All Questions
1,007 questions
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Infrared Telescopes and Surface Area
I have been reading a paper on about exoplanets, specifically measuring the temperature of exoplanets using infrared telescopes.
The paper compares exoplanets with neutron stars (NS) remarking that ...
- 129
0
votes
2
answers
67
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How to track orbit of an exoplanet?
I was wondering if there is an established method to keep track of the orbit of an exoplanet assuming we know $a$ - the semi-major axis of the orbit, $e$ - the eccentricity of the orbit, and $i$ - the ...
- 500
1
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0
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49
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Do Efimov states contribute to fusion reactions other than the triple-alpha process?
An Efimov state is a three-body quantum state in which each two-body subsystem is unbound, but the system as a whole is bound because of the large s-wave scattering length. Intuitively, one can ...
- 4,110
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1
answer
91
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How to correct the Schwarzschild metric in the presence of Dyson sphere?
I was solving a problem in general relativity about Dyson sphere around a star. I don't have any problem solving the problem but in the question Dyson sphere was assumed to be massless. I checked ...
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1
answer
1k
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What is the process of star formation? [closed]
What is the process of star formation and what happens to stars after their death?
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1
answer
28
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What cause protostar to become optically thick?
So far I get that the cloud will contain CO and will reacts with photons which cools the core but at some point the clouds becomes optically thick and allows the core to heat up. What causes the core ...
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0
answers
49
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Minimum energy principle for stars
In Townsend's Black Hole lecture notes, he says that at equilibrium, $E = E_{grav} + E_{kin}$ is a minimum, where $E_{grav}$ is the gravitational potential energy $-\frac{GM^2}{R}$ and $$E_{kin} = nR^...
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1
answer
40
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Is the light impact on universe expansion is neglectable?
Imagine a universe with the below properties in a present time.
It has only two stars
The stars are located 1 light-year apart
The stars have the same properties as our sun today.
The stars are at ...
- 2,167
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1
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86
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Should it be classified as intrinsic or extrinsic variable star if the brightness of the star changes due to the expansion of the universe?
The Wikipedia article on Variable stars says the following:
Variable stars may be either intrinsic or extrinsic.
Intrinsic variable stars: stars where the variability is being caused by changes in ...
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-1
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2
answers
75
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Spectrum of stars
How does the spectrum of F type stars differ from our sun? I have tried to find the information on the internet but I haven't found anything that helps me. I need the information for a novel I am ...
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0
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33
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Research on exoplanets using available data from TESS
I am a high school student who is proposing research on exoplanets for my junior research project, I have several questions:
I have seen studies where researchers survey star systems and then find ...
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0
answers
44
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Star formation rate in different galaxies
I was looking for some scale to compare my result of star formation rate and see if it is moderate or high or low. But I couldn't find any scale. Is there any paper related to such scale where Star ...
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2
votes
1
answer
158
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Proxima Centauri radio signal
I have recently seen an article about an unusual radio signal coming from Proxima Centauri region.
I understand there is a debate around the nature of this signal.
My question is related to this ...
- 611
0
votes
1
answer
37
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Could Black Hole be formed with the center of some stars? [duplicate]
If the LHC might make black holes, why would tiny or not so tiny black holes be potentially created with the very hot and dense core of a really big star?
- 2,288
11
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5
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3k
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Shouldn't some stars behave as black holes?
Some of the "smaller" black holes have a mass of 4-15 suns. But still, they are black holes.
Thus their gravity is so big, even light cannot escape.
Shouldn't this happen to some stars, that ...
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3
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1
answer
155
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Balmer spectroscopic lines from plasma?
In stars, the Balmer lines are usually seen in absorption, and they are "strongest" in stars with a surface temperature of about 10,000 kelvins (spectral type A). Balmer series|Role in ...
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1
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123
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Where does a photon('s energy) originating from the sun's core spend most of its time?
AFAIK the photons inside a star essentially perform a random walk until they leave. Considering these factors:
closer to the core the curvature of the sphere that seperates "closer to the core&...
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3
answers
3k
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What is the origin of the Sun light?
The Sunlight is an electromagnetic radiation.
