Australian astronomers from the International Center for Research in Radio Astronomy (Icrar) announced this week, in the review Nature, the detection of an “object” (star), located about 4,000 light years from Earth, which emits a strong radio signal for thirty to sixty seconds according to Guardian, every 18.18 minutes. An abnormally long period, never observed until now.
“It’s an unusual object,” remarks soberly the radio astronomer Ismaël Cognard, of the French National Center for Scientific Research (CNRS). This discovery, dubbed GLEAM-X J162759.5-523504.3, opens the way to a new field of observation of the sky.
How did the team discover this object?
Astronomers are familiar with celestial bodies that emit regular electromagnetic waves but with much shorter “periods”. The most numerous, the pulsars – a kind of extremely compact neutron star – spin on themselves in an ultra-fast fashion, emitting, like a beacon, regular radiation over a period ranging from a few milliseconds to a few seconds. Another “species” of neutron star, much rarer, the magnetar, goes up to ten seconds.
The team led by Natasha Hurley-Walker, from Curtin University, Australia, came up with the idea of mining the data collected by a giant low-frequency radio telescope in the Australian Outback, the Murchinson Widefield Array. It observes such objects, looking for signals emitted at a longer period than usual. It was a young doctoral student who started the project… and found this “object”.
“It was completely unexpected. It was a bit scary for an astronomer because there is nothing known in the sky that does that, ”says Natasha Hurley-Walker in a statement from Icrar.
A difficult process “because it is technically very difficult and very costly in terms of calculation”, underlines Fabian Schüssler, astrophysicist at the Atomic Energy Commission. Radio telescopes produce mountains of data that require high algorithms and computing power to get a result.
“It’s a good example of a discovery that takes place when you search in a space of unexplored parameters,” adds Fabian Schüssler. In other words, when we look where we don’t have the habit or the means to do so.
Is it a new type of star?
The existence of this object had been predicted by theory, notes astrophysicist Natasha Hurley-Walker. It would be an ultra-long-period magnetar, a kind of neutron star rotating very slowly on itself.
A “possible” hypothesis according to Fabian Schüssler, because “we know that the rotation of a neutron star will slow down as it continues to exist”. Like a spinning top spinning slower and slower.
How to explain the emission of a radio wave every 18 minutes?
Which poses another problem. The Australian astrophysicist indeed noted that the observed object “should not have enough energy to produce this type of radio wave every 18 minutes”. However, its emission is very bright, which does not match with an “object which rotates more slowly and should therefore have a much weaker emission, to the point of becoming undetectable”, according to the astrophysicist at the Atomic Energy Commission.
The signal was recorded over a period of three months, at the beginning of 2018. The object has not disappeared, even if its signal is no longer detected.
Ismaël Cognard, of the CNRS, relies on a theory to explain the strength of the recorded emission: “Some magnetars have very bright emission periods. We begin to imagine that there are cracks in the equivalent of the crust of the magnetar, which would influence its magnetic field, by boosting the recorded emission.
Does the detected mysterious object still exist? ” Yes! “replies the astronomer. It has become undetectable but the hunt is on to find its congeners.