Astronomers have just found the smallest dead star ever discovered

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A dead star the size of the moon is the smallest we’ve ever seen.

It is a white dwarf star, the highly collapsing core of a star in the mass range of the Sun, but only 4,280 kilometers (2,660 miles) wide. It’s also the most massive white dwarf star we’ve ever seen, with a mass about 1.35 times the mass of the Sun.

Just take a second to wrap your head around that – a boy over the mass of our sun packed into a ball a little bigger than the size of the moon. Incredibly beautiful, isn’t it?

And the white dwarf, called ZTF J1901 + 1458 and located about 130 light-years away, is really amazing. Its density and mass put it on the edge of the Chandrasekhar limit – the maximum mass a white dwarf can have before it becomes so unstable that it explodes in a stunning supernova.

“We caught this very interesting object that wasn’t massive enough to explode,” said theoretical astrophysicist Ilaria Caiazzo of the California Institute of Technology. “We’re already investigating how massive a white dwarf is.”

White dwarfs are the smallest class of dead stars in the dead star chain. It is formed from the collapsed nuclei of stars up to eight times the mass of the Sun; When these stars finish the life of their main sequence (nuclear fusion), they explode their outer material, and the remaining core, no longer supported by the external pressure of fusion, collapses into a super-dense object.

Even the Chandrasekhar limit, about 1.4 solar masses, something called electron degeneration pressure prevents the white dwarf from collapsing further under its gravity. At a certain pressure level, electrons are stripped from their atomic nuclei – and because identical electrons cannot occupy the same space, these electrons provide the external pressure that prevents the star from collapsing.

There are many white dwarf stars in binary systems. This means that they are locked in a tropical dance with another star. If the two stars are close enough, the white dwarf will pull material from its binary companion, a process that can flip the dead star beyond the Chandrasekhar limit, often resulting in a Type Ia supernova.

ZTF J1901 + 1458 appears to be a special case.

According to the team’s analysis, the white dwarf is the product of a merger of two smaller white dwarfs. Together, they weren’t massive enough to reach the Chandrasekhar limit and produce a Type Ia supernova.

It is only about 100 million years old, with a white dwarf’s insane magnetic field, a billion times stronger than the Sun. It also has extreme rotation, spinning once every seven minutes. This isn’t the fastest spin of a white dwarf ever, but it’s there. These characteristics indicate a merger in the past.

What happens from this point on can be pretty cool.

“This is highly speculative, but it is possible that the white dwarf is massive enough to collapse further into a neutron star,” Kaizo explained.

“It’s so massive and dense that, in essence, electrons are captured by protons in the nuclei to form neutrons. Because the pressure from the electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.”

Neutron stars – even denser than white dwarfs, and powered by the pressure of neutron decay – form when a star between 8 and 30 times the mass of the Sun reaches the end of its lifespan. Once it transforms into a kablooey, bursting from its outer matter, the stellar core collapses into a neutron star.

ZTF J1901 + 1458, if the team’s analysis is correct, suggests another formation path for lower mass examples of these extreme bodies.

This in turn could mean that ZTF J1901 + 1458 and other stars like it can tell us a lot about the types of white dwarf binaries that turn into neutron stars. The team hopes to find them.

“There are a lot of questions to address, such as what is the rate of merging of white dwarfs in the galaxy, and is it sufficient to explain the number of Type Ia supernovae? How is the magnetic field generated in these strong events, and why is there such a diversity in magnetic field strength among white dwarfs? ?” said Caiazzo.

“Finding a large number of white dwarfs born from mergers will help us answer all these questions and more.”

The research was published in the journal Nature.

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