J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
RELEASE: 13-063
NASA'S NUSTAR HELPS SOLVE RIDDLE OF BLACK HOLE SPIN
WASHINGTON -- Two X-ray space observatories, NASA's Nuclear
Spectroscopic Telescope Array (NuSTAR) and the European Space
Agency's XMM-Newton, have teamed up to measure definitively, for the
first time, the spin rate of a black hole with a mass 2 million times
that of our sun.
The supermassive black hole lies at the dust and gas-filled heart of a
galaxy called NGC 1365, and it is spinning almost as fast as
Einstein's theory of gravity will allow. The findings, which appear
in a new study in the journal Nature, resolve a long-standing debate
about similar measurements in other black holes and will lead to a
better understanding of how black holes and galaxies evolve.
"This is hugely important to the field of black hole science," said
Lou Kaluzienski, a NuSTAR program scientist at NASA Headquarters in
Washington.
The observations also are a powerful test of Einstein's theory of
general relativity, which says gravity can bend space-time, the
fabric that shapes our universe, and the light that travels through
it.
"We can trace matter as it swirls into a black hole using X-rays
emitted from regions very close to the black hole," said the coauthor
of a new study and NuSTAR principal investigator Fiona Harrison of
the California Institute of Technology in Pasadena. "The radiation we
see is warped and distorted by the motions of particles and the black
hole's incredibly strong gravity."
NuSTAR, an Explorer-class mission launched in June 2012, is designed
to detect the highest-energy X-ray light in great detail. It
complements telescopes that observe lower-energy X-ray light, such as
XMM-Newton and NASA's Chandra X-ray Observatory. Scientists use these
and other telescopes to estimate the rates at which black holes spin.
Until now, these measurements were not certain because clouds of gas
could have been obscuring the black holes and confusing the results.
With help from XMM-Newton, NuSTAR was able to see a broader range of
X-ray energies and penetrate deeper into the region around the black
hole. The new data demonstrate that X-rays are not being warped by
the clouds but by the tremendous gravity of the black hole. This
proves that spin rates of supermassive black holes can be determined
conclusively.
"If I could have added one instrument to XMM-Newton, it would have
been a telescope like NuSTAR," said Norbert Schartel, XMM-Newton
Project Scientist at the European Space Astronomy Center in Madrid.
"The high-energy X-rays provided an essential missing puzzle piece
for solving this problem."
Measuring the spin of a supermassive black hole is fundamental to
understanding its past history and that of its host galaxy.
"These monsters, with masses from millions to billions of times that
of the sun, are formed as small seeds in the early universe and grow
by swallowing stars and gas in their host galaxies, merging with
other giant black holes when galaxies collide, or both," said the
study's lead author, Guido Risaliti of the Harvard-Smithsonian Center
for Astrophysics in Cambridge, Mass., and the Italian National
Institute for Astrophysics.
Supermassive black holes are surrounded by pancake-like accretion
disks, formed as their gravity pulls matter inward. Einstein's theory
predicts the faster a black hole spins, the closer the accretion disk
lies to the black hole. The closer the accretion disk is, the more
gravity from the black hole will warp X-ray light streaming off the
disk.
Astronomers look for these warping effects by analyzing X-ray light
emitted by iron circulating in the accretion disk. In the new study,
they used both XMM-Newton and NuSTAR to simultaneously observe the
black hole in NGC 1365. While XMM-Newton revealed that light from the
iron was being warped, NuSTAR proved that this distortion was coming
from the gravity of the black hole and not gas clouds in the
vicinity. NuSTAR's higher-energy X-ray data showed that the iron was
so close to the black hole that its gravity must be causing the
warping effects.
With the possibility of obscuring clouds ruled out, scientists can now
use the distortions in the iron signature to measure the black hole's
spin rate. The findings apply to several other black holes as well,
removing the uncertainty in the previously measured spin rates.
For more information on NASA's NuSTAR mission, visit:
http://www.nasa.gov/nustar For more information on ESA's XMM-Newton mission, visit:
http://go.nasa.gov/YUYpI6
