Questions tagged [gravity]
Questions regarding the attractive force which exists between any two bodies of matter.
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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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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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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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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 ...
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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 ...
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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 ...
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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 ...
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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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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?
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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 ...
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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?
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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 ...
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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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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 ...
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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. ...
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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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Why can't supermassive black holes merge? (or can they?)
The CNet article Astronomers discover two supermassive black holes in a death spiral links to Discovery of a Close-separation Binary Quasar at the Heart of a z ~ 0.2 Merging Galaxy and Its ...
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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 ...
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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.
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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 ?
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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)^{...
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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 ...
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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 ...
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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 ...
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How does gravity have an effect from the inside the event horizon of a black hole with the rest of the universe?
According to general relativity, as I understand it, the space around a black hole's event horizon is distorted by gravity, such that the distance to a point approaching the event horizon from an ...
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What causes objects to become tidally locked?
I'm trying to write a gravity simulation (suns planets etc), and was hoping tidal locking could be one feature demonstrated.
Using a simple equation for gravity has produced some interesting results, ...
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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 ...
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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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What makes protoplanetary disks start rotating? (Initial energy needed to rotate)
Planets form from a protoplanetary disk that has been rotating around its star. The initial energy that makes them rotate really matters to me.
Why did the protoplanetary disk start rotating around ...
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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?
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Can Newton's gravity equation explain why black holes are so strong?
I was just wondering why black hole's gravitational forces are so powerful. I know it's usually explained by Einstein's relativity which states that when an object becomes infinitely dense (a compact ...
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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 ...
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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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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 ...
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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 ...
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Can dark matter be found in the shape of planets, galaxies etc.?
If dark matter has gravity just like normal matter, does that mean it can also form planets, solar systems and so on?
Any answer will be appreciated.
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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?
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Is there a better explanation of Hawking radiation?
I'm writing a piece on Hawking radiation, and find I have something of a problem. The "given" explanation which I find on Wikipedia and elsewhere is unsatisfactory:
"Physical insight into the ...
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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 ...
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Why is gravity only an attractive force?
As per the universal law of attraction, any two bodies (having some mass) experience a force of 'attraction' which is proportionate to ...and ...inverse proportionate ....
Then comes my question: Why ...
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If 50 tons or more of debris falls to earth everyday, is Earth getting heavier?
In turn, would that increase our gravitational pull?
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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 ...
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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 ...
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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 ...
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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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Where do rocks come from?
Consider a loose pile of rocks in an early solar system, say a tiny asteroid. As it accretes more and more material, the pressure at its center eventually becomes great enough to collapse the gaps ...
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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}{...
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Techniques for locating origin of gravitational waves
The gravity wave detections (GW150914 and GW151226) have both been ambiguous in their exact position, the LIGO papers (GW150914 and GW151226) give no precise information about the location of the ...
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Gravitational red shift vs Doppler redshift: Is the universe really expanding?
Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted?
What I think I know thus far is this:
Redshift ...
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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 ...
