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176 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
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74 votes
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Can gravitational waves pass through a black hole?

No, gravitational waves cannot pass through a black hole. A gravitational wave follows a path through spacetime called a null geodesic. This is the same path that would be followed by a light ray ...
John Rennie'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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45 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
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42 votes
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Is it suspicious that gravitational waves propagate at the speed of light?

It is very suspicious! It points to the fact that the speed of light isn't just some random speed that light happens to travel at, but is a fundamental property of the universe. In fact, any massless ...
James K's user avatar
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32 votes

What observations can be expected on LIGO if any when Betelgeuse goes supernova?

Potentially, a short (less than a second) burst of gravitational waves (GWs) would be detected. Much depends on asymmetries in the core collapse, since a spherically symmetric collapse would not ...
ProfRob's user avatar
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29 votes
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Is there an upper limit on the mass of black hole mergers we can detect?

It is quite likely there is an astrophysical upper limit to the mass of a black hole that can be produced during the core collapse of a massive star, caused by the pair instability supernova ...
ProfRob's user avatar
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26 votes
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Why are there not yet any instruments dedicated to registering time dilation caused by passing gravitational waves?

General relativity predicts that there are only two possible polarizations of gravitational waves, the so-called "tensor" polarizations $+$ and $\times$. It turns out you can show that the ...
HDE 226868's user avatar
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25 votes
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Why can't supermassive black holes merge? (or can they?)

The main problem is angular momentum. In order for two gravitationally bound objects to merge (whether black holes, supermassive black holes, planets, stars, etc.), they must shed enough angular ...
NeutronStar's user avatar
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25 votes
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Why does the sensitivity to GWs drops off inversely proportional to the distance?

EDIT I'm leaving the original, highly upvoted answer below, but I've had a fundamental rethink about this, prompted by questions from Keith McClary and a helpful clarification from a Physics SE ...
ProfRob's user avatar
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24 votes

Would a series of gravitational waves from a supernova affect time on a 200 year old clock just as water waves affected clocks on ships in rough seas?

None that is measurable. While an asymmetric supernova would emit gravitational radiation, it would not be particularly strong, and would still be a strain on the order of $10^{-20}$, which is smaller ...
James K's user avatar
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21 votes
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What if the two Black Holes spiraling around each other are evaporating via their Hawking radiation?

Gravitational waves are efficiently emitted by massive black holes orbiting each other - the power emitted increases with mass. Hawking radiation on the other hand is a process that increases with ...
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
18 votes
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Black Hole Collision & Gravitational Waves

Part of the answer is easy. The strain measured in that event was about $0.25\times 10^{-21}$. That is an object $1m$ long would be squeezed by $0.25\times 10^{-21} m$ in one direction and stretched ...
Steve Linton's user avatar
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17 votes

Sound of a black hole merger

What would be heard is vibrations set up by the gravitational wave in the atmosphere, although presumably they would also directly stimulate the parts of the ear too. The amplitude of gravitational ...
Anders Sandberg's user avatar
16 votes
Accepted

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 is the Hubble constant determined from gravitational waves?

If you measure the gravitational waveform from an inspiralling binary, you can at any point measure the amplitude, instantaneous frequency and the rate of change of frequency. The last two give you ...
ProfRob's user avatar
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16 votes

Are there any gaps in the range of gravitational wave frequencies we can detect?

Are there any wavelengths in between the ranges of these different detectors that we wouldn't be able to detect? Yes! There is the millihertz band, which will be detectable by the space-based ...
Daddy Kropotkin's user avatar
16 votes

Could the human body feel the sudden disappearance or end of a gravitational force?

Firstly, the sun can't just "disappear". Even if it were converted by magic into "pure energy", that energy can't go anywhere faster than the speed of light, and Energy has ...
James K's user avatar
  • 125k
15 votes

Why did astronomers believe most or all stellar black holes had masses no greater than 15 solar masses?

The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses. (Actually, I have read that there is no good theoretical reason for ...
Daddy Kropotkin's user avatar
15 votes
Accepted

Can gravitational waves transfer energy or momentum to baryonic matter

The classic thought experiment showing that GW carries real energy is the "sticky bead argument" due to Feynman. Two beads on a rigid rod will be moved relative to each other and the rod by ...
Anders Sandberg's user avatar
14 votes
Accepted

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
  • 155k
13 votes

Why do Earth and moon move apart but binary black holes move closer?

A belated answer, but neither of the existing answers properly explain this. The proper explanation is simple. In Newtonian mechanics, tidal influences make all objects in retrograde orbits and those ...
David Hammen's user avatar
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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
  • 38.7k
13 votes

Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

We can currently only detect gravitational radiation when it is extremely intense: in the last fraction of a second. For example the first gravitational wave detection lasted less 0.15 seconds. The ...
James K's user avatar
  • 125k
12 votes

Is it suspicious that gravitational waves propagate at the speed of light?

The perturbation to the metric of spacetime (known as the strain), caused (for example) by an oscillating mass quadrupole, obeys a wave equation of the form $$ \nabla^2 h^{\mu \nu} = \frac{1}{c^2} \...
ProfRob's user avatar
  • 155k
12 votes

Do tidal forces on moons cause them to emit gravitational waves?

Yes, but the effect is tiny Tim Rias (in a comment below) calculates it to be $10^{-18}$ Watts. (see a paper about doing a similar calculation for neutron stars) Bodies that have spherically ...
James K's user avatar
  • 125k
12 votes

Are gravitational waves emitted equally in all directions?

The gravitational wave strain is not isotropic. More power is emitted (per unit solid angle) along the orbital axis of the binary than in the orbital plane. For a circular orbit (and they tend to be ...
ProfRob's user avatar
  • 155k
11 votes

Can gravitational waves pass through a black hole?

Gravitational waves should be lensed by massive objects in a very similar way to light. Light rays (and by extension, gravitational waves) from a distant object, that pass within 1.5 times the ...
ProfRob's user avatar
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