Researchers from Northwestern University tried to investigate the presence of gravitational waves in the cocoons of debris surrounding a dying massive star. Observatories can only detect gravitational waves from binary systems, but lead researcher Ore Gottlieb believes they can see the first non-binary source in the future.
Searching the Remnants of a Dying Star
Using state-of-the-art simulations, the researchers will prove that these cocoons can release gravitational waves for the first time. Compared to gamma-ray burst jets, the gravitational waves from cocoons are within the frequency bands that can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO).
To make it possible, Gottlieb and his team plan to use models to simulate the collapse of a massive star. As they collapse into black holes, they can generate powerful jets of particles that travel close to the speed of light. This process starting from the collapse of the star to the escape of gamma-ray burst jets, will be simulated by the researchers.
The team's initial plan was to determine if detectable gravitational waves could be emitted from the formation of an accretion disk around a black hole. However, the cocoon disrupted their calculations, which was impossible to ignore. This made them realize the role of the cocoon as a potential wave source.
Cocoons are formed around the gamma-ray burst jets as they collide into collapsing layer of the massive dying star. They are turbulent regions containing mixtures of hot gases and debris which expand in all directions from the jet. The energetic bubble accelerating from the jet perturbs space-time and creates a ripple of gravitational waves.
Although a jet begins deep inside a star, it drills its way out to escape. As the jet punches through the star, the materials of the star get heated up and spill out, forming the hot layers of the cocoon.
Only the gravitational waves from a higher frequency, asymmetrical explosions can be detected by LIGO. The observatory cannot detect single-source gravitational waves emitted by gamma-ray bursts because its frequency is lower than the band that LIGO is sensitive to. On the other hand, it also cannot detect waves from supernovae due to its symmetrical nature. Since cocoons are asymmetrical and highly energetic, Gottlieb is confident that LIGO can easily see them.
"By studying cocoons, we could learn more about what happens in the innermost part of stars, the properties of jets and their prevalence in stellar explosions," said Gottlieb.
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The Role of Gravitational Waves in Understanding the Universe
Gravitational waves are ripples generated by some of the universe's most violent and energetic processes, such as black hole collision, supernovae, and the collision of neutron stars. These space-time waves were predicted in 1916 by Albert Einstein in his general theory of relativity.
Measuring gravitational waves helps astronomers confirm their theories about gravity. It also provides a new insight into looking at the cosmos. Because of this breakthrough, scientists can finally detect events that leave little to no light. In the latest detection by LIGO, astronomers combine gravitational waves with traditional methods of perceiving the universe. It is a great way of untangling the mysteries surrounding the dense, dead objects called neutron stars.
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