Gamma Ray Bursts
Dr Robert Wagner is using the technique of using the MAGIC telescope as a magnifying glass instrument to peer at some of the most distant and cataclysmic events in the universe. Robert Wagner “Under good conditions, as we have them right now, we record 200 gamma ray bursts or cosmic ray showers per second.”
The Earth is constantly being bombarded by high-energy cosmic rays, gamma rays, the most energetic form of light. But Robert Wagner is looking for the most extreme of these – gamma ray bursts from colliding neutron stars or exploding black holes in distant galaxies.
Robert Wagner “Gamma ray bursts are very violent events in the universe and one key characteristic of them is that we cannot predict them. So they can take place at any time at any place on the sky. We get the information from satellite experiments. This information is transmitted in an automatic way down here, it takes about 10 seconds, and then the telescopes will fully automatically go to those gamma ray bursts locations. With these lightweight telescopes were able to move to any point in the sky within only 20 seconds. Those bursts last anything between one and 1,000 seconds. Most of the bursts are really short lived. So it’s of great essence to be there as fast as possible.”
Catching these violent but fleeting events takes many nights of patient observing.
Robert Wagner “Well, this is a place I go right after the observations, and this of course gives a quite different feeling from looking at screens. Look at the real sky and actually the stuff we are observing and hoping to detect is somewhere up there. Those black holes and galaxies, they are so very far away, but at the same time, when you come here, you realise that they are real because, you know, all the photons which hit my eye right now from those stars, they are real.”
Although Robert spends his nights looking out into the far reaches of the cosmos, he is actually trying to find out how the universe works on the very smallest scale.
Robert Wagner “Things up there are so very, very far away. The farthest galaxy we are looking at is shining light at the time when the universe was just half its age, it takes light 7 billion years to get to here. That’s a distance which, personally, I cannot imagine, myself, right? It’s a very abstract number. At the same time, the scales we are looking at if we want to get to the shortest scales are as similarly small as this distance is large. So it’s really hard to imagine these things on scales, which we see here on Earth.”
The Planck Scale
But Robert is not really interested in the explosions of themselves. They act as the biggest particle accelerator in the universe, way more powerful than anything we could ever achieve here on Earth. He is interested in what happens to the particles, in this case, photons, while they travel towards us on their 7 billion year journey through what seems like smooth, empty space. But any distortions in the structure of space-time at the Planck scale would affect photons of different energies in different ways.
Robert Wagner “Essentially, it’s quite comparable to cars driving on a road. A big car will not feel the fine structures of the road, it will just roll along and will be, you know, just as fast as normal. Whereas a small car, like a model car, will feel every tiny ripple in the structure of the street. The large car would be the low-energy photon, because there is nearly no interaction with the structure or the ripples in the road. Whereas the small car would be the high-energy photon, because it’s smaller, there are more interactions with the road, and this makes the photon travel slower.”
The difference in speed is tiny. But the length of the journey, halfway across the universe, would be magnifying the effect into something we might be able to see.
Robert Wagner “We just let those photons travel along the universe, and of course travel for billions of light years, only that long travel time makes this tiny effect visible to us, which is to say, after such a long travel, we expect the few seconds’ delay of photons of different energies, and of course this is a delay which can easily be measured with the MAGIC telescope.”
In 2005, just a few months after switching on the telescopes, a gamma ray outburst from an active galactic nucleus tickled the MAGIC mirrors, giving Robert his first tantalising glimpse down to the smallest place in the universe.
Robert Wagner “It was the first time ever we observed such an effect, or, to put it in cautious words, the hint of such an effect. So clearly we were absolutely stunned. Soon, we realised there is something in this data, which is extraordinary. As soon as we dig deeper and deeper in the data, it became apparent that photons of different energies may have different arrival times at the instrument. Those photons had to travel billions of light years. The effect was on the order of seconds, maybe five seconds.”
The Planck length is so small that after a race of 7 billion years, the photons finished with a gap of just five seconds. There are two possibilities here. The first is that the photons rather inexplicably set off five seconds apart. The other explanation is more revolutionary. This five-second delay could be our first glimpse of the smallest thing in the universe, the first evidence of a lumpiness in space-time. If true, it would shatter one of the most basic rules of physics.
Robert Wagner “To put it in simple terms, speed of light is not constant. It is dependent on the energy of the photon. And that’s revolutionary because it’s one of the fundamental laws of physics. Einstein predicted speed of light is a constant, no matter what you do, no matter where you are. Under no circumstances should there be a difference in the speed of light. The conclusion from our measurements is that this is not the case would mean quite a revolution of physics.”
The MAGIC observations provide tantalising glimpse of what awaits us at the smallest structures of space. But to get there, we’ve had to harness the entire expanse of the universe.
The journey to the very small is one of the most epic in science. It takes us beyond the limits of what we can see… Inside fundamental particles, which may not be so fundamental after all… Through a wonderland of extra dimensions and multiple universes, down to the smallest place in the universe, a place that could change the face of physics.
Gamma Ray Bursts – Wikipedia Page