Gamma-ray bursts provide strong evidence for an elusive and highly sought-after black hole.
An artist's impression of the camera incident. Light (purple) bends around objects in space, like a black hole, splitting into different paths-one arrives faster than the other.
By scanning the catalog of more than 2,700 high-energy deep-space explosions captured by NASA's Compton Gamma-ray Observatory, James Payent's mission was to find a needle in the pile. This doctoral student from the University of Melbourne wanted to find one of these explosions, a gamma-ray burst, which was "lensified"-its path was interrupted by a huge cosmic object on its way to the earth.
By the time he graduated with a master's degree, he had reduced the number of candidates, and after creating some complex analysis techniques, he was left with only one.
The candidate, known as GRB 950830, was detailed in a new study published in the journal Nature Astronomy on Monday. The huge cosmic object that it must make a detour to reach the earth is a "medium-mass black hole." . Astronomers have just begun to understand a rare type of gravitational sink in the universe.
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In space, there are two well-known black holes: stellar black holes, which are formed when a huge star explodes and then collapse on its own, and supermassive black holes located in the center of galaxies. The supermassive black hole at the center of the Messier 87 galaxy is the subject of the first black hole image taken in 2019.
The mass of a stellar black hole can only reach about 10 times the mass of the sun. The mass of a supermassive black hole may be billions of times its mass. The area between them? "Between these two restrictions, we can see nothing," Payent said.
Astrophysicists have theorized the black holes in this so-called "mass gap"-and have begun to detect-black holes are considered to exist intermediate-mass black holes or IMBH. These black holes are 100 to 100,000 times the mass of the sun, and are the missing link between the small black holes scattered in the universe and the supermassive black holes at the center of the galaxy.
Few medium-mass black holes have been clearly detected. Another smaller black hole was discovered in September 2020: Astronomers studying gravitational waves announced that they had discovered an IMBH with a mass about 150 times the sun, formed by the merger of two smaller black holes.
But by contrast, the one discovered by Payent and co-authors, astrophysicist Rachel Webster of the University of Melbourne and astrophysicist Eric Thurland of Monash University, is terrifying.
"Our IMBH is much larger," Payent said. "If it is formed by a stellar black hole, then it has gone through many, many generations of mergers before it can reach its observed mass."
In March 2020, Astrophysical Journal Letters published a similar candidate weighing about 50,000 suns, namely 3XMM J215022.4−055108, but it was destroyed when it tore a nearby star. discover. The method used by Paynter and colleagues utilizes a gravitational lens.
GRB 950830 is a short gamma-ray burst from far, far away. Researchers are not sure where it came from, but it is located somewhere deep in the dark forest of the universe. They suspected that the explosion was caused by two neutron stars colliding with each other, releasing a lot of energy.
Payent is looking for "gravitationally lensed" gamma-ray bursts from NASA's Compton Gamma-ray Observatory's BATSE instrument, which received approximately 2,700 gamma-ray pulses between 1990 and 1999. So we chose BATSE," Paynter said.
GRB 950830 was the only one that the team discovered was shot by the camera.
"My initial excitement was the discovery of the first gravitational lens, GRB, and despite 30 years of searching, I didn't find any statistically reliable candidates," Payent pointed out. "We have developed a sophisticated analysis software that greatly improves the lens inspection methods of the past, which also allows us to strongly reject candidates."
After more analysis, a more exciting discovery emerged. The energy explosion occurred behind a medium-mass black hole.
The incredible gravity of IMBH bends all forms of light and electromagnetic radiation around it. When the gamma ray bursts, it travels through the universe towards us. But when it encounters IMBH, the signal is split. This phenomenon is called gravitational lensing.
The lens has a clear sign, the echo of the signal, because some of the radiation from the gamma-ray burst will take longer to reach the observatory's detectors when it bends around the IMBH. This is a very subtle difference. “Although it took billions of light years to reach us, in our case, the difference in arrival time was only 400 milliseconds,” Paint explained.
This is not a clear test for IMBH, but it is another good candidate. It also helps astronomers estimate how many of these IMBHs might be lurking in deep space. Their calculations indicate that in the Milky Way near us, their number may be about 46,000, but Paint said there is a lot of uncertainty in the measurement. Finding more lens candidates will help reduce uncertainty.
"Ideally, we will also analyze other catalogs in the future," Paint said.
Perhaps Thrane believes that IMBH may be an ancient relic of the early universe before the formation of stars and galaxies. If this is the case, they may be the "seeds of the supermassive black holes that live in the centers of galaxies today."
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