# Tag Info

44

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 circumstances all other elements can be neglected, at least to first order. By mass, H and He account for some 74% and 24% in the present-day Universe, ...

14

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 other bodies of the Solar system combined have less mass than that. So even if they were only made of metals (but the outer planets are mostly made of H and He) ...

11

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 $10^7\,M_\odot$. When quasistars (hypothetical stars powered not by nuclear fusion, but by accretion onto a central black hole) cannot exist today, it is because all gas in the ...

9

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 collisions suggest they would produce large amounts of heavy elements, and regular supernovae would not produce gold in the right amounts to explain the ...

8

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 possible because the elements in a star's photosphere are not fully ionized. Hydrogen - the easiest element to fully ionize because its nucleus only has a ...

8

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 massive envelope. The collapse will happen "inside out", so that the envelope collapses at a slower rate. However, there is a maximum rate at which black holes can ...

7

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 greatly between different environments depending on when you're observing that particular galaxy, star/galaxy cluster, etc. Galaxy mergers, supernova, and stellar ...

7

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, you can deduce it also contains the most of all kinds of metals. Here is an example to illustrate: The milky way contains roughly 0.00011% of $\mathrm{Fe}$ (1....

6

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 make impossible the existence of the usual atoms. Atoms and molecules usually emit their characteristic wavelengths because of the electrons' energy levels... ...

5

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 developments. About half the elements heavier than iron (including gold) must be produced via rapid neutron capture - the so-called r-process. This is not under debate, ...

5

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 is thought to have formed extremely quickly and the interstellar medium from which the stars were formed would have been enriched with metals very quickly. Here ...

5

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 given element; rather they span several orders of magnitude. The same can be said for instance about the distribution of dust grain sizes, the distribution of the ...

3

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. Population III stars would have formed first, then quickly died out. Next came Population II stars. They formed when the galaxy was still somewhat spherical, and ...

2

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 precious because humans only mine about 2.5 million kilograms of the stuff per year. Compare this to the huge amount of infrastructure (and huge cost) needed to ...

2

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 a standard practice in science and mathematics when the numbers range over several orders of magnitude (especially so when they are either very large or very ...

2

The bulge population is old, older than 10 billion years. Its stars have a broad range of metallicities, but are more metal rich than population II, have an average close to solar metallicity and a significant fraction more metal rich than the Sun. The basic idea is that the bulge population is one that formed very quickly, with a high rate of gas infall and ...

2

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 radiation pressure as the core starts to heat up.

1

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 former has been observed to be the dominant coolant of the interstellar medium (ISM) DeLooze et al. (2014) metal-poor local Universe dwarfs galaxies. Cooling of ...

1

The addition of metals (i.e., elements heavier than helium) to a stellar mixture makes it less transparent to radiation. Basically, hydrogen and helium have relatively simple and uncrowded spectra, but the "metals" add many new spectral lines and the mixture absorbs much more light and is more efficiently heated by it and picks up more momentum from it, ...

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