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Kullat Nunu
2008-May-28, 06:44 PM
SDSS press release: New measurements reveal slimmer Milky Way (http://www.sdss.org/news/releases/20080527.mwmass.html)


"The galaxy is slimmer than we thought," said Xiangxiang Xue of the National Astronomical Observatories of China, who led an international team of researchers. "That means it has less dark matter than previously believed, but also that it was more efficient in converting its original supply of hydrogen and helium into stars." Xue is presently pursuing a doctoral thesis at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany.

The new measurements give a mass of ~1 x 1012 MSun (one trillion solar mass). Since there's a huge variety of values in the literature the claim seems a bit exaggerated.

Still, with one trillion solar mass Milky Way may be the dominant galaxy in the Local Group because despite being much larger in size the Andromeda Galaxy may have as little as 0.7 x 1012 Sun's worth of mass.

Cougar
2008-May-28, 08:24 PM
"Slimmer" refers to physical shape, not necessarily mass. :mad:

RussT
2008-May-28, 08:55 PM
"Slimmer" refers to physical shape, not necessarily mass. :mad:

Cougar, these questions are for "You".


So, what 'physical shape' is 'slimmer' then?

How did they come to the 1 trillion sol masses figure for the whole mass of the Milky Way?

AND, how do those masses break down, and where are they 'physically located?

dgruss23
2008-May-29, 12:21 AM
Here (http://arxiv.org/abs/0801.1232) is the abstract for the paper on this study.

Cougar
2008-May-29, 02:08 PM
So, what 'physical shape' is 'slimmer' then?
From the headline, my initial thought was that the galaxy disk was not as thick as previously thought.

dgruss23
2008-May-29, 09:18 PM
From the headline, my initial thought was that the galaxy disk was not as thick as previously thought.

Me too. "Less Massive" would've been a better way to say it.

RussT
2008-Jun-02, 04:45 AM
From the headline, my initial thought was that the galaxy disk was not as thick as previously thought.

Well, sure,,,,,,,,,,,that's the easy part...;)

What about the rest of the questions...:confused: ?

ETA:

And here is some more that may add to the confusion...:)

http://www.solstation.com/x-objects/andromeda.htm



Careful estimates of Andromeda's angular diameter obtained using 2-inch binoculars by Robert Jonckhere from 1952 to 1953 indicated that Andromeda's disk had a diameter of over 200,000 ly (assuming a distance of 2.9 million ly). Hence, Andromeda's spiral disk may as much as twice as large as the Milky Way's. Although Andromeda was long thought to be the most massive galaxy in the Local Group, recent data suggest that Andromeda's visible mass may total around 300 to 400 billion Solar-masses. This is considerably less than more recent estimates of the Milky Way's visible mass of as much as 600 billion or more Solar-masses, which suggests that the Milky Way may be much denser than Andromeda. These results apparently have been confirmed by recent estimates of the total halo masses of the two spirals that account for the gravitational effects of their invisible dark matter, which suggest that Andromeda has a total of around 700 billion to 1.2 trillion Solar-masses compared to 0.93 to 1.9 trillion or more for the Milky Way (more discussion from (Xue et al, 2008; Evans et al, 2000; and Evans and Wilkinson, 2000).

RussT
2008-Jun-02, 05:23 AM
Me too. "Less Massive" would've been a better way to say it.

I am not so sure about just saying 'less massive' being a better descriptive way of describing the dynamics of galaxy morphology/evolution.

Those disc's start out as very thin gas discs and become thicker and thicker with time and star formation.

It has become quite apparent that galaxies have disc 'build up' over time as well as 'core build up' over time. But, it also appears that the 'core' is where star formation starts, and then the 'core builds up' as a bright BCD. As the core becomes brighter and brighter, it outshines the star formation in the arms, UNTIL the arms have enought star formation to be 'seen' despite the brightness of the core BCD.

http://www.narrabri.atnf.csiro.au/public/images/ngc2915/

IF, this were seen 'edge on', with the HI gas blue, this would be the "Thinnest Disc on record"

AND, until this amazing photo was able to be accomplished, this looked like a very small BCD (Blue Compact Dwarf Galaxy), which it is obviously Not.

That is "First Light" star formation in the core, which builds up to become beigger and brighter BCD's, UNTIL finally, the Arms have enough star formation to be seen along with the bright core/BCD....then you have an LSB spiral....


And then the 'core build up' at some point begins to have a 'Bulge Build up' until you get to ellipticals.

Cougar
2008-Jun-02, 02:51 PM
How did they come to the 1 trillion sol masses figure for the whole mass of the Milky Way?

Here's how: link (http://www.sdss.org/news/releases/20080527.mwmass_enlarge.html).


AND, how do those masses break down, and where are they 'physically located?

What do you mean, "break down"? The mass of the nucleus doesn't amount to much compared to the mass of the galaxy as a whole; and the combined mass of the dark matter is about an order of magnitude larger than the mass of the central black hole and all the stars and planets and gas and dust. The general location of the mass is shown by the galaxy's rotation curve.

Sam5
2008-Jun-03, 03:55 PM
Here (http://arxiv.org/abs/0801.1232) is the abstract for the paper on this study.


The full paper is here, about 4 megs:


http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.1232v5.pdf

RussT
2008-Jun-10, 07:01 AM
Here's how: link (http://www.sdss.org/news/releases/20080527.mwmass_enlarge.html).



What do you mean, "break down"? The mass of the nucleus doesn't amount to much compared to the mass of the galaxy as a whole; and the combined mass of the dark matter is about an order of magnitude larger than the mass of the central black hole and all the stars and planets and gas and dust. The general location of the mass is shown by the galaxy's rotation curve.

WIMPS as CDM were completely "Made Up"/fabricated/Contrived.

Computer SIMS are NOT "observations".

When mainstream first hypothesized that Non-Baryonic DM was needed to account for the rotation curves of galaxies, they were Correct...it is needed.

What they first modeled IS the correct answer!!!