Questions tagged [gravity]

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

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If the moon still had a magnetic field how long would have been possible to keep an atmosphere?

Let's assume the Moon had a considerable magnetic field to prevent the atmosphere dispersion caused by solar wind. Given the low gravity of the Moon, how many years would pass before all the gases (of ...
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1answer
202 views

How far out can the sun keep celestial objects revolving?

Astronomers define the Solar System as the distance under the influence of gravity from the Sun. I read that the Oort cloud is probably the farthest object that surrounds the sun. The sphere of this ...
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LIGO gravitational wave chirp signal frequency

This question is about the LIGO gravitational wave signals' frequency. The signals start from about 35 Hz to peak at about 250 Hz, giving evidence of gravitational waves. The question is about the ...
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889 views

Why can't gravity repel things?

Gravity is the result of the curvature of space, so could the curvature actually send objects away from the source?
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Do planets repel?

I know gravity is the result of mass. Gravity is nothing but the attractive force on a body due to its mass. I have a question that may be silly. In magnetism we have attraction and repulsion. Earth ...
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1answer
194 views

Is the gravity on Kepler 39b higher than on the Sun?

According to the formula for gravitational acceleration $a = GM/r^2$ where $G=6.674 \times 10^{-11}$, Jupiter with mass 1.89813 × 10^27 kg and radius 69,911,000 m gives a gravity around 25m/s^2. The ...
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171 views

How would humans with appropriate equipment navigate the surface of Saturn's moon Titan on foot? [closed]

Taking into account the physical characteristics of Titan (e.g. surface gravity, atmospheric pressure), what would be the most efficient method of motion for an astronaut to navigate the surface of ...
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Camera reaching the event horizon

This question came to my mind after reading this. I think it is safe to assume that the supposedly thrown camera would not reach the event horizon in one piece. So my question is : If I dropped a ...
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232 views

Does spacetime return to being flat?

I wrote an experiment in HTML5 and Javascript to try to show what is happening to the curvature of spacetime as a body moves through a region. As time progresses, I'm using the ...
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532 views

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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What is the most oblate astronomical object known?

There are some very vast spinning objects out there. How high can the eccentricity get, or, which I think is easier to understand, how small can the ratio between the polar and equatorial diameter ...
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Are other planets' gravity measurable on Earth?

I understand that we can calculate the gravitational force other planets exert on Earth, but can it be measured?
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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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Why don't globular clusters flatten with a galactic disc?

Globular clusters lie in the galactic halo, outside of the disc. However, galaxies are more or less a collection of material and objects — why is it, then, that most stars form a plane due to the ...
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Does Dark Matter affect the motion of the Solar System?

Would dark matter have a similar effect on the Solar System as it does on the Milky Way? I'd imagine it could help hold together some of the Solar System bodies or at least affect their motion, right? ...
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625 views

Can stellar black holes cancel each other?

Hypothetical question: when a pair of identical stellar black holes are very close to one another wouldn't the side facing each other experience lower gravitational force? How is this logic un/sound?
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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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1answer
112 views

How come moon's difference in thickness between sides does not create an unbalance on its mass?

I've just found out that moon's dark side is 30 miles thicker then the closer side to the Earth. So I'm wondering about moon's mass. How come it's still balanced? Supposing the far side is indeed ...
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1answer
469 views

Requirements for a satellite/planet to be tidally locked to a planet/star

The Moon is tidally locked to the Earth, the Four Galilean are tidally locked as well, and the recently found planetary sistem TRAPPIST-1 has seven tidally locked planets, but Venus or Mercury are not....
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Could this three moons system be stable?

In my fictional world I have selected all parameters to maximize the Hills Sphere of my planet. The planet has three times Earth's mass and it is located in 2 AU from its star that's 1.4 times more ...
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149 views

What are gravitational waves actually? [duplicate]

I read about the LIGo experiment recently, but i didn't understand their significance. Although, it's clear to me that the gravitational waves do exist and are caused by large accelerating bodies in ...
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1answer
221 views

What is the time/size/rigidity ratio for a space object to become mostly round?

In the answer here multiple comets are identified that do not form a single round body. A drop of water will form a round shape in the time it takes to free fall a couple of feet. All of the ...
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Is gravitational lensing a good way to search for negative mass?

Is it possible to verify negative mass with gravitational lensing? The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4 Could this be ...
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Dark matter virtual objects hypothesis [closed]

I've hypothesized for many years in my head that dark matter are the gravitational after effects of objects that have exploded. My understanding of physics is that when an object explodes, its center ...
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1answer
142 views

Gravity of other objects in black holes?

