For the first time, astronomers have experimentally reported a rare type of matter, dubbed “nuclear pasta”, inside the neutron stars that is thought to be responsible for limiting the rotational speed of pulsars.
Neutron star refers to a celestial body consisting entirely of a very dense compact mass of neutrons, the remnant of a star that has collapsed under its own gravity.
The name for the rare state of matter has the word “pasta”, as the nuclei of atoms inside those highly dense stars arrange themselves in different patterns similar to the Italian pasta having non-spherical shapes , as sheets or filaments (lasagna or spaghetti).
“Such conditions are only reached in neutron stars, the most dense objects in the universe besides black holes,” said astronomer José Pons of Alicante University in Spain.
In order to verify the nuclear pasta, astronomers used the rotational speed of pulsars – small dense stars that emit brief, intense bursts of visible radiation, radio waves, and X-rays, and are generally believed to be some form of rapidly rotating neutron stars.
For a long time, astronomers studied pulsars but have never studied any pulsar with a spin period longer than 12 seconds.
“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”, Nanda Rea, a CSIC researcher, from the Institute of Space Sciences (Barcelona) explained. A longer spin period would mean the star is spinning more slowly.
Researchers are of the opinion that these pasta-like formations would hinder the high rotational speed of these neutron stars and the absence of longer spin periods. Pasta like formations inside the stars increases the electric resistivity of the stars making the travelling of the electrons difficult through the material.
This keeps the pulsars to rotate at either a minimum speed, or a maximum period.
Pons, J., Viganò, D., & Rea, N. (2013). A highly resistive layer within the crust of X-ray pulsars limits their spin periods Nature Physics DOI: 10.1038/NPHYS2640