Questions tagged [cosmology]
Questions about the origin, history, evolution and fate of the Universe.
294
questions
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'Little h' usage in cosmological simulations
I am running a cosmological simulation and am having some trouble putting things into code units. The physical distance units in my simulation are in terms of $\text{Mpc/h}$, where $h$ is the ...
0
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0answers
21 views
How to derive the formula of magnitude error caused by peculiar velocity?
I want to understand how to derive the formula of magnitude error ($\sigma_m$) which is caused by peculiar velocity of a galaxy, like this
$$
\sigma_m = \frac{5\ \sigma_V}{cz\ \rm{ln(10)}}
$$
,where $\...
1
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0answers
38 views
Astronomy A Physical Perspective [closed]
Is "Astronomy: A Physical Perspective" by M. Kutner written in 2003 a good introductory textbook? What other textbooks could you recommend? I want to study astronomy on my own but with scientific ...
1
vote
1answer
78 views
Why dimmer high-redshift supernovae means the expansion is accelerating, if the dilated region pertains the distant past?
I must be seeing this wrong, because it seems to me the data indicates faster expansion in the past, contrary to Adam Reiss' study that led to the birth of the notion of 'dark energy'.
In Reiss' ...
2
votes
1answer
58 views
Neutrino Modelling in Friedmann Equation
so I'm trying to model neutrinos in the Friedmann Equation. I've covered the case of the Benchmark Model where we have matter, radiation, curvature, and the cosmological constant, Lambda. I know my ...
2
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0answers
32 views
Paper recommendations for career guidance
I'm an undergraduate student in astronomy and I'm one year from graduating, but I feel I still can't choose what career path I want to pursue. To date I've only had two courses of proper astrophysics ...
5
votes
2answers
148 views
What good is the Einstein de-Sitter model?
Why is the EdS model still taught and used to predict the age of the universe if ours is not an EdS Universe. Does this model have any pros?
1
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0answers
48 views
What exactly is a “conclusive association” in Astronomy?
Phys.org's Astronomers use slime mold model to reveal dark threads of the cosmic web says
A computational approach inspired by the growth patterns of a bright yellow slime mold has enabled a team ...
2
votes
2answers
135 views
The Matter Anti Matter Asymmetry
The matter anti matter asymmetry is still a mystery that still can't be explained. But what if there wasn't an asymmetry? Isn't it possible that there was exactly equal amounts of matter and anti ...
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2answers
95 views
Create an inhabited black hole
Hello I was watching one of Isaac Arthur's videos about the end of time and i just got a crazy idea
Is it theoretically possible to "create" a "solar system" that would look like a supermasive black ...
2
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0answers
77 views
Is the Big Bounce Theory valid? If so does that mean all this have happened before?
IF the universe is just an infinite loop of events from expanding to contracting does that mean all this has happened before? The initial conditions for the next big bang would (or rather could) be ...
1
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0answers
31 views
Absorption line in quasar spectrum
I have quasar spectrum which includes emission and absorption lines. I need to find absorption lines in between 2 wavelength. How can I do it with coding?
2
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0answers
68 views
Force to fix $\sigma_{8}$ or $A_{s}$ for Forecasts
In the context of Forecasts with Fisher's formalism, I make vary cosmological parameters to compute the elements of the Fisher matrix.
First, I generate with CAMB code a linear power spectrum. Then, ...
0
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0answers
76 views
Could the Sun's planetary nebula be dangerous for the planets?
Since the Sun's mass isn't high enough it won't go supernova being a red giant but instead release a planetary nebula. So that seems to be kind of a substitute for a supernova. Would ejecting the ...
2
votes
1answer
104 views
Did Einstein supported Big Bang Theory cosmological model?
Einstein made many predictions, including gravitational waves and the possibility of black holes.
Relativity is taken into consideration for the Big Bang model, so did Einstein agree with it or did ...
2
votes
3answers
75 views
light emission of quasars
I'm studying Astrophysics and I have some video's from a past course. I'm currently studying the reionization of the universe. At the current point in the class, the instructor is talking about ...
