This neutron star is almost too massive to exist

Astronomers at the Green Bank Observatory has recently reported the discovery of a new neutron star, one that can just barely exist as it is, due to almost reaching the limits of its own mass.

Neutron stars, for those unfamiliar, are super compressed stars that are produced from dying stars that have gone supernova. They are called as such because the super intense pressures inside the star cause even elementary particles to lose their identity, and are crushed to simply form neutrons. For instance, if one can extract a sugar cube worth of neutron star matter, it would have the same mass as 100 million tons. Hence, neutron stars are relatively small, several times smaller than our own moon, despite having density levels many times that of our own Sun.

The newly discovered neutron star was discovered to be a rapidly rotating millisecond pulsar. Officially designated as J0740+6620, it has a mass that is equivalent to 2.17 times our own Sun, and is 30 kilometers across. It is accompanied by a white dwarf, which has a confirmed mass of 0.26 our own Sun. The passing white dwarf’s measurements were taken from the signal delay it produces when it passes in front of the pulsar’s energetic wavefront.

One very interesting thing to point out about the 2.17 solar mass calculation is that this value sits very, very close to the what is known in astronomy as the Tolman–Oppenheimer–Volkoff limit. This is the technical mass limit that a celestial body can have where it can still maintain its form as its own. Beyond it, gravitational forces simply take over, and instead of crushing the remaining mass into subatomic particles, the star directly “implodes” into a singularity — transforming into a black hole.

For a (rotating) neutron star, the calculated upper (maximum) estimate for its Tolman–Oppenheimer–Volkoff limit is 2.16 solar masses. This means that J0740+6620 is just right at the very edge of existence. It is at the brink of collapsing and turning into a black hole, yet it won’t so long as it either maintains its mass or rotation speed at its current level.

So what if it suddenly gets a bit heavier? The official press release did not specify, but if in case its companion white dwarf is actually closing in on the neutron star, then generations from our far future might just witness yet another neutron star collapse, and the birth of a new black hole.

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