Galaxy Definition and 528 Threads

Why is the density of matter greater near the galactic center?

Good Morning, I've got a doubt originated from a statement of Berkeley Physics Course, Vol.1 - Mechanics, pg. 107, where in a footnote we read, "The systems are called galaxies, that one which contains our own sun is known as the Galaxy. The Milky Way is part of our galaxy". I've always...

I have read somewhere that the parallax method can be used to measure the distance to stars up to 400 light years away. I did a quick calculation and estimated that it means that our telescopes can resolve an angular movement of 8.15x10-3 arc seconds. Taking the distance between the sun and the...

Just noticed this article. Wonder if anyone here has further info. Sounds very interesting. http://www.bbc.com/news/science-environment-43543195

My last thread got lots of hits and was a success so I thought I would start another discussion based on the Galaxy I was speaking about, In my previous thread we found the distance to the galaxy, now I want to take this further and work at the diameter of the galaxy. If two edges of this galaxy...

I have been having a conversation with a few friends, and we have been discussing the speed of stars in a galaxy base of the wave lengths. We have 2 stars measuring wave lengths 494.6nm and 494.2nm. At rest the wavelength is 486.1nm. From this we managed to deduce that the speed of both stars...

https://phys.org/news/2018-02-high-resolution-image-core-milky-reveals.html This is my first thread here so if I have done something wrong or placed it in the wrong place, I apologies in advance. Otherwise enjoy! I found the images amazing to say the least.

From https://phys.org/news/2018-01-image-hubble-cartwheel-galaxy.html The attached article explains the proposed origin of this nifty ring galaxy.

Galaxies seem to being found further and further back to the BB, At what epoch is it going to be impossible for galaxies to form? https://arxiv.org/abs/0912.4263

... where was our current place in spacetime, call it A, when that photon started its journey 12 by ago? Did A even exist 12 by ago?

I apologize for the simple question, but I am trying to understand the Mass Discrepancy-Acceleration Relation and its relationship to ##\mu(x)## (from https://arxiv.org/pdf/astro-ph/0403610.pdf). The mass discrepancy, defined as the ratio of the gradients of the total to baryonic...

I have been working on a discovery that could explain galaxy rotation curve without dark matter or modification of Newtonian dynamics. However, I was unable to make any comment within this forum since this was unpublished work. However, the same discovery has been made independently by Kenneth F...

Lying 620 million light-years away, this galaxy has the lowest oxygen abundance ever seen in a star-forming galaxy. Link: New Scientist

Wikipedia dixit: The standard model of cosmology indicates that the total mass–energy of the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy ******************************************************************************* According to this, dark matter must be...

I apologize for the simple question, but I have not been able to find the answer. For the inner portion of a galaxy rotation curve (where the outer portion is the part invariant to distance and the inner part is where rotational velocity increases with radius), how much is simply due to...

hi guys I haven't posted any images for a very long time, health/eyesight has been pretty bad and stopping me from getting out with telescope and camera. This image below of spiral galaxy, M83 ( also known as the Southern Pinwheel Galaxy) July 2016 I did a set of 8 x 30 sec images with my...

According to this article millions of Black Holes exist in our Galaxy, And within a few years mergers will be detected by Ligo, According to Kaplinghat, they may not have to wait too long, relatively speaking. "If the current ideas about stellar evolution are right, then our calculations...

This story, "Cosmic Map Reveals a Not-So-Lumpy Universe", https://www.scientificamerican.com/article/cosmic-map-reveals-a-not-so-lumpy-universe/ included an interesting picture of galaxy NGC 1398, Also seen here...

Today's Astronomy Picture of the Day discusses a method for determining the distance to a galaxy that I had not seen before. https://apod.nasa.gov/apod/ap170707.html For a far away galaxy, the distance to M106 is well-known in part because it can be directly measured by tracking this galaxy's...

My understanding: Circuit is ~ 30 million years. Plane of solar system orbit is tilted from plane of milky way. Is milky way plane crossed once or twice? What is error bar for 30 million? How much does dark matter density vary along solar system path?

Why do galaxy and galaxy clusters look so colorful?

Hi all, Recently I am reading some online material about Tully-Fisher relation and Faber-Jackson relation which is describing the dynamical constrain on the mass of spiral/elliptical galaxies. In spiral galaxy, TF relation suggest Luminsoty ≈ (some const) (Vmax)^4 while in elliptical galaxy...

This paper https://arxiv.org/pdf/1705.06859.pdf says that PBHs were the start of galaxy formations at up to Z=10 what do you think? In this connection a natural idea may come to one’s mind, that the SMBH are not created in the galactic halos but, vise versa, galaxies are formed around the...

Ok... so the furthest galaxy (Object: UDFy-38135539) to date has been found by the Hubble Ultra Deep Field cameras which to date goes back some 13.1 billions light years (conservative universe estimate is 13.7 billion light years) so pretty much an object with many questions. See...

I am unsure on what exactly is at the center of the galaxy. I looked up some articles but some stated that scientists are unsure.

The universe is said to be built for life. How many billions of years after the Big Bang when the first supernova spread the first ingredients of life and the first solar system with life possible? Is it 2 Billion years after Big Bang or even less or double that, estimate?

