Strong gravitational lens systems like the Cosmic Horseshoe have been imaged by scientific space telescopes, but have any amateur astronomers accomplished this?
Or are amateur/small ground based telescopes not suited for this?
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$\begingroup$ Cool question! $\endgroup$– uhohCommented May 1, 2021 at 15:08
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1$\begingroup$ I would not have been so quick to accept an answer. I usually give it a week or longer to let the whole community have a chance to think about the question. Just because a few famous objects are far and dim does not mean it's impossible to see something closer and brighter. For example, these little telescopes discovered a particularly interesting type of black hole in our neighborhood. Why not wait for an answer that discusses what's possible from a scientific viewpoint, rather than a "here's two you can't see" answer? $\endgroup$– uhohCommented May 2, 2021 at 21:51
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1$\begingroup$ I can still accept a new answer, but I found that this one showed a major limiting factor, the apparent magnitude. I found this list of gravitational lenses and it suggests that the Einstein Cross seems to be the best there is right now in this regard: lweb.cfa.harvard.edu/castles $\endgroup$– 2080Commented May 3, 2021 at 6:28
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1$\begingroup$ I remeber seeing a photo in an astrophotography newsgroup (long ago) of one of the Abell clusters showing obvious lensing. He said he spent two weeks in the desert in his RV taking it. $\endgroup$– Greg MillerCommented May 23, 2022 at 22:57
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2 Answers
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The cosmic horseshoe is beyond amateur instruments. It is a magnitude 20 object. In a large (2.5 m) professional telescope it looks like:
This image taken from the SDSS III data. It is small (10'', half the size of Mars at opposition) but that is not insurmountable for amateur equipment. But is it very dim. If an object like this was visible in moderate telescopes, it would have been found long ago. It is really only the sky surveys, and computerised searches of the survey data that allows for such objects to be found.
Processsing the SDSS data can bring out more detail, as can be found on the discovery paper https://arxiv.org/pdf/0706.2326.pdf
While this isn't visible, another example of gravitational lensing can be: the Einstein cross is a gravitationally lensed quasar, and it is at the limits of amateur equipment. It is even smaller, but as it is composed of four point-sources it can be seen. Skyhound recommends at least 18 in telescope, but practically 24'' to see the four components, exceptional dark skies, fully adapted eyes and perfect conditions (especially perfect seeing: this object is small). Your reward for this is "four smudges of light embedded in the galaxy" The SDSS view gives an indication of how hard this object is.
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1$\begingroup$ But "to observe" doesn't necessarily mean by passive instruments. Lots of amateurs do astrophotography which might be able to image some objects too dim for human eyes. $\endgroup$– RuslanCommented May 15, 2021 at 19:41
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1$\begingroup$ Update: Mike Merrifield managed to image QSO0957+561 with his telescope: youtube.com/watch?v=nLSBGuPm-DQ :) $\endgroup$– 2080Commented May 27, 2021 at 13:19
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$\begingroup$ @2080 consider posting that as an answer, it will nicely complement this answer $\endgroup$– uhohCommented May 23, 2022 at 19:15
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If you have a good camera, a steady hand, good conditions and a lot of patience, you might.
The Sunburst Arc, at a magnitude of around 17, has been observed with a 132mm refractor by Ian Woodward at astrofotato.blog, by stacking more than 22 hours of exposure with his camera.
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1$\begingroup$ Beautiful! Nicely done! Some amateurs have reflectors with ten times the aperture area which naively suggests one tenth the exposure time. But for very low surface brightness objects very close to bright objects refractors have the advantage of unobstructed apertures so no diffraction from secondary mirrors and/or their supporting structure and much less scattered light from optical surface imperfections, cf. Dragonfly and TESS $\endgroup$– uhohCommented May 23, 2022 at 19:11
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$\begingroup$ and What are the benefits of a large refracting telescope? $\endgroup$– uhohCommented May 23, 2022 at 19:11