Space

Smallest, densest white dwarf ever packs 1.3 Suns into the Moon

Smallest, densest white dwarf ...
An artist's illustration comparing the size of the newly discovered white dwarf to our Moon. This makes it the smallest known white dwarf
An artist's illustration comparing the size of the newly discovered white dwarf to our Moon. This makes it the smallest known white dwarf
View 1 Image
An artist's illustration comparing the size of the newly discovered white dwarf to our Moon. This makes it the smallest known white dwarf
1/1
An artist's illustration comparing the size of the newly discovered white dwarf to our Moon. This makes it the smallest known white dwarf

Astronomers have discovered the smallest but most massive white dwarf ever found: the tiny star is only about the size of our Moon, but packs in more mass than the Sun. That means it’s approaching the theoretical limit of what’s possible without exploding.

When stars of a certain mass reach the end of their lives, they swell up into a red giant, then shed their outer layers, leaving behind a dense core. With no more fusion occurring in their centers, these stellar remnants can no longer hold themselves up against the crushing pressure of their gravity, and collapse into a white dwarf. These objects are much smaller than other stars, but more massive.

And now, astronomers have discovered a white dwarf that breaks the record in both of those fields. Designated ZTF J1901+1458, the star measures just 4,300 km (2,672 miles) across, and contains 1.35 times the mass of the Sun.

For comparison’s sake, most white dwarfs have masses between about 0.5 and 0.7 Suns, and have diameters of roughly 12,000 km (7,900 miles) – about the equivalent of Earth. Instead, this new one is closer in size to our Moon.

The astronomers say that this massive white dwarf was most likely born from a merger between two smaller ones. That’s evident not just in its mass but in its particularly strong magnetic field, almost a billion times stronger than the Sun’s, and its super-fast spin – it takes just seven minutes to make one full rotation.

Intriguingly, the white dwarf is very close to the theoretical limit of 1.44 solar masses. Any more than that, and it would likely explode as a type Ia supernova. But the researchers suggest that perhaps there’s a stranger fate in store for ZTF J1901+1458 – it might just collapse into a neutron star instead, which are normally born from larger stars.

"This is highly speculative, but it's possible that the white dwarf is massive enough to further collapse into a neutron star," says Ilaria Caiazzo, lead author of the study. "It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. 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.”

If so, it could mean that neutron stars form this way relatively regularly. Further study might yield more answers.

The research was published in the journal Nature.

Source: Caltech

1 comment
1 comment
Karmudjun
Ah the 2nd stage of Scientific discovery - the WAGs! After all, science intends to understand the world, and a lack of understanding leads to theoretical explanations of possible mechanisms non-testable (therefore not your average hypothesis) by theoretical astrophysicists who haven't joined the theoretical ecologists in using think-speak to codify a new use of old words so that common people have no clue what they are talking about. But I have to say, reading the source article was much easier than trying to follow an ecology "specialist" or "professor" in lecture on by text. I swear I think some Ivory Tower theoretical specialists smoke dope as they write their tomes!

But - these findings do make you ponder - pass the bong and I'll come up with a theory too!