Program Note: On October 23, Neil Cornish of Montana State University (and a member of the LIGO Collaboration) will give our Physics Colloquium, entitled “The Dawn of Gravitational Wave Astronomy”
It was an event 130 million years in the making yet marked by the speed of light. On October 16 scientists announced they had, for the first time, detected both gravitational waves and light resulting from the collision of neutron stars. The news travelled around the world, and UT’s astrophysicists were among those celebrating the breakthrough and the possibilities and validation it lends to their own research.
Gravitational waves are ripples in space-time that serve as signatures of some cataclysmic event in the distant universe. Albert Einstein predicted them in 1915 and 100 years later the LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration first detected them, with the work earning the 2017 Nobel Prize in Physics.
In August 2017 another chapter to the story was added when scientists from LIGO, the European-based Virgo detector, and another 70 observatories detected gravitational waves—as well as light—from the merger some 130 million years ago of two neutron stars. Gamma ray measurements and gravitational wave detection confirmed Einstein’s theory that the waves should travel at the speed of light. The formal announcement two months later was cheered throughout the worldwide astronomical community.
As Assistant Professor Andrew W. Steiner explained, these colossal mergers are interesting not only because they advance our understanding of the universe well beyond our home planet, but also because they’re thought to be the origin of many of the heaviest elements we encounter on earth: gold, platinum, and uranium, for example. They could also help bring into sharper focus the intricate workings of atomic nuclei.
Squishiness and Supernovae
Steiner’s work figures into Monday’s announcement via predictions his group has made about the tidal deformability of neutron stars (which he describes as "squishiness"). When these stars get close enough to one another, tidal forces are created and deform, generating a “squishiness” that affects the gravitational wave signal in a merger. A LIGO paper published in Physical Review Letters cites these predictions in helping calculate the upper limit for this deformability.
Yet another avenue in LIGO’s scientific quest is the violent death of massive stars (roughly eight times the mass of the sun) in explosions called core-collapse supernovae. These events generate gravitational waves, and their detection would not only further LIGO research but also give astrophysicists more information about how these supernovae occur. UT Physics Professors Michael Guidry and Anthony Mezzacappa, along with Postdoctoral Research Associate Konstantin Yakunin, have been working closely with members of the LIGO Scientific Collaboration and have led an effort to organize the worldwide core collapse supernova modeling community to provide needed theoretical input to this and the European-counterpart, Virgo Scientific Collaboration.
Monday’s announcement continues a spate of positive news for UT’s astrophysicists. They recently won a SciDAC (Scientific Discovery through Advanced Computing) award to use sophisticated computing for astrophysics simulations of mergers and supernovae.