# Questions tagged [gravity]

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

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### What exactly is a 'gravastar'? How is it different from a 'regular' black hole?

The Wikipedia article on gravastar says that it has a 'regular' black hole metric (Schwarzschild, I presume?) on the outside, but a de Sitter metric on the inside.... What exactly does that mean? Don'...
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### Is the gravitational force of the mass a result of combined magnetic field of every single atom in that mass?

Could be the magnetic field of every single atom in a mass combined with other magnetic fields of other atoms, result in a gravitational pull? I will explain what do I mean by that question. I know ...
1 vote
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### How is gravity a force if it is the result of space-time warping and bending?

If gravity is just the result of the bending of space-time, how does that make it a force? Isn’t it just an interaction between celestial bodies?
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### Why are black holes oblate spheroids?

I just heard something I have heard a million times before: "The shape of a spinning black hole is an oblate spheroid." This time, it hit me as odd that a black hole's shape changes with a ...
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### Universe Sandbox and Hillsphere calculation (Updated)

So according to this calculation here including: A Gas Giant of 12 Jupiter Masses A Sun like Star of 1047.57 Jupiter Masses and a semi major axis of the Planet of 1 AU The Gas Giant should have a ...
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### Is the gravitational constant really constant over our Universe?

For instance, if objects are travelling at relatively high speed around 'c', is G the same value for them as for us on earth? I believe a lot of matter is travelling fast away from other matter, so is ...
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### Gravitational forces [closed]

OK so, someone is arguing that if the earth was a globe water would be flung out in space because of the spin...yeah, I know....and no matter how many times I tell her that the centrifugal force is so ...
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### Local anisotropies in the expansion of the universe and tidal forces...?

In the context of the large-scale structure of the universe, there can be local anisotropies (https://www.aanda.org/articles/aa/full_html/2021/05/aa40296-21/aa40296-21.html). I understand from this ...
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### Expanding voids ending being collapsed?

According to some papers I've found 1, 2 expanding voids can be foun inside clouds of denser materials that can cause them to eventually collapse. I have two questions about this: Overdensities ...
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### Light/Dark energy/Dark matter

So I have been working on my comic book project that takes place on another planet. But in my story, there will be warp gates and there will be other civs that can travel between stars. I am ...
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### Black hole explosion due to rotation [duplicate]

I am not an expert, I was just thinking about this scenario: A black hole that, for some reason, will start spinning faster and faster. Is it theoretically possible that the rotation becomes so fast ...
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### Fractal structure of the universe

I decided to return to the question first written here after some time, since a short and succinct phrase had formed in my head that described the phenomenon that I was trying to understand. What are ...
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### Gravity is inversely proportional to the distance squared, and tidal forces to the distance cubed. Is there any phenomenon inv/prop to the distance^4?

Kinda ran out of characters for the title so had to improvise. Gravity decreases with the square of the distance due to the inverse-square law, and tides are inversely proportional to the cube of the ...
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### 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 ...
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### At what velocity would an object have to fall in order to become weightless? [closed]

Assume an object is falling toward the earth then at what velocity would the object be weightless? Taking the air resistance into account might be a factor here so lets assume no air resistance to ...
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### Celestial "orbits"

I heard that we're losing our moon, its slipping away from us in such tiny imperceptible steps that we don't notice any significant change even over kiloyears. The same must apply to planets, inching ...
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1 vote
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### Does dark energy increase eccentricity in orbits of galaxies?

I came across this thesis dissertation which indicates that if a pair of orbiting galaxies are sufficiently far apart (with a sufficiently large orbital radius) then their orbits would change from ...
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### Gravitational waves vs. "normal gravity"

Imagine you have a super sensitive 3D accelerometer/gravimeter alongside the Virgo interferometer. A gravitational wave passes by and Virgo detects a variation in the length of the 3000m long arms. ...
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### Could the human body feel the sudden disappearance or end of a gravitational force?

For example, if the Sun suddenly disappeared, would we physically feel it 8 minutes later (not counting light/temperature), since propagates moves at the speed of light. And if so, would the effect be ...
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### Spiral Galaxies

I only have a very, very, basic understanding of linear motion, much less so of circular motion. What I can recall is my book telling me if you spin a stone tied to the end of a string and the string ...
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### Can black holes even exist [if mass cannot be retained near the collapse threshold]?

A black hole happens because enough material mass exists in an area to create a gravitational field strong enough that nothing escapes (including light). This gravity also exceeds the strength of ...
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### If you are in a deep gravity well, where time goes by more slowly, do you see the unfolding of a cosmic event at a different rate?

If you were on one of those planets orbiting a super massive black hole (ala Interstellar), where time is moving more slowly, would you time astronomical events differently or even the age of the ...
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### Are short-period comets more stable (in their orbits) than long-period ones?

Why the sharp distinction between short-period (P) comets of less-than-200-year orbits and those (C) with even slightly longer ones? To explore the possibility that it has to do with stability, I will ...
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1 vote
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### Eccentricity with a law of gravity different from the classical one

How can I calculate the eccentricity of the orbit of a planet (with mass equal to that of the Earth) around a star (with mass equal to that of the Sun) assuming that the force of gravity is given by ...
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### Velocity of the object in Binary system

how to i can calculate the velocity of the object? If i know the distance of the object from the center of mass, and i know distance between the two (identical) ellipse center... (the two object has ...
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### Does the Earth constantly lose mass?

The Moon is orbiting the Earth in a circular motion. To keep any object in a circular motion we need energy. Hence, does the Earth lose energy by pulling the Moon? In that case, does the Earth's ...
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### 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 ...
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### At what point above Jupiter is the gravity Earth-like?

Jupiter is a massive planet. We get it. However, we have also heard that, since it has such a huge radius, at different elevations it is possible to experience different levels of gravity. We hear ...
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