Page 1 of 5 123 ... LastLast
Results 1 to 10 of 45

Thread: astrophysics - dumb questions

  1. #1
    Troll Magnet Sparko's Avatar
    Join Date
    Jan 2014
    Faith
    Christian
    Gender
    Male
    Posts
    30,491
    Amen (Given)
    2565
    Amen (Received)
    15107

    astrophysics - dumb questions

    So I have been watching some science channel shows about stars and novas and how elements are produced. I figure it is much simplified in the tv show so please forgive my dumb questions.

    From my understanding, the stars start out as mostly hydrogen and will fuse hydrogen into helium, as the star ages it starts fusing helium into higher elements. If the star is large enough it will fuse all the way down to iron at which time it goes nova because it can't fuse iron. As it explodes, the higher elements are produced, like gold, lead, titanium, uranium and so on. And the reason the higher elements are more rare is because they only are created during the brief explosion of the nova. The elements float around in the aftermath of the nova as gas and eventually will condense into new stars and planets, which is how we have a planet with all of the various elements.

    So here are my questions:

    1. If the higher elements are in short supply because of the way they are made during a nova, then why is gold so rare on earth but elements like lead are common?

    2. If we have an iron core and iron is fairly common in this solar system, and planets and our sun are created through gravity, then why do the planets like earth have heavy elements like iron and the sun is made up of hydrogen? Wouldn't it make sense that the heavier elements would be concentrated in the higher gravity planets and especially the sun?

    3. If the sun does have heavier elements like iron it it, why doesn't it either go nova or stop fusing? One of the shows said that once a star produced iron it instantly went nova.

  2. #2
    radical strawberry
    Join Date
    Jan 2014
    Location
    Everglades
    Faith
    Taoist
    Posts
    2,183
    Amen (Given)
    307
    Amen (Received)
    709
    Quote Originally Posted by Sparko View Post
    So I have been watching some science channel shows about stars and novas and how elements are produced. I figure it is much simplified in the tv show so please forgive my dumb questions.

    From my understanding, the stars start out as mostly hydrogen and will fuse hydrogen into helium, as the star ages it starts fusing helium into higher elements. If the star is large enough it will fuse all the way down to iron at which time it goes nova because it can't fuse iron. As it explodes, the higher elements are produced, like gold, lead, titanium, uranium and so on. And the reason the higher elements are more rare is because they only are created during the brief explosion of the nova. The elements float around in the aftermath of the nova as gas and eventually will condense into new stars and planets, which is how we have a planet with all of the various elements.

    So here are my questions:

    1. If the higher elements are in short supply because of the way they are made during a nova, then why is gold so rare on earth but elements like lead are common?

    2. If we have an iron core and iron is fairly common in this solar system, and planets and our sun are created through gravity, then why do the planets like earth have heavy elements like iron and the sun is made up of hydrogen? Wouldn't it make sense that the heavier elements would be concentrated in the higher gravity planets and especially the sun?

    3. If the sun does have heavier elements like iron it it, why doesn't it either go nova or stop fusing? One of the shows said that once a star produced iron it instantly went nova.
    I don't know the answers to these questions, Sparklish, but if there were more OPs like this, I'd stop by more often. I know parts of the answers, though, and would be happy to see who can tell the tale better.

    1. Lead is a prime destination for fission of the transuranics. Gold, not so much. So it's got an enhanced supply chain.

    2. Lighter elements, especially gases like Hydrogen and Helium, are more exposed to the solar wind blowing them away, leaving the heavier elements to form planets and such after the star ignites.

    3. I think you might have misunderstood this. It's not once there's iron, it's once there's nothing but iron, I'm thinking. So long as there's plenty of hydrogen, or any elements lighter than iron, they'll keep fusing, providing pressure to keep the star inflated. When they're used up, it's collapse and blow time, assuming the star is the right size for that.
    There is no lao tzu

  3. #3
    Troll Magnet Sparko's Avatar
    Join Date
    Jan 2014
    Faith
    Christian
    Gender
    Male
    Posts
    30,491
    Amen (Given)
    2565
    Amen (Received)
    15107
    Quote Originally Posted by lao tzu View Post
    I don't know the answers to these questions, Sparklish, but if there were more OPs like this, I'd stop by more often. I know parts of the answers, though, and would be happy to see who can tell the tale better.

