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Questions tagged [gravity]

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

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70 votes
3 answers
20k 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 ...
Yevgeny Simkin's user avatar
44 votes
1 answer
4k views

How large can a ball of water be without fusion starting?

How large can a ball of water be without fusion starting? Peculiar question: some explanation might be necessary. My young son is into ‘space’ and astronomy. One of his posters says that Saturn could ...
jdaw1's user avatar
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43 votes
5 answers
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 ...
Antons Voitov's user avatar
39 votes
5 answers
10k 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 ...
Ky -'s user avatar
  • 766
37 votes
2 answers
7k 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. ...
Ryan_L's user avatar
  • 643
36 votes
7 answers
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.
Scott Taylor's user avatar
35 votes
7 answers
24k 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 ...
bogen's user avatar
  • 2,346
31 votes
1 answer
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 ...
Sebastian Araneda's user avatar
27 votes
5 answers
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 ...
user avatar
26 votes
5 answers
5k 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 ...
Fezter's user avatar
  • 527
24 votes
4 answers
13k views

Why can't we feel the Earth's revolution?

I googled it and checked a few Q&A and there's only things about "Earth's rotation". But why can't we feel the revolution? They say we can't feel the rotation because the Earth spins at a ...
dolco's user avatar
  • 350
24 votes
6 answers
4k views

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 ...
Farid Rjb's user avatar
  • 343
24 votes
4 answers
12k 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. ...
Strikers's user avatar
  • 1,109
23 votes
6 answers
20k 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?
Clausia's user avatar
  • 785
22 votes
2 answers
7k views

Do all the objects in the universe exert force on all other objects?

Do all the objects in the universe exert force on all other objects? Like a type of gravity; also, how much does it decrease as it gets farther away?
Timtech's user avatar
  • 1,685
21 votes
5 answers
4k views

Why does electron degeneracy pressure not stop massive star collapse?

I was thinking a little bit, and never asked myself the following. If white dwarfs do not collapse, because electron degeneracy pressure stops the star from collapsing by its own gravity, and this is ...
martín canullán's user avatar
21 votes
3 answers
2k views

Will Saturn's rings become a moon?

Planets form from disks of matter orbiting around a star; some moons form from disks of matter orbiting planets. If this were going to happen around Saturn, approximately how much time would it take?
Eduardo Serra's user avatar
21 votes
1 answer
7k views

Is it possible to have a stable 3 body system that orbits in a perfect circle?

I.e. a system that has 3 objects of equal mass, rotating around the system's center of gravity like so: Please excuse the crude drawing, but I've just been reading The Three-Body Problem book by Liu ...
ROODAY's user avatar
  • 355
21 votes
1 answer
15k 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 ...
user avatar
20 votes
3 answers
7k views

Can a magnetic field of an object be stronger than its gravity?

Can a planet, star or otherwise have a magnetic field that is stronger or have more range than its gravity?
Muze's user avatar
  • 1
20 votes
4 answers
6k views

If suddenly "knocked" or perturbed from its orbit, would gravity eventually return the Earth to its original orbit?

If suddenly "knocked" or perturbed from its orbit, would gravity eventually return the Earth to its original orbit? I am curious as to whether this is even possible. It seems to me that ...
ifeoluwa king's user avatar
20 votes
7 answers
4k views

Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
Jonathan's user avatar
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20 votes
4 answers
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 ...
uuu's user avatar
  • 311
20 votes
3 answers
1k 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?
Sir Cumference's user avatar
20 votes
4 answers
3k views

Doesn't gravity attract objects in space until they collide?

