Questions tagged [gravity]
Questions regarding the attractive force which exists between any two bodies of matter.
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What will happen because of the energy release and pair production during collapse a Kerr black hole Inside its event horizon to the limit? [closed]
The release of energy inside the event horizon of a black hole during its continued collapse under gravity towards the theoretical singularity could cause significant deviations from the simple "...
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What's the difference between the Roche lobe and Roche sphere?
I am just beginning to look into this topic, so apologies if there are any striking misconceptions in the following.
From Wikipedia, the Roche lobe is "the region around a star in a binary system ...
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2answers
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Are there negative masses that attract each other but repel positive masses? [closed]
Is there law/rule in physics that precludes the existence of a negative mass, wherein similar negative masses attract but positive and negative masses repel?
To keep this on-topic in Astronomy SE: Has ...
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Do Einstein's ten field equations use 20 or 40 variables? (2 or 4 for each tensor equation?)
One site I came across says Einstein's 10 Field Equations use 20 variables, while another said 40.
There are four variables in spacetime - three for space and one for time, right?
But there are two ...
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Does the Schwarzschild metric solution require two (A and B, or g11 and g44) or four components (g11, g22, g33 and g44)?
Different places on the web imply that Schwarzschild's metric uses four components or separate equations, similar to how Einstein's full set requires 6 or 10, or they say only two are needed. Is it 2 ...
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1answer
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How close to escape velocity are most Oort-cloud comets?
User @antlersoft wrote a nice answer to my question on the difference between barycentric and heliocentric models of the solar system when applied to comets (edge cases of the systems). In a comment, @...
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1answer
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Is it true that the 3 body problem can't be solved using the four basic functions, radicals, and integrals?
The two-body problem can be completely solved via two one-body problems, which only uses the four basic binary functions. However, the three-body problem cannot be solved with these functions and ...
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2answers
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How is light unable to escape a black hole if photons are massless? [duplicate]
I understand light will follow the curved space that the BH is causing due to its mass. I also understand that mass attracts other mass but then photons are massless.
So 0(photon) x m2 (the BH) is ...
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Are Gravitational Waves Themselves Affected By Gravity?
Are gravitational waves themselves subject to gravity? That is, if a gravitational wave were to pass by a galaxy cluster, would its form get distorted (even though the wave, itself, is a distortion of ...
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1answer
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Which factor most affects the accuracy of Kepler's Third Law?
We know that Kepler's 3rd Law is not perfectly accurate due to gravitational perturbations of other planets, moons, etc., but which factors most affect the accuracy? Is it the semi-major axis, mass of ...
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Can the Dark Matter / Energy problem be plausibly reframed as an ignorance of gravity problem?
I understand Dark Matter was originally proposed to explain the rotation rate of galaxies. The rate was not explained by observed matter, ergo there must be unobserved matter. An alternate explanation ...
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Physical Meaning of the Principal Tidal Fourier Modes and Their Integers
I'm trying to understand tides evolution of planets, and I often come across the Prinicipal Tidal Fourier Modes expressed as:
$$ \omega_{lmpq}$$
For example, see the discussion after Eq. A15 in ...
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Can the gravitational redshift of our sun be measured?
How much of a wavelength change does our sun’s gravity cause in the light it emits? I imagine this could be measured by the shift in its spectral lines. And by extension, does the earth’s ...
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1answer
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Using Kepler's 3rd law to calculate $\mu$ (standard gravitational parameter)
I'm trying to calculate $\mu$ (the standard gravitational parameter) with this formula
$\mu = 4\pi^2a^3/T^2$
I'm using Earth's orbit is $a=1$ and $T = 365.2564$
for $a^3/T^2$ I'm getting $\approx7.496$...
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1answer
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Why do planets' orbital velocities drop off by less than a third when twice as distant from the sun, rather than three-quarters? If gravity is $1/4$?
Looking at the speeds of the planets in our solar system when traveling around the sun and their distances from it (or, using Kepler's third law,), it seems that when a planets distance is doubled, it'...
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In relativity why does matter bend spacetime in a downward direction [closed]
A major flaw , I think it is in relativity.
