Galaxy Definition and 528 Threads

Homework Statement You wish to travel to another galaxy, which is 1,000,000 light years away. You'd like to be still alive when you get there. How fast must you travel? Given enough fuel, can you do this? Homework Equations t/t(proper)=gamma v=v'+u/1+(uv'/c^2) The Attempt at a...

Why is the closing velocity of Andromeda and our galaxy so high? 100-140 kms^-1 http://en.wikipedia.org/wiki/Andromeda_(astronomy)"

Homework Statement You want to count all the galaxies out to a certain distance R(naught). If the universe were not expanding, then N (number of galaxies) would be proportional to R^3. Justify/derive. For an expanding universe, take into account the finite time that light takes to reach...

In January, a Vanderbilt University astronomer (I forget her name) found that there were probably hundreds of 'rogue' black holes flying about our galaxy. She surmised that the risk to the Earth from these RBH's was infinitesimal. She said that the only possible risk would be that one goes...

GRB's occur once per day. over 10 billion years that's 3650 billion bursts (in the observable universe?). I think there are said to be around 100 billion galaxies in the observable universe so does that mean that 36 bursts occur in each galaxy...

Structure formation is arguably the central problem in cosmology. How did the dilute gas manage to coagulate. On what timetable did stars and galaxies form? What explains the distribution of galaxy sizes and composition--clustering--the wispy cobwebby structure with its various size voids...

http://blackholes.stardate.org/resources/articles/article.php?id=9 This presupposes that dark matter and dark energy interactions play no role?

Very cool image. Does anyone know, is anything in the information we got from this so far at all surprising? Is it likely we will learn anything about gamma ray bursts from this or is more information

When things are kept at the simplest, I've heard that galaxies were formed because gravity pulls stuff together, but there's some things that are not fully making sense. If two objects are far away, and they get attracted by gravity, what happens is that they merely pass each others with some...

Hello there, I'm developing a 4x Space Opera game. For my galaxy generation algorithm I'm using an improved version of the "Accrete" one, which I'm sure some of you may have heard. It generates fairly believable planets. Rocky ones are placed in the inner system, while gas giants in the outer...

According to Kepler third law, the ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. If I can apply this to the rotaion of galaxy, meaning stars in inner part will orbit much faster than the outer ones. But it...

I have been reading this interesting article http://www.subarutelescope.org/Pressrelease/2006/09/13/index.html on one of the earliest galaxies that has ever been observed (z=6.96), that existed when the universe was just 760+/-15 million years old or about 6% of its current age. See also...

Traversing the milky way galaxy! when? Traversing our own galaxy is a lifelong quest for me and I am actually pondering it and long for it all the time, except when I am sleeping. Maybe it's just a fantasy, though I am not into science-fiction version of it, but many of us want to eventually...

This paper http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000074000008000745000001&idtype=cvips&gifs=yes published in the american Journal of Physics seems to be very relevant to some of the recent threads in this forum. The abstract is quoted below...

Lets suppose I live in a planet that is located in the tip of a galaxy that is ubicated at the most distant point from our universe. What would I see if I look up to the sky at night(looking away from the center of my galaxy)? Manuel.

Now suppose for simplicity that the galaxy,and that its physical diameter was w at the time it emitted the light.find the apparent angular size of the galaxy as it would be observed from Earth today. the answer given by Mr.Guth seems imply that the galaxy itself is also expanding and point out...

Congrats to Turbo on "A Catalogue of M51 type Galaxy Associations" Turbo writes: It has been a bit over two years now, but our paper has been accepted at Astrophysics and Space Sciences (a peer-reviewed journal published by Springer) and the preprint is on arXiv...

As a thought experiment, let's imagine assembling a 300 Mpc long rod in intergalactic space, made of an astounding future material which enables it to be both rigid and nearly weightless, while somewhat "stretchy" and "compressible" longitudinally. The rod is centered at the origin of our...

How do scientists know that the Sun orbits the Milky Way? Is this something more ancient scientists knew or could have known hundreds of years ago?

Just recently, I heard that at the speed the galaxy is currently spinning gravity alone is not a strong enough force to hold everything together. If that is true, what is the extra force that keeps the galaxy together?

This is a question I recently posted on Lubos Motl's blog. I am hoping that maybe someone here will also have some insight into this... ------ I have been reading about gravitational waves in hopes that they will prepare me for my inevitable look into the gravitons that I asked you about...

One of the earliest, maybe the earliest galaxies seen so far. Redshift 7.6 reported at conference. If confirmed then the light from it has been traveling some 12.9 billion years and was emitted when expansion was only about 700 million years old. Put 7.6 into either of these calculators to get...

I wasn't certain if this topic strictly belonged in the GR forum. I have read the article 'Singular disk of matter in the Cooperstock-Tieu galaxy model', by Mikolaj Korzynski (http://arxiv.org/abs/astro-ph/0508377). In it, the author finds that the singularity within Cooperstock & Tieu's...

Homework Statement A galaxy is moving away from the Earth at a speed of 2.3\times 10^7 m/s^1. Hydrogen emits light of wavelength 410nm. The speed of light is 3.0\times 10^8 m/s^1 Calculate th frequency of hydrogen light emission that you would expect to measure on earth. Homework Equations...

What would happen if the area a galaxy occupied spanned the influence of gravity and the Hubble flow?

Is it possible for a black hole to "eat" an entire galaxy? Is it possible for a black hole to "eat" an entire galaxy?

