Mysterious Pulsar With Hidden Powers Discovered

Mysterious Pulsar With Hidden Powers Discovered

  7:07:00 PM    Science Lover

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Dramatic flares and bursts of energy -- activity previously thought reserved for only the strongest magnetized pulsars -- has been observed emanating from a weakly magnetised, slowly rotating pulsar. The international team of astrophysicists who made the discovery believe that the source of the pulsar's power may be hidden deep within its surface.

An artistic impression of a magnetar with a very complicated 
magnetic field at its interior and a simple small dipolar 
field outside. (Credit: ESA / Christophe Carreau)

Pulsars, or neutron stars, are the collapsed remains of massive stars. Although they are on average only about 30 km in diameter, they have hugely powerful surface magnetic fields, billions of times that of our Sun.

The most extreme kind of pulsars have a surface magnetic field 50-1000 times stronger than normal and emit powerful flares of gamma rays and X-rays. Named magnetars (which stands for "magnetic stars") by astronomers, their huge magnetic fields are thought to be the ultimate source of power for the bursts of gamma rays.

Theoretical studies indicate that in magnetars the internal field is actually stronger than the surface field, a property which can deform the crust and propagate outwards. The decay of the magnetic field leads to the production of steady and bursting X-ray emission through the heating of the neutron star crust or the acceleration of particles.

Now, research recently published in Science, suggests that the same power source can also work for weaker, non-magnetar, pulsars. The observations, which were made by NASA's Chandra and Swift X-ray observatories of the neutron star SGR 0418, may indicate the presence of a huge internal magnetic field in these seemingly less powerful pulsars, which is not matched by their surface magnetic field.

"We have now discovered bursts and flares, i.e. magnetar-like activity, from a new pulsar whose magnetic field is very low," said Dr Silvia Zane, from UCL's (University College London) Mullard Space Science Laboratory, and an author of the research.

Pulsars are highly magnetized, and as they rotate winds of high-energy particles carry energy away from the star, causing the rotation rate of the star to gradually decrease. What sets SGR 0418 apart from similar neutron stars is that, unlike those stars that are observed to be gradually rotating more slowly, careful monitoring of SGR 0418 over a span of 490 days has revealed no evidence that its rotation is decreasing.

"It is the very first time this has been observed and the discovery poses the question of where the powering mechanism is in this case. At this point, we are also interested in how many of the other normal, low field neutron stars that populate the galaxy can at some point wake up and manifest themselves as a flaring source," said Dr Zane.

A crucial question is how large an imbalance can be maintained between the surface and interior magnetic fields. SGR 0418 represents an important test case.

"If further observations by Chandra and other satellites push the surface magnetic field limit lower, then theorists may have to dig deeper for an explanation of this enigmatic object," said Dr Nanda Rea, Institut de Ciencies de l'Espai (ICE-CSIC, IEEC) in Barcelona, who led the discovery.

This work was part funded by the Science and Technologies Research Council, UK. NASA's Marshall Space Flight Center manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations.

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Young Pulsar Shows Its Hand

Young Pulsar Shows Its Hand

  12:31:00 AM    Science Lover

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This graphic demonstrates the difference in physical size between the nebula around the pulsar B1509-58 and its more famous cousin, the Crab Nebula, seen on the left. The Crab was generated when a star collapsed, as seen in 1054 A.D. Since then, the nebula its pulsar created has increased in size to some 10 light years. In contrast, astronomers think the B1509-58 system is about 1,700 years old, yet its nebula now covers some 150 light years. The discrepancy in these sizes may be due to the different environment each pulsar was born into. (Credit: NASA/CXC/SAO/P. Slane et al.)

A small, dense object only twelve miles in diameter is responsible for a beautiful X-ray nebula that spans 150 light years.

At the center of a new image made by NASA's Chandra X-ray Observatory is a very young and powerful pulsar, known as PSR B1509-58, or B1509 for short. The pulsar is a rapidly spinning neutron star which is spewing energy out into the space around it to create complex and intriguing structures, including one that resembles a large cosmic hand.

In the new image, the lowest energy X-rays that Chandra detects are red, the medium range is green, and the most energetic ones are colored blue. Astronomers think that B1509 is about 1,700 years old and is located about 17,000 light years away.

Neutron stars are created when massive stars run out of fuel and collapse. B1509 is spinning completely around almost 7 times every second and is releasing energy into its environment at a prodigious rate -- presumably because it has an intense magnetic field at its surface, estimated to be 15 trillion times stronger than the Earth's magnetic field.

The combination of rapid rotation and ultra-strong magnetic field makes B1509 one of the most powerful electromagnetic generators in the Galaxy. This generator drives an energetic wind of electrons and ions away from the neutron star. As the electrons move through the magnetized nebula, they radiate away their energy and create the elaborate nebula seen by Chandra.

In the innermost regions, a faint circle surrounds the pulsar, and marks the spot where the wind is rapidly decelerated by the slowly expanding nebula. In this way, B1509 shares some striking similarities to the famous Crab Nebula. However B1509's nebula is 15 times wider than the Crab's diameter of 10 light years.

Finger-like structures extend to the north, apparently energizing knots of material in a neighboring gas cloud known as RCW 89. The transfer of energy from the wind to these knots makes them glow brightly in X-rays (orange and red features to the upper right of the image). The temperature in this region appears to vary in a circular pattern around this ring of emission, suggesting that the pulsar may be precessing like a spinning top and sweeping an energizing beam around the gas in RCW 89.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

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