All Questions
1,007 questions
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What is the mass of the brown dwarf/red dwarf boundary in super metal-rich objects?
I am trying to make a red dwarf with twice the metallicity of the Sun. What could its theoretical minimum mass be in Jupiter masses?
- 13
1
vote
1
answer
44
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When and why does a protostar start to radiate again?
I'm currently the formation processes of stars in Carroll's "An Introduction into Modern Astrophysics" and Bennett's "The Essential Cosmic Perspective" and I'm currently stumped ...
- 85
-7
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1
answer
118
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Does matter-anti-matter burning happen in stars?
I asked ChatGPT at what temperature anti-matter can spontaneously be created and I was told that a billion kelvin would be enough, which puts it into the temperatures at the cores of stars.
That seems ...
- 474
-1
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2
answers
89
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Would a star with the same mass as a Black Hole appear as a dark star?
In the case of the Black Hole (BH) the surface is a few Km from the center of mass whereas in the case of an active star with the same mass as the BH, the surface can be be many millions of Km distant ...
- 4,376
0
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2
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48
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Origin of Angular Momentum in Accretion disk formation
I read this paper, Formation of the Asymmetric Accretion Disk from Stellar Wind Accretion in an S-type Symbiotic Star, I didn't quite understand where the angular momentum came from.
Where I'm ...
- 31
3
votes
1
answer
112
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Can stardust give rise to new stars?
My question is if when a star dies, the material ejected (by supernovae or otherwise) can act as raw materials for the next generation of stars. If I understand correctly, stardust mostly consists of ...
0
votes
1
answer
45
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Combination of line profiles
When combining two line shapes (for example a Gaussian and a Lorentzian), the effect of Both of them combined is the convolution of both (with a Gaussian and a Lorentizan,this is the Voigt function). ...
- 31
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2
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63
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Would a star made out entirely of Helium-4 be a boson star?
Boson stars (https://en.wikipedia.org/wiki/Exotic_star) are hypothetical, exotic matter, models of stars. They usually rely on exotic particles like axions.
However, Helium-4 is considered to be a ...
- 2,878
6
votes
2
answers
199
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Why Cepheids have Period Luminosity relation?
According to my astronomy teacher, Cepheids is a type of variable stars that has Luminosity-Period relationship:
$M \propto log(T)$
, where $T$
is the pulsation period of Cepheids.
But I have a ...
- 453
7
votes
6
answers
3k
views
Why is pressure in the outermost layer of a star lower than at its center?
I have done the math and I have obtained the hydrostatic pressure in a star is lower at the outermost layer of a star than in its center, where the pressure is actually maximum. Although the equations ...
- 1,880
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votes
1
answer
106
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What would happen if the sun became the size of the earth? [closed]
Imagine that a sudden force crushed the Sun from its current size down to the size of the earth,held it at that size for a few moments and then disappeared. What'd happen?
I haven't done any of the ...
1
vote
0
answers
28
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Mass-volume relation for a star - explanation
In the game Universe Sandbox, I created a gas giant (made of pure hydrogen) and begun increasing its mass and watched how its radius changed and how it evolved into a star. While it was already a ...
- 112
0
votes
2
answers
49
views
Stars that have fairly high gravitational redshift and calculation of their surface temperature by Planck emition spectra?
How high can the ratio between gravitational redshift and planck emition spectra be depending on the mass of the star so by how much this gravitational redshift could elongate the Planck spectra of ...
- 2,275
0
votes
2
answers
94
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Relationship between gravitational force and fusion energy in stars [duplicate]
From what I understand, stars like our Sun constantly have a gravitational force on their surface due to their mass, which is balanced out by the fusion reactions taking place in the core of the Sun.
...
- 51
2
votes
1
answer
46
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Trajectory of supergiants on HR diagrams
I am a secondary school student currently studying cosmology. My A Level textbook supplies the following HR diagram with regards to what trajectories different stars follow:
I found myself unable to ...
19
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6
answers
9k
views
If gravity is not a force, what makes massive objects spheroid?
For most of my life, the explanation given for why celestial bodies like stars, planets, etc. are round is due to gravitational force. Simply put, if an object has enough mass, it will, in turn, have ...
