SYDNEY: The supermassive black hole at the core of our nearest galactic neighbour, Andromeda, has suddenly got brighter and started sucking up matter unpredictably, astronomers have discovered.

Over the past 10 years, the black hole (M31*) – which is 70 million times bigger than our Sun – has been absorbing an increased amount of matter, making the object appear brighter, reported Zhiyuan Li at the American Astronomical Society Meeting in Miami, Florida.

These findings provide insight into the way M31* grows by attracting matter around it (a process known as accretion), said Li, the lead researcher on the project from the Harvard-Smithsonian Centre for Astrophysics.

The observations will also help scientists understand other black holes – including the one at the centre of our galaxy, he said.

“It’s important to figure out what’s going on here because the accretion of matter onto these black holes is one of the most fundamental processes governing the evolution of galaxies."

A rapid change

Astronomers believe that most galaxies have black holes, often much larger than the size of our Sun. And it has been known for some time that the brightness of black holes vary according to the amount of mass accretion occurring.

However, the specifics of this accretion and how constant it is over time are poorly understood.

Over the past 10 years, NASA’s orbiting X-ray telescope, Chandra, allowed scientists to observe notable changes in M31*’s behaviour.

Chandra senses high-energy waves that occur as a result of forces around environments such as black holes and stars.

This is the first time these changes occurring in M31* have been monitored over such a short time span

100 times brighter

The sustained surveillance revealed that the black hole was relatively ‘dim’ prior to 2006, suggesting little accretion activity.

But, one day in January 2006, M31* suddenly ramped up its brightness 100 fold, suggesting an increase in the amount of matter falling onto the Andromeda galaxy and therefore a flare-up of X-rays, said Li.

The specific source of the 2006 brightening event is not known.

In the years following, the brightness dimmed, but was still about 10 times brighter than prior to 2006.

The cause of the steady brightness is also not known, but current theories include: M31* capturing winds from an orbiting star, or that a nearby gas cloud spun into the black hole.

A blackhole like our own

M31* is ideal for observation because it is a mere three million light years from Earth and may be similar to the black hole in our own galaxy.

Both our own black hole and M31* are surprisingly ‘quiet’ compared to those in other, more distant galaxies, according to Li.

“Many of the nearby supermassive black holes are faint,” said Christine Jones, and collaborator on the project also at CfA.

“The one in Andromeda and the one in our galaxy give us a chance to study these in great detail.”

Finding 'nothing new'

However, Duncan Galloway, an astronomer at Monash University in Melbourne, didn’t find the observations revolutionary.

“It’s an interesting object but the behaviour isn’t that interesting. We’ve seen variability from the one at the centre of our galaxy,” he said.

Still, fellow Australian astronomer Joss Bland-Hawthorne at the University of Sydney thinks the findings are intriguing.

“This is a wonderful and exciting result. It confirms what we have long believed, that black holes are being fed randomly from in-falling gas, presumably from the torus of gas and dust around the black hole.”

“It's a lot like the stock market. Rises and falls, general trends, occasional bull market peaks followed by crashes,” said Hawthorne.

“It's amazing that on a timescale of only 10 years, we can see a rapid rise. I presume there will be a rapid fade at some time in the future.”