A space mission looking at some of the most violent explosions in the Universe has recently marked its 10th anniversary.
Gamma Ray bursts. They’re pretty nasty stuff.
“They’re the most luminous, high energy explosions that have happened since the Big Bang,” says Neil Gehrels, the leader of NASA’s Swift programme. “It’s like a beam of gamma radiation that’s flying through the Universe.”
What would happen if one of these cosmic death rays of high frequency electromagnetic waves hit the Earth?
Well, as you might have guessed by the whole cosmic death ray part, it wouldn’t be too great for life on our planet. “For a planet 1000 light years away, it would destroy the ozone layer. If it was just 100 light years away it could blow the atmosphere off,” says Gehrels matter-of-factly. Thankfully, he then adds that “The chances of that happening to the Earth are fairly small, about once in a billion years,” he adds. “It’s certainly not as great a threat as a giant asteroid hitting our planet.”
But still, it’s probably a good idea if we have some way of detecting them round the clock. Thankfully, we do.
There is an international team of scientists, led by Gehrels, that operates and monitors the Swift satellite, which keeps an eye on these cosmic death sentences. Named after its ability to respond instantly to the around 90 high-energy flashes of radiation it detects each year, Swift has been in orbit since November 2004.
Before Swift, it wasn’t known for sure what caused Gamma Ray bursts, but thanks to Swift, astronomers now believe that the longer bursts, which last more than two seconds, are caused by the death throes of the most massive stars, as their centres collapse in on themselves. When the stars then explode into oblivion, a jet of gamma rays is emitted to travel the cosmos, hopefully not to strike the Earth.
The shorter of these explosions (less than two seconds) is categorised as short bursts. The Swift team has concluded that these are caused by the collision of two dense neutron stars. Neutron stars are the diameter of just a small city, but have the mass of the entire sun, which is one of the reasons these collisions are so violent.
Surprisingly, the Swift scientists have also discovered is that gamma ray bursts are vitally important to the evolution of the Universe. “When a gamma ray burst goes off near a star with a planetary system, it can have a very important and destructive influence,” says Gehrels.
One of the interesting phenomena that Swift demonstrates; because light from the other side of the Universe takes so long to reach the Earth, some gamma rays bursts spotted by Swift actually began their journey towards us shortly after the Big Bang 13.7 billion years ago. This means that when a blast goes off, it lights up that particular region of space allowing astronomers to get a glimpse back in time to the birth of the very first stars 500 million-or-so years after the Universe came into existence.
This has helped astronomers to confirm some pictures of the early Universe says Gehrels. “When the Universe was born, the only elements were hydrogen and helium but explosions started to seed the galaxy with higher elements like carbon, nitrogen and iron – the elements that make up our bodies.”
Not only do we owe our very existence to cosmic explosions, there is some evidence that the Earth’s ecosystem has been directly affected by these bursts of energy. Research published in 2013 suggested that a blast of radiation that hit our planet in the 8th Century may have been the result of a gamma ray burst, though Gehrels is inclined to reserve judgement.
Excitingly, he believes that even after 10 years of observations, Swift will be able to function for at least another five years, before it becomes just another piece of space debris, but it has already transformed how astronomers see the Universe.
“Before Swift, astronomers used to think the Universe was a steady set of stars and galaxies,” he says. “But if we put on our gamma ray glasses and look up at the sky, it’s always popping and bubbling and flashing – it’s a very different kind of violent Universe.”
And that is most definitely an exciting picture, which hopefully Swift and other programmes will be able to build up further in the coming years.