A “kilonova”—the merging of two neutron stars accompanied by intense gamma-ray bursts—was discovered by astronomers in 2017. Three and a half years after the kilonova explosion, astrophysicists have found unusual X-rays they believe might be the first evidence of a kilonova “afterglow.” This might have been a first detection of stuff going into a newly created black hole, according to astrophysicists.
Laser interferometry is used by LIGO to detect gravitational waves. When two objects are thousands of kilometres away, this technique employs powerful lasers to measure the tiniest changes in their distance. (LIGO has detectors at Hanford, Washington, and Livingston, Louisiana.) In 2016, Advanced VIRGO, a new detector in Italy, went online.) With three detectors, scientists can use triangulation to better pinpoint the location of any audible chirps in the night sky.
While the second run of LIGO from November 30, 2016, to August 25, 2017, detected seven more binary black hole mergers, it also found evidence of a binary neutron-star merger with an accompanying gamma-ray burst and signals across the rest of the electromagnetic spectrum. Since then, it has been referred to as GW170817. Gold, platinum, and uranium were among the heavy elements that were generated by the impact. For decades, astronomers have hypothesised that heavier metals are formed in kilonovas, which are the result of two neutron stars colliding and exploding in the process.
As it turned out, the scientists had been accurate all along thanks to the kilonova discovery in 2017. There had never been anything like this recorded in the history of astronomy before, and it formally heralded the beginning of the new “multi-messenger astronomy.”
It has been over a decade since LIGO/VIRGO picked up a gravitational wave signal for the merging of neutron stars or the hypothetical merger of a neutron star and black hole. Black hole mergers were assumed to not create any optical signatures, therefore there was no sense in searching for one until 2020—when they will finally be possible. So, astronomers began looking for signs of this phenomena around that time. A robotic sky scan and gravitational wave data were used to make the finding.
In spite of this, the 2017 kilonova is still unique, according to the paper’s co-author, a graduate student at Northwestern University. It’s “the unique instance of its sort” and “a treasure box of multiple first observations in our area,” according to Hajela. As part of the Chandra X-ray Observatory mission, she and other astronomers at Northwestern and the University of California, Berkeley have been tracking the progress of GW170817 since it was originally discovered by LIGO/Virgo in 2015.
It has been over a decade since LIGO/VIRGO picked up a gravitational wave signal for the merging of neutron stars or the hypothetical merger of a neutron star and black hole. Black hole mergers were assumed to not create any optical signatures, therefore there was no sense in searching for one until 2020—the year of the expected discovery. When astronomers discovered the first proof of such a phenomena, it was at that time. The finding was made possible by the combination of gravitational wave data with data from a robotic sky scan by the researchers.
Despite this, the 2017 kilonova is still unique, according to the primary author of the new research, Aprajita Hajela, who is a PhD student at Northwestern. It’s “the unique instance of its sort” and “a treasure box of multiple first observations in our area,” according to Hajela. At Northwestern and Berkeley, she has been keeping an eye on GW170817 since it was initially discovered by LIGO/Virgo using the Chandra X-ray Observatory in space.
As a result, a new source of X-rays must be at work. Expansive debris from the merger may have caused a shock wave, similar to a sonic boom, in addition to the jets themselves. After they combined, they couldn’t have imploded into a black hole right away. Instead, the stars sped up for a brief moment. An very quick spin would have temporarily countered the gravitational collapse long enough to create the shock wave-inducing fast tail of heavy kilonova ejecta. During the deceleration of the massive ejecta, the shockwaves transformed its kinetic energy into heat.
There’s no way it wouldn’t come apart. Done.”
There would be no hard surface for material to bounce off and shoot out at high speeds to form this afterglow if the combined neutron stars collapsed directly to a black hole with no intermediary stage, said co-author Raffaella Margutti of the UC Berkeley. “It would simply sink in. Done. Because of the likelihood that we’re witnessing anything other than a jet, I’m ecstatic scientifically. The new small item may ultimately be revealed in the near future.”
According to Columbia University’s Brian Metzger, the X-ray emission might be fueled by debris falling into the newly formed back hole as an alternate explanation. It’s also a scientific first, according to Hajela, because no one has ever seen such a long-term accretion before.
In the coming days and weeks, additional observations will be made, and that data will be used to solve the problem. The kilonova afterglow scenario would be confirmed if X-rays and radio emissions brighten in the coming months or years. As long as there is no accompanying radio emission, the accreting black hole scenario will be confirmed.
Regardless, Joe Bright, a postdoctoral fellow at the University of California, Berkeley, says this is the first time a kilonova afterglow or the first time material has fallen onto a black hole following a neutron star merger has been observed. Regardless of the conclusion, it’s going to be a thrilling race.
