Deep X-ray surveys reveal black hole population

[telfrow]

<i>Data from X-ray observatory surveys show that black holes are much more numerous and evolved differently than researchers would have expected, according to a Penn State astronomer. <br /><br />"We wanted a census of all the black holes and we wanted to know what they are like," says Dr. Niel Brandt, professor of astronomy and astrophysics. "We also wanted to measure how black holes have grown over the history of the Universe." <br /><br />Brandt and other researchers have done just that by looking at a patch of sky in the Northern hemisphere called the Chandra Deep Field-North, using NASA's Chandra X-ray Observatory and a similar patch in the Southern hemisphere called the Extended Chandra Deep Field-South. Surveys are also being carried out in other parts of the sky using both Chandra and the European Space Agency's X-ray Multi-Mirror Mission-Newton. <br /><br />The researchers looked at X-ray emissions because areas around black holes emit X-rays as well as visible light. The penetrating nature of X-rays provides a direct way to identify the black holes. Using X-rays also enables astronomers to pinpoint the black holes at the centers of galaxies without their signal being washed out by the visible light coming from a galaxy's stars, Brandt told attendees at the annual meeting of the American Association for the Advancement of Science in St. Louis, Mo. today, (Feb. 17). The black holes they studied were those that reside at the centers of galaxies and are actively emitting X-rays, therefore they are called active galactic nuclei. <br /><br />"We find active Super Massive Black Holes at the centers of massive galaxies," says Brandt. "Our Galaxy also has its own black hole at its center measuring 2.6 million solar masses. Our black hole is not active today, but we presume it was active in the past." </i><br /><br /> Link<br /><br /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>