fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class. "Red dwarfs are ideal targets for the search for such planets because they emit less light, and the habitable zone is thus much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Any planets that lie in this zone are more easily detected with the radial-velocity method, the most successful in detecting exoplanets. Two years ago, the same team of astronomers already found a planet around Gliese 581 (see ESO 30/05). With a mass of 15 Earth-masses, i.e. similar to that of Neptune, it orbits its host star in 5.4 days. At the time, the astronomers had already seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth, but also clear indications for another one, an 8 Earth-mass planet completing an orbit in 84 days. The planetary system surrounding Gliese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite remarkable system. The discovery was made thanks to HARPS (High Accuracy Radial Velocity for Planetary Searcher), perhaps the most precise spectrograph in the world. Located on the ESO 3.6m telescope at La Silla, Chile, HARPS is able to measure velocities with a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most successful instruments for detecting exoplanets and holds already several recent records, including the discovery of another "Trio of Neptunes" (ESO 18/06, see also ESO 22/04). The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs. "HARPS is a unique planet hunting machine," says Michel Mayor, from Geneva Observatory, and HARPS Principal Investigator. "Given the incredible precision of HARPS, we have focused our effort on low- mass planets. And we can say without doubt that HARPS has been very successful: out of the 13 known planets with a mass below 20 Earth masses, 11 were discovered with HARPS!" HARPS is also very efficient in finding planetary systems, where tiny signals have to be uncovered. The two systems known to have three low mass planets — HD 69830 and Gl 581 — were discovered by HARPS. "And we are confident that, given the results obtained so far, Earth-mass planets around red dwarfs are within reach," affirms Mayor.

srini

The loneliest black holes

The loneliest black holes
Supermassive black holes are actively growing in even the emptiest regions of the universe.
Provided by Drexel University

This artist's impression of a supermassive black hole highlights the accretion disk of gas and stars swirling around the black hole, and the jets of material ejected along the poles. Supermassive black holes are found even where galaxies are sparse and interaction is minimal. These black holes accrete matter at a slower rate than black holes in denser galactic environments. A. Kamajian/NASA

This is a tiny extract from a newsletter to me from the Astronomy magazine. The readers may further enrich their knowledge by subscribing to it.

srini

June 6, 2007

In a study of more than 1,000 void galaxies, using data from the Sloan Digital Sky Survey (SDSS-II), astronomers from Drexel and Widener Universities announced that the growth of these monster black holes — with masses millions to hundreds of millions times that of our sun — are found where galaxies are sparse and interact very little with each other. The researchers also found that the accretion of matter onto these void black holes is slower than in denser galactic environments.These findings shed light on the black hole formation and evolution process by showing that the environment does affect how quickly galaxies proceed through their evolutionary cycle. The simple presence of growing supermassive black holes in the rural outposts of the universe challenges the current theoretical models of galaxy and structure formation and evolution, explained Anca Constantin of Drexel University, lead author of the paper delivered last week at the American Astronomical Society meeting in Honolulu. "Interestingly, we see actively accreting galactic black holes in all phases of evolution in these sparse regions," said Constantin. "This means that the black hole growth process is quite similar in what could be compared to the most reclusive countrysides and in the crowded urban regions of the universe." The void regions, nearly empty, three-dimensional fields hundreds of millions of light-years across, fill half of the universe. Only five percent of all galaxies live in these bubble-like regions. The other 95 percent of galaxies live together in communities, crowded into clusters, filaments, and walls: the cities and suburbs of the universe. Studying a 700-million light year wide 'slice' of the universe, the researchers found that spectra of the centers of void galaxies show hot gases ionized by light emitted from matter swirling around supermassive black holes. Constantin adds that, "the more isolated accreting black holes are however not as active as the ones in more populous environs, and the fuel seems less available for accretion in voids than in 'urban' galaxies." Astronomer Fiona Hoyle, a member of the discovery team from Widener University added: "This is strange given that these reclusive galaxies are forming stars at higher rates than their counterparts in denser regions; this means there is plenty of fuel, but it is not efficiently channeled toward the central engine."


Star formation requires the presence of large amounts of gas and so there must be more than enough gas in the void galaxies if their star forming rates are high, explained Hoyle. The smaller accretion rate observed in void galaxies means that this gas is just not getting down to the nuclear region where accretion happens. Interactions with other galaxies are thought to disturb the gravitational potential, which drives some gas into the nuclear region. "These interactions are not as frequent in voids, so the 'feeding' of the black hole is slower." These rugged individuals in voids do not need to compete with their neighbors for fuel, and their life cycle is rarely bothered, noted Constantin. In contrast, life is more hectic in crowded regions where galaxy interactions are frequent. As a consequence, galaxies are either stripped of their gas or more material is funneled toward the central engine. This means that there are many more chances the accretion onto black holes is enhanced or turned off in more 'urban environments.' "On the other hand, the void galaxy black holes might take longer to reach the mature, low accretion rate phase, which might explain why the most massive, lazy black holes are less frequent in voids," she noted. The data studied by Constantin may also show that active black holes appear to be more common in voids but only among small (less massive) galaxies, while less common among massive galaxies. This is also a clue that the life cycle of black hole growth in voids is delayed or slower compared to that in denser regions. Discovery team member Michael Vogeley of Drexel said that it's particularly puzzling that the few most massive and sluggishly accreting void systems live within the most secluded sub-regions, while their "urban" counterparts are found in the most populated neighborhoods. "Perhaps because massive objects are prone to accreting material around them, such a 'cleaning' process would contribute to emptying the already rarefied neighboring space in voids," Vogeley noted. "This would leave little or insufficient material for future formation of other nearby massive, bright galaxies." In contrast, within galaxy clusters where there is plenty of stuff around, accretion of surrounding material would make a small difference. These results have been possible only because of the sheer number of void regions and void galaxies found in the SDSS-II data, the most ambitious survey of the universe ever undertaken, the researchers said. The sample used in the analysis announced last week comprises more than 1,000 void galaxies. Previously, the black hole accretion in centers of void galaxies had been studied in only a handful of objects contained in only one void region, the Bootes Void.

Acknowledgements: Astronomy magazine's newsletter to me

srini

astronomy

giveawayoftheday

giveawayoftheday