Rare 'Ultra-Massive' White Dwarf Star Created From Stellar Merger, Hubble Study Finds

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Astronomers using the Hubble Space Telescope have discovered a "ultra-massive white dwarf that formed when a white dwarf merged with another star," according to the Goddard Space Flight Center.   Credit: NASA's Goddard Space Flight Center  Paul Morris: Lead Producer  Music Credit: "Zero Gravity" Brice Davoli [SACEM] via Koka Media [SACEM], Universal Production Music France [SACEM] and Universal Production Music

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00:00Astronomers using NASA's Hubble Space Telescope have found a rare, ultra-massive white dwarf

00:06formed from merging stars.

00:09The discovery was made possible by Hubble's sensitive ultraviolet observations and suggests

00:14these unusual white dwarfs may be more common than once thought.

00:19The white dwarf is 128 light-years away and 20% more massive than the Sun.

00:25In visible light, it looked like a typical white dwarf, but Hubble's ultraviolet data

00:29revealed something unusual, evidence of carbon in its atmosphere.

00:35A white dwarf is what stars like the Sun become after they exhaust their nuclear fuel.

00:40Near the end of its life, this type of star expels most of its outer material, creating

00:45a planetary nebula.

00:47Only the hot core of the star remains.

00:50White dwarfs that form from a single star usually have atmospheres made of hydrogen

00:55and helium.

00:56These thick layers cover its carbon and oxygen, or oxygen and neon, surface, preventing their

01:02detection in the star's spectrum.

01:04When carbon shows up in a white dwarf spectrum, it can point to a more violent origin, such

01:10as a collision between two white dwarfs or between a white dwarf and a subgiant star.

01:15These collisions can burn off most of the hydrogen and helium, leaving only a thin layer behind,

01:21allowing astronomers to detect carbon on the white dwarf's surface.

01:26This white dwarf's merger origin would be impossible to identify without Hubble's

01:30ultraviolet sensitivity.

01:32In hotter white dwarfs, spectral lines from elements heavier than helium fade in visible

01:37light and stay bright and ultraviolet, where Hubble can detect them.

01:43Researchers discovered this white dwarf's unusual origin by looking at its ultraviolet spectrum,

01:49noticing that other white dwarfs with a typical visible light spectrum may also be the result

01:54of cosmic collisions.

01:56The team plans to explore this possibility further, and hopes to continue this research

02:01by studying how common carbon stars are among similar white dwarfs, and how many stellar

02:07mergers might be hiding among the normal white dwarf family.

02:11This research will help improve our understanding of the environments in which stars evolve and the

02:16paths that lead to supernova explosions.

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