Questions tagged [stellar-astrophysics]
Questions about inducing chemistry, physics, and many more branches of science into astronomy.
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Estimate the core pressure of a star
Consider a small column at a distance $r$ from the center of a star with a height of $\Delta r$ and a base area of $\Delta S$, a density within the column approximated to be uniform for a value $\rho(...
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What causes the Mikheyev-Smirnov-Wolfenstein (MSW) Effect? Virtual Z bosons?
What causes the neutrinos to oscillate more often or rapidly? Are they being “bounced around” by Z bosons in the intense furnace of the Sun? Is it due to an intense weak current?
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Can a relatively small addition of matter to a small volume of a star turn it into a supernova?
Can a relatively small addition of matter to a small volume of a star turn it into a supernova?
The rate of fusion in the CNO cycle increases very rapidly with increasing temperature, as shown in the ...
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In the onion-like elemental layers of a large mature star the neon is closer to the surface than oxygen, even though it is more massive... Why?
On both Wikipedia (Stellar evolution) and Lumen Learning (The Evolution of more Massive Stars) the Neon layer is depicted as being external to the Oxygen layer despite the fact that neon is heavier ...
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What is the relationship between core temperature and surface temperature in main-sequence stars?
The core temperature of the Sun is approximately 15 million Kelvin. I am interested in understanding the core temperatures of main-sequence stars with various spectral types and surface temperatures, ...
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Metallicity of Celestial Objects: Why "Metal = Non-metal" Source
This is an existing question with good answers at Metallicity of Celestial Objects: Why "Metal = Non-metal"? , but one thing is missing in the answers: a specific source that states that it ...
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Why don't stars 0.5<m<0.8 solar masses undergo a helium flash?
Stars between 0.8 and 2 solar masses undergo a degenerative helium flash, per Wikipedia
and these course notes
The cores of stars <0.5 solar masses never heat up enough for helium fusion. In stars &...
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Do all photons coming out of the Sun go out radially?
I am trying to understand why we can assume that all light rays from the Sun are in parallel.
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Most established length of Gleissberg Cycle
What is the most commonly used length for the Gleissberg Cycle of sunspots? I have reviewed academic literature on the subject and the lengths used are all over the place. Specifically, anywhere in ...
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Why does a white dwarf sometimes go 'nova' and sometimes supernova (type 1a)?
Obviously, when a white dwarf goes truly supernova, there is nothing left, not even, I have heard, a neutron star or black hole...
But when certain white dwarf stars accrete certain amounts or types ...
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Could a red dwarf be "deionized"?
Even the smallest red dwarf stars have amazing flares. But the photosphere temperature can be as low as 2700K, which (I think) is too cool to ionize hydrogen. Even the sun at 5800K is cool enough that ...
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How do changing binary separation and Roche Lobe size of the donor affect the long-term evolution of a binary under conservative mass transfer?
I computed that for a binary system that undergoes conservative mass transfer from the Roche-lobe filling Start 2 to Star 1 (i.e. $\dot M_2<0, \dot M_1=-\dot M_2$ and the change in angular momentum ...
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When analyzing a particle moving at Kepler speed, √(GM/R) in a planetary magnetic field, do we need to convert it to angular speed, √(GM/R^3)?
A charged particle is moving in a planetary magnetic field, in a spherical polar coordinates which is corotating with the magnetic field. To solve the equations of motion numerically what would be the ...
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Mimimum stellar mass and minimum temperature that triggers hydrogen burning
We can derive the minimum mass of a star in the main sequence using the minimum temperature $T_C$ that triggers hydrogen burning in the core. Then using the stellar structure equations we can derive ...
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Unusual amount of white dwarfs in star clusters in my analysis
I'm trying to plot H-R Diagrams of open clusters using data from Gaia DR3. My workflow is something like this:
Plot apparent magnitude vs log(distance) in pc. An overdensity would indicate the ...
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Is the Sun hotter today, in terms of absolute temperature (i.e., NOT total luminosity), than it was in the distant past?
I am constantly reading that the Sun is at least 20% 'hotter', in terms of total radiation/luminosity, than it was a few million years after its formation (i.e., after the Hayashi stage...)