If something falls into a black hole, but has not yet hit the singularity in the center, can we (outside of the black hole) feel its gravity? On the one hand, I've learned that there's no distance ...
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1answer
281 views

How does an absolute horizon form before the apparent horizon?

If I understand it correctly, the apparent horizon is the boundary between where light directed outwards will move outwards, and light directed outwards will move inwards. Even if light is moving away ...
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615 views

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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How to correctly create planetary orbits from kepler elements

I would like to build a gravity model (with 3D graphics) that would build the orbit of the planets based on orbital elements input and the gravity calculation for each element. My initial code is ...
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108 views

Is the SOI a spherical region or a oblate-spheroid-shaped region?

The Wikipedia article on Sphere of influence states that: "A sphere of influence (SOI) in astrodynamics and astronomy is the oblate-spheroid-shaped region around a celestial body where the ...
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Where would an object fly to if it were to leave the gravitational field of Earth? And would it stop somewhere? What would happen to it?

My 3,5 year old son is asking :-) He can take answers for a 15 yo I think. Many thanks for your help!
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Can gravity be amplified by other celestial bodies in its vicinity?

I`m wondering if the gravitational pull from earth that should be constant around the planet, will get amplified by a celestial body like the moon orbiting the earth?
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What's the difference between the apparent horizon and event horizon of a black hole?

The Wikipedia page for apparent horizon is pretty sketchy and requires some GR knowledge. Is there any simple definition?
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1answer
658 views

Strength of gravity during the big bang?

I was watching a documentary on the big bang, one of the astronomers said that initially the four fundamental forces were combined as one, they then emerged to become: The strong and weak nuclear ...
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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 ...
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How does the size of a naked black hole effect its photon sphere?

What effect does the size of a black hole have on the size or density of the photon sphere and it's proximity to the horizon? For example: A person is in space looking at 2 black holes, one of them ...
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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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How does light so travel so fast?. [duplicate]

I've read that photon's have zero mass, hence no force is needed to accelerate them. But then the second question. How can gravity affect something which has 0 mass?. Yes, gravity(black hole) can bend ...
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1answer
2k views

Could the rotation of a black hole cause other planets to rotate?

Because everything rotates so perfectly, and we know that some blackholes rotate and they're the biggest things in the universe, so a silly question comes to mind. If you remove all black holes from ...
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Could gravity waves be used to confirm the existence of a ninth planet?

Shortly after the news of the discovery of gravity waves, my physics professor explained the significance of the discovery by comparing it to a medical X-ray machine. He said that gravity waves can be ...
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Is the Roche limit used this way?

Has the Roche limit affect been observed having an effect on an constructed object gravitational wise to cause damage? Could the Roche limit be used to slow an object?
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1answer
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Could a close passing star be captured by the Sun's gravity?

Earlier I read an article here stating that a binary pair of stars passed within 0.8 light years from the sun. That made we wonder why the stars weren't captured by the Sun's gravity since the sun's ...
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599 views

What causes Earth's gravity? [closed]

Why Earth is like a magnet? how can earth attract any object irrespective of what it is made of? What is the reason behind Celestial Body's gravity? i.e Sun,Jupiter,Moon etc.
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Why does Titan have lower surface gravity than the Moon when Titan is more massive?

Reading on Wikipedia I saw that Titan is 80% more massive than the earth's moon but has only 85% the surface gravity. Why is this?
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A camera and time dilation?

If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. However, what if we sent a probe with a camera to a black hole? When we watch the ...
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What is the Maximum Speed that can be acheived Because of Acceleration Due to Gravity?

Planets and other bodies in the universe have different ranges of gravitational fields. What is the maximum speed that can be achieved because of acceleration due to gravitational field. In other ...
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How much would you weigh if Earth stopped orbiting the Sun? [closed]

I have a curious question. The reason why astronauts are weightless in space is because they are orbiting Earth. If they suddenly stopped orbiting they would fall directly into Earth. Earth is doing ...
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How to determine the orbital period of an asteroid using Kepler laws given its orbit's radius?

Given that the mean distance of an asteroid from the Sun is $450 \times 10^6$ km is it possible that the asteroid completes one rotation around the Sun in two years? According to the third law of ...
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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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Do other planets affect the Earth?

Let say Mercury, Venus, the Moon were all in alignment between the Earth and Sun. They are all closest to each other in respective elliptical orbit. On the other side of the Sun you have the rest of ...
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Are there currently any planned or proposed missions to measure the gravitational fields of other planets in our solar system?

I just recently found out about the GRACE Nasa mission which basically mapped out the gravitational anomalies of earth as well as serving extensively in the study of earths geology and the movement of ...

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