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39 votes

Is Jupiter a failed star?

No. Besides the 13 Jupiter-masses required to ignite deuterium burning, and make Jupiter into a Brown Dwarf, there is a clear difference between the formation pathways of Brown Dwarves and Gas ...
AtmosphericPrisonEscape's user avatar
35 votes
Accepted

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 ...
astrosnapper's user avatar
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29 votes
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How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

The low surface brightness survey at the GBT is looking for H(I) emission, i.e. emission from neutral hydrogen atoms (for example see O'Neil 2023). The most obvious signature they use is the 21 cm ...
ProfRob's user avatar
  • 155k
24 votes

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 ...
zephyr's user avatar
  • 15k
22 votes
Accepted

Replenishing hydrogen in the core of the sun

There is very little mixing in the core of the Sun, where the stratification is fixed by radiative (rather than convective) heat transfer. The heavier helium does "fill the core", but takes about 12 ...
ProfRob's user avatar
  • 155k
20 votes

Where did the hydrogen come from in a type II supernova?

Good question - the answer is that stars are not in general well mixed - or rather, the nuclear-burning core is not well-mixed with the rest of the star. That means that a star will finish hydrogen ...
ProfRob's user avatar
  • 155k
18 votes
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Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?

Yes, the atomic hydrogen is probably mostly left over from the Big Bang. [Edited to add: Not sure how much that is true and how much present-day atomic hydrogen is the result of recombination.] And, ...
Peter Erwin's user avatar
  • 17.1k
15 votes

Is Jupiter a failed star?

Short answer: no It all of course depends on how you define the term failed star. In general, a star should be able to generate heat by fusing atoms together, and it requires about 13 times the mass ...
tuomas's user avatar
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13 votes
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Would stars have formed in the Universe if atomic hydrogen couldn't make molecular hydrogen?

The role of H$_2$ is to allow primordial gas to cool down sufficiently to allow the collapse to start and then to hold the gas at a relatively low temperature as it gets much more dense. The formation ...
ProfRob's user avatar
  • 155k
13 votes
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Is there any way to detect the three-dimensional distribution of baryonic gas in our Universe?

Yes! The cosmic web Matter in the Universe is distributed not uniformly, but in the so-called cosmic web. This large-scale structure consists of sheets and filament of dark matter, baryonic gas, and ...
pela's user avatar
  • 38.7k
12 votes
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Why does lithium fuse at lower temperatures than hydrogen?

The slowest reaction rate in the pp chain determines how quickly hydrogen can "burn" in the core of a sun-like star. That rate-determining step is actually the fusion of two protons to form ...
ProfRob's user avatar
  • 155k
12 votes
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Does the existence of hydrogen in the universe create an obscuration effect similar to the way air does at great distances?

One way of thinking about this is in terms of the physics of the cosmic microwave background. The cosmic microwave background occurs as a phenomenon when a nearly homogeneous universe transitions ...
ProfRob's user avatar
  • 155k
10 votes

Where did the Sun get hydrogen to work with if it is in the 3rd generation of stars?

The question is 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 to helium and something else? ...
David Hammen's user avatar
  • 34.1k
10 votes

Where did the hydrogen come from in a type II supernova?

Where did the hydrogen come from if that is the first element used up in the star's life cycle? Hydrogen is indeed the first element that is fused into helium in the core of a star -- but not ...
David Hammen's user avatar
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9 votes
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Relation between molecular cloud mass and galactic mass

The mass of an average galaxy appears to be totally dominated by dark matter, so your calculation would not give the galaxy mass. Even if all you wanted was the baryonic (non dark matter) mass then ...
ProfRob's user avatar
  • 155k
9 votes

How many generations of stars can be formed in the Stelliferous Era?

One can make a theoretical upper bound by considering the most short-lived star possible $\tau_{short}$, and a large supply of initial hydrogen $M_H$. Then one could calculate the fraction hydrogen ...
Anders Sandberg's user avatar
7 votes

If the Higgs field only formed after the Big Bang, how was hydrogen formed?

