# Tag Info

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The gravitational potential at the point $\vec{x_0}$ of a collection of $n$ point objects of mass $M_i$ each located at a point $\vec{x_i}$ is: \begin{align} \Phi = \Sigma_{i=1}^{n} \frac{-GM_i}{|\vec{x_i}-\vec{x_0}|} \end{align} I'm not entirely use what you are doing with the Green's function array (is this a built in function?), but for this ...

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There is no requirement for a central black hole in a dynamical sense. Many galaxies are not known to have one, or if they do, its mass is relatively small. The gravitational influence of the SMBH can be quite negligible at distances that are only a tiny fraction of the size of a Galaxy. What I mean by this is that say the BH at the centre of the Milky Way ...

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The stars in the galaxy don't really orbit the black hole in the center of the galaxy. They all orbit a common center of gravity. Obviously, a lot of the mass is in the black hole, and the center of gravity could very likely lie inside the black hole's event horizon, but it's not required. Look here for a cool animation of Pluto and Charon orbiting a center ...

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This is all pretty well described in the Wikipedia page on the "big rip". The Friedmann acceleration equation determines the evolution of the scale factor of the universe and can be written as $$\frac{\ddot{a}}{a} = -\frac{4\pi G}{3}\left(\rho + \frac{3P}{c^2}\right)$$ where $\rho$ is the energy density, and $P$ is the pressure, usually parameterized as ...

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According to here, there was no precise definition before this group redefined what it meant for a group of galaxies to constitute a supercluster--before their redefinition, it seems it was just loosely defined as "extended regions with a high concentration of galaxies." They now define a supercluster to be a volume in which "the motions of galaxies are ...

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This new paper addresses exactly this question, albeit with simulations. Here's a partial breakdown of the distribution of matter in the Universe, summarized from the above paper: Dark matter makes up about 26% of the critical energy density budget of the Universe, while "baryonic matter" (which is jargon for "visible matter" and includes all baryons as ...

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There are 4 general contributors to the mass density of our co-moving patch of what may be a larger universe: (1) Visible baryonic matter (including clouds of baryonic matter which may be visible only as shadows blocking galaxies). NASA estimates 4.6% of all matter is baryonic (http://map.gsfc.nasa.gov/universe/uni_matter.html). (2) Dark matter (not ...

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Adding to the answer of the question 3 (How did arms of the spiral galaxies form?) one of the theories suggest an encounter between galaxies. This simulation I found in other answer "shows the influence of a nearby galaxy causing the imbalance which triggers arm formation" and could be interesting to see.

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In $4\times10^9$yr, M31 and MW (Milky Way) will have merged to form an elliptical galaxy. The internal spiral structures of either progenitor and their bars will be destroyed in the process, leaving a smooth ellipsoidal distribution of stars. The supermassive black holes (SMBHs; note that the one in M31 is $\sim100$ times more massive than that in MW) will ...

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Part of the LHC program is to find new particles that can be what dark matter is: very weakly interacting particles. This will show that an extension to the standard model would be correct. This will follow the pattern: "for every particle there exists an antiparticle", or a particle can be the antiparticle for itself, so yes, in this case there will be ...

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Andromeda and the Milky Way belong to a group of galaxies called the Local Group. The two galaxies are the largest galaxies in the group, so to a pretty good approximation their interaction can be treated as a two body problem, with the other galaxies in the group producing only minor perturbations to their motion. So as you suspected, it isn't the case ...

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Their mutual gravity will pull them towards each other, with the more massive galaxy causing more acceleration on the smaller. According to this article the more massive is the Milky Way, so it will cause Andromeda to accelerate more than the Milky Way, not that it really matters. Since interstellar space is mostly empty (i.e. there is a lot of distance ...

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Strictly speaking, the universe has no rest frame (that we know of). If you want to set the rest frame of the CMB to be stationary, (which is reasonable in many applications), you may compare the velocity of the Milky Way and the velocity of Andromeda with respect to the CMB rest frame. (I don't know if anyone has ever done this, however.) The CMB dipole ...

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