Mysterious Dark Matter Blob Confounds Experts 151
mayberry42 writes "Astronomers using the Hubble Space Telescope are mystified by a merging galaxy cluster known as Abell 520 in which concentrations of visible matter and dark matter have apparently come unglued. A report on the Hubble observations, published in the Astrophysical Journal, raises more questions than answers about a cosmic pile-up that's occurring 2.4 billion light-years away. 'According to our current theory,' says Arif Babul, the study team's senior theorist, 'galaxies and dark matter are expected to stay together, even through a collision. But that's not what's happening in Abell 520. Here, the dark matter appears to have pooled to form the dark core, but most of the associated galaxies seem to have moved on.'"
From my understanding... (Score:5, Interesting)
From my understanding of dark matter, isn't it likely yhat they're looking at two entirely different types of matter? I thought dark matter was just matter that we can't "see" but can detect due to it's gravitational effect on visible light. So why would it be so far fetched to think there's more than one type of matter in the universe that we can't currently directly observe?
Dark MAtter theory now falsifiable? (Score:5, Interesting)
Re:Dark MAtter theory now falsifiable? (Score:4, Interesting)
Re:From my understanding... (Score:5, Interesting)
There are other possible ways that the same phenomena could lead to different outcomes. How about this one - galaxies/clusters are composed of stars and hot gas, and that's it - there is no dark matter. However, we exist in a multiverse with many parallel universes overlaying ours but interacting only through gravity. Since matter in different universes attracts each other, galaxies in one universe tend to be piled on top of galaxies in other universes. Much of the mass of any cluster/galaxy is in the hot gas.
Now, let's take the bullet cluster. Let's explain that by the collision of 4 clusters in three universes. Universe A is ours, and B and C are others that are close by and interact gravitationally. Two of the clusters are in A (call them 1 and 2), one is in B (call it 3), and one is in C (call it 4). 1 and 3 overlap, and 2 and 4 overlap. When they cross paths, the hot gas in 1 and 2 interact via electromagnetism, and the hot gas in 3 and 4 only interact gravitationally and aren't slowed down as much. In the end the gas in our universe in clusters 1 and 2 ends up in the middle, and the gas in 3 and 4 are visible as dark matter on the outside.
As the second example let's consider this collision. Let's explain that using 4 clusters in two universes, again with A being ours and B being another one. Clusters 1 and 2 are in ours, and 3 and 4 are in B. 1 and 3 overlap, as do 2 and 4. In this scenario the hot gasses in 1 and 2 interact, and so do the hot gases in 3 and 4. That means that the hot gases all end up in the middle in all 4, and the stars all fly past each other and end up on the outside. So, this time we see hot gas in the middle, plus a lot of dark matter, which is all the hot gas in 3 and 4.
So, we can have "dark matter" behaving in two different ways, not because of any difference in the matter itself, but rather a difference in the space in which it exists.
No doubt somebody much smarter than me has thought up something like this already, and perhaps shot it full of holes as well.
Re:Dark MAtter theory now falsifiable? (Score:4, Interesting)
In theory the cores of galaxies should be rotating faster than the periphery, however observation contradicts this. So the hypothesis was postulated that there was additional 'dark' matter surrounding galaxies which could cause the periphery to rotate faster.
If Abell 520 has had its dark matter removed, its periphery should be rotating in accordance with standard gravitational theory, rather than as effected by invisible dark matter. Its pretty simple really.
Falsifiable ? Yes, but probably not this way. First off, A520 is a cluster of galaxies, not a single one. The dark matter orbiting the galaxy core is going to be tightly bound to that galaxy, and won't be stripped by a cluster collision. And (see my post below), anyway it's not the stars, but the gas that gets separated from the dark matter.