A mosaic of X-ray images of the quasar Q2237+0305, magnified by a gravitational lens. The bright spots are four magnified images of the same quasar, which change in brightness over time.
Credit: Courtesy of Ohio State University
Astronomers have looked under the hoods of quasars, the brightest objects in the universe, and found some of the best evidence yet for the black holes that are thought to power them.
The new study, presented today at the meeting of the American Astronomical Society (AAS) 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 (AU), 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 SPACE.com.
The disks each surrounded an area that was emitting X-rays, a telltale sign that the material at the disk's center is being heated up as it speeds up prior to falling into the black hole.
The astronomers are currently studying 20 such lensed quasars, and they hope to gather X-ray data on all of them.