‘Black neutron star’ discovery baffles astronomers

A mysterious object weighing 2.6 suns bridges the gap between stars and black holes.

Key Takeaways

1. Astronomers are baffled by the discovery of an enigmatic object, possibly the heaviest neutron star or the lightest black hole, defying traditional classifications.
2. The object, with a mass of 2.6 times that of the sun, lies in the elusive “mass gap” between neutron stars and black holes.
3. This groundbreaking discovery was made during the cosmic merger event GW190814, detected on August 14, 2019, by the LIGO-Virgo observatories.
4. The merger involved a 2.6-solar-mass object colliding with a 23-solar-mass black hole, creating gravitational waves observed from 800 million light-years away.
5. Scientists remain uncertain about the object’s identity but agree it challenges existing theories on stellar evolution and compact objects.

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For decades, scientists have pondered the existence of objects between the mass of neutron stars and black holes, an area known as the “mass gap.” Now, researchers from the National Science Foundation’s LIGO and the European Virgo detector have uncovered a groundbreaking find: an object with 2.6 times the mass of the sun. Detected during the cosmic merger event GW190814, this discovery could redefine our understanding of compact stellar remnants.

Discovery of GW190814

LIGO and Virgo detected gravitational waves from the merger of two objects. One was a black hole with a mass of 23 suns, while the other was an enigmatic 2.6-solar-mass entity. The event, observed from 800 million light-years away, marked the most extreme mass ratio (9:1) for any gravitational-wave event recorded to date. The collision resulted in a 25-solar-mass black hole, with some mass converted into gravitational wave energy.

This mysterious 2.6-solar-mass object sits in the long-debated “mass gap.” Neutron stars typically max out at 2.5 solar masses, while black holes start at around 5 solar masses. Researchers are uncertain if the object is the heaviest neutron star or the lightest black hole. Either way, it breaks existing records.

Implications for Astrophysics

The discovery has significant implications for theories of stellar evolution and gravitational physics. If the object is a neutron star, its mass exceeds predictions of modern physics. If it’s a black hole, it represents the lightest one ever observed. This could mean the “mass gap” is an artifact of limited observational data rather than a genuine boundary.

Follow-up observations from dozens of ground-based and space telescopes failed to detect any light or electromagnetic signals from the merger. Scientists speculate this could be because the event was six times farther than the 2017 neutron star merger (GW170817), or that the neutron star, if present, was swallowed whole by its black-hole partner.

The event also allowed researchers to validate Einstein’s General Relativity by measuring higher harmonics of gravitational radiation. Such extreme mergers offer unique insights into the multipolar structure of these waves.

The Road Ahead

Future observations by LIGO, Virgo, and other detectors may reveal additional events in the mass gap, helping researchers classify these mysterious objects. Enhanced detector sensitivity will also enable scientists to refine population statistics and better understand these compact stellar remnants.

“This discovery is yet another example of gravitational-wave astronomy’s transformative potential,” said Pedro Marronetti of the NSF. As astronomers delve deeper into the mysteries of the universe, objects like the one in GW190814 will undoubtedly shape our understanding of the cosmos.