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Questions tagged [galaxy]

Questions regarding systems of large numbers of stars held together by gravity.

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Black holes in galactic rotation [on hold]

I'm wondering whether the total mass of a galaxy's hypothetical black holes, that may have each been formed within the gravitational horizons of larger black holes (that are indirectly apparent, ...
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1answer
55 views

How can we calculate velocity of an object given the distance from an object in parsecs?

If you had the distance from a celestial object, in parsecs, how would you calculate the velocity of the said object? Edit: I'm sorry I don't have more context, the specific questions is: "A galaxy ...
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1answer
71 views

What are the most popular galaxies for which we have images? [closed]

The only galaxies I can think of (not being an astronomer) are Andromeda and Milky Way. There are 51 near galaxies, but they all pretty much say "satellite of Milky way" or "satellite of Andromeda". ...
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1answer
40 views

How is the expansion rate of the universe obtained from Baryon Acoustic Oscillations?

I understand that we can measure the sound horizon from the anisotropies in the CMB. Large galaxy surveys today can construct two-point correlation functions, which reveal peaks at distances equal to ...
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1answer
95 views

Why a blue spot in some hubble images of NGC 4302?

In some images with coloring like in this one: There is a noticeably bluer region in the "bottom left" of the image, and the bottom part of the galaxy on the left. Being an inexperienced galaxy ...
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1answer
63 views

What is the likely closest encounter for a typical star during the Milky Way Andromeda Merger?

This is closely related, but distinct question to What are the chances of a star colliding with another during a galactic collision?. The accepted answer to that question places the odds of the Sun ...
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3answers
194 views

Whereabouts of the Pleiades

I assume they should be in the Milky Way galaxy. I have read about it a little but did not find information on where they are. Which galaxy do the Pleiades belong to?
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1answer
18 views

How to get ellipticities of galaxies from SDSS using casjobs?

How to get ellipticities of a list of random galaxies. I saw few programs written in SQL and they were only giving stokes parameters and isophotes values for ONE galaxy(for which we input the ObjID). ...
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0answers
33 views

Ideas about the origin of the “black hole - galaxy mass” relation?

It has been extensively shown that the mass of black-holes located at the center of galaxies scales with several galaxy properties, most notably the stellar velocity dispersion of the stellar bulge, ...
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1answer
34 views

How to find inverse steradian from $\text{arcmin}^{-2}$ for density of galaxy

I am using a code on EUCLID future mission. The original author of this code has set a value for the density of galaxy equal to : ng = 354543085.80106884 I ...
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0answers
36 views

Universe as 3D projective space? [closed]

Is there any benefit to view the 3D (real) universe as 3D projective space?
2
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1answer
45 views

What has GAIA found out about the dwarf galaxy heritage of stars in the Milky Way, if anything?

I ran across the image below in the August 2000 ESA Bulletin # 103 GAIA – Unravelling the Origin and Evolution of Our Galaxy Figure 3. This simulation shows how a galaxy halo, like our own, may ...
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0answers
19 views

Polarization of an emission line

Say I have a flux density spectrum of a galaxy, as well as polarization spectra for the object in U, Q, and P. I want to find the polarization of some emission line in the spectrum. First, I can fit a ...
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2answers
128 views

Why is the Earth called terrestrial? Can we call the Earth an ocean planet?

Why is Earth called a terrestrial planet even though it is 70% covered by water?
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1answer
140 views

What is that light of the middle of the milky way galaxy?

I'm Being confused what is that light in the middle of milky way galaxy? Image is from Charting the Milky Way From the Inside Out The text with the image explains a lot about the spiral arms and the ...
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0answers
10 views

Clarity on dust extinction terms and implementation: R_V, A_V, and E(B-V)

I have created a model galaxy spectrum using STARBURST99 and want to compare it to an observed spectrum of a particular galaxy. I understand that I need to redden ...
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0answers
25 views

How to correct observed flux densities for redshift

Say I have a spectrum of a galaxy at a redshift $z$, in flux density units of erg/s/cm^2/Angstrom. I'd like to recover the spectrum (in the same flux density units) at z=0, i.e. at its rest ...
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0answers
17 views

How do you fit a model SED to an observed galaxy spectrum with photometric data?

