What is the difference between isolated neutron stars and neutron stars?
What is the meaning of isolated here?
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$\begingroup$ Not orbiting another star. $\endgroup$– Jon CusterCommented Jun 30, 2020 at 21:10
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3$\begingroup$ (Perhaps a socially-distanced neutron star would be a more current description) $\endgroup$– Jon CusterCommented Jun 30, 2020 at 21:58
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$\begingroup$ Also see en.wikipedia.org/wiki/Radio-quiet_neutron_star $\endgroup$– PM 2RingCommented Jun 30, 2020 at 22:40
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1 Answer
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$\textit{Isolated neutron stars}$ (INS) is only the name assigned to the subset of the total amount of observed neutron stars which are $\textbf{not}$ interacting with other stellar objects. This definition does not exclude, however, neutron stars which are surrounded by the material from the supernova explosion, such as "The Crab pulsar", i.e.
https://apod.nasa.gov/apod/ap220821.html
or the young neutron star 1987A,
https://apod.nasa.gov/apod/ap170305.html
since they are formally $\textbf{not}$ interacting with other stars and the surrounding material comes from its progenitor star. Therefore, $\textit{isolated}$ here must be understood as a classification according to the number of stellar companions. Is a neutron star orbiting around another object (Sun-like, white dwarf, another neutron star)? If yes, then it is not isolated anymore and we have a $\textit{binary}$ system.
However, if your question was oriented towards the possibility of ISN being entirely different from "ordinary" neutron stars from the point of view of $\textit{composition}$, then the answer is: no. The composition of $\textit{all}$ neutron stars is expected to be the same, at least in the major portion of them, i.e.$\sim 95\%$ of its mass and volume. The composition are, as far as we know, mainly neutrons, protons, electrons and even muons at its core. At the very surface, i.e. $\rho\geq 10^{8}$ g cm$^{-3}$ and occupying a region of less than 500 meters ($\leq 4\%$ of the total radius of a typical star), the composition might be different from star to star due to accretion of surrounding material. Nevertheless, surface composition does not change the fact they all are $\textit{neutron stars}$.
answered Jun 6, 2023 at 6:11
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$\begingroup$ Perhaps mention that we can't measure the mass of an isolated celestial body, but we can determine mass in a binary system from the orbit axis & period. $\endgroup$– PM 2RingCommented Jun 6, 2023 at 13:33
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$\begingroup$ BTW, it's preferred to use Markdown for styling, eg
*italics*. Only use MathJax for equations, etc. $\endgroup$– PM 2RingCommented Jun 6, 2023 at 13:37