Galaxy Definition and 528 Threads

[Mentor Note: Two threads on the same basic subject have been merged into this one thread.] Dear PF Forum, It's been a long time since I logged in PF, and I hope everybody is in a good health. Recently I'd like to know what is Kardashev scale type II and III I mean, Type 1: All energy from...

How do proponents of modified gravity explain the fact of observation of galaxies, the behaviour of matter in which does not require an explanation in the form of dark matter or modified gravity?

"... the gas between the galaxies collided, becoming turbulent and superheated. While both dark and normal matter are influenced by gravity, the normal matter also interacts via electromagnetism, which slowed it down during the collision. Consequently, the dark matter moved ahead, decoupling...

The paper here. https://iopscience.iop.org/article/10.3847/1538-4357/ad571c From the conclusions. "The measured slope is in good agreement with ΛCDM predictions, 49 given that our measurements fall well within the break radius of the DM density profile predicted by cosmological simulations...

Is it a big assumption that Galaxies should follow Kepler's third law with rotation speeds decreasing with distance from the centre. Is the small tet of the behaviour of the Solar System not too small an example to make such a substantial assumption? Thanks Martyn

What is the consensus on how long it would take for a galaxy to form similar to the ones which I am reading about here with Z=20? Galaxy formation time is probably of much interest right now. Perhaps formation was much quicker shortly after the BB with higher gas densities...

We observe a very distant galaxy, thanks to the JWST. That galaxy has the same laws of physics as we do. Now imagine yourself in that galaxy, in your observable sphere of the universe, using your own telescope, looking in a direction opposite our current one from earth. Would we be able to...

TL;DR Summary: Completely clueless on how to answer this question, came up as part of an assessed lab script Why does 21-cm emission only give the rotation curve of the Galaxy at galactocentric radii less than that of the Solar system? The lab script asking this question made zero...

Let's say I have a galaxy SED like this: from synphot import SourceSpectrum from synphot.models import BlackBodyNorm1D sp = SourceSpectrum(BlackBodyNorm1D, temperature=6170.4796) wave = sp.waveset flux = sp(wave) #Photlam flux_flam = flux.to(u.erg / u.s /...

Why does an Einstein ring sometimes appear and sometimes an Einstein Cross appear? Some say it is due to the distribution of the mass of the galaxy in front, while others say it is due to alignment. What is right? Are both correct? If it is due to the galaxy's mass distribution, I wonder if it...

It is clear that the speed is constant because dark matter hasa gravitational effect on stars, so when a star is further from the core, gravitational force of it is smaller, but the net gravitational force of dark matter is bigger. So the net force acting on each star has to be the same. So...

How can I create a metric describing the space outside a large disk, like an elliptical galaxy? In cylindrical coordinates, ##\phi## would be the angle restricted the the plane, as ##\rho## would be the radius restricted to the plane. I think that if ##z## is suppressed to create an embedding...

I am trying to compute the exposure time needed for an extended object (galaxy), in python. I have found the following formulas: Exposure time app # press the help button at the bottom of the calculator for the formulas used Exposure time calc Let's take for example the M33 galaxy. It has...

What are the non-gravitational ways of determining mass of galaxies, and how accurate are they?

https://earthsky.org/todays-image/supernova-in-m101-pinwheel-galaxy-closest-in-a-decade-how-to-see/

Deur Gravitational self-interaction Doesn't Explain Galaxy Rotation Curves this paper A. N. Lasenby, M. P. Hobson, W. E. V. Barker, "Gravitomagnetism and galaxy rotation curves: a cautionary tale" arXiv:2303.06115 (March 10, 2023). Directly comments on Deur's theory of self-interaction...

Does anyone know where I can find the map animation of the galaxy / nearby galaxy cluster that illustrate the geometry between Earth and M87 at the 29th minute in the Netflix show ? Alternatively if that's not a public source, can anyone recommend a publicly available "map of the universe", I'd...

I'm after some raw data for testing theories of dark matter in galaxies. Basically what I want is table showing visible mass vs total mass within different radii (or, observed rotational velocity vs expected rotational velocity without dark matter). Plus error percentages. And ideally, for...

Are the stars that we see in constellations within the Milky Way galaxy? Should I assume that they are close and within the Milky Way?

Announcement Thursday 1 pm CDT, that's 18:00 UTC. This post was made 1:20 UTC. Conversion help. It's possible they picked up some neutrinos associated with some event observed by other means, or maybe we get an update on extremely high energy neutrinos.

a.) The scale length of the disk is the length over which the surface density of stars decreases by a factor of e. In this case, the surface density decreases by a factor of 10 over a distance of 9 kpc, so the scale length is 9 kpc. The surface density of stars at a radius of r from the center...

Summary: I am looking to confirm a few things on the structure of the galaxy as we know it to make sure I have a credible enough understanding for a sci-fi project I'm working on. Background to question: For my sins, I make sci-fi starships and ground forces wargames models as part of my day...

Here's the image that a lot of pop science articles use: Evidently, a lot of articles say to look for the Great Square of Pegasus, but it seems to me to not be a very noticeable asterism. I use the Cassiopeia's W deeper-side (i.e., right) arrowhead and count 3 lengths of the depth of the...

The article is pop but there is a paper Pop article https://www.vice.com/en/article/g5vvjw/the-universes-oldest-light-reveals-unprecedented-dark-matter-patterns Paper. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.061301 The language is a little bit click bate, I just wanted...