1
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0answers
30 views
Nebula and its Colours [duplicate]
A Nebula boasts of Too Bright Awesome Colors that includes red, blue, green, orange, white, etc?
They're result of excitation of electrons.
Is there a clear explanation as in which Color is ...
4
votes
1answer
62 views
How is the Dating of Samples of Cosmic Objects Performed, Including Pre-Solar Dust?
In the new Space.com article 7 billion-year-old stardust is oldest material found on Earth I had read about some pre-solar grains dating back to 7 billion years. What techniques are used in ...
0
votes
1answer
37 views
Metal lines in Lyman-alpha forest
I need to find metal lines in the Lyman-alpha forest of quasar spectra, without the red side of lyman alpha emission line.
Can you guide me how to do this?
0
votes
1answer
72 views
Why is constant velocity drift not an accepted explanation of Hubble expansion?
Edward A Milne at the Oxford University proposed that what Hubble was
observing was simply a natural sorting of random galactic motions. If
a group of galaxies formed together moving at various ...
3
votes
2answers
74 views
Are there predictions of the distribution of matter at the end of time
Are there any theoretical predictions or "educated speculation" by cosmologists on how matter will be distributed at very, very distant times in the future?
For example, will matter be:
agglutinated ...
1
vote
0answers
16 views
Formula to Compute sigma8 for correction in non-linear regime
I try to explain my issue on this forum since it seems to be appropriate.
I need to apply a correction on $\sigma_{8}$ between linear and non-linear regime to keep it fixed (I make change the values ...
0
votes
1answer
41 views
What reference frame do age-of-the-universe calculations assume?
I'm thinking, in particular, about general relativity. When we speak, for example, of neutrino decoupling, what do we mean when we say this happened in the first second after the Big Bang? Do we mean ...
1
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0answers
122 views
Scale factor 0 for expanding universe
Does the FLRW model have a scale factor $0$ at the singularity, meaning that even infinite distances become $0$ there according to the mapping $x \mapsto a(t)x$, for $a(t)=0$?
I am asking this ...
2
votes
2answers
100 views
Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?
The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s.
It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc.
This ...
1
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0answers
87 views
Aligning of 7 unidentified objects in the sky, what are they? What did I see? [duplicate]
So this morning (4th December 2019, 0518hrs) I was out turning my horses out in the fields and noticed a strange arrangement of what I perceive to be stars, only Iāve never seen it before and wondered ...
15
votes
1answer
290 views
A Sky Map of Gravity - what would it look like?
PREAMBLE
Sky Maps exist which show the distribution and intensity of electromagnetic radiation received on Earth at various wavelengths. An obvious form is a map of the stars (Star Chart).
Maps ...
2
votes
1answer
63 views
Redshift and Velocity relation
Let us say that we have an object so its total velocity is defined as
\begin{equation} v_{tot} = v_{pec} + V_{rec} \end{equation}
Where
\begin{equation} V_{rec} = H_0r \end{equation}
and \...
5
votes
1answer
130 views
At what rate is the observable universe expanding?
The observable universe is $4.4 \times 10^{26} m $ in every direction. I told this to my daughter and then added, "And guess what? It's a little bigger today than it was yesterday."
"Wow!"
But by ...
0
votes
1answer
45 views
who use the GADGET-2 pack for simulation? can I do it with my PC? [closed]
I want to do hydrodynamic simulatin for universe at vary redshifts. How can I do it?
or how can I find an simulation of universe for use my work?
2
votes
2answers
86 views
Could different views of the universe simply be different points in time?
I'm not sure if this is the correct stackexchange site for this question.
I've been reading this article on Vice Motherboard Thereās Growing Evidence That the Universe Is Connected by Giant ...
0
votes
1answer
2k views
Troop of moving stars through a straight line [duplicate]
Last night,I and my brother suddenly saw that some(50-60) dots of light( exactly like stars) were moving through a straight line(from NW to SE) above us with same velocity and towards exactly same ...