Arxiv and google searches turn up hundreds of sources on Galaxy formation. I'm specifically looking for good material on how Dark Matter distorts the motions of galaxies from what we'd expect. Currently I've been using a combination of Binney and Tremaine's Galactic Dynamics and whatever...

So it is a known fact that the Andromeda galaxy will collide and merge with the Milky Way galaxy. In the video it shows the collision. Time 1:40 My question is how does it take only 3 collisions for the merger to take place? First all, can we assume that if no stars/dark matter/planets from...

Thought experiment: Assume two galaxies in a galaxy group, initially at rest (with respect to one another). The distance between the centers of the galaxies is r = 1 Mpc. The total mass of each galaxy is mg = 6 ∙ 1042 kg (including dark matter). This is ≈ 3 ∙ 1012 solar masses. The...

Of all the stars in our galaxy, how much of them belong to clusters?? Is our sun rare in terms of not belonging to any cluster? I can't find any sources on that

I'm looking for a usable method to calculate the bulge mass of, say, the Milky Way or Andromeda. Most of the literature I've read agree that a de Vaucouleurs profile is the way to go. However, I'm unable to get an exact solution using Mathematica. The general form of the integral...

This is a request for a good reference. I'm doing a report on dark matter and am wondering if there's any recent references that collects a bunch of galaxy clusters, their dark masses and the radius of the cluster. Preferably in a table that I can shred or download but I'll copy if I have to...

How o you find the Names of the types of NGC/IC objects: Classifications: G, GiP, GiG, PN, EmG, ISM, Sy2, rG, IG, etc. ex. PN = Planetary Nebula Also is there a database that contains the Common Names of these NGC/IC objects: ex. Pinwheel Galaxy or Blue Snowball Planetary Nebula.

I've been tinkering with a few diagrams in an attempt to illustrate the motion of the solar system in its journey around the Milky Way. I also wanted portray how the celestial, ecliptic and galactic coordinate systems are related to each other in a single picture. Note: in the Celestial, or...

Lying 280,000 light-years from Earth, the Virgo I galaxy emits only 180 times as much light as the Sun, half as much as the previous faint-galaxy champ. The galaxy's proximity to the Milky Way suggests that our Galaxy has hundreds of other satellite galaxies. New Scientist has the exclusive...

I'm familiar with galactic rotational curves and there are plenty of graphs depicting such curves, but I'm interested in the rotation curves of entire galactic clusters at the moment and I'm not too good with sifting through what shows up in the search engines. (not a physicist, just a...

Homework Statement An estimate of the mass of the Coma cluster can be made from the velocity of the galaxies relative to the centre of mass of the cluster; the velocities are around 2000 km s-1. The stars that form the cluster have been together for a long time. Show that a simple model will...

I've searched for a formula of galaxy mass Distribution formula along the radius, often the papers say: ρ∝ex ( ρ is the surface density, x is distance from the Center of the galaxy). is it correct without DM? Or is there any other correct formula?

In this video (), we first took the spectrum of a star and then of a galaxy which look like the following: However, what I don't get is: if we take the spectrum of a star and then of the galaxy the star is in, shouldn't it give me the same spectrum as they're moving in the same speed? And if...

As far as I know, when we use the spectrum of a star, we see where the absorption lines are and using this, we can detect the elements that are present in the star. We also measure whether those absorption lines are supposed to be for a particular element. But why is it not possible that the...

In the following video (, diagram also given for reference), the professor says that if the graph peaks in a short wavelength, then the star is a hot star (or galaxy) and if it does so in a long wavelength, then it's a cold one. However, I fail to understand this. How does it happen that if a...

I know that I'm most galaxies black holes live in the center. I'm wondering if this is true for Galaxy clusters. Are there black holes in the center of galaxy clusters?

I was going through the following paper: https://arxiv.org/pdf/1605.08054.pdf In the 2nd line, it says, "GN-z11, a MUV=-21.1 galaxy at z=11.1." I know, what z=11.1 is. If I'm correct, it's the redshift of the galaxy which helps in measuring its velocity. I'm not quite sure, though, of what...

Galaxies that are further than c/H metres from us, have recessional velocity exceeding c and thus they begin to fade away. Is there any data for how long it takes galaxies to fade away from the perspective of an observer on Earth where when t is zero, the recessional velocity of the galaxy is...

Speaking only of approximately spherical moons, planets, and stars (not asteroids), which rotate about their axis, are the axes all pointed approximately the same direction? Is it true for moons and their parent planet? Is it true for planets and their parent star (solar system)? Is it true for...

Hello! I watched a video on the Youtube channel Kurzgesagt titled How far can we go? Limits of humanity The video attempts to explain why we may be limited to our local galaxy group even with science fiction technologies. During a part of the video (starting at 2:26), they try to explain how...

Supernova in M66 in Leo, announced 30/5/2016: https://Earth'sky.org/todays-image/supernova-erupts-in-m66 cheers Dave

I'm doing research on why some galaxies and other phenomenon like Saturn's rings are flat. There seems to be two answers. Here they are in shortened form: 1) When the galaxy is forming, there is some net angular momentum in some direction.Over time, all particles with an angular momentum...

Homework Statement Hi, I'd really appreciate being pointed in the right direction with this past exam question, as I just have no idea how to approach it and can't find similar examples in my notes anywhere. A nearby star has a spectrum similar to the sun, suggesting it has the same mass. The...