The hibernating stellar magnet: First optically active magnetar-candidate discovered

Sep 24, 2008
Astronomers have discovered a possible magnetar that emitted 40 visible-light flashes before disappearing again. Magnetars are young neutron stars with an ultra-strong magnetic field a billion billion times stronger than that of the Earth. The twisting of magnetic field lines in magnetars give rise to 'starquakes', which will eventually lead to an intense soft gamma-ray burst. In the case of the SWIFT source, the optical flares that reached the Earth were probably due to ions ripped out from the surface of the magnetar and gyrating around the field lines. Credit: ESO/L.Calcada

Astronomers have discovered a most bizarre celestial object that emitted 40 visible-light flashes before disappearing again. It is most likely to be a missing link in the family of neutron stars, the first case of an object with an amazingly powerful magnetic field that showed some brief, strong visible-light activity.

This weird object initially misled its discoverers as it showed up as a gamma-ray burst, suggesting the death of a star in the distant Universe. But soon afterwards, it exhibited some unique behaviour that indicates its origin is much closer to us. After the initial gamma-ray pulse, there was a three-day period of activity during which 40 visible-light flares were observed, followed by a brief near-infrared flaring episode 11 days later, which was recorded by ESO's Very Large Telescope. Then the source became dormant again.

"We are dealing with an object that has been hibernating for decades before entering a brief period of activity", explains Alberto J. Castro-Tirado, lead author of a paper in this week's issue of Nature.

The most likely candidate for this mystery object is a 'magnetar' located in our own Milky Way galaxy, about 15 000 light-years away towards the constellation of Vulpecula, the Fox. Magnetars are young neutron stars with an ultra-strong magnetic field a billion billion times stronger than that of the Earth. "A magnetar would wipe the information from all credit cards on Earth from a distance halfway to the Moon," says co-author Antonio de Ugarte Postigo. "Magnetars remain quiescent for decades. It is likely that there is a considerable population in the Milky Way, although only about a dozen have been identified."

Some scientists have noted that magnetars should be evolving towards a pleasant retirement as their magnetic fields decay, but no suitable source had been identified up to now as evidence for this evolutionary scheme. The newly discovered object, known as SWIFT J195509+261406 and showing up initially as a gamma-ray burst (GRB 070610), is the first candidate. The magnetar hypothesis for this object is reinforced by another analysis, based on another set of data, appearing in the same issue of Nature.

Source: ESO

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Modernmystic
2 / 5 (3) Sep 24, 2008
Interesting. If they aren't neutron stars I'm assuming they are just a "more dense" version of white dwarfs? Their electron clouds are perhaps under more gravitational pressure than your regular white dwarf and aren't jammed into the protons like they are in neutron stars?

On edit: Ah NVM looks like they're just a type of neutron star.
JerryPark
5 / 5 (1) Sep 24, 2008
As young neutron stars, why don't magnetars radiate like other neutron stars?
D666
4 / 5 (2) Sep 24, 2008
As young neutron stars, why don't magnetars radiate like other neutron stars?


You mean light? Neutron stars don't radiate light because a neutron star is formed (usually) when a star runs out of fuel and nuclear reactions cease. The absence of outward pressure from the now-silent nuclear furnace allows the star to collapse. If it's large enough, gravitation collapses the atoms and breaks up the nucleii until you have a soup of neutrons. Any radiation coming from a neutron star at this point is from other effects, like the above-mentioned magnetic effects. But no sunlight, sorry.
thales
not rated yet Sep 24, 2008
Sounds like Vernor Vinge's On/Off star.
yyz
2.8 / 5 (4) Sep 24, 2008
Neutron stars do radiate strongly in Xray and gamma-ray light, thus the initial gamma-ray burst detection. But as a young, highly magnetized, rapidly spinning neutron star, the optical & infrared detections give astronomers valuable information on the physical state of this object. Perhaps this outburst was the result of a 'starquake' in the dense neutron crust of this magnetar. Followup observations of this object should prove valuable in nailing down the properties of this ultradense stellar remnant.
barkster
4 / 5 (1) Sep 24, 2008
Thanks, yyz.... That answered my question before I had to ask it. I'm very curious about the cause for the secondaries (visible and IR flashes).
TheTim
4 / 5 (2) Sep 24, 2008
I've been into amateur astronomy for years, and I've always wondered why the neutrons in a neutron star don't decay into proton/electron/anti-neutrino normally. Or if they do, how does this affect the star's output, etc, etc?
yyz
3 / 5 (2) Sep 24, 2008
Two papers posted at the arXiv.org site for September 25 (arXiv:0809.4043 and arXiv:0809.4231) describe in detail the observations made of this strange object. It seems that this may be the first-ever sighting of a magnetar in the optical band of the EM spectrum. The cause of the optical-IR flaring still remains a mystery, but it is noted that few theoretical models exist that might explain the visible-light outbursts. Also, no x-ray flaring was detected during the optical outbursts, contrary to previously observed x-ray variability of suspected magnetars in outburst.
Eco_R1
3 / 5 (1) Sep 25, 2008
if you just look at its magnetic field, will a human be able to function in such high levels of magnetism. i know magnetism dont affect humans, accept if you have pacemker.... but at that levels?
superhuman
5 / 5 (2) Sep 25, 2008
if you just look at its magnetic field, will a human be able to function in such high levels of magnetism. i know magnetism dont affect humans, accept if you have pacemker.... but at that levels?


Changing magnetic fields induce changing electric fields and both of them induce currents (it is described by Maxwell equations).

Extreme field gradients will induce ionic currents in cytoplasm and bodily fluids which will rip through lipid membranes shredding and boiling cells in the process.

An arbitrarily strong EM field gradient would disintegrate a human in a fraction of a second turning him into a hot plasma (if he somehow managed to get that close in one piece).
genesgalore
not rated yet Sep 25, 2008
does anyone have or know where there are pictures of the auroa that the August 27, 1998 burst created???
yyz
1 / 5 (1) Sep 25, 2008
@ genesgalore I don't know about auroral activity related to the 1998 magnetar outburst, but the AAVSO High Energy Observing program had data on the effects of this outburst on the Earth's ionosphere while this magnetar was in outburst mode.Look for info on SGR 1900 14=PSR J1907 0919.
yyz
1 / 5 (1) Sep 25, 2008
That's SGR 1900(plus)14 = PSR J1907(plus)0919.
Graeme
3.5 / 5 (2) Sep 25, 2008
why the neutrons in a neutron star don't decay
The high pressure is needed to overcome the decay energy. To decay the neutron will have to form a larger (but squashed) hydrogen atom and lift up the upper layers of the star, but it cannot mount enough force to do this, and it stays undecayed.
will a human be able to function in such high levels of magnetism
No, the magnetism is so high that the shape of atoms and molecules is changed in to long and thin. Instead of a ball the atom is shaped like a strand of hair, stretched out along the field lines. Known life forms would not survive.
genesgalore
not rated yet Sep 26, 2008
thanks yyz, i was out in the "storm" that evening. the sky was, horizon to horizon, lit up and pulsating like crazy. it was amazing and beautiful.
yyz
2.3 / 5 (3) Sep 26, 2008
Thanks, Graeme, for the note on neutron decay in neutron stars. I suspected this degeneracy was the answer but wasn't sure.
genesgalore
not rated yet Sep 30, 2008
still haven't found a source for pictures of the august 27-28 1998 event.

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