Questions tagged [hydrogen]

Questions about the simplest and most abundant element in the Universe.

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8 votes
2 answers
2k views

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

I've had this question for a while. I understand the universe is full of "dust". I am also aware of the fact that there is an average measure of particle density in the universe. I am ...
6 votes
1 answer
116 views

What is the elemental composition of the Sun overall, rather than at the photosphere?

Many sources claim that the Sun is around $70-74\%$ hydrogen and $25-27\%$ helium by mass, or $91\%$ and $9\%$ by atom count, without any further caveats - e.g. 1, 2, 3. I believe these sources are ...
3 votes
0 answers
22 views

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 ...
1 vote
1 answer
45 views

Using Saha's equation knowing the overall pressure

Knowing the pressure, $P_g$, how can I calculate $\frac{N_{I+1}}{N_I}$ using Saha's equation? If I assume that $P_g=(n_e+n_{H^+}+n_H)K_B T$ and that $n_e=n_{H^+}$, I can find the electronic pressure, $...
0 votes
2 answers
142 views

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

As far as I know, stars (virtually all stars) begin fusing hydrogen into helium, and the rest happens based on the mass and luminosity and etc. Out of curiosity, I was wondering: is it even possible ...
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3 votes
1 answer
52 views

Is it possible to observe Lyman-continuum emission from extragalactic objects?

Lyman-continuum (LyC) emission is everything blueward of 912 Angstroms (so it includes extreme UV photons, X-rays and gamma rays). There are many low-redshift astrophysical plasmas such as the diffuse ...
4 votes
1 answer
541 views

What is the significance of the velocity resolution in spectral line observations using radio interferometry?

I've always struggled to conceptualize the term "velocity resolution" in spectral observations. In principle, it is simple to calculate. For example, one can take the spectral width and ...
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15 votes
2 answers
2k views

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

Similar questions have been asked before; but, why? Is the monoatomic hydrogen left over from the Big Bang? And hasn't had the opportunity to collide with other hydrogen atoms yet? Or are hydrogen ...
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5 votes
1 answer
121 views

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

As in general case, stars are formed from nebula which in some case itself is the result of a supernova. Also stars need hydrogen to become a star (to do nuclear fusion), but stars consume hydrogen in ...
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11 votes
2 answers
1k views

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

Type II supernovae have hydrogen. Where did the hydrogen come from if that is the first element used up in the star's life cycle? Also if our solar system was seeded from an ancient supernova where ...
5 votes
2 answers
640 views

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

Answers to How does the Sun's gravity have so much force and pull on the solar system? How does it scale? Newton's law of gravity scales on orbits so that we can theorize very small orbits with very ...
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1 vote
0 answers
164 views

How to convert between spectra given in terms of velocity (km/s) to wavelength spectra?

I have H alpha spectra of H II regions in our galaxy. In the paper, the x-axis is in units of km/s and the corresponding line width as well. From this, how can I get equivalent width of the H alpha ...
1 vote
1 answer
213 views

How to isolate H$_\alpha$ from Nitrogen doublet emission lines

I am trying to find out line intensity and FWHM of H$_\alpha$6565 emission line from a quasar spectrum obtained from SDSS DR-14Q. Visual inspection of spectrum shows H$_\alpha$ being contaminated with ...
5 votes
1 answer
199 views

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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7 votes
2 answers
536 views

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

I am reading a great deal about the various forms of hydrogen throughout the universe, and I keep reading that 'molecular hydrogen is notoriously difficult to detect', and other sentiments along those ...
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3 votes
1 answer
237 views

Is most hydrogen in the universe in the form of plasma, atomic neutral hydrogen, ionized hydrogen, or molecular?

I have had trouble finding an answer somewhere.... Some places say most hydrogen is plasma, such as the stuff stars are made of (mostly) and the 'warm-hot intergalactic plasma'. Other places say ...
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2 votes
2 answers
302 views

Can a high enough density ignite a gas giant into a brown dwarf?

I wonder whether the nuclear fusion of brown dwarfs and more massive stars really depends on their mass only or if it could also start nuclear fusion if it is dense enough but not as massive as brown ...
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3 votes
0 answers
110 views

Hydrogen Frost Line? Where, if anywhere, is it cold enough for Oort Cloud objects or rogue planets to have solid hydrogen on their surfaces?

I like the idea of Oort Cloud objects all being crusted with a thin layer of hydrogen snow, though what little information I've managed to find on the topic seems to imply that that is unlikely, ...
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24 votes
2 answers
10k views

Is Jupiter a failed star?

The elemental make-up of Jupiter is about entirely hydrogen and helium, along with a very small fraction of the atmosphere being made up of compounds such as ammonia, sulfur, methane, and water vapor. ...
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12 votes
1 answer
2k views

Replenishing hydrogen in the core of the sun

How is hydrogen supplied to the core of the sun? Shouldn't the radiative zone prevent this? Shouldn't heavier helium fill the core? How much of the hydrogen can the sun fuse?
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1 vote
0 answers
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Is there any possibility that a gas planet turns into a star [duplicate]

Since the sun is made of one of elements hydrogen Why Saturn and jupiter doesnt turn into a star since they have a elements of hydrogen ?
4 votes
1 answer
170 views

Tuning radio telescopes

In a paper called Further Observational Evidence for a Critical Ionising Luminosityin Active Galaxies, Section 2.1, the authors talk about using the ICRF2 to find a tuning frequency in search of the ...
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1 vote
3 answers
235 views

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

These two statements seem to conflict, but since we're here they can't: Electrically charged particles cannot be massless. Hydrogen was created at the moment of the Big Bang. However, the Higgs ...
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31 votes
3 answers
7k views

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

As I see here, the Sun belongs to the Population I group of stars, which is the 3rd generation of the stars in our universe. 1st generation stars are Population III, 2nd generation are Population II, ...
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3 votes
2 answers
180 views

Hydrogen Line observation - Interference from trees

I am setting up a 2.4 metre parabola pointing straight up to observe the 21cm hydrogen line at 1420MHz with meridian drift scans. I'm planning to place the dish on a steel pole embedded in the ...
14 votes
1 answer
706 views

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

A main sequence star will fuse some of its hydrogen, but not all. In massive stars ($>1.5M_\odot$) the core is convective but the rest of the atmosphere radiative and hence does not mix much: as it ...
3 votes
1 answer
242 views

Helium rain inside metallic hydrogen within Jupiter, conditions and experiments?

