Galaxies Definition and 425 Threads

We know that there exists no such thing as a "rigid" substance in relativity. Now suppose we had a disc of uniform density the size of the Milky Way. When the "core" of the galaxy starts to rotate, the effects (tidal and gravitational) of this rotation propagate at the speed of light, which is...

If there are so many galaxies in the universe,Why don't wee see a night sky with full of light(from the galaxies or stars)

In short: Why are galaxies flat? In more detail: A very large mass M is at rest in vacuum, rotating at point O. Its axis of rotation is the xz-plane with angular momentum \vec{L} directed along the positive y-axis. What forces do the following masses experience? (Units of distance are...

Hi Guys! My first post here, I'm working on analysing the output of some contemporary high-volume cosmological simulations for my masters project. As a bit on the side, I've had a go at reproducing how the SDSS telescope would view the simulated galaxies with various colour bands, and creating...

Im wondering, if there is some theory, which is proposing that galaxies were formed from quasars? Or if not, are there some facts which are opposing such formation?

I am reading Richard Feynman's book Vol I. There he tells us how people usually used to find out the distance to some distant objects. I understand triangulation for objects that are near to the Earth or for stars that are near to our solar system. But how did they use the same principle to find...

Ok, so I need to calculate the age of the universe using hubbles law. Problem is that I cannot find enough data: Information I'm looking for: 40 galaxies including all of this three: Redshift(z) velocity(v) and distance(d) Can anyone could direct me to any professional/reliable...

As far as I know, matter and anti-matter are only different in charge and spin. Therefore a star undergoing fusion reactions with anti-matter should give off the same light spectrum we see with fusion reactions in a star comprised of matter, so it would show the same absorption lines. Would...

Homework Statement The number of stars around the Sun, within a distance of 17 ly, is 75. The number of galaxies in the local group, within a distance of 4.0 x106 ly from the Sun, is 26. Calculate the average popluation density, per ly3, of stars and galaxies. Homework EquationsThe Attempt...

Homework Statement I had a homework problem which was already due. I got the solutions for the homework and still don't understand where the solution is coming from. The question and solution are located here: http://ircamera.as.arizona.edu/Astr_540/PS3_soln.pdf The problem is #3. Homework...

The value of the Hubble constant is around 70 km s-1 Mpc-1. Consider two galaxies moving with the Hubble flow of the Universe that are currently separated by 1 Mpc and assume that the rate of expansion of the Universe is constant with time. A. At what time in the past were the galaxies...

In Cosmology books and tv programs it is mentioned the galaxies are accelerating and running away from us. My question relates to this observation. When they are looking through telescope to the edges of visible universe, they find extremely bright supernova or "celestial candles", calculate...

The Hubble deep sky image is 3 x3 arc minutes and shows an estimated 10,000 galaxies. What percent is 3 x 3 arc minutes of the total area? If this ratio is known, one could estimate the number of total galaxies. Thanks

Hello, I read that the density wave theory makes up the shape of the spiral galaxies look spiral? Is there any specific reason for elliptical galaxies to make the shape of a ellipse? Thanks.

"A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy" Published in Nature 3 days ago. Rodrigo A. Ibata, Geraint F. Lewis, Anthony R. Conn, Michael J. Irwin, Alan W. McConnachie, Scott C. Chapman, Michelle L. Collins, Mark Fardal, Annette M. N. Ferguson, Neil G...

If there is supposedly a super massive black hole in the center of each galaxy, wouldn't that eat all the light given off? Also, if the centers are so bright, why can't we see our galactic center from earth?

Dear all, I'm a first year undergraduate student and I've been set an essay on the title of the post. I would be very grateful if someone could explain in layman's terms what these things are, and also if someone could tell me where I can find more information on them, preferably in an...

In my Cosmology course it is stated that the space between galaxies increases with time whilst the size of galaxies (or gravitationally bound space) does not increase. To me, this seems quite unnatural. I understand that the space between galaxies is much larger than the radius of a galaxy...

Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted? Would the speeds of the galaxies necessary for Doppler redshift to explain all of the observed galaxies redshift be unreasonable or is there something...

Some time ago there was a thread which suggested that there was a logic / papers that demonstrated why the the CMBR could not be the result of ligh from background objects / galaxies. Unfortunately, I have not been able to locate the thread or associated material. Is this correct, and could...

like is there any gravitational potential in the space between 2 galaxies due to galaxies mass.?how large is this gravitational potential is it significant..If possible please provide me a link where i can learn more about it..thanks in advance

OK , so Hubbell took a picture of an early infant galaxy as it existed 10 billion years ago or so with its light just now reaching its cameras. . We've all seen the pics. Let's call it Galaxy A. I'd like to know, where is that galaxy A now as it presently exists , 10 billion years later in the...

In a recent article: http://io9.com/5937295/astronomers-discover-milky-ways-twin-magellanic-clouds-and-all Our galaxy is not particularly special in the universe. Its pairing with the Magellanic Clouds — two irregular dwarf galaxies has other similar configurations out there. I...

There is observational evidence for preferred alignment of spiral galaxies with alignment to the so called axis of evil in the CMB (cosmic microwave backgound 2.75K) data. http://arxiv.org/ftp/arxiv/papers/0707/0707.3793.pdf http://arxiv.org/ftp/arxiv/papers/1104/1104.2815.pdf

i have a three part question. how does light act leaving, traveling between, and entering a galaxy? we have come to the conclusion that the speed and direction of of traveling light is effected by its surroundings. I'm wondering what that looks like at a galactic scale. first, leaving a...

