Written by Will Dunham
WASHINGTON (Reuters) – In the midst of their deaths, nearly 97% of all stars turn into blazing stellar zombies called white dwarfs, one of the densest objects in the universe. A newly discovered white dwarf is being hailed as the most “extreme” ever, cramming a terrifying amount of mob into a very small package.
Scientists said Wednesday that this highly magnetic white dwarf rotates 35% faster than our sun, but has a small diameter only slightly larger than Earth’s moon. This means that it has the largest mass and smallest size, contrary to what would be expected, of any known white dwarf, due to its enormous density.
There are only two other types of objects – black holes and neutron stars – that are more compact than white dwarfs.
The birth method of this white dwarf, named ZTF J1901 + 1458, is also unusual. It appears to be the product of a binary star system in which two stars orbit each other. These two stars separately evolved into white dwarfs at the end of their life cycles, then spiraled toward each other and merged into one entity.
Even with more compact masses, this merger would trigger massive stellar explosions called supernovae, said Caltech astrophysicist Ilaria Kayazo, lead author of the study published in Nature. Kiyazu added that it might still explode at some point in the future.
“This white dwarf is really extreme,” Kiazu said. “We found something in order of how small and heavy the white dwarf was.”
It is relatively close in our Milky Way galaxy, about 130 light years from Earth. A light year is the distance light travels in a year – about 5.9 trillion miles (9.5 trillion km).
The white dwarf gradually shrunk and became denser and denser. If it doesn’t explode, it could collapse the nucleus into a neutron star, another type of city-sized remnant that usually forms after some very massive stars go supernova. This would be a previously unknown pathway for neutron star formation.
The white dwarf was discovered by astrophysicist and study co-author Kevin Bridge of the Palomar Observatory at the California Institute of Technology.
“White dwarfs are the most common form of stellar remnant,” said Bridge, who worked on the study at Caltech and is heading to MIT. “So it was amazing to see the most extreme outlier among them.”
With a diameter of about 2,670 miles (4,300 km)-roughly the distance from Boston to Los Angeles or London to Tehran-it exceeds the diameter of the moon by about 2,160 miles (3,475 km).
While our Sun rotates on its axis once every 27 days, this white dwarf does so every seven minutes. Its magnetic field is about a billion times stronger than Earth’s
It is believed that stars up to eight times the mass of our Sun will become white dwarfs. These stars end up burning all the hydrogen they use as fuel through nuclear fusion. At this point, gravity causes it to collapse and blow up its outer layer in a “red giant” phase, eventually leaving behind a dense core that is a white dwarf.
White dwarfs initially have a high temperature but gradually cool down over time, and they lack a new source of energy. In about 5 billion years, our sun is expected to become a red giant and then a white dwarf.
(Reporting by Will Dunham; Editing by Rosalba O’Brien)
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