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Astronomy/Speed of Light and Black Holes


Dear Mr. Gort,

I am Sam and I am studying the universe in Enrichment class and I am wondering if you can answer these questions.

If you could go the speed of light, wouldn't your eyesight bend around you, not just stay the same?

Wouldn't a black hole look bigger than it actually is because it's sucking up the light around it so the reflected light can't get to your eyes?  Are black holes invisible, or can you detect them by noticing a blank spot in space, or do you have to find it some other way?

Thank you for your time,

Hello Sam,

First of all, it's a little confusing when you say that "eyesight bends around you". Your eyesight is your ability to detect light (photons) emitted by a distant object. So it really doesn't bend around anything. Precision of language is very important in science, so remember to define exactly what you mean.

I'll guess you're asking what would happen to the light you see (again, photons) as you approach the speed of light. Say there's a white star in the distance ahead of you, and another white star behind you. As you sped up and your speed started to approach the speed of light, the star in front of you would get bluer and bluer. The star behind you would get redder and redder. If you could measure the speed of light (the speed of the photons) coming at you from the star ahead and from the star behind, you'd find that both measurements are exactly 'c' - the speed of light. Photons would still be hitting your eye (not bending around you) - they're just a different 'color' (or they have different energies, in the language of physics). As you get very close to 'c', the star in front of you and the one behind you would both disappear.

With a black hole, there's no "reflected light". We're not shining a flashlight at distant objects and see them by reflection. For objects in the sky, we see them because they're emitting light themselves (and we capture the photons with our eyes or by telescopes) or they block (or bend) light emitted by something else. Again, we capture those photons. As far as a black hole "looking bigger" than it is, we've never really seen a black hole directly. We've only seem evidence of them, when we observe the light (which includes all types of radiation, including radio, gamma rays, x-rays, etc.) deflected or emitted by gasses spiraling into the black hole. So we've only seen them indirectly. Which also answers your last question. We don't see them as a dark spot in space - because light from behind bends around them, so their "blackness" is difficult to observe. We can only see them indirectly.

Hope that helps.

Prof. James Gort  


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James Gort


Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.


I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

StarDate, University of Texas, numerous Journal Publications

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