All Questions
1,007 questions
2
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How is the CNO cycle able to occur in main sequence stars if they only fuse hydrogen into helium?
From what I understand, main sequence stars only fuse Hydrogen into Helium, and this is mainly due to the proton-proton chain or the CNO cycle.
However, the CNO cycle requires a carbon catalyst. If ...
- 521
0
votes
1
answer
580
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What is the formula to calculate the parallax angle?
The images were rendered in Blender. The two images were rendered 20 meters apart, side by side. The focal length is 50 mm if that matters. What is the formula to calculate the parallax angle θ as ...
- 11
2
votes
3
answers
494
views
Can you explain this line from "A brief history of time"?
Newton realized that, according to his theory of gravity the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point? ...
- 39
12
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3
answers
3k
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What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?
What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?
To my understanding these are the two sources of luminosity for a star, so I'm ...
- 223
18
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6
answers
6k
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If space is a vacuum, how do stars form?
According to what I have read, stars are formed due to the accumulation of gas and dust, which collapses due to gravity and starts to form stars. But then, if space is a vacuum, what is that gas that ...
- 837
4
votes
2
answers
369
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Why is there no stars made of bosons?
Consider the white dwarf (or similarly neutron stars), which can be modeled as a star made of degenerate Fermi gas:
A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed ...
- 480
1
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0
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279
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What is the difference between free-fall timescale and dynamical timescale?
I have encountered these terms quite often in astronomical textbooks, and sometimes they are used interchangeably. I have also heard that the free fall timescale is larger than dynamical timescale. ...
- 425
2
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1
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139
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Can a photon lose all of its energy due to gravitational redshift?
Imagine a photon that is emitted by a star that is at infinity with respect to me. We can observe the gravitational redshift happening to that photon with respect to my reference frame.
I was ...
- 117
10
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1
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848
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What really supports neutron stars?
I have read this question (to Andrew's answer, in the comments):
What supports neutron stars is the repulsion provided by the strong nuclear force between closely-packed neutrons. The central ...
- 29.3k
6
votes
4
answers
3k
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Will a neutron star always collapse into a black hole in the future?
If a star has a mass greater than the Chandrasekhar limit, will it definitely become a black hole in the future or does it need to satisfy additional conditions? Let me explain. Suppose the collapse ...
- 12.3k
6
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1
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469
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A question regarding water and a possible proton-proton chain reaction
I believe it is the case that stars as low as about 0.08 solar masses undergo the proton-proton chain reaction. So if you were to have a gas of more than about that mass of hydrogen in a location of ...
- 1,097
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1
answer
186
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How do we measure the size (not mass but dimensions) of far away galaxies?
I understand how distances to galaxies are measured. I think I even understand how their mass might be measured (by their orbital trajectories?). But how can we know How big far away stars are? Like ...
- 1,729
3
votes
2
answers
119
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If a star gravity can change the apparent location of another star on the sky, can it change the gravitational field vector of that star?
If a star gravity can change the apparent location of another star on the sky can it change the gravitational field vector of the second star? In simple words if a star gravity deflects the position ...
- 1,835
6
votes
3
answers
879
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Schwarzschild metric: stars vs. black holes
Background
The Schwarzschild metric can be used to describe the geometry of the vacuum spacetime outside a spherical massive object. For a star of radius $r$ (which is larger than the corresponding ...
- 105
1
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1
answer
78
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Would an extremely slowly forming star ignite?
Nuclear fusion requires extremely high temperatures and pressures, both of which are created by the collapse of protostars.
But, what if the accretion of matter happened slowly enough that the core ...
- 3,001
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0
answers
54
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What is the definition of Dynamical mass?
I am looking into Protostars and Dynamical masses. I know as a whole system a protostar has a certain mass, which includes the envelope/accretion disk. However, if I wanted the mass of the protostar ...
- 11
1
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0
answers
64
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Calculation of the Collapse of Star into Black Hole [closed]
Using equations or a method of calculation using general relativity, how could one calculate the collapse of a star into a black hole?
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0
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35
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Why are the stellar winds of some stars composed of neutral particles?
