Unanswered Questions
227 questions with no upvoted or accepted answers
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How well conserved is etendue in extreme gravitational lensing scenarios?
This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description:
Light from the background galaxy circles a ...
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7
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256
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Get the expression of probed volume between 2 redshifts
1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume.
2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
CommunityBot
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6
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What is the reason for the dispute over the variation of core mass with heavy metal abundance?
In Metal-Poor Stars IV: The Evolution of Red Giants, Rood writes
The differences in the results of these papers are large enough to introduce appreciable uncertainties into the study of the ...
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6
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Do narrow lines in the spectra of O- and B- type stars always indicate magnetic fields?
I was reading a paper on the differential emission measures of a set of hot O- and B- type stars. As the authors discuss in Section 3 (page 959), two stars, $\tau$ Sco and $\theta^1$ Ori C, have ...
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6
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1
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Could non-supernova carbon, oxygen, or silicon flashes be observed?
I was reading about the helium flash, the short but sudden onset of helium fusion in certain red giant stars. As I understand, the upper (nondegenerate) layers of the star absorb the energy as they ...
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Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow?
Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow? I mean is it mandatory for a jet to be emitted from an accretion disk?
If so, then why?
...
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69
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Type Ia supernova by fallback?
Is it possible for a massive star of more than 1.4 solar masses (probably around 3 or more but below the threshold for type II) to collapse into a white dwarf and a planetary nebula, then go supernova ...
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79
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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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186
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What are some good books/online resources for astronomy problem sets?
I am currently studying for the international olympiad for astronomy and astrophysics (the syllabus can be found here: https://www.ioaastrophysics.org/syllabus/). I am currently using Carroll Ostlie's ...
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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 (...
- 4,533
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110
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How often do comet occultations of stars happen?
By travelling to specific places, astronomers can see three thousand star comet transition events every year at m15 for the major (50km+) comets and asteroids averaging about 20 seconds, perhaps that'...
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123
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How is the age of a star on the Henyey track calculated?
I was reading Stellar Evolution in Early Phases of Gravitational Contraction, by Chushiro Henyey, where he writes,
If $L \propto R^{-\alpha}$ along the path, the age of a star from the time when $R=...
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4
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194
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'Star' appeared dimmer and dimmer over multiple days before disappearing. What could this have been?
This happened a little while ago but I've just been thinking about it!
I was in Wales for a holiday, and over the period of 7 days, a particularly bright 'star'(or at least a bright dot that looked ...
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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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What is the contribution of star-produced axions to the dark matter budget of the Milky Way?
I try to follow the discussion of axions since Peccei, Quinn, Wilzcek and Weinberg. What I still don't understand is how much the speculated stellar production of axions could add to the galactic dark ...
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M Dwarf radiation and habitability at the terminator of a tidally-locked planet?
I know that M Dwarf stars emit intense solar flares, which is thought to pose a potential problem for the emergence of life on planets that orbit them. But I was wondering if the life that might exist ...
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60
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Explanation for Planck 2018 temperature fluctuations strongest peaks
As it can be seen from Plank 2018 Cosmic Microwave Background temperature fluctuations data-
There are 3 sharp peaks at multipole expansions $\ell \approx 250, 550, 800 $. Also as multipole expansion ...
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54
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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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60
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How are plage regions related to the density of medium and velocity FeII ions?
During a literature review (abstract), I found that the intensity of FeII (298.5 nm) ions in the last solar minimum was higher than the two previous solar minima 21 & 22. The velocity of FeII ions ...
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How much more mass would Mars need to currently have enough pressure for liquid water and oxygen?
My question is whether Mars just about failed to meet the threshold or missed it by a lot. It's been dry for 3 billion years. How much bigger would it have needed to be to buy it that extra time? Let'...
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Sun (star) spots (size)
My question is about sunspots size.
Does these spots have a 'typical' size for all kinds of stars (dwarves or super giants), or are they dependent on a star size? In another words, is the statement ...
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101
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From what distances do the atoms in you come from?
If the atoms of a human come from stars, comets, nebulas and magnetrons, then what is the greatest distance that two atoms of a human can possibly have been away from each other previously? Perhaps ...
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Cosmology : Formula for the bias of galaxies
first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
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Why the Hubble constant is so inconsistent?
Having a look on Wikipedia I noticed the following values (of the last 6 years) for the Hubble constant:
67.6±0.7 SDSS-III Baryon Oscillation Spectroscopic Survey
73.00±1.75 Hubble Space ...
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1
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219
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What does the surface of a star look like in visible light?
False colour images of the Sun show a highly complex structure near the surface with matter ejected and suspended in magnetic fields. But are solar prominences and coronal mass ejections visible to ...
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Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?
May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following:
“We can say from our spectra and other observations that the star has a temperature of ...
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3
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151
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When did astronomers accept that fixed stars aren't fixed and are at different distances?
Was it when heliocentric model was spreading in the whole world? I saw a model of the solar system that was made in the 18th century where the sun was in the middle and the planets and comets around ...
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Gravitational recoil with stars/planets...?
