Supernova Shines Light On Black Hole Formation

Astronomers have discovered what could be the birth of a nearby black hole, a discovery that could help scientists understand how black holes form and evolve over time.

The star that exploded, now known as supernova 1979C, was just 50 million light-years away and about 20 times the mass of our sun, astronomers say.

Abraham Loeb, a professor at the Harvard Smithsonian Center for Astrophysics, says that when a star that size explodes, it can end up in one of two forms: "Either it makes a neutron star, which is the densest form of matter that we know about — it has the density similar to an atomic nucleus and the size comparable to a big city," says Loeb. "Or it ends up in a black hole, which is an object you can get in but can never get out of."

The star in question was discovered on the evening of April 15, 1979, by Gus Johnson, who was on a cosmic pursuit in his backyard in Maryland, touring one little corner of the heavens.

"And I decided to share the tour, using the 8-inch telescope, with the pastor of my church," Johnson says. The two men gazed up at a galaxy called M100 in the constellation Coma Berenices.

"For some reason, I don't know why, this little star in M100 caught my attention," Johnson says. On a hunch, he pulled up a detailed chart of all the stars in this part of the sky. It wasn't on the chart. He had discovered a star that was only visible because it was in the throes of a violent explosion. It was a supernova.

From Explosion To Black Hole

So fast-forward to today. To figure out what befell the 1979 supernova, Loeb and his colleagues turned NASA's orbiting Chandra X-ray Observatory to that corner of the sky. And they now conclude that the supernova most likely ended up as a black hole.

"If our interpretation is correct, and indeed SN1979C ended up as a black hole, then of course it's the first time we are seeing a black hole being born in a normal supernova," Loeb says, speaking at a NASA news conference Monday.

But he is quick to add that they see black holes being born all the time in abnormal supernovas — that is, vastly larger cosmic explosions from billions of light-years away. These are seen as a flash of high-intensity gamma rays, and they presumably emanate from a collision of neutron stars, or the explosion of supermassive stars, vastly different from our own sun.

Now, it's still possible this supernova did end up as a neutron star.

Alex Filippenko, an astronomer at the University of California, Berkeley, says in that event, X-rays they witness could be coming from a huge cloud of glowing gas called a pulsar wind nebula, like the picturesque crab nebula. That, he says, would also be a wonderful thing to witness.

"So I'm pretty excited about this discovery, regardless of whether it ends up being a young black hole or a pulsar wind nebula," Filippenko says.