Questions tagged [universe]
Questions regarding all of time and space and its contents.
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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 ...
user38152
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What does it exactly mean for spacetime to have no global symmetries?
Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances?
And if there are, what does it ...
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CMBR: Is the cold spot a hint at the edge of the universe?
Could the big cold spot in the CMBR map be a sign that almost all radiation from that direction has already passed us, and that be a sign that the end of the universe is closest to earth in that ...
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What happens at the edge of a finite and "bounded" universe?
So far, we know only about two types of universes: Infinite and finite universes (Unbounded edition).
In an infinite universe, there is no edge. Because well, an infinite space doesn't have an edge. ...
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If a false-vacuum event occurred, would we be able to detect it?
Ever since I read about false vacuum decay a few years ago, I've always been having thoughts about whether or not it would be detectable (the end is near!). As the vacuum bubble propagates at the ...
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what is the acceleration parameter in a universe?
Obtain the value of the acceleration parameter in a universe, including cosmological radiation and constant.
what is the exactly acceleration parameter in a universe means ?
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Is the acceleration of the expansion of the universe a direct observation or an interpretation?
Is the acceleration of expansion we observe with supernovae direct or is this an interpretation according $\Lambda$CDM model ?
I mean what we observe is luminosity distance versus redshift, so to see ...
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Could the Universe really be 12.5-13 billion years old?
My initial reaction is that "this must be wrong" and apparently that's a lot of people's initial reaction according to the article.
https://www.nbcnews.com/mach/science/universe-may-be-billion-years-...
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Could entropy be reversed eventually in the far future?
In the far future there will be most likely a point where a maximal state of entropy will be reached in the universe and after the last black hole evaporates there could be no more structures and no ...
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Cosmic background radiation - what frequency tells us?
I understand that cosmic microwave background radiation is remnant of the universe after 380,000y of the origin.
To me, this radiation is still a wave which has a microwave frequency and I also ...
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Universe: mass = length
Has there been a moment, where the diameter/radius of the universe in Planck lenghts matched the mass in Planck masses (dark + baryonic)?
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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 ...
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Why does the star formation rate correlate with the total stellar mass in star forming galaxies?
The so-called "Main Sequence" of star-forming galaxies (e.g., Brinchmann et al. 2004; Noeske et al. 2007) clearly points to a linear relation between the stellar mass of galaxies and their star ...
user19333
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How to derive the equation for the age of a flat universe with a positive cosmological term?
Can anyone show the steps involved in deriving this equation from the friedmann equation with the cosmological constant involved
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Do voids expand faster at dark energy domination era or not?
I asked one of the authors of a paper about the expansion of voids and filaments in the cosmic web whether voids expand faster when dark energy started to dominate in the universe. But I am confused ...
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What is Helix Nebula made up of?
The Helix is a planetary nebula, the glowing gaseous envelope expelled by a dying, sun-like star. Helix nebula consists of two gaseous disks, how they are formed or which material is present in it.
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Is there a granted minimum known size of the whole universe? (including the non observable part)
This Forbes article How Much Of The Unobservable Universe Will We Someday Be Able To See?
claims
The unobservable Universe, on the other hand, must be at least 23
trillion light years in diameter
Is ...
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What Parts of the Observable Universe have we Observed?
Everyone talks about how big the observable universe is, all of the complexity, etc... But what parts of the observable universe have we actually seen? What Parts are hidden in relative shadows? Is ...
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Do apparent magnitude (V) and photometric magnitude (specifically in optical V band between 500-600 nm) have a similar scale to stellar magnitude?
I'm graphing a table and I used the magnitude values from this database
https://vizier.u-strasbg.fr/viz-bin/VizieR-4
(It's the V/19/data catalog for "Masses and Ages of stars in 68 open clusters&...
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What is the largest cluster of merging galaxies?
Reading about the Andromeda–Milky Way collision, a galactic collision predicted to occur in about 4.5 billion years between the two galaxies, I went to the galaxy merger page and Wikipedia states that ...
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Probability of collision of another bubble universe with our universe
This is rephrased from a previous question and expanding on it. Considering the model of an "inflating" universe which extends infinitely in past (and possibly future) time, constantly creating new ...
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Invisible Mass Affecting the Expansion of the Universe
Are there enough neutrinos & other invisible particles in a cubic light year of space to significantly affect the expansion of the universe,& at a very rough estimate without taking into ...
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Energy to expand
I do have a small question, which may seem a bit stupid but we are all here to learn. Anyways my question is: Is the universe expanding using the energy it had from the Big Bang? if so what would ...
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Luminosity distance in a FRW Universe
In the following presentation:
https://www.slac.stanford.edu/econf/C0307282/lec_notes/pinto/pinto.pdf
we have the relation for the luminosity distance in a FRW universe:
\begin{aligned}
D_L & =\...
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sun - do gamma rays reach radiative zone
So in the sun's core, gamma rays are produced and right away, in the few milimetters, compton scattering happens.
As I understand the compton effect, gamma ray will first collide with free electron, ...
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Heaviest star in universe
Using the estimated age of the universe, can we calculate the heaviest star in the universe using normal fusion reaction rate of our sun? Assuming the star did not die.
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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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Where can I find galaxy spectra (in the form of FITS files)?
I know there's SDSS and I tried searching for the spectra through the navigate and explore tool under CAS as well as by using RA/Dec coordinates under SAS, but every single time it comes out with 0 ...
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Is the total energy of the Universe not invariant?
Consider a Universe which has only one object (bigger particle). The object exploded (somehow) into two smaller particles (with some release of energy). Consider the two particles to have masses M and ...
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