Galaxy Definition and 528 Threads

Galaxies that are greater than a distance of c/H metres from Earth have recessional velocities exceeding the speed of light and begin to fade. Thus, theoretical astronomers 3 trillion years in the future will see only the Milky Way in the night sky. What is the reason for this fading of galaxies?

I was reading the wikipedia entry for Dark matter halo here: https://en.wikipedia.org/wiki/Dark_matter_halo And they have this graph for the Milky Way galaxy rotation curve: "Galaxy rotation curve for the Milky Way. Vertical axis is speed of rotation about the galactic center. Horizontal...

Q: Estimate the diameter in kpc of the red-shift=6.56 galaxy at the moment when it emitted light. We're assuming that early galaxies with similar red-shifts have the same number of stars to galaxies as in the present state of the universe. I've taken a look at the small angle formula a = s / d...

The Milky Way now has 49 known satellite galaxies, and the new one is the fourth largest. Link: New Scientist

Homework Statement Calculate the number of white dwarf, neutron star and black holes the galaxy will have after 5Gyr of evolution. M<8(solar mass) for white dwarf 8(solar mass) < M < 40(solar mass) for neutron star M > 40(solar mass) for black hole Initial mass function is ξ(M) = AM-s...

Dear PF Forum, Just out of curiosity :smile: Can we (through telescope or HST for example) see stars in Andromeda Galaxy? Is the Andromeda Galaxy the closes galaxy to us. Can we really be sure that there is no other galaxy across Milky Way because our line of sight is blocked by clusters of...

Dear all, I am looking for observational data for the number count of galaxy mass function: \begin{equation} dn/dM\end{equation} in terms of redshift and also mass, to compare with theories. I know that I can use HIPASS data (most probably), but as I am new to the field, I have to idea: 1-...

So looking at pictures of dwarf galaxies and how they're just an irregular (pun intended) mess and they do not have the disk shape that we, ironically, associate with galaxies despite a small minority of galaxies being big enough to have and maintain their disk shape. Like apparently the...

Homework Statement I want to calculate/estimate the average photon energy from a galaxy cluster incident on the mirror of a X ray telescope (Chandra to be specific) . The cluster has redshift z and at constant uniform temperature T Homework Equations Specific Intensity of thermal...

There are 2 unknowns in the formula. The time period of rotation and the mass enclosed by orbit is Star. So how could we calculate the expected time period of rotation of stars in a galaxy and thus velocity of stars.

Lead author is Pascal Oesch Measured redshift is z = 11.1 That means at the moment it emitted the light we are receiving from the galaxy, distances were 1/12 their present size. Technical detail: http://arxiv.org/abs/1603.00461 A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space...

The dark matter crisis: falsification of the current standard model of cosmology Pavel Kroupa (AIfA, Bonn) (Submitted on 11 Apr 2012 (v1), last revised 20 Jun 2012 (this version, v2)) The current standard model of cosmology (SMoC) requires The Dual Dwarf Galaxy Theorem to be true according to...

Has the expansion of the Universe caused less clustering? If the expanding Universe is causing volume of space to increase, to me it would make sense that clustering would be impacted as a result of this.

Hi all, I have recently created an nbody simulation in Vpython for a few thousand particles where each particle is about 4000 times the mass of our Sun. Vpython is doing exactly what I want it to do the only problem being the output is extremely low quality (black spheres on a white...

Dear all, I am new in the field of galaxy formation, so I am sorry if my questions are a bit simple. -what does virialized halo mean? does it mean they obey the virial theorem concerning their kinetic and potential energy? \begin{equation} 2<T>=n<V> \end{equation} -Why should the halos be like...

Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy - arXiv 1512.04661 (free reprint) Apparently there was another thread with a similar title ("Second black hole may lurk at Milky Way's heart") from June 2003, but it really had nothing to do with a second...

What is the density of galactic centre? Thus what form of Kepler's law account for the galaxy rotation curve increasing near the galactic centre?

