dark matter gravitational lensing

trisco · Dec 13, 2005

I just read the story on Space.com and was interrested on how dark matter could be rendered on a deep field image by indirect observations but the same could not be done with black holes.

Saiph · Dec 13, 2005

the problem with black holes: They have a strong gravity, but very localized, so seeing the effects are very hard. And overall, they have less gravity than a huge collection of darkmatter. it's just very focused. Sorta like...geez... Ahh, seing the full rainbow from a single raindrop, vs the rainbow from the entire shower of water. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

trisco · Dec 13, 2005

ok then, but on gravitational lensing... how do we know we are seeing something far off due to GL and not just seeing it "as is"? It's not like we can compare two images of the same cluster with and without GL.

Saiph · Dec 13, 2005

however, there is more to the image than just what it looks like. The images do appear to be distorted, so there's our first clue. But as you said, that alone doesn't tell us they're the same object, and not just two or three oddly shaped objects. The other information is in the information in the light from the objects. They have the same redshift (indicating same distance), they have the same composition, same luminosity function (which describes how bright the object is in the radio, IR, visible, UV, and x-ray wavelengths)... All the details in the light point to the same object, despite the different locations in the sky and the distortion. This leads to the conclusion that it is the light from a single object, being sent to us from different directions, by means of a lense (gravitational in this case). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

bobw · Dec 14, 2005

Deciphering the Dark Matter Pic. has been a chore for me, too, TrisCo. I'm not sure what I'm looking at; I hope some of our members can help me out. It seems to me that, when looking for info. about lensed galaxies, the example galaxies are much more obvious than those in the dark matter picture. I read that astronomers hoped to develop software to reconstruct the original image from some of those extreme cases where the background galaxy is warped into an arc, etc. I guess they must have made some kind of estimate of the degree of distortion to discern the invisible mass that caused it. I had to look real hard to find something that looked lensed to me. Myungkook James Jee et al. sound like rocket scientists <img src="/images/icons/smile.gif" /> Here is a 3X blowup of a section at the top of the purple blob from the big picture link in the SDC article. Does the yellow arrow point to a lensed background galaxy? These things and micrographs bewilder me sometimes. http://www.space.com/scienceastronomy/051213_dark_matter.html <div class="Discussion_UserSignature"> </div>

Saiph · Dec 14, 2005

Apod is wonderful for digging up pictures. http://antwrp.gsfc.nasa.gov/apod/ap011007.html <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

trisco · Dec 14, 2005

I just found this cool image from Hubble. The image is of galaxy cluster Abell 2218 and has a total of seven multiple systems.

Saiph · Dec 15, 2005

the image I linked to is the same one...in color. <img src="/images/icons/wink.gif" /> good legwork though. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

bobw · Dec 15, 2005

TrisCo and Saiph Yes, those are the ones I was thinking of. I at least have an idea for finding the center of mass on that picture, even if it is a wrong idea, and I'm sure I couldn't show that the visible mass is insufficient to cause the lensing. In the new picture the purple was computed, the arcs are a lot more subtle and it definately doesn't look like Abell 2218 to me. I think Jee et al. must have used a something more sophisticated than my perpendicular bisector method. <div class="Discussion_UserSignature"> </div>

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