A few years ago I was visiting a colleague to give the physics colloquium at their university and had a chance to chat with some of the professors in the Physics and Astronomy department. One of the ...
- 15.9k
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2
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68
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Can this question be solved without any calculation?
I came across this question on YouTube:
The formal solution to both models can be done by integration (the solution can be found here: https://youtu.be/cSjVEKVV1ls). After calculation the ratio of ...
- 115
27
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2
answers
4k
views
Why can't hydrogen and helium fuse?
In the hearts of stars, hydrogen atoms fuse together to make helium. After the hydrogen in the core is depleted, the star changes state and conditions at the heart of the star make it possible for ...
- 467
1
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2
answers
125
views
Partial derivative in hydrostatic equilibrium in star
In a simple model, a gaseous, non-rotating star consists of many thin, concentric spherical shells with radius $r$ and mass $\text{d}m$. The total mass of the shells within radius $r$ is $m$. The ...
- 1,169
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1
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238
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How much do clouds scatter UV light?
I understand that clouds are more transparent to UV light than longer wavelengths, but are they transparent enough that you would be able to make out stars in UV at all? What about the moon or the ...
- 173
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4
answers
153
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What would be the likelihood that when the Milky Way formed, it would be composed entirely of sun-like stars? [closed]
So, what would be the likelihood that when the Milky Way formed, it would be composed entirely of sun-like stars? What was the configuration of the gas, the history of the primordial stars, for this ...
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53
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Would a human body flying into the sun extend or decrease the time the sun is undergoing fusion? [duplicate]
Obviously 1 human body is... nothing compared to the sun, so if the question is easier to answer with 1 million, 1 billion, the entire human population that has passed away in history... the amount ...
- 161
4
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1
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297
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What would be the color of a deep, pure and vast liquid $\rm CO_2$ ocean if viewed from space (ignoring the atmosphere's influence)?
So far I had no luck trying to find the visible absorption spectrum of $\rm CO_2$ anywhere, all I get is the far infrared absorption spectrum and stuff like that.
If you just search "what color ...
- 43
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votes
3
answers
865
views
Why do they say universe will become cold with expansion?
The Universe is expanding and they say it will eventually become cold, and new star formation will stop.
But galaxies are only moving away from each other, and each galaxy itself stays intact and the ...
- 283
3
votes
1
answer
208
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Age determination of stars
In the report 'New observations of the most distant galaxies close in on cosmic dawn', an astronomer states: 'Using a well-understood age indicator based on the amount of hydrogen absorption seen in ...
- 1,169
1
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2
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66
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May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again?
May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again? My question is not about would that explosion leave a neutron star as a remnant but ...
- 1,835
2
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1
answer
770
views
What is the heaviest element being produced in Sun?
Helium is being produced currently in Sun. 3 questions.
Other than Helium what other elements are currently being produced in Sun right now.?
Looks like in 5 billion years, when Sun will become a ...
- 1,471
25
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9
answers
5k
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Are the physical structures in our sun of comparable complexity to those in the human brain? [closed]
The writings of Rupert Sheldrake tend to provoke strong emotions, be they ridicule, curiosity, outrage, sympathy, disgust, or otherwise. While Physics SE is not an appropriate forum in which either to ...
- 361
1
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1
answer
62
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Cross section for photon-electron interaction in high temperature, high density plasma
I need a plot for the cross section of the photon-electron scattering at high density and high temperature. I am working on a project for which I have to calculate the opacity of a hot, dense plasma (...
- 1,187
2
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2
answers
184
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Is drinking water an important feature for finding habitable exoplanets? Has it been found?
We need drinking water to live on other planets. Has drinking water been found on other exoplanets? Is drinking water an important feature for finding habitable exoplanets?
I want to (self) study in ...
- 376
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3
answers
1k
views
How can spectroscopy be used to find the composition of exoplanet atmospheres?
How can astronomers use light spectroscopy to measure the composition of different planets when they can't directly image the planet because the star that they are orbiting is so much bigger and ...
