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If a single red photon hits your telescope from the direction of a planet in the Andromeda Galaxy, then all you know that the planet emitted a red photon. Was it caused by a fire? A scattering of starlight through its atmosphere? An Andromedan with a laser pointer? A single photon of light from an unknown source has about as much information as a random ...

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Suppose you are using a CCD or a photographic plate to record your image. The interaction with the light occurs when the detector absorbs a photon, and this happens at a point. So the image is built up from a collection of points - one for each photon that is detected. In everyday life, e.g. taking pictures with the CCD in your phone, the intensity of the ...

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Sort of. This is demonstrated clearest in barred spiral galaxies, which make up about 1/2 to 2/3 of all spiral galaxies. A dramatic example is NGC 1365: Image courtesy of Wikipedia. Others, such as M95, have spiral arms that wrap even further around while still retaining the central bar: Original image courtesy of Wikipedia; color added by me in ...

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This presentation might be helpful to you. Based on dust density and mass density in each pixel of an image, the luminosity is calculated as $$L=L_0 \cdot \exp \left( \int \kappa \rho ds\right)$$ where $\kappa$ is a constant and $\rho$ is the density of the interstellar medium (I believe). A more helpful relation for pixel-mass-to-luminosity is ...

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NO, at least by 3 reasons : recently,as 2003, it was found that 40% of the matter in the vicinity (accretion disk) of the BH will be radiated away. I'm convinced that all the matter, in excess above the limit, will be radiated away before a BH can be formed. quoting from WP-Black-Hole In the case of compact objects such as white dwarfs, ...

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The best paper on I've found on tidal tails is Reshetnikov & Sotnikova (2000). Their simple description of tidal tail formation is: To understand the development of tidal tails, one must recall how the water surface of the oceans get stretched radially by differential gravitational attraction exerted on it by our Moon. The differential forces ...

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You have to distinguish between stellar mass and gravitating mass. The quoted Milky Way mass includes dark matter. Despite searching in the literature, I have yet to find reliable apparent magnitudes and good distance estimates for NGC 1097. The total Blue luminosity of this galaxy is near to Minus B-band absolute magnitude -21, but only ballpark ...

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The primary reason for the asymmetry of the Ly$\alpha$ line is bulk motion of neutral hydrogen, i.e. accreting gas (causing a blueshifted line) or galactic outflows (causing a redshifted line). Mechanism of the Ly$\alpha$ double peak In general, for Ly$\alpha$ photons produced in the center of a blob of neutral hydrogen (i.e. a galaxy), the photons must ...

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As Ben Goldacre says, "I'm afraid it's a bit more complicated than that." Phil Plait (Bad Astronomy) has occasionally written about this. Astronomers don't have a firm definition for the 'border' of a galaxy, tho' certainly objects classified as belonging should show some sort of contained orbit. But it gets worse, as they also have rough categories of ...

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