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About 2,000 light years from Earth, a star catapults towards the edge of the Milky Way. This particular star, known as LP 40−365, is part of a unique race of rapidly moving stars – the remnants of massive stars. white dwarf stars that survived to pieces after a gigantic stellar explosion.
“This star is moving so fast that it almost certainly leaves the galaxy …[it’s] moving at nearly three million kilometers an hour, ”says JJ Hermes, assistant professor of astronomy at Boston University College of Arts & Sciences. But why is this flying object rapidly exiting the Milky Way? Because it’s a shrapnel from a past explosion – a cosmic event known as a supernova – that’s always propelled forward.
In this artist’s rendering, a close pair of white dwarf stars are set to eventually explode in what is called a supernova. This happens when a white dwarf feeds on its companion star until both stars explode, sometimes with only remains. Credit: photo courtesy of Caltech / Zwicky Transient Facility
“To have suffered a partial detonation and survive is very cool and unique, and it was only in the last few years that we started to think that this kind of star could exist,” says Odelia Putterman, a former student of BU which worked in the Hermès laboratory.
In a new article published in Letters from the astrophysical journal, Hermes, and Putterman uncover new observations of this remaining “star shrapnel” that provides glimpses of other stars with similar catastrophic pasts.
“What we are seeing are the byproducts of violent nuclear reactions that occur when a star is blown up.”
– JJ Hermès
Putterman and Hermes analyzed data from Nasa‘s The Hubble Space Telescope and Transiting Exoplanet Survey Satellite (TESS), which monitors the sky and collects luminous information about stars near and far. By examining various types of light data from the two telescopes, the researchers and their collaborators discovered that the LP 40-365 is not only projected out of the galaxy, but that depending on the brightness patterns of the data, it rotates also on its release. .
“The star is actually dropped by the explosion, and we are [observing] its rotation when it comes out, ”says Putterman, who is the second author of the article.
“We dug a little deeper to understand why this star [was repeatedly] more and more bright and fainter, and the simplest explanation is that we are seeing something at [its] the surface rotates in and out of sight every nine hours, ”suggesting its rate of rotation, says Hermes. All the stars rotate, even our sun slowly rotates on its axis every 27 days. But for a star fragment that survived a supernova, nine hours is considered relatively slow.
Supernovas occur when a white dwarf becomes too massive to support itself, ultimately triggering a cosmic burst of energy. Finding the rate of rotation of a star like LP 40−365 after a supernova may give clues to the original two-star system from which it arose. It is common in the universe for stars to come in close pairs, including white dwarfs, which are very dense stars that form near the end of a star’s life. If one white dwarf gives too much mass to the other, the star we land on can self-destruct, resulting in a supernova. Supernovas are commonplace in the galaxy and can occur in different ways, the researchers say, but they are generally very difficult to see. This makes it difficult to know which star imploded and which star dumped too much mass on its star partner.
Based on the relatively slow spin rate of the LP 40-365, Hermes and Putterman are more confident that these are shrapnel from the star that self-destructs after receiving too much mass from its partner. , as they once circled around each other at high speed. Because the stars were orbiting so quickly and closely, the explosion launched both stars, and now we only see LP 40-365.
“This [paper] adds an extra layer of knowledge about the role these stars played when the supernova occurred, ”and what can happen after the explosion, says Putterman. “By understanding what is going on with this particular star, we can begin to understand what is going on with many other similar stars from a similar situation.”
“They are very strange stars,” said Hermes. Stars like LP 40-365 are not only among the fastest stars known to astronomers, but also the most metal-rich stars ever detected. Stars like our sun are made up of helium and hydrogen, but a star that has survived a supernova is mostly made of metallic material, because “what we are seeing are the byproducts of violent nuclear reactions that occur when ‘a star explodes. Hermes says, making star bursts like this particularly fascinating to study.
Reference: “8.9 hour rotation in Partily Burnt Runaway Stellar Remnant LP 40-365 (GD 492)” by JJ Hermes, Odelia Putterman, Mark A. Hollands, David J. Wilson, Andrew Swan, Roberto Raddi, Ken J . Shen and Boris T. Gänsicke, June 7, 2021, Letters from the astrophysical journal.
DOI: 10.3847 / 2041-8213 / ac00a8
This research was funded by a NASA TESS Cycle 2 grant; the European Research Council; a grant from the UK Science and Technology Facilities Council; the Beatriu de Pinós postdoctoral fellowship program, funded by the Secretariat of Universities and Research (Government of Catalonia); the European Union’s Horizon 2020 research and innovation program within the framework of a Maria Skłodowska-Curie grant; NASA’s Astrophysics Theory Program; and by a Leverhulme research grant.
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