But what ...
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Calculation of average FWHM by PSF fitting of all the detected stars in the fits image
I need to calculate the FWHM of all the stars detected via the DaoStarFinder package/any other package by performing PSF fitting in Python. Here is the code for my detection.
...
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Do red dwarf stars get dimmer over time, the opposite of most other main sequence stars?
It is common knowledge, for instance, that the sun has increased in brightness by roughly 40% since its formation... (The apparently early appearance of life has led to the 'Faint young Sun paradox', ...
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Do brown dwarf 'stars' fuse simple hydrogen (p-p reaction) at all?
I sometimes read that only deuterium-deuterium fusion can occur in brown dwarfs... And maybe deuterium-proton fusion? To He-3?
In order to overcome Coulombic repulsion and, occasionally, fuse, protons ...
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Stellar structure equations - mass continuity
Out of the four stellar structure ODEs, I would like to understand why the mass continuity equation was named this way. It reads
$$ \frac{dm}{dr}=4\pi r^2\rho \tag{1} $$
and I understand what it means,...
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Is Barnard's star an M4 red dwarf or an M0? Why is it called an M4.0V?
I have tried to figure this out, but cannot find an answer anywhere...
Are, perhaps, astronomers unsure of its exact spectral class? (I have heard that red dwarfs are usually variable... to an extent....
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Equation describing Energy Transport due to Radiation in the interiors of stars
I am considering a very elementary stellar structure and I'm required to derive an equation to describe the energy transport due to radiation. The answer I am supposed to obtain is:
$$\frac{dT}{dr}= -\...
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How does the entropy diffusivity changes with radius in the Sun?
Could you please explain - How does the entropy diffusivity changes with radius in the Sun?
As far I know, In the convection zone, the entropy diffusivity increases as the temperature and density ...
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Period estimate [closed]
How would you estimate the period or range of periods for two stars, please? I know the right ascension, declination, and distance.
I could estimate the masses and assume that the stars are in ...
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How do I estimate the number of neutron stars and black holes relative to the number of stars in the main sequence and white dwarfs?
Recently, I had a homework question that gave me the mass of a main-sequence star, that is, M_tp = 0.9 M_solar, and the population formed at the same time. I am supposed to use the stellar birth ...
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How do I calculate the flux density of a substellar object?
I am currently trying to generate photometric passband colors for brown dwarfs and planets generated through MESA (Modules for Experiments in Stellar Astrophysics). I believe I understand the ...
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The necessary conditions for driving winds with dust (Dust-driven Wind)
So lately I've read Intro to stellar winds (particularly chapter 7 Dust-driven winds) by Lamers & cassinelli, I forget how many times I've read this but I still don't really understand. So in the ...
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Does the luminosity of a star have the form of a Planck curve?
Figure shows the intensity of the radiant energy emitted from stars A and B over a unit time according to the wavelength. The area between the graph and the horizontal axis is S and 4S, respectively.
...
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Calculate how far we could see through Earth's atmosphere if it had the opacity of the solar photosphere?
I've newly started studying astrophysics. There is a question in the book "An introduction to modern astrophysics" by W. Carroll: Calculate how far we could see through Earth's atmosphere if ...
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What actually are line-driven winds?
I have read several books (viz. intro to stellar winds)/articles about stellar winds (dust-driven, line-driven, coronal winds), but still didn't understand the explanation. I understand that line-...
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How to look up "all things astrophysical" about A=9 (or other light isobars)?
All the light isobars (group with same atomic number mass) are interesting and quirky, but let's use A=9 as an example. 9C and 9Li beta decay to particle unbound states in 9B and 9Be (except to 9Be's ...
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The Relationship between Surface Temperature and Mass of MS and Red Giant
The assumptions about the problem situation are as follows :
The red giant is in the HB at HR disgram, and it's a helium fusion situation. And in this situation, the mass of the red giant is the ...
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Stellar evolution temperature gradient - why the logarithm?
We define the adiabatic temperature gradient as $$\Delta_{ad}= \Big(\frac{\partial \log \mathrm{T}}{\partial \log \mathrm{P}}\Big)_{ad}$$
The goal of this gradient is to show how the temperature ...
