Galaxies Definition and 425 Threads

I am interested in whether it is necessary to account for the effects of the Hubble Redshift in determining the rotation velocities of galaxies exhibiting keplerian motion and, in particular, whether the associated spatial expansion of the Universe is known to result in spectral shifts that...

[Mentor's Note: Post moved to its own thread from here: https://www.physicsforums.com/threads/find-radial-velocity-of-galaxies.813006/] I suppose this thread might be an appropriate place for me to add my request for assistance on the question of rotating galactic systems. I am interested in...

Hi all! My name is Nova and I have recently started a research project on the life cycle of planets, stars, galaxies, etc. I posted this question on reddit, but no one seemed particularly interested. Someone suggested I consult the ultimate physics community on the web, Physics Forums, so here I...

If we look at a galaxy through a telescope, and IF the galaxy arms were ligned up as traight arms from center and out, the arms would look like they were spiral shaped. As the galaxy rotates the light from the closest stars would "hit" the telescope, let's say 100k-500k years, earlier than the...

Hi guys. How do astrophysicists measure the redshift of electromagnetic waves from galaxies due to gravity without the use of General Relativity? If I can be more specific, how do astrophysicists know that the gravitational redshift of light emitted from some part of a galaxy or galaxy cluster...

I searched galaxies and their radial velocities in online but I found nothing can you give me a list about them. Thanks

Hello, I've read the article at http://pages.erau.edu/~reynodb2/LineweaverDavis_BigBang_SciAm_March05p36.pdf that was recommended several times on this forum. At the question "Can we see galaxies receding faster than light?" they answer: "Sure we can, because the expansion rate changes over...

I'm utterly confused by co-moving distance, transverse comoving distance and proper distance. Is comoving distance = proper distance? Then what is transverse comoving distance? Here's what I know so far: The FRW metric can either be expressed as ds^2 = c^2dt^2 - a^2(t) \left[ \frac{dr^2}{1-kr^2}...

Homework Statement Describe what optical astronomers would consider the properties of an active galaxy and also describe what radio astronomers would describe as the properties of an active galaxy and explain how two sets of astronomers came up with these differing conclusions. Homework...

For a lay person such as myself, it's very easy to get confused and stumble around a bit, trying to understand how galaxies can be receding greater than the speed of light when the speed of light is the cosmological speed limit. It's easy to make the mistake of saying 'Ha! There are whole...

In the Hubble Ultra Deep Field ( http://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field ) there are almost 10.000 galaxies and some of them with redshift Z>6 . Making some approximations i need to compute the number of galaxies with redshift z = 7. If the source density ( number / arcmin^2 ) at...

I have been thinking of how black holes help form galaxies and have come up with this idea. Now I will assume everyone who reads this knows about how black holes and quasars work. Now if you can imagine a quasar in the beginning, ie. Without the galaxy...

"The supermassive black hole is sucking interstellar gas, but at the same time it is affecting the star-formation history of the galaxy with its powerful winds," Tombesi said. "Astrophysicists describe this process as a feedback between the central supermassive black hole and the galaxy, which...

The early universe would appear to be contain more material per unit volume than now.This would then gve rise to a first generation big stars and an early develoment of supernova. My interest lies in the inevitable momentum that would be transferred by slingshot from pairs or groups of black-...

With the way our universe looks, different galaxies are angled in various ways from our perspective. What is the cause of this? My initial thoughts would be based on how spacetime is curved, or maybe it's because of the angle of rotation of the black hole at the center of those galaxies...

Hi there, This is my first post but I've been a spectator for a long time now. So I've been working on some of the basics of cosmic expansion and there is one contradiction that I came upon that I can't seem to resolve. I've looked around some of the similar threads but I couldn't find anything...

We can see galaxies/planets light years away determine their composition such such as if they have water et cetera. My question is if light takes billions of years to reach us from there how is that we can determine such things? Is the speed at which a telescope can zoom faster than the speed at...

Apologies in advance: This is my first post; this might be a stupid question; I am not a scientist (just an over-educated carpenter with an interest in science). In any case, here is my question: If the universe started from a single point in space in a "big bang" why is it that the Hubble...

Are galaxies that exist beyond the horizon of the visible universe in a superposition of many different states relative to us? A related question: If we take a laboratory with some scientists inside and put them all in a big box that's perfectly isolated from the rest of the universe, then the...

I have heard and read many times and I’ve also seem many pictures about galaxies that are 13.000 million light years away. One of my favorites (actually I have it as my cell phone’s wallpaper) is the famous “Hubble Space Telescope Ultra Deep Field”. The doubt that I’ve always had is related to...

This may be a stupid question but it has been bothering me for a while. Why do galaxies look the way they do in a spiral? If a typical galaxy is 100k light years across is can take that much longer before the light from the far side to reach the telescope. Unless it is face on of course. If...

In galaxy formations/collisions and planetary dust from newborn solar systems, they begin with an irregularly shaped cloud of matter. But why, over their lifetime, do they form a disk shape? In the case of spiral galaxies and planet orbits.

My understanding is that quasars are galaxies that are billions of light years away. Thus we see them as they were billions of years ago when they were much younger than our own galaxy & other galaxies nearby to us. The immense energy they emit is generated by matter falling into the central...

I have wondered this for a while now, what stops large elliptical galaxies from collapsing due to their gravity? Their rotational speed is relatively small, at the rotational axis perhaps zero, so what is preventing the stars from being pulled towards the center? Do spherical ellipticals flatten...

We know a fair amount about Spiral Galaxies because we can basically see their guts. Elliptical Galaxies are obscured by the outer shell. Can anyone direct me to some non-theoretical data on the mass (density) profile of Elliptical galaxies (i.e. the amount of mass (or density) at a given...

