A month before being shot dead in his official car, in October 1963, United States President John F. Kennedy approved the launch of satellites to warn of the greatest disaster imaginable: the explosion of atomic bombs.
In 1967, this surveillance program called Vela detected mysterious bursts that did not come from Earth, but from outer space.
The matter was kept in a drawer until, years later, it was learned that those signals were the most powerful type of radiation in the universe, possibly arriving from outside our galaxy.
Without anyone having planned it, a new way of observing the universe had been inaugurated: gamma ray astronomy.
Invisible to the human eye, gamma rays are ubiquitous and allow us to study the most violent phenomena in the cosmos.
“In a brief instant, gamma-ray bursts release more energy than all the stars in the universe combined,” summarizes Peter Michelson, astrophysicist at Stanford University (USA) and intellectual father of the
Fermi
gamma-ray telescope .
This space observatory was launched in 2008 by NASA to continue in a more scientific way the surveillance work started by the Cold War satellites.
In a matter of hours, the team of more than 400 scientists from 17 countries associated with this telescope can detect a new source of gamma rays, locate its origin and alert other space and ground telescopes to observe it.
For the first time, those responsible for the main scientific instrument aboard
Fermi
have met in Spain to discuss their new objectives, including understanding a third of all signals, which have an unknown origin.
Representation of a supernova.
POT
Short bursts of gamma rays last fractions of a second.
They occur just as two neutron stars collide, objects so dense and compact that a single teaspoon weighs a billion tons.
Long bursts, lasting a few minutes at most, occur when a star about 30 times larger than the Sun reaches the end of its life and explodes, forming a supernova.
The outer layers are thrown away as its core collapses in on itself.
The force of gravity is so strong that a point of infinite density is formed: a black hole.
“If the hole also rotates on itself, which almost always happens, a jet of gamma rays emerges as powerful as that produced by an entire galaxy,” summarizes Michelson.
No atomic bomb would be capable of producing even remotely similar energy.
Irish astrophysicist Deirdre Horan, a member of the Fermi science team, explains: “Gamma rays are also one of the types of radiation that fluctuates the fastest and most dramatically;
to the point that some sources turn the sky into a discotheque.”
“It's fascinating how nature can produce something like that,” she highlights.
The researcher is referring to pulsars, rotating neutron stars that emit periodic flashes with such accuracy that they can be used as chronometers to measure other phenomena with very high precision, such as the radiation produced by the Big Bang, 13.7 billion years ago.
Fermi
watches 24 hours a day, every day of the week
.
From its orbit, more than 500 kilometers from the 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 point in space literally surrounded by sources of gamma rays, many of them pulsars of exquisite punctuality.
Some signals come from so far away that it is dizzying: it is gamma light that was emitted 12.5 billion years ago, when the universe was almost a newborn.
Due to the accelerated expansion of the cosmos, this object is already 25 billion light years away, meaning that to reach it you would have to travel at the speed of light for almost twice the total age of the universe.
Charged atomic particles pepper
Fermi
's equipment constantly.
Although in theory it was built to last only five years, its ideologues and builders made sure to give it large solar panels that continue to function despite having lost efficiency due to the constant radioactive bombardment.
On at least one occasion the telescope has had to avoid pieces of space debris that could have knocked it out forever.
The scientific team, meeting until Friday at the Institute of Theoretical Physics in Madrid, has calculated that the device can last another decade.
It is crucial that it does so, because without it humanity would be blind to this type of gamma rays;
there is no successor in sight.
Illustration of the Milky Way with the two gamma ray bubbles discovered by the 'Fermi' telescope.NASA
The Extremaduran astrophysicist Miguel Ángel Sánchez Conde will be the new scientific coordinator of the Fermi-LAT collaboration.
One of his main objectives is to use the telescope to try to identify dark matter.
“It would be a discovery that would take us directly to Stockholm to collect the Nobel Prize,” he highlights.
Dark matter makes up 25% of the entire universe, but no one has been able to observe it or determine what it is made of.
“Many of the unidentified sources could be small halos of dark matter that are annihilating, and in doing so emit gamma rays,” details Sánchez.
This possibility could fit with some current proposals to explain dark matter, such as weakly interacting massive particles, WIMPS in English.
One of the “biggest mysteries” facing the team is right in the center of our galaxy, explains Sánchez.
In this place there is a black hole—Sagittarius A*—with a mass four million times greater than the Sun. “Since 2010 we have been capturing a constant signal from the galactic center.
But in the other galaxies with supermassive black holes in the center we do not see anything similar.
It's an excess of gamma rays that we simply cannot understand.
No one knows why this happens, but new studies are published almost every day on this problem.
There are already thousands of studies on this mystery,” confesses the researcher.
In 2010, Fermi discovered a gigantic bubble-like structure located just above and below the center of our galaxy.
The two lobes are so enormous that it would take 50,000 years to cross them from end to end traveling at the speed of light.
Fourteen years later, these Fermi bubbles remain one of the greatest mysteries of our cosmic environment.
It is possible that they are the remains of Sagittarius A*'s last feast when he swallowed a gas cloud about six million years ago.
Or the enigma may be related to that constant gamma ray signal that arrives from the galactic center and which, in turn, could be due to the annihilation of dark matter, argues Sánchez.
For the Irish Horan, another great moment will come in approximately a month, when the three large terrestrial gravitational wave detectors LIGO, Virgo and Kagra, in the US, Europe and Japan, respectively, begin to operate.
“They will send an alert as soon as they detect a gravitational wave, but normally it is not known where it comes from.
Fermi has a huge field of view and can help a lot.
It is very stimulating to see if we can capture electromagnetic signals as a counterpart to gravitational waves.
Theory tells us that two colliding black holes should not emit gamma rays.
But if they are two neutron stars, we could see them.
This already happened in 2017 and it was like, Oh my God, we caught one!
We will probably see many more now,” she details.
Michelson sees all possibilities open.
“I think there are things out there that we haven't even imagined;
and theorists have a lot of imagination.”
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