We Know Less About CDM Than We Did Before

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Dotini
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http://www.sciencedaily.com/releases/2011/10/111017124344.htm

"After completing this study, we know less about dark matter than we did before," said lead author Matt Walker, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics.

"Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy," explained Peñarrubia. "That makes it much more challenging to determine the distribution of dark matter."

Respectfully submitted,
Steve
 
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Dotini said:
http://www.sciencedaily.com/releases/2011/10/111017124344.htm
"Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy," explained Peñarrubia.

I find it bemusing that stars would swarm like bees in a hive instead of orbiting. Can anyone explain this, please?

Respectfully,
Steve
 
Ugh, I hate it when scientists use bad analogies. He doesn't mean that the stars move around randomly. The stars have elliptical orbits but they're not aligned in a plane like in spiral galaxies. The orbital planes of the stars' orbits are randomly aligned. Similar to a globular cluster.
 
Without the rotational aspect that spiral galaxies have (presumably created by Super-massive black holes in the center), why would one assume that the dark matter would clump at the center? The rotation creates a center of mass in the galaxy where I would presume the dark matter would start to accumulate, bringing together the normal matter, then distributing it from there.

Wouldn't you assume that in a dwarf galaxy, basically without a center of mass, the dark matter be more uniformly placed?
 
Dr_Morbius said:
Ugh, I hate it when scientists use bad analogies. He doesn't mean that the stars move around randomly. The stars have elliptical orbits but they're not aligned in a plane like in spiral galaxies. The orbital planes of the stars' orbits are randomly aligned. Similar to a globular cluster.

Here's yet another scientist who uses the same exact bad analogy:

"If you watched a time-lapse movie of our galaxy, you would see the swarm of dwarf galaxies buzzing around it like bees around a beehive," said astronomer Anna Frebel of the Harvard-Smithsonian Center for Astrophysics, who led the study that found the old star. "Over time, those galaxies smashed together and mingled their stars to make one large galaxy ? the Milky Way."
http://www.space.com/7996-milky-cannibal-ancient-star-confirms.html

Slightly off-topic, are the movements of bees random, or are they purposeful or according to some "program"?

Respectfully submitted,
Steve
 
Last edited:
Kronos5253 said:
Without the rotational aspect that spiral galaxies have (presumably created by Super-massive black holes in the center), why would one assume that the dark matter would clump at the center? The rotation creates a center of mass in the galaxy where I would presume the dark matter would start to accumulate, bringing together the normal matter, then distributing it from there.

Wouldn't you assume that in a dwarf galaxy, basically without a center of mass, the dark matter be more uniformly placed?

I still kind of want an answer for this. I'm curious.
 
Why wouldn't a a dwarf galaxy have a center of mass? It absolutely must and does have one. I also don't know how much the black hole really affects the entire galaxy. I don't think it has much to do with the rotation in a spiral galaxy.