Questions tagged [gravity]
Questions regarding the attractive force which exists between any two bodies of matter.
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Could a rogue comet perturb a frequently occurring meteor shower to the extent that debris falls on Earth...and dislodges satellites?
This is for a work of fiction that I started five years ago. Clever people from Astronomy Stacks answered several questions for me back then. Now that I am in the final edit of this manuscript, I find ...
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Could a super-Jupiter exoplanet in the habitable zone have an axial tilt?
I’m wondering if a massive planet (maybe 10 times the mass of Jupiter) in the habitable zone of a G type star could have an axial tilt similar to earth or if gravitational forces would erode the tilt ...
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Could a planet have a massive crater without collapsing due to gravity / other factors?
A severely destroyed planet is a popular trope in media. Here are a few examples from fiction with pictures (spoiler warning).
A crater with a diameter 1/3rd the size of the planet itself:
Earth (...
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RAMSES fine multigrid Poisson solver fails to converge?
I am working on setting up N-body simulations of galaxy mergers. The initial conditions are generated from the DICE code, and looking at them, they seem very realistic. Unfortunately, when I let ...
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If 16 million kilometers were added to Earth's semi-major axis, what measurable effect would there be on Mars' orbit?
I have some education in astronomy, but nothing extensive in astrophysics. I can follow mathematical procedure with assistance. Procedural responses are most welcome!
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Could the universe expand forever even if there is no force (e.g., dark energy or eternal inflation) pushing it apart?
Matthew O'Dowd specifically and repeatedly states in the PBS Space Time video called, "Why the Universe Needs Dark Energy", that even without taking an expansionary field into account an ...
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Initial state for a 3-body problem to create Figure 8 [ restricted to 2D ]
I've made an n-body simulation solution using the naive algorithm of O(n^2) in my library ChelseaaJS.
I was trying to make some pleasing 3 Body simulations.
I wanna do the 8 figure thing.
I know it's ...
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Can two Stars form an Einstein Ring?
We know that when two galaxies are perfectly aligned they form an Einstein Ring by gravitational lensing but can two stars form it? We know gravitational bending by stars, but can two perfectly ...
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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 ...
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What is Gravitational softening length?
I was reading the Aquarius simulation preprint (Springel et al. 2008) The Aquarius Project: the subhalos of galactic halos as a reference for my internship. I came across the term Gravitational ...
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Calculating the "Turnaround Point," where expansion dominates over gravity
I'm trying to understand the point where the expansion of space dominates over gravity, but I'm coming up empty handed when searching the internet. Specifically, I'm trying to find the math for it. I'...
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What is roughly the Lorentz factor between interstellar and inter-galaxycluster space?
Could someone provide a rough estimate for the average Lorentz Factor caused by gravitational time dilation between some point in interstellar space in our vicinity within the Milky Way galaxy and ...
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How much would you weigh at the equator of the fastest spinning pulsar?
Assuming you have a mass of 70 kg, what would your weight be on the equator of PSR J1748−2446ad?
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Is the dark matter/baryonic matter ratio the same in galaxies with supermassive black holes?
My hypothesis is that if the ratio of dark matter/matter in galaxies with supermassive(weighing billions of suns) black holes are higher the black hole itself would be made of a large portion of dark ...
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How can we see black holes collapse if time inside the event horizon is infinite?
My understanding is that if you fell into a black hole, i.e. crossing the event horizon time would be speed up infinitely fast. This means I could see my whole galaxy die, new blackholes develop and ...
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Why are what end up being meteorites not in stable orbit as planets and large asteroids are?
We don't have to worry about Mars, etc. hitting Earth. Is it that, being smaller, small asteroids have less inertia and so are more affected by, I guess, the gravity of various planets?
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Is it coincidence that the change in GPE when falling from deep space into the largest know neutron star is approximately mc squared Joules?
