Stars collide to become 'space snowman'

Artist’s impression of two white dwarfs in the process of merging. (University of Warwick/Mark Garlick)

Scientists out of England believe that a “bizarre” discovery they thought was one star could actually be two stars merging.

An artist’s impression of the scientific discovery depicting a small white-hot star colliding with a larger one has been dubbed a “space snowman.”

“(Scientists) have discovered an unusual ultra-massive white dwarf around 150 light years from us with an atmospheric composition never seen before,” wrote a University of Warwick spokesperson in a press release. The mass, named WDJ0551+4135, is estimated to be two-thirds the size of Earth but heavier than the sun.

The discovery, published Monday in the journal Nature Astronomy, is “the first time that a merged white dwarf has been identified using its atmospheric composition as a clue.”

Researchers analyzed data pulled from the European Space Agency’s Gaia telescope and the William Herschel Telescope to determine that this particular “white dwarf” star had an abnormally high level of carbon in its atmosphere. White dwarfs are left after a star like the sun burns out and sheds its outer layer. This star was nearly twice the average mass of a typical white dwarf star and moved faster than most nearby white dwarfs, which suggested it was older than others. When white dwarfs merge, the process occurs over billions of years, the Warwick press release said.

“This star stood out as something we had never seen before,” said Mark Hollands, from the University of Warwick Department of Physics. “We have a composition that we can’t explain through normal stellar evolution, a mass twice the average for a white dwarf, and a kinematic age older than that inferred from cooling. We’re pretty sure of how one star forms one white dwarf and it shouldn’t do this. The only way you can explain it is if it was formed through a merger of two white dwarfs.”

Artwork by yours truly https://t.co/ImWzMcJUfd

— Mark A. Garlick �� (@SpaceBoffin) March 2, 2020

Want to read the science behind the merging "snowman" white dwarf we announced yesterday? The paper is now on arXiv at https://t.co/dxTu52TXU6 - and see our press release at https://t.co/GFcayLVe4K pic.twitter.com/96hGi9ifh0

— Warwick Astro Group (@WarwickAstro) March 3, 2020

Hollands et al. have discovered an ultra-massive white dwarf that seems to break models of single-star evolution. We could be looking at the result of a WD-WD merger. https://t.co/Gy0kr6tGsv pic.twitter.com/DAMWOy9bhr

— Nature Astronomy (@NatureAstronomy) March 2, 2020