0
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0answers
19 views
Calculate rest flux density from emitted flux density derived from fits data of SDSS data tool
Say I have a spectrum of a galaxy at a redshift z, with flux density units of erg/s/cm^2/Angstrom. I'd like to convert flux density(in the same units) at z=0, i.e. at its rest it's rest emisison. How ...
12
votes
1answer
193 views
The recent results on Hubble constant measurements
In recent news there is this announcement
In the introduction they say:
Distance measurement discrepancy: a $4.4Ļ$ tension on the value of $H_0$
and I understand the discrepancy is with the ...
2
votes
1answer
84 views
Why do we expect Type Ia Supernovae to be brighter in a decelerating Universe than what has been observed?
This seminal review paper in the PNAS by Robert P. Kirshner (https://www.pnas.org/content/96/8/4224) says the following:
If the universe had been deceleratingāāin the way it would if it contained ...
3
votes
1answer
108 views
Time dilation due to the expansion of the universe
This is not a homework question. I want some help in being able to clearly perceive the expansion of the universe and the consequences thereof.
We know that the universe is expanding in an ...
2
votes
1answer
70 views
Difference between 3D real space and 3D redshift space?
With regards to cosmological simulations (e.g., N-body dark matter only simulations), I've seen people talk about the positions of objects (halos, galaxies) in the simulation in terms of 3D real space ...
8
votes
1answer
156 views
How do we know so many details about Big Bang, but we do not know if Universe is finite/infinite?
I understand that this question may be too vague, but I am confused about the following:
On one hand we know a lot of "details" about Big Bang, like really precise details, evolution of universe, age ...
0
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1answer
129 views
Cosmological redshift - How do we know it's not caused by the observer's time dilation?
Instead of cosmological redshift being caused by the metric expansion of space, why couldn't cosmological redshift be caused by our perspective moving faster in time? Said another way, if the ...
2
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1answer
106 views
The energy density of DM (to be fluid,state parameter=-2)increases with time. Does it violate the concept of accelerating universe?
We know that dark energy with value of state parameter $\omega<-1$ is called phantom dark energy model. In this model if we assume dark energy to be a fluid with value of state parameter $\omega=-2$...
6
votes
3answers
381 views
Cosmological redshift vs doppler redshift
I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift.
He ...
2
votes
1answer
37 views
Redshift, velocity, distance
How are redshift, (recessional) velocity and distance of a galaxy related?
I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional ...
1
vote
2answers
85 views
The size of Copernicusā and Ptolemyās corrections
I understand that both Copernicus and Ptolemy needed epicycles, but one might assume that a heliocentric system would need much smaller corrections to account for the non-circular motion of the ...
0
votes
1answer
96 views
Why does an open universe expand forever, while a closed one does not?
It makes sense to me that the universe would eventually stop expanding, as bodies of mass attract each other, and I understand that dark energy can counteract this attraction. However, I don't ...
4
votes
2answers
128 views
What is the effect of this expanding universe on the energy density of it?
We know that our universe is expanding i.e. volume of the universe is getting larger with time with total energy being conserved. My question is whether the energy density is getting smaller with ...
3
votes
1answer
63 views
What is assembly bias in context of cosmology?
I see the term "assembly bias" being used quite a bit in cosmology literature? I have not been able to find a good primer on what it means, and why it is important.
3
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0answers
48 views
Cosmology : Formula for the bias of galaxies
first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
4
votes
1answer
146 views
Observable universe equals its Schwarzschild radius (event horizon)?
The estimated age of the universe is 14 billion years.
The estimated Schwarzschild radius (event horizon) of the observable universe is 14 billion light-years.
What are the ramifications?
2
votes
3answers
255 views
Is the universe older than 13.7 Billion years?
I came to know that the cosmic horizon is the part of universe beyond which we cannot see. So if the light from 13.7 billion years ago is what we can observe, does that mean the universe is older than ...
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1answer
89 views
Does space being at right angles to time imply that the expansion or contraction of each occurs in a direction opposite the other's?
The Minkowski diagrams that are employed to illustrate Special Relativity depict changes in the motion of objects through the dimensions of space as occurring within a field (that's otherwise divided ...
