A black hole has the hiccups – because another one is punching it

Out in the depths of space, a black hole is hiccupping. Why? Because it’s getting punched by another one.

Obviously.

Until 2020, a black hole lying around 800 million light-years away had been sitting quietly at the centre of its galaxy. Then, in December 2020, it suddenly came to life, giving off plumes of gas every 8.5 days before going silent again.

For years astronomers have been stumped as to why these ‘hiccups’ were happening, but now they have an answer.

It seems like the large whirling giant is being bullied by a second smaller black hole that is dancing around the supermassive black hole and slinging material out from the larger black hole’s accretion disk of gas every 8.5 days.

This behaviour in black holes has not been observed until now. 

Scientists previously assumed that black hole accretion disks, which are thick chaotic disks of hot gas, rotate around a central black hole. 

But the new results suggest that the accretion disks are even more varied in their contents – and they may even have stars and black holes within them. 

Study author Dr Dheeraj ‘DJ’ Pasham, a research scientist at MIT’s Kavli Institute for Astrophysics and Space Research said: ‘We thought we knew a lot about black holes, but this is telling us there are a lot more things they can do.’

‘We think there will be many more systems like this, and we just need to take more data to find them.’

Researchers from MIT, Italy, the Czech Republic and other universities used the All-Sky Automatic Survey for SuperNovae (ASAS-SN), a network of 20 robotic telescopes dispersed throughout the Northern and Southern Hemispheres, to make the breakthrough. 

The telescopes explore the sky once a day looking for supernovae and other transitory objects.

Then, in December 2020, they spotted the galaxy brightening by a factor of 1,000. 

So the researchers used another telescope, the NICER one (Neutron Star Interior Composition Explorer from Nasa) and as luck would have it, the time of year meant the team could use the telescope to point at what they wanted to see.

‘It was either use it or lose it, and it turned out to be my luckiest break,’ said Dr Pasham. 

They found that within a pattern during the four-month flare, there were subtle dips in a very narrow band of X-rays that seemed to reappear every 8.5 days.

The patterns are similar to what astronomers see when an orbiting planet crosses in front of its host star, but no star would be able to block a flare from an entire galaxy.

‘I was scratching my head as to what this meant because this pattern doesn’t fit anything that we know about these systems,’ Dr Pasham said.

Then they looked at a recent paper by Czech theoretical physicists which suggested there was a much smaller black hole hidden inside the supermassive black hole at the center of a galaxy. 

They proposed that the secondary black hole would pass by the disk of the parent black hole, and it would emit a plume of gas resembling a bee soaring through a pollen cloud.

Dr Pasham said he was ‘super excited by the theory’.

‘I immediately emailed them to say, “I think we’re observing exactly what your theory predicted”,’ he said. 

The follow-up observations with an X-ray telescope aboard the International Space Station (ISS) allowed scientists to catalogue the dips in X-ray data from the feasting object. 

And this was the black hole hiccuping, as the smaller orbiting black hole punched through the accretion disk, pushing out more material than usual.

However, the term ‘smaller’ does not mean the black hole is small, and scientists estimate it weighs the equivalent of 100 to 10,000 suns, a mass that classifies it as an intermediate black hole. 

‘This is a different beast,’ Dr Pasham said. 

‘It doesn’t fit anything that we know about these systems.’

The study is published in the journal Science Advances.