By employing the resources of one of the fastest supercomputers in the world, astrophysicists in Australia have simulated the last days of very large stars with masses many times that of the Sun. Their simulation provides new valuable insights into how massive stars end with a bang as they explode in supernovae events and how black holes and neutron stars rise out of the ashes.
Cosmic chaos inside a computer chip
The state-of-the-art OzSTAR supercomputer at the Swinburne University of Technology crunched the numbers for various simulations that modeled the core-collapse of three stars. These virtual stars are 39, 20, and 18 times more massive than the sun, respectively.
When such massive stars reach the end of their life cycles, they typically experience a core-collapse supernova. When this happens, they turn into some of the brightest objects in the universe. And, in the aftermath, they are ready to become neutron stars or black holes.
This extremely dramatic stellar death also generates gravitational waves, whose signature can inform astrophysicists about how both black holes and neutron stars are birthed — this was the main aim of this simulation.
For instance, in 2017, astronomers detected a cosmic cataclysmic event: The merger of two neutron stars from 130 million years ago. The force of the collision was so strong that it literally shook the fabric of space-time, generating gravitational waves that eventually reached Earth, where they were detected. The two neutron stars either merged into a huge single neutron star or collapsed into a black hole.
But in order to detect various core-collapse supernovae from gravitational waves, scientists need to know what such signals will look like.
The new simulation modeled complicated physics, informing scientists what kind of signals they should expect to see in their detectors when a star explodes.
“Our models are 39 times, 20 times, and 18 times more massive than our sun. The 39-solar mass model is important because it’s rotating very rapidly, and most previous long-duration core-collapse supernova simulations do not include the effects of rotation,” said Jade Powell, a postdoctoral researcher at OzGrav.
According to the results, which were described in the Monthly Notices of the Royal Astronomical Society, the two most massive virtual stars generated explosions powered by neutrinos, while the smallest virtual star didn’t explode at all.
Such stars that don’t go fully supernova emit lower amplitude gravitational waves, but their frequency is still within detectable ranges of current detectors in use.
The findings also suggest that exploding stars producing large gravitational-wave amplitudes could be detected by the next generation of detectors, such as the upcoming Einstein Telescope.
“For the first time, we showed that rotation changes the relationship between the gravitational-wave frequency and the properties of the newly-forming neutron star,” explains Powell.
