The “cocoons» which are formed as the massive dying stars expel debris, likely to emit gravitational wavesaccording researcherswho presented their study at the 242nd Meeting of the American Astronomical Society.

The research is led by Orre Gottlieb, a fellow at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Among the co-authors of the study is the Greek astrophysicist and director of CIERA, Vicky Kalogera.

So far astrophysicists have only detected gravitational waves from binary systems, the mergers of black holes or two neutron stars. Although in theory astrophysicists should be able to detect gravitational waves from a single, non-binary source, they have not yet discovered these signals. Now Northwestern University researchers suggest that attention should be turned to a new, unexpected and completely unexplored place: the turbulent, energetic cocoons surrounding dying massive stars.

The researchers used state-of-the-art simulations to model the collapse of a massive star. When these stars collapse into black holes, they can create powerful outflows (or jets) of particles traveling at close to the speed of light. The simulations modeled this process from the moment the star collapses until the jet escapes.

“When I calculated the gravitational waves from the black hole region, I found another source that interrupted my calculations, the cocoon. I tried to ignore it but found it impossible to ignore. Then I realized that the cocoon was an interesting source of gravitational waves,” says Ore Gottlieb. In fact, as noted in the study, the LIGO Gravitational Wave Observatory with its laser interferometer may be able to detect these gravitational waves.

Mr. Gottlieb points out that “our study is a call to the community to consider cocoons as a source of gravitational waves,” adding: “By studying them, we could learn more about what happens inside stars, the properties of jets and their predominance in stellar explosions’.

Photo: As a jet escapes from a collapsed star, it slams into a cocoon of stellar debris.Credit: Ore Gottlieb/CIERA/Northwestern University