What would happen if they found a galaxy that dated to older than 13.8 billion years old? How would this affect cosmology?

Hi. I'm a science enthusiast. I haven't been here in a long while. This is something I've wondered about for quite some time. I'm wondering if the temporal differences across something so vast as our milky way galaxy might pose any implications for how our galaxy holds together (ours and other...

Do all the planets in all the solar systems in our Galaxy spin in the same direction ? Clockwise or anti clockwise depending on the viewers POV.

Is this sentence correct? Our Sun lies in one of the spiral arms of the Milky Way, about 2/3 of the way out from the center of the galaxy.

How does the Milky Way galaxy move in the local Group? Is there a circular motion around the center of the local Group like the sun moves around the center of the galaxy?

If the sun is traveling around the center of the Milky Way at a speed of 536,865 mph and we are tagging along with it, couldn’t a spacecraft travel to another solar system by stopping? Would it be possible currently to slow down from that speed to 0 mph? And lastly, why does physics make my...

I saw on another forum mention of Alcyoneus radio galaxy and have been google searching but can't find any information on it from any reputable astronomy related websites. Is it real or just fake news?

I've been reading up a little on IC1101, the largest known galaxy and there is not a lot of info on it, but it seems to have an unusually large mass to light ratio according to this popular article (see half way down): According to this article at 20kpc it's got 12:1 mass to light, at 200kpc...

Hi If the universe is expanding, then why does the Andromeda Galaxy approach us? Does not it contradict Hubble's law?

https://phys.org/news/2021-11-ultraluminous-x-ray-source-galaxy-ngc.html Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55 ULX1 https://arxiv.org/abs/2111.06637 Same paper - https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/stab3307/6428406 From...

https://futurism.com/genesis-project-robots-seed-galaxy-life

The error on photometric galaxy clustering under the form of covariance which is actually a standard deviation expression for a fixed multipole ##\ell## : ## \sigma_{C, i j}^{A B}(\ell)=\Delta C_{i j}^{A B}(\ell)=\sqrt{\frac{2}{(2 \ell+1) f_{\mathrm{sky}} \Delta \ell}}\left[C_{i j}^{A...

Hello everyone - The gravitational force near the edge of the galaxy at point A (see attached image) can be calculated by assuming that all the galactic mass is located in the center of the galaxy. - In order to calculate the gravitational force in the middle of the galaxy (point B) we take...

Magnetic fields as an alternative explanation for the rotation curves of spiral galaxies ABSTRACT THE flat rotation curves of spiral galaxies are usually regarded as the most convincing evidence for dark matter. The assumption that gravity alone is responsible for the motion of gas beyond the...

I just finished rereading the great "A Brief History of Time". To me, what stands out the most in this book, is its ability to keep raising questions while you read it. This thought came up. It's been stuck in my mind for days, so I will humbly post it here to get some feedback. Please forgive...

A void galaxy is a galaxy that exists in a cosmological void like the Bootes void. Most galaxies are clustered into filaments. Here is a link to the Wikipedia page for a void galaxy https://en.m.wikipedia.org/wiki/Void_galaxy Anyway, in Star Wars Legends, the Star Wars galaxy has 7 companion...

I was cleaning out my email archive after being notified I was out of storage. I decided to keep these. Enjoy. (original at: https://dingo.care2.com/cards/flash/5409/galaxy.swf) This one would be impossible on a phone and slow on a laptop, use a fullsize computer if available. I couldn't...

I am trying to follow a calculation from the book of William C. Saslaw, The Distribution of the Galaxies: Gravitational Clustering in Cosmology. The calculation is shown on the pages following page 122 in chapter 14 where the author talks about the Correlation function. I am able to reproduce...

Do we know at which speed the whole milky way is moving around in the universe? Around the next cluster I suppose?

Does intervening mass between two stars decrease the gravitational attraction between these two stars? Is gravity a local phenomenon in that local mass interacts with the surrounding gravitational field caused by the local star and distant stars?

Hello, What I understood from multiple answers on different threads is that the effect of the time dilation is too small to explain the galaxy rotation curve. I was advised to do some calculations in order to see it myself. And this is what I would like to do but I need some help. - What is...

By what means can a galaxy's spin increase whereby matter is expelled from the outer reaches of the galaxy?

FRBs apparently from "...a “run-of-the-mill” magnetar. Astronomers labeled it SGR 1935+2154..." About 30,000 light years away. https://news.mit.edu/2020/ultrabright-radio-flashes-detection-1104 The research paper is behind a paywall, but Abstract at...

Hi everyone! Does using the distance modulus—m-M=5log(r/10)—on type 1a supernovae only provide the distance to the host galaxy at the time of the supernova? If so, how would I mathematically determine the present day distance to a galaxy by taking into account both the expansion of the universe...

The distance of the sun to the Galactic Center is about 7.4–8.7 kiloparsecs. If I use the known data of stars in various stellar catalogues, how can I calculate (approximately) a distance of a given star from the Center? What kind of data I need to look for? can it be calculated from Right...

The speed of the ends of the galaxies is higher than what it should be. Current solution: This could be explained by hypothetical "dark matter", which was not found up to now, or by a MOND theory (MOdified Newtonian Dynamics). Can this be explained instead with rotational frame-dragging...