“It's like the shockwave from a nuclear bomb.”
What happens in the early moments when a star goes “kaboom” is not well understood by astronomers because it is such a complex process — one that has only been observed a handful of times. However, an international team of astronomers has captured the earliest minutes of two exploding stars, and for the first time in history, they got a glimpse of the shockwave generated by one of the star’s collapsing cores.
“It's like the shockwave from a nuclear bomb, only much bigger, and no one gets hurt,” Dr. Brad Tucker, from ANU Research School of Astronomy and Astrophysics, said in a press release.
Stars explode when they run out of fuel — hydrogen — which is converted into helium by a process known as nuclear fusion. As stars continue to build up helium, the core shrinks, and once all of the hydrogen is exhausted, the core gets extremely hot and dense.
The star’s own mass exerts an inward pull of gravity, while nuclear fusion reactions in the core produce an outward push of pressure — it’s a balancing act. But without the outward push of fusion, the star collapses in on itself, resulting in skyrocketing core temperatures which begin to break down the core itself.
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Once the core collapses down to this immense density, forming a neutron star, something called a bounce occurs — this means the core has collapsed to a point where it is just too hard to squeeze anymore, and the bounce takes the form of a powerful shockwave, blasting all of the surrounding material away at a speed of about 24,855 miles (40,000 kilometers) per second. This process creates the nuclear fusion that forms heavy elements such as gold, silver, and uranium.
And this bounce is what the astronomers were able to witness:
The team, consisting of researchers from ANU, the University of Notre Dame, the Space Telescope Science Institute, the University of California Berkeley, and the University of Maryland, only saw a shockwave from the smaller star with a radius 270 times that of the sun. It was seen as a peak in the light emitted from the explosion in the first few days.
Unfortunately, a shockwave was not detected in the second and larger supergiant, with a radius of 460 times that of the sun, but it must have existed, said Tucker. “The star was so large that the shockwave did not travel all the way to the surface.”
Although the shockwave was from the smaller supernova, the hope is that the findings will help astronomers understand how size and composition affect the early moments of star explosions, which are important building blocks that created the numerous elements that make up our solar system, Earth, and all humans.
“We are really probing the process of blowing up,” 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.”
The research was published in the Astrophysical Journal.