Astronomers recover a lost nova

In the tail of Scorpius the Scorpion, a new star appeared briefly nearly 600 years ago. The year was 1437, and the previously unseen star, which flared bright and lasted 14 days before disappearing, was recorded by Korean astrologers at the time. Lost to astronomers hunting for its source since that date, the binary star system that underwent that nova has now been found.

The work, published today in Nature, describes “the first nova that’s ever been recovered with certainty based on the Chinese, Korean, and Japanese records of almost 2,500 years,” according to lead author Michael Shara, a curator in the American Museum of Natural History’s Department of Astrophysics, in a press release. Rediscovering this nova, which now appears to undergo periodic smaller-scale nova explosions, provides key support for the theory that novae have long life cycles, and can go dormant before ramping up again.

A nova differs from a supernova in that the former is not a catastrophic event that destroys its progenitor star. In a nova system, a white dwarf (the remnant of a star like our Sun) pulls material off a companion star, which is still in the hydrogen-burning phase of its life. This material, mostly hydrogen, piles up slowly over the course of something like 100,000 years, until it reaches a critical point. At that point, the hydrogen envelope suddenly fuses into helium, releasing a huge amount of energy that’s seen as a nova. It’s essentially a giant hydrogen bomb, and the white dwarf can shine several hundred thousand times brighter for days or even months afterward.

In a type Ia supernova, which occurs in similar systems, it’s thought that the white dwarf pulls matter off its companion much more quickly, and reaches a critical mass point that triggers a larger explosion, which does tear the white dwarf apart. Thus, supernovae destroy the stellar remnant that creates them; novae do not, allowing the process of hydrogen buildup to occur again and possibly trigger…

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