Astronomers have tracked down the biggest black hole seen in the Universe so far.
Using two different types of measurement, astronomers recently discovered the behemoth of a black hole has almost 10,000 times more mass than the supermassive black hole at the centre of our Galaxy.
The black hole is located five billion light-years from Earth in the heart of one of the largest known galaxies, the Cosmic Horseshoe. This giant galaxy appears to have gobbled up all the galaxies surrounding it, meaning both it and its black hole have grown as large as they possibly can.
The black hole itself weighs a staggering 36 billion times the mass of our own Sun.
The find was even more remarkable, as the black hole isn’t active, meaning it’s not surrounded by a glowing disc of dust.
Instead, a new study recently published in Monthly Notices of the Royal Astronomical Society used a combination of two existing methods to pin down the size of this mega black hole.
“The 'golden' method usually relies on stellar kinematics, which involves measuring how stars are moving within a galaxy,” said Carlos Melo to BBC Science Focus. The PhD student from Universidade Federal do Rio Grande do Sul, Brazil led the study.
The speed of the stars at the centre of a galaxy is closely related to the mass of its supermassive black hole. The astronomers found the stars were moving very quickly, almost 400 kilometres per second (249 miles per second), indicating a truly giant black hole.
“This approach, however, is most effective for galaxies in the very nearby Universe, where our telescopes can better resolve the region around the black hole,” said Melo.
As the Cosmic Horseshoe is a distant five billion light-years away, the astronomers also relied on a second method, made possible because the galaxy is a gravitational lens.
Gravitational lensing happens when the light from a distant galaxy passes close to a massive ‘lens’ object – in this case, the Cosmic Horseshoe’s black hole. The gravity of the ‘lens’ bends the light like a magnifying glass, boosting the light of the background galaxy but also distorting it.
Astronomers can use this distortion to measure how much mass the lens has.
“The Cosmic Horseshoe was unique because we could use both of these powerful methods simultaneously. And with that, we’re more confident and sure about the black hole and its mass,” said Melo.
Both galaxy and black hole reached their colossal scale by merging with their surrounding siblings. This is how all galaxies grow over time, eventually coming to a point where all the surrounding galaxies that could merge together have done so, resulting in a ‘fossil group’ that can grow no larger.
The Cosmic Horseshoe has no other bright galaxies around it, suggesting it has reached this phase.
“This discovery gives us a unique window into the end product of galaxy and black hole formation,” said Melo. “By studying this system, we can better understand how other galaxies and their supermassive black holes might evolve over cosmic time.”
About our experts
Carlos Melo is a PhD student from the Universidade Federal do Rio Grande do Sul (UFRGS) in Brazil.
Read more:
