Six thousand years ago, in a distant part of the Milky Way galaxy, a “death star” exploded with cataclysmic force, annihilating any life forms within perhaps a 50-light year radius. For a few weeks, the star briefly shined brighter than 100 million suns.
It wasn’t until 1604 that the light from the star, called the Kepler Supernova, reached the earth. Today, its remnants are known as Cassiopeia A or, less formally, Cassio. These remnants are a focus of study for researchers at the University.
“We’ve been watching (Cassio) for almost 20 years now, so we can see this thing change over time,” said Tom Jones, chairman of the astronomy department. “We can figure out from that what the motions are going on inside of it, how much energy there is and how it’s sweeping up the material around it.”
Using simulations produced on a supercomputer, Jones and fellow researchers at the University have analyzed how radio waves and cosmic rays are produced in supernova remnants.
Stars are normally powered by the fusion of smaller atomic nuclei, such as hydrogen, to form larger atomic nuclei, such as helium, iron and nickel. When a star has used up this source of fuel, it begins to collapse.
The energy of collapse leads to a complex series of reactions. If the star is at least 12 times the size of the sun, these reactions release so much energy that the star “goes supernova.”
“You can’t see (Cassio) with your eye, but as a radio source, it’s the second-brightest source in the sky after the sun,” said Jones.
In visible light, Cassio is obscured by interstellar dust. But radio and X-rays can pass through such dust.
“The best way to observe supernova remnants is radio sources,” said Jones.
University researchers have produced a paper that provides the most complete available description of how radio emissions are produced by supernova remnants, said Jones.
This description is based on computer simulations of supernovas that were created using the facilities of the University’s Minnesota Supercomputer Center.
“We simulate (supernova) explosions and test them against the observations,” said Jones, before revising the simulation.
It takes hundreds of hours of supercomputer time to create a simulation of this type. Jones receives $80,000 to $100,000 a year from the National Science Foundation.
Beside electromagnetic radiation, supernovas send out a barrage of high-energy subatomic particles called cosmic rays.
“We have published the most sophisticated computations of the production of cosmic ray particles in a supernova explosion,” said Jones.
Supernovas can also take credit for the formation of many of the materials essential for the creation of life.
“All the elements that are on the earth,” said Lawrence Rudnick, an astronomy professor, “were made in the cores of stars and released — a lot of them — through supernova explosions.”
Scientists believe that the solar system condensed from a cloud of dust and gas that was created by a supernova.
If a nearby star went supernova today, it could be all over for life on earth before humanity even knew what hit it.
“The thing that would get you would be the X-rays,” said Jones. “By the time you knew about it, it would be too late.”
The nearest star, which is considered a likely supernova candidate, is Alpha Crucis in the southern hemisphere, about 400 light years away — probably a safe distance, said Rudnick.