Hydrogen was not "created at the moment of the big bang". Particles (leptons and quarks) can attain mass via the Higgs field after the epoch of electroweak symmetry breaking, that occurred about a ...
ProfRob's user avatar
  • 155k
7 votes
Accepted

Can I slice off a piece of the Sun?

The idea of removing material from the sun for either fuel or to lengthen its lifespan is called "star lifting". Various hypothetical methods have been suggested, including heating parts of the ...
Anders Sandberg's user avatar
7 votes
Accepted

How small could an orbital system be in our solar system?

If we only consider gravity, one answer may be found using the Hill sphere. This is the distance the gravity of a body dominates over the sun: $$r_H \approx a \left(\frac{m}{3M_\odot}\right)^{1/3}$$ ...
Anders Sandberg's user avatar
7 votes

Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?

This is one of those questions that is easy to state but complicated to answer - and this won’t at all be a complete answer, but mostly a quick outline of some important factors to consider and terms ...
Eric Jensen's user avatar
  • 4,894
6 votes

What fraction of a star's hydrogen store will be fused over its lifespan?

The answer is as complex as stellar evolution. H-burning takes place in the core during the main sequence; in a shell after the star has left the main sequence until it reaches the tip of the red ...
ProfRob's user avatar
  • 155k
6 votes
Accepted

What percentage of the hydrogen today has never been in a star

About 70% of the baryonic matter in the universe is hydrogen, with a mean density of about $4\times 10^{-29}$ kg/m$^3$. Most of the stars that have ever been born are still alive, since an average ...
ProfRob's user avatar
  • 155k
6 votes

Does the existence of hydrogen in the universe create an obscuration effect similar to the way air does at great distances?

In a sense yes - there is interstellar (i.e. intra-galactic) absorption of Lyman-$\alpha$ photons by neutral hydrogen. This plays a role e.g. when trying to determine how much hydrogen is lost from ...
AtmosphericPrisonEscape's user avatar
5 votes

Hydrogen and oxygen in space

Hydrogen and oxygen only react when there is sufficient energy. For instance, the autoignition temperature of hydrogen at 1 atmosphere is 536 °C. This is why you can do that experiment with mixed ...
hartacus's user avatar
  • 327
5 votes
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Helium rain inside metallic hydrogen within Jupiter, conditions and experiments?

Different sources give significantly different values for the conditions under which hydrogen shifts from molecular to metallic. See the discussion in the comments associated with this question. ...
Steve Linton's user avatar
  • 10.3k
5 votes
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What is the elemental composition of the Sun overall, rather than at the photosphere?

Both your estimate and @ProfRob's answer are roughly in the right area. I've done the integration on an older standard solar model, Model S (Christensen-Dalsgaard J., et al., 1996, Sci, 272, 1286) and ...
Warrick's user avatar
  • 2,847
4 votes

Why is molecular hydrogen (H2) so difficult for astronomers to detect?

There are a few reasons molecular hydrogen (H2) is hard to detect depending on what band you are looking. In the UV, it can be detected in absorption of the electronically excited Lyman–Werner bands, ...
Kyle's user avatar
  • 421
4 votes

How small could an orbital system be in our solar system?

It is difficult to work out an actual numerical answer, but let me point out some things that I think would determine the lower bound. If two objects are close enough, they are attracted by Van der ...
Mark Foskey's user avatar
  • 3,916
4 votes
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What is the significance of the velocity resolution in spectral line observations using radio interferometry?

Short version: velocity resolution is the smallest velocity difference you can measure between two moving objects, using a given spectrum. More details: As you probably know (based on your implicit ...
Eric Jensen's user avatar
  • 4,894
4 votes
Accepted

Is it possible for stars to not begin fusing hydrogen at all?

No. The (unofficial) definition of "star" is "a body supported by the pressure generate by fusion in its core". For fusion to occur a certain temperature must be reached, and ...
James K's user avatar
  • 124k

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