# Tag Info

Accepted

### Is lithium considered a metal in astronomy?

The latter. To astronomers, a metal is any element that is not hydrogen or helium, because these elements together constitute most of the elements in the Universe, by far. This means that, in many ...
• 33.8k

### Metal distribution in our solar system

The metal content of the Solar system is completely dominated by the Sun. The Sun contains $\sim1\%$ of 'metals' (in astronomical language anything but hydrogen and helium is a 'metal'), but all the ...
• 5,276
Accepted

### Why can't a quasistar exist now?

Gas clouds with masses much higher than $10^3\,M_\odot$ are plentiful in galaxies; the typical star-forming cloud (the so-called molecular clouds) have masses of $10^3\,M_\odot$ to $10^7\,M_\odot$. ...
• 33.8k

### Does Gold really come from Supernovas?

We don't need to see things to understand them. It is now generally understood that gold is formed in neutron star collisions. The evidence for this partly theoretical: Models of neutron star ...
• 91.4k
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### How do astronomers detect the 'metals' in a star? If the atoms are presumably completely ionized?

You are correct that the characteristic emission and absorption lines we see in stars' spectra are from electrons that are bound to atoms making transitions between different energy levels. That is ...
• 4,744

### Why can't a quasistar exist now?

If you build a very massive protostar, more than a thousand solar masses, then it is possible for the core of the protostar to collapse directly to a black hole whilst it is still surrounded by a ...
• 118k

### Where/how are metals distributed in our universe?

From the big bang nucleosynthesis (BBN) page is a handy chart of the sources of elements: Since basically all metals come from some stellar process, the question of elemental distribution can vary ...
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### Metal distribution in our solar system

The Sun currently accounts for more than 99.86% of the mass of the Solar System. Based on spectrographic estimates of the composition of the sun and it's centrifugal position and the mass of metals, ...
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### How do astronomers detect the 'metals' in a star? If the atoms are presumably completely ionized?

As @ELNJ answer pointed out, fully ionized the atoms at the star surface are not. It is not hot enough. Star cores are another case, but we usually don't see them. There, both pressure and temperature ...
• 2,150

### Why you use log to measure metallicity in galaxies?

The distribution of metallicities appear to be more evenly spread out in logspace than in linear space. The reason for this can be ascribed to there being no preferred scale for the abundance of a ...
• 33.8k

### Is metallicity low at the central region or nucleus of the Milky Way?

The stars in the Galactic bulge are predominantly metal-rich (by that I mean have a metallicity similar to the Sun or even a little higher). Even though these stars are predominantly old, the bulge ...
• 118k

### Does Gold really come from Supernovas?

Do we really know that the origin of gold was in a supernova explosion? Up until the last few years that was the generally accepted explanation, but things have changed somewhat due to two ...
• 118k
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### Why could Quasi-stars ("black hole stars") have only existed when everything was hydrogen and helium? (no metal "contamination")

The presence of heavier elements makes the medium absorb more radiation. This means a nascent star that would have been able to collapse in the absence of metals, will lose its outer layers to ...
Accepted

### Why is the carbon/oxygen ratio at low metallicities important to study?

I think I can in part answer your questions. The [CII] ($\lambda=158\,\mu m$) and [OIII] ($\lambda=88\,\mu m$) are the most brightest IR emission lines in the local Universe Stacey et al. (1991). The ...
Accepted

### Why are stars more metallic closer as you move closer to the galactic bulge?

It has to do with the formation of the Milky Way. At the beginning, the Milky Way was much more spherical than it is now - perhaps closer to what an elliptical galaxy is like than a spiral galaxy. ...
• 34.1k

### What are the most valuable meteorites and asteroids in terms of precious metals?

I have found an outdated study that says that some siderites contain as much as .001% of gold. Is it genuinely a viable mining research subject? Not yet, and not for quite a long time. Gold is ...
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### Why you use log to measure metallicity in galaxies?

The logarithm is there because the ratio $O/H$ is really tiny. The log converts essentially points out the order of magnitude. If we have $O/H= 10^{-14}$, then $\log(O/H)=-14$. Taking logarithms is ...
• 3,119