Questions tagged [galaxy]

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

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12 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 ...
4 votes
1 answer
41 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-...
4 votes
1 answer
173 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
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 ...
0 votes
0 answers
21 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 ...
2 votes
1 answer
119 views

How to use SExtractor to calculate Petrosian Radius?

I'm using Sextractor to run some benchmarks on the code I'm working on. I'm mainly focused on Petrosial Radius (PETRO_RADIUS). I have two main questions that I could not find in the documentation: ...
3 votes
1 answer
219 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-...
5 votes
2 answers
234 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....
3 votes
1 answer
106 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 ...
2 votes
2 answers
67 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 ...
21 votes
7 answers
4k views

Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
18 votes
3 answers
418 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?
2 votes
1 answer
108 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 ...
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 ...
3 votes
2 answers
223 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 ...
0 votes
1 answer
148 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..
4 votes
2 answers
700 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 ...
0 votes
0 answers
44 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{...
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?
6 votes
2 answers
720 views

Is there a rough analytical expression for the Milky Way's radial mass distribution?

I found the image below in Space.com's article This 3D Color Map of 1.7 Billion Stars in the Milky Way Is the Best Ever Made, although it is not the map mentioned in the title. The caption for this ...
1 vote
1 answer
79 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....
4 votes
4 answers
836 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? ......
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) ...
1 vote
1 answer
76 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 ...
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 ...
2 votes
1 answer
147 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 ...
0 votes
0 answers
42 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 ...
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?
4 votes
1 answer
313 views

What is the current angle of motion of the sun with respect to the Galactic Plane?

I understand that the solar system oscillates in its motion around the Milky Way. However at any given time, there must be a specific angle between the current direction of the solar apex and the ...
1 vote
1 answer
81 views

Nearest spiral barred galaxy undergoing interaction

Which is the nearest spiral barred galaxy undergoing interaction, other than M31 (Andromeda) and our own Milky Way galaxy?
1 vote
6 answers
764 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 ...
2 votes
0 answers
93 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 ...
3 votes
0 answers
82 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 ...
0 votes
2 answers
154 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 ...
0 votes
2 answers
381 views

How do we estimate the dimensions and mass distribution of a galaxy's dark matter halo, beyond the effective limits of its visible matter?

Current research suggests that the Milky Way's dark matter halo may extend up to about 10 - 15 times the size of the visible galaxy, and is believed to be roughly spherically symmetrical. But I don't ...
-5 votes
1 answer
215 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 ...
3 votes
1 answer
47 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 ...
3 votes
1 answer
131 views

What percentage of galaxies are isolated galaxies and what percentage are members of a cluster?

Some galaxies, such as NGC821 are classified as "isolated galaxies", others form parts of distinct groups or clusters (relevant link) Although isolated galaxies may be accompanied by small ...
5 votes
2 answers
2k views

Observing the motion of the solar system and galaxy through space?

This is very perplexing. Conditions: planets are moving around the sun (solar system) solar system is moving as part of the galaxy the galaxy is moving through space on some axis galaxy is part of a ...
3 votes
1 answer
162 views

Method to get data from NED IPAC and NVSS, without manually giving RA/dec input

I am collecting the radio flux data at 1.4Ghz frequency for all 1544 Markarian Galaxies for a study. For that, I have to first put the names of these Markarian galaxies in NED IPAC and from there ...
3 votes
2 answers
95 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. $...
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 ...
0 votes
2 answers
99 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 .
1 vote
1 answer
44 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 ...
1 vote
1 answer
48 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 ...
9 votes
1 answer
2k views

Is the Andromeda galaxy larger than the Milky Way or not?

The Wikipedia article on the Milky Way states that it has an estimated 100 to 400 billion stars. The one on the Andromeda states that it has about a trillion stars. With this, we can conclude that the ...
1 vote
1 answer
117 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 ...
5 votes
1 answer
230 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 ...
4 votes
2 answers
145 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 ...
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 (...

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