166 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. ...
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65 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 ...
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50 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 ...
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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 ...
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41 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 ...
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36 votes
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What did LIGO Actually See? (Gravitational waves discovery)

The actual image isn't much. I was able to find it from Science, and this is all it is: It's just a ripple, seen at slightly different times from two different observatories. The shift fits perfectly ...
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29 votes

What did LIGO Actually See? (Gravitational waves discovery)

First of all, I think your question belies a misunderstanding of the nature of the LIGO observatories. The nature of the detectors is that they act like a microphone, as opposed to a camera. What ...
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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 ...
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27 votes
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Quantum Mechanics after the detection of Gravitational Waves

No more than the observation of light waves disproves quantum mechanics. Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio ...
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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 ...
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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 ...
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24 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 ...
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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 ...
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20 votes

Quantum Mechanics after the detection of Gravitational Waves

The impact of this measurement on the status of quantum gravitation is exactly zero. The proper statement of the incompatibility of general relativity and quantum mechanics is that the quantum field ...
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18 votes

Quantum Mechanics after the detection of Gravitational Waves

Another question, how can we identify the ripple's origin (let's say that if it's the result from the big bang or another big event)? (I'm just answering this part of the question, as James has ...
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18 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 ...
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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 ...
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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 ...
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16 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 ...
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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 ...
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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 ...
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14 votes
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Why do Earth and moon move apart but binary black holes move closer?

Here is how the tides move the moon away from the Earth: The moon orbits the earth, and there is a difference in gravitational force between the the side of the Earth nearest the moon, and the side ...
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14 votes

What did LIGO Actually See? (Gravitational waves discovery)

LIGO didn't "see" anything. It monitors the relative lengths of the paths taken by two laser beams in vacuum pipes about 4km long (although the laser path consists of about 75 trips up and down the ...
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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 ...
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13 votes
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Life planets orbiting black-holes. Can/Do they really exist?

Well, first things first. It's not likely to have a planet orbiting near a black hole and in significant time dilation because the tidal effects would likely tear anything that close apart. ...
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13 votes

Why can we detect gravitational waves?

The short answer is that waves that are "in the apparatus" are indeed stretched. However the "fresh waves" being produced by the laser are not. So long as the "new" waves spend much less time in the ...
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13 votes

Could gravity waves be used to confirm the existence of a ninth planet?

No, they can't. Gravity waves from a small, simple object moving slowly are very, very faint, to the point of being undetectable with current (or foreseeable) technology. The waves that have been ...
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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 ...
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  • 32.3k
12 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 ...
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