Questions tagged [galaxy]

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

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What courses should one take for working towards Astronomy from an AI / Data Analysis perspective?

Note:- This is a suggestions seeking question As a prospective student about to embark on pursuing the MEngg. in Applied AI program, I am eager to align my education with my passion for Astronomy. I ...
Hacker1's user avatar
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1 answer
201 views

What am I doing wrong in this ppxf application?

I am trying to derive the kinematics of a galaxy spectra. To test my results I want to implement the Penalized Pixel Fitting method. For the galaxy spectrum I use a central line with sufficient S/N. I ...
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Determining the rotation curve of a galaxy via given spectroscopic data

Here is the data analysis question from IOAA-2011, 1. Weighing a galaxy: The image 8.2 shows a photograph of the spiral galaxy NGC 7083, which lies at a distance of 40 Mpc, and image 8.3 a fragment of ...
samuraiwarrior's user avatar
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2 answers
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the sun - relationship between gravity and temperature

In the sun's core, we know it's very hot. I was curious to research why it was exactly and I think 99% of answers are not fully correct. They say that it's because of nuclear fusions. I'd not agree as ...
Giorgi Lagidze's user avatar
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sun - do gamma rays reach radiative zone

So in the sun's core, gamma rays are produced and right away, in the few milimetters, compton scattering happens. As I understand the compton effect, gamma ray will first collide with free electron, ...
Giorgi Lagidze's user avatar
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sun's core - how much x-rays get emitted

We know from the sun, we receive x-rays, gamma-rays but at a very small number of photons. Question 1: why not much ? is it because most of the x-rays are absorbed in a process of ionization of the ...
Giorgi Lagidze's user avatar
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Emitting light from the Sun [closed]

I might be asking too many questions here, but they all seem related to each other and knowing them simultaneously is the only way to understand this subject as I have tried my best googling already. ...
Giorgi Lagidze's user avatar
1 vote
1 answer
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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?
SlightDecoy's user avatar
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do we observe emission spectrum? [duplicate]

When light generated by the fusion in the sun goes through the layers of the sun and finally reaches outer layers and in the end atmosphere of the sun, we know it goes through hydrogen for example. ...
Matt's user avatar
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ultra diffuse galaxies and dark matter

There are ultra diffuse galaxies (UDGs) like, NGC 1052-DF2, NGC 1052-DF4, which seem to have very little dark matter. And on the other hand UDG dragongly 44 has lots of it. How many UDGs are known to ...
Angela's user avatar
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How can redshifted light be detected?

I've been reading about redshifts and it got me really curious. Basically, I want to figure out how we know light is redshifted and what's the original emitted light. I found the following question ...
Matt's user avatar
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Planet and star rotation through gas in the galaxy

If 10% of the galaxy is filled with gasses, and stars contribute to only 1%–2% of the total matter, then shouldn't the gas create friction for the movement of stars around the galactic center and also ...
Angela's user avatar
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What is the force that drives electrons along the magnetic filaments of galaxies?

"Milky Way's mysterious filaments have 'older, distant cousins'" https://www.techexplorist.com/milky-ways-mysterious-filaments-older-distant-cousins/54966/?amp=1 Quote from article: "...
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Cosmic background radiation - what frequency tells us?

I understand that cosmic microwave background radiation is remnant of the universe after 380,000y of the origin. To me, this radiation is still a wave which has a microwave frequency and I also ...
Giorgi Lagidze's user avatar
4 votes
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How does carbon end up in the remnants

We know that one way carbon ends up in the interstellar medium which by the way is one or the heavy elements that help form the planet. But we also know that in the core, carbons fuse with another ...
Giorgi Lagidze's user avatar
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Are there any hints in the CMB as to why the James Webb telescope is finding galaxies larger than expected in the early universe?

"James Webb telescope detects evidence of ancient ‘universe breaker’ galaxies | Astronomy | The Guardian" https://amp.theguardian.com/science/2023/feb/22/universe-breakers-james-webb-...
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Can the CMB Cold Spot be explained by dark matter redshifting photons?

One explanation for the Cold Spot in the cosmic microwave background (CMB) is that dark matter is redshifting CMB photons; see Fermilab's article "Scientists move a step closer to understanding ...
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3 votes
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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 ...
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5 votes
1 answer
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Are more stars or more galaxies cataloged, currently, and how has the ratio evolved over time?

