Timeline for Why does the gas in the Bullet Cluster act like a lens?
Current License: CC BY-SA 3.0
17 events
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| Oct 12, 2015 at 16:02 | comment | added | user32023 | @Asher - You are comfortable with the technical term 'squashed', but you take exception to my use of the word 'de-magnify'. You are playing word-salad at this point. The two black holes act, given the right distance apart, like a concave lens in that they de-magnify the background image. | |
| Oct 12, 2015 at 4:06 | comment | added | Asher | @DonaldRoyAirey the image of the distant galaxy would be squashed along the axis between the black holes and stretched along the perpendicular axis. You would also see squashed in the space between the black holes distorted images of all the objects which would be obscured by the event horizon in a Euclidean space. | |
| Oct 12, 2015 at 1:49 | comment | added | user32023 | @Asher - I'm pretty comfortable with my terms, but thanks for the advice. Perhaps you'd like to answer the question about the black holes. If you've got a different vernacular, I'll check it out. | |
| Oct 11, 2015 at 16:39 | comment | added | Asher | @DonaldRoyAirey "lense," "focus" and "magnify" are three separate operations. Please stop using them interchangeably. And please stop using optics terms in a question about gravity. | |
| Oct 11, 2015 at 15:13 | comment | added | user32023 | Scatter as in de-magnify. The geodetics in the center of the black hole pair will perform the opposite of magnification. | |
| Oct 11, 2015 at 3:15 | comment | added | anna v | @DonaldRoyAirey the scattering amplitude between a photon and the gravitational field is infinitessimally small due to the very small value of the gravitational constant. For your two black hole question the answer is : the photon will follow the geodesics between two strong gravitational wells, and images will come through highly distorted. That was my answer to your question, and it is the correct one within the accepted physics frameworks. There will be scattering with dust etc, but that is not the point of gravitational lensing. | |
| Oct 10, 2015 at 19:29 | comment | added | user32023 | @annav - The answer is the light will scatter. Thanks, though, for your generic answer to a question I didn't ask. | |
| Oct 10, 2015 at 18:29 | comment | added | anna v | @DonaldRoyAirey As with all solutions of differential equations it will depend on the exact boundary conditions, i.e. the masses and geometry. The space time will be highly distorted between the two holes and I cannot answer what will come through. The geodesics around a single very strong gravitational field curl around it, distorting the path of light coming from a galaxy behind, and that is why one can see multiple images of the same galaxy.en.wikipedia.org/wiki/Gravitational_lens | |
| Oct 10, 2015 at 17:06 | comment | added | user32023 | @annav - Perhaps I don't understand curved space as much as I'd like. Tell me, please, if I put two black holes next to each other and then look between them at a distant galaxy, am I going to see a magnified image or a scattered image? | |
| Oct 10, 2015 at 16:47 | comment | added | anna v | @DonaldRoyAirey Do you understand what a curved space means? It means that the geodesics that the light has to follow are curved, not straight lines. The geodesics are defined as a solution to the gravitational equations for the masses in the cluster. Generally the larger the masses the larger the space curvature/distortion, which the photons have to follow. | |
| Oct 10, 2015 at 16:14 | comment | added | user32023 | I see your edit (what happened to my pretty picture?). I agree with your statement only if you extend the radius to where the entire cluster can be considered a point mass. But the images used to draw the gravitational contours and X-Ray contours show the impact of the individual components (DM, dust, stellar). Again, I agree totally that the dust will bend light more than the stellar material, but I don't agree that it is able to focus it, which is what would be required to see the effects in a far off place like Earth. | |
| Oct 10, 2015 at 15:43 | comment | added | user32023 | You are correct to point out that I mean 'bend' instead of 'refract' in my previous comment. However, I'm unaware of any data that reflects the ability of individual galaxies to bend light. Would you mind providing a reference so I can read up on the subject. | |
| Oct 10, 2015 at 14:48 | comment | added | Asher | I think you've missed the point: gravitational lensing has nothing to do with refraction. In fact, the gas itself has an index of refraction very close to 1 so it would make a terrible optical lens. But the cloud is very massive. When it comes to gravitational lensing, the more massive spiral galaxies (which are shaped like flat disks) are more effective than the less massive elliptical galaxies (which are more lens-shaped). | |
| Oct 10, 2015 at 14:24 | comment | added | user32023 | I added a contour map of the Bullet Cluster to illustrate my comment. First, it doesn't resemble a circle or a relaxed system in any way. Second, because we can't assume that the system is relaxed, we have no way of de-projecting the surface brightness to a 3D density profile. I just don't see how it's physically possible to make any assumptions about how this mass of gas should refract light. | |
| Oct 10, 2015 at 14:22 | review | Suggested edits | |||
| Oct 10, 2015 at 15:55 | |||||
| Oct 10, 2015 at 14:18 | history | edited | Asher | CC BY-SA 3.0 |
Added additional clarification on optical vs gravitational lensing
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| Oct 10, 2015 at 14:11 | history | answered | Asher | CC BY-SA 3.0 |