Questions tagged [gravity]

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

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28
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5answers
6k views

Is the influence of gravity instantaneous?

When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If all the matter in the Sun magically disappeared instantly, how long ...
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4answers
2k views

Why does gravity make everything round?

I am studying ways to make an anti-gravity machine (!!). I believe it can be done, or theoretically be done using gravity itself as a "force" that pushes outwards instead of inwards. A similar ...
21
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1answer
13k views

Is the moon moving further away from Earth and closer to the Sun? Why?

According to The NASA Moon Facts page: The moon is actually moving away from earth at a rate of 1.5 inches per year. Why is the moon moving further away from the Earth? Is this a result of the ...
12
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4answers
12k views

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?
14
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2answers
11k views

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 ...
10
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6answers
17k views

Why doesn't the sun pull the moon away from earth?

If the suns gravitational pull is strong enough to hold much larger masses in place (all the planets) and at much greater distances (all planets further away from the sun then earth) why does it not ...
19
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4answers
3k views

How can a supermassive black hole cause so much energy to enlighten its matter when its massive gravity prevents light to escape?

To cite the German newpaper article Astronomen beobachten erwachendes Schwarzes Loch: Das Materie-Monster sitzt den Angaben zufolge im Herzen der 42 Millionen Lichtjahre entfernten Polarring-Galaxie ...
6
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3answers
3k views

How does gravity interact with a photon?

If photon is mass-less and gravity can interact only with matter, then how does gravity alter the trajectory of light?
5
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1answer
339 views

What do gravitational waves allow us to understand?

Before reading this question, you should read this paper. From what I understood, we managed to detect gravitational waves for the first time. Is this discovery going to help us understand something ...
11
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3answers
1k views

How does light affect the universe?

When light is emitted by for example a star, that star loses energy - which causes it to reduce its gravity. Then that energy begins a journey for potentially billions of years, until it reaches some ...
15
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5answers
442 views

Orbiting around a black hole

Is it possible (for either a satellite or a planet) to orbit around a black hole? Do they attract everything around themselves into the center? Or they just affect gravitational force just like stars?
5
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2answers
697 views

Spacetime curvature illustration accuracy

When a particle travels through spacetime, this is sometimes illustrated moving in flat grid with various depths. How accurate is this way of imagining gravity? Can the gravity well be infinitely ...
10
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2answers
2k views

The deduction of the Hill Sphere formula

This question may be a little lazy, but can anybody give me a proof of the Hill sphere formula? Acording to wikipedia, the formula for the radius, $r$, is $$r\approx a(1-e)\left(\frac{m}{3M}\right)^{...
14
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5answers
8k views

Does the gravity of the planets affect the orbit of other planets in our solar system?

When one planet passes near another during its trip around the sun, does their gravitational pull is strong enough to disrupt noticeably each other's orbit ?
5
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2answers
572 views

What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very ...
0
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1answer
265 views

How strong is the gravitational stretch we experience from the edge of the universe?

How much gravitational effect do we experience (e.g. maybe -.00001 G or smaller) from the edge of the visible universe? By edge of the visible universe, I am talking about the region of the cosmic ...
34
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5answers
22k views

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 ...
21
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3answers
908 views

Could there be dark matter black holes?

Could dark matter compress and form black holes? Since dark matter is even more abundant than normal matter, a dark matter black hole should not be rare...right?
20
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4answers
10k 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. ...
31
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2answers
6k views

Are black holes spherical during merger?

I've been thinking about black holes, specifically during the final moments before two merge. I'm wondering if black holes, or I guess more specifically their event horizons, are always spherical. ...
16
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4answers
848 views

Why do Earth and moon move apart but binary black holes move closer?

According to the accepted answer on Is the moon moving further away from Earth and closer to the Sun? Why?, the moon is receding from Earth because tidal forces and friction cause energy to be lost. ...
13
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1answer
1k views

How can neutron stars have gaseous atmospheres?

Neutron stars can have small atmospheres. However, they also have extremely strong gravitationally pulls. Shouldn't the all the gas molecules be drawn to the star's surface, and become solids under ...
13
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1answer
3k views

What is the difference between Sphere of Influence and Hill sphere?

Wikipedia's definition of Hill sphere is: An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit ...
19
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1answer
528 views

Are there any alternative explanations for the gravitational force we attribute to dark matter?

It always seemed counter-intuitive to me that we observed an measured a gravitational force and since the universe has not enough mass to account for it, the conclusion was to say there's a different ...
16
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3answers
2k views

How does a gravity slingshot actually work?

From what I know of elliptical orbits, an object speeds up near the periapsis and slows down at the apoapsis, much like we learned in high school physics how a sphere would roll down and back up a ...
11
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2answers
266 views

How precise are the observational measurements for the speed of gravity?

General Relativity says that gravity moves at the speed of c. How precise are the measurements?
9
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2answers
497 views

Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used?

