Questions tagged [general-relativity]

Questions about relativistic theory of gravity. General relativity describes gravity as a geometrical property of space and time.

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-3 votes
0 answers
43 views

Progression of cosmic GP to explain observations attributed to dark matter/energy

Inspired by LIGOS research regarding disassociated gravitational waves verifying Einstein's theory on gravitational frame dragging, I have been considering whether the "c" propagation rate ...
5 votes
0 answers
60 views

Is gravitational lensing "additive" in a line of sight?

As usually depicted, gravitational lensing implies, at least, three objects: a distant source, an observer, and a "massive enough" object in the middle, where enough is the mass needed to ...
-2 votes
1 answer
183 views

Shouldn't the Friedmann equation take into account the massive extra distance traveled during the time for gravity to travel across the universe? [closed]

I’ve got a question that has been bothering me for the past few years that of the few sources that are only somewhat related to this, none of them say anything about this should be wrong so I can’t ...
20 votes
2 answers
2k views

Was the Sun's gravitational lensing observed in other solar eclipses than the one in 1919?

In 1919 the gravitational lensing by the Sun has been observed during a total solar eclipse. Did someone observe the lensing in any other total eclipses? Last year there was a total eclipse in Chile ...
2 votes
1 answer
65 views

Can we measure how fast space is expanding from how quickly gravitationally lensed galaxies or stars are blurring or getting sharper?

A galaxy that lenses another celestial body should as it moves away from Earth alter the sharpness of what it lenses by gravity. Could this be used to determine how quickly space is expanding?
23 votes
3 answers
13k views

Maximum spin rate of a black hole?

I have just been watching a podcast called "Deep Astronomy" and the discussion was about a super fast spinning black hole discovered with the NuSTAR space observatory. This black hole was ...
0 votes
0 answers
31 views

Is the difference of redshift parameter z able to prove expansion is accelerating in flat FLRW universe model?

Sorry for my bad english, this is not my mother tongue. Recently, I've encountered a problem in cosmology class that is about FLRW universe. Assuming that the universe we inhabit is composed of non-...
-2 votes
1 answer
72 views

Does dark matter exist because as Einstein said the laws of physics should be the same inside and outside a black hole?

Spacetime is said to be time like inside a black hole ( two events can happen at the same place at different times). Spacetime is called space- like outside a black hole ( two events can happen ...
2 votes
3 answers
288 views

How can Kerr black holes have a 'speed limit' to how fast they can spin?

Obviously, the speed of light is a presumed limit, at least for 'physical' objects moving 'within' ('through'?) spacetime, but... In recent news some scientists believe they have figured out the ...
0 votes
0 answers
58 views

$v_{GW}$ near a binary star?

In empty space, at large distances from masses and at small amplitudes, GWs propagate at the speed of light. This does not apply near the source, because there is a large mass and the amplitude of the ...
57 votes
6 answers
26k views

If light has no mass, why is it affected by gravity?

Light doesn’t accelerate in a gravitational field, which things with mass would do, because light has a universally constant velocity. Why is that exception?
76 votes
2 answers
11k views

Can gravitational waves pass through a black hole?

As the title says, what happens when a gravitational wave approaches a black hole? I would presume that something interesting happens because of the way spacetime works near black holes but I have no ...
0 votes
0 answers
59 views

Question about how it's possible for black holes to have gravity and a possible resolution [duplicate]

1. Assumptions 1.a: gravity propagates at c (maximum) 1.b: gravitational fields cause time dilation 1.c: escape velocity at the event horizon is c 1.d: gravity "warps" space-time, but in ...
2 votes
0 answers
41 views

Which static spherically symmetric perfect fluid solutions of Einstein field equations are known to be suitable for stellar models?

Wikipedia's (Static spherically symmetric perfect fluid) short list ends in 2005 and lists only in total 5 such solutions. Does somebody know more?
6 votes
3 answers
1k views

Concerning a binary system of stars/planets/black holes could one of them be ejected before eventually merging or colliding?

I was having a discussion with an undergraduate student of physics about binaries and their interactions with external celestial bodies (which could cause the ejection of one of the members in the ...
3 votes
0 answers
67 views

Gravitational recoil with stars/planets...?

