Questions tagged [galaxies]

Galaxies are gravitationally bound systems of stars, interstellar gas and dark matter, often hosting a central supermassive black hole. For questions about the structure, composition, dynamics, classification, etc. of galaxies. This includes small systems of interacting galaxies (i.e. merger, or galaxy + satellite system), but for galaxy groups and clusters use [galaxy-clusters], and for questions specific to our own Milky Way galaxy use [milky-way].

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Why do elliptical galaxies not have large proportion of blue stars?

In an article it was given that elliptical galaxies are also formed when a spiral galaxy experiences continuous star burst thus depleting it's gas. So if this is correct than why do elliptical ...
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Why galaxies with a redshift > 2 have a lower velocity now, compared to when the light was emmited?

I was playing around with astropy cosmology data, and I made the following graph: On the x axis I plotted Redshift, and on the y axis the speed of light as 1c, 2c etc. Until a redshift of ~ 2, my ...
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Thermodynamic ensemble of Stars instead of molecules

If we take an enormous amount of molecules (an ensemble), the laws of statistical thermodynamics become valid: we can use them to make predictions of the macroscopic behavior of the ensemble. I was ...
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Why are most ring galaxies present in the field instead of rich galaxy clusters?

I was reading an article in which it said that mostly ring galaxies are present in the ‘field’ instead of rich galaxy clusters. Can anyone explain why is it so? I read about it's formation and i ...
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Will we see more or fewer galaxies because of accelerating space expansion?

I have read this question: The short answer to this is: We see less stars with time, due to the fact that cosmic expansion is accelerating. Although what we really see at the relevant distances are ...
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Galaxy rotation curve and galaxy mass

Is there a relation between the saturation velocity of the galaxy rotation curve and the luminous mass of the galaxy? To clarify the question, if one were to plot a scatter plot with the x-axis as the ...
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2 answers
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Too many low redshift galaxies in NED database

When using the NED database I found there are too many galaxies with very low redshift (Near zero). I used NEDs search by parameters function to find all galaxies within Z=0 to Z=.03 redshift. I did ...
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Confused about size of the universe in the past

From Wikipedia, I got that the photons of the cosmic microwave background radiation originated when the spherical volume of space which will become the observable universe was 42 million light-years ...
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Does a star that is far from any galaxy tend to rotate slower?

I'm wondering whether the rotation of a galaxy and the buffeting of the gas and dust within it by light and stellar wind and pressure waves makes nebulae or gas clouds in galaxies have more angular ...
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Measured Data Question regarding Galaxies with or without Dark Matter and Supermassive black holes

My understanding is that all Ultra Diffuse Galaxies (UDGs) have no Dark Matter nor do they have Supermassive Black Holes. It is also my understanding that all other galaxies have both Dark Matter and ...
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Can electric charge/electromagnetics effects of stars, particles, etc., be a major factor in motions attributed to Dark Matter/Dark Energy?

Electromagnetic effects of moving charged stars and particle flux on galaxies rotation and space expansion.
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How is perspective compensated when analyzing the rotation of distant galaxies?

I can't find any information about that, but I always wondered: When analyzing a distant galaxy, how is the perspective taken in account when analyzing both its movement and the apparent density ...
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Is HD1 Galaxy a potential Big Bang theory killer?

I have heard some first explanations of why the farthest ever galaxy discovered about 13.27 Bly away the HD1 appears so UV active and about the population III stars inside this galaxy made only from ...
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Questions about first JWST image

Why do the circled galaxies seem to form long circular arcs that surround the white point at the center? And why do most of the galaxies in this image seem to be facing that same point? What is in ...
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Where were the first galaxies formed in our observable Universe, at the center or at its outskirts?

After inflation where were the first galaxies formed? At the center (our home position) of our observable Universe or at its outside rim? I know that for the case of a galaxy the standard view is that ...
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If KE of galaxies is negligible compared to dark energy of space expansion why then we should think matter at Big bang had high KE?

