About Patrick Weiler Expertise I`d be pleased to answer questions about any aspect of astronomy, particularly those related to cosmology, astrophysics, and planetary sciences. I can also provide reliable information on unique topics like dark energy, dark matter, black holes, etc.,.
Experience Teacher, adult after-hours education at local community college, including frequent "star parties." I have my own telescope system, and continue to stay apace of recent developments and emerging theories in the field.
Education/Credentials BA, liberal arts with emphasis on sciences. BS, computer technology.
Expert: Patrick Weiler Date: 9/7/2005 Subject: Red shift and Blue Shift
Question My co-workers and I are trying to figure out this question. If we are correct, we are assuming that all objects are moving away from the center of the universe. We were under the impression that the fastest moving material is at the edges of the universe and that the slower moving material would be closer to the center of the universe. If this is so, then under what circumstances does an object in the night sky show a blue shift toward the Earth? We are all moving away from the center, but what could cause the speeds of the objects closer to the center of the universe to be greater than our galaxies speed? Does it have anything to do with our position in our orbit around the sun, or in our solar system's position in its orbit around the center of our galaxy?
Answer Hello Debbie (and co-workers)...
"...we are assuming that all objects are moving away from the center of the universe..."
The first thing you need to do is forget about the notion that there is a center to the universe; there isn't. It's easy to assume that there is a center because the Big Bang is sometimes incorrectly described as an explosion. An explosion has a center because it occurs IN the universe. We can't say the same thing about the Big Bang because until that event occurred there was no space IN which it could happen. Then where did the Big Bang itself occur? We don't know, nor do we have any way of ever knowing for sure. It's best to try and imagine an infinite and timeless void totally empty of any mass or energy of any kind.
When we gaze outward from our Solar System and galaxy we see most other major structures in the universe rushing away from us. It seems logical to think then that we're at the center of the universe. Not so! If some being on some other galaxy somewhere looks outward from their planet they'd see exactly the same thing---almost all other major structures in the cosmos rushing away. Obviously both perspectives can't be called the 'center' of the universe.
Okay, then what about the red and blue shifts you mention in your question? That's where gravity enters the picture. Within our Milky Way Galaxy gravitational interactions between objects is strong enough to overcome the general outward expansion of space---many Milky Way objects like stars are influenced more by gravity than expansion and move accordingly. Beyond our galaxy, most blue shifts result from the motions inherent to objects, like the rotation of a galaxy; that part of the spinning galaxy that's rotating towards us may exhibit a blue shift, while the other part is spinning away and shows a red shift. If the distant galaxy is close enough for us to pick out individual internal objects some may show a blue shift simply because their movement within the galaxy just happens to be coming our way. Further, our own galaxy belongs to a cluster of galaxies that are relatively close to each other; their gravitational interactions cause some of the grouped galaxies to show a blue shift, while others exhibit red shifts. One example is our relationship with the Andromeda Galaxy (currently about 2.5-million light years distant). It's heading for us (or if you were in the Andromeda Galaxy you could just as easily say that the Milky Way is heading for you)
The red and blue shifts related to all these various motions is then a factor of gravity and the universal expansion of space.
Cosmology is a complex study, and I'm not sure I've answered your questions adequately. If not, be sure and let me know and I'll try to clarify.