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List of J₂ values for solar system bodies beyond the planets; are there any prolates?
J₂ values for the planets can be found in several sources including each planet's planetary fact sheet. Without looking I'm going to assume they are all positive (oblate) because each planet rotates ...
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Why does Titan's (relatively) rapid migration away from Saturn cause the planet to wobble faster, and eventually (maybe) tip onto its side?
Over the past year and a half, multiple articles in the popular press have come out talking about how unexpectedly rapidly Titan is moving away from Saturn, and how this is causing Saturn to wobble ...
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1answer
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How will be changed Hill's radius and Kepler's formulas in case of 2D space instead of 3D?
Imagine that Flatland habitats go into space. All stars and planets are the circles instead of spheres and gravity law is $F=Gm_1m_2/R$ instead of $F=Gm_1m_2/R^2$.
How the other formulas will be ...
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1answer
124 views
How to predict future position of body in solar system (without Kepler's equations, N-body problem)?
I have a solar system where each body interacts with each other by force $F = \frac{Gm_1m_2}{R^2}$
Is it possible to predict future position of some random body after t seconds since bodies velocity ...
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1answer
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How could a captured asteroid enter a circularized orbit?
Ok, the simple answer would be through gravity assists from moons, taking a ballistic capture orbit into a circular orbit. I am wondering the chances of a ballistic orbit becoming a stable (on the ...
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2answers
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Is gravity affected by time dilation? [closed]
I just thought about what time realy is but I can't put my head around this so I was thinking that if time dilation happens at the edge of a black hole that just everything gets slower. But does ...
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1answer
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What is the best visual-aide model that most accurately depicts objects moving through warped spacetime?
so far, the best model I've seen, to help me visualize objects moving through a warped spacetime is this video...
A new way to visualize General Relativity.
Is there a better visual representation to ...
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Density and Velocity profiles of a self gravitating explosion
Suppose an asteroid explodes, into a spherically symmetrical cloud, of radius R, mass M, and surface receding velocity V (normal to the edge of the cloud), initially the density is radially uniform.
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How much mass to make a shperical object?
I was googling around for info for D&D campaign I am going to run. I was wondering about the mass required for a object to pull itself into a shperical shape and it seems that the answer varies ...
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1answer
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Is a black hole's gravity strongest at its event horizon or at least near it?
I know black holes are extraordinarily powerful when it comes to the gravitational pull.
But I wanted to get something clarified - is the gravity stronger at the event horizon (like, on the very edge ...
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2answers
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Is there a better formula for gravitation, besides Newton's?
Many experiments (e.g. changes in Mercury's orbit) show that Newton's Law of Gravity is not exact. According to the theory of relativity, what is the exact formula?
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1answer
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Gravitational influence of other planets?
I have a friend who believes in astrology and she insists that the gravitational influence of the planets has an effect on the child when it's born. The last time she was going on about this a thought ...
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2answers
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How slow would you age on a double gravity planet?
How slow would you age on a double gravity planet?
Gravity of the planet A is 10 units. If you are taken from planet A to planet B where gravity is double that of A, i.e. 20 units. How slowly would ...
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1answer
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Does the Barycenter shift/combine when 2 planets line up with the sun?
On August 1st-2nd, Earth & Saturn lined up together in relation to the sun. Here is a website that discusses it: https://www.healththoroughfare.com/science/saturn-will-line-up-with-earth-and-the-...
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Why do gravitational waves travel "only" at the speed of light but the gravitational scalar potential is instantaneous?
To my old Space SE question Besides retarded gravitation, anything else to worry about when calculating MU69's orbit from scratch? @DavidHammen's excellent answer replies that one should not add a ...
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Is it "nonsense to even talk about" objects outside the observable universe not having gravitational influence on us? (finite speed of gravity)
In this supplemental answer to Is the zero gravity experienced in ISS the “artificial” kind? in Space Exploration SE I said:
Gravity moves at the speed of light so nothing outside out observable ...
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microwave background radiation and dark matter
Does the microwave background radiation predict the presence of a large proportion of dark matter over normal matter a few seconds after the Big Bang, or now?
