The new observations of a very unusual and mysterious star located about 15,000 light-years away from Earth have revealed a bizarre pattern of stellar activity that astronomers say they have never witnessed before.
The star in question is called Swift J1818.0-1607 and was discovered only last year. Swift J1818.0–1607 is what is known as a magnet – a rare race of neutron stars, which forms when supergiant stars fail to reach the supernova, instead of collapsing into incredibly dense nuclei.
Unlike most neutron stars, however, magnetars are known to produce an extremely strong magnetic field. Only about 30 of these strange objects have ever been detected in the Milky Way, but even among their strange collisions, Swift J1818.0-1607 is an unusual sight.
That’s because only a handful of known magnets have ever been observed to emit radio waves of a kind similar to pulsars – another type of neutron star, much more common than magnets, but still remarkable for the way they radiate radiation pulses from their magnets. pillars.
In the midst of this exclusive clade of “powerful radio” magnets, however, none have ever been observed pulsing in the same way as Swift J1818.0-1607, prompting some in the astronomical community to suggest that they might represent some kind of “Missing link” “between magnets and pulsars.
Now, a series of new observations led by astronomers at the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav) in Australia do nothing to suggest that Swift J1818.0-1607’s reputation for strangeness is undeserved.
In eight observations made with the CSIRO Parkes radio telescope over a five-month period in 2020, researchers observed the radio pulses of the magnet that change distinctly in character – resembling the pulses of a pulsar in May, then changing to a different shape. of bright / faint glitter in June, before adopting in July a mysterious mixture of pulsar-type and magnetic-type radio pulses.
The artist’s impression of Swift J1818.0–1607. (OzGrav / Carl Knox)
In the researchers’ new study, they describe this apparent identity crisis in rather sober scientific terms, saying Swift J1818.0-1607 “[exhibited] significant evolution of the time profile during this period “.
But don’t let this language fool you into believing that this wasn’t an extraordinary thing to witness.
“This bizarre behavior has never been seen in any other loudspeaker,” explains the study’s lead author, Marcus Lower of Swinburne University and CSIRO.
“It seems to have been only a short-lived phenomenon, because, through our next observation, it has settled definitively into this new magnet-like state.”
While the mixed messages transmitted by Swift J1818.0-1607 cannot be fully explained, researchers suggest that fluctuations could be a form of stellar evolution that we do not yet fully understand.
In part, this is because, although this magnet may be unique (for now), the truth is that magnets in general, let alone loud magnets, are still a very young field of study.
“This raises a number of questions,” Lower explained Sydney Morning Herald.
“Maybe this magnet has evolved from a more regular pulsar over time … or maybe we’re missing other Milky Way magnets because they’re so far away from us that the low-frequency radio waves we see are too scattered for us to detect. “
In other words, this seemingly bizarre behavior may be more common than we know, only we are limited in what we currently understand about magnets. However, we always find out more.
The new observations of Swift J1818.0–1607 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 a first for a magnet – which usually has magnetic fields aligned with the axis of rotation.
But it could also explain some of the changes in the observed radio emission profile, with potentially reflecting radio pulses being emitted at different altitudes around 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 that version of events. But the team also has a hypothesis for MJD 59062.
“Our best geometric model for this date suggests that the radio beam briefly flipped over to a completely different magnetic pole located in the northern hemisphere of the magnet,” says Lower.
Researchers say that continuous monitoring of the Swift J1818.0-1607 will help us figure out what’s really going on here.
“We look closely at our data to try to capture one of those flips as it happens, because if we could do that, we could map the magnetic field between the magnetic poles,” Lower said Sydney Morning Herald.
“Knowledge of the real geometry of magnets is also quite important in the theory of neutron stars and the ability to predict how they will evolve over time.”
The findings are reported in Monthly notifications from the Royal Astronomical Society.