Suppose one measures the total mass of a galaxy somehow and its total luminosity. What mass to light ratio (in solar units) is considered a signal for dark matter and why? For example if M(galaxy)/L(galaxy) = 10 M(sun)/L(sun), is that considered 'too high' and a signal of dark matter? My...

im doing a problem were i find the mass of the our galaxy and i found the mass. What the problem is saying is to use the mass found to estimate how many stars are in our galaxy?

I have an extremely silly problem I am working on, having to do with celestial mechanics under ridiculous situations, and I have some questions about whether I'm doing it all right, if anyone is willing to spare a few minutes and half their sanity. (I am probably going to post my final results...

Given the redshift z of a galaxy, how can one measure the temperature of a molecule in that Galaxy? ( Assuming it is heated only by the CBR) ?

A distant galaxy is simultaneously rotating and receding from the earth. As the drawing shows, the galactic center is receding from the Earth at a relative speed of uG = 1.5e6 m/s. Relative to the center, the tangential speed is vT = 0.3e6 m/s for locations A and B, which are equidistant from...

Distance from Sun to "outside" galaxy? Does anyone have a general figure regarding the distance from the Sun to the nearest place officially "outside" the Milky Way galaxy? Thnaks.

I read in various places that a supernova can briefly outshine a galaxy, given the number of stars in our galaxy would it be fair to say that there have been a number of SN in our galaxy since mankind evolved ? If so what would be the effect on our planet of a SN in the galaxy ? Would the...

The question I'm about to asked has probably asked before many times b , but I keyed in a "supermassive black holes and galaxy formation" in the PF search engine , and this question has yet to be asked: How can supermassive black holes be aid the formation of galaxies when they are suppose to...

http://galaxyzoo.org/ Heard about this on BBC Radio 4 this morning -- thought a few people on here may be interested but didn't know which forum it belonged in :smile: e2a: http://news.bbc.co.uk/1/hi/sci/tech/6289474.stm

Abraham Loeb is one of the top people in his profession. Interesting that he should be using computer sims to study something very close to home like this. http://arxiv.org/abs/0705.1170 The Collision Between The Milky Way And Andromeda T.J. Cox, Abraham Loeb (Harvard/CfA) submitted to...

Would there be any way to discover dark energy, dark matter, if the only observable body was the galaxy you lived in?

So far i have found two theorise of how they form, the SSPSF shock wave model ,and the Density wave model, or they may form by a combination of the two. As i am not sure how old these theories are, i wonder if there are any new insights on the subject?

The orbits of the Magellanic Clouds about the Milky Way Galaxy have apparently been determined, and the two dwarf irregular galaxies are now about as close as they will get to the MW in their 2.2 billion year orbit. See p. 42 of "Our Growing, Breathing Galaxy" by Wakker and Richter, Scientific...

hey everyone... so I am tryna solve this problem : a galaxy shows an emission line at a wavelenght of 6610.2 A, which we identify as the H-alpha line in the Balmer series of Hydrogen. what is the redshift and velocity of the galaxy relative to us. period= 4.3 days magnitude= 26.25...

can anyone help me out with this: Assuming that our milky way is falling into this cluster with a velocity of 310 km/s due to gravitational attraction , estimate a value for H0 (in km s^ -1 Mpc^-1) using this single galaxy.

I don't understand whether this is true or false. It goes like this: if a distant galaxy has a substantial redshift ( as viewed from our galaxy) then anyone living in that galaxy would see a substantial redshift in a spectrum of the Milky Way galaxy. I know redshift is when the object is...

hey since the Earth turns around itself , turns around sun, sun turns around galaxy, galaxy is in movement (or maybe orbiting something bigger, who really knows ?) Well with all these movements, our velocity must be close to c ? thus , what is galaxy turns around ..., which turns around...

I have heard that in about 3 billion years, the Milky Way will collide with the Andromeda galaxy. I have also heard that they won`t actually collide, because the spacing in between the stars is so great. Instead, they will pass through one another with only a handful of stars colliding. Is this...

Homework Statement Derive and plot the rotation curve of a galaxy with logarithmic potential: \Phi(R, z) = \frac{v_0^2}{2}\ln{(R_c^2 + R^2 + q_{\phi}^{-2} z^2)} where R_c = 2 kpc, q_{\phi} = const. and v_o = 200 kms^{-1}. Note that v_c is defined for z = 0 only. Homework Equations...

i was thinking this for few days suppose glouds of neutral particles ne (m=0,5Mev) exists in galaxys halo. ne would easily decay to electron or positron near atoms nucleus or if its disturbed some way. (so it wouldn't be found in high energy lab) - ne could be produced only by direct pair...

Homework Statement An astronaut wishes to visit the Andromeda galaxy 2 million light years from Earth. He wishes the one way trip to take him 30 years (ie in the frame of reference of the spaceship). Assuming that his speed is constant, how fast must he travel? Homework Equations...

Explaining the structure of Galaxy "Filaments" Are galaxy filaments something that could be explained by the Big Bang theory, but NOT the steady state theory? What makes the scale of galaxies so special that the forms which are generated are unlike what happens in nebulas? Is the expansion...

I was watching a show about black holes at the centers of galaxies. And (perhaps I misheard), but there was a one line comment made to the effect that stars in a spiral galaxy don't always move around the center of a spiral galaxy in accordance with Kepler's laws (which, by that, I assume...

Hi - I had a question on webassign - here is the question. A spherical planetoid in a galaxy far, far away has spin angular momentum of magnitude L = 5.9e+35 kg m2/s directed out of its north pole. An external torque acts on it, such that the planetoid's axis of rotation, and hence its...