# Questions tagged [galaxy]

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

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331 views

### Algorithm to fit galaxies

Do you know of any other data analysis algorithm that fits 2-D analytic functions to galaxies and point sources directly to digital images, other than GALFIT? Especially to subtract lens light from ...
32 views

### Are features in the CMB correlated with features in the SDSS map of the most distant galaxies?

This is a follow up to an earlier question to which @pela gave an excellent answer. Apparently the statistics of the length-scales of the CMB fluctuations are similar to those obtained from other ...
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### How to estimate the inclination of a galaxy between edge on and face on?

I have the images of a galaxy and the field of view and I would like to determinte the inclination of a galaxy between edge-on and face-on. Would that information be enough to do the calculation? Or ...
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### Is there any correlation between the Cosmic Microwave Background (CMB) and the distribution of distant galaxies?

The Cosmic Microwave Background (CMB) is remarkably isotropic but does exhibit a distinct dipolar Doppler shift and also much smaller but measurable fluctuations in intensity and polarization. ...
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### How to calculate the flux of a galaxy merger? [closed]

Say three galaxies, with equal fluxes, $f_1$, merge. How could I calculate their combined flux?
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### I have a scientific paper on gravity, how do I publish it, and will my research benefit me? [closed]

I read a lot about gravity and discovered a hole in it, and I want to publish that hole, but I am not good at mathematics. To show that gap, what should I do? Should I use Newton's equations which are ...
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### Does this galaxy resemble the Milky Way, and is it relatable as the “template” for the Milky Way?

Taking a look at this photo of comet 2I/Borisov and a background galaxy (2MASX J10500165-0152029): And compare it to this rendition of the Milky Way: The two galaxies slightly resemble each other. ...
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### Observing the motion of the solar system and galaxy through space?

This is very perplexing. Conditions: planets are moving around the sun (solar system) solar system is moving as part of the galaxy the galaxy is moving through space on some axis galaxy is part of a ...
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### When calculating absolute magnitudes of distant objects, do you use the light-travel distance or the comoving distance?

I want to calculate the absolute magnitude of GN-z11. Its light-travel distance is 13.4 billion ly (4.1 Gpc), its comoving distance is 32 billion ly (9.8 Gpc), and its apparent magnitude is $25.8$. ...
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### Are the bright dots in this image individual stars?

I saw this picture of M51 (Whirlpool galaxy) and noticed many, many bright dots around and in the galaxy. I have freehand-circled a few as examples. Are these individual stars (probably supergiants) ...
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### How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?

According to quite recent research the observable universe contains about 2 trillion galaxies ($2 \cdot 10^{12}$). But what is counted there? Does this number also contain dwarf galaxies? According to ...
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### How can you find the distance to a galaxy using right ascension and declination?

For example, Galaxy NGC 3689 has the right ascension of 11:28:11 and declination of +25:39:40.0. Using these values, how can we find the distance to the galaxy? If it helps, its radial velocity is ...
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### Schechter Luminosity Function fitting plot of galaxies

I would like to plot the Schechter Luminosity function of galaxies. Here is my data(I have the Luminosity L[Ha] in erg/s). I would like to plot like this figure from this paper. In this paper, they ...
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### Did the density wave theory for spiral arms take account of this phenomenon?

I came across this link. In it the author speculates that in the outer region of a galaxy, the spiral arms overtake the stars, and vice versa for the inner region. That means there must be a middle ...
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### What type of galaxy is LEDA 14884?

A new image of deep space was released yesterday, showing tons of galaxies. One in particular (named "LEDA 14884") looks very puzzling (like an ear), zoomed in below: Article says it's a ...
457 views

### Rotation of far away and near by galaxies

Do the far galaxies rotate the same as does the milky way and the near by galaxies?
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### Using SDSS data / finding a catalog

I am looking for a catalog of low redshift galaxies (preferably SDSS) with information on line fluxes and stellar mass. My Google searches keep pointing me to work by the Portsmouth group, so I ...
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### How do we estimate the dimensions and mass distribution of a galaxy's dark matter halo, beyond the effective limits of its visible matter?

Current research suggests that the Milky Way's dark matter halo may extend up to about 10 - 15 times the size of the visible galaxy, and is believed to be roughly spherically symmetrical. But I don't ...
6k views

### What keeps galaxies together?

The super massive black hole at the centre of Milky Way has a mass of about 4 million times that of our sun. Is this enough to keep the entire galaxy together, is it this black hole which keeps the ...
56 views

### Significantly blueshifted Lyman-$\alpha$

Lyman-$\alpha$ line in galaxies is notably known to show a double peaked profile, mainly due to its scattering in a moving medium, see e.g., the very recent Matthee et al. 2021, The X-SHOOTER Lyman-α ...
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### Getting XYZ coordinates of Luminous Red Galaxies catalogue

So I want to get the XYZ (rectangular/Cartesian) coordinates of the LRG (luminous red galaxies) catalog. The catalog is available for download from here: https://data.sdss.org/sas/dr16/eboss/lss/...
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### Galactic orbits and distance between stars

In the context of whether or not nearby stars were created from the same nebula, this answer states: imagine two stars with very similar orbits, one with a period of 200 million years and the other ...
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### Anatomy of a galaxy cluster: understanding the relationship between dark matter halos and subhalos and galaxies within the clusters?

