Black Hole Fun

COLLAPSING STARS STILL HAVE A FEW SURPRISES FOR ASTRONOMERS

A MASSIVE, dying star astronomers thought would explode and give them a ginormous fireworks show instead quietly collapsed into a black hole. The observation is causing astronomers to rethink what they know about supernovas and black holes.

The star, known by astronomers as N6946-BH1, lived in a galaxy 22 million light-years away. That star cluster, referred to as the “Fireworks Galaxy” for the frequent supernovas— explosions of stars—known to happen there, has held NASA’S attention for several years, culminating in the latest report, published in April in Monthly Notices of the Royal Astronomical Society.

About eight years ago, N6946-BH1 started to weaken. A few years later, the telescopes aimed in its direction could no longer find it. Astronomers kept searching, probing that sliver of the universe with the Large Binocular Telescope and the Hubble and Spitzer space telescopes. But the star, which once shined with the strength of 22 of our suns, was gone.

The disappearance came as a surprise, because most stars perform one final dazzling act before fizzling out. “The typical view is that a star can form a black hole only after it goes supernova,” said Christopher Kochanek, who teaches astronomy at the Ohio State University, in a statement.

But N6946-BH1 never lit up with that anticipated supernova. And every alternative explanation for the star’s disappearance— such as, maybe it was hiding behind a dust cloud; maybe it was just temporarily dim—was disproved. That left just one option: The star had collapsed into itself and become a black hole. Kochanek and his colleagues refer to the occurrence as a “massive fail.” (They aren’t being judgmental.)

Such fails may be more common than previously believed. Krzysztof Stanek, co-author of the new study, says the process makes sense. An explosive death might not leave behind the quantity of mass required for forming a giant black hole, Stanek explained. “I suspect it’s much easier to make a very massive black hole if there is no supernova,” he said in a statement.

During the seven years astronomers have been surveying the Fireworks Galaxy and others for supernovas, they’ve seen fewer such explosions than expected based on statistical calculations. But this death marks the first time they’ve observed a star skipping the supernova state. Researchers now think up to 30 percent of huge stars die without a supernova.

Now, in the space where this massive star once glowed, astronomers see only a small amount of infrared light, which researchers believe is from debris falling into a black hole.

So if you want fireworks, stick to the Fourth of July celebrations.