Enormous ‘Cocoons’ Formed by Dying Stars Distort the Fabric of Space-Time

Recent simulations showcase the formation of colossal “cocoons” of gas released by dying stars, which have the potential to generate space-time disturbances known as gravitational waves. Since the groundbreaking announcement of the first direct detection of gravitational waves in 2016, astronomers have diligently listened to the cosmic symphony created by colliding black holes across the universe. Notably, projects such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) have successfully identified nearly 100 black hole mergers, and occasionally, collisions involving neutron stars. These cataclysmic events reverberate through the fabric of the cosmos, propelling invisible waves throughout space.

However, novel research suggests that LIGO may soon encounter a different type of cosmic disturbance—cocoon-like structures formed by turbulent gas expelled from dying stars. Utilizing advanced computer simulations of massive stars, a team of researchers from Northwestern University demonstrated how these cocoons could produce gravitational waves that are “impossible to ignore.” The findings, presented at the 242nd meeting of the American Astronomical Society, indicate that studying these gravitational waves would offer valuable insights into the violent demise of gigantic stars.

As massive stars exhaust their fuel, they undergo gravitational collapse, resulting in the formation of black holes accompanied by the ejection of powerful jets of rapidly moving particles. While initially investigating whether these jets could produce gravitational waves, the astronomers discovered another prominent factor—the presence of the cocoon.

Lead researcher Ore Gottlieb, an astronomer at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics, explained, “When I calculated the gravitational waves from the vicinity of the black hole, I found another source disrupting my calculations—the cocoon.” This turbulent blob of gas develops when the outer layers of the collapsing star interact with the high-velocity jets released from its core. Just like the asymmetric motion of massive objects is required to generate gravitational waves, the swirling material within the cocoon fulfills this criterion.

Gottlieb further elaborated, stating, “A jet starts deep inside of a star and then drills its way out to escape. It’s like when you drill a hole into a wall. The spinning drill bit hits the wall, and debris spills out of the wall. The drill bit gives that material energy. Similarly, the jet punches through the star, causing the star’s material to heat up and spill out. This debris forms the hot layers of a cocoon.”

According to Gottlieb’s calculations, LIGO should easily detect the gravitational waves emitted by the cocoon during its upcoming observation campaigns. Furthermore, these cocoons also emit light, allowing astronomers to gather simultaneous information about them using both gravitational waves and telescopes—a remarkable achievement known as multi-messenger astronomy.

If LIGO does detect a cocoon in the near future, it would provide a unique opportunity to delve into the inner workings and final stages of stars’ lives. Additionally, it would mark the first instance of LIGO detecting gravitational waves originating from a single object, rather than the interactions between binary objects orbiting one another.

Gottlieb expressed, “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. Cocoons are one of the first places we should look to for this type of source.”

The team’s research has yet to be published in a peer-reviewed journal

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