Questions tagged [stellar-astrophysics]
Questions about inducing chemistry, physics, and many more branches of science into astronomy.
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Is it dark inside the Sun?
This might sound like a strange question, but something got me thinking about it recently.
The opacity of plasma in stellar interiors can get quite high, making for shorter free-paths for photons. In ...
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Would we have more than 8 minutes of light, if the Sun "went out"?
The common theory is, that if the Sun "shut down", we would see the light for eight more minutes (the time that it takes the photons to reach the Earth).
However recently I have read that ...
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Why are there no green stars?
There are red stars, and orange stars, and yellow stars, and blue stars, and they are all understandable save the fact that there is a 'gap': There are no green stars.
Is this because of hydrogen's ...
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Can a magnetic field of an object be stronger than its gravity?
Can a planet, star or otherwise have a magnetic field that is stronger or have more range than its gravity?
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What would the Sun be like if nuclear reactions could not proceed via quantum tunneling?
Without quantum tunneling our Sun wouldn't be hot or massive enough to produce the energy it does at the moment. So what would have been the temperature or mass of our Sun without quantum tunneling of ...
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Open problems in astronomy that an amateur (with a PhD in some other field) would have a chance of solving?
What are some open problems in astronomy that an amateur would have a chance of solving? Suppose the amateur has a PhD in some other field, owns a basic telescope, a set of filters, diffraction ...
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What was the absolute limit to the possible sizes of the first stars formed from "primordial material with no metals"?
This answer to Why don't or (can't) stars be more than 325 or so times the mass of the sun? What limits their size? includes the following:
...The upper limit you refer to is for compositions similar ...
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Can a small black hole orbit a large star?
I recently read about the discovery of a tiny black hole (with only three times the mass of the sun) nicknamed ‘The unicorn’ about 1500 light years from earth. This got me thinking, can this black ...
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Is any consensus forming on the solution to the "Lithium Problem"?
The "Lithium Problem" relates to the fact very-low-metallicity stars appear to have a Li/H ratio approximately one third of what would be expected. The ratio should be the same as the prediction from ...
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Which stellar properties can we describe as "first principles" in which we can derive the rest?
Mass, size, temperature, luminosity, chemical composition, the initial abundance of the molecular cloud, distance, brightness, age, and evolutionary cycle can all be used to characterize a star. A ...
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Are there stars with an average density greater than the central density?
Are there likely to be stars for which the average density is greater than the density at the centre? Intuitively, I would say not, as density tends to decrease outwards, but ideally I would ...
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Can the energy transport by radiation occur in the convection region of a star?
I am new to stellar astrophysics and trying to understand the energy transports in the interior of stars.
Can the energy transport by radiation occur in the convection region of a star?
Here are my ...
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How much more life could the Sun acquire via star lifting?
It has been proposed before that we could use this technique to remove hydrogen from the Sun to lower it's rate of fusion and extend it's life, so it doesn't fry our planet.
I am wondering how much ...
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Why does lithium fuse at lower temperatures than hydrogen?
This is a basic question, but it's been bugging me. In the Wikipedia article for lithium burning, it states that:
Stars, which by definition must achieve the high temperature (2.5 × 10^6 K) ...
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How exactly is the Initial Mass Function (IMF) calculated?
The Initial Mass Function (IMF) is the empirical function which describes the initial masses of a population of stars. My questions are,
1) What are the various IMF's which are used?
2) For each, ...
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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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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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Would stars have formed in the Universe if atomic hydrogen couldn't make molecular hydrogen?
I just saw this YouTube video made by PBS Studios. There they explain that $H_2$ can reduce the traslational kinetic energy of regular $H$ atoms when it is formed since the energy can also be stored ...
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Why doesn't the fusion process of the sun speed up?
Am I correct in saying that the fusion process of the sun is constant, i.e. X amount of fusion happens per day, more or less?
Why does this not speed up, i.e. one fusion event creates energy for two ...
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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 does this tweeted Astronomy Plot of the Week mean? What does it represent?
Twitter user BenneHolwerda (@BenneHolwerda) recently tweeted August 10 Astronomy Plot of the Week:
And I think @SabineBellstedt and @_jessthorne summary graph deserves a spot for sure.
If you work ...
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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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Why does the convective core in an intermediate- to high-mass star shrink?
The image below shows the evolution of the hydrogen mass fraction profile for a 5 solar mass star in the main sequence. I would expect that the size of the convective core stays roughly constant as ...
