45
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Do we know a star that is similar to the Sun when it would be a red giant?
Models for the future behaviour of the Sun do vary, mainly as a result of uncertainty of mass loss during the red giant (H shell burning) and asymptotic red giant (H+He shell burning) phases.
A ...
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37
votes
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When was it worked out/discovered that our Sun can't go supernova?
I think the definitive work is that of Hoyle & Fowler (1960).
They argued that supernovae were produced by two possible mechanisms - what they called an implosion/explosion or an explosion within ...
- 158k
36
votes
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Where did the Sun get hydrogen to work with if it is in the 3rd generation of stars?
Most of the galaxy's gas is not incorporated into stars and remains as gas and dust. This is not really my area of expertise, but papers such as Evans et al. 2008 and Matthews et al. 2018 seem to ...
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33
votes
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Why do stars explode?
Short answer:
A tiny fraction of the gravitational potential energy released by the very rapid collapse of the inert iron core gets transferred to the outer layers and this is sufficient to power ...
- 158k
27
votes
Do stars become more metal-rich as they evolve?
If the star is a solar mass or below it will not produce any metals (anything heavier than helium) within 10 billion years of birth. It will be on the main sequence, fusing hydrogen to helium via the ...
- 158k
25
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Where did the Sun get hydrogen to work with if it is in the 3rd generation of stars?
I think you've answered your own question.
if 1st and 2nd stars generation burned hydrogen to helium and more heavier elements, then should it be like 90% of all universe hydrogen already converted ...
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23
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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?
Because oxygen burning commences at higher temperatures than neon burning.
Neon production takes place chiefly in the C/O core of massive stars at the end of helium burning. The predominant reaction ...
- 158k
22
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Could Black holes forge heavier elements that have yet to be discovered?
The heaviest elements known in nature are forged deep within stars.
No, the heaviest elements are made on Earth in scientific laboratories, or in the extreme gravity of a neutron star's crust.
...
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21
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When will the number of stars be a maximum?
TL; DR Somewhere between now and a few hundred billion years time. (For a co-moving volume) Now read on.
If stellar remnants are included, then the answer is very far in the future indeed, if and ...
- 158k
20
votes
How long does it take for a white dwarf to cool to a black dwarf?
I don't think there is an accepted definition of a "black dwarf" - it is not a term used in the scientific literature.
A popular definition that appears to circulate on the internet is that it is a ...
- 158k
20
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Why do massive stars not undergo a helium flash
After H burning has finished, the he mass of the He core gradually increases, as does its density and temperature.
Low-mass stars have denser cores when they reach a temperature at which He is ignited....
- 158k
19
votes
Does a star fuse helium to beryllium on the main sequence?
Does a star fuse helium to beryllium on the main sequence?
Stars don't fuse helium to beryllium except as a very, very short intermediate step toward carbon. Helium-helium fusion to form beryllium is ...
- 34.4k
16
votes
Do we know a star that is similar to the Sun when it would be a red giant?
Arcturus is a RGB star, probably fairly similar how the Sun will look when it becomes a red giant. Arcturus is slightly more massive than the Sun ($m_{\rm Arc}=1.08 m_{\odot}$), but the main ...
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16
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When did scientists discover that the Sun has a life cycle and that it is going to die?
Although various astronomers have speculated that the Sun was a star (some were imprisoned or even burnt alive for such heresy), this was not known definitively until 1838 when Friedrich Bessel used ...
- 34.4k
16
votes
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What actually are line-driven winds?
The word "line" refers to a spectral line, i.e. an emission or absorption feature in a spectrum. In this case it's absorption.
Line-driven vs. continuum-driven winds
Stellar winds are driven ...
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15
votes
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How much mass does the Sun lose as light, neutrinos, and solar wind?
The solar neutrino luminosity is about 2.3% of its electromagnetic luminosity (i.e. light). So the extra mass lost in the form of neutrino energy is 2.3% of your original calculation.
The average ...
- 158k
15
votes
Do stars become more metal-rich as they evolve?
Yes, it will
Metals in astronomy, are simply elements that are heavier than hydrogen and helium. From that perspective, even oxygen and carbon are "metals" in a astronomical sense, although ...
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15
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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?
Although Neon is heavier than Oxygen, the reaction Ne+He-> Mg occurs at a lower temperature than the reaction O+He->Ne
This is because the oxygen nucleus is especially stable (with 8 protons and ...
- 127k
14
votes
Which stellar properties can we describe as "first principles" in which we can derive the rest?
Starting from a protostar, one would hope to be able to predict everything about its future development if we knew its initial mass, chemical composition and angular momentum.
Mass is fundamental ...
- 158k
14
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Accepted
Order of shells formed in a massive star
There is a reasonable section on this in the wikipedia pages on Neon-burning and oxygen-burning if you can extract the relevant information.
Oxygen-16 is a really stable, "doubly-magic" ...
- 158k
13
votes
Properties of low-mass stellar remnants vs the Earth
Stellar remnants are completely different from planets.
The Earth was never a star and fusion has never occurred in the Earth's core at any time in its history. When a small to medium sized star dies,...
- 127k
12
votes
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Why is $H_\delta$ prominent in type A stars?
H$\delta$ absorption is formed when hydrogen in the level $n=2$ is excited to $n=6$.
To get strong H$\delta$ absorption lines you need large amounts of hydrogen in the first excited state $n=2$ and a ...
- 158k
12
votes
Accepted
How long does it take for a white dwarf to cool to a black dwarf?
I think what you need is here on the Wikipedia. In section "Radiation and cooling," it says "The rate of cooling has been estimated ... After initially taking approximately 1.5 billion years to cool ...
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12
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Are there stars with an average density greater than the central density?
$$\frac{dP}{dr} = - \rho g,$$
is the equation of hydrostatic equilibrium, where $\rho$ and $g$ are the local density and gravity, $P$ is pressure and $r$ is the radial coordinate. This can be ...
- 158k
12
votes
What does this tweeted Astronomy Plot of the Week mean? What does it represent?
TLDR;
Its a diagram showing all the physics and modeling choices that go into different models (the colored boxes in the middle) to compute an SED.
Longer answer:
First a SED is a spectral energy ...
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12
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What is it like to see a brown dwarf turn into a star?
Exactly what this would look like would depend a great deal on how (fast) the mass is accreted and whether there is a significant amount of energy accreted along with the mass.
There are two ...
- 158k
12
votes
Is Barnard's star an M4 red dwarf or an M0? Why is it called an M4.0V?
It's M4V, not M0V.
In principle, spectral classes can be further subdivided, particularly in the M class, because there are significant differences between an M4 and an M5 spectrum for instance.
...
- 158k
11
votes
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Can someone explain this diagram showing the spectral type distribution of bright stars
It's all to do with the relationships between mass, spectral-type and luminosity and the initial mass function of stars.
I think your explanation of points 1 and 2 are completely correct. O and B ...
- 158k
11
votes
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Does a star fuse helium to beryllium on the main sequence?
What defines the main sequence?
Main sequence stars are characterized by hydrogen fusion in their cores, either through the proton-proton chain (for lower-mass stars) or the CNO cycle (for stars more ...
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