Questions tagged [gravitational-waves]

For questions about the propagation of waves carried by space-time, for instance as described by general relativity. Not to be confused with gravity waves, such as ocean surface waves.

Filter by
Sorted by
Tagged with
1 vote
2 answers
74 views

More on frames of reference and coordinates in GR

I have read other questions concerning this subject, and by now I believe that in order to solve a gravitational problem in GR, one has to basically abandon the notion of frames of reference. However, ...
  • 147
2 votes
2 answers
26 views

What type of detail and imaging might we be able to achieve with mature gravitational wave detector arrays?

With the success of LIGO and considering the types of imaging we're able to do with distributed arrays of radio telescopes, what level of detail would we be able to achieve were we to build arrays of ...
2 votes
2 answers
72 views

Does black hole entropy change as a gravitational wave passes it?

The black hole entropy depends on the area of the event horizon. Do gravitational waves change this area? Does the entropy increase and then decrease as the horizon stretches and contracts?
user avatar
1 vote
0 answers
58 views

If a black hole doesn't have all its mass at a singularity and the mass is not uniformly distributed and rotating, would it emit gravitational waves?

Would a black hole with a rotating quadrupole moment in its mass distribution generate gravitational waves?
user avatar
3 votes
0 answers
54 views

Can gravitational waves have event horizons?

Is there a spacetime that contains traveling planar event horizons?
  • 499
1 vote
1 answer
38 views

Closest possible orbital radius for equal masses

If you have two objects of equal mass, then what’s the closest distance that they can orbit at in terms of their schwarzschild radii? How fast would they be orbiting? What About stable orbits?
  • 1,586
2 votes
0 answers
66 views

Is non-linear acceleration a necessary condition for an object to generate gravitational waves?

I was assuming every object that interferes with the gravitational field creates gravitational waves, and someone pointed out that only objects under acceleration do so. I searched through many sites ...
2 votes
2 answers
60 views

Number of gravitational wave events needed to calculate Hubble parameter

How many GW events do we need to measure the Hubble parameter with a precision 1-5%? How do we calculate that number?
  • 5,997
1 vote
1 answer
67 views

Would virtual particles popping in and out be causing gravitational waves?

Would virtual particles popping in and out be causing gravitational waves? Probably need quantum gravity for that, but maybe there is some theories.
0 votes
1 answer
24 views

What is the spin effect of gravitational waveforms?

How can we evaluate the effect of the spin of a GW source on a waveform? That is, how the spin of a rotating body enters in the gravitational wave amplitude/frequency/phase?
  • 5,997
0 votes
0 answers
43 views

Fundamental gravitational wave frequency for Kerr black holes?

Just as the usual rotating pulsars (neutron stars) have fundamental frequency(ies) tied to the rotational frequency, does it happen in Kerr black holes too? What are the frequencies of rotating Kerr ...
  • 5,997
2 votes
0 answers
68 views

Can gravitational waves gain energy in an expanding FRW spacetime?

I was reading this paper (Green's functions for gravitational waves in FRW spacetimes: https://arxiv.org/abs/gr-qc/9309025) I had a specific question about one statement in the paper that I would like ...
  • 1,250
0 votes
1 answer
31 views

Do gravitational waves change the period of spinning neutron stars?

I imagine that gravitational waves can increase and decrease the diameter of a neutron star as they pass through it.Do they alter the speed at which it spins?
user avatar
0 votes
0 answers
25 views

Coordinate transformation and gauge choice in gravitational waves [duplicate]

Assuming weak field : $g_{\mu\nu}=\eta_{\mu \nu}+h_{\mu\nu}$ and considering terms only linear in $h$ We get christoffel sybol as $\Gamma^\mu _{\nu \lambda}=\frac{1}{2}\eta^{\mu \alpha}(\partial_\nu ...
1 vote
0 answers
41 views

What is the current most accurate model for the generation of binary black hole gravitational waveforms? [closed]

As you know there are a lot of models to choose from, and there is constant improvement in both gravitational waveform generation and detection methods. Now some of the most used GW generation models ...
1 vote
1 answer
67 views

What parameters descibe a gravitational wave?

What are the parameters of gravitational waves and how does the configuration of the system that creates those waves affect the result? My current state of missunderstanding is: Frequency (due to ...
  • 844
3 votes
0 answers
46 views

Is the gravitational wave strain unique?

