All Questions
1,007 questions
1
vote
0
answers
23
views
Galactic bars and star formation
I have recently been reading on barred galaxies and am confused as to whether they aid or obstruct star formation as a general rule. Some papers state that they aid star formation, whilst others ...
- 11
-1
votes
3
answers
487
views
Why does the sun and gas planets in our solar system weigh more than the earth?
I was reading a space.com article about What Is The Sun Made Of? The article says that the sun is made of plasma and gas. If this is the case, how is it that the earth which is solid weighs less than ...
- 555
1
vote
2
answers
1k
views
Relation between central density and stellar mass (2)
Comparing stars with different masses, the central density is lower in a heavy star than in a low mass star (assuming that each star has the same composition and has just reached the stage in which it ...
- 1,169
0
votes
1
answer
387
views
What will be the mass of the sun when the core is depleted of hydrogen about 5 billion years from now?
Our sun converts 600 million tons of H to He every second, that is 5 million tons of matter into energy through nuclear fission. However, as the core of the sun continues to shrink the outer layers of ...
- 315
2
votes
0
answers
130
views
How does Buchdahl's interior solution satisfy the Einstein field equations?
I was reading Schutz A First Course in General Relativity (2nd Edition) Section 10.6, where the Buchdahl exact solution was written down as follows:
For $Ar'\le\pi$,
$$
\exp(2\Phi) = (1-2\beta)(1-\...
- 21
4
votes
2
answers
1k
views
Understanding the Chandrasekhar limit for white dwarfs and its relation with supernovas
So if I understand correctly, the Chandrasekhar limit ($\sim 1.4 \ M_{\odot}$) is the maximum mass that a white dwarf can have. Beyond this mass, the degeneracy pressure of the electrons can no longer ...
0
votes
1
answer
121
views
Stellar structure integration
I have some issue regarding the stellar structure. I know analytically the equation of state, and I have been asked to build the structure of the star from these two equations
$\frac{dP}{dr}=-\frac{G ...
- 108
51
votes
9
answers
8k
views
Why doesn't the nuclear fusion in a star make it explode?
I have a rather naive question. In stars such as the Sun, what prevents the whole thing exploding at once? Why is the nuclear fusion happening slowly? I can only assume that something about the fusion ...
- 756
2
votes
1
answer
455
views
In fusion inside stars (sun) or very hot gasses, how do the electrons get bound and what about tritons and $D$-$T$ vs $D$-$D$ fusion?
Most texts I've read focus on just the nuclei to begin with, but eventually start talking about Helium (or other) atoms and isotopes. A few aspects aren't clear to me and I'd be grateful for some ...
- 53
0
votes
0
answers
90
views
Solving coupled integral + differential equations for ionoization and combination of gases near a star
The following set of coupled differential + integral equations appear regularly in the literature (e.g Osterbrock, "Astrophysics of Gaseous Nebulae and Active Galactic Nebulae"):
$ n_H(r) \int_{\...
- 61
0
votes
1
answer
74
views
Electron degeneracy in white dwarfs
Consider a plasma in a star. Now in a plasma electrons are so excited that they can no longer be held by the electromagnetic field of the nucleus. But then when we are talking about cores or red ...
- 195
0
votes
3
answers
261
views
How are the relative distances of celestial objects from the Earth calculated using observations at a single time instant?
How does one find the distances of celestial objects in the night sky, such as the Moon and the stars, from the Earth using a snapshot of information (including, say, the intensity and wavelength of ...
- 2,402
19
votes
7
answers
8k
views
What is a simple argument to prove that the stars in the sky are further away from the Earth than the Moon?
How do we know, without using modern equipment, that the stars are further away than the moon in the night sky? Further, is there a simple and actionable argument to prove that this is indeed the case?...
- 2,402
0
votes
2
answers
46
views
Formation of Life on various planets
Is there any theory that suggests every creature (including bacteria and fungi) in our planet is formed by the atoms of our planet. If that is true, then is it possible that any other organisms will ...
- 143
3
votes
2
answers
146
views
When the star formation begins?
We can separate the history of the universe in different epochs.
Radiation dominated epoch, matter dominated epoch, and dark energy dominated epoch, and we can divide the epochs in different ways.
...
- 439
20
votes
3
answers
7k
views
Why do main sequence stars get bigger and more luminous as they age?
As stars age, the concentration of hydrogen in the core decreases, which lowers the power output, causing an imbalance between outward radiation pressure and inward gravitational pressure. This causes ...
