Starship Asterisk*

by **astro_uk** » Thu Sep 07, 2006 1:44 pm

Hi aabaca

I think really your talking about two different things there. The models I was talking about are essentially cosmological in scale, they do simulate galaxies in them, but not with the intent of matching what is seen in the local group, what they want is to be able to do is look at thousands of similar groupings and work out average properties which can be compared to similar sized samples from the real Universe. There is too much randomness to think that you can take a huge simulation and have the local group drop out at the end. However if you do look at enough similar groupings in the large simulations you are bound to find one that looks almost the same in them somewhere.

However there are people that try to model the local group as it is, to see how the dynamics and so on work, but they essentially take one group of observations and try to use them to predict other ones, they dont try to build the local group from first principles.

by **aabaca** » Thu Sep 07, 2006 1:29 pm

astro_uk, you mention an interesting point about the computer models. I know that we're talking about very large distances and masses. All the interactions that a multiple number of galaxies display basically happened in the past. Is there a model that shows what the current formation of the local group looks like?

by **astro_uk** » Thu Sep 07, 2006 10:33 am

Hi Harry, well I hope your parents are feeling better

There are a couple of points with your last post

A theory that has very little foundations and has not been supported lately by any main cosmologist.

That is clearly not true. If you want names of cosmologists that have recently backed it here they are:
Lord Prof Martin Rees
Prof Carlos Frenk
Prof Simon White
Prof Richard Ellis
Prof Jim Peebles

I could go on but in fact these are the 5 most famous and celebrated cosmologists in the world, you have probably heard of them too. You may have seen Richard Ellis in Time this week. I only list these 5 because I have seen them give talks on the BB and how incredibly robust a theory it is in the last 3 months. Basically you cant get any more main than these guys.

Dwarf galaxies are not created in mergers, for one thing any merger that forms a large galaxy will put any tails (the things you would expect to form new galaxies) on highly elliptical orbits that will soon fall back onto the main body of the galaxy. Its almost impossible to strip material to form small objects that dont just fall back onto the main galaxy.

by **harry** » Thu Sep 07, 2006 10:22 am

Hello Astro

Thanks...............I have been VERY busy with my project and my parents are very sick.

============================================

You are assuming that the Big Bang is a fact. Its only a theory. A theory that has very little foundations and has not been supported lately by any main cosmologist.

So we should work with the observations at hand.

Assume for one second that the Big Bang is wrong. What other options have you got.

Look around, the 1000's of images on galaxy collisions and so on. Work backward from these observations.

The Big Bang has put too many scientists on the wrong track.
=============================================

Look at the way the dwarf galaxies react with the Milky Way. You hear the words "Torn Apart" so many times.

by **astro_uk** » Thu Sep 07, 2006 10:07 am

Hi Harry good to see you back

The MW satellite galaxies are not the remnants of galaxy collisions, they are simply small galaxies. In heirarchical formation picture, galaxies form in the higher density pertubations left by inflation after the BB, inflation expands the Universe from subatomic size rapidly and imprints all the quantum fluctuations that were going on there onto the observable universe (The CMB). Whereever the hotter regions were, when the universe cools down and matter forms more of it will form there, big galaxies and clusters form in the most dense regions and small galaxies form in the slightly smaller overdensities.

It turns out that statistically this is pretty much what we see, except that the models tend to predict far too many small galaxies, so these must tend to get swept up quite efficiently by the larger galaxies. It could be that a large fraction of the MW halo is made up of torn up dwarf galaxies.

by **harry** » Thu Sep 07, 2006 9:04 am

Hello All

The question is:

What galaxy or galaxies was torn apart to form the many small dwarf galaxies around the milky way?

or

Did the milky way just collect roaming isolated left over parts from other galaxy collisiions.

by **astro_uk** » Thu Sep 07, 2006 8:53 am

Hi all

I think Orin meant that as a joke.

Galaxy collisions do generally take about a Gyr for things to settle down again, so in simulations and in fact in some observations it seems that when you hit two equal mass spirals together, its about a Billion years before everything has relaxed nicely again and you have an elliptical galaxy.

They also only really look like an elliptical galaxy after about a Billion years because it takes that long for all the hot blues stars formed in the merger to die and leave all the lower mass stars that look like normal old orange stars. Thats just to say that when you look at solar mass stars they dont change their colour much over their lifetimes, this is especially true for stars less massive than the sun.

by **iamlucky13** » Wed Sep 06, 2006 11:47 pm

orin stepanek wrote:I think it's a wonder that the gravitational influence of the Milky-Way isn't stretching the SMC & LMC apart and absorbing them; unless the time it takes for this to happen is immeasurable as it probably would take millions of years for this to evolve. I think there will be a lot of excitement when Andromeda and the Milky-Way get together.
Orin

Well, I suppose we can think of a simpler system as an analogy. The earth and moon are a small system orbiting the sun, but remain stable because perterbations thrown in by the sun are balanced when the moon moves to the opposite side of the earth.

