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Main
Date: 06 Oct 2006 07:57:13
From: Liam
Subject: dark matter and spiral galaxies
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Listened to an astronomy podcast:
http://www.astronomycast.com/extragalactic/the-search-for-dark-matter/
and the astronomer, or astrophysicist, mentioned one of the evidence
for the existance of dark matter is the rotational rates of galaxies.
She said that without dark matter then the centers of galaxies would
rotate faster than the edges which would trail behind.
So if you start with a straight line from the center of the galaxy to
the edge, as the galaxy spun the line would begin to arc. But because
of dark matter that imaginary line would remain straight as the galaxy
spins.
But for me that begs the question, how did spiral galaxies form? That's
something the podcast didn't address under this theory.
So, can someone help point me to info that explains this appearant
discrepancy?
Thanks!
-Liam
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Date: 06 Oct 2006 20:49:40
From: canopus56
Subject: Re: dark matter and spiral galaxies
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Liam wrote:
> But for me that begs the question, how did spiral galaxies form? That's
> something the podcast didn't address under this theory.
> So, can someone help point me to info that explains this appearant
> discrepancy? Thanks! -Liam
This book available at your local library has a good overview:
Waller, W.H. & Hodge, P.W. 2003. Galaxies and the Cosmic Frontier.
Harvard Univ. Press.
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003gcf..book.....W
Ellipictal galaxies like M87 or the M32 dwarf satellite of the
Andromeda Galaxy are spherical blobs.
http://www.seds.org/messier/m/m087.html
http://www.seds.org/messier/m/m032.html
Stars orbit within them much in the same manner that electrons orbit
around an electron. The orbits are randomnly distributed with respect
to the center of the galaxy and their is no "mid-plane".
Two galaxies then interact with each other. The outside gravity
imparts an angular spin to your spherical blob galaxy and "turns on"
star formation within the galaxy. The angular momentum effect is
self-re-enforcing. Overtime, the spherical blob turns into a rotating
flattened pancake.
Neaby galaxy M51 in UMa is thought to have undergones changes and a
recent burst of star formation as a result of its encounter with the
fainter galaxy NGC5195 seen somewhat "behind" it.
SEDS M51 pic showing NGC5195 in the background
http://www.seds.org/messier/m/m051.html
Hubble close-up of M51 showing high levels of star formation
http://hubblesite.org/newscenter/newsdesk/archive/releases/2001/10/
The evolutionary tracks by which the major galaxy types are created.
in the 1920s and 30s, Edwin Hubble throught that elliptical blob
galaxies "evolved" into lenticular pancake galaxies and then into
spiral galaxies. He organized the major physical types of galaxies in
that order into his famous "tuning fork" diagram:
http://en.wikipedia.org/wiki/Hubble_sequence
Although the tuning fork diagram is still used to mentally organize the
taxomony of the galaxies in the celestial "zoo," galaxies are no
longer thought to evolve in the order suggested by Hubble. For
example, an elliptical galaxy could be created by the near passage of
two spiral galaxies, one of which strips the outer gas and stars off
the second galaxy.
- Canopus56
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Date: 07 Oct 2006 00:59:09
From: Impeach Bush
Subject: Re: dark matter and spiral galaxies
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canopus56 wrote:
> Liam wrote:
> > But for me that begs the question, how did spiral galaxies form? That's
> > something the podcast didn't address under this theory.
> > So, can someone help point me to info that explains this appearant
> > discrepancy? Thanks! -Liam
>
> This book available at your local library has a good overview:
>
> Waller, W.H. & Hodge, P.W. 2003. Galaxies and the Cosmic Frontier.
> Harvard Univ. Press.
> http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003gcf..book.....W
>
> Ellipictal galaxies like M87 or the M32 dwarf satellite of the
> Andromeda Galaxy are spherical blobs.
>
> http://www.seds.org/messier/m/m087.html
> http://www.seds.org/messier/m/m032.html
>
> Stars orbit within them much in the same manner that electrons orbit
> around an ((electron)).
nucleus ?
> The orbits are randomnly distributed with respect
> to the center of the galaxy and their is no "mid-plane".
>
> Two galaxies then interact with each other. The outside gravity
> imparts an angular spin to your spherical blob galaxy and "turns on"
> star formation within the galaxy. The angular momentum effect is
> self-re-enforcing. Overtime, the spherical blob turns into a rotating
> flattened pancake.
>
> Neaby galaxy M51 in UMa is thought to have undergones changes and a
> recent burst of star formation as a result of its encounter with the
> fainter galaxy NGC5195 seen somewhat "behind" it.
>
> SEDS M51 pic showing NGC5195 in the background
> http://www.seds.org/messier/m/m051.html
> Hubble close-up of M51 showing high levels of star formation
> http://hubblesite.org/newscenter/newsdesk/archive/releases/2001/10/
>
> The evolutionary tracks by which the major galaxy types are created.
