The 'Zombie Star' that survived its own supernova
Supernovas are usually the ultimate end for stars, but some survive. LP 40-365 is a low-mass white dwarf star traveling at extreme speeds out of our galaxy. Astronomers discovered that this 'zombie star' experienced a partial thermonuclear supernova. Instead of being completely obliterated, it survived the blast, which kicked it like a rocket across the cosmos.
A Defiance of Stellar Annihilation
In the classical understanding of stellar evolution, thermonuclear supernovas represent the definitive end of a star. When a white dwarf—the dense, dead core left behind by a medium-sized star—gains enough mass from a companion star, it can trigger runaway nuclear fusion. Standard astrophysical models predict that this catastrophic detonation blows the entire white dwarf apart, dispersing its elements across interstellar space and leaving no solid stellar core behind.
The discovery of the unusual star cataloged as LP 40-365 completely disrupted this clean picture of total destruction. LP 40-365 is a low-mass stellar remnant that displays the unmistakable physical aftermath of a thermonuclear explosion, yet it still exists as an intact, shining body. Rather than being utterly obliterated, it survived its own blast, earning the moniker of a zombie star that continues to travel through space long after it was supposed to have died.
An Atmosphere Written in Ash
The primary evidence that LP 40-365 survived a supernova lies directly in the chemical composition of its atmosphere. Typical white dwarfs are wrapped in outer layers of light elements, predominantly hydrogen and helium, with heavier elements sinking rapidly into their dense interiors under intense gravitational fields. LP 40-365, by contrast, shows an atmosphere almost completely devoid of both hydrogen and helium.
Spectroscopic observations reveal that the surface of LP 40-365 is instead saturated with intermediate-mass elements such as oxygen, neon, magnesium, sodium, and aluminum, alongside heavier iron-group elements. This exotic cocktail represents the literal ash of partial nuclear burning. The star's composition can only be explained by deep, explosive nucleosynthesis that consumed the outer envelopes and altered the internal structure without entirely disintegrating the star.