New observations of a very unusual and mysterious star about 15,000 light-years from Earth have revealed a bizarre pattern of stellar activity that astronomers say they have never witnessed.
The star in question is called Swift J1818.0-1607 and was only discovered last year. Swift J1818.0-1607 is what is known as a magnet: a rare neutron star, which forms when supergiant stars fail to reach a supernova, rather than collapsing into incredibly dense nuclei.
Unlike most neutron stars, magnetars are known to produce an extremely powerful magnetic field. Only about 30 of these strange objects have ever been detected in the Milky Way, but even among their strange types, Swift J1818.0-1607 is an unusual value.
This is due to the fact that only a handful of known magnets have been observed to emit radio waves of a similar type to pulsars: another type of neutron star, much more common than magnets, but nevertheless , notable for the way they emit radiation pulses from their magnetic poles.
In the midst of this unique clade of “strong radio” magnets, however, no pulsation has ever been observed in the same way as Swift J1818.0-1607, which led some in the astronomical community to suggest that it could represent some kind of “missing link”. “between magnets and pulsars.
Now, a series of new observations led by astronomers at Australia’s ARC Center of Excellence for Gravitational Wave Discovery (OzGrav) do nothing to suggest that Swift J1818.0-1607’s reputation for strangeness does not be deserved.
In eight observations made with the CSIRO’s Parkes radio telescope over a five-month period in 2020, the researchers observed that the radio’s magnetic pulses changed in character similar to the pulses of a pulsar in May, and then changed to a pulsar. different form of bright / faint blinking in June, before adopting a mysterious mixture of pulsar-like and pulse-like radio pulses in July.
Artist’s print on Swift J1818.0-1607. (OzGrav / Carl Knox)
In the researchers’ new study, they describe this apparent identity crisis in rather sober scientific terms, saying that Swift J1818.0-1607 “[exhibited] “a significant evolution of the time profile during this period”.
But don’t let this language fool you into thinking this wasn’t an extraordinary thing to witness.
“This strange behavior had never been seen before on any other radio magnet,” explains the study’s lead author, Marcus Lower of Swinburne University and CSIRO.
“It seems to have been only a short-lived phenomenon, as by our next observation it had been permanently established in this new magnet-like state.”
Although the mixed messages conveyed by Swift J1818.0-1607 cannot be fully explained, the researchers suggest that fluctuations could represent a form of stellar evolution that we do not yet fully understand.
In part, this is because, while this magnet may be unique (for now), the truth is that magnets in general, let alone high-intensity magnets, still represent a very field of study. young.
“This raises a number of questions,” Lower explained The Sydney Morning Herald.
“Maybe this magnet evolved from a more regular pulsar over time … or maybe we’re missing other magnets in the Milky Way because they’re so far away from us that the low-frequency radio waves we’re seeing are too scattered to detect “.
In other words, this seemingly bizarre behavior may be more common than we know, is that we are only limited in what we currently understand about magnets. However, we are always discovering more.
Swift J1818.0-1607’s new observations suggest that the magnetic axis of the magnet is not aligned with its axis of rotation, but sinks into its southern hemisphere. If so, this is the first for a magnet, which usually has its magnetic fields aligned with its axis of rotation.
But it could also explain some of the changes in the observed radio emission profile, which could reflect radio pulses that are reflected at different heights from the surface of the neutron star.
However, at least one data point (an observation called MJD 59062 on August 1 last year) does not match this version of events. But the team also has a hypothesis about MJD 59062.
“Our best geometric model for this date suggests that the radio beam was tilted briefly toward a completely different magnetic pole located in the northern hemisphere of the magnet,” says Lower.
Researchers say that continuous monitoring of Swift J1818.0-1607 will help us find out what is really going on here.
“We’re looking closely at our data to try to capture one of those volts as it occurs, because if we can do that, we could trace the magnetic field between the magnetic poles,” Lower said. The Sydney Morning Herald.
“Knowing the actual geometry of magnets is also quite important in the theory of neutron stars and being able to predict how they will evolve over time.”
The findings are reported in Monthly notices from the Royal Astronomical Society.