> in the 1920s and 30s, Edwin Hubble throught that elliptical blob
> galaxies "evolved" into lenticular pancake galaxies and then into
> spiral galaxies. He organized the major physical types of galaxies in
> that order into his famous "tuning fork" diagram:
>
> http://en.wikipedia.org/wiki/Hubble_sequence
>
> Although the tuning fork diagram is still used to mentally organize the
> taxomony of the galaxies in the celestial "zoo," galaxies are no
> longer thought to evolve in the order suggested by Hubble. For
> example, an elliptical galaxy could be created by the near passage of
> two spiral galaxies, one of which strips the outer gas and stars off
> the second galaxy.
>
> - Canopus56
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Date: 07 Oct 2006 15:24:09
From: Shawn
Subject: Re: dark matter and spiral galaxies
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canopus56 wrote:
> Stars orbit within them much in the same manner that electrons orbit
> around an electron.
Assume you mean nucleus.
You're implying that a star's orbit in the galaxy is determined by its
quantum state?
I suppose it might be, but quantum mechanics isn't the typical tool used
to calculate stellar motion..
;-)
Shawn
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Date: 06 Oct 2006 16:31:37
From: Bob May
Subject: Re: dark matter and spiral galaxies
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Start by taking any mass of gas and let it start coalescing into a galaxy.
Any differences in the basic motion of the gas will turn into a rotational
motion.
There's a simple little DOS program called GRAVITY that will show you how
this happens. It supports up to 9 (from my memory of the program) masses
but that will show the basics of what is happening. Email me if you can't
find it on the web. It is a freeware program of small size and runs on any
PC.
While nobody has figured out what the dark mass is, I suspect that one
really good candidate would be the mass of light that surrounds a galaxy.
--
Yeppie, Bush is such an idiot that He usually outwits
everybody else. How dumb!
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Date: 06 Oct 2006 20:15:17
From: N:dlzc D:aol T:com \(dlzc\)
Subject: Re: dark matter and spiral galaxies
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Dear Bob May:
"Bob May" <bobmay@nethere.com > wrote in message
news:aJ-dnd-wi4baervYnZ2dnUVZ_sWdnZ2d@nethere.com...
...
> While nobody has figured out what the dark mass is,
> I suspect that one really good candidate would be the
> mass of light that surrounds a galaxy.
The light would have to be closer to the galaxy center than the
object "anomalously accelerated". Light is well distributed all
around all objects... so its net contribution should be near
zero. That is thinking though...
David A. Smith
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Date: 07 Oct 2006 15:02:32
From: Bob May
Subject: Re: dark matter and spiral galaxies
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The thing here is that whatever the dark mass is, it is reducing the
attraction of the center of the galaxies by being outside of the central
area that we see well. Light is pretty much everywhere and is emitted from
the galaxies in large amounts. Interestingly, it is also transparent in
that it doesn't affect other light by diminishing it. If you consider that
light has mass by it's energy, it provides a continous presence everywhere
and thus pulls out the visible masses from the center of the galaxy to the
outer parts.
The question is whether light has been checked for the cause of this dark
mass problem.
--
Yeppie, Bush is such an idiot that He usually outwits
everybody else. How dumb!
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Date: 07 Oct 2006 15:20:09
From: N:dlzc D:aol T:com \(dlzc\)
Subject: Re: dark matter and spiral galaxies
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Dear Bob May:
"Bob May" <bobmay@nethere.com > wrote in message
news:GPGdnf26H-V4vrXYnZ2dnUVZ_uidnZ2d@nethere.com...
> The thing here is that whatever the dark mass is, it is
> reducing the attraction of the center of the galaxies by
> being outside of the central area that we see well.
No, Dark Matter is distributed outside the center of a sprial
galaxy, so that the rim doesn't spin off into open space at the
rate we see spiral galaxies spinning. Dark Matter is required to
assist the central core maintain its hold on the rim.
> Light is pretty much everywhere and is emitted from
> the galaxies in large amounts. Interestingly, it is also
> transparent in that it doesn't affect other light by
> diminishing it.
A requirement of Dark Matter is that it doesn't interact with
light. So sounds reasonable so far.
> If you consider that light has mass by it's energy,
No, but it contributes to gravitation by its energy...
> it provides a continous presence everywhere
> and thus pulls out the visible masses from the
> center of the galaxy to the outer parts.
No. Since it is "present everywhere", it has no net
contribution. Just like if you are in a tunnel through the
center of the Earth, as you approach the center there is no net
gravitational pull. Everything to your "left" is matched by an
equal distribution on your "right".
> The question is whether light has been checked for
> the cause of this dark mass problem.
Well, Dark Matter has near zero net speed with respect to the
normal matter it is travelling with. Can't say that about light.
And what's more, the light represents mass "evaporating", so as
it passes that which it once helped bind...
David A. Smith
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