A Cosmic Explosion Brighter than the Core of the Milky Way

SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA's Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist's illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy.
SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA’s Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist’s illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy. Credits: NASA/ESA/Chandra/Lick/

Hypernova SN 2006gy was over a hundred times brighter than a typical supernova  

Space news (astrophysics: hypernovae; one of the brightest ever, SN 2006gy) – 240 million light-years toward the constellation Perseus in galaxy NGC 1260 –  

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Watch this animation of SN 2006gy. Credits: NASA/ESA/Chandra.

It all started in September of 2006 when a fourth-year University of Texas graduate student astronomer working for the Palomar Transient Factory’s (PTF) luminous supernova program Robert Quimby discovered the brightest celestial event up to this date. An exploding star over 100 times brighter than a normal supernova and shining brighter than the core of its host galaxy NGC 1260. 

SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA's Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist's illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy.
SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA’s Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist’s illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy. Credits: NASA/ESA/Chandra/Lick/Keck.

“This was a truly monstrous explosion, a hundred times more energetic than a typical supernova,” said Nathan Smith of the University of California at Berkeley, who led a team of astronomers from California and the University of Texas at Austin. “That means the star that exploded might have been as massive as a star can get, about 150 times that of our sun. We’ve never seen that before.”  

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Nathan Smith of the University of California at Berkeley. Credit: University of California at Berkeley/NASA

Teams of astronomers working with the Katzman Automatic Imaging Telescope at the Lick Observatory on Mt. Hamilton in California and M.W. Keck Observatory near the summit of Mauna Kea on the island of Hawaii immediately began observing the event designated supernova SN 2006gy. Analysis of data showed it occurred over 240 million light-years away in galaxy NGC 1260 and took 70 days to reach maximum brightness. Staying brighter than any previously recorded event for over three months, SN 2006gy was still as bright as a normal supernova eight months later. 

SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA's Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist's illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy.
SN 2006gy is the brightest stellar explosion ever recorded and may be a long-sought new type of supernova, according to observations by NASA’s Chandra X-ray Observatory (bottom right panel) and ground-based optical telescopes (bottom left). This discovery indicates that violent explosions of extremely massive stars, depicted in the artist’s illustration (top panel), were relatively common in the early universe. These data also suggest that a similar explosion may be ready to go off in our own Galaxy. Credits: NASA/ESA/Chandra/Lick/Keck.

“Of all exploding stars ever observed, this was the king,” said Alex Filippenko, leader of the ground-based observations at the Lick Observatory at Mt. Hamilton, Calif., and the Keck Observatory in Mauna Kea, Hawaii. “We were astonished to see how bright it got, and how long it lasted.”  

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Alex Filippenko, professor of astronomy for University of California, Berkeley. Credits: University of California, Berkeley.

Astronomers were reasonably sure at this point the progenitor of supernova SN 2006gy was one of the largest, most massive types of stars ever to exist. But they needed to rule out the most likely alternative explanation for the event. The possibility a white dwarf star with a mass slightly higher than Sol went supernova in a dense, hydrogen-rich environment.  

Another team of astronomers using the Chandra X-ray Observatory went to work at this point to rule this possibility out of their equations. If this was the case, they knew X-ray emission from the event should be at least 1,000 times more luminous than the readings they were getting.     

“This provides strong evidence that SN 2006gy was, in fact, the death of an extremely massive star,” said Dave Pooley of the University of California at Berkeley, who led the Chandra observations. 

The progenitor star for SN 2006gy is thought to have ejected a large volume of mass before the hypernova event occurred. This is similar to events observed by astronomers in the case of Eta Carinae, a nearby supermassive star they’re watching closely for signs of an impending supernova. Only 7,500 light-years toward the constellation Carina, compared to 240 million for galaxy NGC 1260, this star going supernova would be the celestial event of the century on Earth. It would be bright enough to see in the daylight sky.

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Mario Livio is an internationally known astrophysicist, a bestselling author, and a popular lecturer. Credits: MarioLivio.com

“We don’t know for sure if Eta Carinae will explode soon, but we had better keep a close eye on it just in case,” said Mario Livio of the Space Telescope Science Institute in Baltimore, who was not involved in the research. “Eta Carinae’s explosion could be the best star-show in the history of modern civilization.” 

The massive star Eta Carinae (almost hidden in the center) underwent a giant explosion some 150 years ago. The outburst spread the material that is visible today in this very sharp Hubble image. Even though Eta Carinae is more than 8,000 light-years away, structures only 15 thousand million kilometre across (about the diameter of our solar system) can be distinguished. Dust lanes, tiny condensations, and strange radial streaks al appear with unprecedented clarity. A huge, billowing pair of gas and dust clouds are captured in this stunning Hubble Space Telescope image of the supermassive star Eta Carinae. Credit: Jon Morse (University of Colorado), and NASA/ESA
The massive star Eta Carinae (almost hidden in the center) underwent a giant explosion some 150 years ago. The outburst spread the material that is visible today in this very sharp Hubble image. Even though Eta Carinae is more than 8,000 light-years away, structures only 15 thousand million kilometre across (about the diameter of our solar system) can be distinguished. Dust lanes, tiny condensations, and strange radial streaks al appear with unprecedented clarity.
A huge, billowing pair of gas and dust clouds are captured in this stunning Hubble Space Telescope image of the supermassive star Eta Carinae.
Credit:
Jon Morse (University of Colorado), and NASA/ESA

So many questions

Astronomers think in the case of hypernova SN 2006gy things might have taken a slightly different pathway than previously recorded supernovae. Some scientists think the massive star that exploded could be much more like the supermassive stars that existed during the early moments of the cosmos. Supermassive stars that exploded in supernovae and spread the elements of creation across the cosmos, rather than collapsing to a black hole as theorized.  

