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Questions tagged [galaxy]

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

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Average density of galactic filaments?

How many galaxies are typically in a galactic filament? Is there a known approximate minimum and maximum count?
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Do all galaxies have a black hole in the center?

Would I be correct if I stated that all galaxies have a black hole in the center? Since other galaxies orbit around a center point in a galaxy - the barycenter, right? - I would assume at this point ...
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What are the odds for any two bodies to collide during the milky way-Andromeda collision? [duplicate]

When the two main galaxies of the local group will collide, it is very unlikely for stars to collide with another, but how unlikely is it in the initial collision? And over the whole merging process?
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Are there any stars that one day we could collide with?

I'm not talking about tomorrow but in the far far future could we say our Sun could collide with another star or otherwise within our current detectable range?
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DSO carthesian coordinate estimations

I'm more in the CS based stack exchange, but this question prompted me to come in here. I've been compiling a large set of ephemerides for solar system, stars with mag > 6.8, exo planets etc, and I ...
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Could the Perseus Arm be a mini galaxy that has collided with Milk Way Galaxy?

Because Solar System has an inclination with respect to the galactic plane, is this possible or not?
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Movement of the Sun in space

Does the Sun undergo any cycles or revolutions approximately every 24,000 years or 8.6 million years? In Hinduism it is believed that the Sun revolves in an elliptical orbit around a large mass at ...
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1answer
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How can I estimate the M/L ratio from a fitted SED on a galaxy?

This answer (here in the forum) provides background to my question: https://astronomy.stackexchange.com/a/5953 I am trying to understand the process in which a stellar population synthesis (SPS) is ...
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Number Density of Dark Matter Halos

Is there a way to calculate the expected number density of Dark Matter Halos above a given mass, in a certain redshift range, and in a certain area?
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What would stargazing be like at the edge of our galaxy?

Let's say, for the sake of speculation, we acquire the technology necessary to travel to the outer edge of one of the spiral arms of our galaxy. We go to a star in this "outer rim" and land on a ...
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1answer
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Why is M87's relativistic jet bent?

The end of the relativistic jet that emerges from M87 looks curved like a hook. See here: Data from the VLA array show more of the jet: at the far end, the jet makes a complete 180 degree turn ...
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1answer
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What is the escape velocity of our Galaxy relative to?

I've been thinking that everything has a relative escape velocity, if it has Mass, seemingly. You can escape orbit around the earth by accelerating enough. You can escape the orbit of the sun by ...
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Studies of isotropy from different ends of the visible universe?

Have there been studies to compare structures that are 26 billion light years distant (i.e. from one side of the observable universe to the other) to search for faint differences?
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How bright is Andromeda's center, in magnitudes per square arcminute or something similar?

I'd like to know how bright the Andromeda galaxy's core is as an extended object, not the total integrated brightness. Ideally a contour map or scan across the center might show brightness in ...
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Is it possible to view the Andromeda galaxy with the naked eye in Greece?

I am living in the northern hemisphere in Greece and in class 4 area (light pollution scale). Is it possible to see the Andromeda galaxy with a naked eye?
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1answer
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What distance is considered 'close' for the 9th nearest neighbor of a galaxy?

I am currently working on determining the nth nearest neighbors of a large survey of galaxies. I am not an astronomer by trade, so I am unsure of interpreting some of my results. I have discovered for ...
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Why Tidal Tails in Disk Galaxies, but not in Ellipticals?

Why do tidal tails result from only disk galaxies but not ellipticals. I understand that tidal tails are results of gravitational interactions not strong enough to completely plunge out the material ...
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What does the ']' in the spectral line “CIII] 1909 Å” mean?

The above emission line, as I understand, is a useful probe of early star-forming galaxies. However, I do not understand what the ']' to the right of the 'CIII' means. I could not find any online ...
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Which galaxy is closest to the center of the KBC void?

I was reading up on Bootes void and came across this list of the largest voids in the visible universe, and apparently the one we're in, the KBC void, is not only the biggest, but damned-near ...
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Moving galaxies that exceed the speed of light [duplicate]

I read in a article that there are galaxies moving faster then the speed of light. My understanding of this that is not the galaxy that is moving away from us at the speed of light or faster, but the ...
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What factors determines the size of a galaxy?

Recently i saw a post comparing sizes of different galaxies with the Milky Way. The largest one being the Ic 1011.What makes this galaxy so large? What factors decide the size of a galaxy?
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Can “rogue” supermassive black holes be made this way?

Could two galaxies (one big and one small)intersect at a velocity to allow the smaller black hole to escape but not the galaxy around it?
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What is the fastest a galaxy or other body has been measured to (or can) travel?

Our solar system travels at an average speed of 515,000 mph and our galaxy at 1.3 million mph through space. What is the fastest moving body in space recorded and the fastest can a black hole or ...
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Are galaxies expanding away from us at more than the speed of light? [duplicate]

If you go to the following video, at this certain time: https://youtu.be/Iy7NzjCmUf0?t=435 you will see that the narrator says: "We simply don't know what else is out there because the light from ...
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How far would EGSY8p7 be away now?

Apparently EGSY8p7 is the object with the longest light travel distance, 13.2 gly or a redshift of z = 8.68 (Wikipedia). So the light took 13.2 billion years to travel to us from that object, but we ...
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1answer
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Escape velocity of Milky Way galaxy [duplicate]

I'm wondering that what would be the escape velocity of our Galaxy?
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Why do photos of Earth always have a black background?

if we are in the milky way, and people are able to take photographs from Earth that look like this: Then how come almost all of Earth's photos look like this? In the first photo, we are seeing what ...
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Are magnetic field lines Spiral for Spiral Galaxies? If no, then how it look like topologically?

