Supernova with a shockwave seen by astronomers at ANU. ANU

Astronomers have for the first time captured the shockwave generated by a star's collapsing core while watching two exploding stars. The shockwave was detected only in the smaller supernova.

"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.

As the fuel in the core begins to dwindle, the star collapses under the force of gravity and what is seen is the supernova explosion which is the brightest spot in the galaxy for weeks. During the collapse, energy from the core travels outwards in the form of a shockwave at 30-40,000 km per second. It triggers the fusion required to generate heavy elements in the resulting neutron star.

The team from ANU was able to watch the early stages of a supernova in the explosions of the two red supergiants. Along with the University of Notre Dame, the Space Telescope Science Institute, the University of California Berkeley, and University of Maryland, they saw a shockwave only in the smaller star with a radius 270 times that of the Sun.

In the second star, a large supergiant with radius 460 times that of the Sun, a shockwave could not be detected, which could be because the wave could not reach out to the surface of the large star, according to Dr Tucker.

Besides understanding how the size and composition of a star affects its early moments of explosive death, the astronomers hope to learn more about the processes involved in creating heavy elements like iron, zinc and iodine essential for our survival, or "how we are created".

Supernovas has shown scientists that we live in an expanding universe, says Nasa. They play a key role in recycling elements throughout the universe during the explosion. Most heavy elements found on Earth are made in the core of stars. They go on to form new stars, planets and other objects in the universe.

NASA's Hubble Space Telescope and Chandra X-ray Observatory have captured images of supernovas. While supernovas in our Milky Way galaxy are tough to see because dust blocks our view, back in 1604, Johannes Kepler discovered the last observed supernova in the Milky Way. NASA's Chandra telescope discovered the remains of a more recent supernova that exploded in the Milky Way more than a hundred years ago.