a Nearly Complete Einstein Ring
23 Jun 2007 11:35:09 UTC
Topic 192895
(moderation:
If you want to peer into the furthest reaches of space, a regular telescope won't do. You need to harness the power of a massive galaxy to bend light from an even more distant galaxy - a gravitational lens. And a team of European astronomers have found one of the luckiest discoveries of all, an Einstein ring, where the lens and more distant galaxy line almost perfectly. Because of its unique shape, they're calling it "The Cosmic Horseshoe".
More information: see this link
"souls ain't born, souls don't die"
a Nearly Complete Einstein Ring
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That's a good find! 300° around is pretty good. I tried finding out how many known rings there are, I guess the total's over a hundred, with quite a few more candidates that require follow-up observations.
Exciting to hear that the Cosmic Horseshoe was found first in the SDSS data. I was going to post a raw ('composite') image of it from an online viewer (e.g., Aladin Sky Atlas), but when I went looking for the coordinates, I saw there was already a composite image in the paper submitted to the Astrophysical Journal (here). Looks like this:
The basic strategy to identify candidates in this case was to look for multiple blue, faint, companions around luminous red galaxies (LRGs). Of course, the general idea is to look for objects that would make strong lenses and then see if there are different emission lines, or different red shifts, or different colors in the vicinity of the candidate object.
Neatest thing I learned checking on this is that these kinds of natural telescopes are incredibly valuable for studying dark matter distributions, and also the types of gravitational interactions with normal matter (e.g., causing star formation in some scenarios, or snuffing it out forever in other situations)...
Thought I'd throw this link
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Thought I'd throw this link into someone else's thread. Hope you don't mind.
Title of article: Neutron stars spew like black holes
http://www.msnbc.msn.com/id/19461296
I was wondering what factors
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I was wondering what factors are involved in producing a nearly complete Einstein Ring. The physics on the Wikipedia page for Einstein Rings (so far) is only for the size of the ring, based on the mass of the lens, and respective distances between them and the observer.
But it's possible to learn a great deal about both the lensing galaxy and the source galaxy from the shape of the ring's image. I found this paper, The Importance of Einstein Rings, (already ~7 years old!) which has a nice illustration showing how various maximum and minimum intensities of the ring in the image plane correspond to locations in the source plane. The paper's quite technical, so here's a thumbnail (click for full size) along with the caption to give the basic idea:
Caption: “Fig. 1.— An illustration of ring formation by an SIE [singular isothermal ellipsoid] lens. An ellipsoidal source (left grayscale) is lensed into an Einstein ring (right grayscale). The source plane is magnified by a factor of 2.5 relative to the image plane. The tangential caustic (astroid on left) and critical line (right) are superposed. The Einstein ring curve is found by looking for the peak brightness along radial spokes in the image plane. For example, the spoke in the illustration defines point A on the ring curve. The long line segment on the left is the projection of the spoke onto the source plane. Point A on the image plane corresponds to point A′ on the source plane where the projected spoke is tangential to the intensity contours of the source. The ring in the image plane projects into the four-lobed pattern on the source plane. Intensity maxima along the ring correspond to the center of the source. Intensity minima along the ring occur where the ring crosses the critical line (e.g. point B). The corresponding points on the source plane (B′) are where the astroid caustic is tangential to the intensity contours.�
I think it's fascinating that, from just the shape of the ring, it's possible to determine (independently of anything else) the shape of both the 'lens potential', and the shape of the lensed galaxy...