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# Questions tagged [ligo]

The Laser Interferometer Gravitational-Wave Observatory (short LIGO) is a large interferometer used for the detection of gravitational waves. Use this tag for questions about this specific installation; for questions more generally about the properties of gravitational waves or gravitation, use [gravitational-waves] and/or [general-relativity]

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### How did LIGO scientists determine the source of the gravitational waves they detected? [duplicate]

I read the newspaper today and I found that LIGO had detected gravitational waves. This is from their official website: For the first time, scientists have observed ripples in the fabric of ...
868 views

### Einstein's original papers predicting gravitational waves? [closed]

I came across the original handwritten papers in which Einstein predicted gravitational waves1: and since LIGO announced they've detected a signal confirming the predictions I was wondering if ...
138 views

### Why do numerical relativity papers show $\ddot{h}_\times$ instead of $h_\times$ for gravitational waves amplitude?

I am very confused about why numerical relativity papers, when talking about gravitational wave extraction, usually plot the real part of the fourth Weyl scalar, $\Psi_4$, instead of its double ...
75 views

### How do the LIGO team arrive at the number of round trips in the laser arm etalon?

The quoted number of laser beam round trips in the arm cavity for LIGO on the MIT site is 280 times. How did they arrive such a number? Since the laser frequency is stabilized to less than 1 Hz, the ...
873 views

### Gravity vs Gravitational Waves

I thought I had a reasonable understanding of relativity, the speed of light speed limit, and how this stuff related to gravity. Then I read through all the answers/comments for this question: How ...
115 views

### How does LIGO reduce noise below what it is detecting? [duplicate]

LIGO is designed to detect changes in length on the order of 10,000ths the scale of a proton. I know they are extremely well isolated from their surroundings, but how could we even approach isolation ...
263 views

### Transfer of energy from gravity back to other “more familiar” forms of energy?

In this question I've mentioned an account of the recently reported 2nd observation of gravitational waves, LIGO and Virgo Collaborations, Phys. Rev. Lett. 116, 241103, 15 June 2016, where 1 of the ...
167 views

### Will gravitational wave detectors be able to locate black hole collisions in time to view them?

Can a single LIGO identify the general direction of a black hole collision? Could multiple observatories be able to accurately pinpoint the direction from them so that telescopes could quickly point ...
156 views

### Dark matter and LIGO

In addition to the functioning LIGO detectors (two in USA and one in Italy), I am aware there are some gravitation wave detectors under construction. More detectors should provide more statistical ...
388 views

### Gravitational wave redshifts and LIGO [duplicate]

When I heard about the LIGO gravitational wave detection, I wondered if the distance to the event was determined by the inverse square law of radiation and/or by measured red shifts. Which is/are the ...
72 views

### Could LIGO detect two simultaneous gravitational waves?

Hypothetically if two (or more) gravitational waves were passing through the LIGO detector at the same instant, can the LIGO team deduce from the data that there were two simultaneous waves passing? ...
185 views

### What was the rate of Black Hole - Black Hole mergers expected to be detected by LIGO prior to GW150914?

My question is a more detailed version of the one found here, which elicited some good information but the question was never really answered. From table 4 in a 2010 paper we see the estimated rate ...
117 views

### What causes the 20 second period in LIGO data?

I download LIGO data on GW150914 (gravitational waves) via the code in Mathematica ...
158 views

### Can we “see” into a black hole using gravity?

I believe the "no hair" theorem means all black holes settle down into a state only determined by a few parameters, typically listed as mass, charge and angular momentum. But I don't think they can ...
584 views

### Gravitational waves detection, any news? [duplicate]

Is the detection of gravitational waves a reality with nowadays technology? Are there recent news?
180 views

### Did LIGO detect dark matter?

Which is the title of this preprint They claim that: We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there ...
116 views

### LIGO event - energies involved?

So, we have two Black Holes merging shortly after LIGO turns on after the upgrade. Some questions: a) How lucky was it to see this event? What are the expected rate of occurrence? b) Was this event ...
113 views

### Black hole merger for a distant observer

Recently, the LIGO detections of the gravitational waves from black hole merger events have rightly caused a lot of media attention. There is something I do not quite understand, however. In the ...
151 views

### How to read numbers reported in this LIGO paper?

I am not sure how to read the numbers in this excerpt from the abstract of GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence: Are the +/- small numbers ...
130 views

### Hypothetical - If a gravitational wave was somehow produced on Earth, could its origin be triangulated?

Suppose object X is hidden somewhere on Earth and can, somehow, produce "weak" gravitational waves, that do not cause anything perceivable by people, but can be detected by all gravitational wave ...
219 views

### Black holes are obvious answer to dark matter, why is that wrong? [duplicate]

Primordial Black Holes as dark matter candidate. I think this is interesting and new, in that there is a window of PBH masses (link from Count Iblis) And the first GW event from Ligo is right in that ...
127 views

### Does frequency of light change in the LIGO interferometer arms?

There are a number of questions on the internet and on this site asking about how the LIGO interferometer measurement works given that the gravitation wave stretches both the length of the ...
80 views

### Determine expansion rate of universe from gravitational waves LIGO?

I heard on the TED Radio Hour that the LIGO team was able to make an independent measurement of the Hubble constant and the increasing expansion rate of the universe when they detected the ...
141 views

### Could LIGO have detected R'lyeh if it existed?

In Possible Bubbles of Spacetime Curvature in the South Pacific, that R'lyeh might be exist within a bubble of spacetime. (It appears to be a joke paper since some of the references are fictional, but ...
103 views

