Questions tagged [galaxy]
Questions regarding systems of large numbers of stars held together by gravity.
724
questions
1
vote
1
answer
46
views
How do I find out when sidereal time was 13:30 on a certain date and location?
I live in Lehi Utah and I want to know what time of day it was on sidereal time on a birthday of 2/25/23 Someone said it was 3:32 AM and I wanted to check and see if that was true.. Thanks so much
- 21
0
votes
1
answer
44
views
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 ...
- 711
2
votes
3
answers
176
views
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 ...
0
votes
2
answers
101
views
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 ...
- 1
1
vote
1
answer
40
views
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 ...
- 229
0
votes
0
answers
44
views
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 ...
3
votes
0
answers
38
views
Databases of measurements of galaxies
Where can I download databases on measurements of points in galaxies, for example, as in the attached pictures?
1
vote
0
answers
18
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 ...
- 121
1
vote
0
answers
28
views
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, ...
- 11
1
vote
1
answer
46
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 ...
- 121
0
votes
1
answer
44
views
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 ...
2
votes
0
answers
77
views
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 ...
- 21
1
vote
0
answers
41
views
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 ...
- 11
0
votes
0
answers
17
views
How to reproject a fits file using MontagePy
I am fairly new to image reprojection so I am trying to use MontagePy to go from a bigger fits file to its smaller subsection (which is in a different observation, therefore header) but the output ...
- 1
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 ...
- 3,364
13
votes
9
answers
6k
views
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 ...
- 149
2
votes
0
answers
36
views
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, ...
- 2,394
2
votes
1
answer
95
views
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 ...
- 31
1
vote
1
answer
44
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:
...
1
vote
0
answers
63
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 ...
- 711
1
vote
1
answer
87
views
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 ...
- 341
2
votes
0
answers
43
views
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/...
- 711
5
votes
2
answers
84
views
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 ...
- 711
4
votes
1
answer
89
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 ...
- 519
1
vote
1
answer
101
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 ...
4
votes
1
answer
210
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)
...
- 698
4
votes
1
answer
72
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 ...
3
votes
1
answer
46
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 ...
- 341
3
votes
0
answers
148
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 ...
- 31
1
vote
0
answers
25
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 ...
- 341
5
votes
1
answer
90
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 ...
5
votes
1
answer
142
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 ...
- 698
6
votes
0
answers
87
views
How many galaxies are currently merging?
On the homepage of the galaxies research group at CfA SAO, it states, "Astronomers discovered that as many as 25% of galaxies are currently merging with others." They do not provide a ...
- 4,309
11
votes
1
answer
2k
views
What is the mathematical condition for the statement: "gravitationally bound"?
When talking about galaxy clusters there is the frequently used phrase "gravitationally bound", f.e. we are gravitationally bound to our neighbor galaxy the Andromeda Galaxy. But how is this ...
- 711
2
votes
0
answers
36
views
Different types of line broadening in stellar and galactic spectra
When analyzing stellar and galactic spectra with spectrographs, the spectral lines get broadened from the instrument. Why do the spectral lines get broadened after the light moves through the ...
- 711
7
votes
1
answer
101
views
How could ultracompact galaxies form?
Normally, most galaxies such as our Milky Way tend to be diffused. Sure, the Milky Way, for example has 400 billion stars, but it is spread out over 150,000 light years. Which means that the Milky Way ...
1
vote
0
answers
64
views
Deriving the Tully-Fisher relation from the virial theorem
So I know this is a loose proof and a lot of assumptions are made, but I do not understand how these assumptions lead to the quantities we obtain so I will be asking questions at each step:
start with ...
- 171
4
votes
2
answers
306
views
Are there any (rough) estimates of stars' orbits around the galaxy?
The Sun orbits approximately 26,000 light years away from the galactic center. Are there any other known orbital parameters relative to the galactic plane for the Sun and other stars up to some ...
- 6,474
14
votes
8
answers
9k
views
How did the Milky Way quasar not disrupt terrestrial life?
According to most sources of information I have found (A Quora Link and books), when galaxies become quasars, they destroy all life in their host galaxy, as they output so much radiation that they can ...
7
votes
1
answer
3k
views
Is it possible for the Milky Way and Andromeda to get ejected upon colliding instead of merging?
The Milky Way and Andromeda are destined to collide and merge within the next 4-5 billion years, but I feel like there could be a chance that instead of merging, they could just eject each other. I ...
- 596
4
votes
1
answer
2k
views
What is this yellow star?
In NASAs's August 26 2022 photo of NGC 1156:
Does anyone know what the incredibly bright yellow star is on the middle right?
Bonus: What's the bright (less bright than the yellow one) blue yellow ...
- 2,080
3
votes
2
answers
219
views
How can I convert a galaxy arcmin to light years?
https://en.wikipedia.org/wiki/List_of_largest_galaxies
says galaxy ESO 383-76 has a MA diameter of 1,764,000 light years based on information from
https://ned.ipac.caltech.edu/cgi-bin/objsearch?...
- 1,271
5
votes
1
answer
413
views
What are the blue "stars"?
From NASA September 16 Hubble studies a spectacular spiral:
There are 4 really bright blue stars in this photo of galaxy NGC 1961. For those who can't see them very clearly, you can focus on the ...
- 2,080
2
votes
1
answer
133
views
If a supernova explodes all it's comets into space, can they reach a big number of star systems?
If there's DNA life that arises on a warm planet 2 billion years after the big bang, and meteorite collisions on the planet propagate DNA unicellular organisms into millions of icy rocks orbiting the ...
- 4,098
6
votes
1
answer
382
views
What parameters of the Big Bang model will have to be adjusted to account for JWST's observations of highly redshifted galaxies?
There are a lot of claims, on YouTube at least, that the James Webb space telescope have found too many to old/highly redshifted normal looking galaxies to fit easily into the Big Bang model.
One such ...
- 467
7
votes
1
answer
553
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 ...
- 233
3
votes
1
answer
25
views
RAMSES fine multigrid Poisson solver fails to converge?
I am working on setting up N-body simulations of galaxy mergers. The initial conditions are generated from the DICE code, and looking at them, they seem very realistic. Unfortunately, when I let ...
- 151
8
votes
1
answer
3k
views
Can a photon orbit around a galaxy?
There are a lot of questions about photons orbitting a black hole, but I'm interested if a photon can orbit a galaxy. Our Milky Way for example has a radius of 52000 light years (according to Google) ...
- 191
3
votes
1
answer
79
views
How does instrumental dispersion work?
I am trying to understand the mathematical formulation of instrumental dispersion in galaxy and star spectra. Let $x=ln(\lambda)$. Assuming that the galaxy spectra G(x) is composed of many identical ...
- 711
3
votes
1
answer
193
views
What is mass-weighted age?
This seems to be a common term used in the field of stellar populations and galaxy evolution, but I can't find a good definition besides the fact that it is different from light-weighted age (a term I ...
