New study proves a theory first predicted more than 40 years ago
You may have heard that nothing
escapes the gravitational grasp of a black hole, not even light. This
is true in the immediate vicinity of a black hole, but a bit farther
out—in disks of material that swirl around some black holes—light can
escape. In fact, this is the reason actively growing black holes shine
with brilliant X-rays.
Now, a new study accepted for publication in The Astrophysical Journal
offers evidence that, in fact, not all of the light streaming from a
black hole's surrounding disk easily escapes. Some of it gives in to the
monstrous pull of the black hole, turns back, and then ultimately
bounces off the disk and escapes.
"We observed light coming from
very close to the black hole that is trying to escape, but instead is
pulled right back by the black hole like a boomerang," says Riley
Connors, lead author of the new study and a postdoctoral scholar at
Caltech. "This is something that was predicted in the 1970s, but hadn't
been shown until now."
The new findings were made possible by
combing through archival observations from NASA's now-defunct Rossi
X-ray Timing Explorer (RXTE) mission, which came to an end in 2012. The
researchers specifically looked at a black hole that is orbited by a
sun-like star; together, the pair is called XTE J1550-564. The black
hole "feeds" off this star, pulling material onto a flat structure
around it called an accretion disk. By looking closely at the X-ray
light coming from the disk as the light spirals toward the black hole,
the team found imprints indicating that the light had been bent back
toward the disk and reflected off.
"The disk is essentially
illuminating itself," says co-author Javier Garcia, a research assistant
professor of physics at Caltech. "Theorists had predicted what fraction
of the light would bend back on the disk, and now, for the first time,
we have confirmed those predictions."
The scientists say that the
new results offer another indirect confirmation of Albert Einstein's
general theory of relativity, and also will help in future measurements
of the spin rates of black holes, something that is still poorly
understood.
"Since black holes can potentially spin very fast,
they not only bend the light but twist it," says Connors. "These recent
observations are another piece in the puzzle of trying to figure out how
fast black holes spin."
The new study, titled, "Evidence for Returning Disk Radiation in the Black Hole X-ray Binary XTEJ1550-564,"
was funded by NASA, the Alexander von Humboldt Foundation, and the
Margarete von Wrangell Fellowship. Other co-authors are Thomas Dauser,
Stefan Licklederer, and Jörn Wilms of The University of
Erlangen-Nüremberg in Germany; Victoria Grinberg of the Universität
Tübingen in Germany; James Steiner of the MIT Kavli Institute for
Astrophysics and Space Research and Harvard University; Navin Sridhar of
Columbia University; John Tomsick of UC Berkeley; and Fiona Harrison,
the Harold A. Rosen Professor of Physics at Caltech and the Kent and
Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and
Astronomy.
Written by
Whitney Clavin
Contact
Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu
