A team of astrophysicists has determined through simulations that the debris shed by dying stars may be a source of gravitational waves — those ripples in spacetime predicted by Einstein over a century ago.
Gravitational waves are predicted by the general theory of relativity; they are ripples in spacetime generated by massive accelerating objects. The waves are also produced by the interactions of such objects, like binaries of and mergers between neutron stars and black holes.
Gravitational waves were first detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), which is based in Louisiana and Washington. LIGO detects gravitational waves by measuring minuscule differences in the timing of laser pulses against mirrors in underground facilities; those differences suggest that ripples in spacetime slightly delayed the laser pulses.
Now, a team of researchers is suggesting that a new kind of wave from those yet detected could be rippling through the cosmos: gravitational waves produced by matter shed by dying stars. Their research was presented today at the 242nd meeting of the American Astronomical Society.
“As of today, LIGO has only detected gravitational waves from binary systems, but one day it will detect the first non-binary source of gravitational waves,” said Ore Gottlieb, an astrophysicist at Northwestern University and the study’s lead author, in a Northwestern release. “Cocoons are one of the first places we should look to for this type of source.”
While such waves have not yet been observed, they were predicted in simulations conducted by Gottlieb and his colleagues. The researchers modelled how stars die, flinging material outwards while collapsing inwards, leaving a black hole in the voids they leave behind.
The researchers were trying to determine if black holes’ accretion disks — the superheated material that surrounds black holes and makes their shadows visible in radio telescope images — could be gravitational wave sources.
But in looking towards the accretion disks, the team’s calculations were disrupted by modelled data from the cocoon of material surrounding jets of accelerated material produced by dying stars. The model suggested that the material around the jets could cause perturbations in spacetime that are within the frequency band that LIGO detects.
Detecting gravitational waves from new sources would also be a boon to astrophysicists seeking to trace the gravitational wave background, or the murmur of gravitational waves rolling through the universe at all times. Scientists are searching for the gravitational wave background using pulsar timing arrays, which operate similarly to LIGO but rely on timing the detections of light emitted by rapidly spinning pulsars instead of subterranean laser pulses.
A holy grail of gravitational wave astronomy would be a space-based observatory that would function the same way, but on a much larger scale than LIGO (which has since expanded and teamed up with other observatories to form the LIGO-Virgo-KAGRA Collaboration.) Instead of using LIGO’s 5 km-long (4 kilometre) arms to detect gravitational ›waves, astrophysicists could use the 1.5-million-mile-long (2.41 million km) arms of the proposed LISA mission.
But whenever — if ever — such an observatory comes to pass, it definitely helps if you know where to look.