So, I have a naive question that maybe astro @physicists could help with. The article says the heavy metals are ejected and the star collapses. I’m a little uncertain about how that happens as ejection and gravitational collapse seem opposite.
Perhaps like dust being thrown up in air as a building falls?
That’s what I was assuming but the Wikipedia article on collapsars made me wonder. I would think it would be the heavy elements that would be sucked back in, yet they spread throughout the universe (at least enough for planets to get sizable amounts).
These are atomic nuclei traveling a significant faction of the speed of light. Those particles moving outward have a velocity exceeding the escape velocity of the remaining mass of the exploding star so they may be slowed but not turned toward the star. In fact, as they get further from the star their velocity will increase.
How does that work?
Velocity of particle = F/m minus gravity of star.
As the particle gets further away from star, star gravity decreases resulting in increasing velocity of particle. Newtonian physics works pretty well
You’ve read about Hawking Radiation, yes? And there isn’t even an explosion that generates the outflow of radiation.
So imagine how much more output there is with a gigantic explosion as well?!?!?
So are the heavy metals ejected during the supernova or after the black hole has formed? I guess that’s what my question was.
Think of me as a young child conditioned by the experience of archery with an older cousin who tried to convince me an arrow accelerated after escaping the encumbrance of the bowstring.
But F=ma, no? (according to Newton)
Yes, and F/m = a So the force of the explosion on the particle of mass m accelerates the particle outward against the force of gravity pulling it back in. So these particles that escape have a increasing velocity as they get further away from the star. Yes, Newtonian Physics works pretty well.
That doesn’t make sense. It seems to me they would start out close to the speed of light from the initial kinetic energy applied to them (and thus travel fast enough to be beyond escape velocity), but be continuously decelerated by the gravitational field. As they get further and further away, the gravitational field becomes weaker and thus the rate of deceleration goes down. But since no external force is applied to them, they don’t gain more kinetic energy. So they don’t accelerate.
I don’t see how they could accelerate without having an external force applied to them. So they’d experience a decreasing rate of deceleration, not accelerate.
Listen to Rumraket, Patrick 
@Jordan, there are two major ways that stuff is ejected during a gravitational collapse of massive stars such as the one described in the article.
The first way is through an explosion: as the star collapses, its density and temperature increases, which increases the reaction rate of nuclear fusion. This can lead to an explosion, called a supernova, that spews materials out.
The second way is: as the star collapses, its core forms a black hole. The outer layers of the star, still outside of the newly-formed black hole, then falls into the black hole. If the newly formed black hole is rotating, the infalling matter forms a hot disk of material, called an accretion disk. Through interactions with magnetic fields, an accretion disk such as this one launches a jet from its center, like this picture from wikipedia. This is the same mechanism that powers quasars at the center of galaxies. For a collapsing star, this phase is very brief, but these jets can launch a respectable amount of material away from the star.
The Hawking Radiation is a different, unrelated mechanism to the ones that eject heavy metals as a star collapses.
This is not true, even in Newtonian physics. @AlanFox and @Rumraket are correct. This is a basic conservation of energy problem:
where r_{far} and r_{close} are two different distances away from the star, with r_{far} > r_{close}. In Newtonian physics, this equation becomes
where v_{far} is the velocity of the particle at r_{far} and v_{close} is the velocity of the particle at r_{close}. This gives,
As r_{far} > r_{close}, then 1/r_{far} < 1/r_{close}. This means that
which gives
the velocity far from the star is less than the velocity close to the star; the ejected particle is decelerating.
good job. Thanks.
I don’t understand why this research is regarded as new. Certainly, the standard view has been most of the quantities of “heavier-than-iron” elements come from the merger of neutron stars or the collapse of a neutron star into a black hole. However, from Wikipedia:
“Supernova nucleosynthesis is also thought to be responsible for the creation of rarer elements heavier than iron and nickel, in the last few seconds of a type II supernova event. The synthesis of these heavier elements absorbs energy (endothermic process) as they are created, from the energy produced during the supernova explosion. Some of those elements are created from the absorption of multiple neutrons (the r-process) in the period of a few seconds during the explosion. The elements formed in supernovas include the heaviest elements known, such as the long-lived elements uranium and thorium.”
Perhaps the research provides better insight into the nucleosynthetic pathways involved.
@tim.anderson, the novelty of this research is that it predicts a large amount of heavy elements to come from collapsars. While collapsars are already thought to contribute to heavy element productions in the Universe, previous to this research we thought that the vast majority of heavy elements are produced by neutron star collisions. This research shows that in principle collapsars can account for most of the heavy element production in the Universe.