A Space Mystery Potentially the Lightest Black Hole Ever Found

Something unusual is happening at the edges of the Milky Way. In a star cluster on the outskirts of our galaxy, astronomers have spotted a compact object engaged in an orbital dance with a millisecond pulsar. They believe it could only be a neutron star or a black hole, which would be a thrilling discovery.

Furthermore, should it turn out to be a neutron star, it might be the most massive one observed so far. Alternatively, if it’s a black hole, it would be the least massive among its counterparts.

A Stellar Dance with a Mystery Companion

Weighing between 2.09 and 2.71 times the mass of the Sun, this object resides at the lower limit of a region called the lower mass gap. Notably, from 2.2 to 5 solar masses, this gap is sparsely populated with detected neutron stars or black holes.

Astrophysicist Ben Stappers from the University of Manchester finds both potential outcomes for the companion fascinating. Testing gravity theories with a pulsar-black hole system and gaining new insights into high-density nuclear physics with a hefty neutron star are equally compelling prospects.

Moreover, neutron stars and black holes share a close relationship. They emerge as super-dense entities resulting from the gravitational collapse of a massive star’s core during its demise.

The main difference is in mass. Importantly, degeneracy pressure prevents a neutron star—which has a maximum mass of around 2.3 times that of the Sun—from collapsing entirely. The source of this pressure is the impossibility of particles with comparable quantum qualities inhabiting the same state, including a particular physical space.

The particles within a neutron star densely pack together, resembling a colossal atomic nucleus, squeezing the components to their maximum proximity.

Increasing the mass and even degeneracy pressure becomes insufficient to halt further collapse. As a result, theoretically, more massive cores should undergo complete collapse, forming black holes.

Unveiling the Enigmatic Companion

Although the upper limit for neutron star mass is approximately 2.3 solar masses, remarkably few black holes have been identified below five solar masses. Interestingly, the unexplored range between these figures is called the lower mass gap.

Astrophysicists Ewan Barr and Arunima Dutta from the Max Planck Institute for Radio Astronomy, along with an international team, identified the object through their investigation of a peculiar millisecond pulsar named PSR J0514-4002E. The star cluster NGC 1851 houses this pulsar, situated approximately 54,000 light-years from the galactic center.

Utilizing radio data collected by the MEERKat array in South Africa, researchers uncovered the existence of an undisclosed binary companion orbiting the pulsar every 7.44 days—the investigation aimed to unravel the identity of this mysterious object.

Millisecond pulsars, such as PSR J0514-4002E, are neutron stars characterized by extremely rapid rotation. Spinning at 170 times per second, they emit precisely timed radio waves resembling rhythmic pulses. The accuracy of these pulses allows astronomers to detect minute variations, enabling the calculation of the pulsar’s characteristics, distance, and the presence of any binary companions.

Barr explains that it is comparable to placing an almost perfect stopwatch in orbit around a star nearly 40,000 light-years away and then having the ability to time those orbits with microsecond precision.

A Calculated Approach to Discovery

Using the pulsar timing data, the team calculated the distance to PSR J0514-4002E, the pulsar’s mass, and the overall system mass. By subtracting the pulsar’s mass, they deduced the mass of the enigmatic companion.

The dimness rules out the possibility of the object being a main-sequence star, and its mass exceeds that of a white dwarf (the lighter compact object in the dead star spectrum). This narrows down the options to two: either it’s a neutron star or a black hole.

Neutron Star or Black Hole?

It’s impossible to definitively identify whether it’s a neutron star or a black hole. However, the researchers speculate it could result from a merger between two neutron stars. Drawing parallels to a prior collision detected through gravitational waves, which produced a 2.6 solar-mass object, there’s a possibility that this recent discovery, with an upper limit of 2.76 solar masses, could be a giant neutron star. The caveat is the uncertainty of either being a black hole.

Having made the discovery, the researchers are determined to unveil the identity of the enigmatic object.

To conclude, Dutta emphasizes that their investigation of this system is ongoing. She notes that unraveling the true identity of the companion will represent a pivotal moment in advancing their understanding of neutron stars, black holes, and any other mysterious entities within the black hole mass gap.

Read the original article on: ScienceAlert

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