XMM Newton Zeroes in on Zombie Star
Written by Nancy Atkinson
False colour X-ray image of the sky region around SGR 1627-41 obtained with XMM-Newton. Credits: ESA/XMM-Newton/EPIC (P. Esposito et al.)
Soft Gamma-ray Repeaters (SGRs) are strange and relatively rare objects, with only five known to exist (four in the Milky Way and one in the Large Magellanic Cloud.) Each is between 10 and 30 km across, yet contains about twice the mass of the Sun. SGRs are collapsed cores of large stars that have exploded, called neutron stars, and seemingly, they refuse to die: they will repeatedly flare up after remaining quiet for long periods. Now, ESA's XMM-Newton spacecraft zeroed in on one of these stellar zombies, SGR 1627-41 revealing it to be extremely unique and unusual.
What sets SGRs apart from other neutron stars is that they possess magnetic fields that are up to 1000 times stronger. This has led astronomers to call them magnetars.
SGR 1627-41 was discovered in 1998 by NASA’s Compton Gamma Ray Observatory when it burst into life emitting around a hundred short flares during a six-week period. It then faded before X-ray telescopes could measure its rotation rate. Thus, SGR 1627-41 was the only magnetar with an unknown period.
But now, XMM Newton was able to determine the rotation rate for the first time: it rotates once every 2.6 seconds. “This makes it the second fastest rotating magnetar known,” says Sandro Mereghetti, INAF/Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan, one of the team.
XMM Newton Spacecraft. Credit: ESA
Theorists are still puzzling over how these objects can have such strong magnetic fields. One idea is that they are born spinning very quickly, at 2-3 milliseconds. Ordinary neutron stars are born spinning at least ten times more slowly. The rapid rotation of a new-born magnetar, combined with convection patterns in its interior, gives it a highly efficient dynamo, which builds up such an enormous field.
With a rotation rate of 2.6 seconds, this magnetar must be old enough to have slowed down. Another clue to the magnetar’s age is that it is still surrounded by a supernova remnant. During the measurement of its rotation rate, XMM-Newton also detected X-rays coming from the debris of an exploded star, possibly the same one that created the magnetar. “These usually fade to invisibility after a few tens of thousand years. The fact that we still see this one means it is probably only a few thousand years old”, says Mereghetti.
If it flares again, the team plan to re-measure its rotation rate. Any difference will tell them how quickly the object is decelerating. There is also the chance that SGR 1627-41 will release a giant flare. Only three such events have been seen in the last 30 years, each from a different SGR, but not from SGR 1627-41.
These superflares can supply as much energy to Earth as solar flares, even though they are halfway across the Galaxy, whereas the Sun is at our celestial doorstep. “These are intriguing objects; we have much still to learn about them,” says Mereghetti.
Source: ESA
Filed under: Astronomy, Satellites
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January 13th, 2009 at 6:21 pm
After reading about Brad Schaefer's research on recurrent novae (RNe) posted Jan 12, I was curious to know if RNe that occur more frequently may lead to faster spinning, millisecond pulsars (precursors to SGRs and magnetars) due to the spin up effect of mass transfer between the white dwarf progenitor and its stellar companion. While other factors must surely come into play, I'm curious if any research may have been done looking for any link between frequency of of eruption of RNes and SGRs?
January 14th, 2009 at 2:05 am
Hi Jon,
Recurrent novae are close binary systems one partner of which is a White Dwarf, while the other is a Red Giant which fills up its roche volume. Then, mass from the Red Giant falls into the White Dwarf. Such, the mass of the White Dwarf grows, it gets a layer of hydrogen that is highly compressed by gravity and heated up by the infalling matter, and such every now and then nuclear fusion occurs which produces a nova event, again and again in millions of years. Finally, after many novae of that White Dwarf, its mass has grown beyond the chandrasekhar limit of 1,44 solar masses, and the White Dwarf explodes in a Ia supernova.
Pulsars are neutron stars which are the result of a type II supernova, where a very massive star collapses at the end of its life. Neutron stars have masses of two to three solar masses, they are much more smaller and much more denser than White Dwarfs. The fast spinning observed in neutron stars is a result of the conversation of momentum of the core of the progenitor star, not the result of the impact of matter from a partner star.
