Do galaxies have a minimum mass?

I was kinda thinking the same thing there pal.

My meger understanding of the subject is that dark matter is envolked to explain the unsually fast spin of galaxies, based on our present theory of gravity?

if someone on here would be so kind as shed some... Ahem... LIGHT on the matter, im all ears!

Since when has Science *PROVED* anything! ?

The difference between Science and Maths is that when Maths proves a theory (is correct) it becomes a theorem and is relied upon. When Science *fails* to prove a theory (wrong) it becomes accepted and relied upon.

Scientists haven't "proved the existence of dark matter once and for all" - indeed, they haven't even "proved the existence of normal matter once and for all" - because they can't!

All Science can EVER give us is "given the current state of knowledge, we believe this is the way things are".

Cheers,

Wol

Or something else, like, "Duh, gravity does THIS in longer distaces, see? SEE? Now let's linch that dark matter moron, shall we?"

Maybe?

...

Dust would glow in infra-red, so it's not invisible to an astronomer. It's called 'dark' matter because it doesn't emit any detectable radiation at all.

Apparently the ratio of hydrogen to helium produced after the Big Bang would have come out differently if there was a lot more normal matter around. That's the basis for dark matter being "non-baryonic".

Mind you it could still (perhaps) be lots of tiny black holes, rather than an exotic form of matter. (Although that would probably be almost as weird...)

Dark energy is something completely different. It appears that distant galaxies are accelerating away from us (or rather that all galaxies are accelerating away from each other). This requires some sort of "cosmic repulsion" force to be at work over great distances. Although David Wiltshire claims to have shown that this force isn't necessary if one takes the clumpiness of the universe into account when solving the equations of general relativity (the normal assumption is that the universe is smooth, but of course observations suggests otherwise). Because clocks run at different rates depending on the density of the matter in a region of space, which could also give the appearance of acceleration....

So, you'd probably be safer to doubt dark energy than dark matter!

Chris-

You've asked a couple of questions in the discussion boards here.

Some points:

1) This is a DISCUSSION forum, not a helpdesk

2) If you really want answers, ask better-defined questions

Good luck

G

Hello, Chris

- What lies at the center of the Milky Way is a (theoretical) object called a "supermassive black hole". Most, if not all galaxies are thought to have a SMBH at their centers.

- "Typical" SMBHs have between 10^5 and 1.8x 10^10 times the mass of the Sun.

And DO ask whatever you wish, these are OPEN foums. Just take the answers you get with a pinch of salt - in other words, verify what you read ;)

Cheers.

Hi Chris,

I'm with Acoyauh. (Sorry, George). It's not a bad thing to ask questions any time, anywhere. Just be sure to check everything you read to make sure it's right.

Acoyauh is correct, but there's more - The Milky Way galaxy is about 100,000 light-years across, and contains up to 4 x 10^11 stars, though some estimates reach all the way to 10^12 stars (the vast majority of which are low-mass and thus exceedingly faint red dwarf stars). The mass of the galaxy has been estimated to be anywhere from about 5 x 10^11 up to several 10^12 solar masses, depending on which researchers you read. The higher figures are more likely to better reflect the additional mass provided by the dark matter component, and those reflect the most current thinking). The central core region of a galaxy like ours is composed of a dense concentration of many stars - each an individual sun. The bulge in our galaxy is estimated to contain roughly a 10^11 stars...

As for what lurks at the very center, compared to the thousand-million solar-mass behemoths in giant galaxies such as M87 that Acoyauh referred to, the supermassive black hole in our galaxy's core evidently weighs in at a rather modest 3 or 4 million solar masses. It seems therefore that we do not live in a particularly major system, but it may be that life has a significantly better chance of thriving in smaller and relatively peaceful galaxies like our Milky Way...the significantly bigger ones may periodically "sanitize" themselves with activity from their central black holes, or with an enhanced rate of star formation leading to more frequent supernova explosions.

The supermassive black hole located in our sister galaxy Andromeda is estimated to weigh about ten times as much as ours - about 30 million solar masses. That whole galaxy is roughly 120,000 light-years across, and it contains perhaps twice as many stars and mass as our galaxy does. So it may be proper to regard the Andromeda galaxy as the dominant member of our Local Group of galaxies. This means that popular accounts that speak of the Andromeda galaxy falling toward the Milky Way for a future encounter and merger may be better characterized as us falling into the Andromeda system! (Andromedans will insist that we joined them, not the other way around ;)

Now - be sure to remember to check on all of this to convince yourself that the figures I provided are about right! Don't trust anything you read without corroboration from as many authoritative sources as you can find.