Is it possible that there isn't much dark ...
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2answers
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Is a Hertz ratio to 65M ☉ proof that Betelgeuse had a core collapse in 1491 from a gravitational wave on January 14, 2020? [closed]
By analysis of gravity waves GW150914 to S200114f when compared to a ratio from the Black Hole merger of 65 M ☉ at 260 Hz with Betelgeuse frequency of 64.698303 Hz the gravitational release on January ...
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What if Earth gained 1 km/s orbital velocity?
How would Earth's orbit be affected if we (hypothetically) added $1 {\rm km/s}$ to its orbital velocity? Would Earth reach close to Mars' orbit?
Could Earth get gravitational assist from Mars and go ...
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1answer
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Which A. M. Fridman is the author of this paper on gravitational stability?
Is this paper on globular cluster stability still up to date? links to The Stability of Globular Clusters and Spherical Galaxies. by A. M. Fridman of the:
Institude of Nuclear Physics, Siberian ...
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Is this paper on globular cluster stability still up to date?
I'm looking to better understand the stability of globular clusters for an n-body dynamical simulation, specifically with respect to initial data conditions.
I know that the total potential energy ...
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3answers
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What would I experience on a planet orbiting close to a black hole? [closed]
I can't get my head around it completely. I am standing on an Earth-sized planet circling a black hole. Let's assume the planet to be an incompressible one.
It is observable that matter is sucked in ...
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4answers
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Why doesn't the Sun wobble towards Jupiter instead of away from Jupiter?
This is the page I am referring to. It seems counterintuitive to me that the Sun should be on the opposite side of the barycenter's wobble. I realize I am wrong, but I cannot see why I am wrong. Can ...
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3answers
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Gravitational time dilation
Did clocks run more slowly in the early universe due to gravitational time dilation? Or, alternatively, do they appear to be running more slowly when observed from today, if that is not the same thing?...
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Can a small black hole orbit a large star?
I recently read about the discovery of a tiny black hole (with only three times the mass of the sun) nicknamed ‘The unicorn’ about 1500 light years from earth. This got me thinking, can this black ...
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8answers
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Are there places in the Universe without gravity?
Not sure if that is possible as I couldn't find an answer about it.
Are there places in the Universe where there are no gravitational forces?
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3answers
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Was there a formula-first hypothesis for gravity?
Being a mathematician I wonder, has there been an attempt to blindly approximate a formula for gravitational attraction that would match the data, based on "normal" matter we can see plus ...
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2answers
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Gravity of a gaseous planet without a core
Both Jupiter and Saturn have rocky cores. Is there such of a thing as a gaseous planet without a core? And would a planet without a core have gravity?
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1answer
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Can two neighboring galaxies move apart at steady speed?
While I was trying to understand the three models that obey Friedmann's two assumptions of a non-static universe, I came across a line that says and I quote "It (referring to Big Bang) starts at ...
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4answers
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If a black hole has the same mass as me, then why dont i suck everything at my center of mass?
So, a black hole is very dense that you can get really close to its center of mass that it has a strong pull, well, if i have the mass of a black hole that has a really small event horizon, why doesnt ...
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4answers
204 views
Gravity inside a star?
Recently, I answered this question and need some clarification regarding the gravity when within the radius of a star. I thought that, when something is inside a star (ignoring drag), it will ...
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1answer
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If a black hole has a mass similar to a star, why does it have a different gravitational pull?
Say there is a black hole with 1 solar mass, having the sun's mass, it would have the same gravity as the sun, right? But it still has an event horizon, so why does it have such a strong gravitational ...
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Accretion disk formation
Why a mass transfer in a binary star system, from the less dense star to the denser star forms an accretion disk? Why the material does not fall directly to the denserstar?
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Calculating the radial tidal amplitude on a planet from the fluid Love numbers
How do you calculate tidal amplitudes from the fluid Love numbers? In my course on planetary physics I saw an approximate expression for the displacement from equilibrium tide:
$$\Big|\frac{V_T}{g}\...
