Confused by Brian Cox about stardust
Discussion
A couple of days ago I saw a Cox programme on the universe. The episode mentioned the life cycle of stars and he said, and explained, something which has bothered me in the past.
If a big star explodes as a supernova, bits of it are sent out into the ether. (Yeah, I know, but if it was good enough for Einstein.)
Now the star has been busily converting hydrogen to the heavy metals and, in the process, using up all the H. That bit I think I grasp. And the bit about why heavy metals.
The gas clouds are awe inspiring and I have some as screen savers.
He mentioned the Pleiades and the nebula coming from a supernova and that stars are being born from the cloud and the cycle continuing.
So where's the hydrogen coming from? I thought it had all been used up in the original star that went bang.
If it was already there, why did it need the explosion?
If a big star explodes as a supernova, bits of it are sent out into the ether. (Yeah, I know, but if it was good enough for Einstein.)
Now the star has been busily converting hydrogen to the heavy metals and, in the process, using up all the H. That bit I think I grasp. And the bit about why heavy metals.
The gas clouds are awe inspiring and I have some as screen savers.
He mentioned the Pleiades and the nebula coming from a supernova and that stars are being born from the cloud and the cycle continuing.
So where's the hydrogen coming from? I thought it had all been used up in the original star that went bang.
If it was already there, why did it need the explosion?
Space is mainly hydrogen. https://en.wikipedia.org/wiki/Interstellar_medium
Stellar nurseries form in the denser parts of space, which is also where the supernovae are likely to be. That's all there is to it (I think). Gravity does the rest.
Stellar nurseries form in the denser parts of space, which is also where the supernovae are likely to be. That's all there is to it (I think). Gravity does the rest.
Eric Mc said:
A star dies when it uses up the hydrogen in its CORE. There will still be plenty of unused hydrogen in the non fusing outer bulk of the star. If the star is biog enough to go supernova, all that unfused hydrogen will get blasted out into space.
Thanks for that. It seems very wasteful.Any idea of percentages used:unused.
If hydrogen is never regenerated, eventually the universe will run out of it...
So... fusion makes all elements up to uranium. Therefore eventually we'll have a universe made entirely of uranium, which will then undergo fission into whatever the two products are - strontium 90 and something? And that will be it.
(C) Me 2016.
So... fusion makes all elements up to uranium. Therefore eventually we'll have a universe made entirely of uranium, which will then undergo fission into whatever the two products are - strontium 90 and something? And that will be it.
(C) Me 2016.
The good Professor should have stuck to being a wannabe pop star (imo).
https://www.youtube.com/watch?v=DMEGgYNNrCw
(On keyboards)
https://www.youtube.com/watch?v=DMEGgYNNrCw
(On keyboards)
Simpo Two said:
If hydrogen is never regenerated, eventually the universe will run out of it...
So... fusion makes all elements up to uranium. Therefore eventually we'll have a universe made entirely of uranium, which will then undergo fission into whatever the two products are - strontium 90 and something? And that will be it.
(C) Me 2016.
Not quite.So... fusion makes all elements up to uranium. Therefore eventually we'll have a universe made entirely of uranium, which will then undergo fission into whatever the two products are - strontium 90 and something? And that will be it.
(C) Me 2016.
Fusion in the core of a large star stops at Iron, the production of which does not produce energy but consumes it instead. This is why the star dies as once it gets to Iron, energy production falls rapidly causing the core of the star to collapse.
Not all of the core is iron though - at the point of the star's death - there are shells of elements from hydrogen, Helium and Carbon - through to Silicon Nickel and Iron. Only a small percentage of the star gets converted to these elements however.
Elements heavier than Iron are produced due to high energy collisions between nuclei in the supernova explosion itself and although they are formed in a fusion reaction - they aren't part of the star's normal fusion process and are produced in tiny amounts at the point of the star's death.
Smaller stars like the sun do not have high enough temperatures and pressures to produce elements like Iron. They exist primarily through hydrogen and helium burning with their cores producing only carbon/oxygen.
For the final state of the universe - it is likely to be populated by white, red and brown dwarf stars which are still composed of relatively light elements (Hydrogen, Helium, Lithium etc) but too small to initiate fusion. There will also be a fair few neutron stars and black holes.
https://en.wikipedia.org/wiki/Future_of_an_expandi...
https://en.wikipedia.org/wiki/Compact_star
Derek Smith said:
Thanks for that. It seems very wasteful.
Any idea of percentages used:unused.
It would vary depending on the size of the star. In stellar evolution and stellar fate, size matters. I'm nut sure what the percentage ranges are but it;s quite high from what I remember.Any idea of percentages used:unused.
Nature is not designed to be "efficient". It just does what it does.
MrCarPark said:
In Prof Cox's defence, he gave a Q&A over the summer to an audience of mixed knowledge (kids through to smart adults) and handled it very well.
His explanation of the expansionary multiverse certainly illuminated my understanding
No need to defend him. I think that in popularising science he does a great service to this country. His explanation of the expansionary multiverse certainly illuminated my understanding
The programmes could be a bit better at times. There are lots of images of him standing around looking cool, on top of hills, mountains and buildings. But a small criticism.
Moonhawk said:
For the final state of the universe - it is likely to be populated by white, red and brown dwarf stars which are still composed of relatively light elements (Hydrogen, Helium, Lithium etc) but too small to initiate fusion. There will also be a fair few neutron stars and black holes.
Hawking has established that all Black Holes will eventually evaporate over large time scales.Eric Mc said:
It would vary depending on the size of the star. In stellar evolution and stellar fate, size matters. I'm nut sure what the percentage ranges are but it;s quite high from what I remember.
Nature is not designed to be "efficient". It just does what it does.
How our sun may behave in the future:Nature is not designed to be "efficient". It just does what it does.
http://www.cosmotography.com/images/chemistry_of_s...
lionelf said:
Moonhawk said:
For the final state of the universe - it is likely to be populated by white, red and brown dwarf stars which are still composed of relatively light elements (Hydrogen, Helium, Lithium etc) but too small to initiate fusion. There will also be a fair few neutron stars and black holes.
Hawking has established that all Black Holes will eventually evaporate over large time scales.By 'final state', I was referring to the elemental mixture of the universe once fusion has essentially ceased.
perdu said:
Is he a good professor?
Me, I have me doots
keyboards sounds about right
pun unintended
I found him to be quite a good lecturer back when he was a doctor, he filled in on some of our university courses when Prof Jeff Foreshaw (who I believe has been on the tellybox as well) was out doing something sciency.Me, I have me doots
keyboards sounds about right
pun unintended
Derek Smith said:
No need to defend him. I think that in popularising science he does a great service to this country.
The programmes could be a bit better at times. There are lots of images of him standing around looking cool, on top of hills, mountains and buildings. But a small criticism.
Brian cox talking about the universe, camera pans out to show him on a mountain looking at the sky, there's a light breeze blowing and the Sun's is setting. The programmes could be a bit better at times. There are lots of images of him standing around looking cool, on top of hills, mountains and buildings. But a small criticism.
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