Space Briefs
NASA’s NuSTAR helps solve
riddle of black hole spin
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 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 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, D.C.
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, 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 lowerenergy 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 instru