Why Are There Galaxies?

Astronomers tell us the stars in our galaxy are in lock step. They turn
like the spokes in a wheel. That is true of stars inside the hub.
Because of the great gravity of that huge BH they have to revolve around
the blackhole so very fast that the gravitation that keeps our sun in
lock step with the rest of the galaxy has no effect on stars making up
the hub. Not in the books but that is the way I see it. Bert

My post says inside the hub. It should read outside the hub,and inside
the hub ithe stars are not in lock step Bert

"G=EMC^2 Glazier" wrote in message
...
My post says inside the hub. It should read outside the hub,and inside
the hub ithe stars are not in lock step Bert

It's kind of hart to tell what you mean when you use terms like "in lock
step", but it sounds like you had it right (sort of) the first time.

The bulge exhibits characteristics of solid-body rotation, the disk exhibits
characteristics of differential rotation.

Zinni to Bert:

It's kind of hart to tell what you mean
when you use terms like "in lock step",
but it sounds like you had it right (sort of) the first time.

Got a question for the gurus on non-Keplerian rotation of galaxies- In
our solar system, well over 99% of the mass of the system is contained
in the nucleus (the sun). And the rest of the system naturally obeys the
Keplerian laws of orbital mechanics, orbiting about the massive nucleus.
But in contrast to a solar system, a galaxy's nucleus
(presumably a BH) does not contain the overwhelming mass of the system;
rather it contains a miniscule percentage of the total mass. So the
question is Why should a galaxy be expected to display Keplerian
rotation? Would not a more unitary (or 'frisbee-like') rotation be
expected, just as is observed?

Or, is the mass of the nucleus sufficiently high that Keplerian rotation
*should* be expected? oc

"Bill Sheppard" wrote in message
...

Why should a galaxy be expected to display Keplerian
rotation? Would not a more unitary (or 'frisbee-like') rotation be
expected, just as is observed?

Hey Bill

In fact, Keplerian rotation is not expected IN THE DISK.

Let me back-track for a second. There is a well known result attributable to
Newton that says ...

- Given a spherical shell of uniform density, its net gravitational effect
on a test particle outside of the spherical shell will be exactly the same
as if all of its mass were concentrated in a single point at its centre.

and ...

- Given a spherical shell of uniform density, its net gravitational effect
on a test particle (anywhere) inside of the spherical shell will be exactly
ZERO.

This result also holds true for rings of uniform density and a test particle
in the plane of the ring either inside or outside of it.

So, if we view the galaxy as approximating a series of rings of uniform
density (a good approximation for most of the disk) only the mass internal
to the orbit of a test particle need be considered. As we move out from the
centre of the galaxy there is more and more mass internal to the orbit to be
considered. The rotation curve IN THE DISK is part way between solid-body
and Keplerian. It is only once we get to the outer reaches of the galaxy,
were the visible matter thins to such an extent that we would expect no
appreciable change in the mass internal to the orbit of our test particle as
we move out, that we expect a Keplerian rotation curve to kick in. We do not
however get what we expect, the orbital velocities do not start to drop
according to Kepler, thus leading to the theory of Dark Matter.

Hi oc The sun has 99% of all the mass of the solar system. and gravity
is a mutual attraction. Still it is hard for me to see Neptune and
Pluton so far away from the sun,and staying in orbit. Then we have
Mercury so close to the sun. It has to be revolving very fast as not to
fall into the sun. The planets are not in lock step nor is the solar
system like a solid frisbee. With the huge area of the Milky
Way,and gravity getting weaker the inverse square of distance. There is
no way the blackhole at the center of the hub even with a mass of2.6
million suns can keep our sun that is 26million LY away in orbit,and all
the other millions,and millions of stars from leaving the galaxy and
escaping into space. That is why when they add up the mass of the Milky
Way astronomers tell us 95% of the mass(gravity) is missing. This holds
true for all spiral galaxies(I don't know about elliptical) The term in
lock step means the stars are not gaining on each other. To me it means
the Big,and Little dippers will keep their shape. I hope that stays true
for they are the only constellations I can find Well oc even if they
find a lot of dark matter I can see a problem,for it would have to be
spread out between the stars very evenly,and with the right force of
gravity to accomplish what we observe. Bert

"G=EMC^2 Glazier" wrote in message...
...

Hi Painius Just had this interesting thought. the stars that make up
the hub and have a 2.6 million solar mass blackhole at their center must
be revolving around it very fast. How fast is very fast? Lots of stars
must be falling through the event horizon every day. Stars of great mass
could be colliding(gut feeling thats true) To much stuff and angular
motion in a small area can cause choas. Bert

I don't think anyone really knows how fast, Bert. I *do*
know that most people have some idea that stars are
"thick as thieves" at the galaxy hub, but once you get
there, it's like the asteroid belt. The stars are far
enough apart to mean that collisions are very few and
far between.

I could be wrong, but i don't think the black hole grows
very fast.

Here's a neat article...

http://www.nature.com/nsu/020107/020107-9.html

....raises LOTS of questions, doesn't it.

happy days and...
starry starry nights!

--
Your heart up hanging on the wall
Just dripping tears so painfully,
You ne'er felt love so true as mine,
I want your heart inside me.

Protected from all manner, form
And shape of harm it will e'er be,
If you say no, I fade and die,
I need your heart inside me.

Paine Ellsworth

Hi Painius Thanks for that site. Seems the Milky Way hub is a very
dynamic place I like our spot in right field a lot better. Bert

"G=EMC^2 Glazier" wrote in message...
...

Hi Painius Thanks for that site. Seems the Milky Way hub is a very
dynamic place I like our spot in right field a lot better. Bert

Welcome!

Yes, it appears that for our form of life, i.e. carbon-based,
we're all better off being the hicks of the Milky Way!

Other possible bases for life might be...

silicon
germanium
tin
lead
ununquadium

This is just a reflection that i perceive from the periodic
table of the elements. Carbon-based is probably the
toughest form of life. If a carbon-based lifeform cannot
live at the hub of the Galaxy, nobody can. I *could* be
wrong about this.

Ununquadium-based life would be a manufactured form.

We're not ready for this, are we.

happy days and...
starry starry nights!

--
a Secret of the Universe...
so please don't breathe a word of this--
the Moon above will smile perverse
whene'er it sees two lovers kiss;
(breathe not a single word of this!)

Paine Ellsworth

Hi Painius I have a picture(framed) taken by the Hubble of the
Cartwheel galaxy It has a bright oval shaped hub. I can see arms coming
out of the hub and going to the great big ring around it. The ring seems
very bright,and must have billions of stars making up its structure.
It is good this Cartwheel galaxy was not seen edge on,because than it
would look like a spiral galaxy. I wonder how common this shape galaxy
are? Almost looks like a huge explosion could have caused the ring.
Bert