Record-breaking neutron star packs twice the Sun's mass into a twelve-mile-wide sphere

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The most massive neutron star ever discovered has been found 3000 light-years away. The tiny star is twice as massive as the Sun but its diameter is mere miles across. This discovery confirms these stars really are made of neutrons.

Neutron stars are the end result of collapsed stars that aren't quite big enough to become black holes. The scale of these stars is almost incomprehensible — although they're only about twelve miles in diameter, their masses often exceed that of the Sun, and even a tiny speck of such a star would weigh millions of tons. The previously biggest known neutron star was 1.67 times the mass of the Sun, but the newly discovered PSR J1614-2230 is another 20% bigger, at about 1.97 solar masses.

Even for objects as strange as neutron stars, something that massive is very surprising. Most neutron stars are right around 1.4 neutron stars, so this is a pretty significant deviation from the norm, and one that overturns the theory that neutron stars could only be about 1.4 solar masses. It also rules out the idea that neutron stars are made up of more than just neutrons.


Because of the unimaginably hyper-energetic conditions of neutron stars, they can support forms of matter that remain impossible to generate on Earth, including exotic particles like hyperons and kaon condensates, not to mention free quarks, which is thought to be impossible in the current universe. (For more on why that is, check out our primer on subatomic particles.)

But PSR J1614-2230 couldn't possibly support these types of particles. Because its mass is that much greater than the average neutron stars, the matter within is even more densely squished together, to the extent that it would be impossible for the exotic particles or free quarks to survive without the star collapsing into a black hole. Since this neutron star is stable, it really must be made of just neutrons.


This star is a particular type of neutron star known as a millisecond pulsar, which emits radio pulses and completes a full rotation every few milliseconds. It's in a binary system along with a white dwarf star, which is what allowed them to calculate the neutron star's mass with such precision. The researchers also believe collisions between these unusually massive neutron stars could account for the short-duration variety of gamma ray burst, an extremely energetic explosions whose origins had previously been elusive.

Researcher Scott Ransom of the National Radio Astronomy Observatory mused on why this finding is so exciting:

"Pulsars in general give us a great opportunity to study exotic physics, and this system is a fantastic laboratory sitting out there, giving us valuable information with wide-ranging implications. It is amazing to me that one simple number - the mass of this neutron star - can tell us so much about so many different aspects of physics and astronomy."