Imagine you’re playing Hungry Hungry Hippos, the tabletop game where the animals eat as many marbles as they can.
Suddenly, two of these plastic hippos begin dancing around the board and smash into each other, forming one big and still very much hungry hippo.
Scientists have revealed they’ve seen the cosmic equivalent of this – two black holes merging on the outskirts of our galaxy.
So, to clarify, not giant space hippos.
The black holes – one roughly 140 times the mass of the Sun and the other about 100 solar masses – fused into one pit of infinitely deep darkness 225 times larger than our Sun.
The event, called GW231123, took place possibly billions of years ago about between two and 13billion light-years away.
It’s the largest black hole merger ever recorded by gravitational wave detectors, which pick up tiny vibrations in the fabric of reality.
Black holes are bottomless pits of gravity that are the gravestones of ancient stars that imploded and collapsed.
Sometimes, two black holes begin to orbit one another and merge, wobbling space-time like a bowl of jelly and unleashing gravitational waves.
Two detectors in the US operated by the Laser Interferometer Gravitational-wave Observatory (Ligo) noticed GW231123 in November 2023.
Twitches in space-time thousands of times smaller than the width of a proton and one-tenth of a second long were recorded.
This might not sound like much, but you can’t just drop a pen in front of a gravitational wave detector and get a result – gravity is too weak a force, so this was a serious amount of energy.
Hold up, what’s ‘space-time’?
It’s two little words that mean a lot. Space consists of three dimensions – width, length and depth. You also have a fourth dimension – the ‘direction’, time. Together, you have space-time.
The pair is stitched together and dynamic, forming a seamless continuum. But the best way to wrap your head around the theory is to picture a saggy old mattress.
Matter and energy, like a rough sleeper, distort cosmic geometry as they roll around, producing gravity that forces everything from falling apples to light to follow a path through space.
But the important thing is that we’re talking about a ‘four-dimensional mattress’. You probably can’t buy one during the DFS Boxing Day sale, but these things tossing and turning disturb space and time at the same, well, time.
All together, it’s the general theory of relativity. Space-time, scientists came to discover, is like a Bop-It: you can stretch it, shrink it, jiggle it and rip it. This explains why a lot of weird things exist in the universe, like black holes.
This is the largest of the 100 black hole smashes recorded since Ligo started in 2015, beating GW190521, with a much smaller mass of 140 times the Sun.
Mark Hannam, the head of the Gravity Exploration Institute at Cardiff University, told Metro: ‘Every so often, we find a gravitational wave signal that tells us something new and surprising, and this was definitely one of those!’
The findings, presented at the Edoardo Amaldi Conference on Gravitational Waves in Glasgow today, have scientists scratching their heads for two big reasons, Hannam added.
For one, these black holes were spinning about 400,000 times faster than Earth does, far quicker than what it’s believed they can.
To put it into perspective, a ‘day’ on these black holes would be 0.216 seconds.
The size of these two black holes is also raising eyebrows, especially in terms of how they formed to begin with.
Broadly speaking, astronomers have found black holes in a size small and a large, but never a medium.
Black holes with masses below about 60 times that of the Sun – a size small – are created when a star dies. Yet ones between 60 to 130 solar masses have never been seen, with physicists believing that the dead stars that could turn into them explode before fully forming.
At least one of the black holes in GW231123 probably falls into this size medium range, so they ‘were more massive than we think is possible from standard formation mechanisms,’ said Hannam.
He added that these two ‘forbidden’ sized black holes may have formed from small black holes merging.
Evidence of collisions involving black holes even larger than GW231123, up to 300 times that of the Sun, has been discovered but not confirmed.
‘The more of these extreme, unexpected signals we see,’ Hannam added, ‘the more we learn about how black holes form in the universe, and how the universe evolves.’
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