In 2008, astronomers discovered that a multi-million-solar-mass cloud named Smith's Cloud would hit the Milky Way's disk in about 27 million years. Now new Hubble observations have identified the mysterious cloud's likely origin. Link: New Scientist

According to what I've read, the andromeda galaxy is approaching the milky way galaxy. Also, I've just recently discovered (on the net) that andromeda has a much larger subtended angle than the moon or sun. Hence, as it approaches it's angle subtended will keep increasing. I've also known that...

We see from wikipidea that EGSY8p7 z=8.68 13.2 is only a fraction away from the time of the BIG EVENT how close will a galaxy be to disprove the LCDM.

by Ken Croswell Call it the case of the purloined star cluster. Observations reveal that our galaxy stole a distant globular star cluster from one of its neighbours. Link: New Scientist

I have a few questions. Would a given galaxy contain same amount of stars and gas through its lifetime? I want to say no, but I was thinking for every dead star, there will be a new star forming, and the gases would be preserved in the galaxy. And would the spiral disk component of the Milky Way...

Hi, ignoring Dark Matter, I was wondering on average what portion of a galaxies mass is stars and what portion is gas. I am guessing it fluctuates with redshift so for arguments sake let's say we are only talking about galaxies at z~0.5 Thanks Steve

The diagram below is from https://en.wikipedia.org/wiki/Galaxy_rotation_curve . I would much appreciate a derivation explaining the shape of the "Expected from visible disk" curve in the diagram. Naively, based on Newtonian mechanics for the orbital velocity of a circular orbit, V = √GM/R ∝...

I found this: http://adsabs.harvard.edu/abs/1992A&A...259L..31B document that describes how the X-Ray emissions from galaxy clusters are used to calculate the mass of the cluster. I'm unable to follow the steps to calculating the gas mass. Specifically, in section (2) there is a formula for...

If objects in the universe are built hierarchically, wouldn't one expect a Galaxy Cluster that is roughly spherical to follow the same profile as an elliptical galaxy?

If we look up the sky at galaxy X whose light took Y amount of time to reach us from distance Z, where is the galaxy X now?

Astronomers find galaxy cluster with bursting heart An international team of astronomers has discovered a gargantuan galaxy cluster with a core bursting with new stars - an incredibly rare find. The discovery, made with the help of the NASA/ESA Hubble Space Telescope, is the first to show that...

Astronomers discover how lowly dwarf galaxy becomes star-forming powerhouse A nearby dwarf galaxy poses an intriguing mystery: How is it able to form brilliant star clusters without the dusty, gas-rich environments found in larger galaxies? The answer, astronomers believe, lies in densely...

Neutral hydrogen gas in galaxy clusters Most galaxies are members of a cluster, a grouping of several to thousands of galaxies. Our Milky Way, for example, is a member of the "Local Group," a set of about fifty galaxies whose other large member is the Andromeda galaxy about 2.3 million...

How did we know that our galaxy is spiral?!

http://arxiv.org/abs/1507.02679 Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization Adi Zitrin, Ivo Labbe, Sirio Belli, Rychard Bouwens, Richard S. Ellis, Guido Roberts-Borsani, Daniel P. Stark, Pascal A. Oesch, Renske Smit (Submitted...

In the context of a project, I had to solve numerically Poisson equation with cylindrical coordinates. I put here results for z = 0 on a 3D mesh 256x256x256. Below 1 figure representing the final solution (in absolute value) in the case of a galaxy; I use the CGS units for the potential. I...

I have a modification to MOND that appears to work much better than 'Standard' MOND at the galactic scale. I want to test this model now on larger structures. Does anyone know where I can find kinematic data on galaxy clusters, preferably some 'gold' standard that people have been examining for...

Can anyone tell me where I can find an explanation that only the gravity of the stars inside the orbit of your star is important in a galaxy? Someone told me this and the integration of gravitational effects I did seems to disagree so I wanted to look at what has already been done.

