A gamma ray burst (GRB) is a flash of gamma rays that can last between a tiny fraction of a second and a few minutes and it’s the most powerful kind of explosion in the universe. Nobody can tell exactly how the GRBs are created, but scientists have developed a theory that may explain their origin.
When a massive star runs out of fuel, its life comes to an end. Namely, the star’s matter can no longer defy gravity and it collapses onto the core, creating a black hole. Soon after that, all of the particles from the star start to fall towards the center, where the black hole is. However, a portion of its energy is directed into two beams, after which the rest of the star explodes as a supernova.
Although we may not know the true nature of the gamma ray bursts, we know that they happen very often — averagely once a day. It is because gamma rays are invisible to the human eye that we have been oblivious to the existence of the GRBs up until the late 1960s.
An Unexpected Discovery
In the 1960s, USA suspected that the USSR was conducting nuclear weapons tests in secrecy. The Vela satellites were designed to detect gamma radiation originating from the alleged tests. However, in 1967, Vela 3 and Vela 4 detected a flash of gamma rays that couldn’t be connected to any kind of nuclear weapon. At first, there were multiple suggestions to explain this, such as comets or neutron stars colliding, or even wars between extraterrestrial civilizations.
In the end, after several notable gamma ray burst events, enough proof was gathered to support the theory that they were a product of a high-mass star’s death.
Gamma ray bursts are the result of a dying star’s core collapsing under the force of its own gravity. When this happens, the energy released is not distributed in all directions equally, rather than in two beams. These beams are often directed opposite from each other.
In the 1990’s, we discovered a way to pinpoint where the gamma ray burst is coming from. This is thanks to the bursts’ so called ‘afterglow’, an effect that follows the burst, lasts much longer and is optically visible.
When the gamma ray bursts were discovered, they opened a huge discussion regarding where they came from. Evidence and research favors the theory that the gamma ray bursts come from galaxies beyond the Milky Way. This would allow us to assume the distance between a dying star’s burst and our planet Earth. If the star’s location is in a different galaxy, then it is safe to assume that the distance can reach up to 12 million light years. This hypothesis inevitably triggers another one. We know that a gamma ray burst shines with the brightness of a billion trillion stars. So for the beams of a gamma ray burst that happened 12 million light years away from here to outshine the sun, it would mean that the energy of a gamma ray burst is unimaginably huge. Luckily for us, most of these events happen in distant galaxies and the closest gamma ray burst recorded was around a hundred million light years away.
Effects on Earth
The Ordovician extinction happened 450 million years ago and it is the second largest mass extinction event in Earth’s history. During this period, all known life was contained in the seas and oceans. During the two pulses of extinction, with a period of 4 million years in between, more than a hundred marine families became extinct. While the cause for this is generally known to be the shift of the supercontinent Gondwana towards the South Pole, when gamma ray bursts were discovered, scientists were quick to connect the dots.
There is a group of scientists that believe that this particular extinction event was caused by a gamma ray burst, coming from a hypernova 6000 light years away from Earth. As scientists studied the possible effects of a gamma ray burst closer to Earth in the future, the results matched the events from the Ordovician period.
So what were to happen if a gamma ray burst were to strike our planet? First of all, the sky will turn white, not because of the explosion, but because of the gases released during. Gamma rays from space cannot penetrate to the Earth’s surface. However, a blast of gamma rays that are the gamma ray bursts, would seriously damage the ozone layer. The blast will separate N2 and O2 molecules into separate oxygen and nitrogen atoms. These atoms will then be free to form new molecules – different nitrogen oxide compounds. These compounds will help deplete the ozone layer and will spread a brown haze all over the planet, which will then lead to mass cooling of the Earth. And lastly, the scariest part – the radiation. A gamma ray burst’s radiation would equal a hundred of nuclear bombs exploding just outside of our atmosphere. In addition, because the ozone layer will no longer exist, Earth’s surface will be exposed to the Sun’s UV rays.
There is no way of predicting this kind of an event, so there is little we can do to protect ourselves. In fact, if a gamma ray burst were to hit Earth, it would happen so quickly that it will be too late before we even know it.
WR 104 Binary Star System
We would all like to think that all of this is just a bunch of possibilities and assumptions. However, scientists cannot assure us that a gamma ray burst won’t happen in our own galaxy. In fact, they already have a suspect – WR 104.
WR 104 is a binary star system from the Sagittarius constellation. The primary star is a Wolf-Rayet star and the secondary star is a smaller OB star. As the two stars orbit their barycenter, they eject stellar winds. When the winds from both stars combine, a dusty pinwheel nebula is formed around them. As they rotate, the gases form the winds compress and form a curios spiral.
Both of these stars are massive, which means that they live a short life because they burn through their fuel much faster. So there is no question whether the WR 104 will explode and go supernova in the future. Considering the distance between Earth and the binary system, the explosion will pose no threat. However, if the supernova causes a gamma ray burst, the effect it will have on our planet will be devastating.
When a star is about to collapse, it turns into a flat disc. The rotational axis of the disc will further determine the direction of the energy beams, if a gamma ray burst were to happen. In the case of WR 104, the energy beams would come out from the star’s opposite poles. Astronomers argue whether the direction of the beams matches Earth’s line of sight, or if it is inclined at an angle between 30 and 40 degrees. In the first case, Earth is starring down the barrel of a gun, whereas in the second case, Earth is outside of the danger zone and lives to die another day.
Another pressing question is when will the WR 104 explode? The answer is anytime in the next few hundred thousand years. There is no way of accurately predicting a date, which means it could happen tomorrow or any other day. The Wolf-Rayet star is in the last stable phase of a star’s life known to astronomers and this makes it a ticking time bomb.
Before we start making doomsday plans, however, it’s impossible not to consider the option that the WR 104 will lose enough of its mass to sufficiently decrease the speed of its rotation. Namely, WR 104 loses a lot of its mass through the stellar winds. This makes the star rotate much slower and decreases the likelihood if it producing a gamma ray burst when it collapses.
This scenario certainly relies on more variables than constants. Although it may seem like a long shot to some of us, a gamma ray burst targeting Earth is still a viable possibility and we shouldn’t be too quick to rule it out.
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