### Why are both LIGO detectors nearly co-aligned? [duplicate]

A lot of the papers I've been reading say that's the case, so we needed VIRGO to analyze the polarization of the GWs, but not a single one of them explains the reasoning behind this decision. Why ...
468 views

### How thermal noise is avoided in LIGO?

I think I have understood properly the principle of LIGO, however the sensitivity is around $10^{-18}~\rm m$ of accuracy of distortion. That looks pretty small... just starting with simpler phenomena, ...
175 views

### In GR what is a “source-frame mass”?

In the recent LIGO paper, "GW150914: First results from the search for binary black hole coalescence with Advanced LIGO, (LIGO Scientific Collaboration and Virgo Collaboration)", they refer to the ...
1k views

### How do Black Hole event horizons grow? [duplicate]

I was trying to understand how matter falls into black holes, and I got confused by this thought experiment. A small mass falls into a black hole (which negligibly effects the Schwarzschild radius) A ...
321 views

### Gravitational wave detection and electromagnetic counterpart

Background Referring to this article on Fermi EM signal, 0.4 s after the gravitational wave detection by LIGO, FERMI detected an electromagnetic signal (poorly localized) with a false alarm ...
386 views

### Is the GW150914 signal consistent with a superluminal gravitational wave burst?

I've been following the news about the detection of gravitational waves with interest and had a question for those with a physics background. I've gathered that the preferred explanation for GW150914 (...
444 views

### LIGO Gravitational Waves [closed]

Has LIGO detected any gravitational waves yet, or any hints of them? Is it just that LIGO is not sensitive enough or are we now entering disconfirmation territory? If we never detect gravitational ...
84 views

### Detection of gravitational waves

Gravitational waves are continuously stretching and squeezing the shape of Earth. Using this fact, LIGO is detecting it by interference of light. But the Sun and Moon's tidal effects are also trying ...
285 views

### Can we make any implications about the internal structure of black holes from the 'chirp' that LIGO observed?

Are there any implications about a black hole's internal structure we can make based on the chirp issued? For example that a black hole does in fact contain or does not contain a singularity rather ...
89 views

### Can we see the famous black hole pair or its effect on other stars in any other means but LIGO?

If the source of LIGO's detection is a pair of black holes, can we see them using a traditional electromagnetic/neutrino/some other kind of telescope? Or can we see their effect on other stars in ...
58 views

### How Does LIGO’s Splitter Mirror Cause Two Different Frequencies When a GW is Present?

When a gravitational wave is present in LIGO, how does the splitter mirror work to send out a different frequency than the laser frequency on the arm perpendicular to the laser direction? What are ...
86 views

### Does shortening the path length of an excited etalon do work? What about LIGO?

Start with a high-Q etalon excited on-resonance with a laser for a time long enough that it has built up an essentially stable standing wave. There is a constant outwards-directed force on each mirror,...
494 views

### What are the wave characteristics for the detected gravitational wave?

I'm curious to know what the amplitude and wavelength of the detected gravitational waves are? The paper mentions some characteristics of the detection event, but not what that means for the wave ...
1k views

### Why does LIGO have an arm length of few kilometers? Is the distance dependent on Gravitational Wave wavelength?

Antennas for capturing radio waves need to have $\frac{\lambda}{2}$ length for optimum reception of signal. Does it imply LIGO arm length is $\frac{\lambda}{2}$ of Gravitational Wave it is trying to ...
217 views

### Does LIGO GW detection methodologically constitute discovery of two specific black holes (as astronomical objects)? [duplicate]

It is said that the gravitational waves (GW), recently detected by LIGO, correspond (according to Einstein General Relativity theory equations) to the effect of two black holes merging (with the ...
3k views

### How does LIGO account for curvature of Earth?

Using an earth curvature calculator, I found that at a distance of 4 km (the length of LIGO's arms), more 1.26 m is hidden by the horizon. When constructing LIGO, did they account for the curvature of ...
424 views

### LIGO Gravitational wave discovery - how did they know the cause of spike? [duplicate]

I understand how unbelievably lucky the discoverers were to catch the wave produced billions of years ago by an event that happens so rarely one hour into a test run of their equipment. But one thing ...
109 views

### Why are they building eLISA and what implications would it have?

I understand that the next step after LIGO is to plan and build eLISA, I understand that out in space there are a lot less interferences compared to Earth which makes it a good way to detect things we ...
158 views

### Did LIGO detect gravitational waves from Big Bang Inflation?

I recently watched an installment of "Spaces Deepest Secrets" that examined the efforts of the BICEP2 team. (Strangely, it was titled "When Black Holes Collide.") The team was looking for ...
188 views

### About the working of LIGO [closed]

How is it that the gravitational wave occurred exactly so as to compress one tunnel and expand the other one( as is inferred from the explanations they Caltech gives)? Or is LIGO built in a way that ...
242 views

### How they can estimate when the black holes collided in the recent LIGO discovery? [duplicate]

How they can estimate when the black holes collided in the recent LIGO discovery? If LIGO can detect ripples in the gravitational waves, how they can figure out how old those waves are? Surely ...
268 views

### Is it pure luck to observe a gravitational wave?

I actually have two questions: Since only a gravitational wave that is strong enough can be detected and the GW passes by the earth at light speed, can I say that we are lucky to detect one this time....
280 views

### How did LIGO detect the source location of the black holes mentioned to be the cause of today's announcement?

Today LIGO announced discovery of Gravitational waves. What method was used to determine the source location of the waves?
156 views

### Thermal gravitational radiation and its detection

To my poor knowledge on the topic, the gravitational waves that are most likely to be detected by LIGO or other experiments do not have thermal spectrum. But I'm not certain. I know that Hawking's ...