Scientists find chunk of blown-apart star hurtling through Milky Way at breakneck speed

Artist’s impression of a supernova ejecting a white dwarf star.
Artist’s impression of a supernova ejecting a white dwarf star. (Image credit: Mark Garlick / Science Photo Library via Getty Images)

A chunk of stellar shrapnel is careering toward the edge of our Milky Way galaxy at almost 2 million mph (3.2 million kph), a new study reports.

"The star is moving so fast that it's almost certainly leaving the galaxy," study co-lead author J.J. Hermes, an associate professor of astronomy at Boston University, said in a statement

The star, known as LP 40-365, currently lies about 2,000 light-years from Earth. And calling it a star may be a bit generous, actually; Hermes and his colleagues think it's a hunk of a superdense stellar corpse called a white dwarf that was blown apart in a violent supernova explosion after gobbling up too much mass from a companion. 

Supernova photos: Great images of star explosions

"To have gone through partial detonation and still survive is very cool and unique, and it's only in the last few years that we've started to think this kind of star could exist," study co-author Odelia Putterman, a former Boston University student who has worked in Hermes' lab, said in the same statement. 

The speedy star was spotted during an analysis of survey data gathered by NASA's Hubble Space Telescope and Transiting Exoplanet Survey Satellite (TESS). The researchers noticed that LP 40-365is not only racing along but is also rotating once every nine hours as it goes. 

The rotation in itself is nothing unusual, for all stars rotate; our own sun spins on its axis every 27 Earth days. However, according to researchers, a nine-hour rotational period is considered to be relatively slow for an object that went through something as catastrophic as a supernova. 

It's this sluggish rotation that implies LP 40-365 was once part of a two-star system with an unhealthy feeding habit. 

According to the researchers, stars commonly orbit each other in close pairs, including highly dense white dwarfs. In such binary systems, if one white dwarf transfers too much mass to the other, the result can be a supernova — the largest explosion that takes place in space, according to NASA.

It's usually hard to determine which star was the "donor" and which was the "eater." But because LP 40-365's rotation is relatively slow, the research team feels confident that the object is cosmic shrapnel from the exploded star. As the two stars orbited each other at high speeds and in close proximity, the resulting supernova likely catapulted both stars out at breakneck speed, but we've only been able to spot LP 40-365, according to the statement.

"This [paper] adds one more layer of knowledge into what role these stars played when the supernova occurred," and what can happen after the explosion, Putterman said. "By understanding what's happening with this particular star, we can start to understand what's happening with many other similar stars that came from a similar situation."

These supernova survivors are even more intriguing as they are metal-rich, unlike our sun, which is primarily composed of hydrogen and helium. (Astronomers consider any element heavier than hydrogen and helium a metal.)

"These are very weird stars," Hermes said. "What we're seeing are the byproducts of violent nuclear reactions that happen when a star blows itself up." Strange stars like LP 40-365 are therefore fascinating targets to study, the researchers said. 

The research is described in a study published June 10 in The Astrophysical Journal Letters.

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Daisy Dobrijevic
Reference Editor

Daisy Dobrijevic joined in February 2022 having previously worked for our sister publication All About Space magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the National Space Centre in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K. Daisy is passionate about all things space, with a penchant for solar activity and space weather. She has a strong interest in astrotourism and loves nothing more than a good northern lights chase!