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 are there no enormous galaxies near us?
Recently the James Webb space telescope detected six massive ancient galaxies. They are very old and very far away. But these galaxies must still exist today and be even heavier now. Why can't we see ...
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Recession of Galaxies vs. Black Holes [closed]
Light surrounding black holes is redshifted due to the local warping of space and its velocity relative to other objects. Why is it not possible that objects gaining infinite momentum (including mass) ...
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What is the rough distribution for number of galaxies with a given mass in the observable universe?
Is there a rough formula for the fraction of galaxies in the observable universe with masses between M and M + dM? Or perhaps a graph that displays the same information? I've looked online but can't ...
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Gravitational potential energy of a galaxy
How can the total gravitational potential energy of a galaxy be calculated?
Lets assume for simplicity that the entire galaxy follows an exponential mass density function for an infinitely small ...
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The 'core-cusp' problem for dark matter halos in larger galaxies
TLDR: Do observations of larger galaxies favour 'cuspy' dark matter halo distributions, as predicted by N-body simulations?
I've been trying to understand the 'core-cusp' problem for dark matter halos ...
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Minimum angular size galaxy
I've heard a mention in a lecture that galaxies have a Minimum angular size. Naively, the angular size should drop as $1/d^2$. The effect is supposed to stem from the expansion of the universe.
What ...
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Why do spiral arms occur at potential minima?
I've been learning about the density wave theory of spiral arms, and also how the gravitational potential of galaxies is non-axisymmetric, resulting in a sinusoidal spiral potential.
I've then learnt ...
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How large can the disk of a spiral galaxy theoretically get?
What is the upper limit to the size that the disk of a spiral galaxy can theoretically attain (in terms of diameter in light years)? Is there a limit or is it possible a disk can go on indefinitely (...
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How does the conservation of angular momentum contribute to the flattening of a galaxies shape?
I don't understand this but put down my best attempt at understanding why down below. After it I've included what chatgpt said about the matter.
OK I understand why angular momentum is significant ...
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Seyfert Galaxies: How does this statistical deduction about the age of their nucleus make sense?
As per this book, An Introduction to Active Galactic Nuclei by Bradley Peterson:
The nuclear emission must last more than $10^8$ years, because Seyfert galaxies constitute about 1 in 100 spiral ...
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Pressure and velocity dispersion
I’m reading this paper
whose Eq(2) I’m a little concerned about. Sanders has tried to relate the pressure with the velocity dispersion of particles using the relation $P=
\rho\sigma^2$ where $\sigma$ ...
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What happens to objects along spiral galaxy arms over long periods of time?
Observations of spiral galaxies reveal that objects within the same arm of a spiral galaxy move at around the same speeds, regardless of their distance from the center of the galaxy. Conversely, the ...
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Three-body problem with multiple systems?
The three-body problem has been known for a long time (https://www.spacedaily.com/m/reports/On_chaos_drunks_and_a_solution_to_the_chaotic_three_body_problem_999.html), in which two celestial bodies ...
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Can time in space be years faster than on Earth? [closed]
Is it possible that in some distant solar system from another galaxy, time will be dramatically different from our Earth time, with years passing far faster than on Earth time?
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How would a Supermassive-black-hole-less galaxy behave?
The Supermassive black hole in the center of the galaxy only contains a tiny fraction of the mass of our Galaxy, so it has minimal direct effect on the orbits of most stars. However I have sort of one ...
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If time stop at Sagittarius A event horizon, can time restart the other way inside? [duplicate]
From our point of view in our Galaxy, his center, Sagittarius A, is a super massive black hole. At event horizon of this singularity, gravity stop time.
Is there any reason why time would not run in ...
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How do we know that we will collide with Andromeda? [duplicate]
We know that Andromeda galaxy is heading towards the Milky Way. But how do we know that Andromeda doesn't have a large Transverse velocity? This would cause the Milky Way and Andromeda galaxies to ...
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Stopping galaxies' rotation...?
I have been told that galaxies will never stop rotating because conservation of angular momentum
But, there are planets inside of it can travel through dense nebulae and bodies of gas that would cause ...
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How long would take for other galaxies to be unobservable due to Cosmic Expansion?
I heard that if Universal Expansion continues at some point galaxies will be so separated that a future civilization would have no way to know there are other galaxies, for them the Galaxy they live ...
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How much gravitational lensing do we see from the Milky Way?
I assume that the Milky Way has a dark matter halo just like any other. If that is the case, if we look at a huge part of our own galaxy, do we actually see the gravitational lensing effect? How ...
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Difference between star formation rate and star formation history
When we speak about galaxies evolution, what is the difference between the star formation rate and the star formation history?
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The centre of what we can now see in the universe
If the JWST has just discovered the furthest away galaxies in one place we can now triangulate to where the centre of what we can see
This is observable and appears not symmetric with everything ...
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Could the energy emitted by galaxies contribute to the dark matter phenomenon?
I'm pondering a concept regarding the energy-mass conversion in the context of cosmology, specifically related to the light emitted by galaxies over billions of years.
Einstein's famous equation E=mc^...
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Gravitational field intensity in mass disk
To calculate the gravitational field intensity or acceleration in a mass disk (like a galaxy), should I do a(r)=G×Mt/r^2 or a(r)=G×M(r)/r^2 with Mt being the total mass of the disk/galaxy and M(r) the ...
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Age of the universe due to expansion
"If gravity working on matter is the only force at work on large scales, then the attactive force of gravity will act to slow the expansion. In this case, the universe was expanding more rapidly ...
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How can I make the equation of warped disk?
My teacher gave us the assignment to find the moment of inertia of any shape you want. So I decided to find the moment of inertia of our milky way galaxy.