I was reading a post on 'Starts With a Bang' where they were discussing the merits of Dark Matter over MOND and there was a picture of a large spiral galaxy with many starts in the field behind it. What struck me was that the background seemed to be in perfect clarity. There was no distortion...

I am sure this question must have been dealt with before but i can not find an answer: What came first galaxies or black holes? How did supper massive black holes become so massive? List of most massive black holes http://en.wikipedia.org/wiki/List_of_most_massive_black_holes

If the galaxies are all moving away at speeds of the big bang "explosion" which was moving at speeds defying physics. Because nothing could have altered that speed, should'nt galaxies be moving at the same speed?

It is known that, by the expansion of the universe, galaxies that are roughly 4200 megaparsecs away travel away from each other faster than c. A little thought experiment on this; 1- The equation for relativity suggests that results become unphysical. 2- Time would be stopping or going...

Is it still true that most if not all galaxies have at their center a Black Hole? And that the estimated gravity is about 10% of the total mass galaxies. And is it still true that all stars or 99 % of them are moving out and a way from the black hole. I was just wondering if these black holes...

Most ( or probably all?) galaxies are shaped like flat discs (10/30 times wider than thick). Are their planes all aligned on the same angle (from our point of view) or they vary? If so, is it just casual orientation or it follows a certain pattern, for example the angle grows proportionally...

If we know the mean number density of galaxies in the universe, the redshift z and the Hubble constant. Is it possible to find the mean distance between galaxies at such redshift? The redshift gives a ratio of two distances between the same pair of bodies, at two different time due to the...

Sorry if this has been answered before, I am very new to this forum. So, if the universe is expanding, how is it possible that Andromeda galaxy, and our Milky Way will collide? Should they not be moving away from each other, given that the distance between them is big enough for space...

Not sure how speculative this is but thought it would be of interest- http://www.iflscience.com/space/could-supermassive-black-holes-center-galaxies-be-wormholes and the related paper- http://arxiv.org/abs/1405.1883v1 Distinguishing black holes and wormholes with orbiting hot spots by...

Hello I have a question (well its 2 questions)... I'm not hugely knowledged on the subject so i tend to question things in a more ignorant way but i wanted to know two things: Firstly, how do astronomers weight a galaxy at an accurate level to be confident enough to say there is more stuff...

Hi, I was wondering if the stars in a galaxy are orbiting its centre with (for example) 'anticlockwise' angular momentum. Then would you expect the orbits of the galaxy around the centre of a galactic cluster (if it's in one) to be 'clockwise' or 'anticlockwise' or will it not make much...

Hi all, I'm hoping a pretty simple question. When I read about researchers working on galaxy surveys, they often state they're working on "XX-band selected galaxies". For example, D.J.B. Smith et al. performed analysis on a large number of 250μm-selected galaxies at z < 0.5. Is this as...

Hi. In light of that ridiculous Ham / Nye debate I have someone trying to explain away the red shift of light from galaxies by suggesting it could be due to the photons interacting with electrons or other subatomic particles en-route, thereby loosing energy and increasing their wavelength...

I'm curious about how the temperature of the CMBR compares to the light and temperature of galaxies in general. Basically, I'm wondering how 'hot' are galaxies and how do they contribute to the CMBR readings. Does the temperature of galaxies compare on some scale? Do we have to account for...

Hello dear people, I'm Evrim, 18 years old, from the Netherlands. Dear people, I am this time things investigating about science. I'm almost done with my questions, Really it will be good and u make me than happy if u can help me. - Dear people was during or after the formation of ranges of...

I wondered about them sometime; I came across many theories, such as it might be because the of the black hole at its centre, but another question rises! Why black holes spin? I thought it might be because at first when the black hole was a star just like our sun, before supernovae happening...

Do we assume that all galaxies which are equidistant from Earth are approximately the same age? Or are there galaxies at roughly the same distance from Earth but which vary greatly in age? Are we aware of any galaxies which are significantly younger than the Milky way?

Galaxies radiate energy from their stars, but there is also flows of matter into a galaxy. Is the net energy produced by these flows of matter (evaluated as E=mc^2 under the assumption that it will be processed by stars as nuclear fuel) occurring at a greater or lesser rate than the radiative...

In the far distant future, will all of the stars in a galaxy be pulled into one giant black hole in the center? Are the arms of spiral galaxies like our milky way spiralling in or flying out? Thanks Paul

Hello all, i am beginner in astronomy and want to buy a telescope (which will be my first) but don't know much about it. i am seeking for telescope to see up to nebulas and galaxy, i found some telescope on one online site, they are-...

Hi All, I was just wondering why some galaxies look spiral (e.g. the milky way, andromeda, etc)? Is there a proven explanation for this? Also, it would be interesting to hear your thoughts/opinions.. Thanks! :)

Sorry to harp on the same subject but here's a point of view - without a reasonable explanation of why galaxies are further from us this year than they were last year, why isn't the proposition that new space is coming into existence from out of extra dimensions given any credibility? Do...

1) Are there any experiments/measurements of speed of light from distant (redshifted) galaxies? 2) Are there any experiments/measurements of luminosity distance of bodies moving away relative to us? 3) Where can I find type 1A supernova data (redshift and luminosity distance) for low z...

I understand that the Hubble Space Telescope is able to see these distant galaxies we discover, but how exactly does Hubble do that? I have heard the analogy that our galaxy and our place in it is like being in the middle of a forest. If we look any direction, we cannot see outside the forest...

Hello Dark matter is presumed... to balance the sums... as visible matter doesn't work out (apparently) to a high enough value... ... What part of the calculations was evaluated as being too high... to warrant the need for more matter to be 'somewhere'. Thanks for thoughts