This is the most massive star ever destroyed by a supernova

In November 2016, the European Space Agency's Gaia satellite spotted something intriguing. Astronomers used follow-up observations over the past three years in an attempt to understand what they saw.

Supernova SN2016iet challenged their expectations, and now, astronomers believe that it's the remnants of the most massive star to be destroyed by a supernova, according to a study published Thursday in The Astrophysical Journal.

The supernova has a large amount of energy, long duration, unexpected chemical signatures and a metal-poor environment. That doesn't match up with anything astronomers have observed before.

"When we first realized how thoroughly unusual SN2016iet is my reaction was 'whoa -- did something go horribly wrong with our data?' " said lead study author Sebastian Gomez, a Harvard University graduate student. "After a while we determined that SN2016iet is an incredible mystery, located in a previously uncatalogued galaxy one billion light years from Earth."

Multiple telescopes were used to observe the supernova, including the Magellan Telescopes at Las Campanas Observatory in Chile and the Center for Astrophysics Harvard and Smithsonian's MMT Observatory in Arizona.

"Everything about this supernova looks different -- its change in brightness with time, its spectrum, the galaxy it is located in, and even where it's located within its galaxy, said study co-author Edo Berger, a Harvard University astronomy professor. "We sometimes see supernovas that are unusual in one respect, but otherwise are normal; this one is unique in every possible way."

Before the explosion, the star was 200 times the mass of our sun. Astronomers believe it formed by itself 54,000 light-years from the center of a dwarf galaxy, which is also mysterious.

In terms of a star's life, this one was short. It lasted only a few million years, losing 85% of its mass over that time. Then, when the star exploded, the debris collided with the material the star had shed over time, creating the strange appearance of the supernova that's visible to astronomers today.

"The idea of pair-instability supernovas has been around for decades," Berger said. "But finally having the first observational example that puts a dying star in the right regime of mass, with the right behavior, and in a metal-poor dwarf galaxy is an incredible step forward. SN2016iet represents the way in which the most massive stars in the universe, including the first stars, die."

Astronomers have yet to find the first stars because none of them probably exist anymore, exploding in supernovae to populate the universe with heavy elements. Studying this supernova can inform astronomers about what those stars were like and how they died.

The astronomers will continue observing this supernova to learn more about how it formed and how it could change in the future.

"Most supernovas fade away and become invisible against the glare of their host galaxies within a few months. But because SN2016iet is so bright and so isolated we can study its evolution for years to come," Gomez said. "These observations are already in progress and we can't wait to see what other surprises this supernova has in store for us."