- 413
1
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1
answer
42
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Sudden drop in temperature in Sun convective zone
In the solar temperature graph, why does the temperature drop suddenly in the convective zone? Is it because some energy is needed for ionisation?
- 11
1
vote
1
answer
69
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Obtaining TOV equations
I am trying to obtain the first TOV equation
$$
(\rho+p) \frac{\mathrm{d} \Phi}{\mathrm{d} r}=-\frac{d p}{\mathrm{~d} r}
$$
using the metric
$$
\mathrm{d} s^2=-\mathrm{e}^{2 \Phi} \mathrm{d} t^2+\...
- 161
1
vote
1
answer
36
views
If a star's luminosity doubles, does its received flux double?
If the luminosity of a star increases or decreases in some way, would the received flux increase or decrease by the same amount (linearly) or would it change by the square of the luminosity (inverse ...
- 190
1
vote
0
answers
27
views
Is there a way to calculate the habitable zone distances of a star?
What would you need to calculate the habitable zone distances of a star? I am aware of the Stefan-Boltzmann Law and Wein's Law to calculate the Luminosity of the star, and that the flux decreases with ...
- 190
0
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0
answers
31
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Is the sun multinucleated or is there just one point at or near the center of the sun where fusion is occurring?
I was just reflecting upon my thinking and probably any illustration in books or movies: I assumed a single general area near the "geographical" center where the actual fusion occurs.
But ...
- 2,288
0
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0
answers
21
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A general theory of convection currents using continuity equations
In an Astrophysics & Cosmology summer programme I attended last summer at UCL we were taught that stars seem to transport matter from the regions near the core to the surface through convective ...
- 1,880
1
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1
answer
124
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Luminosity and absolute magnitude relationship
Context : an exercise gives the temperature, mass, distance and apparent magnitude of Sirius B and asks to calculate its density.
One key step of the calculation is to get the luminosity from the ...
3
votes
2
answers
548
views
Is it possible, by monitoring the brightness of stars, to find a “copy of the Earth + Moon” near them?
More than a dozen Earth-like planets have been discovered around nearby stars based on observations of changes in the brightness of their sun as they pass across its disk (transit events). If an Earth-...
- 168
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0
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252
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What if Phoenix A collided with UY Scuti
What if Phoenix A collided with UY Scuti? Phoenix A is estimated to be 100 billion times bigger than the suns radius, while UY Scuti is estimated to be 1700 billion times bigger than the sun. What I ...
- 103
0
votes
2
answers
101
views
Can stars bend light?
Is it possible for a star to be so big that its gravity can bend light like a black hole? If so, would the star appear dark or bright, or would it collapse on itself?
- 103
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1
answer
41
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Determining star position and velocity to deduce closest approach?
I am trying to replicate the results found for Gliese 710's closest approach of ~0.05 parsecs in 1.3 million years approximately. I thought that by plotting the sun at (0,0) and using the stars ra,dec,...
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1
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2
answers
105
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Are black holes XXXL stars?
Am I right to think that black holes are stars that are so dense and heavy that radiation and matter cannot leave from it's surface?
5
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2
answers
1k
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How do neutron stars overcome neutron degeneracy?
In a white dwarf, the star is prevented from collapsing due to the Pauli exclusion principle. If the star is heavy enough, the protons in the star will capture electrons, forming neutrons and ...
- 86
1
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2
answers
105
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Luminosity of stars
Good afternoon, I am attempting to calculate the ratio of temperature and luminosity between two stars, one entirely made of iron and the other of hydrogen, with the same volume.
To do so, I have ...
- 161
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46
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How is the trajectory of a star found relative to the Sun?
So i know we can get radial velocity by measuring blue shift and then we can use the distance to the star and its proper motion to get its tangential velocity. In the case of Bernards star, its ...
- 39
0
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0
answers
67
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What mass fraction of a main sequence star produces energy?
Only some fraction of the total mass of a main sequence star produces energy in the star's centre through the pp-chains, or in heavy stars, the CNO-cycle. My question is about the mass fraction where ...
- 1,169
3
votes
2
answers
82
views
Massive star evolution leading to white dwarf?