1
vote
1
answer
175
views
A question on Przybylski's Star
Przybylski's Star is a rapidly oscillating AP star of 4 solar masses, 355 light years from earth. It contains high levels of unusual elements like strontium, holmium, niobium, scandium, yttrium, ...
- 2,754
1
vote
0
answers
97
views
Im trying to prove that a star can be described by a polytrope by deriving the polytropic relation of $P\sim p^n$ from the stellar structure equations
Suppose that in a star, the only source of energy generation is radioactive decay, so the energy production per unit mass is constant and independent of density and temperature. Further suppose that ...
3
votes
1
answer
391
views
Measuring the interior temperature of the Sun
We frequently measure the "temperature of the Sun" using Wien law: $\lambda_m T = b$ where $b$ is the displacement constant, $\lambda_m$ is the peak wavelength obtained from the spectrum, and $T$ is ...
- 125
0
votes
2
answers
382
views
Is it possible to know in advance that Alpha Centauri has exploded?
Alpha Centauri is 4.3 light years away. If it exploded suddenly, would we be able to know this in advance? As the light from the supernova will not reach us before 4.3 years.
2
votes
1
answer
244
views
distinguishing redshift from star's color
How do scientists find out the true color of the star's light as well as the true doppler shift (relative speed)? Seems to me you wouldn't know how to separate out those 2 values.
- 942
0
votes
1
answer
40
views
How to tell a population 3 star in red shifted galaxy?
I read that population 3 are metal poor stars especially those very very massive ones will quickly exhaust their fuel and goes into supernovae when their internal pressure drops due to pair ...
- 13.1k
12
votes
2
answers
2k
views
How does a spectral line tell us about the magnetic field of a star?
An absorption line in the spectrum can indicate the abundance of a chemical element in a star; but according to NASA, it can also tell us about the magnetic field of the star. Can a spectral line ...
- 13.1k
3
votes
2
answers
223
views
Why is the second stellar structure equation first-order ODE?
the 2nd structure equation is first order, but we seem to have two boundary conditions (e.g., $dP/dr = 0$ in a star’s center and $P=0$ at the surface) – but first-order ordinary differential equations ...
4
votes
0
answers
25
views
Effect (if any) of strong(ish) gravity radiation on stars
Two black holes merge, and a good few percent of their total mass is converted into gravitational radiation.
Years or decades later, the resulting gravity wave passes through nearby stars. Does it ...
- 700
4
votes
2
answers
719
views
Are the muon/tau neutrinos produced in the Sun? If not, then where?
I was reading about Solar Neutrinos, and apparently they are all Electron Neutrinos.
However, there are two other types of neutrinos, the Muon and Tau Neutrinos. Does the Sun produce them? If not, ...
- 704
25
votes
4
answers
5k
views
A star or a galaxy?
When we look into the beautiful sky in the night, exclaiming how beautiful these shining stars are. My question is how could we tell, whether any of these shining "point" is a star or a galaxy?
If ...
- 613
1
vote
2
answers
156
views
HD 140283 and the age of universe
I am watching a video on a star that is supposedly older than the universe. HD140283 (Methuselah). According to the first 20 years of research on the star, scientists believed the star is just over ...
- 2,754
3
votes
1
answer
415
views
Evolution of red dwarf stars
While low mass stars (initial mass approximately $0.1 M_\odot$ to $0.8 M_\odot$) are quite numerous, their evolution seems to draw relatively little attention. The lower central density and ...
- 1,169
6
votes
2
answers
520
views
Why do later fusion stages in a star last shorter?
When most of the hydrogen in the core of a massive star has fused to form helium, the next fusion stages (helium, carbon, neon, oxygen, ...) produce less and less energy in a single fusion reaction. ...
- 1,169
0
votes
0
answers
26
views
Existence and evolution of P-type "asymmetrical binaries"
I'm not sure how those are called so let me explain what I mean by "P-type asymmetrical binaries" - I'm thinking of two stars of very different masses (originally) that orbit each-other fairly closely....
- 31
0
votes
1
answer
66
views
Can I destroy a star faster by trapping it in a spherical mirror? [duplicate]
What would happen, if I were to trap the Sun in an almost perfectly reflective spherical mirror? I'm assuming this would accelerate the life of the sun and reduce the timescale required to turn it ...
- 7,455
2
votes
3
answers
2k
views
How to find transverse component of star's velocity given its proper motion and distance from observation point?
If $\mu$ is the proper motion of a star in arcseconds per year, and $d$ is the star’s distance from us, then the transverse speed, $v_t$ will be
$$v_t=d\sin\mu$$
For small motions (assumed for ...