- 117
1
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1
answer
277
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Looking for a formula or model for planetary equilibrium temperature which takes into account the greenhouse effect
For a project I'm working on, I have made a bunch of hypothetical random planets orbiting random stars. I have come across the Stefan–Boltzmann law, which works nicely for any planet without an ...
- 11
2
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2
answers
136
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Rotational energy of stellar remnants
The theoretical maximum rotational energy a black-hole can have is 29% of its rest mass. We've often observed remnant black-holes spinning at nearly the speed of light. From this we conclude that ...
43
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2
answers
7k
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Is our solar system really that odd?
I have been learning about the solar system from popular science shows. In these shows they suggest that, after having seeing around 2500 other solar systems, astronomers have concluded that our ...
- 1,430
2
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2
answers
94
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The metric exterior of a massive object
The only condition apart from perfect spherical symmetry that is required for the retrieval of the Schwarzschild-metric $g_{ik}$ is actually ($R_{ik}$ being the Ricci tensor, the contraction of the ...
- 10.2k
1
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0
answers
42
views
Atmospheres and oceans on lower gravity planets
Using Earth as an example, how much less gravity could the planet exert and still retain its atmosphere and oceans? Or is it a matter of size, mass, magnetosphere, place in the solar system, all of ...
- 111
1
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2
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94
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Does a star's emitted energy equal the work of its gravitational field?
Based on the formula of this question, it is possible to estimate the difference of the Sun's gravitational potential energy now and after it becomes a white dwarf.
$$\Delta E = GM^2\left (\frac{1}{r_{...
- 17.1k
2
votes
1
answer
169
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Equations of state for white dwarf stars
I am dealing with some model describing the given composition of a white dwarf made with photons, degenerate electrons, positrons and ions. From that, I can get tabulated values of densities ranging ...
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-1
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2
answers
98
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Did we adapt to Earth or Earth to us? [closed]
I often hear that Earth is a unique planet because it has life and it has its own inhabitance. We also see a proper balance between plants and humans and other animals. Why life is not possible on ...
- 12.1k
0
votes
1
answer
113
views
A violation of energy conservation?
Imagine a universe which contains a single sun and nothing else.
The sum of the energy of the univese is then simply the energy contained in the sun and the photons it emits.
If I have a theoretical ...
- 85
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4
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302
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How can the mass of the sun be determined without using Kepler's law or gravitational lensing?
Can the mass of the sun be determined using the abundance of elements or alternative methods? It would be better to ask the question like this if we assume that I have an object that contains baryonic ...
- 71
3
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1
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173
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Why is Big Bang Nucleosynthesis favored over Stellar Nucleosynthesis?
We know that a hot soup of plasma as it cools (as space expands) can produce light elements if the baryon-photon ratio is just right and the space expands quickly enough so that the neutrons and ...
- 584
5
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1
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405
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Strange conservation of energy in Navier-Stokes Equations
We want to roughly model the fluid flow of a star; consider the following proposition:
In the absence of viscosity, and heat conduction, the Navier-Stokes Equations for a steady, spherically symmetric,...
- 4,635
2
votes
3
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130
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What would happen if all protons in the Sun had a charge of 1.000001 times the elementary charge?
The whole sun would be positively charge, but would it explode because of it? Or would it just expand a bit?
0
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1
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258
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How are we able to observe Fraunhofer lines in a star's spectrum?
How is it possible to observe Fraunhofer lines in the emission spectrum of any star, since the elements absorbing the radiation couldn't possibly absorb all the radiation corresponding to a particular ...
- 111
1
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3
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419
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Is the dark night sky paradox (Olbers' paradox) really a paradox if we count with simple astronomical observations?
So, I came recently to watch this video, which explains Olber's paradox and how it was solved with the big bang theory, doppler shift etc.
My question can be split into a more physical question and a ...
- 1,185
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3
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311
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Will energy ever run out? [closed]
Gravity is the source of all energy and it will never go away. So that means there will always be energy for us right? I have seen some places say that energy will go away eventually and the last star ...
- 1
1
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0
answers
82
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Why stars don't precess?
Assuming that rotation of stars, galaxies etc is determined basically randomly, the question is: why do all space objects rotate so 'neatly', with little or no precession? And what precession there is ...
- 127