Evrim Yazgin
Cosmos science journalist
A new model is the first to explain how the lightest known neutron star formed.
The binary system, called J0453+1559, was first reported in 2013 which involves a pair of neutron stars orbiting each other every 4.07 days. The system has been subject to detailed observations as it is only 4,000 light-years from Earth.
One of the neutron stars is about 1.6 times the mass of our Sun. The smaller member of the pair is just 1.174 times the mass of the Sun, making it the lightest known neutron star. It is just 24km across – roughly the size of South Australian capital Adelaide.
Neutron stars are among the densest objects in the universe. A single teaspoon of neutron star material would weigh about 10 million tonnes. They form from the collapsed iron core of a massive star which has gone supernova.
Recently, research has explored how the largest known neutron stars (more than 2 times heavier than the Sun) form.
But less is known about the other end of the spectrum – the lightest neutron stars. Examining these objects could have implications for high-density nuclear physics, stellar evolution and supernova explosion physics.
Current theories have failed to lead to computer simulations which accurately reproduce the creation pathway of neutron stars with masses less than about 1.36 times that of the Sun. These simulations are based on the theory that smaller neutron stars form out of an oxygen-neon-magnesium core, which undergoes rapid electron capture, rather than an iron core.
Now a team of astrophysicists at Australia’s Monash University have successfully simulated the formation of the lightest neutron stars. Their findings are published in the Physical Review Letters.
“This is the lowest neutron star mass ever obtained in 3D simulations, and we now actually have a case where we can test our models and theories against very precise observations,” says co-author Bernhard Müeller.
They tested their simulations on 25 theoretical massive stars.
The stars had masses ranging from 9.45 to 9.95 times the mass of the Sun, and cores which were 1.481 to 1.585 times the mass of the Sun. In each case, they ran simulations of the dynamics when each of the stars underwent a supernova explosion.
Of the 25 potential progenitor stars, 5 models showed promise by leading to the formation of low-mass neutron stars about 1.2 times heavier than the Sun, matching observations of the lightest neutron stars.
Surprisingly, the models also suggest that the lightest neutron stars are not made by electron-capture supernovae, but by iron-core collapse supernovae.
“This whole question of how big neutron stars are and how the masses are distributed are part of a very big puzzle that we can now begin to piece together with detailed simulations.”
“Our findings push the boundaries of what we know about neutron star formation, and by extension about the supernova explosions that accompany them,” Müeller adds.
“While there’s more work to be done, this progress highlights the exciting potential of computational astrophysics to test and refine our theories of the universe,” comments co-author Alexander Heger.
