# Tag Info

162

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) ...

61

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 ...

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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 ...

29

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 phenomenon. There isn't an observational bias against detecting more massive black holes in the range of 100 to a few hundred $M_{\odot}$. Details: The frequency of ...

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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. ...

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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 question. The original answer I gave is the reason that we can detect gravitational waves (GWs) at all. Their coherent nature as single oscillators, means that ...

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 ...

20

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 decreasing mass. As a result only very tiny black hole binaries would emit more power in Hawking radiation than they do in gravitational waves; at least towards ...

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 ...

19

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 ...

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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

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 the "chirp mass", which is related to the product and sum of the binary component masses. The amplitude of the gravitational wave then depends on the chirp mass ...

16

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 by the same amount in the orthogonal direction. The strain drops off linearly with distance from the black hole, so to achieve a distortion of 1mm in something ...

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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 the observed gravitational waves will change over time as recorded in the "chirp" event from the interferometers: the parameters include distance of the event, ...

14

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 ...

13

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 methods of observing the redshift of its host galaxy. If not, the luminosity distance $d_L$ can still be inferred because the amplitude of the GW signal scales ...

13

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 converted into gamma rays. The gravitational wave emission is always "prompt" since any surrounding material is transparent to gravitational waves. In ...

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 ...

12

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 black holes are releasing gravitational radiation with every orbit, but that radiation is too weak for us to detect. It takes a colossal amount of energy being ...

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 ...

11

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 intensity ...

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What are the major assumptions and other measurements that went into these error bars? The error bars in the paper are based on the shortest reasonable distance (to the authors) between the source and the Earth and a zero to ten second lag between gravity wave emission and gamma ray emission. One key assumption is how long it took for the two signals, ...

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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

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 ...

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