In my understanding, galaxy clusters contain dark matter halos, which in turn contain subhalos, and the subhalos are what surrounds individual galaxies. I know that is a simplified picture, but I am ...
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### How many photons does it take to determine the existence of a distant object?

This applies to any object, but I see the recent discovery of the oldest, most distant galaxy and it started me wondering what the limits are. Presumably you can do better with a bigger telescope and ...
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### How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
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### Do we know what's “behind the Milky Way”?

If we do, how? And what are those objects on the other side of the galactic center? We can't see through the dense band of light and dust, but maybe in other spectrums the band is much less dense? But ...
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### What are the odds that the Sun hits another star?

The Sun moves around the Milky Way disk in the same direction as most of the other stars in our galaxy (prograde). But there are a number of older stars in the galactic halo that move in retrograde ...
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### Universe’s Glow Shows There Are Fewer/More Galaxies Than We Thought, Say Scientists

There are several articles like this: Universe’s Glow Shows There Are Fewer Galaxies Than We Thought, Say Scientists NASA’s New Horizons spacecraft beyond Pluto has made a groundbreaking measurement ...
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### Are there any stars that orbit perpendicular to the Milky Way's galactic plane?

Most stars orbit in the Milky Way's galactic disc. But is it possible for one to orbit perpendicular to it? Here on Earth since we're inside the galactic plane we can't get a good view of what the ...
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### Why is dark matter required?

I read somewhere that the galaxy is spinning too fast (in places). Therefore, there must be dark matter. What are the equations that explain how fast the galaxy should be moving, and how are they ...
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### I need to study space, planets and black holes, how do I study them on my own [closed]

I need to study space, planets and black holes, how do I study them on my own, knowing that I am an Arab and I do not know English. I use translation applications. I speak with you. Can you help me ...
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### How to obtain a luminosity from an SED

I have a spectral energy distribution (flux densities measured at several frequencies), and have fitted a 'greybody' model to these points. I am confused about how I use this information to determine ...
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### How co-planar and co-rotatory are the Milky Way and its constituents?

All the planets in the solar system rotate roughly in a plane that intersects the sun. Stars in the Milky Way rotate around its centre forming a rough planar disk. Question Are these planes all ...
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### Do some galaxies collide faster than the speed of light?

If some galaxies expand away from each other faster than the speed of light then do they collide faster than the speed of light? Update 1: I guess my question is what's the max speed/velocity at ...
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### Correlation between supermassive black hole properties and galaxy rotation speed

Is there any correlation between the size or spin - or any other properties - of a galaxy's central supermassive black hole and the speed of galaxy rotation (which I think would also be proportional ...
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### How does a galaxy in Abell 2261 exist without a black hole in the center?

Here a source says that astronomers looked for a black hole in the brightest galaxy in the cluster Abell 2261, A2261-BCG, but found nothing: However, X-ray observations from NASA's Chandra X-ray ...
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### Completeness detection analysis of magnitudes of galaxies

I have a magnitude from the observation. I would like to find the detection completeness of the magnitude. I want to plot the figure like this in python How to plot the Detection completeness and ...
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### Why is the flux density and amplitude different for galaxies than stars?

This might be a simple question, but I'm having a hard time answering it myself - or at least answer it correctly, I think. I'm sitting with different spectrals; many for stars and one for a galaxy. ...
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### Computing the over-density of Lyman-alpha emitters

Let's assume that I have observations of $N$ galaxies in a projected area $A$, within a redshift range $\Delta z = z_{max} - z_{min}$. What is the correct way of computing their number volume density? ...
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### Fate of lone spiral galaxies?

I know Hubble's galaxy classification scheme and the bifurcation from elliptical galaxies into two types of spiral ones. I am also aware of different theories on how spiral galaxies form e.g. through ...
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### Why are galactic nuclei yellow?

So we've seen millions of galaxies, and all of them have a bright, yellow nucleus. What is the cause of the yellowness? Is it because of aging stars, redshift from the SMBH, or something else?
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### What came first: Galaxies or Stars? [duplicate]

In Stephen Hawking's A Brief History Of Time, the book mentions that "in regions that were slightly denser than average...galaxies were born." (pg 123). However, according to many other ...
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### How to find the distance between two galaxies from ra and dec and redshift [duplicate]

I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies. I did like this to find the nearest neighbour galaxies. Suppose I am trying to ...
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### Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?

The axis of rotation of the Solar System makes a large angle of about 60 degrees relative to the axis of rotation of the Milky Way. That seems unusual - for example, most of the bodies within the ...
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### Where to find spectra from Las Campanas Redshift Survey?

I am interested in the optical spectrum of a galaxy. In SIMBAD the reference for the redshift of my galaxy is the Las Campanas Redshift Survey. Hence I am looking for the optical spectrum from which ...
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### The activity of the galactic nucleus is cyclic?

Are there observations/theoretical calculations that prove or disprove a cyclic activity of the galactic nucleus (I mean the nucleus is active than stops than become newly active with a time ...
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### Are Dwarf Galaxies a Subset of Galaxies?

The question is a rather obvious one. In normal English a word like "dwarf" used as an adjective is assumed to modify the following word. Thus a "dwarf galaxy" would be assumed to ...