What if you explode

Supernova: When stars explode

Giant stars always die with a mega bang. As a supernova, they then shine as brightly as galaxies made up of billions of celestial bodies. But how does the explosion come about? What is happening in the meantime? We take a close look at the cosmic fireworks

Some spectacles amaze even experienced astronomers like Subo Dong. In 2015, the researcher from Peking University examined a spot of light in the sky with a telescope. When he calculates its distance, he can hardly believe the result at first. The point is a whopping 3.8 billion light years away! That means: Even light, the fastest thing in the universe, took 3.8 billion years to get from there to earth and in front of Subo Dong's telescope!

What kind of super light is that? Subo Dong determines that it must have been as bright as 570 billion suns combined. Yes, 20 times more radiant than our entire Milky Way! And that it is probably a supernova, a celestial phenomenon that lights up brightly for a short time. "The rest of the night I was too excited to sleep," he later reports.

Supernova ASASSN-15lhHow the lamp is later called is still a mystery to researchers today. What triggered it? And where did she get her energy from? Nobody knows. "All theories reach their limits," admits Subo Dong. But he and his colleagues have already answered some questions about such cosmic spectacles.

What is a supernova?

In a nutshell: an exploding star. When a giant star dies, it always does it with a bang. In doing so, it throws a large part of its mass into space. Supernovae (so many of these cosmic fireworks) can also be caused by star corpses like a "White dwarf“Arise. It sucks in the gas from another star and then bursts.

How can a star explode?

To understand this, we need to look at his life. You can imagine stars as balls made of hydrogen, the lightest element in space. Its nuclei fuse to form helium nuclei inside the star (see box on page 65). During this reaction, energy is released that heats up the star and makes it shine. But it also inflates the ball - like hot air in a hot air balloon.

As long as the hydrogen “burns”, the star is therefore stable. But at some point this fuel in the center is used up. The star collapses.

Is the star at the end? Not yet! Because now he switches to a reserve fuel. It fuses the resulting helium nuclei into a new element - carbon. At the same time, the hydrogen there ignites in the bowls. This is how it continues: if one fuel is used up in the center, the next one is used. Heavier and heavier elements are created: oxygen, sodium, sulfur ... That works well until iron comes out. Then the reaction stops. Because iron cores that collide do not fuse. They no longer provide energy.

Now it's getting dramatic. Everything collapses: first the iron star center. Its particles are so strongly pressed into one another that they transform into new particles, so-called neutrons. These neutrons form an insanely dense sphere. A tablespoon of it would weigh billions of tons on earth. About as much as all cars on our planet!

Then the next layers of the star collapse. They race towards the core, ricochet off it - and shoot outwards again. In the mega-impact, even heavier substances such as gold or uranium are produced. When the shock wave hits the star's outer gas envelopes, it flashes brightly and shoots into space. And that's exactly what we see as a supernova.

Does our sun also die in a supernova?

No, it's too small for that - Luckily. While giant stars cheer up their fuel in a few hundred thousand to millions of years, the little sun will burn hydrogen for another five billion years. Only then does its core collapse while the outer shells expand. The sun becomes a red giant that also devours the earth. After this rearing up, it will soon be over: the sun collapses into a white dwarf that will glimmer for billions of years before slowly going out.

How do astronomers recognize a supernova?

Supernovae reveal themselves when they suddenly light up in the sky. The researchers then measure the brightness of the explosion and how it changes over weeks. They determine the distance and study the composition of the star. Then they divide the supernovae into different categories. Exploding white dwarfs, for example, belong to type 1a. The astronomers use computer simulations to conclude what happened inside the exploding star. They make assumptions about what processes take place in the star and calculate whether the simulated star would explode in the same way as the observed supernova.

Do supernovae affect our lives?

And how! Some researchers suspect that the radiation from a supernova 444 million years ago even triggered a mass extinction on Earth. But most of all, they throw new “building material” into space during the explosions: hydrogen, for example, from which new stars are created. And the heavier stuff that they formed inside. The planets of the solar system arose from these. And later we ourselves. Because we too are made of stardust.

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