Dark Matter Exists!

[Bozo Erectus]

I know what dark matter is. Its 'manna'.

 

[Perfection]

HOLY FREAKIN' CRAP!

AWESOME!

Now if we could figure out what the hell it's made of...

 

[warpus]

HOLY FREAKIN' CRAP!

AWESOME!

Now if we could figure out what the hell it's made of...

It's made of PEOPLE

 

[Bartleby]

It's made of PEOPLE

Tell everyone!

 

[brennan]

To explain:

This is an image of two Galactic clusters (looks like a Hubble image to me) that collided at some point in the past. They have now moved right through each other):

Using gravitational lensing they mapped out the distribution of matter in the clusters:

Now, this is the awkward bit: The matter that shows up blue on the second image is mostly Dark Matter, however most of the normal (baryonic) matter (the stuff stars and planets and whatever are made of) within the galaxies consists (in these clusters) of X-ray emitting gas. Now when the clusters passed through each other we would expect the dark matter (which only interacts weakly with itself or with normal matter) to be largely unaffected, however the bulk of the normal matter (the X-ray gas) we would expect to crash together and be effectively knocked out of the dark matter cloud (the stars seen on the visual images would be unlikely to actually hit each other so should stay more or less unaffected within the dark matter cloud).

If we then look at the X-ray image:

we see two clouds of X-ray emiiting gas that have been 'held back' by the collision and are now trailing the Galactic Clusters as they move apart, confirming our theory.

The QT clip shows well the different interaction between the Normal and Dark matter during the collision - the former collides, while the latter is largely unaffected.

 

[Bozo Erectus]

This is your brane. This is your brane on dark matter.

 

[Tank_Guy#3]

This is interesting, but not much else than that. To me anyways.

Was the person who thought of the name "Dark Matter" at one point in time a Neurologist?

(i.e. Gray and White Matter)

 

[brennan]

This is your brane. This is your brane on dark matter.

 

[Perfection]

So, how exactly did they measure the gravitational lensing?

 

[Masquerouge]

So, how exactly did they measure the gravitational lensing?

Usually by measuring the arcs of distorted galaxy's images going through the lens.

 

[Perfection]

Usually by measuring the arcs of distorted galaxy's images going through the lens.

Huh?

 

[betazed]

Huh?

Since mass changes the path of a photon, by measuring how photons from galaxies behind our target bends as it passes our target on the way to us, we can measure the mass of our target.

Gravity Lensing

Its a pretty standard tool in Astronomy today.

edit: In this particular case, there are hundreds of galaxies in teh background that provided data for the lensing.

 

[Masquerouge]

Huh?

http://en.wikipedia.org/wiki/Image:Abell.lensing.arp.750pix.jpg

Basically when the light from distant galaxies are distorted by gravitational lenses it forms arcs on the pictures. Analyzing these arcs tell you where and how big the gravitational lens is.

 

[Perfection]

I understand gravitational lensing, but how can they tell that something has been lensed? I mean you see all these photos of clear cut examples of lensing, but how can you tell in this case?

The article talks about "minor" distortions, well what sort of minor distortions and how can we tell that these are distortions?

 

[IglooDame]

I understand gravitational lensing, but how can they tell that something has been lensed? I mean you see all these photos of clear cut examples of lensing, but how can you tell in this case?

I'm guessing, different frequencies show different amounts of bending?

 

[betazed]

I understand gravitational lensing, but how can they tell that something has been lensed? I mean you see all these photos of clear cut examples of lensing, but how can you tell in this case?

As I said there are many galaxies in the background. Each of them are for all practical purposes point light sources to us. Now if you see two light sources with pretty much the same spectrum on two sides of a putatively massive object, then you can theorize that probably that pair of light sources are the same object gravitationally lensed; because chances that two sources will have the same spectrum is small.

if you see dozens of such pairs then you know that they are gravitationally lensed.

edit:

I'm guessing, different frequencies show different amounts of bending?

No. bending of light owing to gravity does not depend on the frequency of the light.

 

[Perfection]

I'm guessing, different frequencies show different amounts of bending?

I don't think that could happen, the lense just changes its angle and position, its frequency should be the same, just like any ordinary lense in optics.

As I said there are many galaxies in the background. Each of them are for all practical purposes point light sources to us. Now if you see two light sources with pretty much the same spectrum on two sides of a putatively massive object, then you can theorize that probably that pair of light sources are the same object gravitationally lensed; because chances that two sources will have the same spectrum is small.

if you see dozens of such pairs then you know that they are gravitationally lensed.

And even in the cases of such diffuse sources as this you can see doubles?

In these weaker cases is one double significantly weaker then the other?

 

[betazed]

And even in the cases of such diffuse sources as this you can see doubles?

yes. with enough patience and enough hours of time on Chandra and Hubble you can. Of course you need to add enough number of hours on computers churning out tentative solutions to Einstein's equations and matching them to observed bending.

In these weaker cases is one double significantly weaker then the other?

I am guessing yes.

 

[betazed]

Sidhe was good enough to send me some more interesting links on this which I am posting here.

Especially Baez's This week's find in Mathematical physics (the last link) is a very interesting site. I never miss any of his week's find.

Here's a couple of websites that have the information from the horses mouth so to speak, an audio press release was suposed to be released yesterday but hasn't been forthcoming yet.

I thought you might find them usefull in a watch this space sort of way if you'll pardon the pun, hopefully you can post the press release when it's forthcoming, hot from the presses. Thought it might be useful.


http://www.nasa.gov/home/hqnews/2006/aug/HQ_M06128_dark_matter.html

http://www.nasa.gov/home/hqnews/2006/aug/HQ_M06128_dark_matter.html

I don't want to count the chickens before they've hatched but this is starting to look momentous even from the most conservative view point.

http://www.nasa.gov/vision/universe/starsgalaxies/dark_matter_proven.html

A more in depth article.

http://math.ucr.edu/home/baez/week238.html

A blog that may be of interest.

obviously feel free to post this stuff if you like.

 

[brennan]

I love fractals: beautiful.