We can calculate the change in GPE in falling from a very long distance to the surface of a star or planet from
$$\Delta{GPE} = \int_{r}^{\infty}mg\,dh $$
But taking into account that g will change ...
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Why is gravity constrained to speed of light of gravity itself affects space time?
Gravity(gravitational waves)they say travels at the speed of light. But speed is distance/time. If gravity affects space-time or “time” then how can we be sure that gravity indeed travels with a ...
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Is a black hole really a neutron star with a gravitational time dilation factor of 1.0
Here's why I'm asking.
The gravitational time dilation factor at the surface of a star or planet can be expressed as $$gr/c^2$$
In theory, the same equation should apply to the gravitational length ...
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Could the forces that hold the galaxies together already have changed?
Since the theory is, that effect of gravity travels at the speed of light, could the forces that hold galaxies together already have changed as we are 20k light years are so away from the centre ? And ...
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Do any equivalent of Lagrange points exist between galaxies?
I'm wondering whether there is a similar effect between Galaxies as we have between a planet and it's star. I know there are tidal waves between galaxies and that gravity seems to always be attractive ...
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By dint of some 'reverse engineering' I have produced the equation below. Does anyone recognise it? Does it come from general relativity?
The equation is
$$a = \frac{\sqrt{2} \cdot c^2}{k}$$
where a is the acceleration due to gravity, c is the speed of light and k is the radius of curvature of the geodesic. The equation is dimensionally ...
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If Earth was a moon of Jupiter orbiting at the same distance as Metis (Jupiter's innermost moon), then how much lighter would a 100 kg person feel?
Metis is Jupiter's innermost moon, orbiting at a semi-major axis of 128,000 km. If Earth were to magically replace Metis, then how much lighter would a human weighing 100 kg be?
There's no need to ...
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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 ...
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How does general relativity explain gravity?
General relativity explains that gravity is the curving of spacetime by massive objects. This makes sense, like when I throw a ball, it follows the curve of spacetime, which is towards the center of ...
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Classifying 3C273 as a quasi-stellar object
I am currently reading A Brief History of Time and Chapter 6 about black holes.
Now, here it says
He found it too large to be caused by a gravitational field: if it had
been a gravitational redshift, ...
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How does this Toomre GI criteria have the period in the denominator?
I saw this equation in a literature review recently talking about the Toomre criterion for gravitational instability:
Given here in section 2.1.1: https://arxiv.org/pdf/1801.06117.pdf, viz.
But I am ...
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Can planetary rings distort the shape of a planet?
I was watching this Kurzgesagt video on what would happen if the moon crashed into the Earth, and it mentioned that at the very end the tidal forces would tear the moon apart and create planetary ...
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Units for orbital period and gravitational constant
Using this site for binary system orbital period calculations: https://www.omnicalculator.com/physics/orbital-period
The formula given there is
$$T_{binary} = 2 \pi \sqrt{\frac{a^3}{G (M_1+M_2)}} $$
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Time in 0 gravity points
If being close to a supermassive body like a black hole makes time pass more slowly for us than for an observer from a point of view with a weaker gravitational field, if we get to be at a point in ...
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Great Attractor's gravity vs Universe Expansion
I would like to know if the trajectory of our galaxy has been calculated because it is usually said that the cosmos is emptying due to the expansion of the universe but at the same time there is a ...
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Why is the L1 point (Lagrange) almost 1 million miles from Earth? Shouldn't it be closer to us?
Try to follow my simple logic:
The Sun is almost exactly 333,000 times as massive as Earth, and gravitational strength increases linearly with mass, so the Sun's gravity is about 333,000 times ours.
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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 ...
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What's the difference between the Roche lobe and Roche sphere?
I am just beginning to look into this topic, so apologies if there are any striking misconceptions in the following.
From Wikipedia, the Roche lobe is "the region around a star in a binary system ...
