Astronomers witness birth of binary star system for the first time
- by Amanda Heroux
- in Science
- — Oct 13, 2018
But things won't end well for these two stars. These dense stellar remnants will ultimately spiral into each other and merge in a spectacular explosion, giving off gravitational and electromagnetic waves.
The researchers realized that this massive star wasn't alone, and that a companion star - invisible to them - was using gravity to siphon away the star's mass before it exploded.
A team of astronomers led by Caltech's Kishalay De has discovered the first recorded "ultra-stripped" supernova - a faint type of supernova that is believed to play a role in the formation of compact neutron star binary systems.
When a massive star runs out of fuel, it collapses inward on itself, creating a bright explosion known as a supernova. After the star's outer layers have been blasted away, all that remains is a dense neutron star. Or as the researchers explained it, a teaspoon of the neutron star would weigh as much as a mountain.
Usually, a lot of material - many times the mass of the Sun - is observed to be blasted away in a supernova.
However, the supernova that De and co-authors observed, called iPTF 14gqr, ejected matter only one fifth of the Sun's mass.
"We saw this massive star's core collapse, but we saw remarkably little mass ejected", Kasliwal says.
"We call this an ultra-stripped envelope supernova and it has always been predicted that they exist".
The fact that the star exploded at all implies that it must have previously been enveloped in lots of material, or its core would never have become heavy enough to collapse. So scientists began to investigate the mystery of the missing mass.
The researchers inferred that the mass must have been stolen by some kind of dense, compact companion, either a white dwarf, neutron star, or black hole, which is close enough to gravitationally siphon away its mass before it exploded. The neutron star that was left behind from the supernova must have then been born into orbit with that dense companion. Observing iPTF 14gqr was actually observing the birth of a compact neutron star binary. The close proximity of the stars means they will eventually collide and succumb to an explosive neutron star collision.
Not only is iPTF 14gqr a notable event, the fact that it was observed at all was fortuitous since these phenomena are both rare and short-lived.
When the violent death of a massive star concluded with a whimper instead of a bang, astronomers weren't sure what to make of it.
"You need fast transient surveys and a well-coordinated network of astronomers worldwide to really capture the early phase of a supernova", De said.
"A typical massive star explosion ejects about five times the mass of the sun", he added.
This event was what Piro and a team of astronomers from Carnegie and UC Santa Cruz saw back in August 2017 at Palomar Observatory as part of Palomar Transient Factory (iPTF).
This paints a pretty vivid picture of the birth of a neutron star binary.
The research was primarily funded by the National Science Foundation under the PIRE GROWTH project.
