Neutron stars are one of the possible end products of supernovae. When a star reaches the end of its life, it throws away its outer layers in a gigantic explosion and its core collapses into a dense object. This object is a neutron star – not much larger than a city, but with a bigger mass than the Sun.
Sometimes neutron stars are in compact pairs that can end up merging into one. Researchers now think they might have observed the formation of such a system for the first time. Findings from the event, called supernova iPTF 14gqr, were published in Science.
The Caltech-led team noticed that instead of a massive ejection of material from the supernova, there was only a small ejection. These explosions can throw into space plasma a few times the mass of the Sun, but iPTF 14gqr threw at most one-fifth of our star’s mass.
"We saw this massive star's core collapse, but we saw remarkably little mass ejected," co-author and principal investigator Professor Mansi Kasliwal, from Caltech, said in a statement. "We call this an ultra-stripped envelope supernova and it has long been predicted that they exist. This is the first time we have convincingly seen core collapse of a massive star that is so devoid of matter."
Going supernova requires a star to have a lot of mass. So where does this mass go instead of being thrown into interstellar space? That’s where a dense companion comes in. The exploding star had a companion that siphoned the extra mass as it exploded. It doesn’t have to be another neutron star, it could be a white dwarf or a black hole. The companion just needs to be dense and close enough.
The discovery was possible thanks to the intermedia Palomar Transient Factory, a nightly survey that looks for transient events in the sky such as supernovae. iPTF 14gqr was snapped within the first hour of it going supernova and was then continuously followed up by other observatories across the globe.
"You need fast transient surveys and a well-coordinated network of astronomers worldwide to really capture the early phase of a supernova," lead author Kishalay De, a graduate student at Caltech, explained. "Without data in its infancy, we could not have concluded that the explosion must have originated in the collapsing core of a massive star with an envelope about 500 times the radius of the Sun."
The Palomar Observatory is now running a different transient survey, called Zwicky Transient Facility, which is examining a much larger area of the sky. The team hopes that it will be able to catch more of these rare events.