I recall that there are of order 100 billion stars in a galaxy and 100 billion galaxies in the (observable) universe, or something roughly like that. Since we are IN a galaxy we have an opportunity to ...
uhoh's user avatar
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Have we discovered a Galaxy lacking in Dark matter?

This question is relevant but it was speaking about a specific discovery reported by pieter van Dokkum, and the answer then mentioned it was disputed whether the paper's conclusion is even correct. I ...
Hisham's user avatar
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How do I find out when sidereal time was 13:30 on a certain date and location?

I live in Lehi, Utah, USA and I want to know what time of day it was on sidereal time on February 25th, 2023. Someone said it was 3:32 AM and I wanted to check and see if that was true.
Lorin Bishop's user avatar
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2D Galaxy Spectrum taken by long-slit-spectrograph

I have the 2D data (shape(1125,2058) taken by a long slit spectrograph, which looks as follows: The y-axis corresponds to the distance from the center, where the center is at the most bright green ...
trynerror's user avatar
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2 votes
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How to calculate distance between stars?

I have data on nearby stars, including galactic coordinates and distance from Sun. And I have a dilemma. In a story I'm writing, I have two starfaring alien civilisations. One originates from a planet ...
Krišjānis Liepiņš's user avatar
2 votes
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Will the Milky Way galaxy revolve around the Andromeda galaxy or vice versa?

As all of you know, in the Milky Way galaxy, the Solar System revolves around the Milky Way to complete the Galactic year (because we have the supper massive black hole in our Milky Way galaxy) then ...
Pash0002's user avatar
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What parameters about galaxies can be measured using SAO DS9?

I am trying to determine and plot various parameters for galaxies on SAO DS9. RA & dec, angular size to a fair extent, and contour plotting are a few of the aspects which I could determine using ...
Dhruv Nayak's user avatar
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How to draw galactic coordinate grid?

For my story, I need a galaxy map with star positions in the galactic coordinate system. 2D with a view of the galaxy from above would be enough. I have gathered data from Atlas of the Universe and ...
Krišjānis Liepiņš's user avatar
1 vote
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23 views

Surface brightness of transparent vs opaque galaxies

When describing surface brightness of galaxies, I would imagine that in some wavelengths some galaxies are mostly transparent and in other wavelengths some are somewhat opaque (for example galaxies ...
user1247's user avatar
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Magnitude cuts in different bands/surveys

I have data on around 142,000 galaxies. Some of these galaxies have apparent magnitude data in different bands. For example, many of my galaxies have SDSS PSF data in ugriz bands,GALEX FUV, GALEX NUV, ...
Bobasheto's user avatar
1 vote
1 answer
49 views

Interpreting the color of galaxies in deep field images

The HST produced some deep field images in mostly visible light, which contain thousands of galaxies that range in color from white to red (e.g. see here). I understand that the interpretation of ...
user1247's user avatar
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Galaxy shape and time differentials

Can it really be said that something as large as a galaxy can have a "shape", which the positions of its constituent stars are their positions at various times in the past? A star 100K ly ...
Ray Walker's user avatar
2 votes
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How does one estimate the mass of a galaxy using the Balmer break region?

I am currently reading the recent astrophysical paper "A population of red massive galaxies ~600Myr after the Big Bang'. In the first paragraph/abstract it mentions, "It has been difficult ...
shram's user avatar
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Full Orientation of the Andromeda and Triangulum Galaxies

I can find the degree of inclination compared to Earth for both the Andromeda and Triangulum Galaxies wherever I search. For instance, the Triangulum Galaxy has an inclination of 54 degrees compared ...
Novaje's user avatar
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15 votes
3 answers
3k views

Is there more dark matter than we previously thought?

With the recent Nature publication showing that M dwarfs did not form in prior epochs as frequently as we had thought, what implications does this have on galaxy mass estimates and, by extension, the ...
Justin T's user avatar
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9 answers
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How do we know we're not getting bigger?

Alright so I've been thinking a lot about how the universe expands and I've always wondered if we're getting bigger as well. Since everything would be getting larger at an equal rate (tools of ...
Landon's user avatar
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What is the Chołoniewski method of estimating galaxy luminosity functions?

