# Questions tagged [galaxy]

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

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1 vote
13 views

### Mass resolution in cosmological simulations

I've been reading papers about different cosmological simulations and they all talk about the "mass resolution" of those. Can someone please explain what does "mass resolution" ...
1 vote
16 views

### Can this ppxf fit work?

I am trying to do kinematical analysis of spectra using ppxf-algorithm from Capellari. The velocity dispersion I get seems to be to high and I am not sure what the reason could be. On the website of ...
• 359
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### Kinematical galaxy spectral analysis using ppxf?

I am trying to implement an Fourier based algorithm to derive the kinematics of an elliptical galaxy. To check/reproduce my results I wanted to use the open source ppxf tool (https://pypi.org/project/...
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+100

### Evaluating Potentials using Galpy

I am trying to model galactic disks. From the past research we have discovered that the halo follows the logarithmic potential, the disk follows the Miyamoto-Nagai potential and the bulge follows the ...
57 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 ...
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1 vote
58 views

### redshift puzzle

I have the central line of the spectrum of an elliptical galaxy (NGC:4697) and a template K-star. I have calculated the redshift z by computing the crosscorrelation function between the galaxy and the ...
• 359
1 vote
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### Does the north pole of the Solar System (with respect to the invariable plane) point towards the galactic center?

How is our Solar System as a whole (not the wobbly Earth) tilted with respect to the invariable plane of the Milky Way? I understand our Sun's north pole is largely pointing towards our direction of ...
• 3,375
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### What is the sharpest stellar number density variation known?

In the solar neighborhood the stellar number density is about 0.14 stars per cubic parsec. This changes with a length scale of 220-450 pc as we move up or below the Milky Way disc, and 2.6 kpc ...
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### What are those stars that cross the galactic center?

I found this GIF by the European Southern Observatory (ESO) in the Wikipedia article on the galactic year, with the following description: Visualisation of the orbit of the Sun (yellow dot and white ...
• 1,402
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### How many stars can we resolve?

Wikipedia estimates the number of stars in the Milky Way at 100 to 400 billion. One of our most ambitious astrometry projects, Gaia, has been able to resolve and map almost 2 billion stars in the ...
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1 vote
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### Distribution function for distance to nearest stars from any given star in our galaxy

If I pick any random star in our galaxy, what is the mean & std dev of distances from that star to its, say, 5 nearest neighbors? As this distribution likely depends on the distance from the ...
• 3,578
1 vote
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### How do we measure the current positions of galaxies?

I do wonder how do we measure current position of galaxies since all the information transfer speed of the universe is limited by the light speed. My understanding is the we can only measure the ...
• 145
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### How could I see Andromeda as large as in this picture?

In this question an image is shown (repeated below) which gives an idea of the "true" angular extent of the Andromeda galaxy in our sky. When I see Andromeda it is usually a bit of a smudge ...
• 115k
1 vote
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### What object(s) are furthest above/below the galactic plane?

This is kind of a spin-off of a question I did about a space telescope surveying the galaxy from above the galactic plane. So, it made me wonder, which object in the Milky Way has been spotted ...
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1 vote
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### How far above the galactic plane would a telescope array need to be in order to image the whole galaxy?

I hope this isn't a stupid question, but Google searches are turning up nothing relevant. I was just thinking about how it's difficult for us to determine the true shape and composition of the Milky ...
• 615
1 vote
22 views

### Will the upcoming experiment PICO measure kSZ temperature anisotropy? [closed]

I know for sure PICO will be measuring polarization anisotropies with high fidelity. In addition, the PICO science paper shows that it will make full-sky Compton-y maps but the plots are mostly ...
• 49
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### How to fit LOSVD of a galaxy with gauss hermite parametrization

I have recovered the following LOSVD from an elliptical galaxy, that I now want to fit a gauss-hermite-parametrization to and derive the kinematical parameters rotational velocity, velocity dispersion ...
• 359
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### How to model galactic rotation curves?

I have R (kpc)- distance from galactic center and v(km/s) rotational speed at that distance. I was thinking of creating a simple model comprising of 3 terms 1 for Keplerian component another for rigid ...
67 views

### The plane of revolution of planets around the Sun, and that of the solar system around the center of Milky way

We claim to have understood much about our galaxy without going beyond even our solar system - which is just a small portion in one of the arms of the galaxy. I assume that the plane in which planets ...
• 187
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### Where can I find galaxy rotational data?

I want to do a small project of generating rotational curves for different galaxies, and need data for some prominent stars in other galaxies (data needed: distance from center, rotational velocity) ...
1 vote
145 views

### Calculating "maximum" distance to an alien civilization

I'm planning on making a video related to Fermi Paradox, and I've used Omni Calculator's Alien Civilization calculator as a reference. I noticed they have a field that calculates the "maximum&...
112 views

### Do any equivalent of Lagrange points exist between galaxies?

I'm wondering whether there is a similar effect between Galaxies as we have between a planet and it's star. I know there are tidal waves between galaxies and that gravity seems to always be attractive ...
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1 vote
206 views

### Do we live in a cosmic void?

Why is it thought that we live in a void, when there are so many galaxies around the Milky Way? There are galaxies close by and also far away, so where do they see a void that we are in?
• 1,523
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### How to build an adjacency matrix of stars connectivity from their physical kpc distances?

I'm probing into the Illustris API, and gathering information from a specific cosmos simulation, for a given redshift value. This is how I request the api: ...
• 153
1 vote
107 views

### Could life develop in a galaxy with a quasar at its centre?

Quasars are a type of Active Galactic Nucleus that inhabit the centres of some galaxies. They are among the most energetic objects known in the universe, emitting up to a thousand times the energy ...
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### Are new galaxies being formed and if so where?

