Hubble telescope pix from another angle

I bet it's weird to be on a planet whose star has been ejected from a galaxy. I suppose the night sky would look pretty dark except for that one galaxy that was wisible to the naked eye.
 
Not really. There are more galaxies out there than stars. And there are a bunch you can see with the naked eye. As long as you can resolve them, the surface brightness of all spiral galaxies (including our own) is about the same, so you can see other spirals whenever you can see the Milky Way.

M31 is a bright naked eye galaxy in Andromeda, rising in the northeast around 3AM this time of year. It's mag. 3.5, so you'll have some trouble seeing it in a brightly lit city. But that's easily visible at a dark site.
 
MAKG1 said:
Not really. There are more galaxies out there than stars.
Click to expand...

I have to ask for an explanation for that. I thought Galaxies were large collection of stars so how could there possibly be more galaxies than stars.
 
About 50 sec. into the sim, realistic dynamic planar interrelations between the two galaxies is inaccurately depicted.
 
JOhnH said:
I have to ask for an explanation for that. I thought Galaxies were large collection of stars so how could there possibly be more galaxies than stars.
Click to expand...

The question was about naked eye stars. There may be lots of really dim stars in other galaxies, but only a tiny handful of naked eye stars.

Even with a powerful telescope, the number of galaxies you can resolve more than a couple of O and B stars in is a very short list. You can do it for the brightest local group galaxies, but not much more.

I'd suggest taking a small telescope (or even a pair of binoculars or a good camera, as long as you can hold it still enough) out to a dark site and seeing what a galaxy other than our own looks like in real life. Most of them look something like boogers. Not collections of stars.
 
Last edited:
I'm considering the two spiral galaxies as primarily spinning planes, or discs made up of particles of course but, during the collision and during the specified time, the new orientations relative to each other are not accurate with respect to the most massive concentrations of matter and gravitational forces.

Prior to that time it is accurate.
 
You're assuming dynamics that isn't there. The mass distribution around a spiral galaxy is known not to look like the stars. How? You can measure the rotational velocity as a function of radius from the center, using the Doppler shift off a well-defined emission line. It is not consistent with mass = light for any spiral galaxy at any size. Rather, the rotation speed is constant with radius. That means mass arranged in an isothermal (inverse square density) sphere.

This has been known for some 50 years, confirmed thousands of times, and it is the strongest evidence for dark matter out there. To make a stable sphere, the matter needs to be self-interacting only through gravity. But if you want some more dynamical evidence, our galaxy is currently colliding with its nearest neighbor -- the Large Magellanic Cloud -- and the trailing "Magellanic stream" behind it traces an isothermal mass distribution. So does the forest of globular clusters around our galaxy.

Hernquist very definitely includes this effect in his simulations. He shows the luminous matter (stars and hot gas) and not the dark matter because that's what Hubble sees.

When you collide two simulated disks together, you get something that doesn't look anything like the observations -- they rip into little pieces, among other things. With an isothermal shroud several times bigger than the luminous mass, it's not bad. Isothermal spheres are sticky given observed parameters.
 
Last edited:
How does the number of naked-eye galaxies compare with the number of naked-eye stars?
 
Palmpilot said:
How does the number of naked-eye galaxies compare with the number of naked-eye stars?
Click to expand...

Not a lot, but it goes up really fast with even tiny amounts of magnification.

Not that a naked eye galaxy looks like much -- well, except for the Magellanic Clouds and the Milky Way.
 
MAKG1 said:
Not a lot, but it goes up really fast with even tiny amounts of magnification.

Not that a naked eye galaxy looks like much -- well, except for the Magellanic Clouds and the Milky Way.
Click to expand...

The reason I asked is that my comment was about what the sky would look like to the naked eye.
 
You must log in or register to reply here.
Back
Top