A star that scientists have long referred to as "Nasty 1" is starting to live up to its weird nickname, scientists have said, after observations from the Hubble Space Telescope revealed that the massive, mysterious star is surrounded by a huge, pancake-shaped disk of gas.
That's not what you'd expect from a Wolf-Rayet star like ol' Nasty, a team of astronomers said in a new paper published in the Monthly Notices of the Royal Astronomical Society earlier this week. Typically, Wolf-Rayet stars appear as "twin lobes of gas flowing from opposite sides of the star," as the massive, late-stage stars lose all their hydrogen-heavy outer layers, exposing a bright helium-burning core.
Scientists haven't seen a disk like this around a Wolf-Rayet before. The disk "may be evidence for a Wolf-Rayet star forming from a binary interaction," lead researcher Jon Mauerhan, of the University of California at Berkeley, said in a statement. In other words, there's another star eating up all that tasty gas Nasty is letting off. There are "very few examples in the galaxy of this process in action," Mauerhan explained, partially because the phase doesn't last for a very long time. The process itself might last about 100,000 years, producing a visible disk for under 10,000 years, he said.
The researchers believe the nebula around Nasty 1 is a few thousand years old. The star system might be as close as 3,000 light years away from us.
As scientists continue to study Wolf-Rayet stars, they're learning that more and more of them are likely part of a binary system like Nasty 1 appears to be. At least 70 percent of the massive stars in the galaxy are part of two-star systems, the researchers explain. A large star at least 20 times the mass of the sun, towards the end of its life, could become a Wolf-Rayet as it expands and loosens its grip on its own outer hydrogen envelope. That hydrogen could be pulled away from the star by the gravitational pull of a companion star. The companion star then begins to gain mass.
By observing Nasty, the researchers hope they'll learn even more about how this process works. The heavy gas encircling Nasty, however, makes it difficult for astronomers to get a clear view of the two stars themselves through Hubble.
Here's what Hubble sees when it looks at the system:
"We think there is a Wolf-Rayet star buried inside the nebula, and we think the nebula is being created by this mass-transfer process. So this type of sloppy stellar cannibalism actually makes Nasty 1 a rather fitting nickname," Maurhan said.
Scientists don't know what will happen to Nasty 1 as this stellar snack time continues and the cannibalizing companion star runs out of matter to eat. "But it will definitely not be boring," Mauerhan said.
"Nasty 1 could evolve into another Eta Carinae-type system," Mauerhan said, referring to a nearby system that contains one of the brightest stars in our galaxy. "To make that transformation, the mass-gaining companion star could experience a giant eruption because of some instability related to the acquiring of matter from the newly-formed Wolf-Rayet," he said. The star system might also result in a stellar merger.
"Or, the Wolf-Rayet could explode as a supernova." Mauerhan explained. "The future could be full of all kinds of exotic possibilities depending on whether it blows up or how long the mass transfer occurs, and how long it lives after the mass transfer ceases."
The nickname, by the way, comes from the star's catalog name, NaSt1, after Jason Nassau and Charles Stephenson, who first spotted it in 1963.