    1. Lead is a prime destination for fission of the transuranics. Gold, not so much. So it's got an enhanced supply chain.
    ok that makes sense.
    2. Lighter elements, especially gases like Hydrogen and Helium, are more exposed to the solar wind blowing them away, leaving the heavier elements to form planets and such after the star ignites.
    But why don't all of the heavy elements just collect in the center (the star) and all of the lighter elements like hydrogen stay far away? Why does the hydrogen collect in the center and create a star? I would think you would just end up with a huge rock in the middle made up of heavier elements, surrounded by a cloud of hydrogen.
    3. I think you might have misunderstood this. It's not once there's iron, it's once there's nothing but iron, I'm thinking. So long as there's plenty of hydrogen, or any elements lighter than iron, they'll keep fusing, providing pressure to keep the star inflated. When they're used up, it's collapse and blow time, assuming the star is the right size for that.
    did some googling and here is what I found about the iron. It does happen pretty quickly.

    http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html

    massive_star_core.gif
    An inert iron core builds up at this time where successive layers above the core consume the remaining fuel of lighter nuclei in the core. The core is about the size of the Earth, compressed to extreme densities and near the Chandrasekhar limit. The outer regions of the star have expanded to fill a volume as large as Jupiter's orbit from the Sun. Since iron does not act as a fuel, the burning stops.

    The sudden stoppage of energy generation causes the core to collapse and the outer layers of the star to fall onto the core. The infalling layers collapse so fast that they `bounce' off the iron core at close to the speed of light. The rebound causes the star to explode as a supernova.
    ...
    Supernova Core Explosion:

    Once the silicon burning phase has produced an iron core the fate of the star is sealed. Since iron will not fuse to produce more energy, energy is lost by the productions of neutrinos through a variety of nuclear reactions. Neutrinos, which interact very weakly with matter, immediately leave the core taking energy with them. The core contracts and the star titers on the edge of oblivion.

    As the core shrinks, it increases in density. Electrons are forced to combine with protons to make neutrons and more neutrinos, called neutronization. The core cools more, and becomes an extremely rigid form of matter. This entire process only takes 1/4 of a second.

    sn_explosion.gif

  4. #4
    radical strawberry
    Join Date
    Jan 2014
    Location
    Everglades
    Faith
    Taoist
    Posts
    2,183
    Amen (Given)
    307
    Amen (Received)
    709
    Supposedly, according to this confirmation email, I'll have a car from the Enterprise across the street from the motel in about 3 hours. I'm outside, having a cigarette, talking to a couple right now who are trying to get home to Marathon Key and a PTSD vet of their own they left behind in their condo, but the roads are still closed down there.

    Quote Originally Posted by Sparko View Post
    ok that makes sense.
    Doesn't mean it's right, lol.

    But why don't all of the heavy elements just collect in the center (the star) and all of the lighter elements like hydrogen stay far away? Why does the hydrogen collect in the center and create a star? I would think you would just end up with a huge rock in the middle made up of heavier elements, surrounded by a cloud of hydrogen.
    As far as I know, everything collects at the center. Or centers, that is. Just so happens most everything is Hydrogen. The sun, and big bodies away from the sun, have enough pull to keep their Hydrogen after the star ignites, . Says here, Jupiter is mostly Hydrogen, too.

    What is Jupiter Made Of?

    Composed predominantly of hydrogen and helium, the massive Jupiter is much like a tiny star. But despite the fact that it is the largest planet in the solar system, the gas giant just doesn't have the mass needed to push it into stellar status.

    I don't know what's at the sun's core, but I found a decent, short, discussion with folks who sound like they know more than I do.

    What is the Sun's core made of?

    Do the heavier elements "sink" to the "bottom" of the core, like iron has during planetary formation?

    Actually, yes, they do! We refer to these processes as atomic diffusion. The one you're thinking of is known as gravitational settling. In short, yes, heavier elements "sink" towards the centre. This process takes a long time to make a meaningful difference: billions of years. For the metals, it isn't important, but it is actually important for the helium abundances. There was a minor revolution in the mid-1990's when this effect was included for the first time, and it led to a much better fit of solar models with respect to helioseismic observations.

    did some googling and here is what I found about the iron. It does happen pretty quickly.
    Looks pretty good to me.

    Some of the above discussion above says our sun, in particular, needs to heat up quite a bit before it'll burn anything other than Hydrogen into Helium, though there's a minor, catalyzed cycle, that bumps up Carbon, Nitrogen, and Oxygen.
    There is no lao tzu

  5. #5
    tWebber TheLurch's Avatar
    Join Date
    Jan 2014
    Location
    Northeast USA
    Faith
    MYOB
    Gender
    Male
    Posts
    858
    Amen (Given)
    57
    Amen (Received)
    246
    Quote Originally Posted by Sparko View Post
    1. If the higher elements are in short supply because of the way they are made during a nova, then why is gold so rare on earth but elements like lead are common?
    Certain fusion pathways are more probable than others, so heavier elements aren't all made in equal quantities. On Earth, abundance in the crust - what we typically mean when we use terms like "rare" - is also dominated by how well an element mixes with iron. If the answer is "well", then most of that element is in the core with the iron.

