Black Hole Lenses

You’ll venture into the truly bizarre world of relativity and black holes. If you’ve watched the fairly recent movie, Interstellar, you have probably started thinking about black holes, time dilation and gravity. If you haven’t seen the movie, don’t worry, you don’t have to watch it to participate this week (but it’s certainly a fun summer flick to rent if you have the time). The movie really plays with the concept of time dilation, but for this discussion, focus on something that might be easier for all of us to visualize and ponder. Near a black hole time is certainly dilated, but other interesting things happen in the vicinity of all that tightly packed mass. Light is shifted to longer wavelengths as it struggles to overcome the large gravity-well of the compressed object. A fun property that observational astronomers can take advantage of is that light is also lensed (bent and focused) so that objects directly behind the black hole appear to the observer as bright bands that runs around the edge of the event horizon or as multiple images of the object. This gives astronomers here on Earth a unique way of observing really distant objects that our telescopes would otherwise never see! For your discussion this week we’d like for you think about the concept of a gravitational lens (you’ll see this used in a variety of ways) and for your initial post, describe in your own words how black holes (either stellar mass or super massive black holes) can lens distant objects. Then citing a specific source or sources from the internet, give an example of a situation where astronomers used this unique property of black holes to discover something new in the galaxy or universe. Each group member should aim to contribute at least two unique and significant facts about your example – you are encouraged to include facts and details on the science and/or theories tested or proposed. Support your facts using/citing documents and articles, photos, graphs, etc. found in textbooks, on the internet, or in science-related magazines. Please refer to the attached rubric for how this group assignment will be graded. Since you have had several weeks of discussions under your belts, we expect to see more interaction early on this week. Please remember to comment on and discuss your fellow group member’s posts.

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