IE 11 is not supported. For an optimal experience visit our site on another browser.

Blast may herald a black hole's birth

Space.com: Startled astronomers peered through an apparent crack in the expanding bubble from an exploded star to glimpse what may be the youngest black hole ever detected.
An artist's impression shows Supernova 1986J, with an expanding reddish nebula surrounding the central black hole or neutron star, which is shown in blue.
An artist's impression shows Supernova 1986J, with an expanding reddish nebula surrounding the central black hole or neutron star, which is shown in blue.Michael Bietenholz and Norbert Bartel
/ Source: Space.com

Startled astronomers peered through an apparent crack in the expanding bubble from an exploded star to glimpse what may be the youngest black hole ever detected.

It is the closest researchers have come to witnessing the birth of a black hole, from the explosion two decades ago to the recent emergence of a dense object amid the chaotic scene. The object may be a neutron star instead of a black hole, however. Scientists hope to figure that out with continuing observations, they said Thursday.

Other teams have recorded many stellar explosions, called supernovas. And they've discovered many black hole candidates presumed to be the result of previous supernovas. But no one has confirmed the connection so strongly.

"This is the first time we've seen it happen," said Michael Bietenholz of York University in Toronto. "We've never seen a supernova leave behind a black hole, and the only supernovae we've seen that left behind neutron stars are several centuries or more old, and we only know them from historical records."

Bietenholz and his colleagues described the series of events as a textbook example of how things were theorized to go.

"No matter whether the central source is a black hole or neutron star, it would be by far the youngest of either ever observed," he told Space.com.

In fact, this explosion occurred a long time ago, too. The star, SN 1986J, is about 30 million light-years away, so observations of the scene over the past 20 years represent light that took 30 million years to arrive. With that in mind, here's what happened, in terms of the observations:

Around 1983, the core of the star ran out of fuel and was no longer able to support itself against its own gravity. It began to collapse.

"This collapse is extremely fast, and the core collapses into a neutron star in about one second," Bietenholz explained. "It stops, at least momentarily, at this point."

The outer layers of the star were then thrown outward with a bounce, generating a classic supernova explosion that was first spotted in 1986. Exactly what happened next is not known.

"If the core winds up with less than about 1.4 times the mass of our sun, it will remain stable as a neutron star," Bietenholz said. "If the core mass is larger, it will continue to collapse into a black hole, with this further collapse occurring in a fraction of a second."

The star's original mass is not known, so there's a roughly equal chance that the remaining central object is a neutron star or a black hole. Either dense object would generate intense magnetic fields, creating charged particles that would have allowed the researchers to detect it.

Radio Images of Supernova 1986J. The background shows a radio image of the edge-on galaxy NGC 891, in which the supernova can be seen toward the bottom right from the center. The foreground shows three very-long-baseline-interferometry radio images of Supernova 1986J at three frequencies, at approximately 60,000 times greater magnification, with the center of the supernova indicated by the crosses. The left-most image, in red, is at the lowest radio frequency (5 GHz) and shows the expanding, distorted shell of material thrown off in the explosion, with a hot spot to the upper left of the center. The right image is at the highest radio frequency (14 GHz) and shows the newly discovered nebula around the black hole or neutron star, which is almost exactly in the center. The middle image is at an intermediate frequency (8 GHz) and shows a blend of the shell and the nebula around the black hole or neutron star.

The outer layers of the star initially raced into space at more than 44 million mph (20,000 kilometers per second). The expansion continues but has slowed since.

The layers of material remain "pretty dense, and we didn't yet expect to see through them right into the center to see the neutron star or black hole nebula," Bietenholz said. "The fact that we can suggests that, as they expand, they are also fragmenting, so we are seeing in through a crackthat has developed in the shell."

The discovery required several radio telescopes: the National Science Foundation's Very Long Baseline Array, Robert C. Byrd Green Bank Telescope and Very Large Array; and telescopes from the European Very Long Baseline Interferometry Network.

More observations are planned.

"We'll be watching it over the coming years," said Michael Rupen of the National Radio Astronomy Observatory in Socorro, N.M. "First, we hope to find out whether it's a black hole or a neutron star. Next, whichever it is, it's going to give us a whole new view of how these things start and develop over time."

The discovery is detailed in Thursday's online version of the journal Science.