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An “Early warning system” can be built for neutron star collision events Information transmission up to 1 minute in advance | Sorae space portal site

A huge star leaves at the end of its lifea neutron star” is a celestial body so dense that the whole can be compared to a single atomic nucleus. When these neutron stars collide, at that momentSuper high temperature and super high pressure estimated at 1 trillion degrees Celsiushappens, and “KironovaAn energy release phenomenon called ” occurs.

At Kironova, nuclear reactions proceed at high speed simultaneously, producing heavy elements such as gold and uranium. As elements heavier than iron are not believed to be produced in nuclear fusion reactions in the core of stars, kilonova are thought to be one of the reasons why heavy elements exist in the universe. As elements heavier than iron are important compounds for the earth and living organisms, their formation processes are of interest.

【▲ Figure 1: Strong gravitational waves are generated by merging neutron stars, but gravitational waves are also generated before the merger. Capturing this would allow us to predict a merger in advance, but the signal strength is too weak to normally be distinguished from noise (Credit: NASA / R. Hurt / Caltech-JPL)]

When neutron stars collide with each other, there are electromagnetic waves of various wavelengthsgravitational waves” is also dropped. If we can catch this gravitational wave, it will reveal a lot of detailed information. Ripples in space-time are gravitational waves moving at the speed of light, caused by the motion of objects with mass. A high-density neutron star with a mass comparable to a compressed star has strong gravity. In fact, three gravitational wave telescopes in the United States and Europe collaboratedLIGO-VirgoThe network captures a number of gravitational waves believed to have originated from merging neutron stars. At the moment when neutron stars merge, the collision point becomes so dense that electromagnetic waves cannot pass through it, so only gravitational waves can convey information from such regions to the outside . If we can capture gravitational waves, we will be able to get a lot of information that cannot be captured by electromagnetic waves.

However, in merging neutron stars, there is only one example in the past where observations using electromagnetic waves and gravitational waves have been linked. Viewed on August 17, 2017″GW170817in. This astronomical event is a valuable example of how gravitational waves and electromagnetic waves could capture the state of an explosion, but cooperation among observatories in various places cannot be said to be perfect. The LIGO-Virgo network sent the first notification to observatories around the world 40 minutes after observing the gravitational waves, and the rough site four and a half hours later. However, at that time, the visible object sank below the horizon as seen from many observatories in the northern hemisphere, making it invisible. The source of GW170817 was observed optically and found to be the Hydra galaxy NGC 4993 about 11 hours after the source rose above the horizon again.

* GW170817 is the catalog name for gravitational waves, and is also known as the catalog name for supernova “AT 2017gfo” and the catalog name for gamma-ray burst “GRB 170817A”.

[▲ Ffigur 2: System rhybudd cynnar ar gyfer uno cyrff nefol a ddyfeisiwyd yn yr ymchwil hwn. Mae tonnau disgyrchiant a gynhyrchir cyn uno yn wan, felly mae'n anodd culhau'r amrediad, ond gallant ddarparu rhywfaint o gyfeiriad cyn uno.  (Credyd Delwedd: Ryan Magee, et al.) ]

[▲ Ffigur 2: System rhybudd cynnar ar gyfer uno cyrff nefol a ddyfeisiwyd yn yr ymchwil hwn. Mae tonnau disgyrchiant a gynhyrchir cyn uno yn wan, gan ei gwneud yn anodd culhau eu hystod, ond gallant roi rhywfaint o gyfeiriad cyn uno (Credyd: Ryan Magee, et.al.)]

Such a gap in the observation period is a major obstacle to our understanding of rapidly developing astronomical phenomena such as neutron star mergers. However, since neutron stars emit gravitational waves just before they merge, if we can observe them,It is possible to build an “early warning system” that sends predictive information just before the merger.There is a possibility. However, in conventional systems, such gravitational wave signals were truncated by the software. This is because the strength of the signal is so weak that it is difficult to distinguish it from the noise that is normally present, and there is a possibility that it will be full of false alarms.

Research teams such as the California Institute of Technology have shown that such a system can be built from past gravitational wave observational data. As a result of verification, for example, in the case of GW170817, it was found that gravitational waves emitted from neutron stars can be detected before merging for up to 6 minutes.

Based on this result, the research team built two software with different algorithms, “GstLAL” and “SPIIR”, and read a lot of gravitational wave data to see if it is possible to send early warning information to the database . As a result, GstLAL was able to send early warning information 82 times and SPIIR 141 times. The time from initial signal detection to information transmission was up to 15 seconds. Considering this,We can predict a merger between celestial bodies on average 10 seconds before a collision, and about 1 minute before a collision every 5 times.Will be. This shows the possibility of transmitting predictions to observatories around the world before the collision and discovering the location as soon as possible after the merger.

Future updates to the gravitational wave observing system are under consideration. For example, the KAGRA gravitational wave telescope installed in Japan is due to join the LIGO-Virgo network, and a general upgrade is considered for 2027. If these are realized, it may be possible to observe as many as 100 events neutron star merger per year.

In addition, radio telescopes such as the long-wavelength array “OVRO-LWA” and Caltech’s future “DSA-2000 (2,000-antenna Deep Synoptic Array)” are capable of detecting neutrons. designed to capture the sudden radio emission predicted for star merger events. It is theoretically assumed that such radio emissions will occur at the time of impact, or shortly before impact. To catch this phenomenon, the radio telescope needs to be pointed in the direction of the merger event in advance, but it can be done by using early warning information transmitted based on the gravitational waves before the merger, I guess. In order to further strengthen the observing system for the mysterious merger of neutron stars, it is hoped that the gravitational wave telescope will realize an early warning system for merger events.

Source

  • Ryan Magee, et al. “First Demonstration of Early Warning Gravitational Wave Signals”. (Astrophysical Journal Letters)
  • Surabhi Sachdev, et al. “An Early Warning System for Electromagnetic Follow-Up to Gravitational Wave Events” (Astrophysical Journal Letters)
  • Whitney Clavin. “Can Cosmic Collisions Be Predicted Before They Happen?”. (California Institute of Technology)

Text: Riri Ayae

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