Astronomers detect shockwave from supernova

An international team of scientists recently discovered evidence of what they call “shock breakouts,” or the visible shockwave that occurs after the death of a star.

The team, led by Peter Garnavich of the University of Notre Dame, submitted their findings to Astrophysical Journal last week.

“This validates theoretical calculations of how supernovas work,” said research team member Ed Shaya in a phone interview with The Christian Science Monitor.

As stars run out of fuel at the end of their lives, the density of the core gets higher. Eventually the core becomes too heavy for the star to survive and it collapses, creating what is called a Type II supernova.

“Stars that are larger than eight times the mass of the sun will run out of mass in their center,” said Dr. Garnavich in a phone interview with the Monitor. “When that happens, their core collapses, and that collapse results in a shockwave that blows off the outer layers of the star.”

That shockwave is the “shock breakout” that astronomers have been hoping to spot for decades. According to NASA, the Kepler Space Telescope made this discovery possible.

Although shock breakouts were first proposed in a 1978 paper by a well-known astrophysicist named Roger Chevalier at the University of Virginia, and have been spotted using an X-ray telescope, says Garnavich, Kepler’s imaging capabilities allowed researchers to actually see the flash of a shock breakout for the first time in visible light.

“In order to see something that happens on timescales of minutes, like a shock breakout, you want to have a camera continuously monitoring the sky,” said Garnavich in a NASA press release. “You don’t know when a supernova is going to go off, and Kepler's vigilance allowed us to be a witness as the explosion began.”

Shock breakouts happen over the space of about 20 minutes, or the blink of an eye in astronomical terms. The team examined light data from 400 galaxies taken in by Kepler every half-hour over a three-year time span, beginning in 2011.

In all that time, they found six supernovas. Four occurred after the deaths of white dwarf stars – the stars were too small to create a shock breakout. Two, however, came after the deaths of red giant stars. The stars, KSN 2011a and KSN 2011d, are about a billion light years away from Earth, and are about 300 to 500 times the size of our sun, respectively.

Only one of the supernovas created a visible shock breakout. The other may have generated a shock breakout, but scientists were unable to see it due to a cloud of gas or dust obscuring their view.

“One had a rise to maximum light,” Garnavich told the Monitor, “and we suspect that it would have had a shock breakout but it had gas surrounding it.”

Why is it so important to understand this phenomenon when it only occurs for a specific sort of star, under specific conditions?

According to Steve Howell, Kepler’s project scientist, understanding supernovas is key to understanding the universe and its development.

“Supernovas teach us about the destiny of our universe, because they are incredibly large objects that we can see over great distances,” Dr. Howell told the Monitor by phone. “If we don’t understand how bright they are, and what happens to them, then we are using them, but we are using them incorrectly.”

In the NASA press release, Howell also reminded readers that supernovas create heavy elements that serve as some important building blocks for life, including life on Earth.

"Life exists because of supernovae,” he said.