The Magnificent Seven (neutron Stars) - Research

Research

The seven objects seem to be the best laboratory to study neutron star atmospheres and, probably, internal structure. The holy grail of neutron star astrophysics is the determination of the equation of state (EOS) of matter at supra-nuclear densities. The most direct way of constraining the EOS is to measure simultaneously the neutron star mass and radius. If a neutron star emits blackbody radiation from its surface of radius at homogeneous temperature, the received flux at distance is:

So, if distance is known and can be determined by spectral analysis, the previous relation immediately yields the star radius. Reality is somewhat more complicated, but this oversimplified analysis catches the essence of what is needed in order to measure the neutron star radius: distance, flux and surface temperature. Observing the star thermal emission is therefore crucial. Among all thermally emitting neutrons stars the Magnificent Seven are the only ones with a purely blackbody spectrum. Their clean thermal emission, unmarred by contamination from magnetospheric activity, a surrounding nebula or supernova remnant, makes these sources ideal targets for such a study: the Magnificent Seven are the perfect neutron stars.

Despite many attempts, no radio emission is detected from these sources. The preliminary results from latest deep search with the GBT telescope are presented by Kondratiev et al. There are claims that some signal was detected at very low frequencies, but these results are not very certain and require confirmation.

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