At several million km/h: White dwarfs can can eject each other from galaxies
Artistic representation of the formation of a hyperfast white dwarf
(Bild: Technion – Israel Institute of Technology)
After several hyper-fast white dwarf stars were discovered, there is now an explanation. The objects are the product of a double star explosion.
When two white dwarf stars of a very specific type collide with each other, a double explosion of one can catapult the other to a speed of more than 8 million km/h and hurl it out of a galaxy. This is the result of simulations now presented by a German-Israeli research team [1], which probably provide the explanation for precisely such hyper-fast stars, several of which have already been discovered. For the first time, modeling can now explain not only the enormous speed of such objects, but also their unusual temperature, explains the Technical University of Israel in Haifa.
Ejected from the galaxies
Hyper-fast white dwarfs have only been known for a short time, with various discovered two years ago [2] in the data from the Gaia space telescope [3]. They have speeds of more than 1300 km/s (4.7 million km/h) in common, with the fastest of them even reaching a speed of 8.5 million km/h. This is enough to defy gravity. This is enough to escape the gravitational pull of the Milky Way, but how they were accelerated in this way was a mystery until now. In addition, the stars are unexpectedly hot. Researchers from the University of Potsdam and the Max Planck Institute for Astrophysics have now also been involved in the modeling with computer-intensive simulations.
The group discovered that several circumstances have to come together before these "stellar cannonballs" are shot through the galaxy. The starting point is two white dwarf stars of a certain type that collide dramatically with each other. The smaller one is partially disintegrated, while the larger one explodes twice [4]. This heats up the smaller one and catapults it into space at precisely these extreme speeds. The team is now arguing in favor of searching for further specimens in the Gaia data. The research [5] was published in Nature Astronomy.
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This article was originally published in German [11]. It was translated with technical assistance and editorially reviewed before publication.
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[1] https://www.technion.ac.il/en/blog/article/new-study-reveals-origin-of-the-fastest-white-dwarfs-in-the-galaxy/
[2] https://astro.theoj.org/article/84548-the-fastest-stars-in-the-galaxy
[3] https://www.heise.de/news/Treibstoff-alle-Bahnbrechendes-Weltraumteleskop-Gaia-beendet-Forschungsarbeit-10241596.html?from-en=1
[4] https://www.heise.de/news/Erster-sichtbarer-Beweis-fuer-doppelte-Explosion-eines-Weissen-Zwergsterns-10473526.html?from-en=1
[5] https://www.nature.com/articles/s41550-025-02633-4
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