As the universe age, the distance to the cosmic horizon increases, and previously hidden galaxies beyond the horizon should become visible. Due to the expansion of the universe though, the distance between the galaxies increases. This has the effect that a galaxy that we can see today, would...

I'm pretty sure this answer is not known but it always good to double check. Dark energy causes space to expand but the space inside a galaxy does not. Does anyone know why? I'm pretty sure the answer is not known, so I have a guess as to why this might be the case. Particles send out...

Hi, I understand the idea of red shift and how that explains that galaxies are receding, etc. I just don't understand how the measurement is made. I know that, in labs, we can shine white light at hydrogen and analyze the absorption spectrum. Some black lines are going to show up, due...

in weinberg's first three minutes he wrote: I'm starting to regret reading this book. he came out with an updated edition in 1993 but it looks like he didn't correct his mistakes. it looks like he just put a small forward at the end of the book because clearly there are some things that were...

In the hunt for antimatter galaxies, the tools that we are currently using look for gamma rays that would be emitted due to annihilation events, because everything else about these galaxies is predicted to be the same emission-wise. The hypothesis is that these annihilation events would occur...

Probably a stupid question as I'm sure we don't but stargazing gets me thinking. The last prevailing theory that I heard of was a massive black hole at the center of the milky way (and all other galaxies). However, the core of the galaxy is the brightest part by far and other than extremely...

I can't post a link so just bing or google the topic. I have heard a little bit about this phenomenon and was wondering if anyone knows more about it or can give me a reference. If galaxies farther away from the milky-way are moving faster as they get more distant, then should galaxies...

why do planets move around stars in the same level ? why do stars move around black holes in the same level? why don't some of them move in horozintal level & the others in vertical level?

Good evening. I just watched a documentary called The Universe-Light Speed. In it, astrophysicist Alexei Filippenko said that galaxies which are very far are moving away from us faster than the speed of light. Also, cosmologist Alan Guth said that during inflation the universe expanded faster...

Well, First there arose a interesting question of how entropy increases when particles due to gravitation form huge mass. I guess i read john baez's online page. Heat/energy so forth concept was applied to explain it. Then, Taking its reverse, does not receeding of galaxies then decrease...

When astronomers speculate the distance of galaxies are they talking about its... When astronomers speculate the distance of galaxies are they talking about its distance now or when the light was emitted? Since things are moving and the universe is expanding the distance from the object now is...

Its been noted through the Doppler Effect (or red shift maybe? not 100% sure atm) that some of the farthest galaxies seem to be moving away from us faster than the speed of light (c+). Since there is no axis point to measure the speed of these galaxies from, other than the milky way, could it...

Hi all, this is my first post; apologies if it seems a bit basic, I suspect there's something fundamental I'm not getting here :smile: Say I observe the spectrum of a galaxy, and I calculate its redshift. I then use the Hubble Relation to find its distance, which is, say, ten billion light...

Does how black holes inside galaxies orbit around the central black hole tell us anything useful? Could be my noobness, but the idea of a bunch of black holes orbiting a central black hole just seems messy. ha. Have we got the jist of what would happen if a black hole ate another black hole? if...

First excuse my grammar english is not my first language My question is does the speed at which the planet is revolving on itself, the speed at which the Earth is rotating around the sun and the speed at which the milky way is traveling throught space is affecting the rate at which time flows...

I'm trying to fully understand how Cepheid variables are able to give us accurate distance approximations to galaxies. If these galaxies are receding away from us at ever-increasing speeds, wouldn't we notice the variable stars' periods getting longer and longer over time? How can we accurately...

If I take a big, uniform blob of gas that is not spinning, and mark its limit as the limit of a system, then even if that big blob of gas coalesces to make a galaxy, it will not start spinning by itself: its own gravity is an internal force, and conservation of angular momentum says I need an...

If dark matter is actually there and not just some flaw in our understanding or mathematics then how can galaxies be made of both and not just one or the other. If dark matter doesn't interact with anything else like light then how can a dwarf galaxy be made of "mostly dark matter"?I know its...

I recently read an article about elliptical galaxies. The article mentioned that the stars have basically radial motions. What does that mean ? Do these stars oscillate between the center and some mid-radius? Stars in spiral galaxies have on average orbital motions in one direction around...

Hello, I am reading a fabulous (though somewhat older book) called "Intelligent life in the Universe" by s. Sagan and I.S. Shklovskii. They describe intense magnetic fields extending from the galactic core that channel interstellar gas and dust into the spiral arms which are the primary site...

Hi Pf, I've searched through the forums for an answer to this question and have found bits and pieces but not a full answer. Why are spiral galaxies planar (I know there are exceptions to the rule, I'm just trying to understand the why). From what I understand, it is a bit of a battle between...

Ive heard the space between galaxies grows over time and that the universe is expanding in every direction..ive also seen the balloon explanation were they make dots on a balloon and blow it up to demonstrate the expansion of the universe, if this is true how is it we have colliding galaxies...

Hello there! Sorry for the dumb question, but for years I have been very curious and confused about this: I just read that they discovered a galaxy 13.7 Bn light-years away -- therefore its light was emitted 13.7 Bn years ago and traveled 13.7 Bn light-years in some line. But, 13.7 Bn years...

As we look out into space, soon we shall be able to see the last scattering in every direction. So my thinking is, how could more galaxies enter out visible universe? The only way I can think is that they would enter gradually, by forming before our eyes. Due to time dilation this already...

if there is dark matter every where, why it is noticed near galaxies? why can't we do some very sensitive lab experiments of gravity to find the effect of dark matter?