I am an undergraduate doing summer project at USO. I am working on Sun's Magnetic field model. I got spiral graph for that, which looks like any spiral Galaxy. Do you think that there is some ...
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Efficiently calculating power spectra from galaxy catalogs

I am dealing with a problem which requires calculating either the correlation function or the power spectrum. At times, the 2-point-correlator seems the better route, at others, the PS. Right now I am ...
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Correctly scaling Power Spectrum and Correlation Function of Galaxies from Mock Catalogues

I'm currently writing a code to compute the two-point correlation function of a set of galaxies. As I work with a loooot of galaxies, it was suggested to me not to do it in real space, but to compute ...
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1answer
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Generating random galaxy catalogs for correlation functions

The galaxy correlation function, when computed directly from a galaxy catalog, relies on computing a randomly generated counterpart catalog. When dealing with a simulated galaxy mock-catalog, where ...
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What's the profound reason(s) why the star formation rate drives the scatter of the mass-metallicity relation in galaxies?

Since decades it's well known that a correlation between stellar mass and metallicity (Z; both stellar and gas-phase Z, but here I focus on the gas-phase Z) exists (e.g., Tremonti+04; analysis of >...
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2answers
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What other galaxies can be seen with the naked eye in the night sky?

What other galaxies can be seen with the naked eye in the night sky? Can we see any other galaxy besides Andromeda and Magellanic Clouds?
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1answer
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Do we see stars from other galaxies (not Milky way) in the night sky with the naked eye?

I saw reports that only Andromeda Galaxy and Big/Small Magellanic Cloud galaxy stars could be visible with the naked eye (how many stars would be from them out of a few thousand visible?) This ...
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How many galaxies can be seen in a given patch of sky

Similar to the question asked here, but my question is not about what can be seen with the naked eye but rather what might be seen if pointing my Newtonian reflector (full specs outlined below) at an ...
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1answer
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Question from Introduction to Modern Cosmolgy by Andrew Liddle

The exact question goes like this: In the real Universe the expansion is not completely uniform. Rather, galaxies exhibit some random motion relative to the overall Hubble expansion, known as their ...
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Looking for a Dwarf Galaxy < 500 L.y. in Diameter, which is not a Satellite / Companion, or is at least 500 000 L.y. away from another Galaxy

My goal is to learn about an example of a Dwarf Spheroidal or a Dwarf Irregular Galaxy which is not a Satellite / Companion Galaxy (or is at least 500 000 L.y. away from another Galaxy), and doesn't ...
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1answer
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Relationship between galactic rotation and stellar lifetime

I have read that the lifetime of stars is much less than the period of rotation for a spiral galaxy. For example https://www.coursera.org/learn/evolvinguniverse/lecture/wlYhz/the-origin-of-spiral-arms ...
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What will happen to the shape of a galaxy when a super massive black hole lying in its center dies(evaporates out)?

What's at the Center of the Milky Way? In this article it is said that a supermassive black hole lies in the center of milky way galaxy. At its center, surrounded by 200-400 billion stars and ...
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Tests for code that computes two-point correlation function of galaxies

I'm currently writing a code to compute the two-point correlation function of a set of galaxies. As I work with a loooot of galaxies, it was suggested to me not to do it in real space, but to compute ...
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1answer
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Redshifting restframe SED

I have a template spectral energy distribution (SED) at z=0. I want to shift the template SED to an arbitrary redshift (z>0), how to do this in python?
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1answer
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Photometric redshift

I have decided to do undergraduate thesis on "estimating photometric redshift" or something related to this using machine learning. Reading previous papers, I have come to know that work has been done ...
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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 ...
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Names of specific galaxies in Hubble's XDF

I'm working on a little side project that traces and identifies galaxies in Hubble's XDF using OpenCV. This is my current progress with tracing the more prominent galaxies: I was wondering if there ...
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Is this an actual nebula or CGI?

I'm thinking of putting a large wall paper with an astronomical motive on a wall. I found quite a number of wall papers by various vendors, but most of them are obviously computer generated images, ...
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What's the stellar density at points of the Milky Way?

I'm trying to work this out and getting conflicting numbers... (All based on numbers from Wikipedia) On the one hand, the galaxy is between 100k and 180k light years across, and has between 100 and ...
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1answer
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What are six different methods to measure distances in Astronomy?

What are six different methods to measure distances in Astronomy in regards of their respective range in terms of astronomical objects? So far I can name 4: Parallax method, radar ranging, main-...
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How to convert from Cartesian J2000 coordinates to Cartesian Galactic coordinates?

I'm using a star database (the HYG database) which has xyz positions and velocities for the stars. This has +X towards the vernal equinox, +Z towards north celestial pole, +Y towards Right Ascension 6 ...
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What's that limit, where we start to see infrared galaxies?

All the nearby galaxies we see come in visible range, many are visible from ground based telescopes. And the farthest galaxy that hubble discovered recently, 13.4 billion light years away is in infra ...
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Is it “weird” that all disc galaxies rotate once every billion years?

In a recent paper (Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies by Meurer, et al.), it was noted in the conclusion that: [This] implies a constant orbital time of ∼...