If the formula to calculate the force of gravity between two objects is: $$F = GM_1M_2/r^2,$$ why do planets stay in orbit? Or is there another formula at work?
CharlieK's user avatar
  • 341
20 votes
3 answers
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 ...
Jack R. Woods's user avatar
20 votes
1 answer
3k views

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 ...
uhoh's user avatar
  • 30.7k
20 votes
2 answers
2k 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,...
FrenchKheldar's user avatar
19 votes
4 answers
6k views

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 ...
AdiBak's user avatar
  • 655
19 votes
1 answer
5k views

Moon's unusual gravity

We know that the Moon's gravity is about one-sixth that of Earth. Then I recently read that the mass of the Moon is about one-eightieth the mass of Earth. Since gravity depends on the mass of the 2 ...
John Canon's user avatar
19 votes
4 answers
5k 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 ...
uhoh's user avatar
  • 30.7k
18 votes
8 answers
7k 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?
aybe's user avatar
  • 467
18 votes
3 answers
6k views

Intuition about why gravity is inversely proportional to exactly square of distance between objects

What is the intuition behind why gravity is inversely proportional to exactly square of distance between two object and not cube or not some multiplier. Basically how Newton came up that its exactly ...
jrp's user avatar
  • 322
18 votes
6 answers
7k views

If the Sun disappeared, could some planets form a new orbital system?

If the sun were to suddenly disappear, the planets would continue to travel tangentially to their former orbits. (This I know from this answer to a somewhat related question here.) In such a scenario, ...
Psychonaut's user avatar
18 votes
3 answers
8k views

Why do astronauts move so slowly in zero gravity? [closed]

When astronauts are floating about in a spaceship or space station, they nearly always move very slowly. After doing a bit of research I can't see why being in zero gravity would restrict movement to ...
metaDesign's user avatar
18 votes
2 answers
22k views

Will Earth lose the Moon before the Sun goes into supernova?

I've read that the Moon is moving away from the Earth by 1-3cm per year. Is this enough to make the Earth lose the Moon before the Sun goes supernova? I'm asking because I would like to do the ...
hawaii's user avatar
  • 345
18 votes
3 answers
7k views

Why don’t we feel the Earth rotating beneath us?

I’m not sure all of the details in the experiment but basically it went as follows. Someone marked their location of take off in a hot air balloon and went straight up in the air. They stayed ...
Begons18's user avatar
  • 316
18 votes
2 answers
2k views

Why haven't Earth and Venus got any tiny moons? Or have they?

Why haven't some meteoroids gotten caught in Earth's or Venus' orbit? AFAIK most meteors are tiny fragments from comets. Shouldn't some comet tail sometime have passed Earth orbit at velocities ...
LocalFluff's user avatar
  • 11.4k
18 votes
3 answers
3k 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 ...
Ky -'s user avatar
  • 766
18 votes
1 answer
989 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 ...
Eduardo Serra's user avatar
17 votes
4 answers
4k views

What is the shape of orbit assuming gravity does not depend on distance?

We know that the orbit of the earth is elliptical considering the force of gravity is inversely proportional to the square of the distance. But assume that, gravity does not depend on distance. ...
Arafat's user avatar
  • 171
17 votes
1 answer
2k views

How could low-gravity dust in the early solar system have formed hard stones?

I wonder how very low-gravity dust could make bind together and make hard and dense stones that later on will merge together and make some of the planets? I read some meteorites as hard as a hard ...
abbassix's user avatar
  • 365
17 votes
4 answers
23k views

What is the difference between our time and space time?

I am trying to understand the phenomenon of space-time. But, everything on internet seems to be too complicated for me since I do not have a background in physics. Can anyone give me simple ...
Asadullah Ali's user avatar
16 votes
4 answers
4k views

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 ...
Bookaholic's user avatar
  • 1,559
16 votes
4 answers
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?
damned truths's user avatar
16 votes
4 answers
681 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?
Zoltán Schmidt's user avatar
16 votes
1 answer
632 views

A Sky Map of Gravity - what would it look like?

PREAMBLE Sky Maps exist which show the distribution and intensity of electromagnetic radiation received on Earth at various wavelengths. An obvious form is a map of the stars (Star Chart). Maps ...
steveOw's user avatar
  • 1,444
16 votes
1 answer
4k 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 ...
sampathsris's user avatar
16 votes
1 answer
820 views

Is it safer to be near a star or a black hole?

If a star or black hole neared the solar system, which would do the least damage? For the sake of a good comparison, lets assume the candidate star is an "average" 5 solar mass star, and the black ...
Jonathan's user avatar
  • 4,381
15 votes
4 answers
1k 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. ...
Gnubie's user avatar
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