A supernova brighter and larger than any other on record has been discovered by scientists at the Center for Astrophysics, a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory.
A supernova is an extremely bright and powerful explosion of a dying, massive star that’s at least five times the mass of the sun, according to NASA. Enormous stars burn large amounts of nuclear energy at their cores, which in turn makes the centers very hot. The heat generates outward pressure that prevents the star from collapsing.
However, that pressure has something to fight against as a star’s gravity tries to compact it into the smallest, tightest ball possible. When a star runs out of energy, and thus heat, the pressure drops and gravity takes over. The star then collapses, creating shock waves that cause the outer part of the star to explode.
The researchers spotted this super bright supernova in 2016 using data from the Panoramic Survey Telescopes and Rapid Response System. Pan-STARRS is located at the Haleakala Observatory in Hawaii and consists of telescopes, astronomical cameras and a computing facility that continually survey the sky for objects and offer data on them.
The research team measured the newly discovered supernova using two scales: The total energy of the explosion, and the radiation – or the amount of the explosion’s energy that’s visible as light, according to a study published Monday in the journal Nature Astronomy.
The light emitted in ordinary supernovae is usually less than 1% of the total energy. But this supernova, called SN2016aps, radiated more than five times the explosion energy of a typical supernova. After observing the explosion for two years, the scientists found the mass was between 50 to 100 times greater than the sun. The mass of a normal-sized supernova is between eight to 15 times greater.
The researchers were searching the night sky trying to pick out the “most exotic and the most rare types of supernova explosions,” Edo Berger, professor of astronomy at Harvard University and co-author of the study, said.
“This is one of the best examples we’ve had,” he added. “This is the type of event we estimate is something like one in 1,000 to one in 10,000 stars end their life in this way. So this is an extremely rare type of explosion and incredibly energetic. And this is exactly what we set out to find.”
A rare object
The astronomers chose to follow up on this supernova because it seemed to be in the middle of nowhere. But as it turns out, the supernova only appeared to be without celestial neighbors because it outshone its own host galaxy.
The galaxy in which the explosion was found doesn’t have a name yet. But for now, we know the galaxy is about four billion light years away and is very reminiscent of the Magellanic Clouds, two dwarf galaxies that orbit our own galaxy, Berger said.
Because of its mass and brightness, the star could be a model of a pulsational pair-instability supernova – a supernova event that occurs in stars at around 100 to 130 solar mass, the authors wrote in the study. This is incredibly rare for two reasons, Berger said.
“To get to the regime where stars can experience this type of explosion, they need to be born with incredibly high masses. At least 70 times the mass of our sun and maybe up to 250 times the mass of the sun,” Berger said. “So stars like that are just incredibly rare. The other ingredient that’s required is that the stars need to be born from gas that has low metal content. So it hasn’t been enriched by previous generations of a lot of supernova explosions in order to build up these very massive stars.
“In the Milky Way Galaxy, which has experienced a lot of supernova explosions over its lifetime, we don’t actually see stars like this. So the only way we can study them is by finding them when they explode in other galaxies,” Berger said. “That’s why these pulsational pair-instability and these pair-instability supernovae are so rare. They need these very special conditions that only allow one in 10,000 stars to achieve that.”
The star’s incredible size may be attributable to two smaller (but still huge) stars that merged before the explosion, the study said.
When a star explodes, usually a nebula or black hole is left behind. But because SN2016aps is so bright and massive, it’s taking years to fade enough to let astronomers see what’s behind it.
“These galaxies are collections of 100 billion stars,” Berger said. “And yet this one supernova explosion outshone the entire galaxy for more than two years.”
We’re just now seeing the supernova, although it technically occurred four billion years ago, because it took this long for its light to reach us.
The future of space exploration
Discovering events like this explosion is “starting to get us on a track of understanding what these stars are doing in the last few moments of their lives,” Berger said.
“This is amazing [that] a star like this probably lives somewhere between five and 10 million years ago, and we’re seeing that in the very last, tiny fraction of that entire lifetime this star is becoming incredibly unstable,” he added. “That to me is one of the questions that’s kind of driving the need to find more of these types of explosions.”
A separate study published Monday in Nature Astronomy found novae – a star that increases in brightness, then fades to normal over time – illuminate the sky via the shocks from explosions that create them.
Because SN2016aps was so luminous, we’re very likely to be able to see other supernovae with next generation technology such as the Large Sypnotic Survey Telescope and NASA’s James Webb Space Telescope, Berger said.
“Now that we know something like this exists in the universe, it gives us hope that with these next generation facilities, which are only two, three years away from being available, we might be able to see similar explosions like this from the first few hundred million years after the Big Bang.”