# Tag Info

3

Yes, Newtonian Physics works on a galactic scale. Still, for long distance interactions on fast objects you might want to take into account the finite speed of gravity, but I don't think it is necessary for ordinary galaxies simulations. Conversly a lot of phenomena occur that impact the galactic material: writting a decent simulation is not easy.

27

They do! There's an entire class of galaxy, called a 'satellite galaxy' which is defined entirely based on them orbiting a larger galaxy (which would be called a 'central galaxy'). Our own milky-way is known to have many orbiting satellite galaxies, or at least 'dwarf-galaxies'. If dwarf-galaxies aren't enough, the milky-way itself is gravitationally ...

89

There are plenty of satellite galaxies orbiting larger galaxies. The question is how long are you willing to wait for an orbit? The Milky Way has a mass $M$ of something like $6\times10^{11}$ solar masses, or $10^{42}\ \mathrm{kg}$. The small Magellanic Cloud is at a distance $R$ of $2\times10^5$ light years, or $2\times10^{21}\ \mathrm{m}$. A test mass ...

1

To answer your first question. No, we cannot easily see the Galactic bulge with the naked eye from Earth. The reason is dust extinction, which limits our view to around a few thousand light years or less when looking in the plane of the Galaxy, which is considerably closer than the Galactic centre. When we look out of the Galactic plane, there is less dust ...

4

The first picture is a view of the center of the galaxy, as observed from Earth. There's quite a lot of dust in between it and Earth, so on many wavelengths (including visible light), we can't see much. The first picture is actually only part of a larger picture, including the Paranal Observatory: Image courtesy of Wikipedia user Nikthestunned, under the ...

-1

What we see in the photo is within a spiral: hydrogen black clouds and relatively dense areas of stars more or less hidden, + some Halpha regions (faint red-pink nebulas). I would say that the most luminous place corresponds to the borders of the bulge region. About the shape, it's the same problem with all panoramic photograph: you might chose different ...

1

On the scale of galactic spiral arms, the central black hole is gravitationally utterly insignificant. I'll illustrate with an example, NGC 524. Of spiral galaxies (this is technically an S0, but there's still spiral structure) with measured black hole masses, NGC 524 has one of the most massive. Here's a picture of the galaxy: The visible disk has a ...

2

Rotational and turbulent motion cannot "deepen" the gravity well in a galaxy of galaxy cluster. The contribution of kinetic energy to the stress-energy tensor is negligible compared to the rest-mass energy in non-relativistic systems. Assuming you mean something like, 'how does rotational and turbulent motion contribute to the equilibrium configuration of ...

0

In agreement with the above answer, a good zero order "motivation" can be found in: http://www2.astro.psu.edu/~caryl/a480/lecture7_10.pdf. Since Tully-Fischer boils down to the mutual interaction between the baryonic mass of galaxies and the dark mass of their halos (star formation, angular momentum exchange, ...) there is no "derivation" in a textbook ...

1

A Galaxy cluster could have $10^{14}$ solar masses within a radius of 5 Mpc. In this case $GM/Rc^2 \sim 10^{-6}$, equivalent to a velocity shift of less than 1 km/s. Our own Milky Way has a mass of around $10^{12}$ solar masses within 100 kpc. This gives a gravitational redshift of about 100 m/s. These are completely negligible compared to cosmological ...

0

You don't need to worry about any spherically symmetric distribution of matter, dark or otherwise, that lies outside the radii you have measurements for. It has no effect (see the shell theorem). Your velocities tell you something about the mass interior to your velocity measurements. Unless you have lots of measurements as a function of radius, there's ...

2

The gravitational red shift is only significant for black holes – where the coefficient may grow arbitrarily large in the vicinity of the horizon – and the neutron stars – where the frequency drops to something comparable to 50%. For all other celestial objects, the red shift is much smaller than one. And only planets and white dwarfs are objects for which ...

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