- 2,520
2
votes
2
answers
668
views
Is hydrogen produced in the universe? [duplicate]
Since stars use hydrogen initially for fusion which then produces heavier elements. Where does all this hydrogen come from? Does all the hydrogen come from the birth of universe? If yes then will new ...
- 21
0
votes
2
answers
105
views
Effect of star's binding energy due to general relativity?
Due to the curvature of space-time the distances near the star are length contracted. So if that's the case then doesn't that mean that the binding energy of star should be more since the distance ...
- 1,288
5
votes
0
answers
110
views
How would a quark star maintain degeneracy near the surface?
I'm still not exactly understanding how a quark star could possibly exist for more than a fraction of a second. Neutron stars are already hypothesized to have degenerate quark matter at their cores, ...
- 170
0
votes
1
answer
73
views
Why is the temperature of a star not intensive?
The temperature of a star obviously depends on its mass. Does this mean that temperature is not always intensive?
- 586
0
votes
2
answers
51
views
What would the effect of an antimatter star be upon a normal matter planet? (Thought experiment)
Based on the answers from this question: Would the solar wind from an antimatter star be any different from a non-antimatter star?, it seems that an antimatter Sol type star would conduct fusion ...
- 143
5
votes
3
answers
209
views
What's lowest mass object that can form from collapsing gas?
Is there a minimum mass for an object that can form on its own from collapsing interstellar gas without being bound to a larger star's protoplanetary disk first?
There are red dwarfs, brown dwarfs, ...
- 8,260
0
votes
3
answers
112
views
Would the solar wind from an antimatter star be any different from a non-antimatter star?
Antimatter is any element of matter with an opposite charge than normal matter.
As such, would an antimatter sun conduct fusion normally such that it would it radiate photons, or would it radiate ...
- 143
0
votes
1
answer
142
views
Thermal fission of gold? [closed]
Here's a slightly silly idea that arose from this question "What elements would be created in a star composed entirely of gold?":
If we accumulate a lot of gold (really a lot) fast enough, it will ...
- 709
1
vote
0
answers
69
views
Theoretically, Is it possible to create a nova by firing large masses into a sun?
In a science fiction story (Bobiverse) a nova is created by accelerating two small planets at relativistic speeds into a sun from opposite sides.The shockwave creates hydrogen fusion on opposite sides ...
- 1,035
3
votes
2
answers
1k
views
What would Happen if a Primordial Black Hole, with 5-10x time the mass of Earth, were to fall into our Sun?
So lately i heard of this theory that planet 9 might be a Primordial Black Hole (PBH) with 5 - 10 times the mass of Earth. I was thinking to myself, what would happen, if such a PBH (if it even exists)...
- 41
5
votes
1
answer
700
views
Could Alpha Centauri be made of anti-matter? [duplicate]
How can we tell if a star is made of matter or anti-matter? For example, is there any difference spectroscopically? Or could we tell from cosmic rays?
If half of the stars were made of matter and ...
0
votes
1
answer
97
views
Temperature function for stars?
I was thinking that for a star to be stable, the rate of energy emittance through a shell of radius r is constant, otherwise there would be a buildup of energy which would change the temperature and ...
- 2,020
0
votes
1
answer
61
views
Looking for a good book on star stability
Can anyone recommend me any resources from which I could learn about how stars maintain a stable form, maybe using some thermal and nuclear physics, and maybe fluid dynamics, but not so advanced. ...
0
votes
2
answers
2k
views
How do Astronomers Measure the Mass of a Planet using Doppler Spectroscopy?
So, I am making an essay explaining planet-hunting techniques. And while I do get how astronomers measure the semi-major axis of a planetary orbit (using Kepler Laws), I don't get how they measure the ...
- 835
0
votes
2
answers
92
views
What conditions provide the oldest star?
If we define the start of the lifetime the protostar and the end of the lifetime a red giant (at max volume), what conditions would make this time the longest when the star was first formed and ...
- 2,700
1
vote
0
answers
71
views
Shooting Star Anomaly
Tonight I was walking home from the supermarket and saw an unusual shooting star.
It appeared at a point in the sky, bright red and accelerated to a visible extent far faster than any other shooting ...
- 131
0
votes
2
answers
201
views
Why does the formation of iron in stars not produce any energy?
Why does the formation of iron in stars not produce any energy. I have a hunch that it might have something to do with the fact that iron has the highest binding energy per nucleon and hence (...
- 49