PDA

View Full Version : Discussion: Dark Matter at the Heart of ...



Fraser
2005-Apr-07, 05:50 PM
SUMMARY: When you look at a galaxy, you can only see a fraction of its total mass. The rest is made up of mysterious dark matter, which only interacts through its gravity. This dark matter usually extends as a giant halo around the galaxy, extending much further than the visible stars. But researchers in the UK have found ancient fossil galaxies concentrating dark matter at their centres. These fossil galaxies are the result of an entire galaxy cluster collapsing into a single enormous galaxy. Why the dark matter is concentrated is still a mystery.

View full article (http://www.universetoday.com/am/publish/dark_matter_concentrated.html)

What do you think about this story? Post your comments below.

wstevenbrown
2005-Apr-07, 06:35 PM
ancient galaxy groups in which all of the large galaxies have gradually merged to form one central giant galaxy.

I have a tough time reconciling 'ancient' and 'gradual'. If the mergers happened when the galaxies were ancient, they weren't gradual. It's not surprising to see merged objects at z less than .2-- If we still see merged objects of this size at z = 6+, we should start rearranging our BB furniture. The source article (RAS reportage) was scarce on detail as to how long ago the observed mergers took place, or how that date was determined. Best regards-- Steve

Greg
2005-Apr-07, 08:09 PM
It is probably true that most of the activity took place closer to 10 billion than 5 billion years ago. To understand how these formed, it would be most productive to look back at high redshift galaxies to spot the progenitor galaxies to these giants. Needless to say the fact that these giants exist speaks to the diversity of the environment that must have existed in the earliest age of the universe. Apparently matter was not at all evenly distributed back then. I suppose we should not be surprised by that, since the early universe was likely a chaotic place with a degreee of randomness involved in matter distribution.
The main thrust of the article is about dark matter and its properties. Since I still consider the existence of dark matter speculative, I have a hard time embracing conclusions based on assumptions. I wish the article would focus more on gravatational effects than drawing more than just speculative conclusions based on dark matter.

Mild mannered
2005-Apr-08, 08:48 AM
I don't want to get into the is Dark matter real or not debate - but assuming it is for the thrust of this article - IE: that it is located at the centre instead of around the edges as a Halo to the Galaxy - then could it be that the DM is a halo to a (or a series of) Uber massive blackholes at the centre of these fossil Galaxies? So located more centrally as it constrained there because of the super Gravity concentration.

Could there be a limit like the event horizon on Black Holes that is relative to their mass and spin. IE: 18.5 kilometeres per sol mass or whatever.

Mild

wstevenbrown
2005-Apr-09, 02:37 PM
Apparently matter was not at all evenly distributed back then. I suppose we should not be surprised by that, since the early universe was likely a chaotic place with a degreee of randomness involved in matter distribution.

The WMAP data were supposed to place limits on this inhomogeneity (perhaps that's why current data are delayed in release?), based on the current standard model(s?) of cosmology. Cosmology, like exobiology, is good exercise, but we are reasoning from woefully incomplete data.

Example: We have not completed the census of the Local Group, or any other nearby galaxy cluster, but we continue to draw conclusions about earlier galaxy populations including words like 'must' and 'ought to' , when we should be using 'might' and 'could be'.

Example: In projecting the evolution of a physical model, one needs the relevant physical laws and an accurate statement of the initial conditions. Running the model backwards in time requires the same. We continue to draw conclusions about the initial attoseconds of the BB universe without specifying the initial conditions. We don't know its normal matter makeup, much less its DM/DE makeup.

It's good exercise. I do it myself, to prevent the brain from silting up while awaiting new data. I'm just not married to the hypotheses du jour-- too many painful divorces. :lol: Steve

Greg
2005-Apr-10, 08:53 AM
I hear you. It can be frustrating sometimes realizing how little of the fine detail we know about the universe. Just how much of it are we not able to see due to the still relatively low power of our intruments? Probably we are missing alot of it. One of the most irksome to me is not knowing how objects are moving relative to one another and not knowing their actual distances. This will resolve over time with repeated observations, but if I wanted to make a 3d model of a section of the universe and set it in motion over time to see what happens, I cannot with our current knowledge. Similarly I can't rewind the model back in time to see how things got to where they are now.
Yet if you want to get a paper published, you have to draw conclusions. Maybe most authors feel that they won't get published if there are too many suppositions, assumptions, possibilities, probabilities, maybes and what ifs in their conclusions. Maybe it is just ignorance of the ramifications of what they do not know on their conclusions rather than arrogance and a narcassistic desire to get published that drives them to overstate the significance of their little thought experiments based on their incomplete observations.

Mr. Smartypants gamer guy
2005-Apr-15, 04:01 PM
one question is dark matter any way related to matter or is it closser to energy? i mean there are difrent ways to describe somthing and charactirize it. also why is there so much of it?

antoniseb
2005-Apr-15, 04:58 PM
Originally posted by Mr. Smartypants gamer guy@Apr 15 2005, 04:01 PM
one question is dark matter any way related to matter or is it closser to energy?
Dark matter is most likely particles little different from very heavy neutrons that for various quantum-number reasons cannot intereact strongly with the kinds of particles we are more familiar with. It is not just some kind of energy.

Guest
2005-Apr-18, 01:18 AM
k... now why is ther more of it than us hu?