Dying stars’ cocoons could be new source of gravitational waves, based on simulations performed to assess was happens with the debris found around stars as they enter their final years. Cocoons form as a massive star sheds debris while it collapses into a black hole. As jets collide into collapsing layers of the dying star, a bubble, or a “cocoon,” forms around the jet. Cocoons are turbulent places, where hot gases and debris mix randomly and expand in all directions from the jet.
Gravitational waves are associated with binary systems, such as the mergers of two black holes, or two neutron stars, or one of each. However, it has been speculated by astrophysicists that gravitational waves could be produced from a single, non-binary source.
According to Northwestern University researchers the turbulent, energetic cocoons of debris that surround dying massive stars could also be a source of gravitational waves.
Gravitational waves are waves of the intensity of gravity generated by accelerated masses in space in the form of waves that move outwards from their source at the speed of light. These waves exert an influence on spacetime, squeezing and stretching anything in their path.
The simulations will be tested using real data, focusing on cocoons’ gravitational waves. The primary data source will be by studying the frequency band that the Laser Interferometer Gravitational-Wave Observatory (LIGO) can detect. LIGO observatories are located in Hanford Site, Washington and at Livingston, Louisiana.
The LIGO observatories have the aim of detecting gravitational waves by laser interferometry. The observatories deploy mirrors spaced four kilometres apart which are capable of detecting a change of less than one ten-thousandth the charge diameter of a proton.
Even with advanced technology like LIGO, scientists can only detect gravitational waves from higher frequency, asymmetrical explosions. Fortunately, the cocoons, around dying stars are both asymmetrical and highly energetic.
Lead researcher Ore Gottlieb has presented his research during a virtual briefing at the 242nd meeting of the American Astronomical Society. The presentation, titled “Jetted and turbulent stellar deaths: New LIGO-detectable sources of gravitational waves”, took place at 12:15 p.m. EDT on Monday, June 5 (2023), as a part of a session titled “Discoveries in Distant Galaxies.”
Gottlieb and his collaborators used new state-of-the-art simulations to model the collapse of a massive star. When massive stars collapse into black holes, they may create powerful outflows (or jets) of particles traveling close to the speed of light. Gottlieb’s simulations modelled this process — from the time the star collapses into a black hole until the jet escapes.
The simulation showed an unexpected source disrupting the calculations, a phenomenon that was traced to the cocoon, indicating that the cocoon was an interesting gravitational wave source.
The simulations were made possible by use of the U.S. Department of Energy Oak Ridge National Laboratory supercomputer Summit and National Energy Research Scientific Computing Centre supercomputer Perlmutter.