When two black holes are merging, the resulting merge can be ejected if one of the black holes had less mass than the other one, so the gravitational waves emitted by both of them is unbalanced, and ...
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127
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What is the average and the median mass and luminosity of a star?
I've heard in many places that the Sun is an average star, but in Wikipedia it says that about 75% of stars are M-type stars that are way less massive and fainter that the Sun. So how massive and ...
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46
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How can I calculate evolutionary timescales of low mass stars?
How can I calculate how long a star of a given mass will spend on an evolutionary branch before evolving off it?
I'm thinking about the evolution of low mass stars from the subgiant branch to the red ...
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56
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Potential energy in an expanding universe
A question you wonderful geniuses can hopefully answer. Imagine a piece of string drawn between two galaxies. Space between the galaxies is expanding. What force is being applied to the string? Where ...
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79
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Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an accelerating expanding spacetime (like it happens in our Universe), are ...
- 1,017
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Cosmic microwave background the same as the first visible light at 379,000 yrs after the Big Bang? How do these measure the age of the universe?
Was the CMB emitted at the same time as visible light at 379,000 yrs after the BB ? Was this a one time event ? If headed away from us, how does it measure the age of the universe?
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Pulsations in massive stars
Why are tidally induced pulsations not typical for massive binary stars? For which kind of binaries they are typical? I read it in the last but one paragraph in Discussion of https://iopscience.iop....
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How can a busy high school student get into learning Astronomy?
I'm a high school student that has loved physics for quite some time, but have only started dabbling with the more complex things. I know a fair bit about quantum mechanics and such as I like it, but ...
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What is the main difference between cyclotron, synchrotron, and gyrosynchrotron radiation?
How are these various types of radiation generated? What is the main difference between them? Can someone suggest a book related to these radiations?
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Estimate the shape of an object based on flux curve
Is there an aproximation to know the shape of a dust cloud,etc based on the magnitude/flux curves of stars they transit? Example, can I know if the shape is (at least in 2 dimensions) elliptical, ...
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How to distinguish primary hosts (stars) and orbiting satellites (planets) and tertiary bodies (moons) by their mass and trajectory?
Suppose one has run a gravitational simulation of N bodies (has the mass, vector positions, vector velocities, etc for each body), but knows nothing a priori about ...
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53
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How to determine the temperature of a star according to the strength of the line in the spectra?
Based on the comments, I have changed some things.
Below is a graph showing the relative strength of $H_\gamma$ and Fe I lines of two stars. Which star is hotter?
This is a question from the book:An ...
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What is the theoretical maximum variability a pulsating red giant can have such that a habitable planet can stay habitable for long periods of time?
I was reading about red giants and came across this statement:
Some research suggests that, during the evolution of a 1 M☉ star along the red-giant branch, it could harbor a habitable zone for ...
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Strength of core-envelope coupling in stars (again)
I asked this on the physics SE but it received little attention:
Consider a high-mass zero-age main-sequence (ZAMS) (e.g., $m_{\rm ZAMS} \gtrsim 30\,$M$_{\odot}$) star.
I understand that the core-...
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65
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Why are CMB peak heights sensitive to the physical densities
A very simple question: why should it be that the CMB power spectrum allows constraints to be placed on the combination of parameters
$$\omega_c = \Omega_c h^2$$
$$\omega_b = \Omega_b h^2$$
as opposed ...
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379
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Why do some stars twinkle more than others?
This is a child's question I failed to answer. When observing some stars with naked eye, some stars (e.g. Regulus) appeared to blink significantly more than others, but I did not have the patience to ...
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Can mass loss via accretion occur on stellar remnants?
We know that normal stars can lose mass to a binary companion. But can this happen to neutron stars and white dwarfs? Let's say a stellar black hole is being orbited by a white dwarf or neutron star. ...
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New method for exoplanet detection based on iridescence?
Could it be possible to detect exoplanets that have an abundance of iridescent minerals by analyzing their star's spectra over time as the angle in observation would lead to changes in absorbed ...
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Superconducting space dust; what transient fields could induce persistent current loops?
Science Alert's Superconductivity Has Been Discovered in Meteorites For The First Time quotes from Superconductivity found in meteorites (Wampler et al. PNAS March 23, 2020)
The paper describes the ...
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Information on Planetary nebula formed from the death of our star the 'Sun'!
I want to know the expansion rate, composition, mass and density of hydrogen present of a Planetary nebula similar to that which will be formed after the death of our star the sun.
Knowing these ...
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Combined mass of binary stars
This is Question 17 from USAAAO Practice Round 2015. The answer is D. It would be best if someone can detail out the workings.
In a nearby star system, two stars are seen to orbit each other every
...
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Can "rock stars" form from interstellar dust?
Imagine a large and massive dust cloud made of solid phase micrometeoroids, asteroids and larger planetoids, all material in it is in solid phase, and contains no hydrogen or other volatiles in gas ...
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Mass of the universe
How do we calculate the mass of the universe taking into consideration dark matter?
Mass of visible matter can be computed by stellar method, but how do we calculate mass of dark matter which we don'...
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