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Questions tagged [galaxy]

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

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Is gravitational lensing a good way to search for negative mass?

Is it possible to verify negative mass with gravitational lensing? The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4 Could this be ...
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Star rotational axes and Solar system orientations

How does the orientation of stars axes of rotation and any planetary systems relate to the plane of the galaxy? Is there any relationship that has been detected, are they grouped from their parental ...
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Stellar nurseries in the “Shedding New Light on the Whirlpool Galaxy” video

Captions in the Hubble Space Telescope YouTube channel video Shedding New Light on the Whirlpool Galaxy say: (visible) Along the dark dust lanes, bright pink nebulae are the birthplace of new stars....
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Why do we see galaxies with their actual spiral shapes?

Since the actual position of stars is relative, and we see the light they emitted long time ago, and one galaxy has thousands of millions of stars, and those stars can be separated by hundred of ...
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How tightly clustered are the CHIME-detected FRB repeats?

In the past few days, journalists have been playing the usual "X could be aliens" game. This time, X is repeating FRBs from a galaxy 1.5 billion light years away. (Or is it 1.5 billion years ago? The ...
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Galactic mass estimation from apparent magnitude and distance

Can we estimate the order of the total mass of any galaxy from the apparent magnitude and its distance to us? Just like \begin{equation} M_{galaxy}=c\times 10^{8}M_{\odot }, \end{equation} where $c$ ...
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Deducing distance of closest neighbor galaxy from expression of correlation and mean galaxy density

The original post was on physics exchange but I prefer to move it here : I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors $\text{d}N$ into ...
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What is the bright star or planet in eastern sky on dec 18 2018? [duplicate]

What is the bright star or planet in eastern sky on Dec 18 2018 in Laurens SC. It is very bright and beautiful on a clear night. I have been seeing it for about a month or more. It seems to follow the ...
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Which direction does the Earth face as it travels through the Galaxy

According to the Helical model, as the Sun orbits around the galaxy, the planets that orbit the sun are travelling perpendicular to the path of the Sun. This is better shown in this video: https://...
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Compute the total stellar mass of galaxy with major influence of Red Giants luminosity

Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago If the luminosity in the B band (absolute magnitude in B-band is equal to -21.22) is dominated by ...
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From original burst, fraction of stellar mass still surviving on Main sequence

Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars ...
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number density of Dark Matter Halos Versus number density of Galaxies

Can we count only one dark matter halo for each Galaxy ? Indeed, I am trying to estimate the total density of galaxies in given volume and I have often seen on physics exchange and other forums the ...
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Total number density of galaxies and problematic expression in practise

This post comes from physics exchange forum, I have transfered it here, maybe I will be luckier since I have not received answers on the other forum. Here is the issue : I am asked to give the ...
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What's the easiest way to get 3D-positional data of galaxies

Is there a database with cartesian coordinates (x, y, z) of galaxies? I only need positional data and calculating that using degrees and redshift for all galaxies could take a while and would be ...
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What would the night sky look like from a planet at the centre of a ring galaxy?

If there were an observer on a planet in the centre of a ring galaxy (omitting the galactic core) what could they expect to see in their night sky? I am currently under the impression that their night ...
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Can we learn anything from observing galaxies edge-on, like the Spindle Galaxy?

I was reading about NGC 5866, sometimes referred to as the Spindle Galaxy. It's notable because of its inclination relative to Earth; we see the disk from the side, rather than face-on. The difference ...
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Why is the metallicity of elliptical galaxies low?

As far as I understand, metallicities of old stars are usually low and those of new stars are usually high. If elliptical galaxies form after merger of galaxies, then surely that means the elliptical ...
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Catalog of Galaxies in the Visible Universe

I have seen the Gaia project from here which is about mapping the stars in the Milky Way galaxy. But I'm wondering if there is any open data on the positions (or something like "positions" since it ...
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How active was the Milky Way in its first 5 billion years?

When I look into the history of the Milky Way, it seems like the Milky Way has been the pinnacle of stability. It seems highly likely that our galaxy has eaten several smaller galaxies/dwarf galaxies ...
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How the Galactic objects are moving? [duplicate]

We know that the Galaxies are moving very fast, not only the Galaxies other known and unknown objects in the universe, are moving. But when it was started where is the starting point, and how it move ...
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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?
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How much greater is the star density in our galactic bar?

How much denser is it in the galactic bar than the "normal" density at the same radius? Is it just a few percent? or is it, say, "three times" as dense? Or are other factors at play: star brightness,...
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Galactic rotation speeds - questions from a non-astronomer

Are there any observations that more distant galaxies appear to rotate more slowly than closer galaxies? What methods are used to measure the rotational speed of galaxies? (both orbital speed ...
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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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1answer
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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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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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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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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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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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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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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 ...