Questions tagged [galaxy]

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

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2
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0answers
87 views

What is the meaning of ellipticity of a galaxy being more than 1?

I was recently doing a project on calculating ellipticities of galaxies using SDSS data. I downloaded the stokes parameter values (q and u) from data $e = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + ...
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1answer
75 views

Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy). I ...
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1answer
176 views

Will intergalactic travel be impossible in roughly 15 billion years?

Even if we (or aliens somewhere in the universe living at that time) somehow invent something that can go just short of the speed of light, will intergalactic travel still be impossible in roughly 15 ...
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80 views

What decides the shape of a galaxy?

As I know, most galaxies are spiral, some elliptical, and a rare type is ring-shaped. What causes a galaxy to become a specific shape (i.e. ring vs spiral)?
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1answer
683 views

Are there galaxies with 2 or more super massive black holes orbiting each other?

We now know that most stellar systems have 2 or more stars orbiting each other. Do we know of any galaxies which have 2 or more super massive black holes orbiting each other? Is it possible?
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5answers
133 views

What kills us in the event of two galaxies combining?

I find the joining of galaxies interesting as the two eventually become ONE. On series I saw on a discovery channel stated we die. Everyone dies. What is it that causes us to die when the galaxies ...
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28 views

SMC and the Milky Way

Do astronomers have any reason to believe that the Small Magellanic Cloud (SMC) collided with the Milky Way? If so, how do astronomers think about the concept of collision? Would a collision only ...
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4answers
181 views

Could the solar system survive in a void?

If the solar system were suddenly placed in the middle of a large void... would everything still function as normal? Would we even notice any difference here on Earth apart from the night sky? ......
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2answers
3k views

Which star / galaxy is moving away from us the fastest?

I know that we have measured the rate a lot of stars and galaxies move away from us using the doppler shift, and I know that the further a star / galaxy is the faster they accelerate away from us due ...
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Cosmology : Formula for the bias of galaxies

first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
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2answers
94 views

Sagittarius star cloud?

I was using SkySafari with my phone, but the compass didn't quite work. So as I knew where the cardinal points were, I think I have shot the Sagittarius star cloud, at least a part of it. Can you ...
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3answers
9k views

Does the Milky Way orbit around anything?

We know most of the objects in the Universe have a spherical or elliptical shape. The object which has less mass and gravitational pull orbits around the nearest object with more mass and ...
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Q: Calculating the luminosity of a galaxy

I am currently working on a project on which I am calculating the luminosity of galaxies by using the SDSS data. They use a system of asinh magnitudes, and according to their website they use a system ...
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0answers
33 views

Number of obscured AGN compared to unobscured AGN

Urry and Padovani 1995 proposed a unified model for Active Galactic Nuclei, which has since been recognised as a good model for AGN. If AGN are randomly oriented, then I'd expect there to be more ...
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43 views

How to calculate the distance to galaxies with standard candles?

I was wondering how the distance in Mpc could be calculated between Earth and a galaxy using the luminosity provided? Do not be shy to use all math necessary :)
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1answer
296 views

Where can I find a database of galactic spectra?

I was wondering where spectra of galaxies at various redshifts are to be found. I'm looking for ones that can be used to find the recessional velocity of the galaxy and eventually the Hubble Constant. ...
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1answer
60 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
74 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
42 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
98 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
65 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
214 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
24 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
40 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
42 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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38 views

Universe as 3D projective space? [closed]

Is there any benefit to view the 3D (real) universe as 3D projective space?
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1answer
48 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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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
137 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
213 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
12 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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1answer
97 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
23 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
40 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
108 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
122 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
27 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
100 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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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
151 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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1answer
70 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 ...
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1answer
53 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
148 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
95 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
42 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
69 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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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 ...