    Quote Originally Posted by Sparko View Post
    2. If we have an iron core and iron is fairly common in this solar system, and planets and our sun are created through gravity, then why do the planets like earth have heavy elements like iron and the sun is made up of hydrogen? Wouldn't it make sense that the heavier elements would be concentrated in the higher gravity planets and especially the sun?
    Apparently, the sun is 0.14% by mass iron. It's just a small fraction because the sun has so much other stuff as well. Same thing with Jupiter. The rocky planets have much higher percentages simply because they never


    Quote Originally Posted by Sparko View Post
    3. If the sun does have heavier elements like iron it it, why doesn't it either go nova or stop fusing? One of the shows said that once a star produced iron it instantly went nova.
    Minor terminology issue: a nova is different from a supernova. Supernova is the one that involves iron fusion.

    And here, the issue is not the fusion of iron itself, but what that means to the energy balance of the star. A star exists in a balance between gravity wanting to crush it and fusion releasing energy that creates an outward pressure that counteracts that. Fusion of lighter elements produces energy, and as long as that's happening, the star won't collapse, even if some iron's being produced.

    But as your later link indicates, iron probably won't be produced, because it requires especially high energies and pressures, and those don't exist until the star is well on its way to collapse.

  6. Amen Sparko amen'd this post.
  7. #6
    Troll Magnet Sparko's Avatar
    Join Date
    Jan 2014
    Faith
    Christian
    Gender
    Male
    Posts
    30,491
    Amen (Given)
    2565
    Amen (Received)
    15107
    Quote Originally Posted by lao tzu View Post
    Supposedly, according to this confirmation email, I'll have a car from the Enterprise across the street from the motel in about 3 hours. I'm outside, having a cigarette, talking to a couple right now who are trying to get home to Marathon Key and a PTSD vet of their own they left behind in their condo, but the roads are still closed down there.



    Doesn't mean it's right, lol.



    As far as I know, everything collects at the center. Or centers, that is. Just so happens most everything is Hydrogen. The sun, and big bodies away from the sun, have enough pull to keep their Hydrogen after the star ignites, . Says here, Jupiter is mostly Hydrogen, too.

    What is Jupiter Made Of?

    Composed predominantly of hydrogen and helium, the massive Jupiter is much like a tiny star. But despite the fact that it is the largest planet in the solar system, the gas giant just doesn't have the mass needed to push it into stellar status.

    I don't know what's at the sun's core, but I found a decent, short, discussion with folks who sound like they know more than I do.

    What is the Sun's core made of?

    Do the heavier elements "sink" to the "bottom" of the core, like iron has during planetary formation?

    Actually, yes, they do! We refer to these processes as atomic diffusion. The one you're thinking of is known as gravitational settling. In short, yes, heavier elements "sink" towards the centre. This process takes a long time to make a meaningful difference: billions of years. For the metals, it isn't important, but it is actually important for the helium abundances. There was a minor revolution in the mid-1990's when this effect was included for the first time, and it led to a much better fit of solar models with respect to helioseismic observations.



    Looks pretty good to me.

    Some of the above discussion above says our sun, in particular, needs to heat up quite a bit before it'll burn anything other than Hydrogen into Helium, though there's a minor, catalyzed cycle, that bumps up Carbon, Nitrogen, and Oxygen.
    Jupiter and the outer planets being hydrogen/helium actually fits with what I was asking, if the heavier elements would condense in the center of the solar system, the lighter elements would stay at the edges. I guess I am still wondering why the sun ended up with all that hydrogen instead of just collecting all the heavy elements and not leaving any for planets.

    but it does bring up another question, why do the gas giants have all rocky moons? Again, seems like the heavy stuff would collect in the middle and the less dense would be in the periphery, yet the lighter stuff (hydrogen) collected into Jupiter and the denser stuff became its moons.

