Astronomers using the Hubble Space Telescope have found surprising new clues about a large, fast aging star that has never been seen before in the Milky Way galaxy. In fact, the star is so different that astronomers have nicknamed it "Nasty 1," a play on its catalog name of NaSt1. This strange star may represent a brief transitory stage in the evolution of extremely massive stars.
The star was first discovered decades ago when it was identified as a Wolf-Rayet star, a rapidly evolving star that is more massive than the sun. The star loses its hydrogen out layers quickly, exposing its super-hot and extremely bright helium burning core. But Nasty 1 doesn't look like a typical Wolf-Rayet star.
"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."
In the research teams proposed scenario, the massive star evolves quickly but as it begins to run out of hydrogen, it swells. This can happen much faster compared to the life of other stars and researchers estimate that Nasty 1 is only a few thousand years old and is located approximately 3,000 light years from Earth.
"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, who is a co-author on the new NaSt1 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."
Observing Nasty 1 hasn't been easy. The system is so heavily covered by gas and dust that it even often blocks the Hubble's view of the system.
"What evolutionary path the star will take is uncertain, but it will definitely not be boring," said Mauerhan. "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."