5 Sep 2018 Urbana-Champaign - If you've followed any science-based news over the past few years, you've probably read a thing or two about gravitational waves, and how recent discoveries have provided some of the strongest evidence to support Albert Einstein's Theory of Relativity. Back in 2015, researchers from the Laser Interferometer Gravitational Wave Observatory (LIGO) used detectors in Washington and Louisiana to identify gravitational waves emitted by a cosmic black-hole binary collision.
This discovery opened the door for exploring the universe in a new manner, leading to more black-hole binary detections. In 2017, the discovery of a binary neutron star merger by both LIGO and Virgo, the interferometric gravitational-wave antenna in Italy, along with electromagnetic follow-up from the astronomical community, demonstrated the high-impact science achievable with multi-messenger astronomy. While we can now identify these compact-object mergers, how they form in the first place is still an open question.
That's where Miguel Holgado, a Ph.D candidate in astrophysics at the University of Illinois, comes in. One of Miguel Holgado's research focuses is on binary stellar evolution, which ends in the formation of binary compact objects.
"Gravitational waves can be used to understand how binary compact-object mergers form", stated Miguel Holgado.
A member of the Gravity Group at the National Center for Supercomputing Applications (NCSA), Miguel Holgado studies these grand cosmic events thoroughly, which has led to the publication of his research in the Astrophysical Journal earlier this summer. For his work, Miguel Holgado examined common envelope evolution, where a neutron star enters the envelope of massive primary star, possibly causing the emission of gravitational waves. The common-envelope phase of binary stellar evolution is one channel for producing compact binaries.
"In order to bring the neutron star in, it needs to be able to enter in the massive star's envelope", Miguel Holgado stated. "There's gravitational drag in the massive star that brings the neutron star into a closer orbit. If common-envelope evolution is successful, what you get from that is a helium star remnant of the previously massive star and the neutron star now at a closer distance such that once the system evolves into neutron-star binary, the binary merges due to gravitational waves. The common-envelope phase of evolution is still very uncertain and requires a very large numerical simulation, but we believe these events may produce observable gravitational waves."
Through numerical simulation, Miguel Holgado and his collaborators determined that these common envelope events with neutron stars could be sources of gravitational waves detectable by LIGO.
Due to the massive nature of the simulations that Miguel Holgado needs to run, having access to NCSA's Blue Waters supercomputer is critical to making his research timely and accurate.
"Blue Waters is especially helpful because its quite well-suited for hydrodynamic simulations", stated Miguel Holgado. "It has the capability not only to simulate intensive problems in a timely manner, but also allows for the inclusion of additional physics that may be needed in order to appropriately model this phase of binary stellar evolution."
With his research on Common Envelope Evolution now published, Miguel Holgado intends to turn his search for gravitational waves to new mergers in hopes of identifying more places to search for potential gravitational wave emissions, giving us a greater understanding of these mysterious cosmic events.
"The next step is to look at a case of a compact object merging with a primary star, or when common-envelope evolution fails. In that scenario, when a compact objects gets close to the core, it may get close enough that gravitational waves might be emitted."