UNITED STATES: Researchers at the Laser Interferometer Gravitational-wave Observatory (LIGO) initially discovered gravitational waves (GWs) on September 14, 2015, almost seven years ago.
Six months after their findings were made public, the discovery team received the Nobel Prize in Physics for their work.
Since then, 90 signals produced by binary systems comprising two black holes, two neutron stars, or one of each have been seen. For astronomers, the latter scenario offers some very intriguing opportunities.
A merger between a black hole and a neutron star will result in GWs and a spectacular light show!
A group of astrophysicists from Japan and Germany were able to model the entire process of the collision of a black hole with a neutron star, which included everything from the final orbits of the binary to the merger and post-merger phase, using data gathered from the three black hole-neutron star mergers we’ve detected so far.
Future studies that are sensitive enough to investigate unions and GW events in great detail may benefit from their findings.
Kota Hayashi, a researcher at Kyoto University’s Yukawa Institute for Theoretical Physics, served as the team’s leader (YITP). Numerous coworkers from the Albert Einstein Institute at the Max Planck Institute for Gravitational Physics (MPIGP) in Postdam, Germany, and the YITP and Toho Universities in Japan joined him.
Their research was published in a study that was recently published in the academic journal Physical Review D under the direction of YITP Prof. Koto Hayashi.
To summarise, GWs are enigmatic spacetime ripples that Einstein’s General Theory of Relativity first anticipated. They are produced whenever two enormous objects collide, causing tidal changes to the Universe’s structure that can be seen from a great distance (thousands of light-years).
A binary system of a black hole and a neutron star has only undergone three observed mergers so far. Astronomers discovered an electromagnetic analogue to the GWs produced by one of these, GW170817, which was discovered on August 17, 2017.
More excellent sensitivity telescopes and interferometers are anticipated to see considerably more from these phenomena in the upcoming years.
Scientists predict that black hole-neutron star mergers will result in the ejection of stuff from the system and a massive discharge of radiation based on the underlying mechanics (which might include short gamma-ray bursts). To test these hypotheses, the scientists created simulations of black hole-neutron star mergers.
They used two alternative black hole and neutron star model systems, with the black hole’s mass set at 5.4 and 8.1 solar masses and the neutron star’s mass at 1.35 solar masses. These settings were chosen to increase the likelihood that tidal forces would shatter the neutron star.
The Department of Computational Relativistic Astrophysics at the MPIGP used the computer cluster “Sakura” to simulate the merger process.
Director of the Department and co-author Masaru Shibata stated in a press statement from the MPIGP: “We gain knowledge of a procedure that lasts one to two seconds. Although this period seems brief, a lot occurs during it, including the disruption of the neutron star by tidal forces, the ejection of matter, the formation of an accretion disc around the developing black hole, and further ejection of matter in the form of a jet.”
“This high-energy jet is most likely also the cause of brief gamma-ray bursts, which are yet unknown in their origin. Additionally, according to the simulation results, the ejected stuff should produce heavy metals like gold and platinum”.
The group also posted information on its simulation on the Max Planck Institute for Gravitational Physics’ Youtube channel in the form of an animation (displayed above).
The simulation’s left side shows the system’s matter ejected as foggy white masses, the magnetic field lines that enter the black hole as pink curves, and the density profile as blue and green contours.
The magnetic field intensity of the merger is shown on the right side in magenta, while the field lines are shown as light-blue curves.
The neutron star is split apart by tidal forces during the merger process in a matter of seconds, according to their models. In the initial few milliseconds, the black hole ate almost 80% of the neutron star’s matter, adding another solar mass to the black hole’s mass.
The neutron star formed a one-armed spiral structure in the ensuing ten milliseconds. Part of the matter was ejected from the system, and the remaining material (02.-0.3 solar masses) formed an accretion disc around the black hole.
The accretion disc entered the black hole when the merger was finished, creating a concentrated jet-like torrent of electromagnetic radiation and matter. Similar to Active Galactic Nuclei (AGNs), this jet comes from the poles and has the potential to produce a brief gamma-ray burst. The simulations’ creation took two months, but it was truly unique that they only took two seconds to complete! Dr. Kenta Kiuchi, the departmental group head for Shibata who created the simulation code, said.
Astronomers can also investigate the mechanism behind brief gamma-ray bursts using long-term simulations (GRBs). GRBs are the most energetic phenomenon in the Universe, and astronomers are eager to learn more about them.
They are a transient phenomenon, like Fast Radio Bursts (FRBs), which also last for only seconds or milliseconds. Shibata and his colleagues are currently working on more complex numerical simulations to understand neutron star mergers and the outcomes.
Gamma-ray bursts and electromagnetic effects from the merger of neutron stars are also anticipated. This study shows how GW research has evolved significantly in recent years and how sensitive observations are keeping up with advances in simulations and computation. As a result, we’re making strides in comprehending the universe at an accelerating rate.
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