Bizarre White Dwarf Leaves Metallic Marks Following Consumption of Planet

Astronomers have discovered a white dwarf star with strange metallic scars on its surface. The scar likely formed when the star tore apart and ate a small planet in its orbit.

Researchers often find white dwarfs with traces of metal in their atmospheres that came from planets that fell into the star. It has long been thought that metals should be evenly distributed across the surfaces of these so-called contaminated white dwarfs; Jay Farihi Researchers at University College London have discovered a strange concentration of metal debris.

Researchers monitored the star, called WD 0816-310, for two months using the Very Large Telescope in Chile. They discovered that the white dwarf had an opaque piece of metal on top of one of its magnetic poles, blocking some of the star’s light as it rotated. This position indicates that material may have been funneled into the star by its magnetic field. “This is the same process that causes auroras on Earth: charged particles follow magnetic fields to the surface,” Farihi said.

The planet that WD 0816-310 destroyed was small, probably about the same size as the solar system’s asteroid Vesta, which is about 525 kilometers in diameter. Its interior is now prominently displayed on its host star, which could make it relatively easy to study what its geochemistry was like before it was engulfed. Such studies may even be one of the best ways to observe small worlds outside our solar system, even after they disappear.

And there may be many other stars that have been similarly damaged. “When we find something outlandish, it’s often because they all looked that way and we just weren’t asking the right questions,” Farihi says. “This is the first, but it probably won’t be the last.” In fact, researchers have already discovered two white dwarfs that appear to have similar scars. If we go back and observe similar stars over and over again, we may discover even more stars.