Scientists untangle mysteries of gamma-ray bursts — the cosmos’s most powerful explosions

Researchers may be a step closer to ascertaining how gamma-ray bursts are among the most powerful explosions in the known universe. For context, a single gamma-ray burst (GRB) can produce far more energy within seconds than the sun will radiate in billions of years. Because of this massive power, experts hypothesize that GRBs are created by some of the universe’s most violent events. This includes events like supernova explosions that mark the deaths of colossal stars and the collision and merger of two neutron stars (“dead” stars composed of the densest matter we know of), plus outbursts from baby black holes.

The facets of these blasts still remain veiled in mystery, including the exact mechanism that launches a gamma-ray burst and what exactly causes a “long” GRB that lasts more than 2 seconds as opposed to a “short” GRB that lasts for less time. One team of researchers from the Huntsville-based University of Alabama, for instance, has been studying the light emissions of gamma-ray bursts and how they change over time to better model these eruptions and finally crack their mysteries.

“Despite being studied for over fifty years, the mechanisms by which GRBs produce light are still unknown, a great mystery of modern astrophysics,” team leader Jon Hakkila (a scientist at the University of Alabama in Huntsville), said in a statement. “Understanding GRBs helps us understand some of the most rapid and powerful light-producing mechanisms that Nature employs.” “GRBs are so bright, they can be seen over the breadth of the universe, and — because light travels at a finite velocity — they allow us to see back to the earliest times that stars existed.”

Putting some light on GRBs

One of the primary reasons gamma-ray bursts have remained so hard to comprehend is that theoretical models to describe them have been incapable of explaining the behaviour of their light curves, which are graphs that display how the light intensity of an object changes over time. Further confounding the situation is the fact that no two gamma-ray burst light curves are exactly the same, and the duration of the bursts can last from mere milliseconds to tens of minutes.

Hakkila and associates modelled GRBs as a series of energetic pulses, considering these pulses to serve as the basic units of GRB emission. “They indicate times when a GRB brightens and subsequently fades away. During the time a GRB pulse emits, it undergoes brightness variations that can sometimes occur on very short timescales,” Hakkilastated. “The strange thing about these variations is that they are reversible in the same way [palindrome] words like ‘rotator’ or ‘kayak’ are reversible.”The scientist added that it is very tough to understand how this reversibility can be the case because, contrasting the letters in a word, time can only be read in one direction.”The mechanism that produces light in a GRB pulse somehow produces a brightness pattern, then subsequently generates this same pattern in reverse order,” he said. “That is pretty weird, and it makes GRBs unique.”