  8. #7
    radical strawberry
    Join Date
    Jan 2014
    Location
    Everglades
    Faith
    Taoist
    Posts
    2,183
    Amen (Given)
    307
    Amen (Received)
    709
    Quote Originally Posted by Sparko View Post
    Jupiter and the outer planets being hydrogen/helium actually fits with what I was asking, if the heavier elements would condense in the center of the solar system, the lighter elements would stay at the edges. I guess I am still wondering why the sun ended up with all that hydrogen instead of just collecting all the heavy elements and not leaving any for planets.

    but it does bring up another question, why do the gas giants have all rocky moons? Again, seems like the heavy stuff would collect in the middle and the less dense would be in the periphery, yet the lighter stuff (hydrogen) collected into Jupiter and the denser stuff became its moons.
    As best I know, it's all about being big enough to hold onto the lighter elements that would otherwise be blown away. Left to their own devices, in the presence of a burning star, just about everything would be blown away by the solar wind.

    But if those elements are close enough to a massy body, gravity wins. Those massy bodies, though, pull heavier elements into their cores, where the gravity wells are deepest, leaving lighter elements, especially gases, exposed, fending for themselves in the shallower part of the well, the upper atmosphere, unless the bodies are really big, with really deep wells, like Jupiter, Saturn, Uranus, or Neptune, and the Sun.

    Earth and Venus are big enough to hold onto an atmosphere, but not big enough to hold onto their hydrogen and helium, unless they're bonded into molecules with heavier elements. Helium is heavier than hydrogen, but it doesn't bond much, so it didn't last in our atmosphere, either. Mercury, moons and asteroids weren't big enough to hold onto any atmosphere at all. Most of Mars atmosphere is gone, too, for the same reason, and also because it doesn't have a magnetosphere big enough to shield the atmosphere by steering away charged particles.
    There is no lao tzu

  9. #8
    radical strawberry
    Join Date
    Jan 2014
    Location
    Everglades
    Faith
    Taoist
    Posts
    2,183
    Amen (Given)
    307
    Amen (Received)
    709
    Quote Originally Posted by Sparko View Post
    I guess I am still wondering why the sun ended up with all that hydrogen instead of just collecting all the heavy elements and not leaving any for planets.
    Hitting this separately, it seems to me we need to remember all of these atoms forming the solar system were originally swirling around the center of mass. Most of the swirling was slow enough to allow what was about to become the sun to capture them in the center.

    But some of it, maybe one percent, had enough angular momentum to resist the pull. That's what condensed into the planets and asteroids, almost certainly with big hydrogen and helium atmospheres, too, until the solar wind took care of that.
    There is no lao tzu

  10. #9
    tWebber Roy's Avatar
    Join Date
    Jan 2014
    Faith
    Atheist
    Gender
    Male
    Posts
    3,218
    Amen (Given)
    328
    Amen (Received)
    945
    Quote Originally Posted by Sparko View Post
    Jupiter and the outer planets being hydrogen/helium actually fits with what I was asking, if the heavier elements would condense in the center of the solar system, the lighter elements would stay at the edges. I guess I am still wondering why the sun ended up with all that hydrogen instead of just collecting all the heavy elements and not leaving any for planets.

    but it does bring up another question, why do the gas giants have all rocky moons? Again, seems like the heavy stuff would collect in the middle and the less dense would be in the periphery, yet the lighter stuff (hydrogen) collected into Jupiter and the denser stuff became its moons.
    The simple answer is that the sun, planets and moons all started off with roughly the same ratio of elements, but the smaller planets and moons don't have enough mass to retain hydrogen and helium so consist only of the heavier elements.

    More complex answers take into account solar wind, ice formation, etc.

    I don't know offhand what % of solar system iron is in the sun, but I suspect it's more than 95%.
    JohnMartin: "My assertions are fact. They are so fact that even when you deny them, you assert them by implication as shown above.
    Hansgeorg: "3 is not a number"
    37818: "What makes you think you are self aware?"
    granpa: "we are sons of noah even though noah lived long before the first hominids "

  11. Amen Sparko amen'd this post.
  12. #10
    Troll Magnet Sparko's Avatar
    Join Date
    Jan 2014
    Faith
    Christian
    Gender
    Male
    Posts
    30,491
    Amen (Given)
    2565
    Amen (Received)
    15107
    Thanks.

    OK something else I thought of while watching shows about finding exoplanets...

    They detect them by measuring the light dip as a planet passes the star, right?

    So the only planets we can see would be those whose ecliptic lines up with our line of sight, right? If the solar system's ecliptic were 90 degrees from our line of sight (we would be looking at the north or south pole of the star) we would not be able to see if it has planets or not, right?

    secondary question, does the ecliptic of all of the stars in the galaxy pretty much line up with ours (maybe because of the galaxy's rotation) or do they vary all over the place?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •