The Universe's Hungriest Black Hole Is 34 Billion Times As Massive As The Sun

An artists's impression of a quasar from the early universe. The brightest quasar yet discovered is brighter than should be possible for its age. ESO/M. Kornmesser

Measurements of the mass of the fastest-growing black hole confirm a major problem for theories about the early universe. Even at 34,000,000,000 times the mass of the Sun, this object is not the most massive black hole measured, but such a mass should be impossible at its age.

Black holes grow by sucking in material around them, but their mass sets a ceiling on how much they can absorb, since their gravity must overcome the outward pressure produced by the light they emit when swallowing new material. This limits how large any black hole can get in a certain amount of time after the Big Bang.

Astronomers have noticed quasars apparently in breach of these rules. Quasars are powered by the material absorbed by their central black hole. The more mass consumed, the brighter they get, but some quasars' brightness requires an inexplicably massive black hole. Most of the anomalous quasars known have holes only a little too large, leaving open the possibility of measurement error. Then along came J215728.21-360215.1.

As the brightest quasar ever found, J215728.21-360215.1's black hole must consume the mass of the Sun every day to sustain itself. That's mind-blowing to laypeople, but the astrophysicists who found it were more bothered by the fact J215728.21-360215.1 is so far away we are seeing it as it was 1.2 billion years after the birth of the universe. Yet only a hole of at least 20 billion solar masses could consume so much.

To get that big, J215728.21-360215.1 either needed to grow far faster than a black hole should theoretically be able to do, or have started out much larger than known methods of black hole formation allow. One of the most crucial things we think we know about black holes is wrong, but we don't know which one.

In Monthly Notices of the Royal Astronomical Society, J215728.21-360215.1 has been measured at 34 billion solar masses – if 20 billion was too large for existing theories, this is clearly much worse. It is feeding at 40 percent of the maximum theoretical rate for its mass.

The brightest quasar ever observed looks like a faint red spot, outshone by ordinary nearby stars, because it is so far away. That very distance, and the red shift that makes its white light look red, indicates how far back in time we are looking. Skymapper Southern Survey

First author Dr Christopher Onken of the Australian National University put this epic mass in context in a statement. “The black hole’s mass is also about 8,000 times bigger than the black hole in the center of the Milky Way," Onken said. "If the Milky Way’s black hole wanted to grow that fat, it would have to swallow two-thirds of all the stars in our galaxy.”

Onken told IFLScience his team measured the mass by observing the speed with which it is sucking in ionized magnesium, which produces a distinctive spectral line. This speed is determined by the J215728.21-360215.1's gravity, which in turn depends on its mass.

Even the initial minimum estimate for J215728.21-360215.1's mass was double any known black hole of similar age. Since then, “There have been a couple of discoveries that fill in the gap, but none have surpassed it,” Onken added.

Since J215728.21-360215's discovery an even more anomalous black hole has been discovered – only (!) a billion solar masses, but so much younger it is even harder to explain. 

Onken told IFLScience we still don't know how these objects came to be, but finding and measuring them accurately gives us the pieces to eventually put together the picture.

 

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