A black hole can tear a neutron star apart in less than two seconds

For nearly seven years (September 14, 2015), researchers at Laser Gravitational Wave Observatory (LIGO) detected gravitational waves (GWs) for the first time. Their results are shared with the world after six months The discovery team obtained Nobel Prize in Physics the following year. Since then, a total of 90 signals generated by binary systems from two black holes, two neutron stars, or one of each have been observed. This last scenario presents some very exciting opportunities for astronomers.

If the merger involved a black hole and a neutron star, the event would produce gigawatts and a dangerous light show! Using data collected from the three black hole mergers and neutron stars we’ve discovered so far, a team of astrophysicists from Japan and Germany He was able to model the entire process of a black hole colliding with a neutron star, which included everything from the binary’s final orbits to the merging and post-merger phase. Their results could aid future polls that are sensitive enough to study mergers and GW events in much greater detail.

The research team was led by Kota Hayashi, a researcher at Kyoto University Yukawa Institute of Theoretical Physics (YITP). He was joined by many colleagues from YITP, Toho University in Japan and Albert Einstein Institute In the Max Planck Institute for Gravitational Physics (MPIGP) in Potsdam, Germany. The paper describing their findings led by Professor Koto Hayashi at YITP and recently appeared in the scientific journal physical review d.

Mergers of compact bodies detected so far by LIGO and Virgo (in O1, O2, and O3a). Credit: LEGO Virgo/Frank Ilavsky Collaboration, Aaron Geller/Northwestern

To summarize, GWs are mysterious ripples in spacetime that were originally predicted Einstein’s general theory of relativity. They are created when massive objects merge and create tidal disturbances in the very fabric of the universe, which can be detected thousands of light years away. So far, only three mergers have been observed involving a binary system consisting of a black hole and a neutron star. During one of these – GW170817, discovered on August 17, 2017 – astronomers discovered an electromagnetic isotope of the gigawatts it produced.

In the coming years, telescopes and interferometers with greater sensitivity are expected to see more of these events. Based on the mechanisms used, scientists expect that black hole and neutron star mergers will involve material ejected from the system and massive releases of radiation (which may include short bursts of gamma rays). For their study, the team modeled what black hole and neutron star mergers would look like to test these predictions.

They chose two different model systems consisting of a rotating black hole and a neutron star, with the black hole at 5.4 and 8.1 solar masses and the neutron star at 1.35 solar masses. These parameters were chosen so that the neutron star is likely to be torn apart by tidal forces. The merging process was simulated using MPIGP’s ‘Sakura’ computer suite Department of Computational Relativity Astrophysics. in MPIGP press releaseSection director and co-author Masaru Shibata explained:

“We get insight into a process that takes one to two seconds — that sounds short, but actually a lot happens during that time: from terminal orbits and disruption of the neutron star by tidal forces, ejection of matter, to formation of an accretion disk around the emerging black hole, and more ejection Matter is in a plane. This high-energy jet may also be the cause of the short gamma-ray bursts, the source of which remains a mystery. Simulation results also suggest that the ejected matter must make up heavier elements such as gold and platinum.”

The team also shared details of the simulation in an animation (shown above) via the Max Planck Institute for Gravitational Physics. YouTube channel. On the left side, the simulation shows the density profile as blue and green lines, magnetic field lines penetrating the black hole as pink curves, and matter emitted from the system as cloudy white lumps. On the right side, the magnetic field strength of the fusion is shown in purple, while the field lines are shown as light blue curves.

In the end, their simulations showed that during the merger process, the neutron star is torn apart by tidal forces in a matter of seconds. The black hole consumed about 80% of the neutron star’s matter in the first few milliseconds, increasing the black hole’s mass by an additional solar mass. In the next ten milliseconds, the neutron star formed a single-arm spiral structure, part of the matter was expelled from the system while the rest (mass of 02.-0.3 solar) formed an accretion disk around the black hole.

After the merger was completed, the accretion disk plunged into the black hole, causing a focused jet-like outpouring of electromagnetic radiation and matter. This flux is emitted from the poles, similar to what is often seen with active galactic nuclei (AGNs), and can result in a brief gamma-ray burst. What was especially amazing was that while the simulations took two months to generate, the simulated merger process lasted about two seconds! Dr. Kenta Kiuchi, group lead in the Shibata division that developed the simulation code, said:

Such general relativity simulations are time consuming. That’s why research groups around the world have so far focused only on short simulations. In contrast, end-to-end simulations, such as the one we have now performed for the first time, provide a self-consistent picture of the entire process for certain binary initial conditions defined once in the beginning. “

Artist’s illustration of two merging neutron stars. The narrow beams represent a gamma ray burst, while the undulating spacetime lattice indicates gravitational waves. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonet

Long-term simulations also allow astronomers to explore the mechanism behind short-lived gamma-ray bursts (GRBs). In addition to being a transient phenomenon, such as fast radio bursts (FRBs) that also last only seconds or milliseconds, GRBs are the most energetic phenomena in the universe, and astronomers are keen to research them further. Looking to the future, Shibata and colleagues are working on more complex numerical simulations to model neutron star mergers and the results.

Neutron star mergers are also expected to include electromagnetic contribution and short-lived gamma-ray bursts. This study illustrates how the GW study has progressed apace in recent years and how more sensitive observations keep pace with improvements in computing and simulation. The result is breakthroughs in our understanding of the universe that are occurring at an ever-increasing rate! Who knows what discoveries might be close to the next corner?

In-depth reading: MPIGPAnd the physical review d