Starship Asterisk*

Ann wrote:Oxygen, in fact, is formed in stars (and even in supernovae, I think). But our dear old Earthly O₂, which we breathe, is formed by green plants through photosynthesis. But those tadpoles don't get to breathe any of that. Lucky us, though!

Chris Peterson wrote:

Ann wrote:
Oxygen, in fact, is formed in stars (and even in supernovae, I think). But our dear old Earthly O₂, which we breathe, is formed by green plants through photosynthesis. But those tadpoles don't get to breathe any of that. Lucky us, though!

That's a somewhat confusing statement, with the word "form" being used in two different ways.
Oxygen is primarily created in the CNO hydrogen/helium fusion process.

http://en.wikipedia.org/wiki/Triple-alpha_process wrote:

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<<The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon.

Older stars start to accumulate helium produced by the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle in their cores. The products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium-8 respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei. When the star starts to run out of hydrogen to fuse, the core of the star begins to collapse until the central temperature rises to 108 K (8.6 keV). At this point helium nuclei are fusing together faster than their product, beryllium-8, decays back into two helium nuclei.

Once beryllium-8 is produced a little faster than it decays, the number of beryllium-8 nuclei in the stellar core increases to a large number. Then in its core there will be many beryllium-8 nuclei that can fuse with another helium nucleus to form carbon-12, which is stable:

Because the triple-alpha process is unlikely, it needs a long time to produce much carbon. One consequence of this is that no significant amount of carbon was produced in the Big Bang because within minutes after the Big Bang, the temperature fell below that necessary for nuclear fusion.

Ordinarily, the probability of the triple alpha process is extremely small. However, the beryllium-8 ground state has almost exactly the energy of two alpha particles. In the second step, 8Be + 4He has almost exactly the energy of an excited state of 12C. These resonances greatly increase the probability that an incoming alpha particle will combine with beryllium-8 to form carbon. The existence of this resonance was predicted by Fred Hoyle before its actual observation, based on the physical necessity for it to exist, in order for carbon to be formed in stars. In turn, prediction and then discovery of this energy resonance and process gave very significant support to Hoyle's hypothesis of stellar nucleosynthesis, which posited that all chemical elements had originally been formed from hydrogen, the true primordial substance.

As a side effect of the process, some carbon nuclei can fuse with additional helium to produce a stable isotope of oxygen and release energy:

• ¹²C + ⁴He → ¹⁶O + γ (+7.162 MeV)

This creates a situation in which stellar nucleosynthesis produces large amounts of carbon and oxygen but only a small fraction of these elements is converted into neon and heavier elements. Both oxygen and carbon make up the 'ash' of helium-4 burning. The anthropic principle has been controversially cited to explain the fact that nuclear resonances are sensitively arranged to create large amounts of carbon and oxygen in the Universe.

Fusion processes produce nuclides only up to nickel-56 (which decays later to iron); heavier elements (those beyond Ni) are created mainly by neutron capture. The slow capture of neutrons, the s-process, produces about half of these heavy elements. The other half are produced by rapid neutron capture, the r-process, which probably occurs in a core-collapse supernova.>>

Ann wrote:Thanks for putting me straight, Chris.

neufer wrote:The CNO hydrogen/helium fusion process mostly produces unstable oxygen isotopes
(or stable oxygen isotopes that quickly burn into fluorine by fusing with hydrogen).

MarkBour wrote:
If I understand the APOD's intro description, then the blue I am seeing all over the image is from oxygen being very prevalent in this area? I don't see any green and very little red. That confuses me, because I thought there'd be lots of hydrogen about. Is there something I'm not understanding here?

Beyond wrote:Why is it that one always has to be able to see the bigger picture, before one can understand something of what one normally sees

Boomer12k wrote:

Beyond wrote:Why is it that one always has to be able to see the bigger picture, before one can understand something of what one normally sees

So a person "sees" things in the proper context....without which you would not have as complete, or clear, understanding of the small part you are focusing on....

:---[===] *

MarkBour wrote:Tadpoles are amphibians. That's why this discussion is all about how they get oxygen.

If I understand the APOD's intro description, then the blue I am seeing all over the image is from oxygen being very prevalent in this area? I don't see any green and very little red. That confuses me, because I thought there'd be lots of hydrogen about. Is there something I'm not understanding here?

MarkBour wrote:If I understand the APOD's intro description, then the blue I am seeing all over the image is from oxygen being very prevalent in this area? I don't see any green and very little red. That confuses me, because I thought there'd be lots of hydrogen about. Is there something I'm not understanding here?

Chris Peterson wrote:
First of all, you aren't seeing much blue in this image. What you're seeing is closer to cyan- a mix of green and blue showing the mix of hydrogen and oxygen.

Cerulean, also spelled caerulean, is a color term that may be applied to certain colors with the hue ranging roughly between blue and cyan, overlapping with both.

geckzilla wrote:You could argue left and right about whether that color is blue or cyan but mathematically it is somewhere between pure blue and pure cyan.

Ann wrote:

Chris Peterson wrote:
First of all, you aren't seeing much blue in this image. What you're seeing is closer to cyan- a mix of green and blue showing the mix of hydrogen and oxygen.

I'd like to (politely) disagree, Chris. If you compare wikipedia's definition of cyan with wikipedia's definition of blue, I'd say that the central parts of IC 410 look more blue than cyan. Of course that's a question of how we define blue and cyan.

Nitpicker wrote:That's beautiful. It took me a while to get the orientation of this image (which for some reason I am always compelled to do). The tadpoles are very close to the backside of the galactic plane. They appear to be swimming south in galactic terms, or south-west in celestial terms. Looking back towards the galactic centre from there, I imagine we form part of a nice bit of foreground fluff, obscuring the view in some aesthetic way.

Anthony Barreiro wrote:IC 410 is a remarkable nebula. Although it lies in the galactic plane, and at about 12,000 light years it's pretty far away from us, you can see it faintly through 10x50 binoculars in a dark sky. Because it lies in an outer arm of our Milky Way galaxy, there's not too much dust and gas between IC 410 and us, so its light is less attenuated than light coming from sources closer to the galactic center. IC 410 forms the western point of a nearly equilateral triangle about two degrees on a side with the much brighter open clusters M38 and M36. As seem from Brisbane, Australia IC 410 culminates around 30 degrees above the northern horizon, so you might be able to see it!

Nitpicker wrote:With my scope in my back yard, I'm sure I could capture NGC1893, M38 and M36 with my camera, or get a greatly diminished view of them through the eyepiece. I think I'd have to drive for an hour or so to have a hope of IC410. I've not been to truly dark skies since I developed a real interest in learning the sky. I fear I would quickly get lost in the dazzle.