Is it possible that a star with an initial mass greater than $12 M_\odot$ loses so much mass in the giant phase that it eventually becomes a white dwarf? If it is possible, what constellation or ...
- 1,169
1
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0
answers
37
views
Why are the hottest stars appear mostly in blue or blue-white? [duplicate]
Does it have to do with anything regarding wavelengths and frequencies..
- 11
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0
answers
18
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What is a simple way to estimate $σ_{RV}$ assuming photon noise in radial velocity measurements?
Hello there i have been trying to figure out what is wanted in the question "Simple way to estimate σ_RV assuming photon noise" for a presentation. But i can not seems to find much, but i ...
2
votes
0
answers
57
views
Would ocean tides on the moon of a gas giant really be kilometers high?
I was reading an article on exomoon habitability constrained by illumination and tidal heating. The article imagines an Earth-like exomoon around Jupiter-like host planet. That got me thinking about ...
- 21
4
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2
answers
341
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How to measure the ratio of a planet's radius to a star?
I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information.
One of ...
- 1,723
1
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2
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125
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Number of red giant phases for stars between 2.2 - 8 solar masses
It is my understanding that stars the size of our sun will go through two red giant phases. The first one will occur when fusion of hydrogen to helium begins to happen in a shell surrounding the ...
- 405
4
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0
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117
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Hills Mechanism
The Hills mechanism postulates that when a stellar binary system is perturbed by a supermassive black hole (SMBH), the tidal forces at play result in the capture of one star while simultaneously ...
- 1,327
-4
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1
answer
84
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Are there laws of creation for biological life? [closed]
I am no scientist, but I do love science as well as the unknown. Are there laws of creation for biological life? Would it be safe to assume that our bodies are made up from things that came directly ...
8
votes
3
answers
4k
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What is the most highly charged celestial body in the universe?
Generally speaking, the universe is electrically neutral and
the universe abhors an unbalanced charge.
Wherever there is a positively charged object, you can bet there is a negatively charged object ...
0
votes
1
answer
72
views
Color temperature and space
I often think about the universe and lately about the color spectrum. so I wanted to ask how much the temperature of the body depends on the color. the hottest star I've found is 200,000 k and its ...
14
votes
2
answers
1k
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Is gravitational binding energy or gravitational self-energy a source of gravity?
The gravitational binding energy or self-energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. Equivalently, the ...
1
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0
answers
99
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How can there be supermassive stars of 10000+ solar masses?
Wouldn't such supermassive stars blow themselves apart first via radiation pressure (per the Eddington limit)?
But they apparently exist, or at least are plausible:
Assistant Research Fellow, Ke-Jung ...
- 22.1k
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1
answer
45
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Salpeter mass function - past paper question [duplicate]
I'm doing a past paper and this is the question I'm struggling with (it's a standalone question with no other information given outside of this screenshot):
To answer it, I used the Salpeter mass ...
- 105
1
vote
2
answers
217
views
What is the total energy of newtonian polytrope stars of index $n > 5$?
In classical newtonian theory, we could find a general expression for the gravitational potential energy of a polytrope sphere (of pressure $p(\rho) = \kappa \rho^{\gamma}$, where $\gamma = 1 + \frac{...
- 7,677
2
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1
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543
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What is the equation of state (EoS) of a polytrope in general relativity?
I'm trying to numerically integrate the TOV (Tolman-Openheimer-Volkof) equations, using Mathematica. The code works, but I'm having issues with the polytropic equation of state (EoS). The equations ...
- 7,677
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2
answers
285
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What are the hex color code equivalents for the different classifications of stars?
Stars appear to be of various colors based on the visible light they emit. I am wondering if there is a hex color code that can be considered to be typified or average for the various classifications ...
- 143
1
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0
answers
59
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Olbers' paradox and thermodynamics? [closed]
So consider our universe as an isolated system which has reached thermal equilibrium. Now using the first law of thermodynamics:
$$ \underbrace{T dS}_{\text{Total energy}} = \underbrace{P dV}_{\text{...
- 1,349
4
votes
1
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262
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Could electron "Stars" exist? [duplicate]
Is there a point of balance where the gravitational pull of a sphere of electrons is equal to their electromagnetic repulsion?
That is to say, could it be possible to create stars that are made purely ...
- 41