I have a spectrum of a galaxy from HST data and SDSS data (resulting in a nearly continuous SED from the FUV~1000 Angstroms through infrared). I have created a model SED with the galaxy simulation ...
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0answers
29 views

Luminosity of the Milky Way compared to Seyfert galaxies

This page lists the total luminosity of the Milky Way Galaxy to be $4\times10^{10}$ $L_{sol}$, and $L_{sol}=3.86 \times10^{33}$ ergs.sec$^{-1}$; this gives a total luminosity for the MW of $1.54\...
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1answer
96 views

Can Fermi Bubbles be produced in non-spiral galaxies?

In 2010 observations with the Fermi Gamma-ray Space Telescope discovered giant bubbles which have been named Fermi Bubbles. Similar structures have also been discovered by Pshirkov et al. (2016) ...
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1answer
115 views

How to determine the mass of a galaxy?

I am having a slight disagreement with my professor. We can measure the mass of a distant star cluster from: A.Its color B.Its radius C.Its metallicity D.Smearing of lines in ...
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0answers
73 views

What pole is closer to the galactic edge? [duplicate]

Suppose 2 spaceships leave from the earth's north and South Pole going straight up which one will exit the galaxy first (assume they have the same speed and are going in a totally straight line) ? ...
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0answers
24 views

Can galaxy formation process explain Tully-Fisher relation in dark matter theory?

I read that, unlike MOND theory, Tully-Fisher relation is believed to result from galaxy formation in dark matter theory. What is the exact current status regarding the explanation of Tully-Fisher ...
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1answer
92 views

What is the farthest blueshifted object to our galaxy?

Is it also roughly the limit where gravity will be able to overcome space expansion? In other words, we can only hope to get to there, or at least see them, in the very far future?
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0answers
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Modeling Malmquist Bias [closed]

I am studying astrophysics on the side and came across this problem in the textbook: I am not quite sure how to approach it but I do know I need to account for the Malmquist bias to account for the ...
3
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2answers
145 views

Is gravitational lensing a good way to search for negative mass?

Is it possible to verify negative mass with gravitational lensing? The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4 Could this be ...
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0answers
45 views

Star rotational axes and Solar system orientations

How does the orientation of stars axes of rotation and any planetary systems relate to the plane of the galaxy? Is there any relationship that has been detected, are they grouped from their parental ...
3
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1answer
52 views

Stellar nurseries in the “Shedding New Light on the Whirlpool Galaxy” video

Captions in the Hubble Space Telescope YouTube channel video Shedding New Light on the Whirlpool Galaxy say: (visible) Along the dark dust lanes, bright pink nebulae are the birthplace of new stars....
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2answers
146 views

Why do we see galaxies with their actual spiral shapes?

Since the actual position of stars is relative, and we see the light they emitted long time ago, and one galaxy has thousands of millions of stars, and those stars can be separated by hundred of ...
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0answers
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How tightly clustered are the CHIME-detected FRB repeats?

In the past few days, journalists have been playing the usual "X could be aliens" game. This time, X is repeating FRBs from a galaxy 1.5 billion light years away. (Or is it 1.5 billion years ago? The ...
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2answers
82 views

Galactic mass estimation from apparent magnitude and distance

Can we estimate the order of the total mass of any galaxy from the apparent magnitude and its distance to us? Just like \begin{equation} M_{galaxy}=c\times 10^{8}M_{\odot }, \end{equation} where $c$ ...
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0answers
40 views

Deducing distance of closest neighbor galaxy from expression of correlation and mean galaxy density

The original post was on physics exchange but I prefer to move it here : I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors $\text{d}N$ into ...
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0answers
54 views

What is the bright star or planet in eastern sky on dec 18 2018? [duplicate]

