June 14, 2013
Evidence Of New Phase In Neutron Stars Discovered
Lee Rannals for redOrbit.com — Your Universe Online
University of Alicante researchers have discovered the first evidence of a new phase in neutron stars.
The scientists wrote in the journal Nature Physics that they have detected what may be the first observational evidence of existence of a new exotic phase of matter in what is known as the "inner crust" of neutron stars, or pulsars.
"This may be the first observational evidence of existence of the phase of nuclear ℠pasta´ inside neutron stars, which may allow that future missions of X-ray observatories can be used to define aspects of how nuclear interaction works, which is not yet entirely clear," said JosÃ© A. Pons, lecturer at the University of Alicante´s Relativistic Astrophysics Group and Director of the Department of Applied Physics, who led the work.
Nuclear pasta occurs when the combination of nuclear and electromagnetic forces favor the ordering of the nucleons in non-spherical shapes. Pulsars are born spinning more than 100 times per second, but as their magnetic fields slow them down, it increases the rotation period.
"Meanwhile, the inner crust corrodes the star's magnetic field and when it becomes weak, it is unable to further slow down the rotation of the star: the pulsar is 'al dente', with a period of about 10-12 seconds," says Daniele ViganÃ², a doctoral student at the University of Alicante.
Radio pulsars have been known to have a limited spin period with no theoretical explanation. This limit is typically thought to be a simple observational effect in which those with slower rotation are less bright in radio and cannot be observed.
"Space missions in the past decade have identified a growing number of isolated X-ray pulsars, and to our surprise, none of them has a rotation period longer than 12 seconds, but there was no theoretical explanation for this phenomenon," said Nanda Rea, a CSIC researcher, from the Institute of Space Sciences (Barcelona) explains.
Rea was part of another research project recently that discovered that magnetars are more common than previously thought. Magnetars are neutron stars that have a relatively low spin rate while also generating occasional large blasts of X-rays, which derives from magnetic energy stored within it.
Rea and colleagues, along with Pons, said they believe that about once a year in every galaxy a quiet magnetar is born.