A new type of supernova is forcing astronomers to rethink the lives of the largest stars
By: Michael Moyer
When summer comes to an end for our sun in about five billion years, it will fade away and become an inactive white dwarf. Larger stars go out in the process of exploding. If their mass is greater than 10 times the mass of our Sun, they collapse with enough force to ignite a supernova, one of the most energetic events in the universe. For decades, astronomers have suspected that there is an even bigger type of stellar explosion: a "pair-instability" type supernova, whose energy is 100 times greater than the energy of a normal supernova. In the last year, two teams of astronomers finally discovered it, drawing at once a new limit to the size that things in our universe can reach.
In all stars there is a balance between gravity and pressure. As light elements such as hydrogen fuse (that is, undergo fusion or nuclear fusion) in the core of a star, the reactions create photons that exert outward pressure and balance the gravitational pull. In larger stars, the pressure in the core is high enough to fuse heavier elements such as oxygen and carbon, a process that produces even more photons. But in stars larger than about 100 solar masses it is not so simple. As the oxygen nuclei begin to fuse with each other, the reaction releases photons so energetic that they spontaneously transform into electron-positron pairs. Without photons there is no outward pressure, and the star begins to collapse.
There are two possibilities for what happens next. The collapse can create even more pressure, igniting enough oxygen to create a burst of energy. This burst is strong enough to blow away the outer layers of the star, but not to create a full-blown supernova. This cycle can repeat itself in pulses, and astronomers call such a situation a "pulsating" pair instability supernova. The pulsations continue until the star loses enough mass to end its life in a normal supernova. A research group led by Robert M. Quimby from the California Institute of Technology (Caltech) announced that it had identified such a supernova and submitted a paper on the subject for publication.
If the star is really big, and here we are talking about more than 130 solar masses, then the collapse happens so fast and accumulates so much persistence that even oxygen fusion cannot stop it. So much energy develops in such a narrow space that eventually this whole array explodes, leaving nothing behind. It is "the real thing, the biggest there is," says Avishi Gal-Yam, an astronomer at the Weizmann Institute of Science in Rehovot, whose group claims in an article recently published in the journal Nature that it is the first to discover a full pair instability supernova (Scientific American belongs to the Nature publishing group) .
Before these findings, most astronomers argued that massive stars in nearby galaxies shed most of their mass before dying, so a pair instability supernova was out of the question. Now those ideas are being rethought, after these biggest explosions proved their existence in eye-popping style.
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Itzik,
The relevant timetable for a super nova is not from the moment the last two hydrogen atoms have fused, and this is because there is no necessity for this to happen in the outer layers of the star - what is relevant is what happens in the core.
In the core of a star that melts into a supernova, the oxygen is melted into helium and it is melted into carbon and oxygen and then into heavier and heavier elements up to iron. The last combustion processes last on average days-hours from the moment they started until the supernova. At a certain point, when the pressure is increasing and the core is already made of iron and very dense (held by the degeneracy pressure of electrons similar to a white dwarf), the event that starts the supernova happens - the electrons and protons are so energetic (due to the degeneracy pressure) that suddenly, they become energetically worthwhile become a neutron.
This process reduces the volume of the core and thus, the core shrinks and becomes denser - that is, it is useful for additional electrons and ferrons to become the opposite of the electron and thus, within a fraction of a second, the entire core of the star turns into a ball of neutrons (neutron star).
The mantle, when nothing is holding it back collapses inward and if it hits the neutron ball it is blown back and creates a shock wave - this is the supernova
Cornelius
After the supernova - if the remaining mass is over 3 solar masses, then a black hole is formed.
Look at the picture 'the life cycle of a star' in the link:
http://he.wikipedia.org/wiki/%D7%A1%D7%95%D7%A4%D7%A8%D7%A0%D7%95%D7%91%D7%94
Wait, something confused me, what about turning the mass into a black hole or a white dwarf? It happens after the supernova, instead?
Thanks Rukh, don't know how I missed it 🙂
And what about my question? Can anyone give a schedule?
Yair
The answer is in the body of the article:
'There are two possibilities for what will happen next. The collapse can create even more pressure, igniting enough oxygen to create a burst of energy. This burst is strong enough to blow away the outer layers of the star, but not to create a full-blown supernova. This cycle can repeat itself in pulses, and astronomers call such a situation a "pulsating" pair instability supernova. The pulsations continue until the star loses enough mass to end its life in a normal supernova.'
When the mass of the star is so great, the star loses a certain mass - up to a certain limit - at which limit the star explodes as a supernova.
I have no formal knowledge of these subjects, but from what I understood, the matter is related to photons. When a star of this magnitude ends its life, at some point in the process photons are created that are so energetic that they spontaneously turn into pairs of electrons and positrons. Without photons there is no outward pressure, and the star begins to collapse.'
That is, a collapse begins to that limit where the star will lose a certain mass that will allow the star to explode as a supernova, and this does not happen all at once. Because if the star loses mass that does not yet reach that certain limit to produce a supernova, the star 'needs' to lose more mass up to that certain limit where a supernova is possible. (At least that's what I understood).
Well, none of the geniuses here have an answer for me?
How long does it take until the explosion in the formation of the super nova? Suppose from the moment the last pair of hydrogen atoms merged?
Yair, no one will answer you here, those who don't volunteer unfounded theories are ignored. Make up some New Age nonsense and you'll get all the explanations you want
I didn't understand something, why after the collapse there was another explosion to the outside? After all, we said that the star's nuclear fuel runs out and then the enormous force of gravity causes the star to collapse in on itself, so why doesn't it remain a small, highly compressed mass of matter? What causes it to explode outwards again?
Thanks in advance.
When more powerful explosions are discovered and it becomes possible to measure them (such as neutron star mergers), they will find that those stars create holes in space in the form of black holes. 🙂