159

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. 2017a). It spectacularly corroborates the reality of the GW detection technology and analysis. The progenitor has been unambiguously located in a (relatively) ...


58

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 travelling in the same direction, and gravitational waves are affected by black holes in the same way that light rays are. So for example gravitational waves can ...


48

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 neutrons is large. For a long time, the competing theories and sites for the r-process have been inside core-collapse supernovae and during the merger of neutron ...


39

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 force, and how gravity works - So what? Another guy called Maxwell had this idea of how light could actually be waves of electromagnetic fields - does this matter?...


34

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 by shifting it by the speed of light difference in their locations. Thus is the proof of gravity waves. It should be noted that the reason there are two ...


28

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 waves are made of photons, but individual radio wave photons are pretty hard to detect. I'm not sure that we have directly detected individual photons with ...


26

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 that means is that they are sensitive to gravitational waves coming in from most directions, but don't have an ability to distinguish where the waves came from. ...


22

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 theory of general relativity is not renormalizable. Renormalizability essentially means that the theory is well-defined at all energy scales, which seems like a ...


19

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 already answered the main part about GR vs QM.) LIGO have produced an image which shows their best estimate of where these two black holes were: All they can say ...


17

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 observers following-up the event can be found in the GCN circular archive here. This doesn't quite give the whole story of the time line of events, but is a good start ...


16

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 momentum for their orbital separation to become small enough. Average orbital separation (semi-major axis) is determined entirely from the angular momentum of the ...


13

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 far from the moon. This difference in force tends to pull the Earth into a oval shape with its long axis pointing towards the moon. But the Earth is also ...


13

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 interferometer than it takes to expand them (which takes roughly 1/gravitational wave frequency), then the effect you are talking about can be neglected. ...


13

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 detected come from the merger (a very fast movement in the last orbits) of two black holes (two very big masses). And they were just detected over the noise level....


13

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 arms) and at right angles to each other. A gravitational wave, travelling at the speed of light, changes the ratio of these lengths (one gets shorter, one gets ...


12

The arms are $4\,\mathrm{km}\,\times\, 1.2\,\mathrm{m}$: From the LIGO webpage: The 1.2 m diameter beam tubes were created in 19-20 m-long segments, rolled into a tube with a continuous spiral weld. While a mathematically perfect cylinder will not collapse under pressure, any small imperfection in a real tube would allow it to buckle (a crushed vacuum ...


11

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 objects in prograde orbits below the equivalent of geosynchronous radius spiral inward. Only objects orbiting prograde above the equivalent of geosynchronous ...


10

The way I see it, there are three reasons it's such a big deal. The first, as you say, is the (further) confirmation of Einstein's theory of gravity. Newtonian gravity doesn't have gravitational waves. Their existence was already quite established by Hulse and Taylor's discovery and analysis of the binary pulsar PSR B1913+16. The system's orbit is decaying ...


10

Harry (2009) cited several different sources stated that, as far we know, the rate of detectable events will be 40 neutron star mergers per year 30 10 M$_\odot$ black hole mergers per year 10 neutron star/black hole mergers per year This is within a radius of about 200 Mpc. This cannot, however, be used to extrapolate the total rate of such events, because ...


10

The gravitational waves are actually emitted as long as you have a quadrupole moment with a second time derivative that is non-zero. The quadrupole is defined as: $$ Q_{ij}^{tt}(x) =\int\rho \left(x^i x^j - \frac{1}{3}\delta_{ij}r^2\right)\mathrm{d}^3x.$$ To simplify this, here is a rule of thumb: if you have a system that is not spherically symmetric and ...


10

Actually the peak luminosity for the first binary black hole merger LIGO detected was $3.6 \times 10^{49} \,\text{Watts}$ (source). Whereas the brightest supernova ever recorded was ASASSN-15lh which had a peak luminosity of $2 \times 10^{38} \,\text{Watts}$ (source). In fact the energy radiated by the binary black hole merger during the $0.2 \,\text{s}$ it ...


9

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. Certainly a planet orbiting a stellar mass black hole would need to be quite far away so as to not be torn apart, so any time dilation would be pretty small. Around ...


8

I think the wikipedia page gives a reasonable overview of why gravitational waves give us a window on the universe that is either not observable or is complementary to the view we get from electromagnetic waves (or neutrinos). But let's have a specific example. The potential of LIGO, as we have seen today, is to detect the gravitational wave signatures of ...


8

There are four aspects to this: You suspend the mirrors and other components using the best suspension mechanism that has ever been built. This is very effective at isolating the experiment. There are two detectors thousands of km apart. To claim a genuine signal it should be seen identically in both in less than the light travel time between them. Many of ...


8

The answer here is very similar to if you were asking about light. In principle gravitational waves might allow us to fractions of a second after the big bang. Electromagnetic waves can see back to where the cosmic background radiation formed, about 400,000 years after the big bang. You are right, the universe has expanded. At the present epoch it is ...


8

The "radius" (there is no physical surface) of the event horizon of a rotating black hole, depends on both it's mass $M$ and angular momentum $J$, and is given by the equation $$ r = \frac{GM}{c^2} +\sqrt{\left(\frac{GM}{c^2}\right)^2- \left(\frac{J}{Mc}\right)^2}.$$ It is thus difficult (for me anyway) to give a straightforward answer to your question. ...


8

There are two issues: Would there be gravitational waves to be detected and would LIGO detect them. On the first issue, gravitational waves are quadrupolar, and a cylindrically symmetric system will not produce any. (Specifically, the second time derivative of the quadrupole moment of an isolated system's stress–energy tensor must be non-zero in order for ...


8

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 Schwarzschild radius (for a non-spinning black hole) have trajectories that take then towards the event horizon. Waves on such trajectories cannot escape from the ...


7

Gravitational waves from the big bang may be "heard" but not by LIGO. The waves emitted at or around the inflationary epoch of the big bang are expected to be at much lower frequencies (milli-Hz or lower) than those announced today by LIGO. There are various sources of noise that make LIGO insensitive to GWs at frequencies below about 10 Hz. It will take ...


7

The waves pass by at the speed of light. So you you would'nt see ripples, they would pass too fast, and remember the waves would be passing through you too. The wavelength was (relativly) long about 3000km. The wave doesn't pass you, you are inside the wave. The amplitude of the waves detected by LIGO was small, one part in $10^{21}$, Now while the ...


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