Astronomers have discovered a bizarre star with a chemical composition unlike any previously known.
But by using space and ground-based telescopes to probe a star about 150 light-years from Earth, the scientific community believes they know why it looks so strange: it has swallowed up a nearby star.
The study, published Monday in the journal Nature Astronomy, examines an unusual dying star called WD J055134.612 + 413531.09 (WDJ0551 + 4135, for short), which was first spotted by the European Space Agency's Gaia telescope. The Gaia Telescope spotted WDJ0551 + 4135 in 2018, and subsequent work showed that it was an especially large white dwarf, nearly twice the size of similar stars that were discovered.
Using the ground-based telescope of William Herschel, located in the Canary Islands in Spain, the research team studied the composition of the white dwarf to find out what components it consists of. They could do this because the light emitted from WDJ0551 + 4135 can help identify the chemicals present. Like stars at the end of their lives, white dwarfs cool off, and they usually consist of a mixture of carbon and oxygen or oxygen and neon surrounded by layers of helium and hydrogen.
While examining the stellar composition, astronomers were surprised to find carbon levels much higher than they would expect for a white dwarf of this size.
“This star stood out as something we've never seen before,” Mark Hollands, an astrophysicist at the University of Warwick and lead author of the study, said in a press release. “When we looked at her, it didn't make any sense.”
It made a little more sense that perhaps WDJ0551 + 4135 was not just a dying star, but at some point more than a billion years ago merged with another white dwarf. This explanation seemed to be in line with the unusual composition and size that astronomers saw in WDJ0551 + 4135.
More evidence comes from how the star moved around the Milky Way. It looks like WDJ0551 + 4135 is Usain Bolt among white dwarfs – faster than 99% of similar stars. It was another clue that Hollands said only leads to one explanation: the merging of two white dwarfs.
If the theory is correct, then astronomers for the first time were able to detect the merger of white dwarfs by studying the chemical composition of the star. Confirmation will require further study, however, and Hollands proposes a technique known as asteroseismology – studying how stars pulsate and wobble – could lead to independent verification, revealing exactly what the star's core is made of.
Sources: Photo: Mark Garlick / University of Warwick