This paper describes a method to estimate the reddening of AGN using various methods, mostly to do with the intensity ratios of different absorption lines. It also mentions the Chołoniewski method, ...
Jim421616's user avatar
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2 votes
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What is the diameter of a telescope lens that will capture the surface of Proxima Centauri b?

I been trying to find the way I can calculate the telescope lens diameter needed to see a star by the distance of the star or the planet from the earth. Is there any mathematical relation we usually ...
xone-a's user avatar
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2 votes
1 answer
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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: ...
Igor Kolesnikov's user avatar
1 vote
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68 views

Which stars are elliptical galaxies constituted by?

I know that elliptical galaxies are old galaxies, with almost no star formation and an old stellar population. This can be seen by their dominantly red spectra in the optical. I am trying to get a ...
trynerror's user avatar
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1 vote
1 answer
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Expansion-Collapse cycle in cosmological structures?

Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by ...
vengaq's user avatar
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Formation scenarios for elliptical galaxies?

I am trying to get an overview of the latest research on different formation scenarios for elliptical galaxies and filter out old scenarios in the literature that are today proved to be not sufficient/...
trynerror's user avatar
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5 votes
2 answers
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What is meant by " elliptical galaxies stabilize due to the chaotic motion of stars"?

I read that elliptical galaxies stabilize due to the chaotic motion of stars. As I understand that means that the stellar motions are more nearly random in direction. So they perform independent ...
trynerror's user avatar
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5 votes
1 answer
184 views

What is the distance of the closeset galaxy outside our local group and what is its name?

The Milky Way is 2.5 million light years from Andromeda and the size of the Local Group has a diameter of approxmiately 10 million light years across. What is the distance from this Local Group to the ...
Sedumjoy's user avatar
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1 vote
1 answer
145 views

Galaxy plane and Earth's orbit. Connection to seasons?

From my understanding, the Earth (Solar System) crosses a center line of the galactic plane (ecliptic *edit wrong definition, sorry!), while orbiting around the Sun. The Sun also wobbles up and down ...
Michael Eccher's user avatar
4 votes
1 answer
217 views

Sky density of milky-way stars vs external galaxies

I am interested to know if any particular slice of sky contains more galaxies or more stars (in the milky way, although would be interested to factor in extra-galactic stars, and even rogue planets) ...
Rabbi Kaii's user avatar
4 votes
1 answer
161 views

What accounts for a Lyman-break for all wavelengths shorter than 91.2nm if the Lyman limit is the highest energy photon that neutral hydrogen absorbs?

From this description of Lyman-break galaxies, I don't understand how: ...radiation at higher energies than the Lyman limit at 912 Å is almost completely absorbed by neutral gas around star-forming ...
Rich McDaniel's user avatar
3 votes
1 answer
54 views

Can objects join the Hubble flow for a given amount of time and then somehow abandon it?

When two objects (e.g. two galaxies) are sufficiently far apart, they join the Hubble flow and they get further away from each other. Normally, this would last "forever" (until, from the ...
vengaq's user avatar
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3 votes
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174 views

How do star orbits, density wave theory and dark matter distribution work together?

I got confused while trying to combine these 3 concepts. Would love to hear some detailed explanation. Density wave theory states that spiral arms are formed by tilted elliptic orbits. Bertrand's ...
YaaZ's user avatar
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1 vote
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29 views

Are there any experiments or observations indicating that the Hubble flow can influence AGNs, quasars and galactic winds (outflows)?

Galactic winds (or outflows) are produced by AGNs (Active Galactic Nuclei), quasars, supernovas...etc which basically eject matter usually in form of waves or spheres, sometimes even arriving to the ...
vengaq's user avatar
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5 votes
1 answer
294 views

Surface Brightness Definition

I know the surface brightness is calculated by taking the apparent magnitude of an object and then divide by the size of the thing. But this is more of "observed" surface brightness, how do ...
JOAQUÍN HERNÁNDEZ's user avatar
5 votes
1 answer
153 views

Is it theoretically possible to see a spiral galaxy head on, and side on, if there is a convenient gravitational lensing effect?

I was thinking this when I heard Professor Mike Merrifield say something to the effect of "unfortunately we've never seen the same galaxy side on and head on, so we can compare notes on our ...
Rabbi Kaii's user avatar

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