Scientists Spot Largest Supernova on Record in Distant Galaxy

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A supernova is, by definition, a huge event. We’re talking about exploding stars, after all. Still, some supernovae are bigger than others, and astronomers recently identified what appears to be the largest supernova we’ve ever observed. The event, dubbed SN2016iet, included a long duration, unusual chemical signatures, and more conundrums. The researchers believe this supernova could challenge our models of star death

Scientists from the European Space Agency (ESA) made the first sighting of SN2016iet in 2016 using the Gaia satellite. Astronomers from multiple institutions have used the last three years to study the data and make additional observations. In a new paper, scientists point to SN2016iet as the largest supernova ever seen, but it wasn’t easy to get there. SN2016iet was so out of character for a supernova that astronomers initially thought there could be something wrong with the data. 

SN2016iet exploded a long time ago in a galaxy far, far away. The team estimates its distance at about one billion light-years in a previously uncatalogued dwarf galaxy. It formed about 54,000 light-years from the center of that galaxy. It was among the largest of stars with a mass of at least 200 suns. As a supergiant star, its life was short, just a few million years. It lost about 85 percent of its mass during the final phase of its life.

Using the MMT Observatory and Magellan Telescopes at the Las Campanas Observatory in Chile, the team confirmed that SN2016iet looks so unusual in large part due to the material ejected prior to the supernova. The star formed a cocoon of matter around itself, and the supernova blast collided with that material. 

SN2016iet grew in brightness considerably when it finally exploded.

The team says this is an example of a pair-instability supernova, something long-theorized but never observed. In a pair-instability supernova, production of electrons and positrons inside the star temporarily reduces internal pressure, leading to a partial collapse and accelerated runaway nuclear reactions. The resulting explosion completely obliterates the star without leaving a black hole or other solar remnants. This can only happen with very large stars in metal-poor galaxies. 

Scientists will continue observing SN2016iet for years to come. Most supernovas fade away in a few months, but this one should be visible much longer, providing an unprecedented opportunity to better understand solar processes.

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