Are neutron stars considered to be exotic matter

The crowd gives it away

Neutron stars are, so to speak, the super-dense corpses of massive stars that have exploded in a supernova. Since its entire mass is concentrated in a sphere that is no larger than a smaller city, the matter inside is extremely dense. For example, a thimble full of it would weigh more than 500 million tons. Such conditions cannot be reproduced on earth and are also difficult to simulate. Therefore, neutron stars are ideal natural laboratories with which to study the densest and most exotic states of matter known in physics.

The object now analyzed is a binary star system consisting of a white dwarf star and a millisecond pulsar. It is a neutron star that rotates around its own axis at more than 300 revolutions per second and - viewed from Earth - emits light pulses in the radio wavelength range at extremely regular intervals. In the system itself, the two partners circle each other within about nine days. The special constellation of the orbit of the pulsar and the white dwarf allowed the researchers to determine the mass of the neutron star and its companion so precisely. To do this, they used the so-called Shapiro delay, a consequence of Albert Einstein's general theory of relativity, which is much more pronounced under these conditions than in other systems. The principle: The radio waves emitted by the pulsar are influenced by the gravity of the white dwarf on their way to Earth, so that they arrive late. This delay makes it possible to determine the mass of the white dwarf relatively precisely - and from this, with the help of the known data on the orbital behavior of the system, the mass of the neutron star can be inferred fairly precisely.

The unexpectedly large mass of the pulsar is now helping the researchers led by Paul Demorest from the National Radio Astronomy Observatory in Charlottesville to put the existing theories on the structure of neutron stars to the test - especially since some of them differ in terms of their theoretically possible maximum mass. According to the researchers, it is very unlikely that neutron stars are composed of very exotic particles. Such models could therefore be discarded.

Scott Ransom, one of the co-authors, raves about the discovery,? It's incredible that a single number? the mass of this neutron star? can tell us so much about so many different aspects of physics and astrophysics.

P. B. Demorest (National Radio Astronomy Observatory, Charlottesville) et al .: Nature, vol. 467, p. 1081, online pre-publication, doi: 10.1038 / nature09425 dapd / Agnes Hoffmann
October 28, 2010