Mysterious Dark Matter Blob Confounds Experts

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.'"

Comments

Re:Observed Dark Matter?

[Tablizer]

We can't directly observe air either (in most cases), but can still measure its effects.

Mysterious Dark Matter Blob Confounds Experts

[busyqth]

I'm pretty sure this headline is about my recent visit from the plumber.

Move on

[oldhack]

The galaxies are gone. Horse has already left the barn. Spilled milk. Water under the bridge.

Dark matter needs to buck up, get it together, and move on, get on with the life. There is a whole universe out there.

Re:Observed Dark Matter?

[JoshuaZ]

We can't. What we can observe is the gravitational pull of dark matter (which is the entire reason we know it is there). In this case, they can see where the dark matter is because of its gravitational effects.

From my understanding...

[Zakabog]

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?

Re:From my understanding...

[Rich0]

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:Observed Dark Matter?

[Ruie]

One way to figure out gravitational field from a static image is to look at galaxy distribution behind the gravitational field. If it is squishes space in one direction while stretching it in the other, you will see more galaxies longer in one direction then in the other, so you can build a map of distortion and compute gravitational field from it. The result will be coarse, but you will see large concentrations of matter.

Re:Observed Dark Matter?

[JoshuaZ]

They detected it by gravitational lensing. http://en.wikipedia.org/wiki/Gravitational_lens. The dark matter is massive enough that it bends the light passing through it. So you can for example see that a star looks bent and not as spherical if it is behind a lot of dark matter. In the really blatant examples of gravitational lensing you get things like the Einstein Cross http://en.wikipedia.org/wiki/Einstein_Cross where you can see multiple copies of the same object.

Awoken

[roman_mir]

Awoken the Grue has been.

Oddly enough, The Fifth Element is on right now

[GodfatherofSoul]

Make sure to call me if that blob starts moving towards earth!

Dark MAtter theory now falsifiable?

[RichyRoo]

If Abell 520 has had the DM 'stripped from its galaxies' (from the link) and since DM was originally postulated to explain the difference between theoretical and observed rotation rates of the core and periphery of galaxies... shouldnt the galaxies of Abell 520, stipped of their DM, now be rotating in accordance with the original theory? That is to say, if gravitational theory predicts that, sans DM, the cores of galaxies will rotate more quicky than the periphery, and these galaxies are now 'sans DM', wouldnt that open the opportunity to provide falsification or support to the DM hypothesis by checking if the galaxies of Abell 520 are indeed rotating differently now that the DM has been removed?

Re:Dark MAtter theory now falsifiable?

[RichyRoo]

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.

Re:Dark MAtter theory now falsifiable?

[mbone]

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.

Re:Observed Dark Matter?

[Ruie]

Here is general description and large annotated Hubble image

Re:Not to be pedantic, but

[Daniel Dvorkin]

It's pretty conventional, when discussing astronomical observations, to use the present tense for "when we see it." Since it can't possibly have any effect on us before the light from the event gets here (assuming relativity is correct, yadda yadda) this makes sense. Also, having to say "2.4 billion years ago 2.4 billion light-years away" would just get annoyingly redundant after a while.

There's pedantry which serves the useful purpose of correcting other people's mistakes, and then there's pedantry of the "look how clever I am" variety; posts like yours, which seem to get posted to every single story on any kind of astronomical event that takes place outside the solar system, are examples of the latter.

The Default

[rust627]

The default position for scientists is "I don't know"
everything else is trying to define and explain
this is why nothing is set as a certainty but always as a theory
a Theory (theory of gravity, theory of climate change etc.) is usually the best most simple hypothesis that explains experimentally verifiable data.
you can create any theory you want from the incredibly convoluted to the overly simplistic (because god made it so strikes me as an overly simplistic theorem).
Usually the simplest (but not most simplistic) theory will be the one that gains the most credence in the scientific community.
the KISS rule applies very much in science too.

Re:Not to be pedantic, but

[bmo]

There's pedantry which serves the useful purpose of correcting other people's mistakes, and then there's pedantry of the "look how clever I am" variety; posts like yours, which seem to get posted to every single story on any kind of astronomical event that takes place outside the solar system, are examples of the latter.

There is an excellent word for this and it means far more than just "pedant" and it's Finnish.

The word is pilkunnussija, literally "comma fucker"

The more you know.

--
BMO - perkele

Re:Observed Dark Matter?

[hughJ]

http://www.youtube.com/watch?v=7ImvlS8PLIo#t=1582s Worth watching the whole thing, but this portion briefly addresses gravitational lensing.

Re:Observed Dark Matter? roxy

[hughJ]

"Dark matter" isn't simply regular matter/particles that we just can't see due to not emitting light. We may not know quite what it is, but we have a pretty good idea about what it is not, and that's regular matter as we know it.