When asked this question the answers tend to be evasive, dwelling on the development of existing galaxies by absorption. Are there nearby proto-galaxies or gas clouds expected to form a galaxy ...
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### Which galaxies have the most well known / estimated dark matter halos?

For this I guess you need accurate circular velocity measurements of the stars in the galaxy a decent luminosity profile for the galaxy some analysis which looks at the discrepancy between the two ...
29 views

### Pairs of galaxies that look like the Whirlpool-galaxy with companion?

I need examples of pairs of galaxies that look like the Whirlpool-galaxy with its companion NGC-5195. That is spirals with a companion galaxy attached to one arm, see picture below. I already know ...
80 views

### Reasons for extremely high number density of galaxies at low redshift

I am currently analyzing the SDSS data especially in the extremely low redshift area, in order to measure the cosmological statistics. What I mean by extremely low is z<0.1. One peculiarity that I ...
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### How are shockwaves used to study magnetic fields of merging galaxy clusters?

Recently i read an article about how a shockwave 60 times larger than milky way galaxy is generated.When these shockwaves interacts with magnetic field, radio waves are emitted. I wanted to know how ...
40 views

### What's the angle between the sun's galactic speed and the ecliptic?

I know the sun wobbles up and down the galactic plane around 35myr. I don't mind about that component. I'd like the know the angle between the linear speed of sun around the Milky Way (just the ...
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### How did Hubble know the red shift difference between "moving away" and "old"?

My 9yo daughter is very into space at the moment and asked a question that my physics knowledge (6th form college, 20 years ago) is way too poor to answer. Her space book tells us that as stars age, ...
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### In what ways does dark matter help in "binding" celestial bodies together in a Galaxy?

Earlier in history, it was said that the celestial bodies in galaxies were bound by "mutual gravity". There is still a common misconception that the gravity of supermassive black holes binds ...
• 2,595
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### Why do stellar-mass black holes fall to the centers of their galaxies? [duplicate]

This answer here says that black holes will "sink" to the centers of the galaxies they're in. How does this happen? It's not like there's a buoyant force in the vacuum of space. Shouldn't ...
• 1,394
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### Is it possible that a star is the center of a galaxy?

I read that the black hole at the center of the galaxy has much less mass than the galaxy itself and that it is somehow held together by dark matter. So now I am wondering if it is possible that there ...
• 141
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### Flashes in the Sky

Short Version: went camping into a very dark, remote location with clear air, no moon. Was able to see everything from the Pleiades and Orion, to the Southern Cross and the Magellanic Clouds (I live ...
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### Is there a tool to convert N-body RAMSES simulation file formats to GADGET 2 format in Python?

I am looking for a way to convert RAMSES files to GADGET-2 binary files because I want to use the package SimSpin (https://github.com/kateharborne/SimSpin/blob/master/R/make_simspin_file.R) which is ...
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### Databases for galaxy luminosity profiles and velocity rotation curves

I'm looking for databases of the following for a variety of different galaxies, but have so far struggled to find anything. Any help hugely appreciated. Firstly, I'm looking for observations which ...
1 vote
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### what is the difference between Composite Stellar Population and Galaxy Spectral Energy Distribution?

I am reading Conroy et al. (2013), an extensive review on Stellar Population Synthesis technique, and I really can't get the difference between Composite Stellar Population and Spectral Energy ...
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1 vote
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### Approximately what fraction of the galaxy's stars are in the bulge? [closed]

In the text of the question it is said to consider density uniformly
• 11
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### What is that stuff around Andromeda Galaxy

I know Andromeda Galaxy is one of the closest galaxies to our Milky Way, but there are photographs showing it to be surrounded by smaller bodies. Are there any that are closer, or are they all farther ...
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### What are some astrophotography editing options and strategies for taking photos of galaxies with a telescope and a cell phone?

We purchased a phone adapter for my sons telescope and got some amazing pictures, BUT we believe that they can be clearer. What is the best, or a really good, image editing program for amateur ...
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### Is our Milky Way galaxy (and its neighbors?) moving through the universe at 370 km/s (~828,000 mph) or 370 miles/sec (~1,332,000 mph)? [duplicate]

I swear that exactly half of the many, many sites I found say that our Galaxy and its immediate neighbors are moving towards the Leo Constellation (I believe) and, ultimately, supposedly, the 'Great ...
• 3,375
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### Why are Galaxy doppler Light Curves rising from the center of the Galaxy? Stars near the center of a Galaxy are moving faster than those near edge

Why are Galaxy Doppler Light Curves rising from a low point near the center of the Galaxy? Stars near the center of a Galaxy are moving faster than those near the edge. I understand that we probably ...
• 21
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### Measuring the mass of the luminous matter in a galaxy

The mass of total matter in a galaxy can be measured using the rotation curve of the galaxy. However, how do people determine the mass of luminous matter in the galaxy, as a function of the distance ...
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### how would you explain the motions in the solar system? [closed]

like so i don't get it it does not make sense I'm confused
1 vote
177 views

### Does dark energy make galaxies expand over long periods of time?

Does dark energy expand galaxies slightly over time? I would think this could be verified easily (observe if galaxies far away / further in the past smaller and denser), and might make a good ...
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1 vote
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### Is a black hole found in the centre of the low-surface-brightness and dark-matter-free galaxy AGC 114905

Per information found on Internet: AGC 114905 was discovered while observing the constellation Pisces with the VLA ground-based radio telescope. The galaxy is about 250 million light-years distant ...
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1 vote