Magnetars
Magnetars
In many cases the field of these magnetic stars is periodic; the field's direction as well as its magnitude may vary with time. Magnetic stars may have enormous starspots (analogous to sunspots), which would account for the strong magnetic fields. Field strength and direction could be expected to vary as the star's rotation carried particular starspots to the far side of the star.
These amazing stars not only possess and incredible magnetic field, but also temperatures on these starts reach an amazing 18,000,000 F. This extreme condition is partly due to the interaction of the magnetic field and the gravitational forces. Furthermore, the intense magnetic causes the crust to fracture, releasing energy in the process. As a result, this energy is perceived as a burst of X-rays. These rays are the basis of the SGR, and when our detectors find these bursts we are witnessing a starquake.
Magentars in action
Quicktime movie showing scientist's concept of a magnetic reconnection-driven burst from a magnetar.
Credit: Dr. Robert Mallozzi of University of Alabama/Huntsville and NASA
In the 1960's, the cold war was raging in full effect and the threat of a nuclear attack pervaded the minds of many. To detect any nuclear activity, the Dept. of Defense launched a series of satellites in project "Vela" to detect gamma emmsions from the explosions. To make sure the satellites would not sound an alarm from coincidental gamma emissions from space, scientists on the project went through pages of data collected from the satellites and found unexplained bursts of gamma emissions.
These bursts were totally different from those resulting from an explosion and could not be explained by solar flares, supernova or other sources as there were no phenomena coinciding with the times of the bursts. These discoveries were actually purely luck as the satellites were incorrectly calibrated and were oversensitive or else they would not have detected the emissions.
Once the bursts were discovered, the team used the the different satellites to find the location of the source and found that it was far outside our solar system and most likely outside of our galaxy as well. It was determined that larger detectors should be sent up on balloons to retrieve more data and track more bursts. It should be noted that beer cans were essential to this project as they were used to shield sensitive equipments on the balloons.
In 1991, a new array of satellites was launched named the Compton Gamma Ray Observatory which have much larger detectors and have collected much more data on these phenomena. Then in 1992, astrophysicists Dr. Robert Duncun and Dr. Christopher Thompson offered a magnetic theory that modeled the violent afterlife of the neutron star lasting about 10,000 years.
Finally, in 1996, this theory was confirmed and determined these repeating sources were determined to be neutron stars with intense magnetic fields, magnetars.
Magnetars are an important discovery as they explain the repeating gamma emissions in space. These emissions are most likely connected to the extremely large magnetic fields of the magnetars. These fields are the result of a new neutron star rotating quickly. When the star is forming, there is convection due to the hot fluid, consisting mostly of neutrons and some charged particles, trying to cool off by the surface. The hot fluid on the inside moves quickly and finds its way to the cooler surface. Since there are charge carriers, the magnetic field lines become trapped in the fluid. This moving fluid in combination with the rotation creates the magnetic field of the star.
Since a newborn neutron star is extremely hot and rotating very fast, an enormous magnetic field can be formed. This field becomes trapped when the surface cools and solidifies into a dense, super-magnet. In the first ten thousand years, a magnetar is still very hot so it emits x-rays off its surface. The star quakes recently discovered are caused by the intense field shaking the surface, disrupting the solid crust. There is an intense emission of x-rays, which are the main form of electro-magnetic waves given off from the sta,r during these quakes . It is not yet know exactly how many magnetars there are in the galaxy but they seem to account for about 10% of the neutron stars in the sky.
It is not yet know exactly how many magnetars there are in the galaxy but they seem to account for about 10% of the neutron stars in the sky and this number may actually be as large as 50%. There may be millions of magnetars in the universe but after about 10,000 years, the magnetic energy sources start to dissipate which corresponds to the fact that no old soft gamma repeaters have been found. This makes finding old magnetars somewhat difficult making the analysis of how prevalent they are difficult.
Picture demonstrating the Pulsar Geometry. Credit:
NASA Space Science News
Physics A35-2 Prof. Ellis (1 pm.)
Reseach: Fernando Zumbado and John Kucera
Web page design: Fernando Zumbado
Northwestern University http://www.nwu.edu