Astronomers Have Found a Really Massive Supermassive Black Hole

There have been some big discoveries in space lately. Huge discoveries, actually. Astronomers have found the biggest black hole ever recorded, weighing in at a whopping 17 billion times the mass of our Sun. Even on a galactic scale that’s mind-bogglingly massive.

Astronomers have been observing galaxies for centuries and know that they all share common properties. All galaxies are a collection of billions of stars and clouds of gas and dust that have collapsed on themselves and are held together by gravity. And most of them have a black hole at their centers, a feature astronomers didn’t find until the 1980s. But finding the black holes has helped us understand a little more about the galaxies that host them.

There’s a correlation between the mass of the galaxy’s black hole and the mass of the galaxy’s inner region called the bulge – a bigger bulge means a bigger black hole. There’s also a correlation between the black hole’s mass and the mass of the whole galaxy. These relationships suggest that black holes offer something to be learned about how galaxies form, but that, as of yet, is an unsolved mystery.

A typical galaxy’s black hole takes up about 0.1 percent of its total mass. Our galaxy, the Milky Way, has a bit of a lightweight black hole weighing just 0.01 percent of the galaxy’s total mass – that’s four million times as heavy as the Sun. So if we’re the exception on the light end of the black hole weight spectrum, galaxy NGC 1277 is champion on the heavy end.

The disk-shaped galaxy NGC 1277 is about 250 million light years from Earth in the constellation Perseus. Its black hole is massive, a staggering 17 billion times more massive than the Sun. That’s about 11 times as wide as Neptune’s orbit around the Sun. It’s the most massive black hole astronomers have ever found. But that’s not the strangest bit.

For astronomers, the relative masses of the black hole compared to its galaxy’s bulge is really significant, and NGC 1277’s bulge is disproportionately tiny, weighing in at less than half the mass of the black hole. And the whole galaxy weighs only about 120 billion solar masses. So at 17 billion solar masses, NGC 1277’s black hole is 14 percent of the total galaxy’s mass. Compared the Milky Way’s black hole mass of 0.01 percent, NGC 1277’s black hole is well outside the realm of what astronomers consider to be normal.

But this doesn’t mean we know anything about how NGC 1277 came to host such a big black hole, though there are some theories.

Galaxies of different ages look different. The furthest, oldest galaxies are small and shapeless, while younger galaxies are larger with distinct forms. One theory is that modern galaxies have gained mass through galactic cannibalism; one ingests the other when two collide, causing their black holes to merge. But this theory doesn’t explain NGC 1277. Two galaxies merging should have black holes and bulges that grow at the same rate, not one black hole that grows substantially while the bulge remains the same.

Another puzzle is that NGC 1277 contains only old stars. The youngest are about eight billion years old, which is almost twice the age of our Sun. So its not clear whether this is a bloated cannibal galaxy or a stalled galaxy that’s been sitting in this state since the Big Bang.

NGC 1277 might be the extreme case but it’s not the only exception. In a galactic survey of 700 galaxies, astronomers found five others near NGC 1277 that look to have the same abnormally heavy black hole relative to the bulge. And they all seem to be compact galaxies, smaller than you might think given their mass. But this could explain their bizarre properties.

As astronomers peer further into the heart of NGC 1277, they will likely end up revisiting the rule about a galaxy’s black hole mass relative to its bulge. And they’ll likely end up uncovering a host of new questions at the same time. Or, this discovery could be the jumping off point for a new class of galaxy-black hole systems. Whatever the result, anything that challenges common perception is bound to return some awesome new science.