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Are there negative masses that attract each other but repel positive masses? [closed]
Is there law/rule in physics that precludes the existence of a negative mass, wherein similar negative masses attract but positive and negative masses repel?
To keep this on-topic in Astronomy SE: Has ...
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Do Einstein's ten field equations use 20 or 40 variables? (2 or 4 for each tensor equation?)
One site I came across says Einstein's 10 Field Equations use 20 variables, while another said 40.
There are four variables in spacetime - three for space and one for time, right?
But there are two ...
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Does the Schwarzschild metric solution require two (A and B, or g11 and g44) or four components (g11, g22, g33 and g44)?
Different places on the web imply that Schwarzschild's metric uses four components or separate equations, similar to how Einstein's full set requires 6 or 10, or they say only two are needed. Is it 2 ...
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How close to escape velocity are most Oort-cloud comets?
User @antlersoft wrote a nice answer to my question on the difference between barycentric and heliocentric models of the solar system when applied to comets (edge cases of the systems). In a comment, @...
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Is it true that the 3 body problem can't be solved using the four basic functions, radicals, and integrals?
The two-body problem can be completely solved via two one-body problems, which only uses the four basic binary functions. However, the three-body problem cannot be solved with these functions and ...
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How is light unable to escape a black hole if photons are massless? [duplicate]
I understand light will follow the curved space that the BH is causing due to its mass. I also understand that mass attracts other mass but then photons are massless.
So 0(photon) x m2 (the BH) is ...
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Are gravitational waves affected by gravity?
Are gravitational waves affected by gravity? When a gravitational wave passes by objects, do their gravitational fields warp or change it?
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Which factor most affects the accuracy of Kepler's Third Law when applied to solar system planets?
We know that Kepler's 3rd Law is not perfectly accurate due to gravitational perturbations of other planets, moons, etc., but which factors most affect the accuracy?
Is it the semi-major axis, mass of ...
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Can the Dark Matter / Energy problem be plausibly reframed as an ignorance of gravity problem?
I understand Dark Matter was originally proposed to explain the rotation rate of galaxies. The rate was not explained by observed matter, ergo there must be unobserved matter. An alternate explanation ...
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Physical Meaning of the Principal Tidal Fourier Modes and Their Integers
I'm trying to understand tides evolution of planets, and I often come across the Prinicipal Tidal Fourier Modes expressed as:
$$ \omega_{lmpq}$$
For example, see the discussion after Eq. A15 in ...
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Can the gravitational redshift of our sun be measured?
How much of a wavelength change does our sun’s gravity cause in the light it emits? I imagine this could be measured by the shift in its spectral lines. And by extension, does the earth’s ...
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Using Kepler's 3rd law to calculate $\mu$ (standard gravitational parameter)
I'm trying to calculate $\mu$ (the standard gravitational parameter) with this formula
$\mu = 4\pi^2a^3/T^2$
I'm using Earth's orbit is $a=1$ and $T = 365.2564$
for $a^3/T^2$ I'm getting $\approx7.496$...
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Why do planets' orbital velocities drop off by less than a third when twice as distant from the sun, rather than three-quarters? If gravity is $1/4$?
Looking at the speeds of the planets in our solar system when traveling around the sun and their distances from it (or, using Kepler's third law,), it seems that when a planets distance is doubled, it'...
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In relativity why does matter bend spacetime in a downward direction [closed]
A major flaw , I think it is in relativity.
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List of J₂ values for solar system bodies beyond the planets; are there any prolates?
J₂ values for the planets can be found in several sources including each planet's planetary fact sheet. Without looking I'm going to assume they are all positive (oblate) because each planet rotates ...
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Why does Titan's (relatively) rapid migration away from Saturn cause the planet to wobble faster, and eventually (maybe) tip onto its side?
Over the past year and a half, multiple articles in the popular press have come out talking about how unexpectedly rapidly Titan is moving away from Saturn, and how this is causing Saturn to wobble ...
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