Galaxy Definition and 510 Threads

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...

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...

Since our galaxy and the andromeda galaxy are drifting towards each other. How long will it take to look as big as the moon today in the night sky?

heya all, i need some help on a homework question. Here is the question-- We are located about 28000 light-years from the galactic center and we orbit the center once every 230 million years. How fast are we traveling around the galaxy? Give your answer in both km/hr and mi/hr. Okay, i know...

A question. Has there ever been an instance where a single galaxy split into two separate gallaxies or a recorded view where that would seem to be the case. Thank you. Sunblock

http://physicsweb.org/articles/news/10/6/3/1?rss=2.0 ===sample quote=== Levine and colleagues took previously obtained data from the hydrogen "21-cm emission lines" and applied a technique called unsharp masking to increase the contrast between high and low signal regions. They found that the...

Some time ago i post this topic, but i think my explanation was not very clear , i hope now could be better understood My new argument is this: suppose that much billions years ago existed in what now is our Solar System an alien civilization, suppose they have developed the videorecording...

The typed question and attempt at it are below: Question: The Sun orbits the black hole in the center of the Milky Way galaxy. It takes approximately 225 million years for the sun to make one revolution, and the sun is approximately 26,000 light-years away. Using this information and...

Hello. I'm plowing through Linda Sparke's "Galaxies in the Universe: An Introduction". I'm enjoying it quite well and learning a lot. But then I get to Equation 1.18 in the book and am a little confused because it uses variables not previously introduced. Not sure if I can do it here but...

two exiled stars are leaving our galaxy forever They are surely traveling fast!

After the discovery of galaxy HUDF-JD2 is the big bang theory to be revised?

Dark Galaxy found!? You know, I've always been secretly hoping that dark matter was an aberration of our observations or calculations, some value to be tweaked or some normalizing factor to be applied thing that was making galaxies turn faster than formulae predicted. I just couldn't believe...

The Andromeda glaxaxy is two million light-years from earth, measured in the common rest frame of the Earth and Andromeda. Suppose you took a fast spaceship to Andromeda, so it got you there in 50 years measured on the ship. If you sent a radio message home as soon as you reached Andromeda, how...

I decided to post a new thread to distinguish from my other post The paradox is as this: suppose that 10 billions years ago a guy was born ( let's call him "Universeguy"), in a place near the Earth (because obviously Earth doesn't exist yet), first, he was a lucky guy , he discover how to...

Why are the planets in our solar system spread out in a plane instead of being more randomly spread around the Sun? And why is our galaxy in the shape of a plane instead of all the stars in our galaxy being more randomly spread around the middle of our galaxy? Thanks,

The post that held the link to this paper has been moved. I would like to see comments on this paper, including impressions of the mechanism responsible for the interaction of the quasar and the associated galaxy. http://arxiv.org/ftp/astro-ph/papers/0509/0509433.pdf I objected to the...

This topic brings up the Fermi Paradox, once again. I just want to hear the boards opinion on this...should the galaxy have been colonized by now? and a decent portion of it has been colonized would we able to "see" it?

New pics. These are a month old, but I forgot to upload them. They are from Sept 29. That was the first night it got really cold and I drove to the Poconos to set up shop, so while the sky was very clear and very dark, it was also very windy. First is another shot at the Andromeda Galaxy...

for the following question: In its own frame of reference, a proton takes 5min to cross the Milky Way galaxy, which is about 10^5 light-years in diameter. What is the approximate energy of the proton in electronvolts? my problem: v*5*60=(10^5)*3*(10^8)*[1-(v^2/c^2)] however, i can't...