What is the bright star or planet in eastern sky on Dec 18 2018 in Laurens SC. It is very bright and beautiful on a clear night. I have been seeing it for about a month or more. It seems to follow the ...
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0answers
68 views

Which direction does the Earth face as it travels through the Galaxy

According to the Helical model, as the Sun orbits around the galaxy, the planets that orbit the sun are travelling perpendicular to the path of the Sun. This is better shown in this video: https://...
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46 views

Compute the total stellar mass of galaxy with major influence of Red Giants luminosity

Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago If the luminosity in the B band (absolute magnitude in B-band is equal to -21.22) is dominated by ...
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1answer
36 views

From original burst, fraction of stellar mass still surviving on Main sequence

Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars ...
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1answer
40 views

number density of Dark Matter Halos Versus number density of Galaxies

Can we count only one dark matter halo for each Galaxy ? Indeed, I am trying to estimate the total density of galaxies in given volume and I have often seen on physics exchange and other forums the ...
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0answers
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Total number density of galaxies and problematic expression in practise

This post comes from physics exchange forum, I have transfered it here, maybe I will be luckier since I have not received answers on the other forum. Here is the issue : I am asked to give the ...
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0answers
34 views

What's the easiest way to get 3D-positional data of galaxies

Is there a database with cartesian coordinates (x, y, z) of galaxies? I only need positional data and calculating that using degrees and redshift for all galaxies could take a while and would be ...
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1answer
84 views

What would the night sky look like from a planet at the centre of a ring galaxy?

If there were an observer on a planet in the centre of a ring galaxy (omitting the galactic core) what could they expect to see in their night sky? I am currently under the impression that their night ...
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1answer
74 views

Can we learn anything from observing galaxies edge-on, like the Spindle Galaxy?

I was reading about NGC 5866, sometimes referred to as the Spindle Galaxy. It's notable because of its inclination relative to Earth; we see the disk from the side, rather than face-on. The difference ...
3
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2answers
205 views

Why is the metallicity of elliptical galaxies low?

As far as I understand, metallicities of old stars are usually low and those of new stars are usually high. If elliptical galaxies form after merger of galaxies, then surely that means the elliptical ...
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3answers
77 views

Catalog of Galaxies in the Visible Universe

I have seen the Gaia project from here which is about mapping the stars in the Milky Way galaxy. But I'm wondering if there is any open data on the positions (or something like "positions" since it ...
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0answers
51 views

How active was the Milky Way in its first 5 billion years?

When I look into the history of the Milky Way, it seems like the Milky Way has been the pinnacle of stability. It seems highly likely that our galaxy has eaten several smaller galaxies/dwarf galaxies ...
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0answers
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How the Galactic objects are moving? [duplicate]

We know that the Galaxies are moving very fast, not only the Galaxies other known and unknown objects in the universe, are moving. But when it was started where is the starting point, and how it move ...
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3answers
148 views

Does the rotation of galaxies precess?

Does the axis of a galaxy as a whole "wobble" the same way that the Earth does? If so do we have any idea how much or how fast the Milky Way is doing so?
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2answers
155 views

How much greater is the star density in our galactic bar?

How much denser is it in the galactic bar than the "normal" density at the same radius? Is it just a few percent? or is it, say, "three times" as dense? Or are other factors at play: star brightness,...
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0answers
46 views

Galactic rotation speeds - questions from a non-astronomer

Are there any observations that more distant galaxies appear to rotate more slowly than closer galaxies? What methods are used to measure the rotational speed of galaxies? (both orbital speed ...
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2answers
3k views

Do all galaxies have a black hole in the center?

Would I be correct if I stated that all galaxies have a black hole in the center? Since other galaxies orbit around a center point in a galaxy - the barycenter, right? - I would assume at this point ...
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0answers
38 views

What are the odds for any two bodies to collide during the milky way-Andromeda collision? [duplicate]

When the two main galaxies of the local group will collide, it is very unlikely for stars to collide with another, but how unlikely is it in the initial collision? And over the whole merging process?