A Problem in Cold Dark Matter Theory Resolved?

[toastywombel]

The Cold Dark Matter theory, found here, has been used to explain how the universe formed into a cosmic array of galaxies from the moment of the big bang.

 

This is from the above link:

 

"In the cold dark matter theory, structure grows hierarchically, with small objects collapsing first and merging in a continuous hierarchy to form more and more massive objects. In the hot dark matter paradigm, popular in the early eighties, structure does not form hierarchically (bottom-up), but rather forms by fragmentation (top-down), with the largest superclusters forming first in flat pancake-like sheets and subsequently fragmenting into smaller pieces like our galaxy the Milky Way. The predictions of hot dark matter strongly disagree with observations of large-scale structure, whereas the cold dark matter paradigm is in general agreement with the observations."

 

However, the Cold Dark Matter theory is not perfect, again from the above link,

 

"1. The cuspy halo problem is that cold dark matter predicts that the rotation curves of halos be peaked much more strongly than what is observed in galaxies.

 

2. The missing satellites problem is that cold dark matter predicts large numbers of small dwarf galaxies about one thousandth the mass of the Milky Way. These are not observed."

 

The second is actually wrong, well not exactly wrong, but it is definitely not a correct statement. Wow something on wikipedia wrong? I know right. The Cold Dark Matter theory actually does predict dwarf galaxies, and these galaxies are observed by astronomers. However, the theory predicts that these dwarf galaxies should have more matter and be much more massive at their cores. The following is from http://www.space.com/scienceastronomy/dark-matter-galaxies-100113.html

 

"It has long been a mystery why small galaxies don't have as many stars and matter in their centers as predicted. Now scientists have found the answer with a new simulation of galaxy and star formation."

 

"The so-called cold dark matter theory does very well at explaining how most large structures in our universe form. But it cannot describe dwarf galaxies that well: It predicts that they should have more mass, including both normal and dark matter, in their cores than they do. "

 

Although I think that wikipedia article should be corrected, and new information be cited that is not the point of this post. The interesting point is that scientists may have finally found out why these small (dwarf) galaxies do not have as many stars or matter in them as predicted by the Cold Dark Matter Theory.

 

A research team led by an astronomer from the University of Washington has released a report that involved using millions of hours of supercomputing power. The following is from http://www.sciencedaily.com/releases/2010/01/100113131454.htm

 

"The simulations showed that as the most massive new stars exploded as supernovas, the blasts generated enormous winds that swept huge amounts of gas away from the center of what would become dwarf galaxies, preventing millions of new stars from forming."

 

So the super massive stars that formed in the early years of our universe exploded as supernovas. The blast caused the gases that are needed to form stars to be pushed out of these galaxies. It seems rather trivial and simple, but it provides an reasonable explanation to how small dwarf galaxies formed. I am sure now astronomers are going to begin observing the night sky for evidence of this. Finally, I think the mistake by wikipedia should be noted again:

 

"2. The missing satellites problem is that cold dark matter predicts large numbers of small dwarf galaxies about one thousandth the mass of the Milky Way. These are not observed."

 

This statement seems to imply that dwarf galaxies have not been observed, this is completely wrong. A simple google search provided me a link to an newspaper article from the Albany Times, check that link and others verifying that there have been observations of dwarf galaxies.

 

"For the first time, a dwarf galaxy has been detected as it merges with the Milky Way, researchers say."

http://www.encyclopedia.com/doc/1G1-156782661.html

 

"We give a summary of the current status of our Hubble Space Telescope (HST) Snapshot Survey of probable nearby dwarf galaxies. The purpose of this ongoing survey is to fill in the nearby galaxy census and to derive basic properties of galaxies which are suspected to be nearby on the basis of previous groundbased exploratory studies. The survey has been approved for 75 orbits in cycle 8, and 125 orbits in cycle 9. Within each orbit we obtain 600 second exposures in F606W and F814W of one nearby galaxy candidate using WFPC2. The resulting color-magnitude diagram can be used to determine the general characteristics of the stellar population, as well as the distance to a galaxy with an old stellar population using the TRGB method. Data for selected galaxies will be presented, as well as the summary of all galaxies observed to date. Of the 37 galaxies observed to date, almost all of them turn out to be nearby (within 4 Mpc) dwarf galaxies."

http://aas.org/archives/BAAS/v32n2/aas196/409.htm

 

Even in a book, Near Field Cosmology with Dwarf Elliptical Galaxies, released by the International Astronomical Union, which can be found here on google books states that there are 38 probable candidates for the classification of Local Dwarf Spheroidal Galaxies and has a chapter discussing the Local Population of Stellar Dwarfs in the Universe.

 

As you can see from the news paper article above, the Hubble Telescope observations, and the book, Near Field Cosmology, dwarf galaxies have been observed. Although it is good to note that there is not as many small (dwarf) galaxies observed as there are predicted by the Cold Dark Matter Theory.

 

Summary of Links:

http://www.space.com/scienceastronomy/dark-matter-galaxies-100113.html

http://www.sciencedaily.com/releases/2010/01/100113131454.htm

http://en.wikipedia.org/wiki/Cold_dark_matter

http://www.physorg.com/news182674516.html

http://books.google.com/books?id=NSFNfFZT284C&dq=observed+dwarf+galaxies&printsec=frontcover&source=in&hl=en&ei=pktPS4_1I4zosQOQwJ3_Bw&sa=X&oi=book_result&ct=result&resnum=12&ved=0CDUQ6AEwCw#v=onepage&q=observed dwarf galaxies&f=false

http://www.encyclopedia.com/doc/1G1-156782661.html

Edited January 14, 2010 by toastywombel

[Martin]

The Cold Dark Matter theory, found here http://en.wikipedia.org/wiki/Cold_dark_matter , has been used to explain how the universe formed into a cosmic array of galaxies from the moment of the big bang.

 

This is from the above link:

 

"In the cold dark matter theory, structure grows hierarchically, with small objects collapsing first and merging in a continuous hierarchy to form more and more massive objects...

 

Have to be careful with Wikipedia. Pick and choose your articles. Some articles have stuff which is wrong, or partly wrong, or misleading.

 

The first danger signal with a Wikipedia article is if there is a self-critical warning banner at the top. The Wikipedia organization has the policy of putting warnings at the top of their own articles which they consider inadequate or possibly unreliable for some reason. The staff doesn't have time to fix everything which some incompetent or biased contributors might post. So they just tag it.

 

The one you cited has a banner like that.

 

I would normally advise ignoring such an article. It's kind of like seeing "proceed at your own risk." This particular warning is because the article lacks references to reliable sources.

 

But even if someone fixed that and put in some links to something that passed for reliable, the article would still be misleading because of that business about stars forming first.

 

That is not how modern theory of structure formation goes. It is not hierarchical with small objects forming first, and then building up. The article refers to some ideas some people had back in the 1980s. AFAIK contemporary models of CDM structure formation do not have small objects forming first.

 

So if the article gives you the impression that it is talking about contemporary astronomy, and is relevant, then it seems misleading. It somehow should include mention of what current scenarios are, current models of structure formation.

 

A good source at a popular level might be George Smoot's talk. Google "Smoot TED". It talks a lot about CDM and structure formation but it is definitely not hierarchical bottom up with small objects first. They run computer models and that is not what happens.

 

I can't give you an authoritative picture. Have to go. I'll try to get back later and add some detail. Maybe someone else can fill in the picture in the meanwhile.

Edited January 14, 2010 by Martin