“In terms of the effect on the early universe, there’s a huge difference between these two possibilities,” said Smith. “One [sprinkles] the galaxy with large quantities of newly made elements and the other locks them up forever in a black hole.” 

Why would these supermassive stars be different than other huge stars observed in the Milky Way? The human search for answers to these and other mysterious questions before us continues as we journey backward to the beginning of space and time. 

We’ll update you with any additional data astronomers come across as the journey continues. Until next time, keep dreaming of the possibilities. 

Warren Wong 

Editor and Chief 

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Wolf-Rayet Star “Nasty 1” Transitional Stage in Evolution of Massive Stars

A very rapidly evolving, supermassive star with a newly formed nebula only a few thousand years old

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Space news (supermassive stars: Wolf-Rayet stars; star NaSt1) – 3,000 light-years away on the edge of a pancake-shaped disk of gas moving at 22,000 mph – 

Astronomers using the Hubble Space Telescope have discovered new clues concerning a nearby supermassive, rapidly aging star they have nicknamed “Nasty 1”. Designated NaSt1 in astronomy catalogs, “Nasty 1” when first discovered decades ago was identified as a non-typical Wolf-Rayet star with an orbiting disk-like structure. A vast disk estimated to be almost 2 trillion miles wide astronomers now think formed due to a companion star snacking on its outer envelope. Putting NaSt1 in a class of Wolf-Rayet stars astronomers haven’t observed often during the human journey to the beginning of space and time. A star type possibly representing a transition stage in the evolution of supermassive stars. 

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“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.” 

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Study leader Jon Mauerhan of the University of California, Berkley. Credit: University of California, Berkley.

In the case of NaSt1, computer simulations show a supermassive star evolving really fast and swelling as it begins to run out of hydrogen. Its outer hydrogen envelope is loosely bound and is gravitationally stripped from the star- astronomers call this process stellar cannibalism – by a more compact, nearby companion star. In the process the more compact star gains mass, while the more massive star loses its hydrogen envelope, exposing its helium core and eventually becoming a Wolf-Rayet star. 

The mass-transfer model is the favored process for how Wolf-Rayet stars evolve at the moment and considering at least 70 percent of supermassive stars detected, so far, are members of binary star system, this seems logical. Astronomers used to think this type of star could also form when a massive sun ejects its hydrogen envelope. But the direct mass loss model by itself can’t account for the number of Wolf-Rayet stars observed relative to less-evolved supermassive suns in the Milky Way.  

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“We’re finding that it is hard to form all the Wolf-Rayet stars we observe by the traditional wind mechanism because the 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.” 

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Co-author of study Nathan Smith of the University of Arizona in Tucson. Credit: The University of Arizona.

Astronomers computer models show that the mass-transfer process isn’t always perfectly efficient. Matter can only transfer from NaSt1 at a certain rate, left over material begins orbiting, creating a disk-like structure. 

“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.” 

Observing Nasty 1 (star NaSt1) through the clock of gas and dust surrounding this star system hasn’t been easy. The intervening disk-like structure even blocks the view of the Hubble Space Telescope. Scientists haven’t been able to measure the distance between the stars, their mass, or the volume of material transferring to the smaller companion star.  

Astronomers have been able to discover a few items concerning the disk-like structure surrounding Nasty 1. Measurements indicate it’s traveling at around 22,000 mph in the outer nebula, a slower speed than recorded in other stars of this type. Scientists think this indicates a much less energetic supernova than was recorded for other events, like Era Carinae. In this case and other similar stars, the gas in the outer nebula has been recorded in the hundreds of thousands of miles per hour. Nasty 1 could be different supernova animal altogether.  

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High atop the Cerro Manqui peak at the Las Campanas Observatory in Chile the twin the Walter Baade Telescope is the first of the twin 6.5-meter Magellan telescopes to be completed. Credit: Ico.cl

Nasty 1 could also lose its outer envelope of hydrogen intermittently. Previous studies in the infrared light provided clues indicating the existence of a dense pocket of hot gas and dust close to the central stars in the region. More recent observations using the Magellan Telescope located at the Las Campanas Observatory in Chile has also detected a bigger pocket of cooler gas and dust possibly indirectly blocking light from these stars. Astronomers think the existence of warm dust in the region implies it formed just recently, perhaps intermittently, as elementally enriched matter from the stellar winds of massive stars collides, mixes, flows away, and cools. Irregular stellar wind strength, the rate at which star NaSt1 loses its outer envelope, could also help explain the observed clumpy structure and gaps noted in the outer regions of the disk.  

Astrophysicists used NASA’s Chandra X-ray Observatory to measure the hypersonic winds screaming from each star. Readings showed a scorching hot plasma, indicating colliding stellar winds producing high-energy shockwaves that glow in X-rays. This is consistent with previous data collected on other evolving Wolf-Rayet star systems. We’ll get a better view once the outer hydrogen of Nasty 1’s (star NaSt1) depleted, and the mass-transfer process completes. Eventually, the gas and dust in the lumpy, disk-like structure will dissipate, giving us a clearer view of this mysterious binary star system.   

 

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NASA’s Chandra X-ray Observatory has shown the cosmos is full of objects and events far beyond anything we imagined when we first started the human journey to the beginning of space and time. Credit: NASA/Chandra

Nasty 1’s still evolving!

“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.” 

Astronomers continue to study Nasty 1 and its peculiar, unusual disk-like structure looking for clues to explain the mysteries surrounding its origin. 

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