NASTY1 HAS A COMPANION STAR THAT HAS BEGUN CANNIBALIZING IT.
ASTRONOMERS ARE STUNNED, AS THIS ENTIRE UNIT SHOULD NOT EXIST!
NASA/ESA/G. Bacon (STScI)
"A star which has never been seen before in the Milky Way, or anywhere else for that matter, has been spotted by the Hubble Telescope. The star is around 3000 light-years away from Earth and many, many times larger than our own sun..
Although the star has been labelled as Wolf-Rayet 122, its nick name has been inspired from its catalogue name NaSt1 and how the star devours the outer ring full of hydrogen gas, from its neighbours.
The star was previously sighted, shrouded in a dense nebula of CNO-processed material, back in 1961 by astronomers Jason Nassau and Charles Stephenson. However thanks to Hubble Space Telescope’s narrow-band imaging and Wide-field Camera 3, clearer pictures emerged which revealed that the star has a disc surrounding it, which is approximately 2 trillion miles wide. Scientists believe that the present phase of the Wolf-Rayet 122, which has never been seen before, will most likely be a short-lived one."
Astronomers from NASA stated that they have never observed such a gas-like disc surrounding a Wolf-Rayet star and believe that the nebula is a couple of thousand years old
DISCOVERED DECADES AGO, IN 1963, THIS WOLF-RAYET SYSTEM IS FAR FROM THE NORM.
The star’s catalog name, NaSt1, is derived from the first two letters of each of the two astronomers who discovered it in 1963, Jason Nassau and Charles Stephenson.
Nasty 1 doesn’t look like a typical Wolf-Rayet star.
The astronomers using Hubble had expected to see twin lobes of gas flowing from opposite sides of the star, perhaps similar to those emanating from the massive star Eta Carinae, which is a Wolf-Rayet candidate.
Instead, Hubble revealed a pancake-shaped disk of gas encircling the star. The vast disk is nearly 2 trillion miles wide and may have formed from an unseen companion star that snacked on the outer envelope of the newly formed Wolf-Rayet.
“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 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 10 thousand years or less.”
According to the team’s scenario, a massive star evolves very quickly, and as it begins to run out of hydrogen, it swells up. Its outer hydrogen envelope becomes more loosely bound and vulnerable to gravitational stripping, or a type of stellar cannibalism, by the nearby companion star. In that process, the more compact star winds up gaining mass, and the original massive star loses its hydrogen envelope, exposing its helium core to become a Wolf-Rayet star.
“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. “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.”
Previous observations of Nasty 1 have provided some information on the gas in the disk. The material, for example, is traveling about 22,000 mph (35,400 km/h) in the outer nebula, slower than similar stars. The comparatively slow speed indicates that the star expelled its material through a less violent event than Eta Carinae’s explosive outbursts, where the gas is traveling hundreds of thousands of miles per hour.
Nasty 1 may also be shedding the material sporadically. Past studies in infrared light have shown evidence for a compact pocket of hot dust close to the central stars. Recent observations by Mauerhan and colleagues at the University of Arizona, using the Magellan telescope at Las Campanas Observatory in Chile, have resolved a larger pocket of cooler dust that may be indirectly scattering the light from the central stars. The presence of warm dust implies that it formed recently, perhaps in spurts, as chemically enriched material from the two stellar winds collides at different points, mixes, flows away, and cools. Sporadic changes in the wind strength or the rate the companion star strips the main star’s hydrogen envelope might also explain the clumpy structure and gaps seen farther out in the disk.
The chaotic mass-transfer activity will end when the Wolf-Rayet star runs out of material. Eventually, the gas in the disk will dissipate, providing a clear view of the binary 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.”
Viewing the Nasty 1 system hasn't been easy. The system is so heavily cloaked in gas and dust, it blocks even Hubble's view of the stars. So Mauerhan's team cannot measure the mass of each star, the distance between them, or the amount of material spilling onto the companion star.
To measure the hypersonic winds from each star, the astronomers turned to NASA's Chandra X-ray Observatory. The observations revealed scorching hot plasma, indicating that the winds from both stars are indeed colliding, creating high-energy shocks that glow in X-rays. These results are consistent with what astronomers have observed from other Wolf-Rayet systems.
Upper panels: MagAO Ks , L’ , and M’ images of NaSt1 in false color.
The images are 2.7 arcsec square in angular size and oriented in detector coordinates.
Lower panels: the Ks-band image of NaSt1 with logarithmic intensity contours (left) and the HST [N II] narrowband image with the Ks contours overlaid (right).
An ellipsoid of extended Ks emission is clearly resolved, and is approximately aligned with the major axis of the optical nebula.
The lower images are oriented with north up and east toward the left.
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