Waves show a mystery object merging with a star

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The LIGO/VIRGO/KAGRA collaboration searches the universe for gravitational waves produced by the mergers of black holes and neutron stars.
The collaboration provided specifics of their analysis of the merger and the “mystery object” in a draft manuscript posted to the physics arXiv, suggesting that the object might be a very low-mass black hole.
LIGO detects gravitational waves via laser interferometry, using high-powered lasers to measure tiny changes in the distance between two objects positioned kilometers apart.
Early detected mergers involved either two black holes or two neutron stars, but in 2021, LIGO/VIRGO/KAGRA confirmed the detection of two separate “mixed” mergers between black holes and neutron stars.
The range between the heaviest known neutron star and the lightest known black hole is known as the “mass gap” among scientists.
With no corresponding electromagnetic signal to accompany the gravitational wave signal, astrophysicists were unable to determine whether that object was an unusually heavy neutron star or an especially light black hole.
And now we have a new mystery object within the mass gap in a merger event dubbed “GW 230529.”
If so, the finding implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts, per the authors.


In order to find gravitational waves, which are created when black holes and neutron stars merge, the LIGO/VIRGO/KAGRA collaboration scans the universe. It has now declared the discovery of a signal pointing to the merger of two compact objects, one of which has an unusual intermediate mass, meaning it is lighter than a black hole but heavier than a neutron star. In a draft manuscript uploaded to the physics arXiv, the collaboration shared details of their analysis of the merger and the “mystery object,” speculating that it might be a very low-mass black hole.

By measuring minute variations in the distance between two objects placed kilometers apart with powerful lasers, LIGO uses laser interferometry to detect gravitational waves. There are LIGO detectors in Livingston, Louisiana, and Hanford, Washington state. In 2016, Advanced VIRGO, a third detector located in Italy, went live. KAGRA is the first subterranean gravitational wave detector in Asia, and it was constructed in Japan. Under construction, LIGO-India is scheduled to come online after 2025, according to physicists.

Since its first Nobel Prize-winning discovery, the collaboration has found dozens of merger events to date. LIGO/VIRGO/KAGRA confirmed the detection of two distinct “mixed” mergers between black holes and neutron stars in 2021, in contrast to the early detected mergers, which involved either two black holes or two neutron stars.

The majority of the objects involved in the mergers that the collaboration found can be classified as either stellar-mass black holes, which have masses between a few solar masses and tens of solar masses, or supermassive black holes, which have masses between hundreds of thousands and billions of solar masses, like the one at the center of our galaxy. The formation process of the latter is still somewhat unknown, but the former are the product of massive stars dying in a core-collapse supernova. Scientists refer to the range between the lightest known black hole and the heaviest known neutron star as the “mass gap.”.

Gravitational wave indications of compact objects falling into the mass gap have been seen previously. As previously reported, LIGO/VIRGO detected a gravitational wave signal in 2019 from a black hole merger known as “GW190521.” This signal produced the highest energy detected to date and appeared in the data more as a “bang” than the typical “chirp.”. The two merging black holes were locked in an elliptical orbit, not a circular one, and their axes of spin were significantly more tipped than normal in relation to those orbits, making them even more bizarre. Furthermore, the newly formed black hole as a result of the merger had an intermediate mass of 142 solar masses, which puts it squarely in the mass gap.

A compact binary merger involving an unidentified object that was also within the mass gap was detected by the collaboration in the same year as GW 190814. Scientists were unable to identify the object as either an exceptionally light black hole or an exceptionally heavy neutron star because there was no accompanying electromagnetic signal to the gravitational wave signal. Recently, a merger event known as “GW 230529” has revealed a new mystery object inside the mass gap. “.

Co-author Sylvia Biscoveanu of Northwestern University stated, “This system is especially exciting because it’s the first gravitational-wave detection of a mass-gap object paired with a neutron star, even though previous evidence for mass-gap objects has been reported in both gravitational and electromagnetic waves.”. “This system’s observation has significant ramifications for electromagnetic counterparts to compact-object mergers as well as theories of binary evolution. “.

Beginning its fourth observing run in the spring of last year, LIGO/VIRGO/KAGRA quickly detected the signal of GW 230529. According to scientific measurements, the mass of one of the two merging objects—likely a neutron star—was between 1.2 and 2 times that of our sun, while the mass of the other object fell between 2.5 and 4.5 times that of our sun in the mass-gap range. The team was unable to determine with certainty the nature of the more massive mystery object, which is located about 650 million light-years from Earth, because, like with GW 190814, there were no accompanying bursts of electromagnetic radiation; however, they believe it is most likely a low-mass black hole. If that is the case, the authors conclude that the finding suggests a higher predicted rate of neutron star–black hole mergers with electromagnetic counterparts.

“The properties of compact objects, such as black holes and neutron stars, were indirectly inferred from electromagnetic observations of systems in our Milky Way before we started observing the universe in gravitational waves,” explained co-author Michael Zevin, an astrophysicist at the Adler Planetarium). These electromagnetic observations gave rise to the notion of a gap between the masses of neutron stars and black holes, which has persisted for 25 years. The discovery of GW230529 is noteworthy as it suggests that the “mass gap” may not be as empty as previously believed by astronomers. This finding could have significant effects on compact object formation through supernova explosions and on possible light displays that may arise from a black hole rupturing a neutron star. “.

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