What causes the gamma ray burst?Their super bright flashes hold the clues

In July 1967, At the height of the Cold War, the US launched satellites in search of Soviet nuclear weapons tests. Found something completely unexpectedThe Vela 3 and 4 satellites have observed brief flashes of high-energy photons or gamma rays, which appear to come from space.Later, in 1973 paper A dozen of these mysterious events are collected, and astronomers call them gamma-ray bursts. “Since then, we have been trying to understand what these explosions are,” said Andrew Taylor, A physicist at the German Electron Synchrotron (DESY) in Hamburg.

After the initial discovery, astronomers debated the source of these gamma radiation bursts-this is the key clue that powers them. Some people think that this bright light source must be near our solar system. Others argue that they are in our galaxy, and there are others outside the universe. Theories abound; the data do not.

Then in 1997, an Italian and Dutch satellite called BeppoSAX comfirmed Gamma-ray bursts are outside the river, in some cases originating billions of light-years away.

This finding is puzzling. To explain the brightness of these celestial bodies—even if they were observed from such a distance—astronomers realized that the events that caused them must be almost unimaginable. “We don’t think you can get so much energy from the explosion of any object in the universe,” said Sylvia Zhu, an astrophysicist at DESY.

When a star collapses and explodes, the gamma-ray burst will release the same energy as a supernova, but it will take seconds or minutes instead of weeks. Their peak luminosity can be 100 billion times that of our sun, and even 1 billion times higher than the brightest supernova.

It turned out that they were lucky to be so far away. “If a gamma-ray burst occurs in our galaxy and the jet is directed at us, the best thing you can hope for is rapid extinction,” Zhu said. “You would want the radiation to break through the ozone layer and kill everything immediately. Because the worst case is that if the distance is farther, it may cause some of the nitrogen and oxygen in the atmosphere to be converted to nitrous oxide. The atmosphere will turn brown. . This will be a slow death.”

There are two forms of gamma-ray bursts, long and short.The former can last up to a few minutes and is thought to be produced by stars More than 20 times the mass of our sun Collapse into a black hole and explode into a supernova.The latter lasts only about one second and is caused by two merging neutron stars (or perhaps a neutron star merges with a black hole). It is Confirmed in 2017 When the Gravitational Wave Observatory detects a neutron star merger and NASA’s Fermi Gamma-ray Space Telescope captures the related gamma-ray burst.

In each case, the gamma-ray burst did not come from the explosion itself. Instead, it comes from a jet that is emitted from the explosion in the opposite direction at a speed a fraction of the speed of light. (The exact mechanism that powers the jet is still a “very basic question,” Zhu said.)

“It is the combination of speed at high energy and focused jets that make them very luminous,” said Neil Tanville, An astronomer at the University of Leicester, UK. “This means we can see them from far away.” On average, people think An observable gamma-ray burst In the visible universe every day.

Until recently, the only way to study gamma-ray bursts was to observe them from space, because the earth’s ozone layer prevents gamma-rays from reaching the surface. But when gamma rays enter our atmosphere, they will collide with other particles. These particles are pushed faster than the speed of light in the air, which causes them to emit blue light, called Cherenkov radiation. Scientists can then scan for these blue light bursts.