This record-breaking discovery is either a black hole or a neutron star

Is this the lightest black hole we’ve ever seen? Or the heaviest neutron star?? It’s one or the other, but scientists aren’t quite sure which.

There’s an object in space about 40,000 light years away in the globular cluster NGC 1851, and scientists aren’t quite sure what it is. It orbits a rapidly spinning pulsar, which is a dense neutron star (think the mass of our sun squeezed into 10 or 20 miles in diameter) that gives off pulses of radio waves, spinning at 170 times a second. Scientists were able to use the reliability of this pulsar to determine that the object in orbit of this pulsar was in a gray area of mass — not quite massive enough to be a black hole but too massive to be a neutron star.

That’s because we characterize most space objects by mass. Want to know the difference between a planet and a star, in terms of how we categorize them? It’s just mass, basically. We’ve defined a planet as, among other things, an object that has enough mass to clear its orbit (so it’s either attracted or repelled any significant objects in its path). If a planet gains enough mass to begin fusion at its core and start fusion, it might become a star. If the fusion process is short-lived because it doesn’t gain quite enough mass to become a star, it might instead become a brown dwarf, which is the in between of a planet and a star.

Now the question is whether what scientists have discovered in NGC 1851, which this discovery was made using the MeerKat telescope, is another in between?

A neutron star is the dense core of a dead star — basically all these neutrons have been crushed into a small space. When a neutron star gains enough mass to collapse in on itself, scientists think it becomes a black hole. If this particular object is indeed a neutron star, it appears to have gained mass, but it hasn’t collapsed.

Basically scientists think for a neutron star to collapse into a black hole, it has to have around 2.2 times the mass of our sun. Any more than that, and the quantum pressure that keeps the neutrons separate will be overridden and the structure will collapse into a black hole. The smallest black hole we’ve ever found is around 5 times the mass of our sun. It’s possible the object is a massive neutron star, it’s possible that it’s a tiny black hole. The gray area in between the two is what’s known as the “black hole mass gap.”

Scientists do have a theory on what this object might be, and it has to do with the globular cluster it’s in. Stars in globular clusters tend to be tightly packed, but the stars in NGC 1851 are even more packed in than usual. That means these stars are regularly interacting with and even colliding with one another. (This may be because scientists have found that the stars in NGC 1851 have differing ages, which is unusual for a globular cluster, and has contributed to the theory that this cluster may be the result of two separate clusters that collided with their host dwarf galaxy to become this massive globular cluster we see today).

Anyways, because the objects within NGC 1851 are so densely packed, scientists have posited that the dense object may actually be two neutron stars that collided with one another. If this is true, this would bring into question the idea of the black hole mass gap and that the mass limit for neutron stars is 2.2 times that of our sun.

Main source: Science