‘Extreme’ white dwarf sets cosmic records for small size, huge mass

WASHINGTON, June 30 (Reuters) – In their death throes, roughly 97% of all stars become a smoldering stellar zombie called a white dwarf, one of the densest objects in the cosmos. A newly discovered white dwarf is being hailed as the most “extreme” one of these on record, cramming a frightful amount of mass into a surprisingly small package.

Scientists said on Wednesday this highly magnetized and rapidly rotating white dwarf is 35% more massive than our sun yet boasts a petite diameter only a bit larger than Earth’s moon. That means it has the greatest mass and, counterintuitively, littlest size of any known white dwarf, owing to its tremendous density.

Only two other types of objects – black holes and neutron stars – are more compact than white dwarfs.

The way this white dwarf, named ZTF J1901+1458, was born also is unusual. It apparently is 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 one another and merged into a single entity.

With even a smidgen more combined mass, this merger would have resulted in an immense stellar explosion called a supernova, said Caltech astrophysicist Ilaria Caiazzo, lead author of the study published in the journal Nature. It still might explode at some point in the future, Caiazzo added.

“This white dwarf is really extreme,” Caiazzo said. “We found an object that is really at the limit of how small and heavy a white dwarf could be.”

It is located relatively nearby 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).

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