Gravitational waves: collision of a black hole gives riddle

Astronomers have found gravitational waves that indicate a collision of a black hole with a still unclear celestial body that does not fit into current theories. The gravitational wave detectors Ligo and Virgo have detected the signals on 14. August 2019 measured, explains the research team, which was coordinated by Vicky Kalogera of Northwestern University. The gravitational waves GW190814 originate from the collision of a black hole of 23 times the mass of our sun and an object of 2.6 times the mass of the sun. This is actually too massive for a neutron star and not massive enough for a black hole.

Neutron star or black hole?

As the researchers now explain, the most massive stars collapse into black holes, while lighter ones explode in supernovae, leaving compact neutron stars behind. But there is a gap between the most massive neutron stars of just over 2 solar masses and the smallest black holes of 5 solar masses. Until now, it was not clear whether there were objects in this gap. However, the amount of mass of the smaller object in the now observed collision is very robust and quite a challenge for astrophysical models. Researchers present their work in the Astrophysical Journal Letters.

The collision was also unusual in that the mass of the two objects differed by a factor of 9. More than any before. According to the report, it occurred at a distance of 780 million light years, too far away for visible traces to reach us. Moreover, the rather massive black hole probably swallowed the smaller object completely, so not much light was emitted anyway. We will probably not learn anything more about the nature of this collision, but astronomers hope for similar collisions in the future.

Gravitational waves: collision of a black hole gives riddle

Some pairs whose collision was observed.

The mysterious object, however, is not the first to fall into the so-called mass gap between the smallest black holes and the most massive neutron stars. Already in the fall, astronomers had reported a black hole that, at 3.3 solar masses, also does not fit the theories. Such objects are a challenge to our current understanding of extremely dense matter and the evolution of stars, says Pedro Marronetti of the National Science Foundation. The collision traces now observed show once again the immense potential of gravitational wave astronomy, he is convinced.

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