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Do elements like magnesium and sulfur form a layer inside massive stars?
For an evolved massive star, elements such as hydrogen, helium, carbon, oxygen, magnesium ... iron are involved, but from the picture below, there doesn't seem to have a layer of magnesium fusion ...
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Why do neutron stars collide instead of just revolving around each other like planets revolve around the Sun?
We know about events like two neutron star colliding and resulting in a black hole, also collision of black holes, and collision of galaxies. But we never see a satellite such as a moon colliding with ...
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How can I convolve a template spectrum with a photometric filter response spectrum?
Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms ...
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Is it possible for stars not to rotate?
I'm just curious about that the existence of non-rotating stars. Is it physically possible for a star not to rotate at all? Does magnetic braking eventually stop the stellar rotation?
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What effect does stellar granulation to have on a chemical analysis of a star's spectrum?
The spectrum from stellar granules will obviously be for hotter gas, while the spectrum from the lanes between them will be for cooler gas.
Does this "average out" so that an average ...
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Why we define Stellar motions with respect to sun?
We take observations from earth but to define radial velocity, transverse velocity and the proper motion of stars, why we consider them with respect to the sun? and then we do some corrections due to ...
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Why could Quasi-stars ("black hole stars") have only existed when everything was hydrogen and helium? (no metal "contamination")
This informative answer to What was the absolute limit to the possible sizes of the first stars formed from “primordial material with no metals”? led me to Wikipedia's Quasi-star; Formation and ...
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Activity of M dwarf stars
Why are M dwarf stars the most active (in terms of starspots and faculae) of all stars?
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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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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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Why do M dwarfs emit more X-ray radiation than larger, more luminous stars?
I have read that "The relative amount of harmful radiation (to life as we know it) that stars emit can be 80 to 500 times more intense for M dwarfs relative to our Sun". Source This seems ...
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Is there a star simulation software that can handle mass ejections and supernovae?
I use MESA right now to play around with stellar dynamics, but it can't do mass ejections and therefore, I can't think of a way to let the simulated stars explode as supernovae.
What simulation ...
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Do star systems stripped from galaxies have different expected behavior?
Another way of stating this question: Does the fact that a star system (or comparable concentrated mass) exists in a galaxy affect its long-term evolution, in terms of expansion, contraction, ...
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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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Where does energy at the beginning of a star's lifecycle (before any nuclear reactions) come from?
David Christian's Maps of Time has this to say about the period during which the first stars started to form from the diffuse clouds of hydrogen and helium that then made up the universe:
Under the ...
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How do we find the exact temperature of a star?
This is a very basic question, but I am a little confused. As far as I know, the temperature of a star is analyzed based on the color of the light it emits. So, if a star is moving away from us, then ...
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Why are the wings of many strong lines, including hydrogen lines and most metal lines, stronger in Dwarfs than in Supergiants?
What is the reason? Is it because Dwarfs have higher surface gravity (log g), in turn related to pressure, than Supergiants so there is more contribution from van der Waals and Stark broadening?
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Why do massive rapid-rotating stars move bluewards off the zero-age main sequence (ZAMS)?
I'm reading a well-cited paper by Szecsi et al. 2015 titled "Low-metallicity massive single stars with rotation". The paper can be found here. I was surprised that figure 5 depicted an HRD ...
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Why is the Sun's brightness and radius increasing, but not its temperature?
On the Sun's article on Wikipedia, there is an image showing how the Sun's brightness, radius and temperature have changed over time:
For the past (and next) few billion years, I see the luminosity ...
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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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death of a red dwarf star / minimum mass needed for a white dwarf?
OK, first, I know there's a variety of sizes and types of red dwarf stars and the universe is too young for any of them to have reached the end of their main sequence phase yet, so it's all ...
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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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Obtaining the derived period of $\omega$ Canis Majoris
I have read these two papers:
On the nature of the Be phenomenon I. The case of ω Canis Majoris
Stellar and circumstellar activity of the Be star ω CMa
II. Periodic line-profile variability
In the ...
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Strength of core-envelope coupling in stars
For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope?
I understand that the core-envelope boundary is only (...
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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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Why there are less massive stars than low mass stars?
What factor determines the selection of star mass?
And how we know that the number of massive stars is less than the number of low mass stars?
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What is the difference between emission line and recombination line?
When an electron jumps from higher level to lower level a photon is emitted. This is seen as an emission line. But what exactly is a recombination line? I found them similar. Can you please tell me ...
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