COSI Blog
07
May
2013

Flash!

Credit: NASA/DOE/Fermi LAT Collaboration

Just over three and a half billion years ago, in the direction of the constellation Leo the Lion, something big happened – something very, very big. That very big something caused a beam of intensely energetic (yet invisible) light to fly our way. It's been traveling toward us all this time, as our Earth evolved and changed, until finally, on April 27, 2013, it reached our planet.

On that date, astronomers operating telescopes in orbit around the Earth recorded the most powerful gamma ray burst they'd seen in decades. Now those same astronomers are anxiously watching the same patch of sky for what they believe must follow, a giant stellar explosion called a supernova. If they can spot it, they will learn much about stars, their moments of death, and the origin of us all.

So what's the big deal about gamma rays?

Gamma rays are the most energetic kind of light we know. Light comes in many different forms, from low-energy radio waves and microwaves that we use to talk on our phones and cook our food, to higher energy visible light that let us see a beautiful painting and spot a fly ball against a cloudy sky, to even higher energy x-rays that the dentist uses to peer inside our teeth. For pure energy, gamma rays beat them all.

On April 27, the Fermi Gamma Ray Space Telescope and the Swift Telescope recorded a burst of gamma rays from a target 3.6 billion light years away. The burst was so powerful that it released more energy in a few seconds than our Sun will produce in ten billion years! Anyone near such a burst would be fried instantly – fortunately the light years between it and us protected us from that fate.

What might cause such an enormous outpouring of energy? This is still a great mystery, but scientists believe gamma ray bursts are just one step in the process of a stellar explosion called a supernova. As an aging star uses up its fuel in a process called nuclear fusion, the weakening outward push of the star's light begins to lose a battle with gravity. The star's own enormous weight begins to crush its center into a black hole. As matter from the star falls toward the black hole, it is super-heated and emits an intense beam of gamma rays. These gamma rays fly away from the star's North and South poles and out into space.

But that's just the beginning. As the star continues its internal collapse, a rebound occurs (see the activity below*) and some of the star's outer material flies away in a giant explosion called a supernova. This supernova is so bright it can outshine an entire galaxy for a short time. It is this supernova that scientists hope to see next. If they do see a supernova in the same part of the sky, it will confirm that we do, indeed, understand a little bit about the details of how stars die.

But why should we care? What difference does it make that a star blew itself up so long ago and so far away? Look at your hand. Just below your skin flows a river of life-giving blood. At the heart of every blood cell is a molecule called hemoglobin, carrying oxygen to each of your cells. And at the heart of each hemoglobin molecule is a single atom of iron. That iron atom has not been around forever, but instead was born in a supernova explosion that itself occurred billions of years ago. Stars are the places that iron, carbon, oxygen, and almost all other elements are forged, and it is in supernovas that those elements are scattered throughout the universe. We are made of starstuff.

Keep watching this blog for updates on the story; will the expected supernova show up? What will it teach us about the universe? Science is always moving forward; we are always learning more. What will we discover next?

*You can recreate your own supernova explosion with nothing more than a tennis ball and a basketball. Hold the two balls apart from each other, the same height from the floor. When you drop them at the same moment, they hit the ground together. This shows that each falls at the same rate. Yet the basketball, being heavier, has much more momentum.

Now stack the tennis ball on top of the basketball. Drop them again (be careful to keep the tennis ball right on top, or it may come back and hit you!). This time, the tennis ball goes flying skyward with surprising speed. This is like what happens in a supernova explosion, as the outer parts of the star collapse and bounce off the dense inner surface of the collapsing star. You just created a supernova!

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