Astronauts see strange activity from one of the strongest magnets in the Universe

Astronauts from the ARC Center of Excellence for Gravitational Wave Detection (OzGrav) and CSIRO have just seen an unprecedented strange behavior from a ‘radio-high’ magnetar – a rare type of neutron star and one of the strongest magnets in Universe.

Their new findings, published today in the Monthly notices from the Royal Astronomical Society (MNRAS), suggesting that magnetars have more complex magnetic fields than previously thought – which could challenge theories of how they are born and how they develop over time.

Magnetars are a rare type of neutron rotating star with some of the most powerful magnetic fields in the Universe. Astronauts found only thirty of these objects in and around the Milky Way – most of which were detected by X-ray telescopes after a full-energy revolution.

However, a handful of these magnets have been shown to emit pulse-like radio beats – the less magnetic cousins ​​that emit radio wave action from their magnetic poles. By observing how the pulses from these ‘radio-high’ magnets change over time bring a particular window into their evolution and geometry.

In March 2020, a new magnet named Swift J1818.0-1607 (J1818 for short) was discovered after a clear X-ray explosion was emitted. Discover quick snapshots of radio beats emanating from the magnetar. Strangely, the appearance of the radio pulses from J1818 was quite different from those seen from other high-radio magnets.

Most radio beats from magnetars maintain a constant brightness across a wide range of observation frequencies. However, the pulses from J1818 were much brighter at low frequencies than high frequencies – similar to those seen in pulsars, another more common type of radio-emitting neutron star.

To better understand how J1818 would grow over time, a team led by scientists from the ARC Center of Excellence for Gravitational Wave Detection (OzGrav) watched it eight times using a CSIRO Parkes radio telescope (ris also known as Murriyang) between May and October. 2020.

During this time, they discovered that the magnetar was under a brief identity crisis: in May it was still emitting the unusual pulsar-like blows previously discovered; however, by June it had begun to blink between a bright and weak state. This fragile behavior reached a peak in July where they saw it spray back and forth between the emission of pulsar-like radio beats and a magnetar.

“This strange behavior has never been seen before in any other high-radio magnetar,” explains lead study author and Marcus PhD at Swinburne University / CSIRO. “Apparently it was just a short-term surprise because with our next observation it was permanently settled in this new magnetar-like state.”

The scientists also looked for changes in pulse shape and brightness at different radio frequencies and compared their observations with a 50-year theoretical model. This model predicts the expected geometry of a pulsar, based on the twisted direction of its polarized light.

“From our observations, we found that the J1818 magnetic axis is not aligned with its rotational axis,” Lower said.

“Instead, the radio-emitting magnetic pole in the southern hemisphere appears to be located just below the equator. Most other magnets have magnetic fields that are exposed to the equator. either according to their spinning axes or somewhat skeptical. ”

“This is the first time we’ve actually seen a magnetar with an unmarked magnetic pole.”

Surprisingly, this magnetic geometry seems to be stable over most observations. This implies that any changes in the profile of the pulse are directly due to changes in the height at which the radio beats are emitted above the surface of a neutron star. However, the prospect of 1 August 2020 stands out as a strange one.

“Our best geometric model for this date suggests that the radio conduction traveled over to a completely different magnetic pole in the northern hemisphere of the magnetar,” says Lower.

A particular lack of any changes in the shape of the magnetar pulse image indicates that the same magnetic field lines induced by the ‘normal’ radio pulses must depend on the pulses seen from the other magnetic pole.

The study suggests that this is evidence that the radio beats from J1818 come from loops of magnetic field lines connecting two poles with a large area, such as those seen connecting the two poles of a horseshoe magnet horses or sunspots on the Sun. This is in contrast to most conventional neutron stars which are expected to have north and south poles on either side of the star connected by a magnetic field in the shape of a donut.

This unique magnetic field configuration is also supported by an independent study of the X18-ray pulses from J1818 detected by the NICER telescope aboard the International Space Station. The X-rays appear to come from either a separated area of ​​magnetic field lines emanating from the surface of the magnetar or two smaller sections, but with a large area.

These findings can affect computer simulations of how magnetars are born and evolved over a long period of time, as the geometry of more complex magnetic fields changes as quickly as their magnetic fields are expected to change. decline over time. In addition, theories showing rapid radio explosions emanating from magnetars must account for potential radio pulses from multiple active sites within their magnetic fields.

Capturing a flip between magnetic poles in action may be the first opportunity to map a magnetic field.

“The Parkes telescope will be keeping a close eye on the magnetar over the next year,” said scientist and study co-author Simon Johnston, of CSIRO Astronomy and Space Science.

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