A recently discovered celestial object, located 40,000 light-years away within the NGC 1851 star cluster, has left astronomers intrigued, as it could be the heaviest neutron star or the lightest black hole ever identified — or possibly an entirely novel entity in the realm of astrophysics.
This mysterious object was detected through the rapid flashes of its accompanying celestial body, a pulsar, residing inside a dense globule of stars. The pulsar, rotating and emitting a beam of light every 6 milliseconds, unveiled the enigmatic entity.
Researchers propose that the newfound object falls within the historical “mass gap,” a zone between black holes and neutron stars, presenting the ambiguity of being either. Published on January 18 in the journal Science, the findings open avenues for exploring gravitational theories in a pulsar-black hole system or gaining insights into nuclear physics at extreme densities with a heavy neutron star.
Both black holes and neutron stars emerge as remnants of massive stars following supernova explosions. Despite their common origin, these objects exhibit significant mass differences, with supermassive black holes reaching billions of solar masses and neutron stars rarely exceeding three solar masses. The challenge arises when distinguishing the lightest black holes from the heaviest neutron stars, as they may appear similar at a distance.
Historically, astronomers faced limitations in detecting neutron stars exceeding twice the mass of the sun and black holes lighter than five solar masses. This left a considerable mass range, known as the mass gap, unexplored until 2019 when the Laser Interferometer Gravitational-Wave Observatory (LIGO) identified gravitational waves indicative of a celestial body falling within this range. However, direct observations through traditional telescopes remained elusive.
To pinpoint the newly discovered object, astronomers utilized the MeerKAT radio telescope in South Africa to survey the NGC 1851 globular cluster, a densely packed congregation of stars prone to orbital disruptions and collisions. The detection of faint radio pulses occurring 170 times per second led researchers to the pulsar. By scrutinizing subtle variations in its rhythmic pulses, scientists determined its orbital dynamics, revealing the pulsar’s binary system with an object approximately 3.9 times the mass of the sun, precisely within the mass gap.