If KE of galaxies is negligible compared to dark energy of space expansion is then correct think that matter particles at Big bang had high KE while moving away from each other? Is reasonable think ...
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Can empty space 'press' galaxies?

If gravity slows the effects of time, then empty space will see greater expansion than space inhabited by massive objects. So the space within a galaxy will be expanding more slowly than the space ...
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Do the stars in galaxies expand wrt each other because of dark energy?

Expansion of space is observed between galaxies. In the galaxies themselves, the effect is very small obviously. But is space, no matter how little, actually expanding or is it countered by local ...
5 votes
2 answers
496 views

Do supermassive black holes at galactic centers and the galaxis containing them spin in the same axis?

If the galactic mass is rotating around a central supermassive black hole, should their spin axis not be the same, just as we would obtain for the rotation of a star and its planets ?
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Can Black hole eat white hole or white hole eat black hole? [duplicate]

No light can enter black holes, but is it possible for a white hole to enter a black hole? Or vice versa? Could there be black holes inside the white holes? Or were there black holes inside them that ...
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Cosmological expansion around ropes between galaxies

The FLRW cosmology is a fair approximation of cosmological expansion for space between galaxies and clusters, however within galaxies themselves, is known to not hold, and in fact observational ...
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About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

What is this all about?: At 12 May 2022 at the ESO official announcement live streaming event the EHT representatives claimed that the Sgr A* BH accretion disc spin axis is sort of facing Earth's ...
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How can we extract the Doppler shift of supernovae?

My understanding is that supernovae are used as standard candles, whose spectral lines indicate the recession velocity of the host galaxy. But the material from the supernova is ejected at a ...
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Does magnetism play a role in the formation of galaxies?

Forgive my ignorance as I know next to nothing about physics. From my layperson's understanding, galaxies are formed primarily by the interaction of gravitational forces of stars and planets, however, ...
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Could the center of the galaxy explode as a result of a chain reaction of stars going supernova?

I was reading "Ringworld" by Larry Niven. I'll spare you most of the details of the story, and say that one of the parts of the plot is that the center of the Milky Galaxy blows up, because ...
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6 answers
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Are we totally limited to the Milky Way for all stellar astrophysics?

Simply put; Are we able to make any observations of the individual stars in other galaxies? Is the depth of our scientific knowledge on star systems, based solely on stars in the Milky Way Galaxy ...
2 votes
3 answers
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Why is the ratio of dark matter to normal matter larger in galaxies than the cosmic average?

There seems to be a discrepancy between the ratio of dark matter to normal matter in the Universe (about 5 to 1 according to $\Lambda$-CDM) and the ratio of the average dark matter halo mass to the ...
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What is the reason for density fluctuations in the primary matter of the early Universe? [duplicate]

After a period of inflation and nucleosynthesis, small density fluctuations appeared in the primary gas, which became the "seeds" of the first stars and galaxies. What led to the appearance ...
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1 answer
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How many full orbits around the galactic center our Earth has done so far since its creation?

I have read that the estimated age of our Milky Way galaxy is 13.61 billion years which is by using our current size and status of our galaxy about 59.17 Galactic years which each galactic year ...
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1 answer
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Do counter rotating galaxies have dark matter?

Have counter rotating dark matter galaxies been observed? Counter rotating galaxies, you may already know, are galaxies where some stars or arms rotate in one direction and other stars or arms rotate ...
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In what type of trajectory do the Magellanic clouds move through our galaxy?

In what type of trajectory do the Magellanic clouds move through our galaxy? Can be estimated is it a elliptical, parabolic or hyperbolic trajectory? Although it may be a problem due to dark matter ...
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1 answer
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How do simulations of galaxies or star systems account for the propagation delay of gravity?

I've made simple $N$-body gravity simulations as a programming and physics exercise in the past. But they've never accounted for speed-of-light time delay. The way I'm thinking about this is ...
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What is the effect of a supermassive black hole at the centre of the galaxy on this galaxy's spectrum?

