More than 50 years ago, NaSt1 was discovered by Jason Nassau and Charles Stephenson and classified as a Wolf-Rayet star. 50 years later, NaSt1 is surprising astronomers and is getting a nickname – ‘Nasty 1.’
You’re probably wondering what is a Wolf-Rayet star? This type of star quickly evolves and is a lot bigger than our sun. Wolf-Rayet stars lose their hydrogen-filled layers fast, leaving its extremely bright helium-burning core exposed.
NASA’s Hubble Space Telescope shows this Wolf-Rayet star is rather unique. Its “behavior has never been seen before in our galaxy,” according to NASA.
When observing the star, astronomers expected to see twin lobes of gas flowing from opposite sides of it. This is what they see from Eta Carinae, a Wolf-Rayet candidate star. Instead, astronomers were greeted by a 2 trillion miles wide pancake-shaped disk of gas circling the star.
Why the disk? Astronomers think an unseen companion star may have taken a few cosmic bites out of NaSt1.
“We were excited to see this disk-like structure because it may be evidence for a Wolf-Rayet star-forming from a binary interaction,” said study leader Jon Mauerhan of the University of California, Berkeley. “There are very few examples in the galaxy of this process in action because this phase is short-lived, perhaps lasting only a hundred thousand years, while the timescale over which a resulting disk is visible could be only ten thousand years or less.”
Raw image from the Hubble. (NASA)
Current estimates put the age of the gas disk at just a few thousand years old. Plus, it may be close – about 3,000 light-years from Earth.
A companion star is a must in astronomers’ current theory for Nasty 1. A compact companion star would be able to strip Nasty 1’s outer hydrogen envelope and expose its helium core.
The traditional method of Wolf-Rayet star formation focuses on stellar wind, but that theory isn’t holding up.
“We’re finding that it is hard to form all the Wolf-Rayet stars we observe by the traditional wind mechanism, because mass loss isn’t as strong as we used to think,” said Nathan Smith of the University of Arizona in Tucson, co-author of the NaSt 1 paper. “Mass exchange in binary systems seems to be vital to account for Wolf-Rayet stars and the supernovae they make, and catching binary stars in this short-lived phase will help us understand this process.”
This exchange isn’t always smooth. The massive gas disk around Nasty 1 is a byproduct of the cosmic wrestling match between the pair of stars.
“That’s what we think is happening in Nasty 1,” Mauerhan said. “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.”
What’s next for Nasty 1? Mauerhan isn’t sure, but he promises it will be epic:
“Nasty 1 could evolve into another Eta Carinae-type system. 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. Or, the Wolf-Rayet could explode as a supernova. A stellar merger is another potential outcome, depending on the orbital evolution of the system. 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.”