One of the largest black holes in the universe has just been measured, and it may confirm a dark, violent theory about how they grow so huge.

University of Cambridge scientists studied X-ray emissions from H1821+643, a supermassive black hole at the center of a galaxy 3.4 billion light years away, using Nasa's Chandra X-ray observatory .Using X-ray emissions as a measure, they were able to determine how fast the black hole was spinning, a major characteristic of black holes.

Scientists at the Institute of Astronomy the University of Cambridge have foundat  that H1821+643's black hole rotates about half as fast as most black holes weighing between a million and ten million suns. It's a million-dollar question: why

A new study based on Chandra's observations published in Monthly Notices of the Royal Astronomical Society confirms a theory about how black holes grow so large - by eating other black holes

The event horizon of a black hole prevents any light from escaping. Black holes are mysterious objects whose effects on the matter around them are observed mostly through observations. In our own Milky Way galaxy, the shadows of black holes are only the shadows of the black holes, engulfed in the hot gas that whirls around them, awaiting consumption

According to lead author Julia Sisk-Reynes, also a Cambridge astronomer, 'every black hole can be defined by two numbers: it's mass and its spin.' 'It has been incredibly challenging to determine these values for most black holes.'

Chandra measured X-rays emitted by superheated matter whirling around the supermassive black hole very close to the event horizon, beyond which nothing escapes its crushing gravity.

Scientists were able to measure the speed of a spinning black hole by measuring its X-ray emissions because black holes don't just spin within space, they drag space around with them.

There is some explanation for why it spins slower than other black holes. Compared to the supermassive black hole at the center of our galaxy, which weighs about four million times the mass of our Sun, the black hole in H1821+643 weighs 30 billion solar masses.

According to this theory, the largest black holes form not by accumulating gas and matter gradually, but by violently merging with other black holes and absorbing huge amounts of matter from different directions. Nonlinear accumulations of matter could also slow, speed up, or even reverse the spin of a black hole.

In a statement, study co-author and Cambridge astronomer James Matthews said the moderate spin of this ultramassive object reflects the violent, chaotic history of black holes. When the Milky Way collides with Andromeda and other galaxies billions of years from now, it may also provide insight into what will happen to our galaxy's supermassive black hole.