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Astronomers detect gravitational waves from collisions between neutron stars and black holes. Astronomers using NSF’s Laser Interferometer Gravitational Wave Observatory (LIGO) in the United States and the Virgo detector in Italy have observed gravitational wave signals from two compact binary inspiralis corresponding to neutron star and black hole binaries.

Gravitational Waves

The two events occurred at least 900 million light years apart; In each case, the neutron star was swallowed whole by its black hole companion. An artist’s impression of a merger between a black hole and a neutron star. Image Credits: Carl Knox, Ozgrave, and Swinburne University. With this new discovery of a neutron star-black hole merger outside our Milky Way, we’ve found the kind of binary that’s missing, Dr. Astrid Lamberts said.

“Eventually we can begin to understand how many of these systems exist, how often they merge, and why we haven’t seen examples in the Milky Way yet.” The first of two gravitational wave events, called GW200105, was detected on January 5, 2020. It produced a strong signal in one of the two LIGO detectors, but a small signal-to-noise ratio in the Virgo detector. The other LIGO detector was temporarily offline.

By looking at the nature of gravitational waves, astronomers speculated that the signal was caused by a black hole about 9 times the mass of our Sun that collided with a compact 1.9 solar mass object, which was later identified as a star. neutrons. This merger took place 900 million light years away.

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Although we only see a strong signal in a detector, we conclude that it is real and not just detector noise, said Dr. Harald Pfeiffer, an astronomer at the Max Planck Institute for Gravitational Physics. It passes all of our strict quality checks and stays out of all the noisy phenomena we see in the third observation run.

While gravitational waves alone don’t reveal the structure of a lighter object, we can estimate its maximum mass, added Dr. Bhushan Gadre of the Max Planck Institute for Gravitational Physics. Combining this information with theoretical predictions of the expected neutron star mass in such a binary system, we conclude that a neutron star is the most likely explanation.

The second merger, GW200115, was detected on January 15, 2020 and involved a 6 solar mass black hole and a 1.5 solar mass neutron star. It was detected by both the LIGO detectors and the Virgo detector and occurred about a billion light years away from Earth.

These were not events where black holes chewed up neutron stars like the Cookie Monster and threw chunks, ”said Professor Patrick Brady, an astronomer at the University of Wisconsin-Milwaukee and spokesperson for the LIGO collaboration. That ‘fight’ is what would produce the light, and we don’t think it happened in these cases.

Professor Susan Scott, an astronomer at the ARC Center of Excellence for Gravitational Wave Discovery (Ozzgrave) and the Australian National University, said the events occurred about a billion years ago, but were so massive that we can still observe their gravitational waves. currently. These collisions have shaken the universe to its core and we have detected the waves that are spewing through the universe.

Each collision is not just a mix of two massive, dense objects. It’s actually like Pac-Man, with a black hole completely swallowing its neutron star companion. These are notable events and we have waited too long to see them. So finally catching them is amazing. The results appear in Astrophysical Journal Letters.

Discovery of a new source of gravitational waves: a collision between a neutron star and a black hole. Professor Somak Raychaudhuri, director of the Interuniversity Center for Astronomy and Astrophysics (IUCAA), told The Indian Express that the development was long overdue, but was not confirmed.

New source of gravitational waves

Scientists are very excited about the first confirmed confirmation of a neutron star-black hole (NS-BH) collision. This unprecedented gravitational wave discovery from a pair of NS-BH mergers was published Tuesday in Astrophysical Journal Letters.

Professor Somak Raychaudhuri, director of the Interuniversity Center for Astronomy and Astrophysics (IUCAA), told The Indian Express that the development was long awaited, but not confirmed. To confirm this finding, a new analysis was conducted, which has now been published in an international journal, Raychaudhuri said.

So far, the LIGO-Virgo (LVC) collaboration of gravitational wave detectors has only been able to observe collisions between black holes or pairs of neutron stars. For the first time, in January 2020, a detector network detected gravitational waves from a pair of NS-BH mergers.

Raychaudhuri said that there is a lot of interesting science to learn from this. “For example, a neutron star has a surface and a black hole does not. A neutron star has about 1.4-2 times the mass of the Sun, while another black hole is much more massive. Very interesting effects of very mergers. disparate that can be traced, ”he said.

“While the data shows how often they merge, we will also get clues about their origin and how they formed,” said Dr. Shaswath Kapadia of the International Center for Theoretical Sciences (ICTS) in Bengaluru. Dr. Kapadia helped estimate the ns-BH fusion rate using a jointly developed method.

“The authors of this article are Bhushan Gadre, who was until recently a PhD student at IUCAA and participated in many of our extension programs in Marathi. He now he is at the Max Planck Institute in Germany, ”said Roychowdhury.

According to the Director of IUCAA, the technique used here for signal detection is called coincidence filtering. “It was also used for the first discovery of gravitational waves. It should be remembered that it was developed in the 1990s by Sanjeev Dhurandhar and others at IUCAA,” he said.

“Basically, we are detecting binary black hole mergers and binary neutron star mergers (so far). It’s a hybrid collision,” according to scientists at the Laser Interferometer Gravitational Wave Observatory, India (LIGO-India).

When he contacted LIGO-India spokesperson Dr. Tarun Souradeep, he said that LIGO-India researchers have contributed to this great discovery. “This is an ongoing effort and the reason for strengthening the detector network is to discover a new type of phenomenon,” Souradeep said. This is a clear indication of a neutron star-black hole merger, said Professor Rajesh Nayak from the Center for Excellence in Space Sciences, IISER, Kolkata.

LIGO-India scientist Professor Sanjit Mitra said that with development, LIGO-India will significantly improve Aakash localization of these events. “This raises the possibility of observing these distant sources using electromagnetic telescopes, which, in turn, will give us a more accurate measure of how fast the universe is expanding,” Mitra said.

“These observations help us understand the formation and relative abundance of such binaries. Neutron stars are the densest objects in the universe, so these findings can also help us understand the behavior of matter at extreme densities. Neutron stars In the universe”. also the most precise ‘clocks’, if they emit extremely periodic pulses. The discovery of pulsars moving around black holes could help scientists investigate the effects under extreme gravity, “the scientists said.

How was it detected?

As the two densest and most massive bodies orbit each other, they move closer together and eventually merge, as energy is lost in the form of gravitational waves. Gravitational wave signals are buried deep in a large amount of background noise. To look for signals, scientists use a method called match filtering.

In coincident filtering, the different expected gravitational waves predicted by Einstein’s theory of relativity are compared to different parts of the data to produce quantities that indicate whether the signal (if any) in the data matches any given wave.

An event is detected whenever this match (“signal-to-noise ratio” or SNR in technical terms) is significant (greater than 8). The observation of an event in several detectors separated almost simultaneously by thousands of kilometers leads scientists to believe that the signal is of astrophysical origin, which is the case for both events.

How sure are we that they are an NS-BH merger?

Using parameter estimation tools, scientists infer the possible masses, turns, distances, and locations of these mergers from the data. Both events occurred a billion light years apart. Since gravitational waves also travel at the speed of light, this means that we saw a merger that occurred ~ 1 billion years ago, long before life appeared on Earth!

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