Is it known what is the origin of this radiation? Can it be adequately described by classical electrodynamics (Maxwell's equations) as a motion of ...
- 2,291
1
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423
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How does metallicity affect stellar evolution?
The main sequence evolution of a solitary star depends most of all on its initial mass. Other factors influencing its evolution are the initial metallicity, rotation and magnetism.
Question: how does ...
- 1,169
3
votes
1
answer
125
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How does a black hole capture an approaching star and force it to start an elliptical orbit?
Let's assume that a standing still black hole attractor can have a star orbiting it in an orbit if the star was somehow a result of the same past proccesses as the black hole.So the star must be on a ...
- 1,835
2
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1
answer
84
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Textbooks on cosmology *after* recombination
I am a theoretical physicist and I have a reasonable understanding of the early universe, inflation, FLRW metric, leptogenesis, baryogenesis, perturbations, the works (mainly in the style of the ...
2
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4
answers
544
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If the Sun's temperature is around 5000K to 6000K which means it is a yellow star, why does it appear white in space? [duplicate]
If the thermal radiation of stars is close to the thermal radiation of a black body the sun should appear yellow but yet it appears white because of emitting all of visible wavelengths which combine ...
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1
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1
answer
110
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Nuclear reactions in stars: do they all proceed by tunneling?
Energy production in stars occurs mainly when a nucleus absorbs a proton or fuses with another nucleus. Some examples:
(i) $\rm{p}(\rm{p},\rm{e}^+\nu)\rm{d}~$ and $~\rm{d}(\rm{p},\gamma)^3\rm{He}~$ ...
- 1,169
2
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1
answer
229
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Physical relation between adiabatic constant $\gamma$ and polytropic index $n$
I am study about stellar model of stars by using polytropic equation of state $$P=k\rho ^{\gamma}$$ or $$P=k\rho ^{1+1/n }.$$
I studied that different values of polytropic index $n$ describes ...
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2
votes
2
answers
375
views
Calculating apparent density of stars in sky, given an area and distance away from my viewpoint
According to this source, there are $5077$ visible stars in the night sky, and a full sky area of $41253$ square degrees of sky. This makes for a density of $0.12$ stars per square degree of the sky. ...
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2
votes
1
answer
375
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Why is the isotope Nitrogen-14 formed preferentially to Nitrogen-15 in the CNO-cycle in stars?
Most of the universe's nitrogen is formed in larger, main sequence stars using the CNO Cycle, right?
But I cannot find a good, specific explanation as to why $^{14}$N, with both an odd number of ...
- 4,709
2
votes
1
answer
71
views
Death of Stars and Red Giants [duplicate]
As a matter of fact, I was learning stellar astrophysics where I couldn't understand the chain of events at the time of death of stars,
Once the hydrogen fuel core is exhausted, the stars start ...
- 2,062
2
votes
1
answer
127
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Jupiter-sized planet orbiting a white dwarf?
I read this news about a Jupiter sized planet orbiting a white dwarf.
It is still puzzling to the scientists that how it remained as a single piece.
NOTE: I went through the Astro.SE link given in ...
- 8,476
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votes
2
answers
51
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Does the Sun have enough gravitation to bind its hydrogen/helium plasma?
"Does the Sun have enough gravitation to bind its hydrogen/helium plasma?"
So my question arises from the fact that high energy (or high temperature in other words) hydrogen or helium gas ...
- 115
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2
answers
3k
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Why is Stephenson 2-18 so large?
How does a star as large as Stephenson 2-18 get this big? It is 2500 times larger than the sun.
Did it start out as a large star with a lot of gas left over that gradually consumed the gas growing ...
- 2,754
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1
answer
103
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Equations for developing a hypothetical Solar System
I am currently going down the rabbit hole of writing a story but I would like it to be set in a universe which is believable. Therefore I am trying to create a hypothetical solar system in which the ...
4
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2
answers
578
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Matching Metrics of Gravitational Collapse in Weinberg's Gravitation and Cosmology
In chapter 11, section 9 of Weinberg's Gravitation and Cosmology, the metric of a collapsing pressureless star of uniform density $\rho(t)$ is derived. In comoving coordinates, it essentially looks ...