Pulsars are thought to create eruptions by stellar quakes, while recurrent novae create eruptions by nuclear fusion reactions on their surface. These two scenarios are very differnet one from the other, there is no likely link between the two.
Regards
Günther
January 14th, 2009 at 9:40 am
'revealing it to be extremely unique and unusual'
There is no such thing as 'extremely unique'. Its either unique or it isn't.
January 14th, 2009 at 12:52 pm
Hi GBendt, Thanks for your kind response regarding Type Ia and Type II SNe remnants. I take it that no superdense remnants (neutron, quark stars) are produced in Type Ia SN remnants? My initial impression was that millisecond pulsars in globular clusters were due to mass transfer between white dwarfs and red giants although initial conditions between such systems in globular clusters must be quite different than isolated WD-RG systems in interstellar space.Exactly what type of stellar systems are proposed to account for millisecond pulsars in globular clusters? I've read of WD-WD mergers or WD-NS mergers possibly being culprits in millisecond PSRs in globular clusters. Thanks for your thoughtful reply to my inquiry. Regards, Jon
January 14th, 2009 at 1:05 pm
There's been so much learned in the period since the space telescope,other orbiting detectors and very large telescopes created. Before about 1990, most thought the universe was relatively quiet, now, there are so many violent events I was able to shut-up most of these wacko co-workers who believes in UFOs and 'aliens' among us when I tell them no amount of technology can overcome the gamma rays bursts,etc which is deadly to advanced life-forms. Perhaps there are many robotic probes roaming deep outer space, millions/billions of years after their living creators ceased to exist.
January 14th, 2009 at 1:39 pm
Somewhat away from the subject, I thought a type 1a supernova was a white dwarf star that gathered enough matter from its companion it will explode like a super nuclear bomb when it neared critical mass of 1.44 solar mass, leaving no remnant. Yet, in 2006, the most powerful type 2 supernova
was observed, at least 100billion times the light,power of the sun, that no remnant was found, not even a black hole-this was at one time a super heavy mass star-perhaps this was one of the last of the modified early type super heavy mass stars the early universe
had, perhaps 300=1000 times the mass of the sun.I sure hope our galaxy don't have one of these super monsters!.
January 14th, 2009 at 3:20 pm
Is the exceptional rotational velocity of a magnetar a result of the original rotational velocity of the star shedding excess mass in an explosion and there by increasing in speed by reducing it's circumference the same way an ice skater spins faster when she draws her arms in close while pirouetting?
January 14th, 2009 at 7:03 pm
# Pedant Says:
January 14th, 2009 at 9:40 am
'revealing it to be extremely unique and unusual'
There is no such thing as 'extremely unique'. Its either unique or it isn't.
>>>Your name says it all Pedant. I'm glad you realise it. Too bad nobody else cares.
January 14th, 2009 at 7:05 pm
Silver Thread Says:
January 14th, 2009 at 3:20 pm
Yes Silver Thread – that is the basic principle. Conservation of Angular Momentum it's called.
January 15th, 2009 at 9:54 am
If "unique" is defined (and there are many variations) as, "different from the status quo"… then adding a subjective adjective is fine. In this manner, it can be used by the author to communicate some excitement about the object or subject.
Really though… this is a informational site / WEBLOG. Which means it is an INFORMAL means of communication. If you are going to sit in front of your computer, with your ass so puckered up to the point you are going to judge and play "grammar police", I suggest you find someplace else to feed your insecurities and need to be more intelligent than others.
January 17th, 2009 at 10:06 am
Initially, I thought this object to have a Type Ia progenitor, a probable recurrent novae consisting of a white dwarf drawing matter off its' red giant companion & in the process spinning up the resultant neutron star & winding up its magnetic field as seen in magnetars. GBendt lays out the case that this object was probably a Type II event( subtype non-specified) which implies a 'core-collapse' event by a single star. No mention was made in the ESA press release as to the progenitors' type (Note that a Type II event can also spin-up a neuron star-magnetar)(Thanks GBendt). But nowhere can I pin down exactly what type of SN event produced this SGR-magnetar. Colliding WD-NS and NS-NS scenarios also can't be ruled out. So my question is what was the leading theory for the progenitor(s) of this enigmatic object?