Are Galaxies as old or big as we think?

[OneEyed]

Under our estimates, it takes roughly 500 million years for our Milky Way Galaxy to make a complete rotation. Is it really possible for the spiral shape to have happened within the Galaxy's lifetime?

Gravity and Light work very differently within the Earth's atmosphere and outside of it. Why wouldn't this also be true of the Sun's Heliosphere? Couldn't red shifting happen much more quickly due to entering stars' atmospheres? This could literally reduce the size of the Universe by more than half. Do we have to run tests outside the heliosphere before we can even begin to assess that our calculations are correct?

I'm just having a hard time understanding how the shapes take form within the time frame we've estimated. It's hard to understand how we can differentiate so many different wavelengths and their distance traveled. For instance, we have a Star at 100 light years, sending a green light. Then we have another Star at 500 light years, which red shifted it's light source into a green light. How do we tell the difference?

 

[neilsox]

The evidence that the universe and our galaxy are lots younger or lots older has been debunked, perhaps improperly debunked in some cases. I'm not sufficiently expert to make that judgement.
A star that produced more than 25% green light would be evidence of a very advanced civilization. Typical stars produce a broad spectrum of colors, but do have various pastel tints, due to a small excess of one or two colors. Exceptions are computer enhanced to make the picture nicer, and/or convey other information.
I agree, there is a slight possibility that things are much different, beyond the heliopause, but evidence has been debunked. Perhaps there will be new evidence, in a few years as some of our early probes are about to pass beyond the heliopause.
To me, it is counter intuitive that a galaxy would be spiral shaped. Even if it was spiral shaped the spiral would be wound tight in about one billion years = 2 revolutions, as the inner stars orbit faster than the outer stars = much faster in radians per hour instead of kilometers per hour. Perhaps someone will explain to both of us? Neil

 

[MeteorWayne]

Under our estimates, it takes roughly 500 million years for our Milky Way Galaxy to make a complete rotation. Is it really possible for the spiral shape to have happened within the Galaxy's lifetime?

It's mpre like 200 million years for the sun

Gravity and Light work very differently within the Earth's atmosphere and outside of it.

No they don't. WHat makes you think that? gravity and light work the same everywhere.

Why wouldn't this also be true of the Sun's Heliosphere? Couldn't red shifting happen much more quickly due to entering stars' atmospheres? This could literally reduce the size of the Universe by more than half. Do we have to run tests outside the heliosphere before we can even begin to assess that our calculations are correct?

Red shift is caused by objects receding from us. It has nothing to do with any atmosphere, stellar or otherwise.

I'm just having a hard time understanding how the shapes take form within the time frame we've estimated.

What, tens of billions of years? Spirals are not among the first galaxies, almost all of the early ones we find are elliptical or irregularly shaped. It is thought that spirals result from the merger of smaller, earlier galaxies.

It's hard to understand how we can differentiate so many different wavelengths and their distance traveled. For instance, we have a Star at 100 light years, sending a green light. Then we have another Star at 500 light years, which red shifted it's light source into a green light. How do we tell the difference?

Spectra are identified by the absorbtion and emission of specific elements at specific wavelengths. It's then easy, once you identify the elements to calculate the recession velocity.

MW

 

[drwayne]

Note also that it is not simply the color that is looked at. The spectra of stars have discrete bright and dark
lines* that occur at standard locations in a rest frame. These lines move towards the red or blue due to
relative motion.

Wayne

*The structure of these lines tell you what kind of star you are looking at. I was moderately good at it,
way back in about 1980.

 

[MeteorWayne]

Typical stars produce a broad spectrum of colors, but do have various pastel tints, due to a small excess of one or two colors. Exceptions are computer enhanced to make the picture nicer, and/or convey other information.

Well that's not entirely true. Star colors are an indication of surface temperature. Red stars are cooler, blue white stars are the hotter with more UV as well. Brown dwarves, cooler still, radiate mostly infrared.

To me, it is counter intuitive that a galaxy would be spiral shaped. Even if it was spiral shaped the spiral would be wound tight in about one billion years = 2 revolutions, as the inner stars orbit faster than the outer stars = much faster in radians per hour instead of kilometers per hour. Perhaps someone will explain to both of us? Neil

A few misconceptions here. First of all the spiral is a density wave, not a group of stars that rotate together. Stars move through the spiral, it's just a place where the density is higher at a given time when we look.

Second of all, a galaxy is not like a planetary system where the inner planets rotate much faster around the star then the outer planets. Galaxies act differently, the curve is much flatter as far as rotational speed...that's how dark matter was shown to exist. The outer parts rotate faster than the would unless there's a lot of hidden mass, much of it outside the visible stars. Also, as I said above, the brighter spiral does not rotate as a block...each star has it's own orbit. At times they are closer together in those spiral bands, but the density moves on as each star continues in it's own orbit...in a sense it's an optical illusion. They are thought to be a reflection of the gravitation effects of the galaxy merger that created the spiral galaxy.

MW

 

[drwayne]

Here are some more detailed solar spectra, the absorption lines are centered at locations specified by the
elements in the stellar atmosphere