Hubble spots a sloppy, Nasty star in Milky Way

22 May 2015

Illustration of Nasty 1 binary star system via NASA, ESA, and G. Bacon (STScI)

There are few things nastier in the universe than ‘Nasty 1’, a star that is ageing so rapidly and acting in such a peculiar way that its formal name – NaSt1 – led to it being dubbed our galaxy’s nasty star.

At over 3,000 light years away from Earth, Nasty 1 was first discovered over 70 years ago as a rapidly-evolving star that overshadows the size of our own sun multiple times over.

Known as a Wolf-Rayet star, the Hubble Space Telescope was called into action to take a look at the Milky Way’s nasty resident and had expected to see twin lobes of gas flowing from opposite sides of the star, common among Wolf-Rayet stars.

However, Hubble actually revealed a pancake-shaped disk of gas encircling the star with a width of 2trn miles that NASA says may have formed from an unseen companion star that snacked on the outer envelope of the newly-formed star.

Researchers analysing Nasty 1 believe that a Wolf-Rayet star is most likely born out of an example of stellar cannibalism after one massive star burns too fast and bright and as it expands after losing its hydrogen, is absorbed by the gravitational mass of the nearby smaller companion star and exposing the original star’s helium core.

Nasty 1 diagram

Diagram of Nasty 1 via J. Mauerhan (University of California, Berkeley)

Nasty star is rather sloppy

Another, more troublesome theory for researchers is that a massive star ejects its own hydrogen envelope in a strong stellar wind streaming with charged particles.

The binary interaction model where a companion star is present is gaining traction because astronomers realise that at least 70pc of massive stars are members of double-star systems.

“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 publishing the latest Hubble Space Telescope findings. “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.”

However, Jon Mauerhan of the University of California, Berkeley believes the disk that surrounds Nasty 1 suggests a much sloppier process: “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.”

The team will now just have to wait and see how Nasty’s sloppiness plays out before they can view the binary star system.

Colm Gorey was a senior journalist with Silicon Republic