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Q: I watched the episode: "Exploding Stars and Black Holes" and was mystified by some of the conclusions reached. Putting pencil to paper, and invoking some high school physics, I find that the period of a star of unknown composition, orbiting some unknown massive companion, has a mass greater than 3 solar masses only if the period is less than 5 minutes (Star is bright, indicating possibly very dense core). Can the authors explain how, with only the period of the visible star as reference, it was concluded that the invisible object had better than 7 solar masses ?
-- Don

A: By measuring the orbital period and the velocity of the optical star (using the Doppler effect), and using Kepler's law, one can determine a quantity called the "mass function". This depends on the mass of the unseen companion, and on the inclination angle of the orbit. However, it can be easily shown that the mass of the compact object must be at least as high as the value of the mass function. Hence, by finding that the value of the mass function is larger than 3 solar masses, we find that the compact object must be a black hole.

Q: If light is sucked into a black hole because of the intense gravitation, that infers that light has mass. Didn't Einstein say that as something approaches the speed of light it becomes infinitely massive? Seems like paradox to me.

OK, how about this one. If light is sucked into a blackhole it must slow a little bit. What does it become then? Please don't say dark! Thanks.
-- Allan Kuenn, Phoenix, AZ

A: The photon has a zero rest mass, and therefore it does not become infinitely massive even though it moves at the speed of light. The correct way to think about it is in General (rather than special) relativity, where what gravity does is it makes the space time curved, and the photons then followthe curved paths, which near a black hole never escape. Indeed, the effect of the gravity on the light is that it becomes less energetic, and therefore of a lower frequency (redshifted).

Q: How do you describe or define SPACE? How was SPACE created? What is SPACE made of? Does it has a shape, size, limit? I understand matter, mass, stars, etc. but SPACE itself is what I cannot comprehend?
-- Anonymous

A: Space, and indeed time (or together space-time) was created at the big bang. Space is not made of anything, space-time, if you like, provides the coordinate system in which "events" are occuring. When we describe a particle, for example, we must say where and when this particle is located, we therefore must give its space-time coordinates.

Q: When ever we see pictures during the programs about novas, super novas etc. some of the pictures have blue hues and other colors associated with them. Are these colors the result of a radio telescope and computer imaging process or do the images actually emit color or spectrums of the light they emit?
-- Anonymous

A: Astronomical images appear sometimes in what is called "true" colors, and sometimes in "false" colors. What is meant by true colors is that the images were taken in several filters, which transmit a certain part of the spectrum which generally corresponds to a given color. Those colors were then combined to form the colors you see in the image.

Q: On the recent episode of Mysteries of Deep Space, you mentioned the slowing of the expansion of the universe. My question is, if the universe gradually slows down and stops, will it eventually contract and then result in a big bang?
-- Anonymous

A: At present it seems that the density in the universe is not sufficient to actually stop the universe in its expansion, even though it is slowing down. If the density was enough, then indeed it would have started contracting, and eventually reach a "big crunch."

Q: I am just a simple viewer who loves to learn about the universe. I loved both the shows but became very confused about black holes and gravity. If I understand gravity correctly it is the result of mass and rotation,? yes? More mass, more gravity.

My question gravity a entity or the result of other actions. It seemed that what the program was saying was that gravity acts on its own, i.e. light. But it also seemed that gravity is just the result of other actions, mass, rotation, etc. If this question makes any sense. I'd love an answer. I wish I could put it in more educated terms.
-- Louise Mattice, Maplewwod, NJ

A: Gravity is indeed one of the four basic interactions (forces) that we see in the universe today. Gravity is the action of mass (nothing to do with rotation). Gravity (which is generated by masses) acts on other masses and on light.

Q: I am an engineer with a well balanced education and scientific background. My key mentor, Albert Einstein, was a very strong advocate of the KISS (Keep it simple stupid!) principle.

I am interested in how many of the scientific community disagree with the "fact" that the universe is expanding. Has anyone considered that this may simply be a misintrepretation of observed data. My background in testing and emperical sciences has taught me that this is a VERY common problem. Are there alternative theories relating the observed red shift to possible influences due to the perceived black matter?

My difficulty with the expanding universe theory is that it is a simple answer to complex questions that, to me, isnot elegant. Your response will be greatly appreciated.
-- Craig D. Sellers, Houston, TX

A: There are very few scientists who at this point disagree with the expanding universe. Most of the alternative theories rely on complex plasma physics and electromagnetic effects, which are much less elegant and which encounter serious difficulties sooner or later. There are a few scientists who think that the redshift is not the result of receding motion. Those try to place quasars relatively nearby. Most of those interpretations suffered a fatal blow with the discovery of gravitational lensing, which does put the quasars at cosmological distances.

Q: The images of distant galaxies and quasars that we are looking at now are formed by the light that left them 12 to 14 billion years ago, so we are looking at 12 to 14 billion years old information. What can we say about the status of these objects now?
-- Anonymous

A: Absolutely nothing. We can only rely on observations we can make.

Q: Is there a mechanism for the formation of miniature black holes? I once read a sci fi story where they used a miniature black hole as a gravity wave transmitter. Has anyone measured gravity waves yet? How fast do such waves travel in theory? I enjoyed the show immensely and would like to watch something similar that went into even more detail!
-- Chester Riemann

A: Mini black holes could have formed during the big bang. However if they were less massive than about 10^15 grams, they have eveporated already, by Hawking radiation. Gravity waves were not measured yet directly, but observations of many binary systems are fully consistent with the expectations. A project called LIGO will measure them directly in the near future. Gravity waves travel at the speed of light.

Q: When you look at the fine structure of the spectra of supernovae can you determine the isotopes of the elements in the ejecta of the supernovae explosions? If so, can you then determine their relative abundance? Being a retired physicist, myself, you can get as detailed technically as you wish. Unfortunately, optical spectra analysis was not my specialty. Further, have you any suggested references? Thank you for any help you can give me. :-)
-- Dan W. Crockett, Loveland, CO

A: Absolutely. The relative abundances of many elements are determined from the spectra of supernovae. Furthermore, it is the presence (or absence) of certain hydrogen, helium and silicon lines that defines the different classes of supernovae. A reasonable reference would be: A.G. Petchek, Supernovae (Berlin:Springer), 1990.

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