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View Full Version : Triple Whammy: Milky Way More Massive, Spinning Faster and More Likely to Collide



Fraser
2009-Jan-05, 10:40 PM
For many of us, looking closely in the mirror and stepping on the bathroom scale just after the holidays can reveal a substantial surprise. Likewise, astronomers looking closely at the Milky Way have found our galaxy is more massive than previously thought. High-precision measurements of the Milky Way disclose our galaxy is rotating [...]

More... (http://www.universetoday.com/2009/01/05/triple-whammy-milky-way-more-massive-spinning-faster-and-more-likely-to-collide/)

George
2009-Jan-05, 11:56 PM
I assume this would be independent of the mass of Dark matter, right? If so, now how many stars are there out there in our galaxy, up to 600 billion?

trinitree88
2009-Jan-06, 05:52 PM
Since they are finding the Milky Way more massive, but not more luminous, that means the amount of missing baryonic matter for the Milky Way is reduced, and the Milky Way's gravitational interaction in the Local Group requires that they, too are more massive and have less missing dark matter, as their relative proportion of mass to luminosity is increased also. Since the inferred mass/luminosity goes down the extragalactic line, less missing mass ought to be shown there too...No? pete

Michael Noonan
2009-Jan-06, 08:51 PM
Prediction 2009:-

This is just the start. The calculated speed of the rotation will continue to rise and within a few years exceed one million miles an hour.

George
2009-Jan-07, 12:10 AM
Since they are finding the Milky Way more massive, but not more luminous, that means the amount of missing baryonic matter for the Milky Way is reduced, and the Milky Way's gravitational interaction in the Local Group requires that they, too are more massive and have less missing dark matter, as their relative proportion of mass to luminosity is increased also. Since the inferred mass/luminosity goes down the extragalactic line, less missing mass ought to be shown there too...No? pete

But can't the Milky Way be more luminous? If more baryonic matter has been found and we assume much is in the form of instellar gas and dust, wouldn't our galaxy necessarily be more luminous in absolute terms? [Is there an absolute magnitude term for galaxies?]

Jeff Root
2009-Jan-07, 06:30 AM
Since they are finding the Milky Way more massive, but not more
luminous, that means the amount of missing baryonic matter for the
Milky Way is reduced, and the Milky Way's gravitational interaction
in the Local Group requires that they, too are more massive and
have less missing dark matter, as their relative proportion of mass
to luminosity is increased also. Since the inferred mass/luminosity
goes down the extragalactic line, less missing mass ought to be
shown there too...No? pete
I agree with your premises but come to the opposite conclusion.

They find the Milky Way more massive than previously thought,
but not more luminous, since they aren't examining luminosity.
That means the amount of dark matter is increased. Other
galaxies aren't affected by the new measurements, since their
masses are determined by other means.

-- Jeff, in Minneapolis

mfumbesi
2009-Jan-07, 12:12 PM
Interesting findings.
It is still one of my improbably fantasies that I will be abducted by aliens with FTL technology and be granted flight out of the Milkyway and observe the galaxy from outside.

trinitree88
2009-Jan-09, 12:41 AM
Interesting findings.
It is still one of my improbably fantasies that I will be abducted by aliens with FTL technology and be granted flight out of the Milkyway and observe the galaxy from outside.

mfumbesi...it's awesome...:shifty::lol:

pete

mfumbesi
2009-Jan-09, 05:41 AM
You've seen it?
Was there any orifice probing involved in your alien deal?
I'm just asking, I might also want to use them......

Note:
The above is my attempt at humor, not meant to offend sensitive readers.

Gigabyte
2009-Jan-09, 04:06 PM
(ponders the little red triangle thingy ... ) http://www.bautforum.com/images/buttons/report.gif

:D

kzb
2009-Jan-28, 06:38 PM
I seem to remember the rotation speed of a galaxy is primarily explained by baryonic matter? That being the case, these results suggest the baryonic mass of the milky way has been underestimated up to now?

George
2009-Jan-28, 08:05 PM
I seem to remember the rotation speed of a galaxy is primarily explained by baryonic matter? It is not, as discovered by Vera Rubin. She recalled the work of Zwicky who discovered as early as 1933 that galactic clusters must have about 10x more dark matter to keep them from flying away from each other.

kzb
2009-Jan-29, 01:29 PM
George wrote:
<<It is not, as discovered by Vera Rubin. She recalled the work of Zwicky who discovered as early as 1933 that galactic clusters must have about 10x more dark matter to keep them from flying away from each other. >>

That's galactive clusters not galaxies themselves. This is about the rotation speed of spiral galaxies. Some time ago on here I'm sure there were in-depth discussions and I'm sure the experts said that dark matter hardly figures in the actual rotation speed. It is only brought in to the theory to account for the fact the rotation speed versus distance from the centre does not decline as fast as it ought to.

