Star Explodes After Black Hole Devours It From the Inside

Astronomers have observed the signs of a star swallowing a compact object that they believe is a black hole, and that object then devouring the star's core from the inside. The process resulted in an explosion that left the star obliterated and the black hole standing alone.

The gruesome cosmic event, that occurred in a dwarf star-forming galaxy 480 million light-years from Earth, resulted in a powerful burst of radio energy as bright as one that would normally be associated with an exploding star or supernova. This energetic burst was picked up by the 27 antennae that comprise the Very Large Array (VLA) telescope located in the desert of New Mexico in 2017.

What made this signal worthy of further investigation was the fact that it hadn't been present in earlier radio surveys, indicating a sudden and violent cosmic event had occurred.

This caught the attention of Dillon Dong, an astronomer at the California Institute of Technology, and along with his team, he began to further investigate the dwarf galaxy with the VLA and a telescope located at the W.M. Keck Observatory, Hawai'i.

Dong is the lead author of a paper discussing the findings published in the journal Science.

It was with the W.M. Keck Observatory telescope, which views the Universe in the same optical light region of the electromagnetic spectrum that our eyes see in, that Dong and his team saw a bright outflow of material stretching out in all directions from at a speed of around 3 million kilometers per hour.

The astronomers traced the source of this outflow to a central point at the edge of the dwarf galaxy. They also discovered that a burst of X-rays from the same point had been picked up by an instrument aboard the International Space Station (ISS) in 2014.

From all this data, Dong and his crew were able to piece together a history of the event.

Before the star was devoured from the inside out by the black hole the two had been locked in a spiraling dance for centuries. Born as binary stars (two stars orbiting each other), the more massive of the two burned through its fuel more quickly, reaching the end of its lifecycle, exploding in a supernova, and collapsing into a black hole or possibly a neutron star.

As the two circled each other, the black hole moved closer to the star. Around 300 years ago it entered the star's atmosphere causing gas to be ejected outwards forming a donut-like shape, or torus, around the two.

The black hole then worked its way into its stellar companion, disrupting the nuclear fuel burning that prevents stars from collapsing. As the star's core collapsed a disk of material was formed around the invading compact object. This caused a jet of material to be launched from the core, ripping through what was left of the star and escaping into space at near-light speed.

The star then went supernova just as its companion had, albeit much earlier than it would have without the intervention of its black hole companion.

The bright radio emission picked up by the VLA was triggered by the fast-moving material shed by this second supernova catching up with and slamming into material that had been shed by the earlier stellar explosion and causing powerful shocks.

Theorists have long suspected events like this, referred to as merger-triggered supernovas, occur but until now hadn't spotted evidence of them.

Debris Escapes From a Merger Triggered Supernova
Illustration showing the aftermath of an explosion caused when a black hole ate its way free of a dying star Bill Saxton, NRAO/AUI/NSF/NRAO