In October 1963, a month before he was shot in his official car, US President John F. Kennedy approved the launch of satellites to warn of the greatest disaster imaginable: the detonation of atomic bombs. In 1967, this monitoring project, called Vela, detected mysterious explosions that did not come from Earth, but from space. The matter was shelved, and years later, the signals became known to be the most powerful radiation in the universe, possibly coming from outside our galaxy. Unplanned by anyone, it…
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In October 1963, a month before he was shot in his official car, US President John F. Kennedy approved the launch of satellites to warn of the greatest disaster imaginable: the detonation of atomic bombs. In 1967, this monitoring project, called Vela, detected mysterious explosions that did not come from Earth, but from space. The matter was shelved, and years later, the signals became known to be the most powerful radiation in the universe, possibly coming from outside our galaxy. Unexpectedly, a new way of observing the universe was introduced: gamma-ray astronomy.
Invisible to the human eye, gamma rays are ubiquitous and allow us to study the most violent events in the universe. “In a short period of time, gamma-ray bursts emit more energy than all the stars in the universe,” summarizes Peter Michelson, an astrophysicist at Stanford University (USA) and the intellectual father of the gamma-ray telescope. Fermi. The space observatory was launched by NASA in 2008 to continue more scientifically the monitoring mission started by the Cold War satellites. Within hours, a team of more than 400 scientists from 17 countries associated with this telescope could detect a new source of gamma rays, trace its origin and alert other space and ground-based telescopes to observe. For the first time, they were responsible for the main scientific instrument on board Fermi They discussed their new objectives in Spain, one third of which was to decipher signals of unknown origin.
Short bursts of gamma rays last fractions of a second. As they occur when two neutron stars collide, objects weighing a billion tons a teaspoon are very dense and compact. Long bursts, lasting a few minutes at most, occur when a star 30 times the size of the Sun reaches the end of its life and explodes, producing a supernova. The outer layers are thrown away as the core collapses in on itself. Gravity is so strong that a point of infinite density forms: a black hole. “If the hole rotates itself, which it always does, a jet of gamma rays emerges as powerful as that produced by an entire galaxy,” Michelson summarizes. No nuclear bomb is even remotely capable of producing the same amount of energy.
Irish astrophysicist Deirdre Horan, a member of the Fermi science team, explains: “Gamma rays are one of the fastest and most dramatically fluctuating types of radiation; Some sources even turn the sky into a discothèque.” “It's interesting how nature creates something like this,” he points out. Pulsars, which emit periodic flashes with precision that can be used as chronometers to measure other phenomena with very high precision, such as the radiation created by the Big Bang 13.7 billion years ago, are rotating. The researcher refers to neutron stars.
He Fermi 24 hour guard every day of the week. From its orbit, more than 500 kilometers above Earth's surface, it can cover the entire sky every three hours. Since its launch, it has identified more than 7,000 sources of gamma rays from inside and outside the Milky Way. Their findings show that Earth is a tiny dot in space Really surrounded Gamma ray sources, many of which are pulsars of exquisite timelessness. Some signal comes from so far away that it's dizzying: it's gamma light emitted 12.5 billion years ago, when the universe was almost newborn. Due to the rapid expansion of the universe, this object is already 25 billion light-years away, which means that to reach it you would have to travel at the speed of light, almost twice the total age of the universe.
Charged nuclear particles are intriguing devices Fermi continuously. Although in theory it was built to last only five years, its ideologues and builders made sure to provide large solar panels that would continue to function despite losing efficiency due to constant radiation bombardment. On at least one occasion the telescope had to avoid a piece of space debris that would have knocked it out forever. The scientific team, which met until Friday at the Institute of Theoretical Physics in Madrid, calculated that the device could last another decade. This is important because without it humanity would be blind to this type of gamma rays; No successor in sight.
Extremaduran is an astrophysicist Miguel Angel Sanchez Conte Fermi-LAT will be the new science coordinator of the collaboration. One of its main objectives is to try to detect dark matter using a telescope. “This will be a discovery that will take us directly to Stockholm to receive the Nobel Prize,” he highlights.
25% of the entire universe is dark matter, but no one has been able to observe it or determine what it is made of. “Many unidentified sources may be small haloes of dark matter that annihilate, emitting gamma rays as they do so,” explains Sanchez. This possibility may fit with some current proposals to explain dark matter, namely weakly interacting massive particles, or WIMPS in English.
Sanchez explains that one of the “big mysteries” the team faces lies at the center of our galaxy. At this point is a black hole – Sagittarius A* – with a mass four million times that of the Sun. “Since 2010 we've been capturing a steady signal from the galactic center. But we haven't seen anything like it in other galaxies with supermassive black holes at the center. It's an excess of gamma rays that we can't understand. No one knows why this happens, but the problem is growing every day. “New studies are being published. There are already thousands of studies on this mystery,” admits the researcher.
In 2010, Fermi discovered a giant bubble-like structure located just above and below the center of our galaxy. Both lobes are so massive that it would take 50,000 years to cross them traveling at the speed of light. Fourteen years later, these Fermi bubbles remain one of the greatest mysteries of our cosmic environment.
They are the remains of the last party of Sagittarius A*, which swallowed a gas cloud six million years ago. Or the puzzle could be related to a steady gamma-ray signal coming from the galactic center, and that could be due to the annihilation of dark matter, Sanchez argues.
For Irish Horan, another great moment will come in about a month, when the three largest terrestrial gravitational wave detectors, LIGO, Virgo and Kagra, will be operational in the US, Europe and Japan respectively. “They send out an alert when they detect a gravitational wave, but usually don't know where it's coming from. Fermi has a big vision and can help a lot. It's very exciting to see if we can catch electromagnetic signals parallel to gravitational waves. Theory says that two colliding black holes shouldn't emit gamma rays. “But if they are two neutron stars, we can see them. This already happened in 2017, and oh my god, we caught one! We can now see many more,” he described.
Michelson is open to all possibilities. “I think there are things out there that we've never even imagined; And theorists have a lot of imagination.
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