to meet the oldest magnetar in the galaxy?

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Australian researchers announced on Wednesday that they had observed a radio wave flash that repeats itself every 18.18. minute at the edge of our galaxy. This is unheard of and experts are wondering what the cause may be.

It appeared every 18.18. minute (18 minutes and 16 seconds). It was a very intense flash of radio waves that repeated itself at a certain place in the Milky Way, and which today “intrigues astronomers”, assures Natasha Hurley-Walker, astrophysicist at Curtin University, a member of the research team who discovered it.

Their observations, published Wednesday, January 26, in the scientific journal Nature, quickly triggered a wave of articles about this new “rummy mystery,” embodied by a light signal of unknown origin, visible with the punctuality of a three-month-old Swiss cuckoo. in 2018 before it disappears completely.

On the trail of massive stars that exploded

These radio flashes were emitted by an as yet unidentified space object, dubbed GLEAM-X J162759.5-523504 and located 4,000 light-years from Earth. When it lit up every 18.18. minute, it was simply the “brightest point visible from Earth,” the study authors say. Even more than “the radio emissions of supermassive black holes, which are nonetheless the brightest we know in this wave spectrum”, assures Natasha Hurley-Walker. A feature that is already exciting enough in itself.

But there was an apparently much bigger mystery that has to do with the speed at which GLEAM-X J162759.5-523504 “turned on”. It is certainly not the only space object that emits glimpses of radio waves at regular intervals. It is even one of the trademarks of pulsars or neutron stars, which is what is left “after the explosion of a large star about eight to ten times the size of our sun”, explains Ismaël Cognard, astrophysicist at the Laboratory of Physics and Chemistry in the Environment and Space of Orléans and specialist in pulsars, contacted by France 24.

Once formed, these pulsars begin to ignite on their own; first very fast, then gradually slower (over periods of several million years). Their poles emit the famous glimpses of radio waves, which can be picked up by telescopes as they enter their field of view. Hence the impression that they turn on and off.

But none of the 3,000 currently identified pulsars complete their revolution in 18.18 minutes … “In general, they spin much faster, about a second. The slowest ever observed to date takes 23 seconds to complete its rotation”, says Ismaël Cognard.

GLEAM-X J162759.5-523504 can not be the naughty little pulsar either. “When these neutron stars rotate too slowly, they no longer have the energy to emit their radio flash and turn off completely,” says this astrophysicist.

A released energy equal to 1010 Hiroshima bomber

“When I realized we had never seen anything like it before, I got cold sweats. After all, there’s just one big community looking for just that: space radio signals that repeat themselves and could be signs of the presence of Extraterrestrial life, “wrote Natasha Hurley-Walker. In other words, would Earth have missed its third kind of encounter in 2018?

However, all indications are that these emissions are of natural origin. “The energy released every 18 minutes by these flashes corresponds to the energy that the sun has sent to Earth for 100 days or corresponds to that of 1010 Hiroshima bomb blasts. I can not imagine a civilization, no matter how advanced, capable of doing so “, emphasizes Diego Gotz, astrophysicist at the Commissariat for Atomic Energy and Alternative Energies (CEA), contacted by France 24.

However, pulsars or potentially small green men are not the only ones capable of transmitting radio signals. “The most likely person responsible is the magnetar,” assures Ismaël Cognard. When a massive star explodes, it is not doomed to become a pulsar. It can also transform into a magnetar, which is another form of neutron star. “The big difference is that the magnetic field around them is 100 to 1,000 times stronger than that of the pulsars,” says Diego Gotz.

A crucial feature: it allows the magnetar to continue emitting radio flashes much longer “by drawing its energy from this magnetic field, which the pulsar does not have”, explains the CEA expert.

The fact is that until now, “the longest rotation ever observed for a magnetar was just over a minute,” emphasizes Ismaël Cognard. Most flash every 2 to 12 seconds. But for him it is theoretically very possible.

GLEAM-X J162759.5-523504 would simply be the oldest magnetar ever observed. Its 18.18-minute rotation suggests it is “around the age of our galaxy,” concludes Diego Gotz.

The trace of the very old magnetar is also the trace favored by the Australian scientists who discovered this strange phenomenon. But “it can also be a type of space object that has never been observed before, simply because we have not yet looked for radio signals that repeat themselves over such long periods of time,” notes Natasha Hurley-Walker. In that case, this would only be the beginning of the adventure.

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