Questions tagged [galaxy]

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

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How can I convert luminosity from [erg/s/Hz] to [erg/s]

I have the dust-corrected luminosity in the Ks band in the unit erg/s/Hz. I want to convert it to erg/s. I would like to know which method is correct: $L[erg/s]=L[erg/s/Hz]\times(C/\lambda)$ $L[erg/s]...
Fatemeh Abedini's user avatar
1 vote
1 answer
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Does anybody know of a top down map of andromeda in the style of existing (artistic) milky way maps?

I'm looking to make a digital model of the local group of galaxies and I can't find a good representation of the Andromeda galaxy from a top-down view.
warcrimeswilly's user avatar
13 votes
1 answer
1k views

Are galaxies growing, shrinking or stable?

When I look at spiral galaxies they look a bit like the whirlpool of water going down a sink and I wonder if eventually they shrink to a small point (or a giant black hole?). On the other hand they ...
KDP's user avatar
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Efficient method for generating combined spectra from N-body simulation data using Python (convolution)

(I asked this same question also in StackOverflow, due to being both astronomy/coding problem, here link : https://stackoverflow.com/questions/78166419/efficient-method-for-generating-combined-spectra-...
mamark's user avatar
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Deriving Faber-Jackson Relation from Milgrom's Law

I am reading Famaey & McGaugh 2011, a review paper on Modified Newtonian Dynamics. My question concerns bullet 3 in Sec 5.2, where the authors try to explain how Faber-Jackson Relation can be ...
Ambica Govind's user avatar
4 votes
1 answer
183 views

Voyager spacecraft distance from Earth

According with NASA JPL the earth catches up with the spacecraft because Earth is moving a lot faster than the spacecraft. Can one calculate the times when the spacecraft gets closest to Earth
dimitri33's user avatar
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How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

I just came across a New York Times article talking about a newly found Low Surface Brightness (LSB) galaxy (also called “ultra-diffuse galaxies” or “dark galaxies”). The new galaxy, J0613+52, was ...
Curious Layman's user avatar
5 votes
2 answers
238 views

What simulator would I use to create an image of what our solar system looks like from Alpha Centauri?

The wikipedia article on Alpha Centauri has an image of that system from earth. I'm hoping to make the opposite image. I realize that there are various discussion of roughly what it would look like (e....
jackisquizzical's user avatar
2 votes
2 answers
77 views

Where can I find the $\mu$ value in galaxy clusters for ideal gas law?

I am studying hydrostatic equilibrium in galaxy clusters and encountered the following expression: $P=(kT/\mu m_p)\rho$ The interpretation of this formula is obvious. It is just the ideal gas law ...
Youngsub Yoon's user avatar
2 votes
1 answer
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Do we know two neighbor galaxies that are parallel?

Do we know two galaxies where the plane of their orbit is (almost) parallel and one is the neighbor galaxy of the other, or doesn't that exist? Almost co-planar: +/- 5° Neighbor galaxy: one galaxy is ...
Thomas Weller's user avatar
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Baryonic Tully Fisher Relation slope

I'm studying the Baryonic Tully-Fisher relation. In the textbook I'm reading there is written that in order to construct this relation, one needs to derive a stellar mass, obtained for example by ...
Al01's user avatar
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How fast is Andromeda approaching in miles per hour

Apparently Andromeda is going to get here in 5 billion years and is 2.5 million light years away. I tried to work this out myself but I'm not sure I believe the answer..
Michael Mcgarry's user avatar
4 votes
2 answers
836 views

Spiral Galaxies

I only have a very, very, basic understanding of linear motion, much less so of circular motion. What I can recall is my book telling me if you spin a stone tied to the end of a string and the string ...
Agent Smith's user avatar
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Consistent values for density of galaxies between degree squared and steradian

I have a table of densities of galaxies : Expected number density of galaxies for photometric survey per unit area and redshift intervals, $\mathrm{d} N / \mathrm{d} \Omega \mathrm{d} z\left[\mathrm{...
guizmo133's user avatar
1 vote
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61 views

What happens when two galaxies each with relativistic jets collide?

Would the relativistic jets create new particles where they meet and would all the gas from the two accretion discs be blown away leaving just two black holes?
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1 vote
1 answer
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Why does the metallicity of stars decrease with increasing galactocentric radius and height above the galactic plane?

Metallicity decreases with the Galactocentric radius and height above the Galactic plane (Bergemann et al. 2014; Duong et al. 2018). https://www.aanda.org/articles/aa/abs/2014/05/aa23456-14/aa23456-14....
user avatar
3 votes
2 answers
228 views

how to make postage stamps of galaxies

I am trying to follow the work in this paper, Reproducible k-means clustering in galaxy feature data from the GAMA survey, and I noticed that there are a few postage stamps of some galaxies. I am not ...
user3236841's user avatar
13 votes
1 answer
3k views

How do Spiral Galaxies become flat?