Maybe we can think of the SMC and LMC as bigger, more complex versions of the earth moon system, with the sun being analogous to the Milky Way. The SMC and LMC should be relatively stable in their (gigantic) orbits around the Milky Way. Now if another galaxy were to wander into the picture gravitationally, that could throw things off and draw out the clusters into elongated shapes. Similarly, if Venus happened to wander close past the moon, wouldn't it's short term gravitational tug yank the moon into an extremely eccentric orbit, or even out of orbit completely?

And I suppose it probably does take millions of years for a galactic collision to happen. Remember these things are 10's of thousands of light years across, and they're moving relatively slowly.

by **aabaca** » Wed Sep 06, 2006 1:14 pm

I just hope it doesnt happen past my bed time.

by **Orca** » Wed Sep 06, 2006 4:14 am

Yeah, I can't wait! I hope it happens on a clear night..

by **orin stepanek** » Wed Sep 06, 2006 12:51 am

I think it's a wonder that the gravitational influence of the Milky-Way isn't stretching the SMC & LMC apart and absorbing them; unless the time it takes for this to happen is immeasurable as it probably would take millions of years for this to evolve. I think there will be a lot of excitement when Andromeda and the Milky-Way get together.
Orin

by **aabaca** » Tue Sep 05, 2006 10:21 pm

Well, that's very interesting. But, now I wonder if the sun shows characteristics by virtue of it's resonnance, might the galaxy as well perhaps demonstrated by slight variations in the CMBR?

by **iamlucky13** » Tue Sep 05, 2006 6:31 pm

I concur with astro_uk. Our galaxy is thought to be somewhat similar to the others in our local cluster, which also have satellite galaxies. There is another galaxy, NGC 7331, that is called "the Milky Way's twin" because it looks as a whole very much like the Milky Way is thought to, but I don't know if it has satellites.

When I read your question, I dropped by the wikipedia entry on the Milky Way. It's a good read and can probably give you some insight to your question. In particular, I found this tidbit interesting:

In January 2006, researchers reported that the heretofore unexplained warp in the disk of the Milky Way has now been mapped and found to be a ripple or vibration set up by the Large and Small Magellanic Clouds as they circle the Milky Way

by **astro_uk** » Tue Sep 05, 2006 5:55 pm

The shape of the galaxy is not really that well known, mostly because its really hard to measre accurately where stars are on the far side of the galaxy because of all the dust and gas in the way.

Saying that I don't think the galaxy can be that irregular due to the influence of the magellanic clouds or the other dwarf galaxies nearby, these objects are really puny and probably located far enough away that they shouldnt interfere too much with the spiral structure. Even the saggitarius dwarf galaxy which is actually close enough is being torn up and incorperated into the galaxy doesnt seem to have had too much effect on the MW.

Im sure someone should be able to clear this up, cosmo perhaps?

by **craterchains** » Tue Sep 05, 2006 2:05 pm

I think so.

Norval

, , , and welcome to Asterisk.

by **aabaca** » Tue Sep 05, 2006 1:55 pm

In the APOD for 2Sep2006, there is mention of the fact that the shape of M66 is influenced by the interaction of neighbouring galaxies. Well, we have the Megellanic Clouds and other objects in our neighbourhood. Is it possible that the shape of our galaxy is rather irregular as well?

by **astro_uk** » Sun Sep 03, 2006 10:46 am

Hi all

It is a star, I just checked out the digitized sky survey image, the stars number in the guide star catalog is N2001102132 and it has a V band magnitude of 9.9, so it is pretty bright. Definitely in our galaxy.

by **craterchains** » Sun Sep 03, 2006 3:16 am

I'll agree with Harry, for once.

Norval

by **harry** » Sun Sep 03, 2006 2:56 am

Hello Julian

http://antwrp.gsfc.nasa.gov/apod/ap060902.html
Dusty Spiral M66

Looks like a star. The name???????? and I would say within the Milky Way

by **julianwilson** » Sun Sep 03, 2006 2:37 am

What is the super bright object above M66 in the APOD? Thanks.

Starship Asterisk*

The shape of our galaxy; bright object? (APOD 2 Sep 2006)

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The shape of our galaxy. (APOD 2 Sep 2006)

The shape of our galaxy; bright object? (APOD 2 Sep 2006)