Jul 1, 2021 - Science

Scientists find the smallest, most massive white dwarf star yet

Artist's illustration showing the Moon at half phase with a white dwarf star

Artist's illustration of a white dwarf star and the Moon. Image: Giuseppe Parisi

A newfound white dwarf star 130 light-years away is the most massive and smallest ever discovered, according to a new study.

Why it matters: The star — thought to be the result of two white dwarfs smacking into one another and merging — can act as a laboratory for astronomers to learn more about how extreme objects in the universe evolve.

What they found: The new study in the journal Nature suggests the white dwarf — named ZTF J1901+1458 — is about the size of the Moon but has a bit more than the mass of the Sun packed into it.

  • It likely formed when two stars in a binary system burned through their fuel and became white dwarfs that eventually merged with one another.
  • Sometimes, those mergers can create supernova explosions if the two stars are massive enough, but in this case, the white dwarf appears to be teetering right on the edge of being massive enough to explode.
  • "We caught this very interesting object that wasn't quite massive enough to explode," Ilaria Caiazzo, an author of the new study, said in a statement. "We are truly probing how massive a white dwarf can be."

The intrigue: The scientists behind the study don't think the star is likely to explode now, but its fate is still unclear.

  • It's possible the white dwarf is massive enough to eventually collapse into a neutron star, according to the scientists.
  • Usually these types of dead stars form after supernova explosions, but if this white dwarf is a progenitor to a neutron star, there could be many more like it out there.
  • "It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons," Caiazzo added. "Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed."

The bottom line: One day, our Sun will burn through its fuel and eventually become a white dwarf. By learning more about these objects, scientists are ultimately also investigating the fate of our star and solar system.

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