Questions tagged [gravity]

Questions regarding the attractive force which exists between any two bodies of matter.

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7
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2answers
1k views

Do stars in galaxies also move in elliptical orbits?

There is a gravitational force between every pair of objects, because of which planets revolve around the Sun in elliptical orbits. My question is: as planets move in elliptical orbits with the Sun at ...
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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
115 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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3answers
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Roche limit - calculation with centrifugal forces

Let's assume there is a small natural satellite oribiting a massive planet. The satellite rotates synchronously (revolution period = orbital period) on a circular orbit, both bodies are homogenous and ...
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5answers
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Does a planet's mass or gravity affect the height of it's mountains?

According to this Wikipedia page, the top five highest mountains on Mars (and the highest on Venus) are all taller than Mount Everest (and Mauna Kea as measured from the ocean floor). Does a planet's ...
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1answer
66 views

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
136 views

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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6answers
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What is the minimum mass required so that objects become spherical due to its own gravity?

Is this minimum mass known? or maybe, is it given in terms of density? If so, how much density is the minimum to have an spherical object due to its own gravity?
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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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0answers
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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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0answers
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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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If an asteroid twice the size of Earth passed super close would half of the Earth be pulled towards it?

So let's say that an asteroid the twice the size of Earth passed by going relatively slow say in between the Moon and Earth. Among so many other things (and perhaps you can touch on some of the ...
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2answers
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Parking a telescope at a Lagrange point: is this a good idea from a debris point of view?

The James Webb space telescope is supposed to be located at the Earth-Sun L2 Lagrange point. Do we expect the region around that point to have a higher concentration of space debris, asteroids, dust,...
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1answer
485 views

How to determine the mass of a galaxy?

I am having a slight disagreement with my professor. We can measure the mass of a distant star cluster from: A.Its color B.Its radius C.Its metallicity D.Smearing of lines in its total spectrum My ...
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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
139 views

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
95 views

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
80 views

Kinetic energy and galaxy arm rotation rate

The higher than expected rotational velocity of stars and gas clouds in the outskirts of galaxies is explained today by invoking dark matter that supplies not only the additional gravitational mass ...
2
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1answer
60 views

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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2answers
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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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1answer
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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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2answers
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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
168 views

Can eternal inflation and gravity explain dark energy?

First of all, I have absolutely no background in astronomy and physics. I just watch a lot of "i-hope-scientific" youtube channels talking about physics and astrophysics and I can kind of follow the ...
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1answer
193 views

Theoretically could the expansion of the universe affect acceleration due to gravity?

I was wondering if theoretically the universe expanding affects speed or acceleration due to gravity, compared to if space weren't accelerating. The way I have it in my head, something is falling ...
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1answer
50 views

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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0answers
41 views

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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1answer
201 views

Do the Bullet Cluster remnants prove that dark matter consists out of particles?

Some time ago the remnants of a collision between two collections of stars were discovered. These remnants are called the Bullet Cluster: The color blue (non-visible in reality) represents the ...
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1answer
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In 'Modified gravity' theories like MOND, are galaxies and stars actually, slowly accelerating? In the normal sense?

In the Modified Theory of Newtonian Gravity or MOND, they say that massive objects, accelerating slowly, experience this modified gravity. But are they actually gaining in velocity, albeit very slowly?...
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3answers
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Would time go by infinitely fast when crossing the event horizon of a black hole?

If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the ...
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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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2answers
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Why is it strange that outer stars in a galaxy are travelling with the same speed as inner while the total mass is also increasing?

Astronomers say that it's strange that the outer stars of a galaxy are travelling with the same speed as the inner stars. Therefore they introduced dark matter to solve this strangeness. The theory ...
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8answers
6k views

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
103 views

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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3answers
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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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5answers
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Do asteroids have a gravitational field?

I know that asteroids are huge chunks of rock, orbiting a solar system. Do asteroids have a gravitational field and do they gravitationally attract each other to form planets?
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1answer
180 views

Stability of solar system

My question is simple: Is the Solar system stable? You can see this Wikipedia page. Edit: Sorry, because i think my question is more about mathematics and classical mechanics of planets in ...
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0answers
61 views

What influence does the Interplanetary Magnetic Field have on Planetary Orbits?

CONTEXT The equation $F_D=\frac{GMm}{D^2}$ is a standard equation in Newtonian gravitation. It describes the centripetal force exerted, by a source mass$M$, on a target particle of mass $m$ located ...
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3answers
447 views

Do photons slow down as they approach the event horizon of a black hole?

So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)? Do photons ...
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3answers
187 views

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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4answers
11k views

Is Jupiter made entirely out of gas?

I heard that Jupiter is made out of gas. But in school I learned that Jupiter has gravity which is 2.5 times that of Earth (Gravity that can tear apart a comet) and gravity is proportional to mass. ...
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4answers
167 views

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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2answers
1k views

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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7answers
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What's the fastest moving object in the universe?

We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or ...
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4answers
199 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
31 views

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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1answer
114 views

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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