The Black Hole at the Heart of This Galaxy May Be Among the Biggest in the Universe

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Direct measurements of Holm 15A* suggest it clocks in at at 40 billion times the mass of the sun. sdecoret/Shutterstock

When you drive through some galactic neighborhoods, you definitely want to keep your windows rolled up.

The heart of our own Milky Way galaxy, for example, may have as many as 20,000 black holes. And all of them are handily eclipsed by the granddaddy of voids, the supermassive Sagittarius A*.

But some black holes are so vast, they reduce even supermassive things to squintable proportions. In fact, they get their own membership card for being ultramassive black holes.

Such is Holm 15A*, the light-bending beast that calls the Holmberg 15 galaxy home, a merciful 700 million light-years from where you're currently sitting.

While astronomers have noted the likely presence of a black hole in the heart of the elliptical galaxy — indirect measurements even pegged its mass at around 310 billion times that of our sun — a new, more reliable measuring stick has given it even more daunting dimensions.

Holm 15A* is probably closer to the mass of 40 billion suns, according to scientists who submitted their research this week to The Astrophysical Journal.

The team, led by Kianusch Mehrgan from Germany's Max Planck Institute for Extraterrestrial Physics, measured the black hole based on star movements.

"This is the most massive black hole with a direct dynamical detection in the local universe," the team noted in the paper, which has yet to be reviewed by peers.

By "local'' researchers mean an area that sprawls about a billion light-years in radius — a somewhat necessary stretch of the term, considering the infinite expanse that is the universe.

How big is it?

If we're talking about the entire universe, Holm 15A* wouldn't even be the biggest known black hole. You'd have to pry that title from the cold, soul-sucking hands of TON 618, a quasar that has been indirectly measured at 66 billion solar masses.

But Holm 15A* certainly makes a pipsqueak out of our own galaxy's Sagittarius A*, which is around 4.6 solar masses.

"This is a remarkable observation of an extremely massive black hole at 40 billion solar masses," Andrew Coates, a professor at University College London who wasn't involved in the study, told Newsweek. "This makes it the most massive in our region of the universe, and one of the most massive ever found."

An elliptical galaxy at the center of the galaxy cluster PKS 0745-19
The black hole at the center of the galaxy cluster PKS 0745-19 is another example of the ultramassive variety. NASA/CXC/Stanford/Hlavacek-Larrondo, J

Now, if at all possible, let's try to put that into perspective. Like every black hole, Holm 15A* has an event horizon — the surface of edge from which nothing can escape. In other words, it's big, scary mouth.

The event horizon for Holm 15A*, as ScienceAlert puts it, would engulf "all the orbits of all the planets in the Solar System, and then some."

And we're just talking about the mouth, not the hungry hippo that owns it.

Still a little too mind-numbingly abstract?

Let's try imagining Greenland (before all of its ice disappears). You would be able to fit Greenland into Holm 15* about, errr ... carry the two over the four ... let's see ... who are we kidding? Greenland wouldn't even be on the kiddie menu for Holm 15A*.

There are just some things in this universe that exist on such a grand scale, we simply can't give their girth a human framework.

Holm 15A* is one of those things.