A new kind of cosmic flash may reveal something never seen before: the birth of a black hole.
According to well-established theory, when a massive star dies, its core collapses under its own weight. As it collapses, the protons and electrons that make up the core merge and produce neutrons. This collapsing process also creates neutrinos, which are particles that zip through almost all matter at nearly the speed of light. As the neutrinos stream out from the core, they carry away a lot of energy, representing about a tenth of the sun’s mass.
This rapid loss of mass means that the gravitational strength of the dying star’s core would abruptly drop (according to a little-known paper written in 1980 by Dmitry Nadezhin). When that happens, the outer gaseous layers, mainly hydrogen, still surrounding the core would rush outward, generating a shock wave that would hurtle through the outer layers at about 1,000 kilometers per second (more than 2 million miles per hour).
Tony Piro, a postdoctoral scholar at California Institute of Technology, examines in his new study what might happen at the moment when the shock wave hits the star’s surface. “That flash is going to be very bright, and it gives us the best chance for actually observing that this event occurred,” he explains. It would be luminous enough to be detectable in nearby galaxies. The flash, which would shine for 3 to 10 days before fading, would be very bright in optical wavelengths.
Piro estimates that astronomers should be able to see one of these events per year on average. Surveys that watch the skies for flashes of light like supernovae, such as the Palomar Transient Factory (PTF), are well suited to discover these unique events. The intermediate Palomar Transient Factory (iPTF), which improves on the PTF and just began surveying in February, may be able to find a couple of these events per year.