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Was the rapid spin delay in 2017 the collapse of neutron stars into black holes?

In this artist’s expression, when two neutron stars merge to form a black hole (hidden in a bright bulge in the center of the image), they heat the material around the star and emit X, opposite. A high-energy particle jet (blue) has been generated. -Rays (reddish clouds). The Chandra X-ray Astronomical Observatory continues to detect X-rays from events today. They can be produced by the shock waves of matter around the black hole, or by matter that falls violently into the black hole (the yellowish disk around the central bulge). Credits: X-ray data from NASA, CXC, Northwestern University / A. Hagera; Visual by NASA / CXC / M.Weiss

When two neutron stars swirl and fuse with each other to form a black hole (an event recorded by gravitational wave detectors and telescopes around the world in 2017), will it soon become a black hole? Or does it take time to spin down beyond the event horizon to a black hole before it collapses under gravity?


That 2017 continuous observation merger According to the orbiting telescope Chandra X-ray Observatory, the latter suggests that the coalesced object is probably stuck for a brief moment before it finally collapses.

Evidence is in the form of X-ray afterglow due to the merger, called GW170817. This is unforeseen in the event of a merger. Neutron star It soon collapsed into a black hole.Afterglow can be described as a rebound of merged materials neutron Performer, It cultivated and heated the matter around the dual neutron star. This hot material has been steadily shining for more than four years since the material was thrown out by the merger. Kilonova.. The X-ray emission from the jet of matter detected by Chandra shortly after the merger would otherwise be dim now.

Excessive X-ray radiation observed by Chandra can result from debris in the accretion disk swirling and falling into a black hole, but astrophysicist Rafaela Margutti of the University of California, Berkeley, theoretically Supports the expected delayed collapse hypothesis.

“If the coalesced neutron star collapses directly into a black hole without an intermediate stage, it would be very difficult to explain this X-ray excess we are seeing now, as there is no hard surface for objects to bounce off. It pops out fast to create an afterglow, “said Margutti, an associate professor of astronomy and physics at the University of California, Berkeley. “It just will fall. Done. The real reason I’m scientifically excited is that we may be looking at more than a jet. We’re finally getting information about the new compact object. May get. “

Margutti and her colleagues, including lead author Appragita Hagera, who was a graduate student at Northwestern University before moving to the University of California, Berkeley, analyzed X-ray afterglow in a recently approved paper. Is reporting. Astrophysical Journal Letter..

Was the rapid spin delay in 2017 the collapse of neutron stars into black holes?

X-ray source captured by Chandra. The upper part contains the black hole first observed in 2017, formed by the merger of two neutron stars. Credits: NASA, CXC, Northwestern Univ. / A.Hagera

Kilonova Radioactive Glow

The gravitational waves from the merger were first detected on August 17, 2017, in collaboration with the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo.Satellite-based and ground-based telescopes quickly followed up to record gamma-ray bursts and visible and infrared radiation together. Confirmed the theory Many of them Heavy element Produced in the aftermath of such a merger in hot ejecta that produce bright Kilonova. Kilonova glows because of the light emitted during the decay of radioactive elements such as platinum and gold. These elements are produced in merged debris.

Chandra also turned to observe GW170817, but no X-rays were seen until 9 days later. This suggests that the merger also produced a narrow jet of matter that emits a cone of X-rays when it collides with matter around a neutron star. It first missed the earth. After that, the head of the jet expanded and began to emit X-rays with a wider jet visible from Earth.

For 160 days after the merger, the X-ray emission from the jet increased, and then the X-ray emission steadily decreased as the jet slowed and expanded. However, Hagera and her team noticed that from March 2020 (about 900 days after the merger) to the end of 2020, the decline stopped and the brightness of the X-ray radiation remained nearly constant. ..

“The fact that the X-rays stopped fading rapidly was our best evidence that something in addition to the jet was detected in the X-rays of this source,” Margutti said. “It seems that we need a completely different source of X-rays to explain what we are seeing.”

Researchers suggest that excess X-rays are produced by shock waves that are different from the jets produced by the merger. This impact was probably the result of delayed collapse of the coalesced neutron stars, probably because their rapid spins canceled the gravitational collapse for a very short time. By sticking for an extra second, the material around the neutron star gained extra bounce, producing a very fast tail of the Kilonova ejecta that caused the impact.

“We believe that the afterglow emission of Kilonova is produced by the impacted matter of the circumbinary planets,” Margutti said. “It was the material in the environment of the two neutron stars that was shocked and heated by the fastest edge of the Kilonova ejecta driving the shock wave.”

She said the radiation only reaches us now, as the heavy volcanic ejecta slowed down in a low-density environment and it took time for the impact to convert the kinetic energy of the ejecta into heat. This is the same process as jet radio and X-ray generation, but because the jet is much lighter, it is quickly decelerated by the environment and shines with X-rays and radio very early on.

Was the rapid spin delay in 2017 the collapse of neutron stars into black holes?

The merger of the two neutron stars produced a black hole (center, white) and a burst of gamma rays generated by a narrow jet or beam of high-energy particles shown in red. Initially, the jet was too narrow to be detected by Chandra, but over time it slowed and spread (blue) as the material in the jet hit the surrounding material, and when the jet became directly visible to Chandra, X-rays. Radiation has risen. .. This jet and its opposite counterpart may have been created by a substance that falls into a black hole after it has been formed. Credits: NASA / CXC / K. DiVona

Another explanation is that X-rays come from matter that falls towards a black hole formed after the fusion of neutron stars.

Co-author Joe Bright, a postdoctoral fellow at the University of California, Berkeley, said: “Both results are very exciting.”

Chandra is currently the only observatory that can still detect the light from this space collision. However, Chandra and radio telescope follow-up observations could distinguish between alternative explanations. In the case of Kilonova afterglow, it is expected that radio radiation will be detected again within the next few months or years. If X-rays are generated by falling material into a newly formed black hole, the X-ray output should remain stable or drop rapidly, and radio radiation is detected over time. not.

Margutti found that LIGO, Virgo, and other telescopes capture gravitational waves and electromagnetic waves from more neutron star mergers, more accurately identifying the sequence of events before and after the merger, and the physics of black hole formation. I hope it helps to clarify. Until then, GW170817 is the only example available for research.

“Further research on GW170817 can have widespread impact,” said co-author Kate Alexander, a postdoctoral researcher at Northwestern University. “Detection of the afterglow of Kilonova means that the merger did not immediately produce a black hole, or this object tells astronomy how the matter falls into a black hole years after its birth. May provide an opportunity to study black holes. “

Margutti and her team recently announced that the Chandra Telescope detected X-rays in the GW170817 observations made in December 2021. Analysis of that data is underway. No X-ray related radio detections have been reported.


Kilonova afterglow may be discovered for the first time


For more information:
Appearance of new X-ray source from dual neutron star merger GW170817, arXiv: 2104.02070 [astro-ph.HE] arxiv.org/abs/2104.02070

Quote: Was the rapid spin delay in 2017 the collapse of neutron stars into black holes? (March 5, 2022) Obtained March 5, 2022 from https: //phys.org/news/2022-03-rapid-collapse-neutron-stars-black.html

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Was the rapid spin delay in 2017 the collapse of neutron stars into black holes?

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