Our galaxy has been described as roughly the shape of a pizza and the Andromeda galaxy, though I've never heard it described that way, appears similarly disk shaped. Spiral galaxies make up (roughly) ...
userLTK's user avatar
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1 vote
1 answer
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Gas mass and velocity in galaxy

I was going through the SPARC data on galaxies (http://astroweb.cwru.edu/SPARC/) The velocity of gas in the SPARC data is in http://astroweb.cwru.edu/SPARC/MassModels_Lelli2016c.mrt The gas velocity ...
Angela's user avatar
  • 201
2 votes
7 answers
5k views

Could a galaxy be the sun of a planet?

For the purpose of science fiction, could an entire galaxy essentially be a planet's equivalent to our Sun for Earth? If a planet were far enough away from other objects in the galaxy but still ...
Gatoyu's user avatar
  • 160
2 votes
1 answer
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Measuring magnitudes in ds9

I'm currently working on a project which involves measuring several Cepheids to determine the distance to a galaxy. I have been using 12 images from the Hubble telescope taken over a period of about a ...
ergoldan675's user avatar
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43 views

calculating mass of galaxy from luminosity

A very elementary question, just to make sure I got this thing right. Suppose we are given that the mass to luminosity ratio of a galaxy is $2 \frac{M_{\odot}}{L_{\odot}}$. Let us say, that the ...
Angela's user avatar
  • 201
2 votes
0 answers
53 views

Are there any galaxies that spin "out of balance" as wet towels sometimes do in the washing machine spin cycle?

Can a spinning galaxy be "out of balance" like wet towels in the spin-cycle?
TimR's user avatar
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3 votes
1 answer
109 views

Distribution of Galaxy sizes (star count)

First off, I realize how hard this is to even come close to estimating, but I'm trying to get a "general feel" for the distribution of galaxies by star count. I realize everything from rogue ...
Cameron Critchlow's user avatar
2 votes
0 answers
94 views

Orientation of the Dark Matter Halo in Andromeda Galaxy

In this paper: https://iopscience.iop.org/article/10.1088/0004-637X/789/1/62#apj496316t3 Refer to the Discussion and Concluding Remarks section. It says, "This result also indicates that the ...
Angela's user avatar
  • 201
3 votes
0 answers
88 views

SExtractor parameters for identifying Star Forming regions

I am using SExtractor (Source Extractor) to identify Star-Forming regions in a galaxy. The problem is I am unable to choose the parameters required for it. SExtractor is just a tool to identify the ...
Abhinna Sundar's user avatar
0 votes
2 answers
155 views

Why is the Milky Way today about the same diameter as the visible universe was when recombination happened 378000 years after the Big Bang?

Has the Milky Way undergone an expansion of space time independent of the universe as a whole or did the gas that created the Milky Way heat up and expand? Whatever the answer, why the current ...
user avatar
-5 votes
1 answer
237 views

Has the "Big Bang" theory been disproven?

The Space telescope has detected some mature Galaxies close to the edge of the Universe. That means that they had formed more than 13.8 billion years ago . If the Big Bang occurred, then we would see ...
Peter U's user avatar
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3 votes
1 answer
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Is it possible to detect lyman alpha blobs (LABs) with the lyman-break method?

LABs are luminous extended nebulae of hydrogen gas in the early universe (z ≥ 3) found in overdensities of LAEs (lyman-alpha emitters) and LBGs (lyman-break galaxies). I was wondering if LABs could be ...
Ankit Biswas's user avatar
3 votes
2 answers
97 views

Is the object mass distribution different for galaxies of different diameter?

Let's say we compare two elliptic/spiral galaxies with the bigger having a diameter 100 times the smaller. Now we count every separated object inside them and classify them into mass categories e.g. $...
J. Doe's user avatar
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2 votes
0 answers
32 views

Sloan Digital Sky Survey - Obtaining Spectral and Photometric Datasets

I am working on a soft computing (fuzzy logic), genetic algorithm, explainable AI (XAI) classification system for astronomical objects from the Sloan Digital Sky Survey. The dataset I am currently ...
todd45040's user avatar
1 vote
1 answer
45 views

Elliptical galaxy classification

The elliptical galaxy (Hubble) classification goes from E0 to E7, with E0 being spherical and E7 being the most flattened. I understand that the angle at which the elliptical is viewed affects this ...
user374355's user avatar
0 votes
2 answers
100 views

Galaxies contracting

How fast is our galaxy contracting? Could our "expanding universe" measure actually be a measure of how fast our galaxy is contracting from other contracting galaxies. Thank you .
Justathought's user avatar
1 vote
1 answer
49 views

Do researchers create their own convolutional neural network models for their work or do they use existing ones (e.g. YOLO, detectron2, etc)

When a researcher first decides to use AI to solve a basic classification problem, such as training a neural network to determine the morphology of a galaxy, are they more likely to start by using ...
Chris K.'s user avatar
1 vote
1 answer
142 views

How to get star position from the Gaia data set?

