# Tag Info

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### Why is the discovery of merging neutron stars important?

Reasons why this is important: It is the first simultaneous detection of a gravitational wave and electromagnetic signal, and the strongest GW signal yet in terms of signal to noise (Abbott et al. ...
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### Which atom is a Neutron star made of?

Yes neutrons can exist outside the atom (or nucleus). In free space a neutron will beta decay into a proton, and electron and an anti-neutrino on a timescale of 10 minutes. However, in the dense ...
• 118k
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### Are binary neutron star mergers needed to explain the abundance of gold?

The creation of some very heavy neutron-rich elements, like gold and platinum, requires the rapid capture of neutrons. This will only occur in dense, explosive conditions where the density of free ...
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### Why is the discovery of merging neutron stars important?

Because its awesome (SMBC) So this guy called Copernicus suggested that the Earth orbits the Sun (not the other way round) - What changes? This guy Newton had a theory for how a mass responds to ...
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### Have we observed any static neutron stars?

The absence of evidence of spin cannot be evidence for the absence of spin. We lose the ability to measure the spin of single neutron stars when they slow down below the pulsar "death line" ...
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### Shape of neutron stars

I don't think you'll find a single agreed shape for a rotating neutron star, not least because we don't have an agreed single model for the equation of state of the material in a neutron star (which ...
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### Rotation direction of Pulsars

Does the Earth rotate clockwise or anticlockwise? If you are floating above the north pole of Earth you would see the Earth rotating anticlockwise(*) if you were floating above the south pole, you ...
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### Why does electron degeneracy pressure not stop massive star collapse?

You have the wrong idea about degeneracy pressure. There is no limit in principle on how closely together you can squeeze electrons (or other fermions) and at no point is the Pauli Exclusion Principle ...
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### Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

Birkhoff's theorem is very useful: in general relativity, if you are in vacuum and there is a spherically symmetric gravitational field, then it will be the Schwarzschild solution. This solution only ...
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### How does neutron star collapse into black hole?

Just to focus on one part of your question. Whilst it might be possible for a neutron star to accrete material, or for two neutrons stars to collide, in order to form black holes, this kind of event ...
• 118k
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### Do all neutron stars spin?

I think it is absolutely safe to say that all neutron stars spin. Conservation of angular momentum ensures that as they collapse from a massive stellar core the size (roughly) of the Earth, to ...
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### Which atom is a Neutron star made of?

A more historical/linguistic than physical answer: Democritus proposed that matter could not be divided infinitely, but that at some point one would reach a smallest possible piece, which he called ...

### Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

If they were spinning they would be distinguishable (in principle), otherwise not. Astrophysical black holes and neutron stars are expected to spin. In the case of a neutron star that automatically ...
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### How far away is the nearest compact star remnant likely to be?

There can be no closer white dwarf. The coolest, oldest white dwarfs (3000K), would be rare, but are still luminous enough $6\times10^{-6} L_{\odot}$ to have been easily detected at distances closer ...
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### "Who saw" the binary neutron star merger first? What was the sequence of events? (GRB/GW170817)

The initial Fermi trigger can be found here, and the following sequence of alerts that were sent out by the LIGO Scientific Collaboration/Virgo Collaboration (LVC) and various electromagnetic ...
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### Metallicity in gravitational wave astronomy

As you say, metallicity in this context refers to the proportion of the interstellar medium a star forms from that consists of elements heavier than helium. It can be expressed as a (mass) fraction (...
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### Is there a possibility that a white dwarf can turn into a neutron star or a black hole?

The answer is: to a neutron star - possibly; to a black hole, no. The process whereby a neutron star is formed is known as an accretion induced collapse and is being seriously debated, especially in ...
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### How far away are the events that caused the gravitational waves that have been detected?

Yes, it is possible to calculate (within an error range) the distance of observed gravitational wave events. It is known that a variety of parameters will affect how the amplitude and frequency of ...
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### Does the average proton/electron density in a neutron star change with mass?

The ratio of neutrons to protons (and electrons, since the fluid is neutral) does depend on the overall density. In an ideal n,p,e fluid, the ratio is of order 100 to 1 at average neutron star ...
• 118k
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### How big would a telescope have to be to get a good look at the nearest neutron star?

The angular resolution is just $\sim \lambda/D$ (in radians), where $\lambda$ is the wavelength and $D$ is the telescope diameter (or the size of an interferometer). So plug in the numbers you like. ...
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### What does it mean for a proto-neutron star to be opaque to neutrinos?

Opaque in this context means the same thing as it would optically, for light. The neutrinos do not pass through and are either scattered or absorbed due to the density of the matter in the star.
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### Is it possible to break apart a neutron star?

It would appear theoretically possible (to some degree) through extreme applications of recycling to trigger mass shedding in pulsars. Pulsars are rapidly spinning neutron stars, the fastest class of ...
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### Position of Neutron stars in H R diagram

The HR diagram is an observational diagram. Whilst neutron stars could be placed in the HR diagram in the same way as white dwarf stars are, it turns out to be impractical to do so because the ...
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### How could a neutron star collapse into a black hole?

The scenario you describe may occur. On the other hand it may actually be that neutronisation in a white dwarf is the trigger for a thermonuclear type Ia supernova. You may be misunderstanding the ...
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### Why can there be several seconds of lag between a binary neutron star merger and the emission of gamma rays from the same area?

The paper (section 5.1) discusses three possibilities in the context of a relativistic fireball model, where some of the kinetic energy in relativistic jets of material emerging from the explosion is ...
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### Have we observed any static neutron stars?

Everything rotates at some rate. The rotation-powered pulsars mentioned in ProfRob's answer need to spin fast to generate their radiation. Accretion-powered pulsars do not, so they may be observed at ...
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### Why does electron degeneracy pressure not stop massive star collapse?

A neutron star contains relatively few electrons. In a white dwarf, electron degeneracy pressure does prevent further collapse. But if you add more matter to a white dwarf, it will shrink in volume, ...
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### Would a tablespoon of a neutron star remain intact?

If we take neutron star material and somehow transport it somewhere for examination (say the Earth!), the results would be catastrophic. At say a density of $\sim 10^{17}$ kg/m$^{3}$ the neutrons have ...
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### What happens over time as a neutron star cools?

The cooling history of a neutron star can be divided into an extremely rapid neutrino cooling phase, followed by an indefinitely long cooling phase due to the emission of photons from its surface. ...
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