Caltech: Ghosts of Ancient Explosions Live On in Stars Today

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Caltech: Ghosts of Ancient Explosions Live On in Stars Today

Post by bystander » Thu Aug 08, 2019 7:40 pm

Ghosts of Ancient Explosions Live On in Stars Today
California Institute of Technology | 2019 Aug 05

The chemical composition of certain stars gives clues about their predecessors, stars that have long since exploded and faded.

When small, dense stars called white dwarfs explode, they produce bright, short-lived flares called Type Ia supernovae. These supernovae are informative cosmological markers for astronomers—for example, they were used to prove that the universe is accelerating in its expansion.

White dwarfs are not all the same, ranging from half of the mass of our sun to almost 50 percent more massive than our sun. Some explode in Type Ia supernovae; others simply die quietly. Now, by studying the “fossils” of long-exploded white dwarfs, Caltech astronomers have found that early on in the universe, white dwarfs often exploded at lower masses than they do today. This discovery indicates that a white dwarf could explode from a variety of causes, and does not necessarily have to reach a critical mass before exploding. ...

Studying Type Ia supernovae is a time-sensitive process; they flare into existence and fade back into darkness all within a few months. To study long-gone supernovae and the white dwarfs that produced them, Kirby and his team use a technique colloquially called galactic archaeology.

Galactic archaeology is the process of looking for chemical signatures of long-past explosions in other stars. When a white dwarf explodes in a Type Ia supernova, it pollutes its galactic environment with elements forged in the explosion—heavy elements like nickel and iron. The more massive a star is when it explodes, the more heavy elements will be formed in the supernova. Then, those elements become incorporated into any newly forming stars in that region. Just as fossils today give clues about animals that have long ceased to exist, the amounts of nickel in stars illustrates how massive their long-exploded predecessors must have been. ...

Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies ~ Evan N. Kirby et al
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