Spin of massive black hole accurately measured for the first time
For the first time in space history, the spin of a super massive black hole was accurately measured. The black hole at the center of galaxy NGC 1365 is more than 2 million miles wide, (that’s eight times the distance from Earth to Moon), and spins so fast, its surface travels at nearly the speed of light.
With the help of the Nuclear Spectroscopic Telescope Array (NuSTAR) and European Space Agency’s XMM-Newton X-ray satellites, astronomers managed to measure the spin rate of this immense black hole at the heart of the spiral galaxy NGC 1365. The results show that this black hole is spinning almost at the maximum possible rate.
The astronomers measured X-rays from the center of the galaxy to determine the black hole’s mass and spin. These two numbers say everything one needs to know about a black hole. The spin, in particular, reveals the past and future of the black hole and its host galaxy. As Guido Risaliti, leader of the team and member of the Harvard-Smithsonian Center for Astrophysics (CfA), said: “The black hole's spin is a memory, a record, of the past history of the galaxy as a whole".
The black hole in NGC 1365 is as massive as several million Suns and it grew that big by ‘swallowing’ stars, gas and other black holes, over a period of billions of years. Its high spin suggests it grew through “ordered accretion” and not by randomly pulling matter from all directions.
To measure the spin of a black hole, scientists spread the X-ray light of the accretion disk that swirls around the black hole into different colors. Each color signifies a different element, for example iron. Then they track how these colors disperse and distort from the immense gravity of the black hole. The amount of distortion monitored can reveal the spin rate of the black hole. The only problem is the obscuring clouds around the black hole that obstruct the measurements. NuSTAR solved that particular problem by ‘piercing through’ the obscuring clouds. As Risaliti claimed, “This is the first time anyone has accurately measured the spin of a supermassive black hole."