Image: optical image of the quasar
Ohio State University
An optical image of the quasar RXJ1131-1231, magnified by a gravitational lens. The red spot in the center is the galaxy that is acting as a lens, while the four bright spots (three top, one bottom) are magnified images of the same quasar.
updated 10/5/2006 4:37:54 PM ET 2006-10-05T20:37:54

In two studies released Thursday, astronomers said they have found the best evidence yet that black holes power quasars, and NASA said it has mapped the location of every local galaxy with an active supermassive black hole at its center.

A study, presented at the meeting of the American Astronomical Society High Energy Astrophysics Division in San Francisco, lends further confirmation to the idea that quasars are anchored by supermassive black holes and the flattened disks of material spiraling into them.

Astronomers have puzzled over quasars for decades before deciding each is a very active and developing galaxy most likely containing supermassive black holes that formed billions of years ago. This cosmic yin-yang between the darkest and brightest space objects has made understanding quasars difficult.

Black holes are so dense that nothing, not even light, can escape their gravitational clutches, making them impossible to observe directly. And even though quasars, or quasi-stellar radio sources, are the universe’s most powerful sources of constant light, they are billions of light-years away. So even with the most powerful telescopes they appear as pinpoints of light. On top of that, the dust and gas lit up by a quasar makes seeing inside one a great challenge.

The researchers led by Xinyu Dai and Christopher Kochanek of Ohio State University were only able to view the interior structures of the two quasars, named RXJ1131-1231 and Q2237+0305, when a galaxy lined up between them and the Earth, magnifying their light — a phenomenon called gravitational microlensing. Like a Sumo wrestler rolling over and deforming a soft mat, the weighty galaxy dented, or curved, the fabric of space-time, rerouting and in this case focusing light from the quasars behind it.

The magnification allows astronomers to see quasars that would otherwise have remained invisible.

"Luckily for us, sometimes stars and galaxies act as very high-resolution telescopes," Kochanek said. "Now we're not just looking at a quasar, we're probing the very inside of a quasar and getting down to where the black hole is."

With NASA's Chandra X-Ray Observatory, coupled with measurements from optical telescopes, the astronomers were able to measure the size of the so-called accretion disk inside each quasar, one of which spanned about 14 astronomical units, where one AU is the distance from Earth to the sun.

“It's the first time anyone has measured the size of the disk around one of these black holes,” Kochanek told

NASA maps supermassive black holes
Scientists also announced in San Francisco that a new census compiled by astronomers contains the location of every local galaxy with a supermassive black hole at its center.

"We are confident we are seeing every, active supermassive black hole within 400-million-light-years of Earth," said Jack Tueller of NASA Goddard Space Flight Center in Maryland who led the census effort.

Called active galactic nuclei, or AGN, these black holes have masses of up to billions of tons compressed into a region about the size of our solar system. The all-sky census , performed using NASA's Swift satellite over a nine-month period, detected more than 200 nearby AGN.

Supermassive black holes are thought to lie at the hearts of nearly every massive galaxy, but only a few percent appear to be active. The black holes of some galaxies, like our Milky Way, were likely once active but are now dormant for reasons that are still unclear. One idea is that they've simply consumed all the material in their immediate vicinities. Such dormant supermassive black holes were not counted in the survey.

Among the key findings from the survey was the detection of AGN in so-called "starbursts" galaxies with intense star forming activity. These discoveries will enable scientists to test a theory called "co-evolution," which states that black hole activity and star formation go hand in hand, the researchers say.

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