Messier 87's black hole is unusually massive for its age, indicating early black holes were typically overmassive. Photo / Getty Images
They’re huge. They’re invisible. They collapse space and time into infinity.
But black holes are also proving to be the centre of, well, everything.
Astronomers have discovered the most monstrous supermassive black hole ever. At 36 billion times more mass than our sun, it’s so big it’s pushing back the boundaries of possibility. They’ve even had to redub it “ultra” massive to convey the extent of its scale.
But size is just the start of the story.
It’s also about the stars of the giant elliptical galaxy Messier 87 surrounding it: their speed, number and age.
Put them together and you get a remarkable puzzle. Black holes devour stars and interstellar gas. This causes them to grow. But they also turn into quasars, excreting blasts of raw energy back out into space, sparking another cycle of star formation.
So which came first?
Is a black hole a chicken? Or an egg?
“With this latest find, we have another clue to the greatest chicken-and-egg puzzle in all the universe,” says astrophysicist and science communicator Ethan Siegel. “With a little luck, we’ll have an even better picture of how our Universe actually grew up in just a few years.”
It may have all started with a Big Bang.
And the accepted understanding goes that as the first stars aged, some collapsed in on themselves to create Albert Einstein’s worst nightmare.
But a “Cosmic Horseshoe” has up-ended this argument.
Instead, it points to a cosmos seeded with these impossible vortices of uncreation from the very beginning. And it was they that spun the stars and galaxies out of the primordial soup.
Messier 87 is one of the largest galaxies ever found. It is located some 5 billion light-years away, meaning the light reaching us was emitted at a time when the universe was only two-thirds its current age.
It was already a fossil galaxy by that time, meaning it had devoured all of its surrounding smaller galaxies, star clouds and gas.
“It is likely that all of the supermassive black holes that were originally in the companion galaxies have also now merged to form the ultramassive black hole that we have detected,” says researcher Professor Thomas Collett, of the University of Portsmouth.
It’s called the Cosmic Horseshoe because of the effect it has on the space around it.
Its gravity is so powerful that it has bent the light of stars in a distant blue galaxy behind it into a near-perfect circle.
It’s an effect first predicted by Einstein more than a century ago. Hundreds of examples have since been found.
Now, a new study published in the Monthly Notices of the Royal Astronomical Society has calculated the black hole at its core as being 10,000 times more massive than that at the centre of our own galaxy.
“This is among the top 10 most massive black holes ever discovered, and quite possibly the most massive,” says Collett.
This particular gravitational lens was first spotted during a deep space survey only a few decades ago. But the power of its magnification has given astronomers a rare opportunity to observe such a distant and ancient structure in detail.
“We detected the effect of the black hole in two ways – it is altering the path that light takes as it travels past the black hole, and it is causing the stars in the inner regions of its host galaxy to move extremely quickly [almost 400km/s].
“By combining these two measurements, we can be completely confident that the black hole is real.”
“So we’re seeing the end state of galaxy formation and the end state of black hole formation,” says Collett.
But the Cosmic Horseshoe black hole should not exist.
It’s too big for its age.
And astronomers are finding increasing numbers of similar overmassive black holes in the earliest stages of the universe.
But Messier 87 is evidence of a different creation story.
“When you looked at galaxies today, you’d find a correlation between how much mass is in the form of stars within the galaxy and how heavy the supermassive black hole is,” explains Siegel.
That ratio is about 1000 to 1.
“Then, when you looked at galaxies at earlier times, you’d expect that the correlation would remain the same [with the same ratio] for some time, before ‘tilting’ at early times to favour more stellar mass and lower supermassive black hole mass,” he adds.
That’s because the young black holes wouldn’t have had much time to gorge themselves on their surrounding stars.
But, because of its size and age, Messier 87 indicates that this is not the case.
Its ultramassive black hole is too big. It’s eaten more than it could have.
“When compared with galaxies found more locally, the team of scientists found that … its black hole is much more massive than its central stellar velocity dispersion would indicate,” Siegel explains. “Additionally, the black hole appears to be overmassive compared to the total stellar mass of the galaxy.”
Messier 87 is not the first galaxy containing a supermassive black hole to indicate this. But it is the biggest. And the oldest.
“What we find, remarkably, for the earliest galaxies of all … going all the way back to just 420 million years after the Big Bang … is that nearly all of the ones with black holes display overmassive black holes.”
They appear to have star-to-black hole mass ratios of 100-to-1 or 10-to-1 instead of the currently observed 1000-to-1.
“In other words, early on, ‘overmassive’ black holes are actually typical,” Siegel concludes. “This is interesting and highly suggestive of the notion that black holes, and not stars, came first.”