This newly updated answer to How precise are the observational measurements for the speed of gravity? and this answer to How is the most accurate value of 𝐺 measured? cites the November 2017 arXiv ...
6
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1answer
239 views

Gravitational pull needed to keep a gas in atmosphere

How can you determine the gravitational force needed to keep a particular gas in the atmosphere of a planet (for example, carbon dioxide (CO2))? I came across the following formula $\left(\frac{8RT}{...
5
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3answers
151 views

Can't pulsars and stars be used for gravitational wave measurement?

Suppose that we collected photons from a distant star, and they arrive regularly at 15 photons every microsecond onto a CCD, when a gravity wave bends space time, wouldn't the regular 15 photons graph ...
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4answers
376 views

Instantaneous gravity in equation of motion for ephemerides calculation

The equation of motion used for the calculation of orbits of solar system objects (Eq(27) in https://ipnpr.jpl.nasa.gov/progress_report/42-196/196C.pdf ) is formulated in terms of instantaneous ...
19
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2answers
794 views

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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2answers
3k views

What are “non-Keplerian” orbits? What are some familiar examples in our solar system, and can some still be closed?

This excellent answer to Forms of stellar orbits around the galactic center invokes the following concepts: non-Keplerian orbits closed orbits I have a fairly good idea what these mean and so might ...
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6answers
2k views

Are black holes really singularities?

Can't black holes just be super dense objects? They could still be black (having the color of black never really required special physics, after all) and have a really strong gravitational field. If ...
9
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1answer
230 views

What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
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1answer
318 views

How was the hypothetical ninth planet kicked so far out of the Solar System?

I was reading this article on science news and ran into the following statement: Such a remote super-Earth probably originated closer to the sun only to be kicked out by the other giant planets ...
9
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3answers
4k views

Why are stars so far apart?

So, this is mere musing, but it seems that stars are quite extremely far apart. I tried to determine the mean distance between nearest neighbors for stars (in just our galaxy) but I'm not sure what it ...
5
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1answer
196 views

Have more recent LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity further?

This answer to How precise are the observational measurements for the speed of gravity? says: ...in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down. ... [T]he ...
4
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1answer
186 views

Satellite's orbit

What is the maximum distance for a satellite to orbit the earth? Does earth's gravity has the impact on satellite? I do know that earth's gravity will never be zero and it's gravity is inversely ...
4
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1answer
101 views

If an event occurs at a point in space time what will an observer experience first, it's gravity or the light from it?

Let's assume a person is close enough to an object in space time to be able to observe it's gravitational effects and the light coming from it. If that object suddenly pops out of existence (...
33
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6answers
7k views

What did LIGO Actually See? (Gravitational waves discovery)

I am trying to find an original video/image of what LIGO actually saw, but all I can find is artist renditions of gravitational waves.
60
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3answers
17k views

If a massive object like Jupiter flew past the Earth how close would it need to come to pull people off of the surface?

I understand this is a silly hypothetical but I'm asking for a 7 year old so please bear with me. Imagine an interstellar stray gas giant comes flying through our solar system. If we were not ...
41
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5answers
8k views

Why does gas form a star instead of a black hole?

When a space gas gets pulled together a star is formed. On the other hand, when a massive star dies, it collapses to a black hole. You would think that the initial mass of the gas would be bigger ...
10
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2answers
1k views

How can gravitational waves escape from the gravity of black hole?

I know that even light can't escape from a black hole's gravity and the velocity of light and gravitational waves are the same. How can only gravitational waves escape from its gravity?
29
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1answer
4k views

If dark matter bends light, how do we know the stuff in the sky is where we think it is?

We measure movement, position, and many other things of an object in space because of its light and what we can measure with it. But as far as I know there's supposed to be a HUGE amount of dark ...
20
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3answers
2k views

Existence of gravitons?

For a lot of my uninformed life, I have doubted the existence of gravitons or even that gravity is an actual "force" (like electromagnetism). This is because my vision of general relativity was that ...
19
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4answers
3k views

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 ...
26
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5answers
7k views

How does gravity really work

I am only 12 years old and I'm constantly wondering and trying understand how gravity really works. On YouTube everyone always talks about objects warping space time around themselves and uses the ...
17
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4answers
4k views

What is Gravitational Lensing?

What is the effect known as gravitational lensing? How does it work? What objects would be able to cause this effect?
8
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1answer
446 views

Horseshoe orbits and integration in C

I'm studying a particular case of the restricted three-body problem. It's been found that some objects follow a horseshoe orbit pattern, and I'm trying to sort out something through an integration ...
5
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2answers
820 views

How would water waves behave in partial gravity?

Would an "indoor" pool of water on the Moon or on Mars behave differently than on Earth? Would the waves caused by a splash be higher or lower? Would they propagate faster or slower? Would boyance be ...