We know for a binary merger system the detected gravitational wave strain is dependent on the following parameters. Chirp mass $$M=\frac{(m_1m_2)^{3/5}}{(m_1+m_2)^{1/5}}$$ symmetric mass ratio $$\...
  • 31
2 votes
1 answer
53 views

Approximation concerning gravitational waves from binary neutron star

I'm interested in studying two neutron stars orbiting each other and producing gravitational waves. In textbooks the calculation for the power of the radiation is done by considering the neutron stars ...
1 vote
1 answer
32 views

Detecting gravitational wave polarization

We know that in TT gauge frame the gravitational wave has two polarization components, and the actual gravitational wave we are detecting is a linear combination of those two states , now a natural ...
0 votes
1 answer
37 views

About gravitational wave polarization in the detectors output

Gravitational wave detection with Michelson interferometers gives the gravitational wave strain(the amplitude) , in TT gauge frame we know there are two polarizations, now in some literature it says ...
2 votes
1 answer
45 views

Is the Hamiltonian a pure boundary term in linearised gravity?

It's well-known that in general relativity, the Hamiltonian consists purely of a boundary term: the so-called ADM Hamiltonian. This is because the bulk term is an integral of the constraint operator $\...
0 votes
2 answers
120 views

*Observational* Consequences of Energy Nonconservation in GR

What are the experimental or rather observable consequences of the non-conservation (or conservation) of energy in GR? Imagine our instruments were $10^3$ or even $10^6$ more sensitive, better ...
  • 11.7k
1 vote
0 answers
40 views

For which of the candidate gravitation theories has LIGO been able to establish a 5 sigma exclusion of gravitational wave polarization predictions?

In "Gravitational Wave Polarizations: A test of General Relativity using Binary Black hole mergers" the candidate gravitation theories and their gravitational wave polarizations are given in ...
  • 1,237
0 votes
1 answer
75 views

How much energy does a star absorb from gravitational waves as it orbits a black hole?

suppose: a star could orbit a black hole in its own solar system. So I wonder how much gravitational wave energy it absorbs from that black hole and does its mass increase as it absorbs gravitational ...
3 votes
1 answer
145 views

Argument that the massless bosonic string describes gravitation

I'm attempting to learn about string theory through a series of lectures by Freddy Cachazo. Starting 43 minutes into part 6, he begins to explain why we can associate the traceless, massless, closed ...
3 votes
1 answer
786 views

How are objects kept free falling in the LISA experiment?

I'm watching a video about the LISA experiment, which will be used to detect gravitational waves. In there, three space stations will be launched and will follow the Earth in its revolution around the ...
0 votes
0 answers
35 views

Why quantum gravity can't be described by spin-1 bosons? [duplicate]

As the title suggests, why quantum gravity can't be described by spin-1 gravitons?
1 vote
2 answers
167 views

Could Dark Matter Be Fully or Partially Explained by Gravitational Waves?

This is something I have wondered for a long time and cannot see why it is not a possible solution. Basically, any motion of matter (Mass may be a more accurate description here) through space time ...
1 vote
1 answer
64 views

Would a gravitational wave accelerate a single ball?

Suppose I have two balls floating in space. If a gravitational wave with the correct polarization passed by, it would create an oscillating strain causing the balls to accelerate together, then apart, ...
0 votes
0 answers
41 views

Is there some mathematical or physical model that postulates that gravitons exist? [duplicate]

Is there some model, mathematical or physical, that postulates that gravitons exist? For example is there mass missing from some particle decay that is thought to form gravitons? Or something in the ...
  • 3,943
4 votes
1 answer
79 views

How much energy from gravitatational waves does the sun absorb?

I was wondering how much energy from gravitational waves the sun could absorb since it is so big and also has a massive gravitational pull. Is it possible for the sun to trap gravitational waves ...
0 votes
1 answer
129 views

In pure GR can a black hole spontaneously appear?

In a universe without matter and just gravitation fields, can a black hole spontaneously appear? I would assume it could since such a black hole would evaporate purely into high energy gravitons. The ...
  • 6,508
0 votes
1 answer
70 views

What defines the speed of waves? [closed]

Why the speed of sound or speed of electromagnetic/gravitational waves have values which they have? What defines it? Why do it not two times slower or two times faster, for i.e.?
  • 620
0 votes
2 answers
88 views

I know that gravitational waves are generated by accelerated masses, but do all accelerated masses generate gravitational waves, even small masses?

