Thursday, August 5, 2021

Strange star is coming out of the Milky Way at enormous speed

 About 2,000 light-years away from Earth, there is a star catapulting itself towards the edge of the Milky Way.  This particular star, known as LP 40−365, is part of a unique race of fast-moving stars – remnants of massive white dwarf stars – that have survived in shreds after a gigantic stellar explosion.
 “This star is moving so fast that it's almost certainly leaving the galaxy (…) [it's] moving at nearly 3 million kilometers per hour,” said JJ Hermes, assistant professor of astronomy at Boston University's College of Arts and Sciences. (USA).  But why is this flying object leaving the Milky Way?  Because it's a shrapnel from a past explosion – a cosmic event known as a supernova – that's still being propelled forward.  
 "Having gone through a partial detonation and still surviving is really cool and unique, and it's only been in the last few years that we've started to think that this kind of star could exist."
 stellar shard
 In the article, Hermes and Putterman discover new observations about this remaining “stellar shard” that give a glimpse of other stars with similar catastrophic pasts.
 Putterman and Hermes analyzed data from NASA/ESA's Hubble Space Telescope and the Transiting Exoplanet Survey Satellite (Tess), which surveys the sky and collects light information on nearby and distant stars.  By looking at various types of light data from both telescopes, the researchers and their collaborators found that LP 40−365 is not just being launched out of the galaxy: based on the data's brightness patterns, it's also spinning on its way out. .
 “The star is basically being 'slingshot' from the explosion and we're [watching] its rotation as it leaves,” said Putterman, who is the second author of the article.
 “We dug a little deeper to find out why that star [was repeatedly] getting brighter and dimmer, and the simplest explanation is that we're seeing something on [its] surface rotate in and out of view every nine hours , suggesting that this is its rate of rotation,” Hermes said.
 slow rotation
 All stars rotate – even our Sun rotates slowly on its axis, every 27 days.  But for a star fragment that has survived a supernova, a nine-hour rate is considered relatively slow.
 Supernovas occur when a white dwarf gets too big to support itself, eventually triggering a cosmic detonation of energy.  Finding the rotation rate of a star like LP 40−365 after a supernova can provide clues to the original binary system where it came from.
 It is common in the universe for stars to come in close pairs, including white dwarfs, highly dense stars that form at the end of a star's life.  If one white dwarf gives the other too much mass, the star receiving that mass can self-destruct, resulting in a supernova.  Supernovas are common in the galaxy and can happen in many different ways, according to the researchers, but they are often very difficult to see.  This makes it difficult to know which star imploded and which star dumped a lot of mass on their partner.
 strange suns
 Based on the relatively slow rotation rate of LP 40−365, Hermes and Putterman feel more confident that it is a splinter from the star that self-destructed after being fed too much mass by its partner, when they were orbiting each other. at high speed.  Since they were orbiting each other so quickly and closely, the explosion hit both stars, and now we only see LP 40-365.
 "This [article] adds another layer of knowledge about the role these stars played when the supernova occurred," and what might happen after the explosion, said Putterman.  "By understanding what's going on with this particular star, we can begin to understand what's going on with many other similar stars that have come from a similar situation."
 These stars are very strange,” said Hermes.  Suns like LP 40-365 are not only some of the fastest stars known to astronomers, but also the richest metals ever detected.  Stars like our Sun are made up of helium and hydrogen, but a star that has survived a supernova is mostly made up of metallic material, because "what we're seeing are the by-products of violent nuclear reactions that happen when a star explodes," Hermes said. .  This makes star shards like this especially fascinating to study.
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