In our first blog on “Gamma-Ray Bursts the cosmic snipers”, we briefly introduced Gamma-Ray bursts, their energies, types, and sources in a nutshell. Now, let’s start digging into the first type of these bursts, which are “long GRBs.” Long-duration Gamma-Ray Bursts are intense bursts of gamma photons lasting for two or more than two seconds. They are believed to occur during supernova explosions, which are incredibly violent deaths of stars.
When a star 9 times more massive than the sun cant handle its gravity, it erupts into a type-II supernova. Other supernova types are also believed to cause GRBs, but type-II is the most famous. As the star’s life comes to an end, the chaos doesn’t just end there. As evil as it was before, the explosion only makes it worst. It either ends up becoming a black hole or a neutron star. It’s pretty notorious, I know! About a supernova leading to a gamma-ray burst, let’s find out how that happens.
How Supernova explosions cause Long GRBs?
A star with the help of fusion powers itself and balances its gravity with an outward force produced by fusion. As it fuses elements into heavier ones, the process continues till it reaches the point when we have an Iron and a Nickel core. At this point, things get messy. For further fusion, energy is required, and the star, which was depending on fusion for stability, loses its life-line. With no energy to balance gravity, the star collapses into a supernova. You might feel sad about the star, but don’t get deceived just yet. After the explosion, what’s left is a dense mass called a neutron star, or if the star was 20 to 30 times more massive than the sun, then we get a black hole.
Hypernova or Collapsar
In the case of a very massive star > 30 times the mass of our sun, the explosion is even more spectacular, resulting in a hypernova or a collapsar. A hypernova is associated with a long Gamma-Ray Burst, but the mechanism behind it is still unclear. A jet formation accompanies the hypernova as the core implodes the in-fall of the material towards the centre drives the relativistic jets. Internal collisions within this jet produce gamma-ray photons, and this phase is called the prompt phase of the Gamma-Ray Burst. When the burst ejecta interacts with the external medium, that phase is called the afterglow phase in which low energy photons like x-ray, optical, and radio photons are released.
Where do long Gamma-Ray Bursts occur?
Both short and long Gamma-Ray bursts are detected from random locations in the sky every day. This randomness shows how scattered these bursts are but with powerful telescopes; we can now pinpoint their location. Most of the Gamma-Ray Bursts detected are long GRBs and are located within star-forming regions. The farthest GRB 080913 was detected at a distance of 12.8 billion light-years. That’s quite far, right!
The star responsible for it died when the universe was less than 1/16th its present age. As this star was very far away, locating its host galaxy was very hard, but for closer cases, we can study the host galaxies. Considering another case of the long GRB 031203, which on the contrary, is the closest GRB to be detected at 1.3 billion light-years away. It was found to be located in the HG 031203 galaxy, which is a Wolf-Rayet Galaxy.
What are the advantages of exploring long GRBs?
Scientists who study long GRBs find it relatively easy to study them as compared to short ones. The reason is that the signal of long GRBs has wider pulses. To study individual pulses and the mechanism behind them is thus more manageable. In “short GRBs,” the pulses overlap to a degree, which makes their study tricky. Another noticeable fact is that the three most energetic GRBs ever to be detected are all long GRBs. This fact makes long GRBs all the more valuable.
Considering the above information about long GRBs, we see that they are related to hypernovae, star-forming regions, black holes and can be very old. Thus we can understand various entities in the universe better. While studying these bursts, we can further understand how high energy events occur and how our universe is evolving. Studying the host galaxies is another perk.
All of this makes long Gamma-Ray bursts a beneficial tool. The exact mechanics behind GRB jets is unclear, but with time as progress in science advances, it will soon be much clearer to us. Studying these bursts at first suggests that these are just explosions occurring randomly in the sky, but they are much more than that. They are like a door taking us a little closer to a lot of our answers. What fascinates you the most about long GRBs? Tell us in the comments section and if you want to explore Gamma-Ray bursts more, then stay tuned for more blogs.