In other words, is there an accelerated mass that is too small to generate gravitational waves?
  • 11
0 votes
1 answer
32 views

Invariance of binary black hole gravitational waves

Why BBH gravitational waves can be parameterized with the mass ratio? (and is not necessary the value of the two masses explicitly)
1 vote
1 answer
49 views

Difference between Gravitational wave solution in TT gauge vs pp-waves

I am studying gravitational waves and I am trying to understand two types of wave solutions I have seen for the metric. In various texts (Carroll, Wald, etc.), they discuss the gravitational wave ...
  • 941
0 votes
0 answers
22 views

High frequency (HF) gravitational wave generator [duplicate]

I see this US patent for a high frequency (HF) gravitational wave generator: US10322827B2 In the patent they mention virtual photons. Can anyone tell me what a "virtual photon" is?
2 votes
1 answer
32 views

Do stars lose spin angular momentum, to planets, radiation, or gravitational waves, or in some other way get a longer period?

A spinning star is throwing off stellar wind, and electromagnetic radiation, which might be carrying away angular momentum, so that the star loses angular momentum, and its angular momentum per unit ...
1 vote
0 answers
32 views

GW gauge choice shortcut

When solving the linearised Einstein field equations for gravitational waves, we define the trace reversed metric $\bar{h}_{\mu\nu}$ for which we write the coordinate transformations $x^\mu \...
5 votes
3 answers
3k views

What do we mean when we say gravitational waves are non-linear and do not superpose like EM waves?

I have read this question: Now it's not actually true that general relativity obeys a law of superposition, but it is an extremely good approximation for a small-amplitude gravitational wave passing ...
0 votes
2 answers
117 views

Let $Q(t,\vec x)$ solve $\partial_t^2 Q = \nabla^2Q$. Why $\partial_t^2Q = 2 (\partial_r + r^{-1})\partial_{t-r}Q$?

On page 5 of Bondi et. al. (1962) (https://doi.org/10.1098/rspa.1962.0161), a suitable method for solving the gravitational wave equation is demonstrated for the case of the scalar wave equation. ...
  • 567
2 votes
1 answer
66 views

Transverse component of distorsion tensor in GR

On pages 164-165 of Eric Gourgoulhon's lecture notes on Numerical Relativity, the author introduces the decomposition (9.49) for the distorsion tensor related to a foliation $(\Sigma_t)_{t\in \mathbb{...
  • 270
1 vote
1 answer
65 views

Question about gravitational waves

Gravitational waves are measured by interferometers, in particular by the change in length of one of the arms, with respect to the other. In this scenario, the light that has always the same speed, ...
0 votes
0 answers
21 views

Gravitational waves strain drop off

For the gravitational waves detected by LIGO back in 14.09.2015, how do we measure how strong the strain from the gravitational waves would be if the collision happened say 1000AU away from Earth? How ...
  • 1
0 votes
1 answer
43 views

Does SXS catalog for NR simulations have non-spinning, non-eccentric blackholes?

I am looking for NR waveform for two non-spinning and non-eccentric black hole binary merger for small mass ratio. Somehow, on the SXS catalog website, I don't see any such description. Thanks
  • 119
3 votes
1 answer
33 views

What are the $f$-modes, $g$-modes,...of GW in neutron stars and compact objects?

Reading gravitational wave astronomy papers, sometimes is mentioned the importance and relevance of $f$-modes and $g$-modes of gravitational waves. What are exactly the $f$-modes/$g$-modes in ...
  • 5,997
1 vote
0 answers
108 views

Calculating Gravitational Waves Given Boundary Conditions

How can I calculate the gravitational waves emitted by a system in which the initial and final angular momentums are known? Can you provide me with an explicit example? Say the system starts at rest ...
1 vote
0 answers
92 views

What is the significance of a constant, $C$ in a damped cosine function? [closed]

I've used to fit some scattered points by an equation of damped cosine with a constant function ($(A\cos({kx})+C)e^{-Bx}$) and that equation fits better than only a damped cosine $A\cos({kx})e^{-Bx}$, ...
  • 11
2 votes
0 answers
82 views

Viscous damping in general relativity

In Minkowski spacetime, waves are modeled via the wave equation $$(\partial_t^2-\Delta)u=0.$$ When viscous damping is present, one studies the damped wave equation $$(\partial_t^2-\Delta+W(x)\...
0 votes
0 answers
31 views

How do I convert between + and x polarizations of a gravitational wave?

Let's say I have a gravitational waveform h(t) that is completely +-polarized. How do I convert it to one that has some x-component? Or is completely x-polarized?
  • 1

1
2 3 4 5
23