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5

10km is about right, 5km is definitely wrong and there are theoretical arguments and also observational evidence that this is the case. The Schwarzschild radius, inside which an object would be a black hole, is $3(M/M_{\odot})$ km. As neutron stars have a typical mass of $1.5M_{\odot}$ then a 5km radius would have them hovering just above disappearing ...


4

Yes, there are lots of optical observations of isolated (non-pulsar) neutron stars. Such observations have been done for many, many years. An early example would be Kulkarni & van Kerkwijk (1998) who detected optical radiation from the counterpart to RX0720.4-3125. http://arxiv.org/abs/astro-ph/9803024 The authors discuss various mechanisms that ...


3

Most of the books which I looked at give approximately 10 km as the radius of a neutron star. Just yesterday I looked at a book by Dave Goldberg titled The Universe In the Rearview Mirror (2013) which says that they're "only about 5 km in radius" [p.225]. Is this true, [i.e., is there some recent evidence for this], or did he make a mistake here? These are ...


2

There have been a few detected in the visible range by Hubble Space telescope and Keck observatory. The magnitude is less than 25 for the Hubble image(PSR0656+14). Neutron stars are very hot, 600,000 or more Kelvin and very small (Hubble star was 28 kilometers in diameter) so their visible luminosity is very low. The emission is redshifted due to General ...


-2

The nearest one, as far as I remember is about a 1000 light years away. So, its technically almost impossible to observe them using optical means(that is by visual means, if that is what you mean), because of tremendous red shift. They have been detected by X-ray telescopes. Any radiation emitted by such distant objects will get shifted towards the low ...


1

5 km in radius seems like a mistake. a 3 solar mass object has a schwarzschild radius of about 9.0 km. (Hence the 10 km estimate for the size of a Neutron star). A little smaller than that and it becomes a black hole. Also, as I understand it, Neutron stars, like white dwarfs, grow smaller as they add mass. Less massive Neutron stars in the 1.4-1.5 ...


0

I've answered the questions I can below. @John Rennie already gave a link to Lemaitre's paper. Here's a summary from John Gribbin's The Scientists, on page 596-597: ...the Belgian astronomer Georges Lemaitre (1894-1966), who was also an ordained priest, independently published similar solutions [to those of Aleksandr Friedmann's] to Einstein's ...



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