177 votes
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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. ...
ProfRob's user avatar
  • 146k
61 votes
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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 ...
ProfRob's user avatar
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51 votes
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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 ...
ProfRob's user avatar
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50 votes
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What is the hottest thing in the universe?

Energetic neutrinos have been observed from the core of a supernova (SN 1987A). The inferred temperature at the "neutrinosphere" is about 4 MeV (equivalent to 50 billion K - ($5\times 10^{10}...
ProfRob's user avatar
  • 146k
44 votes

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 ...
James K's user avatar
  • 116k
26 votes

What is the hottest thing in the universe?

Note that while we haven't observed anything even close, there is a theorized Absolute Hot along the lines of absolute zero. Its theorized value is ~ $1.416 \cdot 10^{32}$ Kelvin. Above this ...
SoronelHaetir's user avatar
25 votes
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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" ...
ProfRob's user avatar
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23 votes

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 ...
ProfRob's user avatar
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22 votes
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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 ...
StephenG - Help Ukraine's user avatar
22 votes

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 ...
Lee Daniel Crocker's user avatar
22 votes
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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 ...
James K's user avatar
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21 votes

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 ...
Anders Sandberg's user avatar
20 votes
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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 ...
ProfRob's user avatar
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20 votes
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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 ...
Matt Pitkin's user avatar
20 votes

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 ...
ProfRob's user avatar
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18 votes

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. ...
ProfRob's user avatar
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18 votes
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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 ...
ProfRob's user avatar
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18 votes

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 ...
ProfRob's user avatar
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18 votes
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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 (...
ProfRob's user avatar
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16 votes
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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 ...
ProfRob's user avatar
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16 votes
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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 ...
antlersoft's user avatar
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16 votes
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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. ...
ProfRob's user avatar
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15 votes
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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 ...
ProfRob's user avatar
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15 votes

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.
GrapefruitIsAwesome's user avatar
14 votes
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Parent stars of our Sun - Where are its remains?

We have no way of identifying where the Sun was born, what the surrounding environment was, or where the Sun's siblings are right now. This is easy to see from some bare numbers: the Sun's current ...
Emilio Pisanty's user avatar
14 votes
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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 ...
ProfRob's user avatar
  • 146k
14 votes

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 ...
John Doty's user avatar
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14 votes

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, ...
James K's user avatar
  • 116k
13 votes
Accepted

Why aren't neutron stars full of dark matter?

Yes, neutron stars might actually accumulate weakly interacting dark matter and this allows some observational constraints on its nature. Basically, the temperature and continued existence of neutron ...
Anders Sandberg's user avatar
13 votes

How far away are the events that caused the gravitational waves that have been detected?

Yes, it's possible, but less straightforward than for "normal" objects. If the optical counterpart of the GW signal is located, as in the case of GW170817, the distance can be inferred by standard ...
pela's user avatar
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