At the end of September 2007 we became aware that a new phenomenon had appeared in the sky, something that astronomers did not even know existed. It all happened when astrophysicists Duncan Lorimer and David Narkevic reanalyzed data received six years ago at the Parkes radio telescope in Australia and found a tremendous explosion that occurred at a distance of 1,500 million light-years. In the 5 milliseconds that it lasted, the same amount of energy that our Sun emits in 15 days was released . How could something like this have been missed by the astronomers who collected the observation data in 2001? They didn’t miss it, but they dismissed it because they thought it was some kind of terrestrial radio interference: they couldn’t get it through their heads that such a phenomenal burst of energy had a cosmic origin. These are the FRB or Fast Radio Burst (fast radio burst).
Despite the stillness of our night sky, the universe is not a quiet place, quite the contrary. There are stars that explode at the end of their days, becoming as luminous as all the stars in the Galaxy put together. That is the fate that awaits, either tomorrow or in the next 100,000 years, Betelgeuse, a bright star in the Orion constellation. When it happens it will be as bright as the first quarter Moon. But in the Cosmos there are other more terrible explosions, such as the so-called Gamma Ray Burst or gamma ray burst (GRB): on average, once a day, at some point in the sky and during a period of time that goes from the fraction of a second to a few minutes, the universe gifts us with “something” that emits as much energy as 200,000 milky ways put together .
Little did we know about the origin of these GRBs until January 23, 1999, when space-based X-ray and gamma-ray observatories detected an impressive flare of energy at a point in the sky in the constellation of the Boyero . Two waves of radiation arrived at Earth 25 and 40 seconds after the explosion began. During the next 50 seconds other weaker pulses arrived until finally calm was made. Calculated the energy released, the result was impressive: if it had happened just 2,000 light-years from us in the sky, a star twice as bright as our own Sun would have appeared.
Hiding behind those unappealing names astronomers use to catalog celestial events, GRB 990123 will go down in history as the first time a GRB was observed in the visible light range. In fact, it was so bright that it could have been seen with good binoculars… if we had known where to look. GRBs were first detected on July 2, 1967 by the American satellites Vela 3 and Vela 4, which were intended to measure gamma radiation produced by Soviet nuclear tests . That day they detected a flash of gamma radiation whose structure did not conform to that which was usual for atomic explosions. We had to wait more than 30 years, for that January 23, 1999, to be able to photograph this cataclysmic phenomenon and, thanks to it, identify its origin: a very faint galaxy located 9,000 million light-years away. Now, what happened in that distant galaxy for “something” to shine as bright as 200,000 milky ways together? This is where we have the mystery.
Some astronomers think it was a hypernova. Its name comes from a comparison with supernovae, the most apocalyptic end a star can have, when its nuclear fuel is finished, it explodes becoming as bright as a billion stars. Well, a hypernova is at least 100 times more intense . Nobody knows how and why it happens, but it is assumed that it occurs when the most massive stars (with more than 30 times the mass of the Sun) collapse to form a black hole in a process that lasts 10 to 20 seconds. They are difficult to observe because they are very rare: one appears for every million supernovae.
Regarding the origin of FRBs and GRBs, there is no consensus on who or who can cause such deflagrations. In addition to the hypernova hypothesis, there is thecollision between two neutron stars, stars with one and a half times the mass of our Sun crammed inside a sphere ten kilometers in diameter. This exotic collision -and that its detection from gravitational waves was the reason for the 2017 Nobel Prize- was one of the explanations offered by Duncan Lorimer, director of the group that discovered this unusual phenomenon. Of course, he has also proposed another even more striking explanation: “the last gasp of a black hole completely evaporating.” Lorimer refers to what is known ashawking evaporation, a mechanism described by the famous British physicist by which a black hole continuously loses energy until it disappears with a large gamma-ray burst. Now, calculations made by theoretical physicists reveal that a black hole of about 3 solar masses will disappear after a whopping 1066years, that is, a million billion billion billion billion billion billion years. How can we be observing an evaporation now? Because if the theoretical predictions are correct, during the big bang large amounts oftiny micro black holes, with the mass of a mountain. It is these, at this time, who would be evaporating, releasing large amounts of gamma radiation in an infinitesimal second… as is being observed. The only problem with this is that micro black holes remain an unverified theoretical prediction.
