Astronomers catch dwarf stars gobbling up their orbiting companions

As far as fairytales go, dwarfs can be Bashful, Sleepy, Grumpy or Dopey. But in space, dwarfs might be better called Hungry, according to a pair of studies published Monday in Nature Astronomy.

These are dwarf stars, of course. Some dwarf stars are small, dim stars that can be orbited by other dwarf stars or planets. Our own sun is a yellow dwarf star; other types include orange and red dwarfs. White, brown and (if proven to exist) blue dwarfs are the dead remnants of stars or failed stars. Understanding these stars and their remains is key to unlocking the history of galaxies—and planets.

In the new research, scientists describe two dwarf stars—one red dwarf and one white dwarf—seemingly acting out: eating the objects that orbit them.

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The observations “seek to understand the effect stars have on the planets that they host,” says Jamie Williams, lead author of one of the studies and a Ph.D. student at the University of Warwick in England.

“The key takeaway is that planets don’t exist in isolation, but their evolution is directly tied to the star they orbit,” he says. “In order to understand the life of planets, we must understand star-planet interactions.”

Williams and his colleagues observed a white dwarf that showed some unusual chemical signatures, including zinc, copper and niobium. At the same time, the star’s brightness seemed to dim periodically, suggesting an orbiting planet. Together, the results suggest the planet formed after the star had died and that its atmosphere is now feeding the white dwarf.

The finding suggests “planetary systems can experience a rebirth,” a phenomenon astronomers haven’t observed in our solar system before, Williams says.

The second study also reveals a never-before-seen interaction: a red dwarf slowly and steadily consuming its orbital object, a brown dwarf. Usually, either a star and its companion mind their own business or the star completely and rapidly devours its neighbor. In this system, material seems to be flowing from the brown dwarf to the red dwarf in a process that could continue for millions of years.

The discovery was “a happy accident,” says Aaron Householder, lead author of that study and a graduate student at the Massachusetts Institute of Technology. Now that the team has observed this, Householder adds, he’s curious what else is out there.

“We’re excited to see if we can find a star eating a planet or maybe even two planets eating each other—different types of combinations of these objects,” he says.

Both studies have implications for our own planet. A second-generation planet could theoretically form after our own sun dies, Williams says. Meanwhile, Householder’s research suggests that rather than make a quick and fiery meal of Earth, the sun might one day nibble away at our atmosphere.

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