May 24, 2011 09:59 GMT  ·  By
Black holes that grow through accretion spin slower than the ones that grow through mergers with other black holes
   Black holes that grow through accretion spin slower than the ones that grow through mergers with other black holes

In a new scientific research, experts were able to figure out that black holes across the Universe are today spinning a lot faster than they used to when the Cosmos was only a fraction of its current age.

The reasons why this happens remain unexplained, but investigators are proposing a series of theories that might help explain the mystery. Recently, experts in the United Kingdom took a shot at developing a plausible explanation for this phenomenon.

The spin acceleration mostly affects giant black holes, of the type that exists at the core of all galaxies, investigators say. This was discovered by using radio, optical and X-ray data, collected by an international collaboration of telescopes.

In a paper published in the latest issue of the journal Monthly Notices of the Royal Astronomical Society, University of Portsmouth Dr. Alejo Martinez-Sansigre and University of Oxford professor Steve Rawlings detail how they made this discovery, and what its implications might be.

One of the most interesting proposals the team makes is that galactic black holes that accumulate matter through accretion will continue to spin as slow as they did when the Universe was only half of its current age (13.75 billion years).

On the other hand, dark behemoths that grew to their impressive size (between 1 million and 1 billion solar masses) by merging with other black holes tend to spin extremely fast. Only a small part of the black hole population the team sampled spun tremendously fast.

In order to carry out this research, investigators used X-ray telescopes to image the radiation being emitted by the accretion disks around black holes. They also used ground-based radio observatories to look at the radio waves emitted by the black holes.

This allowed them to gain a new insight into how large the structures were, and how fast they spun.

“The spin of black holes can tell you a lot about how they formed. Our results suggest that in recent times a large fraction of the most massive black holes have somehow spun up,” Dr. Martinez-Sansigre explains.

“A likely explanation is that they have merged with other black holes of similar mass, which is a truly spectacular event, and the end product of this merger is a faster spinning black hole,” he adds.

“Later this decade we hope to test our idea that these supermassive black holes have been set spinning relatively recently. Black hole mergers cause predictable distortions in space and time – so-called gravitational waves,” professor Rawlings goes on to say.

“With so many collisions, we expect there to be a cosmic background of gravitational waves, something that will change the timing of the pulses of radio waves that we detect from the remnants of massive stars known as pulsars,” he adds.

“If we are right, this timing change should be picked up by the Square Kilometre Array, the giant radio observatory due to start operating in 2019,” Rawlings concludes, quoted by Daily Galaxy.