It was identified as a gamma-ray burst, resulting from a massive explosion in a distant, young galaxy. Then astronomers realised that this flaring object was much closer to home, in fact it was a gamma-ray source within the Milky Way. Astronomers detected 40 visible-light flashes, only for the source to vanish as quickly as it mysteriously appeared. So what generated this huge firework display for astronomers to originally mistaken it for a gamma-ray burst?
It seems we have an answer, and it has surprised many.
One of the rarest objects ever observed may have sprung to life in our galaxy after a long period of calm. This object is a young neutron star with a magnetic field a billion billion times stronger than the Earth’s, otherwise known as a magnetar…
I’ve been captivated by magnetars ever since I wrote “Pulsars are Exploding Unexpectedly and “Magnetars” Might be to Blame” for the Universe Today back in February. On that occasion, observations of once-periodic pulsars exploding with the intensity of “75,000 Suns,” indicated something rather exotic was happening to our once-regularly spinning neutron stars. And it seems as if it has happened again, only this time within our own galaxy.
Neutron stars are the result of supernovae, an extremely dense lump of neutron-degenerate matter, held together by a balance between an intense gravitational field and the Pauli Exclusion Principal; it is one step before matter is completely overcome by its own gravity, collapsing it into a singularity (or black hole). There could be an intermediate step known as a “quark star,” but this has yet to be confirmed observationally. Not only does the neutron star conserve the angular momentum of its parent star, thereby making it spin hundreds of times per second soon after formation, it also conserves the magnetic field of its parent star. The intense magnetic field channels intense beams of electromagnetic radiation from the neutron stars poles, thereby creating a pulsar.
However, sometimes neutron stars are not as well behaved as pulsars. Sometimes they can evolve into an entirely different creature. Due to a stronger magnetic field, magnetars can be born from neutron stars, magnetic field lines becoming forced together, reconnecting and releasing vast amounts of energy. This is when magnetars become visible to observers, and it seems that the recent magnetar eruption, only 15 000 light-years away (near the constellation of Vulpecula), unleashed a huge amount of magnetic energy, making astronomers mistake it for a gamma-ray burst.
The science behind magnetars is still in its infancy, and this event is the first ever magnetar eruption observed in visible light. This magnetar is known as SWIFT J195509+261406 (as it was identified by NASA’s Swift gamma-ray observatory), but it was initially allocated a gamma-ray burst identifier, GRB 070610.
“We are dealing with an object that has been hibernating for decades before entering a brief period of activity.” -Alberto J. Castro-Tirado, lead author of “Flares from a candidate Galactic magnetar suggest a missing link to dim isolated neutron stars,” Nature.
It is thought that many magnetars populate the Milky Way, but they can only be observed when they erupt sporadically, after remaining dormant for decades. Therefore only a handful have been identified.
It is thought that neutron stars eventually grow out of the “magnetar phase,” gradually losing magnetic energy, retiring into a quieter state. It is hard to prove this theory however, no evolutionary candidate has been observed so far that suggests it was once a magnetar. I don’t think these mysterious objects are about to surrender all their secrets too soon…