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At first glance, the sky seems like a quiet place. But, if we look at gamma radiation, the so-called "violent universe" appears, full of explosions coming from distant galaxies, although it is not easy to observe them at the moment they occur. After 15 years of operation, the Magic Observatory of the Canary Islands has just marked an astronomical milestone by detecting the most intense gamma ray eruption ever seen.
The finding came on the night of January 14, 2019 and is published this week in the journal Nature . The immense gamma ray outbreak, whose light emitted an energy one billion (million million) times greater than that of visible light, "was a total surprise, since such a bright source had never been detected," recalls Juan Cortina , scientist of the Center for Energy, Environmental and Technological Research (Ciemat) and one of the more than 300 signatories of the two reports detailing the results.
The outbreak marked two records: first, photons (particles of light) had never been detected at such high energies in this kind of astronomical phenomena. If the red light has little energy and the blue one, more energy, in this case we would talk about the most intense blue that has been observed, far from what the human eye can see and accessible only for gamma-ray telescopes. On the other hand, no glowing rash had been recorded so far. The standard for measuring the brightness of an astronomical object is the Crab Nebula, always visible in our sky, and this emission reached a brightness 100 times higher than it, which took scientists by surprise.
"The fact that an outbreak emits at such high energies was something that was considered impossible," Cortina adds. The event was caused by the explosion of a massive star, which originated a supernova and this, in turn, left a black hole as a trace of its explosion. "A typical outbreak emits as much energy in a few seconds as the Sun over its 10 billion years of life," says Gemma Anderson of Curtin University in Australia.
It lasted only a few seconds, as usual in these events, but, being "caught in fraganti , after only 30 seconds", the gamma light bathed the mirrors of the Magic telescopes for 20 minutes, something unusual. Gradually, his trail vanished during the following hours. Before, an "astronomical telegram" was sent from the Canary Islands to alert the international community of the existence of GRB 190114C, as the event was called.
In this way, all the observatories of the world with the right conditions could contribute to their study and observe it in different wavelengths (infrared, visible light, ultraviolet ...). In fact, radio broadcasts that arise after the outbreak can still be detected "months or even years" later, Anderson says. The energy released during the outbreak reached one teraelectronvolt (that is, one billion electron volts).
A second similar outbreak
The same issue of Nature also publishes a third report that tells of a second gigantic gamma explosion, observed this time from the HESS telescopes in Namibia, on July 20, 2018. This is another important detection, also caused due to the birth of a black hole, although its energy emission was somewhat lower and was not seen as immediately as that of the Canary Islands. In both cases, the emissions came from galaxies located around 7,000 million light years, a relatively close distance when we talk about this kind of explosions.
Both at the Magic Observatory, located in the Roque de los Muchachos de la Palma, and in the Hess of the Khomas region (Namibia), the gamma outbreak detection process was the same, although with more fortune in the first case . At first, as soon as the energy source was registered, the NASA Swift and Fermi satellites automatically alerted from space. The ground telescopes received the notice online and were able to study the phenomenon in detail, thanks to its greater capacity and detection area. However, the conditions were not equally suitable in both cases.
In the outbreak observed from Namibia there was not as much luck as in the Canary Islands because there was the circumstance that, in the African country, it was still day when the outbreak occurred. Therefore, we had to "wait 10 hours to start the observations," says Mexican researcher Edna Ruiz Velasco, a doctoral student at the Max Planck Institute in Germany and lead author of the report detailing this second gamma ray emission.
The Magic , however, began the observation in record time. This pair of telescopes is programmed to automatically leave the tasks you are performing and, as soon as you receive the alert, point to the gamma light outbreak to dedicate all your systems to investigate it. "We don't want to lose a second," says Cortina, who details that each 60-ton telescope takes a maximum of 40 seconds to go to any point in the sky.
In this case, exactly 27 seconds passed between the outbreak in space was detected and the Canary observatory began to scrutinize its details. In both the Canary Islands and Namibia, whose outbreak was baptized GBR 180720B, it has been concluded that the photons did not reach their immense energy peaks in the supernova explosion itself, but were intensified when the gamma bud interacted with the matter around it, through a process on which experts expect to know more in the future.
"The matter that is ejected by these jets (jets) interacts with magnetic fields and with the matter that is in the interstellar space near the black hole, and this produces light radiation," says Ruiz Velasco. "They are going to be writing papers (scientific reports) for years," says Curtain.
Emotion and cold head
In the case of the HESS, although the response had to wait until it was dark, the discovery was also lived with intensity: "Despite the emotion, one tries to keep a cool head, so, in addition, we spent several weeks more checking the data and making sure, "says Ruiz Velasco.
Gamma outbreaks, and more so if they are as intense as those just observed, have great scientific interest for several reasons. "They are produced by mechanisms that are not yet known, they have theorists in check," Cortina explains. "These are very exceptional phenomena, in which one would expect the discovery of exceptions to the laws of physics."
For example, it is in these very high energies that one looks for whether the speed of light, considered a universal constant, could vary under certain extreme conditions. Or where the behavior of elementary particles could undergo changes not anticipated by current models.
Given their origin in distant galaxies, these astronomical phenomena also become "a window" towards them, which, in turn, "helps to understand how the universe has evolved," says Ruiz Velasco.
In the near future, scientists will also have even more powerful and sensitive telescopes, so the catalog of explosions is expected to grow rapidly. One of them, neighbor of the Magic, will be the Large Size Telescopes (LST) observatory, even larger and composed of four telescopes of 23 meters in diameter each, in front of the 17 meters of Magic . The 4 new telescopes that we are building in La Palma are called Large Size Telescopes (LSTs). Next to them, another set of 12-meter diameter telescopes will be added and together they will form the so-called Cherenkov Telescope Array. A monster to continue to surprise us how much happens in the confines of the cosmos.
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