Astronomers have spotted what appears to be two supermassive black holes locked in a death spiral at the heart of a distant galaxy – and they could collide in as little as 100 years.
The pair, discovered at the centre of the galaxy Markarian 501 around 500 million light-years away, was identified after researchers analysed decades of radio telescope observations.
Rather than finding one jet of particles blasting out from the galactic core – as is the case in most galaxies – they found two.
Each jet is thought to be powered by a separate black hole, each weighing between 100 million and a billion times the mass of the Sun.
The findings were published in Monthly Notices of the Royal Astronomical Society.
"Realising that this was a second jet was awesome," lead author Priv-Doz Dr Silke Britzen of the Max-Planck Institute for Radio Astronomy told BBC Science Focus. "For me it was like: that's how it works? I was so amazed and overwhelmed – and wanted to tell everybody what we just found."
The two black holes orbit each other roughly every 121 days, separated by only 250–540 times the Earth–Sun distance – vanishingly small for objects of such colossal mass.
In June 2022, the geometry aligned so perfectly that light from the second jet was bent by the foreground black hole's gravity into a so-called ‘Einstein Ring’, adding further weight to the likelihood that the system is indeed two supermassive black holes.
“The binary model provides a self consistent solution,” Britzen said. “Since these jets are directed towards us, an Einstein ring supports the scenario.”
When the pair finally merge, the collision will send gravitational waves rippling across the Universe, far more powerful than those produced by the stellar-mass black hole mergers so far detected by observatories like LIGO.
“We expect one (merged) black hole to remain,” Britzen said. “I am really curious to observe how this ‘dance’ will continue.”
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