When two black holes are merging, the resulting merge can be ejected if one of the black holes had less mass than the other one, so the gravitational waves emitted by both of them is unbalanced, and ...
3 votes
1 answer
132 views

When two galaxies with dark matter halos merge do they provide evidence for fermionic or bosonic dark matter?

If dark matter is made from fermions these should collide and cause dark matter to become denser in some places than others Bosons wont collide in this way so there should a different effect .So is ...
1 vote
0 answers
86 views

If astronomers didn't know about redshift could we still determine the universe is expanding?

What other evidence is there for the expansion of the universe? Would the equations of physics look wrong without it?
6 votes
2 answers
280 views

Light or neutrinos graze or pass through the Sun and arrive at Earth - need an expression for Sun's gravitational effect on observation direction/time

Skyfield's Github has discussion Jupiter hiccup #815 which then links back to to Non-physical gravitational deflection corrections for Solar System bodies #734. The script and plot from #815 are shown ...
1 vote
2 answers
367 views

How far can a gravitational-wave pass through space?

Is there any equation which shows how far a train of gravitational waves will travel from a source until it loses its ripples and amplitude? The wave train will lose energy as it travels. It has a ...
1 vote
0 answers
34 views

Modelling dark energy as a potential?

Dark energy is the cosmological constant.However can we model dark energy as some form of field with a corresponding potential?
0 votes
1 answer
43 views

bent space-time by Energy can radiate gravitational-wave?

as we know , both mass and energy can bend space-time , and we know that accelerate mass can radiate gravitational-wave , but my question is that : bent space-time by energy can also radiate ...
4 votes
1 answer
66 views

What's the relation between the parallax distance and the luminosity distance?

I have read that Riess and his team are able to measure $H_0$ from supernovae calibrated using Cepheid in a model independent way. from what I have gathered they find the absolute luminosity of ...
0 votes
0 answers
28 views

Can the cosmological constant be coupled to redshift of radiation

Can space-time be more embedded with the things inside it than we actually think?Can the redshift of radiation be a property of spacetime and that dark energy exists only to conserve the overall ...
-4 votes
2 answers
143 views

What is the minimum amount of dark matter to start controlled nuclear fusion in nature?

In large spaces where there is a lot of dark matter, Stars are born in groups and not alone, so what is the minimum amount of dark matter to start controlled nuclear fusion in nature?
0 votes
0 answers
134 views

Does the other side of the Big Bang factor into JWST observations?

Our (roughly) 13.6 billion light year view to the point of origin (big bang) is just along a radial axis. Assuming most matter ejected in a (roughly) spherical pattern, the diameter of the universe is ...
8 votes
1 answer
2k views

Is Webb or any near-future telescopes like ELT capable of observing redshift changes to confirm General Relativity?

The (Davis and Lineweaver (2003)) "Expanding Confusion" paper states that "the expected change in redshift due to cosmological acceleration or deceleration is only ∆z ∼ 10^(−8) over 100 ...
6 votes
1 answer
298 views

Has GAIA learned anything about General Relativity looking near Jupiter? (Gerry Gilmore: "oblate rotating mass moving in a deeper (Solar) potential")

From Gerry Gilmore (2018) Gaia: 3-dimensional census of the Milky Way Galaxy 4.4 Fundamental physics Relativistic effects are highly significant for Gaia measurement accuracy, with tests of General ...
1 vote
1 answer
74 views

When gravitational waves pass through a star or gas cloud do they cause mixing of plasma and gas?

Does the compression and stretching of space stir up molecules and atoms?
4 votes
1 answer
78 views

Gravitational wave intereference

Is it possible to conduct a hypothetical experiment where gravitational wave interference occurs and where areas of constructive and destructive gravitational wave interference are present? If such ...
3 votes
2 answers
344 views

Gravitational-Wave Strain and Power (watt/square metre)

If we detect a gravitational wave with a strain of, for example, $h=10^{-20}$, what is the flux of power carried by this wave, in SI units, $W/m^2$ ? How can flux of power be calculated for a given ...
2 votes
2 answers
156 views

Does MOND change general relativity?

Newton's inverse square law appears in General relativity for small masses . Since MOND uses 1/radius instead of 1/radius squared has General relativity been modified to accommodate this?
7 votes
3 answers
709 views

What produces gravitational waves with "periods between about 100 - 8000 seconds"?