I used the ##v^2=MG/R## to calculate mass of milky way.Now ##v=225000## m/s G=6.7 10-11 and r is 16 kpc source (https://upload.wikimedia.org/wikipedia/commons/7/77/Rotation_curve_%28Milky_Way%29.JPG) If I plut them I get ##50,625,000,000=v^2## and the other side G=6.6 10-11 and R =49.6 1019...

Dear all, I am trying to plot the cumulative number counts of galaxy cluster (N>S) as a function of X-ray flux. The method I am following is using the mass function and scaling relation to calculate dN/dVdz. Then I do a double integrate over the redshift range and flux range. But the plot that...

There was a NYT item today by Dennis Overbye about what I think is this: http://arxiv.org/abs/1504.01734 CBS headline said "brightest galaxy in early universe". I don't yet understand what all the excitement is about. But I think that is the link to the professional paper that is getting the...

Is there general consensus that the universe is to young? arXiv:1506.01377 [pdf, ps, other] The Impossibly Early Galaxy Problem Charles L. Steinhardt, Peter Capak, Dan Masters, Josh S. Speagle Comments: 7 pages, submitted Subjects: Astrophysics of Galaxies (astro-ph.GA) The current hierarchical...

Below are two URLs to Hubble telescope photos of galaxy clusters. I would like to know if every single white or colored splotch in these photos is a galaxy, or do single/individual stars/suns manage to get mixed in there? Thank you for your time...

Homework Statement In a flat FRW universe, for a source moving radially at velocity v (at emission time) relative to the local comoving frame, what is the redshift observed by a comoving observer? Homework Equations ##c=1## Proper time to cosmological time ratio...

Dear PF Forum, I have a question that puzzles me. Galaxies are moving away from us, except Milky Way which is in collision to us in some 4 billions years. I think there are other collisions as well from any other galaxies pairs. So, 1. Galaxies are moving away from us. Are they also SPEEDING...

Using the Hubble Space Telescope, astronomers have discovered that the immense halo of gas enveloping the Andromeda galaxy is about six times larger and 1,000 times more massive than previously thought. http://scitechdaily.com/halo-around-the-andromeda-galaxy-is-larger-than-previously-thought/...

I am curious about mass of a galaxy without dark matter and with dark matter.I searched but I couldn't found.I ll be happy If you help me. Thanks

I need someone with more experience in the field who has knowledge of excel to check over my work. Given the gravitational attraction between two bodies is F = (GMm)/r^2, and the centripetal force required to keep a body in orbit is F = (mv^2)/r, therefore (mv^2)/r = (GMm)/r^2 therefore...

Homework Statement The number of stars in the galaxy is N=10^12 and the radius of the galaxy is Rgalaxy = 20 kPc Let m be the average mass of a star in the galaxy. what is the velocity of a star at the edge of the galaxy (relative to the center of the galaxy) Homework Equations The Attempt at...

If I have two galaxies... i.e Ellipticals.. with same mass, size and velocity dispersion approaching each other and merging to form a bigger galaxy, what would be the total energy of the system? I'm assuming they would be approaching each other from 'infinity', so E=0 initially. I'm guessing...

Homework Statement Taking light collected by the telescope and shine it through a diffraction grating with a 765.5 lines/mm. Using the filter that just the brightest Helium II line. you cast the diffraction grating's diffracted pattern on a screen is 22.000cm away and there are 3 dots, m=-1...

Hello PPer's, I have been considering the effect to which electromagnetic radiation emitted from stars might play in the gravitational coalescence of galaxies. Surrounding every galaxy there must be a halo of electromagnetic radiation streaming outwards at the speed of light which diminishes...

What is your reason for studying physics and what do you want to do with it. I actually got thrown into my schools physics program by accident. I began at a community college studying nanotechnology and when i transferred schools it was supposed to be a two-plus two program meaning I would get...