In response to today being pi day (also see http://www.piday.org/), NASA has published it's fifth annual pi in the sky day 5 activity set (see also NASA goes the distance and Celebrate Pi Day with ...
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6 votes
3 answers
469 views

Can I slice off a piece of the Sun?

Bear with me. I want to explain this to my 6 and half year old. If, all things being equal, we could reach out to the Sun with a suitable implement, a gigantic space knife, could we cut a piece off ...
4 votes
1 answer
83 views

Relation between molecular cloud mass and galactic mass

Would it be true to assume that the mass of a galaxy is approximately the mass of all molecular clouds detected within it, let's say, through CO observations and then converted to H$_2$?
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1 vote
2 answers
448 views

Hydrogen and oxygen in space

chemistry tells us that when mixing hydrogen and oxygen the result is an explosion and water. my question is: does this happen on astronomical scale? for example, did they ever observe planet-size ...
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8 votes
1 answer
888 views

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

It stands to reason that some of the hydrogen and helium that formed directly as a product of the big bang might never have fallen into a star to re-ejected when that star explodes. My question is, ...
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2 votes
1 answer
288 views

Are all gas planets guaranteed to produce their own magnetic field?

All gas giants in the solar systems have two things in common: abundant hydrogen gas and a magnetic field. I'm wondering: could there be a gas planet that somehow can't produce any magnetic field on ...
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8 votes
1 answer
1k views

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) ...
4 votes
1 answer
82 views

Population of excited H levels in a Strömgren Sphere

In chapter 2.2 of Astrophysics of Gaseous Nebulae and AGN Ostriker and Ferland claim that, as far as ionization is concerned, one can assume all atoms to be in the ground state in a Strömgren Sphere ...
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2 votes
2 answers
296 views

If there are neutron stars, would most stars be considered "proton stars"?

For example, the Sun is a giant sphere of positively charged plasma. About 72% of the elements in it are protium. This means that these protium atoms would have had to lose their electrons, right? If ...
5 votes
1 answer
366 views

Why does hydrogen ionization happen in HII regions?

Why does hydrogen ionization happen in HII regions? Why is the hydrogen there ionized?
1 vote
1 answer
227 views

Are hot stars like O-type stars entirely composed of helium?

Hot stars like O-type stars show no hydrogen in their spectra. Does this mean they are made entirely of helium? Any explanation would be really helpful.
3 votes
0 answers
42 views

What are the implications if the Sun was formed in a warm nebula?

Molecular oxygen O2 has been found on comet 67P/C-G in a ratio of 3.8% to water, which is much higher than expected. An explanation proposed is that the Solar System formed from a molecular cloud ...
2 votes
1 answer
108 views

Could evaporating hot Jupiters have metallic hydrogen on their surfaces?

Jupiter is believed to have metallic hydrogen in its core. And gas giants that migrate to become hot Jupiters are believed to evaporate, have their atmospheres blown away by their nearby star. Can ...
26 votes
1 answer
1k views

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 ...
1 vote
1 answer
729 views

Is the sun too small to self-ignite?

I recently heard in a discussion that the sun is not massive enough to self-ignite via core-pressure. It simply has not enough mass to "generate" the gravitational force needed for that. The reason ...
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2 votes
2 answers
2k views

What is the minimum size of a ball of gas to become a star?

I know there are two criteria to meet in order for nuclear fusion to occurs. High temperature (many times temperature at Sun's core) High pressure (protons are very close to each other) [Goal] ...
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3 votes
1 answer
741 views

How are stellar elemental abundances quoted?

Close to the bottom of page 4 of this article (marked as page 164 in the upper left corner) states Values are given in the logarithmic scale usually adopted by astronomers, A$_{e\ell}$ = log N$_{e\...
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12 votes
3 answers
2k views

Is there enough hydrogen left after a star dies so another star will have enough to light up?

A star consumes quite a lot of hydrogen in its life, and is pretty much "vacuuming" everything in its vicinity. After it dies (eventually by supernova which will spread all its composition over light ...
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3 votes
1 answer
950 views

In the end what is the ultimate matter/element in the universe, due to fusion process in stars?

We know that, in stars, hydrogen is used by the stars and due to the fusion in two hydrogen elements we get helium -> Carbon -> Oxygen ->Other elements -> Iron -> then Super/Hypernova. If everywhere ...
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7 votes
1 answer
136 views

Density of hydrogen between galaxies

From watching a video on youtube, it states that Dark Matter is 6 times more abundant than known matter. I was wondering if it was possible to have hydrogen clouds between the universes galaxies. The ...
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3 votes
2 answers
273 views

Could dark matter particles be unstable?

Is it possible that dark matter particles are unstable and the existing dark matter will decay in the long run and turn into hydrogen, for example? What would be possible mechanisms for such a decay? ...
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