An international collaboration of scientists has announced this week that an unusual signal detected last year comes from the collision between a black hole and a dense unidentified object.
The signal of origin, detected on August 14, 2019 by the observatories LIGO (United States) and Virgo (Italy), corresponds to the gravitational waves produced by that extreme event in the cosmos.
The gravitational waves they are vibrations in space-time generated by the movement of bodies. When two or more objects concentrate a lot of mass and move quickly within a region, they cause remarkable vibrations that propagate through the universe at the speed of light.
Simulation of two bodies producing gravitational waves. Source: LIGO.
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The gravitational waves that reached Earth that day were traced to a region 800 million light-years away, where two bodies rotated together until merging. The protagonists, a black hole 23 times the mass of the Sun and a compact object 2.6 times the mass of the Sun, according to new research.
An object that does not fit
According to the authors, this body could only be another black hole or a neutron star, the two densest types of objects in the universe. Both are born from the death of massive stars, which usually end up as explosions called supernovae: if it had enough mass, what remains will collapse into a black hole, a body possessing such extreme gravity that it does not let even light escape. On the other hand, if the star was not so ‘heavy’, it will become a neutron star, an object dominated by intense magnetic fields.
The big problem is that, according to astrophysical theories, a neutron star cannot exceed 2.5 solar masses, while the smallest known black hole has at least 5 solar masses. For decades, astronomers had wondered if there was any object in the universe that was in the middle of those calculations, the “Mass gap”.
Representation of the fusion of the black hole with the foreign object. Source: Virgo / EGO / Alex Andrix.
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“The mysterious object It may be a neutron star merging with a black hole, an exciting possibility theoretically expected but not yet confirmed by observation. However, at 2.6 times the mass of our sun, it exceeds modern predictions for the maximum mass of neutron stars and, instead, may be the lightest black hole ever detected, “said astrophysicist Vicky Kalogera, one of the authors of the study published in The Astrophysical Journal Letters June 23.
This cosmic event, called GW170817It also stands out because the strange body was practically swallowed by its partner, a black hole 8 times ‘heavier’. It is the detection of gravitational waves with the most extreme mass difference known so far. “Either way, it breaks a record,” added Kalogera.
Representation of a neutron star, a star that has a powerful magnetic field. Source: NASA
Whatever the nature of the “mysterious object”, it is a discovery that will change theories about these astrophysical phenomena. For example, if it is a neutron star, you would have to perform new calculations to find out how much mass they can support without collapsing. Conversely, if it turns out to be a ‘light’ black hole, it could mean that stars don’t have to be so massive to become one.
“We are pretty sure that the universe is telling us, for the umpteenth time, that our ideas about how compact objects form, evolve and merge are still very confusing,” said Mario Spera, another expert who collaborated on the research.
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