The events that occur in the universe do not stop surprising the scientific community. Until now, gravitational waves coming from the merger of two black holes or two neutron stars. However, the Virgo detectors (located in Italy) and LIGO (with two facilities in the United States) have recently picked up the signal of a unpublished cosmic cataclysm: the collision between black holes and neutron stars.
Repeated phenomenon in ten days
In his study, published this Tuesday in The Astrophysical Journal Letters, the experts explain that two events of this type were detected in which a black hole and a neutron star, spinning around each other, merged into a single compact object. The January 5, 2020, one of the two LIGO observatories (the one in Livingston, Louisiana) and the one in Virgo (in Italian Tuscany) captured the first merger, called GW200105. From the gravitational wave signal, they found out that it was generated at a distance of 900 million light years from Earth So what a black hole of 8.9 solar masses and a smaller compact object, a neutron star, of 1.9 solar masses were involved.
The surprise was even greater when ten days later, the January 15, the two LIGO detectors and the Virgo detector picked up a second gravitational wave signal from the spiral phase and fusion of a similar binary system, baptized as GW200115. On this occasion, the merger occurred between a 5.7 solar mass black hole and of a 1.5 solar mass neutron star at a range of 1 billion light years from our planet.
“The black hole and neutron star pairs were indeed the ‘missing binary system’ for astronomers. With this new discovery, we can finally begin to understand how many of those systems exist, how often they merge, and why we haven’t seen examples in the Milky Way yet”, He adds in statements to the Sinc Agency Astrid Lamberts, CNRS researcher and member of the scientific collaboration between LIGO and Virgo who captured the signals.
Electromagnetic radiation flare
Another test of the detection of a mixed system of a neutron star and a black hole could be electromagnetic radiation detection along with gravitational waves. In fact, if the masses of the two compact objects are similar, the neutron star, as it approaches the black hole, would be subject to such tidal forces that it would fragment. In this case, in addition to the gravitational emissions, one could also observe a spectacular flare of electromagnetic radiation, due to the disintegration of stellar matter around the black hole.
This is unlikely to occur with GW200105 or GW200115, since, in both cases, the black hole was much bigger than the star, so the merger was sudden, he explains in The country Toni Font, member of the collaboration between LIGO and Virgo: “The black hole swallows the entire star, at once and without decomposing it first. This appears to have been the case in the two events that we have captured.