Milky Way — the galaxy — not snack-sized anymore

Associated Press ^ | Jan. 5, 2009 | Seth Borenstein

[decimon]

Take that, Andromeda! For decades, astronomers thought when it came to the major galaxies in Earth's cosmic neighborhood, our Milky Way was a weak sister to the larger Andromeda. Not anymore.

[Heavyrunner]

While it is possible for something other than an increased galactic mass to contribute to a star’s velocity, it is not possible for another phenomenon to account for this speed within a given orbit.

By this I mean that for a star to remain in orbit around the galactic core, it *must* be going a certain speed. If it goes faster, it will be escaping the Milky Way, and if it’s going slower, it’s orbit will be decaying toward the central sigularity.

If a star’s orbit is measured over a certain minimum sample, it can be determined faily easily mathematically if the orbit is stable or transitory.

Armed with this, 10 stars tracked over a sufficient sample period and with a good degree of accuracy is a fair test of the observable universe.

If you’re arguing that maybe the stars move faster because God wants them to, or for some similarly unobservable reason, I cannot disprove this, but based on our understanding of physics, the reported test is entirely valid.

I have to give Milky Way researchers an admiring nod from time to time because their job is essentially to see the forest in spite of the trees, as it were. May as well try to determine the size of a wheat field by laying on your back amongst the grass, and looking from side to side.

[Scythian]

Ping me if you want on the “Make believe Astronomy Science and Other Outlandish Science Claims Ping List” ....

[messierhunter]

By this I mean that for a star to remain in orbit around the galactic core, it *must* be going a certain speed. If it goes faster, it will be escaping the Milky Way, and if it’s going slower, it’s orbit will be decaying toward the central sigularity

That's not accounting for elliptical orbits. All orbits are somewhat eccentric. Without knowing the exact value for a star's eccentricity WRT the galactic center you can't make an exact determination of how much the galaxy is actually pulling on the star (hence its mass). Elliptical orbits can be very stable, yet have velocities at periapsis that would be "abnormally high" for a similarly positioned star in a more circular orbit. If you track it over a sufficient time period you can determine an object's orbit, but for a star's galactic orbit that should be a time period of many years. It's like when trying to determine a new comet's orbit from observations taken over the course of a day or two - the calculated orbit always changes alot once observations are made at widely different time points.

[Darth Dan]

Ping. can you put me on? The list, I mean ;)

[SunkenCiv]

newer, similar topic:

Milky Way a Swifter Spinner, More Massive, New Measurements Show
Harvard-Smithsonian Center for Astrophysics | 1/5/09 | CfA
Posted on 01/05/2009 2:41:26 PM PST by NormsRevenge
http://www.freerepublic.com/focus/chat/2159221/posts

[SunkenCiv]

Thanks decimon.

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[Sudetenland]

If you are a physicist or living in space or another planet, it makes a difference; for people living on Earth and likely to read the story that fact is irrelevent...and yes I was fully aware of that-Church Lady.

[SIDENET]

when andromeda comes to take us on a few billion from now, we’ll be ready. bring it.

MW will kick its ass.

[Sopater]

Yeah, after the holidays it's not uncommon to notice that you've accumulated more mass, that's like weight.