- Some stars that aren't big enough to create black holes when they die become neutron stars instead.
- Neutron stars are so dense that one the size of Earth can be more massive than a sun.
- Using the smart new observational technique, scientists discovered the biggest one ever confirmed, with 2.3 times the mass of the sun.
There are several ways a star can die.
At the end of a star’s life cycle, it expands into a gas giant and sheds most of its material in a violent explosion, then the remainder collapses into a tiny leftover. For small stars like our sun, that stellar remnant is a white dwarf; for the largest stars, that remnant is a black hole. But for stars in between, that remnant is a neutron star. Now .
Neutron stars can be smaller than the Earth but much heavier than the sun. They’re formed when a star’s gravity is so strong that it overcomes the quantum forces produced by protons and electrons, which forces all the star’s matter to collapse and turn into neutrons. With no other forces to keep them apart, these neutrons then stack together as tightly as billiard balls, resulting in the densest matter known to science.
Because neutron stars are so dense, they tend to be tiny. There’s actually a limit to how big they can get because at a certain size they turn into black holes. The largest neutron stars ever confirmed (before now) had around twice the mass of the sun. Using a new method, though, a group of scientists has found one with a mass 2.3 times that of the sun.
The new method involved looking for neutron stars orbiting together with a sun-like star. Researchers can determine the size of the neutron star by measuring how fast its companion star orbits. The faster the orbit, the heavier the neutron star.
Typically, researchers can measure how quickly a star orbits by looking at the spectrum of light emitted by the hydrogen inside the star. But this particular star was also getting exposed to radiation from the neutron star, making it hard to see the hydrogen on the star’s far side. In response, the researchers substituted hydrogen with magnesium in their measurements, allowing them to accurately estimate the companion star’s rotation speed, and by extension, the neutron star’s mass.
This new method could help astronomers hunting for neutron stars, as well as black holes and other astronomical objects. It may even help to locate exoplanets, although the radiation involved would make any planets discovered this way unsuitable for life.