Questions 1-11 are based on the following
Adapted from "NASA's NuSTAR Helps Solve Riddle of Black Hole Spin." © 2013 by NASA.
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, for the first time, the spin rate of a black hole
5 with a mass two 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
10 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
15 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.
20 "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, NuSTAR principal
investigator Fiona Harrison of the California Institute of
Technology in Pasadena. "The radiation we see is warped
25 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
30 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
Until now, these measurements were not certain because
35 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
40 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.
Measuring the spin of a supermassive black hole is
fundamental to understanding its past history and that of
45 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
50 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-
55 like accretion disks, formed as their gravity pulls matter
inward. Einstein's theory predicts that 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.
60 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
65 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
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
75 in the previously measured spin rates.