Astronomers Discover White Dwarf Supernovae

Lee Rannals for — Your Universe Online

White dwarf supernovae that occurred millions of years ago have popped up in the Virgo Cluster galaxy and part of the sky labelled as “anonymous.”

Southern Methodist University (SMU) researchers say they’ve confirmed two bright stars that showed up in our skies in February and November are supernovae. Supernovae are the result of stars that have reached the end of their life, resulting in a large explosion that can consume anything in its path.

In November, Farley Ferrante, a graduate student at SMU, made the initial observation of a supernova, Supernova 2012ha or “Sherpa,” that derived from the Virgo constellation, about 230 million light years away. Another supernova, Supernova 2013X or “Everest,” was discovered on February 6, sitting 450 million years away in a part of the sky labeled “animus” near the faint constellation Canes Venatici.

“Everest and Sherpa aren´t noteworthy for being the youngest, oldest, closest, furthest or biggest supernovae ever observed,” Ferrante said. “But both, like other supernovae of their kind, are important because they provide us with information for further science.”

Both supernovae are considered Type 1a, which are the result of white dwarf explosions. A white dwarf star has a mass comparable to that of the Sun and its core is a comparable size to that of the Earth. According to Robert Kehoe, physics professor and leader of the SMU astronomy team in the SMU Department of Physics, a teaspoon of a white dwarf star would weigh about as much as Mount Everest.

When a white dwarf heads towards the end of its life, it grows to about one and a half times the size of the sun and eventually collapses and explodes, resulting in a Type 1a supernova.

“We call these Type 1a supernovae standard candles,” Ferrante said. “Since Type 1a supernovae begin from this standard process, their intrinsic brightness is very similar. So they become a device by which scientists can measure cosmic distance. From Earth, we measure the light intensity of the exploded star. As star distances from Earth increase, their brilliance diminishes.”

He said while Sherpa is a standard Type 1a, Everest is the result of two white dwarfs that collide, and then merge. Sherpa reached a brightness magnitude of 16, dimmer than the eye can see, while Everest’s explosion reached magnitude 18. Astronomers use this scale as a class to describe the brightness of an object in the sky.

Ferrrante says discoveries of supernovae like Everest and Sherpa allow scientists to have a little more information about the mysteries regarding dark energy, which is thought to make up about 73 percent of the mass-energy in the universe.

“Every exploding star observed allows astronomers to more precisely calibrate the increasing speed at which our universe is expanding,” Ferrante said. “The older the explosion, the farther away, the closer it was to the Big Bang and the better it helps us understand dark energy.”

Supernovae are so powerful, their explosions can be felt from very far away in the universe. Recently, scientists believe the Cassini spacecraft witnessed a shockwave from the aftermath of a supernova on Saturn. Cassini is a European Space Agency satellite that orbits Saturn.

Scientists wrote in the journal Nature Physics that Cassini detected a jump in subatomic particles around Saturn, hinting at the possibility the planet may have experienced the effects of a Supernova. This was the strongest shock wave ever encountered on Saturn, based on the data we currently have about the planet.