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What happens to the non-fusion formed metals in stars?
Let’s consider a population I star of some given metallicity.
I know that depending on the type of star, different structures are possible with convection zones and radiative zones trading around ...
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Stars as nozzles; how important is thermodynamics and the de Laval nozzle equation for understanding the speed of the solar wind vs distance?
Seeing What determines the speed of a star's solar wind? I'm having flashbacks from undergraduate days where the professor started their lecture on solar wind by writing something that they called ...
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Spectrum features of main sequence and giant stars with the same spectral type
Hence, the spectral features of the supergiant are different from those of the Sun-in accordance with the Saha equation- even though both stars are essentially at the same temperature. The pressure ...
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What is the relation between Kelvin-Helmholtz timescale and free-fall timescale?
What is the actual difference between these two timescales? Both of these timescales define the time for collapse when there is only gravity. Also, what does it mean by saying Kelvin-Helmholtz ...
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Do the newly-created deuterons in our Sun release any photons? In addition to a positron and an electron neutrino?
Perhaps this is a nuclear physics question, but....
When two colliding protons deep inside our Sun finally turn into a deuterium nucleus or deutron (after approximately ten octillion chances, on ...
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how to plot Gauss-Hermite moment maps from arrays of star velocity values in Python?
I want to calculate Gauss-Hermite moments, such as h1,h2, h3, h4 moments from the values in an array of numbers which represent velocity distribution of stars in a galaxy. How would I fit a curve to ...
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Density of Plasma in Solar Corona
The Sun's atmosphere, also known as the solar corona, is known to be extremely hot, much hotter than the Sun's surface. What is the plasma density in the solar corona?
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Mass-age stellar phase diagram
The HR diagram is a sort-of "phase diagram" (in a very rough sense) for stars, where a particular star's location on the diagram says something about what "kind" of star it is. ...
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How did Parker Solar Probe take what looks like 2D cross-sections of the solar wind in photographs; high contrast streaks in focus from volume effect?
The new NASA Goddard video NASA's Parker Solar Probe Touches The Sun For The First Time shows what looks like they might be photographs of the solar wind.
I'm having a hard time understanding how such ...
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Did astronomers "track back" solar wind switchbacks to the surface of the Sun to individual convection cells?
The new NASA Goddard video NASA's Parker Solar Probe Touches The Sun For The First Time explains that the spacecraft passed many times through "switchbacks" or kinks in the solar wind, where ...
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The Sun's Alfvén critical surface; what was known about its existence and location before Parker Solar Probe "touched the Sun"?
The new NASA Goddard video NASA's Parker Solar Probe Touches The Sun For The First Time seems to suggest that the existence of the Sun's Alfvén critical surface was a given, but the location and ...
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What kind of opacity should I use when I simulate stellar structure?
I am tring to simulate the evolution of a star. As we know, opacity plays an important role and has many forms like: free-free, bound-free, bound-bound, electron scatter.
But I am confused about their ...
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Stellar and gaseous surface mass density spiral galaxies
I have a database with more than 1000 rotation curves of spiral and lenticular galaxies (xxx-gxx notation is ESOxxx-G0xx). I am working on dark matter mass modeling and I would like to know whether ...
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Help finding a database or analysis of plage regions on the Sun
Plages are phenomena of stellar activity.
A plage is a bright region in the chromosphere of the Sun, typically found in and around active regions. The term itself is poetically taken from the French ...
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When will Alpha Centauri A and B overtake Proxima Centauri as the closest stars to us?
There are 3 stars in the Alpha Centauri system: 2 large stars orbting around each other (A & B) and a distant Proxima Centauri (C) orbiting around both.
Right now it just happens that Proxima ...
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Telescope/s functioning from underground mines
Theoretically and Practically,
Can a Telescope function for the astronomer observed from underground mines? By "telescope" I mean the instrument used by astronomers to observe stars, planets ...
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What would solar calculations look like in another system? [closed]
When you are determining things (area, luminosity, radius etc) in a star, there are certain things that involve our suns characteristics like solar mass and solar radii. Say I were in another system- ...
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