After analysing the spectrum of the spiral galaxy (featuring flat rotation curve) we are asked to draw a sketch showing the effect on the galaxy spectrum if the galaxy were to have a supermassive ...
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What is the smallest scale at which the effect of dark matter can be observed? [duplicate]

Dark matter is primarily postulated in the context of large scale things e.g. spiral galaxies, in order to provide additional forces where vanilla gravity doesn't seem sufficiently strong to explain ...
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Galactic Dynamics: spherical coordinates velocity integral help!

I have been studying galactic dynamics and the following is an extract from Binney and Tremmaine's 'Galactic Dynamics' book. I have been having some trouble to understand how in the (4.37) integrals, ...
9 votes
1 answer
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Why are galaxies much closer spaced (relative to their size) than stars?

I have read this question: So the average spacing is somewhere in the range of 10 - 100 times the size of the biggest galaxies. The peas I had for lunch today were (at a guess - I didn't measure them!...
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Scale for Hénon-Heiles Potential

I was reading about the Hénon-Heiles Potential and I read that it describes "non-linear motion of a star around a galactic center with the motion restricted to a plane" (Wikipedia Link). So ...
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Questions on observations of faster than light recession of galaxies [duplicate]

I've been reading several threads here and online articles trying to absorb the current understanding of observations of far galaxies receding faster than the speed of light, it is said because the ...
5 votes
2 answers
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Gravitational binding energy as alternative to dark matter?

Pondering this question: Casimir effect and negative mass and, in particular, the response of John Rennie "as the mass of any bound system is slightly less than the mass of its parts" I ...
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Is the center of mass of the visible galactic arms located close to the center of mass of the whole galaxy?

Is the center of mass of the visible galactic arms located close to the center of mass of the whole galaxy?
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Galaxy filaments data access

I'm a PhD student in applied mathematics seeking to analyze geometric structure of galaxy filaments and walls, specifically the curvature and branching nature of the filaments and walls. I'm curious ...
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Is it possible in principle to observe all galaxies in the observable universe?

Are there fundamental physical limitations that prevent the observation and cataloging of all (or almost all) galaxies in the observable universe? If there are no physical limitations, then what ...
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Does gravity affect dark matter?

On this photo the red color is ionized gas and a blue color is a fark matter. We see the shockwave on gas but the clouds of dark matter move through each other without any interactions. The dark ...
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Why does the classic textbook by Goldstein say that distant galaxies are inertial reference frames?

Why does pp 2 of the classic textbook by Goldstein say that distant galaxies is inertial reference system in the context of the mechanics of astronomical bodies? How could we identify an inertial ...
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Is Dark Matter in Motion?

What is known about the motion of dark matter, especially in galaxies? It seems as though a particular distribution of dark matter might be required to cause the very flat galactic rotation curves ...
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Would light sails be a practical means of travel in the center of Andromeda? [closed]

I've read that at Andromeda's center, stars are only 0.008 lightyears apart from each other. Is this a short enough distance for light sails to be a practical means of space travel, or is this still ...
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Do more distant galaxies move faster with respect to the cosmic background radiation rest frame?

Aparently our galaxy is moving approximately 1/500th lightspeed with respect to cosmic background radiation. While this is certainly fast, it stands to reason that it could had been a lot faster, so ...
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1 answer
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What is the "temperature" of the galaxy?

The temperature of a gas is a measure of internal energy density. If the atoms have a high kinetic energy, the temperature is high. Can we do the same thing with the galaxy, where the stars are like ...
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Is it possible something in the universe is not orbiting anything?

I thought I heard that astronomical bodies could be ejected from a galaxy. If a body was ejected from a galaxy, could it have been ejected faster than the escape velocity of the galaxy? If that is ...
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How do bars in barred spiral galaxies form?

There is this same question in astronomy stackexchange. But its only answer is unfortunately a rather unsatisfying quote which I could not even find within the provided link. Also, that question is ...
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