There is evidence that the explosion of this star, W49B, left behind a black hole (Image: X-ray: NASA/CXC/MIT/L.Lopez et al.; Infrared: Palomar; Radio: NSF/NRAO/VLA)

Lost neutrinos may help set off weak flashes of light that signal a black hole’s birth.

It’s thought that very massive stars explode when they die, and the stuff left behind collapses into either a neutron star or a black hole. But models of dying giant stars don’t reliably produce supernova explosions, says Elizabeth Lovegrove of the University of California, Santa Cruz. “Some stars are harder to blow up than others,” she says.

Previous work suggested that most of the stars that form black holes implode instead, making them hard to spot. “Is it possible for a star to just disappear inside a black hole without a trace?” wondered Stan Woosley, also at UCSC.


Neutrino exodus

Lovegrove and Woosley realised the key to seeing an imploding star may lie in the large number of neutrinos released from a dying star’s core. Without the neutrinos, the core suddenly becomes lighter. According to their model, this change sends a shock wave through the star’s outer layers, which then fly off, glowing brightly as they do.

In a separate study, Anthony Piro of the California Institute of Technology in Pasadena calculated what would happen to the released gas in the first few days after the star’s collapse. He found that the flash of light from a dying supergiant star would be weaker than a supernova, but bright enough for us to see and identify with current and future telescopes.

Christopher Kochanek, an astronomer at Ohio State University who was not involved with the current research, is excited at the prospect: “What would beat seeing a black hole form? How much cooler can you get?”

Journal reference: arxiv.org/abs/1303.5055 and arxiv.org/abs/1304.1539