Gigabyte
2009-Jan-29, 04:50 PM
Interesting.

kzb
2009-Jan-30, 01:15 PM
I had a thread 25-July-2006 Andromeda or milky way -which is biggest? There was a lot of dicussion and references about galactic rotation speeds in that thread. The thread petered out with this question from me:

<<There's one thing still worrying me re rotation velocity. The whole point of dark matter halos is to account for flat rotation curves. Now, since the references above are pointing to the Milky Way being MORE massive than the Andromeda spiral, how come the Andromeda galaxy rotates faster ?>>

Gigabyte
2009-Jan-30, 05:45 PM
Even more interesting.

BigDon
2009-Jan-30, 11:48 PM
So a galactic year isn't ~290 million solar years anymore?

kzb
2009-Feb-02, 12:44 PM
<<Even more interesting.>>

Robinson, I am going to put something else, and I expect something better than "even more interesting than last time" or similar:)

My point is, the theory of galactic rotation speeds is based on baryonic mass, as I understand things. If the MW rotates faster than the current standard model, that implies more baryonic mass, not more dark matter mass.

After all, M31 was said to rotate faster than the MW precisely because it had more baryonic matter, not because it had more dark matter. (In fact the reverse was said to be the case, the MW having more dark matter.)

It's true the flat curve, speed vs radius, is explained by a dark matter halo, but that covers a much greater volume of space.

So there seems to be some discrepancies to be explained here to me.

Gigabyte
2009-Feb-02, 03:02 PM
Oh there are discrepancies. There are also papers that explain Galaxy rotation with out a mythical "Dark Matter" halo. But the consensus says DM is the truth, so any discussion of alternatives gets shoved to the lovely ATM category, effectively shutting down a discussion of them.

IMNSIO of course.

Gigabyte
2009-Feb-02, 03:04 PM
IMNSIO = In my not so informed opinion

kzb
2009-Feb-09, 06:52 PM
This is an attempt to link to an old thread, which becomes very interesting to re-read in the light of the current story:

http://www.bautforum.com/space-astronomy-questions-answers/44472-milky-way-andromeda-largest.html

Gigabyte
2009-Feb-09, 07:28 PM
Fascinating. Thanks for the linky.

kzb
2009-Feb-10, 06:43 PM
Robinson, glad you found that "fascinating" rather than "even more interesting". Let's go for "even more fascinating" now, see this old thread:

http://www.bautforum.com/space-astronomy-questions-answers/43591-number-stars-galaxy.html

Gigabyte
2009-Feb-10, 09:16 PM
Funny you should say that.

My last post before reading here was --> this! (http://www.bautforum.com/space-astronomy-questions-answers/84582-number-stars-universe.html)

Extrasolar
2009-Mar-23, 03:07 PM
Question :)

So, according to some sources, the mass of the Milky Way is about 3 trillion solar masses with this new estimate. How much of that mass is actually stars?

kzb
2009-Mar-24, 01:10 PM
Before anyone say's it's all non-baryonic dark matter, so there's no need for extra stars, they need to explain how that relates to the Tully-Fisher relation.

http://www.scholarpedia.org/article/Tully-Fisher_relation

Luminosity is proportional to the fourth power of rotation speed. This is for spiral galaxies within a certain mass range. The correlation is said to be tight with very little scatter and few exceptions.

To me, if the MW rotation speed has gone up by 15%, that means the luminous mass has gone up by 1.15 to the fourth power, or a factor of 1.75.

This is from a Harvard-Smithsonian Center for Astrophysics news release from 2006:

Barmby and her team used the Spitzer data to make drastically improved measurements of Andromeda’s infrared brightness. They found that the galaxy shines with the same amount of energy as about 4 billion suns. Based on these measurements, the astronomers confirmed that there are roughly one trillion stars in the galaxy.

The new MW rotation speed is very close to that of M31. As I understand things, for the MW to have a substantially different luminous mass to that of M31, one or both galaxies would have to be exceptions to Tully-Fisher?

Dgennero
2009-Jul-18, 08:06 PM
I've written a sort of complaint in Wikipedia:
http://en.wikipedia.org/wiki/Talk:Milky_Way#News_article_.3D_.22Milky_Way_Galax y:_Snack-Sized_No_More.22
They won't change the estimated mass.
If anybody is with me we could put the pressure on them.