The Ulysses mission has a compelling story. It was sent to Jupiter to perform a gravitational assist shooting it out of the plane of the ecliptic in order to fly over the Sun's north and south poles ...
1 vote
0 answers
50 views

Does the (relative) distance of the photon sphere from the center of a black hole vary according its mass?

I know that the photon circle or photon sphere is located at around 1.5 times the radius of the Schwarzschild event horizon, but wouldn't it be comparatively further out for smaller black holes? After ...
8 votes
2 answers
1k views

Do tidal forces on moons cause them to emit gravitational waves?

As moons orbit planets, they get squashed by uneven gravitational forces acting on them. Does this make a moon emit gravitational waves?
2 votes
3 answers
211 views

Do you need to understand the detailed mathematics of general relativity to be a professional astronomer?

Could I become an astronomer by understanding how to use the main results of general relativity such as cosmological redshift or would I need to understand the whole theory?
3 votes
2 answers
159 views

Do gravitational waves produce a surrounding gravity field?

Massless light beams produce a surrounding gravity field. A massive particle will move towards it and at the same time be dragged along in the direction of the beam's velocity. But what will happen ...
4 votes
0 answers
65 views

What does it exactly mean for spacetime to have no global symmetries?

Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances? And if there are, what does it ...
1 vote
0 answers
66 views

Non-homogeneous and anisotropic metric and laws of physics...?

In this popular science article, they say that if our universe resulted to be non-uniform (that is highly anisotropic and inhomogeneous) then the fundamental laws of physics could change from place to ...
1 vote
1 answer
278 views

Does the expansion of space stretch the space-time fabric?

This question appeared to me when I was thinking about General Relativity. During the expansion of space, the space in which particles reside is expanded. Now, general relativity states gravity is the ...
1 vote
0 answers
26 views

Spacetimes where symmetries vary from place to place?

Are there spacetimes or metrics where symmetries (like Poincaré, Lorentz, diffeomorphism, translational... invariances) are only local and the symmetries of one local neighbourhood are not, a priori, ...
13 votes
1 answer
2k views

How would "dark matter", subject only to gravity, behave?

If we were to hypothesise that the Universe contained a significant mass of "dark matter" particles subject only to gravity, presumably general relativity would give us a good idea of how ...
1 vote
1 answer
77 views

Are there non-smooth metrics for spacetime (that don't involve singularities)?

I found this statement in a discussion about the application of local Lorentz symmetry in spacetime metrics: Lorentz invariance holds locally in GR, but you're right that it no longer applies ...
1 vote
1 answer
71 views

Other Hubble spheres with no Lorentz symmetry?

Perhaps this may be a stupid question but anyways here it goes... If the Lorentz symmetry is not global but rather local, wouldn't that mean that is possible that other Hubble spheres outside our ...
3 votes
3 answers
233 views

Viewing black holes?

How could you possibly see a black hole when there are stars etc in front of it and then the matter being drawn into it , all you would view surely would be the objects in front of the black hole ?
27 votes
3 answers
3k views

Is it possible to detect gravitational lensing of stars behind the Moon?

Eddington waited for a total solar eclipse to happen to be able to observe gravitational lensing of the stars behind the Sun. And nowadays, amateurs can do the same thing. Of course, the Moon is much ...
5 votes
3 answers
164 views

Problem with the Orbital Precession predicted by the Relativistic Acceleration equation used in the JPL D440-D441 Ephemerides - please advise

I have previously encountered a problem with the equation used by Yeomans and others for determining the gravitational acceleration of comets (see update in my answer to the previous question Can ...
4 votes
2 answers
507 views

Can General Relativity indicate phase-dependent variations in planetary orbital acceleration?

In a previous question about differences in Newtonian and GTR gravitional force for the case of star-planet gravitational interactions an approximate relationship was noted between the expressions for ...
4 votes
1 answer
614 views

Observable Speed of objects orbiting a black hole

This is a mostly hypothetical question and thought experiment, and I am aware of some aspects plausibility of it are open for debate. Also, this is Version 2 of the question, as the first question was ...
7 votes
2 answers
3k views

How do two black holes merge?

Since at the Event Horizon, time stops completely, how do two black holes merge together? Shouldn't they should stop moving due to time dilation when they get closer to each other's Schwarzschild ...

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