I’m trying to recreate the Milky Way as a particle system inside Houdini, and I wanted to explore using the Gaia data as a starting point. I’ve downloaded an example source file from the data set but ...
kinkersnick's user avatar
5 votes
1 answer
234 views

What do we know about properties of individual stars in the Andromeda Galaxy?

According to the answers to Visible Stars in Andromeda Galaxy, is it possible to distinguish between different stars in Andromeda galaxy. What I am curious about is how much information are we able to ...
Presto's user avatar
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1 vote
0 answers
45 views

Where to find data about as many stars as possible?

I need computer-readable data about as many stars as possible, with their: distance to the Earth (or Sun), their masses, and if possible: coordinates, age, brightness distance to the center (...
Dimitre Novatchev's user avatar
1 vote
1 answer
138 views

What is the relation between column density and surface density of neutral hydrogen gas HI?

I know the column density distribution of neutral hydrogen gas (units: cm^-2). I want to calculate the corresponding surface density distribution of the neutral hydrogen gas (units: M_solar/pc^2). How ...
SlightDecoy's user avatar
3 votes
1 answer
226 views

Could macroscopic primordial black holes have created metals shortly after the big bang?

After seeing articles about the JWST like these two: https://news.cornell.edu/stories/2023/02/astronomers-discover-metal-rich-galaxies-early-universe https://www.livescience.com/james-webb-space-...
Nathan Stanton's user avatar
3 votes
1 answer
323 views

As redshift increases are there more large galaxies from mergers because there was less dark energy in the past?

Dark energy moves galaxies apart.Is this reflected in an increasing number of large galaxies as redshift increases and dark energy decreases?
user avatar
1 vote
0 answers
18 views

How to obtain the SDSS’s five-part imaging ID number for a list of galaxies whose Ra Dec is known?

I am trying to obtain the FITS file of a few hundreds galaxy from SDSS DR12 Survey. SDSS tries to download the FITS File with the link that contains the information about SDSS’s five-part imaging ID ...
B. S.'s user avatar
  • 11
0 votes
0 answers
38 views

Finding Position angle and ellipticity to Deproject galaxy image using IRAF

I am trying to obtain position angle and ellipticity for a galaxy image by fitting elliptic isophotes using IRAF routine stsdas.isophote.ellipse package. After fitting the isophotes, I have a table ...
B. S.'s user avatar
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4 votes
2 answers
146 views

Can the collapse of a gas cloud lead to an elliptical structure?

Is it likely, unlikely, or impossible for an elliptical structure to form when a gas cloud collapses? Due to the conservation of angular momentum, one would expect that disk structures are much more ...
trynerror's user avatar
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3 votes
0 answers
45 views

Has the missing dark matter in some galaxies been explained yet? [duplicate]

There are galaxies that should have dark matter to explain their existence but they do not. "Mystery of Galaxy's Missing Dark Matter Deepens | NASA" https://www.nasa.gov/feature/goddard/2021/...
user avatar
0 votes
1 answer
41 views

What is the unit of the correlation function between logarithmically rebinned galaxy spectrum and stellar template spectrum?

Assume I have a logarithmically rebinned galactic spectrum $G(x)$ and a stellar template spectrum $S(x)$, where $x = \ln{\lambda}$. When $[\lambda] = 1 Å$, then $[x] = 1 Np/Å$. The fourier transformed ...
trynerror's user avatar
  • 849
1 vote
1 answer
124 views

How does superfluid dark matter keep stars orbiting at high speeds in galaxies?

According to A paper on Ultra-Light Dark Matter, Superfluid dark matter is a kind of Bose-Einstein condensate. But how does it help stars keep their high or velocities in galaxies. Can somebody ...
user avatar
3 votes
1 answer
135 views

When two galaxies with dark matter halos merge do they provide evidence for fermionic or bosonic dark matter?

If dark matter is made from fermions these should collide and cause dark matter to become denser in some places than others Bosons wont collide in this way so there should a different effect .So is ...
user avatar
3 votes
1 answer
771 views

Can someone explain the strange case of NGC 4319 and Markarian 205 and its controversial redshifts and later convinced by reddening?

(source) When they saw in neutral hydrogen wavelength they saw a neutral hydrogen bridge, while the Hubble Space Telescope concluded that the light from the quasar was redshifted. So if it's ...
starwatcher_65's user avatar
0 votes
1 answer
72 views

If a supernova explodes close to the centre of the milky way does its light get blueshifted by dark matter by the time it reaches the Earth?

Does the dark matter halo of the milky way cause most of the change in wavelength or is baryonic matter responsible?
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0 votes
0 answers
61 views

Creating a small data pipeline

I wanted to create a small data pipeline such that it consists of images of sky in the filters F125W, F160W, F606W and F850LP. The 4 images for a single object should be in a single FITS File which ...
Astrophile's user avatar

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