I found out that our galaxy is shaped like a ...
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How do we know if a distant galaxy's light we see today was also reaching our location before approximately 4.5 billion years (Earth formation)?
This has actually to do with the estimation of of how distant an observed galaxy is?
How we can be sure if we do not know if we could see the light comming from the galaxy even before the Earth was ...
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Do all galaxies in our observable universe have more or less the same age?
What is the current consensus about the age variation of the existing galaxies in our observable universe?
Not to be confused with the age of very distant galaxies as observed today by our telescopes ...
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How cosmologists know if the observed redshift of galaxies is due to expansion and not intrinsic to the galaxy?
Is there a way to experimentally test if the cosmological red shift observed is due to the expansion or intrinsic to the galaxy? If anyone knows how to do this or how to extract from the data please ...
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How do we know that there is matter-anti-matter asymmetry? [duplicate]
It is often said that there's more matter than anti-matter, How do we know that there is more matter,
Can't there be a galaxy made up of antihydrogen? Will that galaxy be any different from ours?
How ...
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At which rate does visible matter decrease from the galatic center?
At which rate does the visible matter density in galaxies decrease when moving away from the galactic center?
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How much greater is the average distance between stars in the spaces between spiral arms? How much lower is it in them?
I've read about the overall average distance between stars in the milky way, and I've read that one of the best explanations for spirals arms is that they are density waves - that is, they are indeed ...
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Is there dark matter in intergalactic space?
Reference: the rotation speed of galaxies in a galaxy cluster:
Is the dark matter associated with each galaxy in a cluster, sufficient to explain the rotation speed of galaxies in the cluster, or ...
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Galaxy S4G database: convert pixel to kpc
I am referring to S4G database (https://irsa.ipac.caltech.edu/data/SPITZER/S4G/overview.html ).
The information on the length of galaxies, and various length parameters are given in terms of pixels.
...
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Is dark matter present in all galaxies?
The rotation speeds of nearby galaxies like M31 or our own milky way are determined by observations. And we know there that luminous mass does not explain the rotation curve. Are there any galaxies ...
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How do telescopes see many billion light years distant object in our universe?
How do telescopes see many billion light years distant object in our universe?
As an individual with limited expertise in the field of astronomy, my current understanding suggests that the observation ...
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Understanding the Meszaros Effect in terms of Hubble Drag
In Frank van den Bosch's Theory of Galaxy Formation Lecture 6 Page 41 he says that
The stagnation of growth in pressureless matter perturbations during
radiation dominated era is known as the ...
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Theory of gravity and dark matter? [closed]
Most people assume that in order to have agreement between GR and the rotation curve of galaxies:
GR isnt correct
There is hidden matter which makes the galaxies rotate faster at their edges.
GR is ...
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Dwarf galaxy rotation speed around Andromeda/Mily way
We know that the rotation speed of stars around the center of a galaxy is roughly flat.
But how fast does the dwarf galaxy rotate around the bigger galaxy, say andromeda or milky way?
Do they also ...
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Solving Poisson equation for galaxy rotation curves
Can someone point me to the numerical methods to solve the Poisson equation for the galaxy rotation curves?
I've heard of some tools like PETSc or OpenFOAM. But I'm not sure if these are the right ...
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Keck versus Webb: discrepancies in the redshift measurements of the galaxy GN-z11 (the most distant galaxy discovered with the Hubble Space Telescope)
Two years ago Nature Astronomy published a paper based on measurements from the Keck Telescope stating that the redshift of the galaxy GN-z11 (discovered by Hubble) is:
$$ z=10.957 \pm 0.001 $$
Source:...
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Biermann Mechanism [closed]
Biermann mechanism says that due to different masses of electrons and protons, the motion of former leads to the latter. This effect produces non-zero circular currents which induce vertical magnetic ...
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Identifying the Milky Way uniquely [closed]
Let’s suppose you wanted to elegantly represent the Milky Way in a minimalist fashion in a way that would make sense a billion years hence (ie let’s set aside the damage wrought by colliding with ...
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Is sun orbiting the center of the Milky Way? [closed]
Are all the celestial bodies in our galaxy (along with the Sun) orbiting the center of the Milky Way Galaxy?
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Database for galaxy luminosity (or mass) distribution
I'm trying to get data on luminosity (or mass) distribution for galaxies.
I came across one paper (https://arxiv.org/abs/1106.3564) which gives luminosity distribution for Andromeda.
But is there any ...
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Incompatibility of constraints set by MAGIC ICAT telescope on NGC 1068 neutrinos flux with observation by IceCube
Data from the MAGIC ICAT telescope, when used to provide constraints on the neutrino flux from NGC1068, predicts maximal event rate of neutrino detection to be about 0.07 per year. As described in the ...
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Distance $r$ between galaxies inside the galaxy cluster
I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance $r$ between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z ...
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Impact of distance from galactic centre on the value of energy in the cosmic ray spectrum where knee is observed?
This question is based on the recommendation and great explanation by @Kyle_Kanos. Is it known what causes the "knee" in the observed Cosmic Ray spectrum?
Accepting the reason for the ...
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How do we know that distant galaxies are not made up of antimatter primarily?
This question addresses the first part of my question. In that it tells us how we would theoretically differentiate antimatter galaxies from regular matter galaxies.
How would we tell antimatter ...
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If spiral galaxies form due to perturbations, why aren't there more spiral galaxies in galaxy clusters, where interaction/perturbation is likely?
I read the other article with an excellent explanation of simulation results and the mathematics behind spiral arm formation yet was left baffled by the point that the principal influence that would ...
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