Black Hole Weighing More Than A Billion Suns Spins Slower Than Its Peers, NASA's Chandra Finds

The black hole powering the quasar H1821+643 is the most massive black hole to have an accurate measurement of spin. Weighing more than a billion Suns, the black hole spins slower than its peers.

NASA's Chandra X-ray Observatory has found a black hole weighing more than a billion solar masses that spins slower than its peers. The supermassive black hole powers a quasar called H1821+643, which is located about 3.4 billion light years from Earth. 

A quasar is a brilliant beacon of intense light from the centre of a distant galaxy that can outshine the entire galaxy, and is powered by a supermassive black hole violently feeding on inflating matter. 

The black hole powering H1821+643 is the most massive black hole to have an accurate measurement of spin. The actively growing black hole in the quasar contains between three and 30 billion solar masses. This makes the black hole one of the most massive known. Meanwhile, the black hole at the centre of the Milky Way galaxy weighs about four million Suns.

The paper describing the results has been published in the journal Monthly Notices of the Royal Astronomical Society.

What The Colours In The Image Of The Quasar Denote

According to NASA, the composite image of the quasar contains X-rays from Chandra. These are depicted in blue. The radio data from National Science Foundation's (NSF) Karl G. Jansky Very Large Array (VLA) is depicted in red. Data from an optical image from the PanSTARRS Telescope in Hawaii has also been combined with the Chandra and VLA data, and is represented in white and yellow.

According to NASA, the supermassive black hole is located in the bright dot in the centre of the radio and X-ray emission.

The X-ray data can show how fast the black hole is spinning because a spinning black hole drags space around with it and allows matter to orbit closer to it than is possible for a non-spinning one. 

The amount of energy as a function of wavelength, or the spectrum of the quasar indicates that the black hole is rotating at a modest rate compared to less massive black holes that soin close to the speed of light. NASA states that this is the most accurate spin measurement for such a massive black hole.

Why Is The Black Hole Spinning Half As Fast As Lower Mass Peers?

The manner in which supermassive black holes grow and evolve may explain why the black hole is spinning slower than its peers. Most massive black holes like the one discussed in the study undergo most of their growth by merging with other black holes, or by gas being pulled inwards in random directions when their large discs are disrupted. This could explain why such massive black holes have a relatively slow spin compared to lower mass black holes.

According to the study, the supermassive black holes which grow in this manner are likely to often undergo large changes of spin. These include being slowed down or wrenched in the opposite direction. According to astronomers, most massive black holes should be observed to have a wider range of spin rates than their less massive relatives. 

Meanwhile, less massive black holes are expected to accumulate most of their mass from a disc of gas spinning around them. The incoming matter always approaches from a direction that will make such black holes spin faster until they reach the maximum speed possible, which is the speed of light. This occurs because such discs are expected to be stable.