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2
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1
answer
98
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Astronomical objects that should have magnetic bubbles similar to those found by the Voyager probe at the edge of our solar system
I've known about the existence of magnetic bubbles at Solar System's edge from a video edited by NASA from an official channel of YouTube, I refer [1] (as explicitly stated in the title, it was a ...
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4
answers
182
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Why are black holes so special? [closed]
When reading about black holes, I have also read about things relating to black holes like holographic principles, parallel universes, black hole connecting multiple universes, etc. But black holes ...
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2
votes
2
answers
95
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Could you know in advance specifically when a star will go supernova?
I've been thinking about star trek 2009 and star trek Picard in which they happen to talk about a sun inside a fictional solar system which goes supernova destroying a particularly important planet to ...
9
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2
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2k
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Why is there more lead and mercury in the universe than gold?
I am watching a Science Channel program on the collapse of massive stars and it got me wondering... What is the distribution of heavier than iron elements in the universe. (It is my understanding ...
- 2,754
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3
answers
405
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Why don't main sequence stars continuously expand?
I understand main sequence stars become subgiant when hydrogen is depleted in their cores and they start hydrogen shell burning. But I don't understand why this process is divided into two distinct ...
- 133
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1
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166
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How do we experimentally estimate the luminosity of a distant star?
While calculating the matter density of the universe, we need to find luminosity. How do we experimentally estimate the luminosity of a star?
0
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1
answer
74
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Definition of eclipsing binaries?
In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
- 849
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1
answer
118
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Does light return to its starting point in a closed universe?
I was reading about the possibility that our universe could be a closed sphere.
from Sean Carroll “in a closed universe, one that wraps around on itself to form a compact geometry, like a three ...
- 998
4
votes
1
answer
449
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How come gravity generates enough pressure to start a fusion reaction in stars even though it is the weakest force?
Given the fact that gravity is the weakest of all forces, how does a gas cloud manage to collapse on itself under gravity and start a fusion reaction, outweighing the electromagnetic and nuclear ...
- 1,378
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1
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173
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Books for Solar physics
I am thinking about applying for an internship at a university under a professor who does Helioseismology.
What resources would you recommend me for being ready for such an internship?
Can you suggest ...
3
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2
answers
537
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What would happen to the Sun if you reflect all its emitted e.m. radiation back? [duplicate]
What would happen to the Sun if you would reflect, in whatever way, all the outgoing electromagnetic radiation (Solar winds can be neglected)?
user267867
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2
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Number of seemingly brightest stars: minimum around G-stars
This plot gives the amount of the seemingly 10000 brightest stars.
Can someone help me to explain why there's a minimum at number 3, I know how to explain 1 (there are less
big stars) and 2 (small ...
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1
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0
answers
44
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When do planets formed via core accretion in a proto-planetary disk stop gaining mass?
I was just trying to go over some of the contents in my exo planets course and wanted to know that if all the planets that form via core accretion continue to attract all the dust in a proto-planetary ...
- 1,545
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2
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290
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Stellar nucleosynthesis
I would like to learn more about fusion in stars. The question I have is whether there exists a graph showing exactly which elements take part in the reactions.
Here, I managed to find some data ...
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0
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89
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Datasets for calculation of exoplanet properties
I would like to create program for calculation exoplanet properties, but I only found transit dataset from Kepler on NASA website. From light curve I can calculate:
planet radius $r$ from $\frac{r_{...
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3
answers
84
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Investigating colour of a star when in motion [closed]
The star Alpha Centauri is 4 light years from Earth. For an astronaut travelling at $c/2$ from
Earth to Alpha Centauri. So, this apparently means
The colour of a distant star perpendicular to the ...
1
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1
answer
46
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Which planets of our solar system could be discovered from another solar system with present technology?
Recently many exoplanets have been found orbiting nearby stars. Assume there is a civilization with identical technology residing in a nearby (< 100 light years) solar system. Could they discover ...
- 1,251
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132
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Trouble understanding exactly why core of sun does not mix with outer layers
I’ve had trouble understanding exactly why there is not more mixing of plasma at the core of the sun with the outer layers.
I understand the difference between the radiative zone and the convective ...
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