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Are there any neutron stars near enough for astronomers to get a good size-estimate, based on direct observation? I know that there are many theories regarding what happens inside neutron stars, but I want to know if there are any direct observations of nearby neutron stars which give us a clue as to their actual size and density. Other answers have not helped me, because they were based on THEORY, not DIRECT OBSERVATION !!

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I think if there is a binary system of stars then the size of neutron stars can be estimated. This method i would call direction estimation because even for most direct observations various theories are always involved.

When the neutron star passes over the burning star its intensity is dimmed. How much it is dimmed depends on the size ratio of visible and neutron star, how long it remain dimmed will depend on the velocity of the neutron star (or star binary) and diameter of the visible star.

The binary star rotates about its center of mass with some speed and that can be estimated from Doppler shift.

Combining these factors can give you the size of neutron star.

This article may be helpful

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  • $\begingroup$ I understand what you are saying, but need to remind you that the amount of radiation which the objects should emit is based on theory, so that the amount of dimming would also be based on theory ... I want to know if there is a neutron-star near-enough to get a clear, disk-like, image ... from what I've learned since asking this question here, I believe that there are no such observations !! $\endgroup$ – PERFESSER CREEK-WATER Jul 16 '16 at 20:28
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    $\begingroup$ @PERFESSER I have take issue with you again. It is incumbent upon you to learn something about scientific methods. The estimation of the sizes of stars through eclipsing binary systems is a fundamental, geometric method of measuring stellar sizes. Your objection is incorrect. However, unfortunately, there are no eclipsing binaries with a neutron star that have a measurable secondary eclipse. $\endgroup$ – Rob Jeffries Jul 16 '16 at 21:13
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    $\begingroup$ @PERFESSER Furthermore, if we were to do science your way, the only star with a known size would be the Sun, since no other star, bar just about Betelgeuse, has a resolvable disk with a telescope. $\endgroup$ – Rob Jeffries Jul 16 '16 at 21:15
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    $\begingroup$ To expand on what Rob said about secondary eclipses: even though neutron stars emit little light, this is because they are small. Per unit area they emit lots, and so the eclipse we are interested in is the lesser one (compared with the NS going behind the other star). In fact, this secondary eclipse will block out the same fraction of the larger star as an equal-sized planet. We have a hard enough time measuring transits of Earth-sized planets, and this signal would be 1000 times smaller. $\endgroup$ – user10851 Jul 16 '16 at 22:12
  • $\begingroup$ @ChrisWhite Yes, I agree that you are both right about the possibility of measuring the size of a neutron-star by "eclipsing binary" method: I stand corrected, and thank you for correcting me ... my aim is to LEARN, not to promote any pet theory $\endgroup$ – PERFESSER CREEK-WATER Jul 17 '16 at 19:46

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