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Questions tagged [galaxy]

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

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How to count observable number of galaxies at a given latitude considering interstellar extinction?

If galaxies are uniformly distributed in space, then in the absence of extinction, the number of galaxies per square degree brighter than magnitude m is given by $$\log_{N_0}(m) = 0.6m + C$$ How will ...
M. Islam Nafees's user avatar
2 votes
2 answers
173 views

Can we detect gravitational waves from galaxies merging?

How strong are the signals and how long do waves persist.Can ancient mergers be detected?
DaveTheWave's user avatar
1 vote
1 answer
243 views

Is this a galaxy?

I took a photo last night (Wed 3 July 2024) around 23:45 (BST) from a small town outside of Chesterfield, UK. I uploaded it to a site to identify the stars which is shown via the green annotations in ...
user7290573's user avatar
2 votes
0 answers
32 views

Dual mode in SExtractor

I wanted to use SExtractor for source detection. I have 7 NIRCam filter data from the JWST CEERS catalogue. How can i proceed with the source detection. I read about using dual image mode in which a ...
Walker's user avatar
  • 51
0 votes
1 answer
71 views

Using SExtractor for JWST data

I am new to this tool for catalogue creation(SExtractor). I want to know about how to set parameters for the extraction for JWST data. The parameter file looks like this. ...
Walker's user avatar
  • 51
0 votes
0 answers
24 views

calculating the color of a galaxy and making the k correction

I want to know if this is correct: I have in my dataset: $u_{mag}, u_{mag_{err}}, r_{mag}, r_{mag_{err}}$ Calculating the $u_{r_{color}}$: $u_{r_{color}} = u_{mag} - r_{mag}$ $u_{r_{color_{err}}} = u_{...
sky's user avatar
  • 1
1 vote
1 answer
85 views

Are the rotational axes of galaxies ever aligned?

My friend thinks that the expansion of the the universe should cause the galaxies on the same side of the sky to be aligned. I don't believe that because I haven't seen any evidence of it, but he came ...
Miss_Understands's user avatar
0 votes
1 answer
74 views

What is a "re-simulation"?

In the context of galaxy formation and evolution simulations, what is a re-simulation and how is it different from a simulation?
eneguev's user avatar
  • 37
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0 answers
42 views

Finding the algular size of galaxy cluster when given the RA and dec cordinates of all the galaxies in the cluster

I have the RA and dec values of all the galaxies in a cluster and i need to find its angular size i do not know how to calculate it
Meredith Grey's user avatar
13 votes
2 answers
1k views

Why is the metallicity of dwarf galaxies low?

The "Astronomy Picture of the Day" today sent me down a rabbit-hole. It had a picture of Leo I, with a note that it may have a supermassive black hole at the center, so I went to Wikipedia ...
Rich Jensen's user avatar
0 votes
1 answer
74 views

The distribution of mass in the bullet cluster

Can someone point me to a database which contains the luminous and gas mass distribution of the bullet cluster?
Angela's user avatar
  • 221
1 vote
1 answer
109 views

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
2 votes
2 answers
121 views

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
  • 373
4 votes
1 answer
55 views

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
  • 43
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0 answers
24 views

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
262 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
  • 167
16 votes
1 answer
3k views

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
247 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
101 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
113 views

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
2 votes
0 answers
34 views

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
  • 21
0 votes
1 answer
179 views

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
944 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 ...
Hudjefa's user avatar
  • 355
0 votes
0 answers
46 views

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
0 answers
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?
user avatar
1 vote
1 answer
83 views

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
235 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
  • 24.1k
1 vote
1 answer
80 views

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
  • 221
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
181 views

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
0 votes
0 answers
50 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
  • 221
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
  • 121
3 votes
1 answer
118 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
95 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
  • 221
3 votes
0 answers
104 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
319 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
  • 1,619
3 votes
1 answer
57 views

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
99 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
  • 245
2 votes
0 answers
33 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
47 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
102 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
189 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
245 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
  • 161
1 vote
0 answers
49 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
191 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
240 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

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