Astronomers glimpse supernova shockwave for the first time

Australian National University

22 March 2016 Astronomy Now

The brilliant flash of an exploding star’s shockwave — what astronomers call the “shock breakout” — has been captured for the first time in visible light by NASA's planet-hunter, the Kepler space telescope. Simulation credit: NASA/STSci.
The brilliant flash of an exploding star’s shockwave — what astronomers call the “shock breakout” — has been captured for the first time in visible light by NASA’s planet-hunter, the Kepler space telescope. Simulation credit: NASA/STSci.
Astronomers have captured the earliest minutes of two exploding stars and for the first time seen a shockwave generated by a star’s collapsing core.

The international team found a supernova shock wave — or shock breakout — only in the larger supernova, a finding that will help them understand these complex explosions that create many of the elements that make up humans, the Earth and the Solar System.

Dr. Brad Tucker. Image credit: Stuart Hay, Australian National University.
Dr Brad Tucker. Image credit: Stuart Hay, Australian National University.
“It’s like the shockwave from a nuclear bomb, only much bigger, and no one gets hurt,” said Dr Brad Tucker, from ANU Research School of Astronomy and Astrophysics.

Supernovae like these — known as Type II — begin when the internal furnace of a star runs out of nuclear fuel causing its core to collapse as gravity takes over.

Supernovae are so bright that they can be seen in distant galaxies, which has helped astronomers learn much about the large-scale structure of the universe. However, very little is known about the early stages of these explosions.

The research, published in the Astrophysical Journal, reports the explosions of two old-age stars, red supergiants.

As the core of a supernova collapses to form a neutron star, energy bounces back from the core in the form of a shockwave that travels at 30,000 to 40,000 kilometres per second, and causes the nuclear fusion that creates heavy elements such as gold, silver and uranium.

The diagram illustrates the brightness of a supernova event relative to the Sun as the supernova unfolds over time. For the first time, a supernova shock wave, or shock breakout, has been observed in visible light wavelengths as it reached the surface of the star from deep within the star's core. The explosive death of this star, called KSN 2011d, reached its maximum brightness in about 14 days. The shock breakout itself lasted only about 20 minutes (see inset). Illustration credit: NASA Ames/W. Stenzel.
The diagram illustrates the brightness of a supernova event relative to the Sun as the supernova unfolds over time. For the first time, a supernova shock wave, or shock breakout, has been observed in visible light wavelengths as it reached the surface of the star from deep within the star’s core. The explosive death of this star, called KSN 2011d, reached its maximum brightness in about 14 days. The shock breakout itself lasted only about 20 minutes (see inset). Illustration credit: NASA Ames/W. Stenzel.
The team from ANU and US institutions the University of Notre Dame, the Space Telescope Science Institute, the University of California Berkeley, and University of Maryland, saw a shockwave only in the smaller star (known as KSN 2011a, with a radius 270 times that of the Sun, some 700 million light-years away), shown as a peak in the light emitted from the explosion in the first few days.

In the second star (known as KSN 2011d, 1.2 billion light-years away), a large supergiant with radius 460 times that of the Sun, a shockwave could not be detected, although it must have existed. “The star was so large that the shockwave did not travel all the way to the surface,” said Dr Tucker.

The observation will help astronomers fine-tune their understanding of how the size and composition of the star affects the early moments of their explosive death.

“We are really probing the process of blowing up,” Dr Tucker said. “Supernovae made the heavy elements we need to survive, such as iron, zinc and iodine, so we are really learning about how we are created.”

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