Musings on Przbylski's Star and Gamma Ray Bursts

[The Admiral]

Sorry, this should have gone in the physics and space science category. Would a mod move it please?

In a recent thread a question was posed about about the origins of the relatively short-lived transuranic elements found in Przbylski's (apparently pronounced 'sha-bil-ski') Star. Being short lived, they must be being continuously generated within the star. But how? In the article in 'Astronomy Now', the production of such elements was considered by Vladimir Dzuba as possibly being due to the decay of super-massive elements with masses way beyond what we can currently manufacture on earth.

On earth, of course, these transuranic elements are produced as a by-product of a process of nuclear fission in a nuclear reactor. The fission process gives rise to a large neutron density within which the transuranic elements can build from the uranium fuel. Such a process can also occur naturally; there is evidence that some 2bn years ago, within the uranium-rich deposits in the Gabon, the same process took place for a million years or so! This fission chain reaction can also take place in a rather uncontrolled way, such as in nuclear weapons. Such 'critical events' occur over very short timescales and there is the potential for large amount of energy to be released over short periods of time.

Musing on this, at this point I started to take leave of my senses and to speculate somewhat wildly . Apparently, one of the features of this star is that the star's associated magnetic field traps the various elemental species in layers in the star's atmosphere. I began to wonder whether it would be possible for a shell of fissile material to build, and for this to undergo a fission chain reaction. This could be a fairly sedate and continuous process, a bit like the nuclear reactor situation, building up the transuranics that we believe we can detect. On the other hand, I wonder if the fissile material could build to the point where a spontaneous chain reaction can take place, spreading throughout the shell and around the star in a flash. A nuclear explosion, if you will, engulfing the whole of the star's surface! That would yield a vast amount of energy over a short time, and, in turn, could also build the transuranics. Perhaps the cycle repeats itself every so often, to keep the short-lived transuranics in place. So the star is undergoing both fusion in its core, and fission in its outer layers.

And then another wild thought crossed my mind. One of the features of such brief 'criticality' events is the production of a spike of gamma radiation. So, extrapolating to the stellar situation, I began to muse on whether the rapid chain reaction could be the origin of gamma-ray bursts! It would be interesting to know if spectra have been acquired from such bursts, and how they might compare with what would be got from a nuclear criticality event.

Well, there's no harm in letting the imagination run wild! It also helps not being too well versed in stellar evolutionary processes . Mind you, Przbylski's Star is a bit of an enigma, so perhaps that's not important anyway.

Ian

 

[ronin]

Fission tends to be the breaking down of a heavy element to a light one. To go "up" after iron takes energy.

GRB's now seem associated with Neutron Star - Neutron Star merging a "dise product of this merging is that there are large quantities of neutrons thrown off at high energy and that these can collide and "stick" (Neutron capture) with other atoms and so increase them in mass. Charge alters by Beta radiation of Neutron -> Proton decay.

So after a neutron capture the mass is uip by 1 and the charge is 1 higher owing to the Beta decay. Prof Nial Tanvir of Leicester has an excellent talk about this. Easy to follow so if you able to get to the talk (Gravitational waves from NS-NS Mergers, or similar) take the opportunity to get along.

There may be many tons of fissionable material, that is only partially relevant, it needs to be concentrated enough in order to do anything, and if it did then it goes bang and spreads the remaining stuff out so reducing further pops going off. There are many tons of Uranium on Earthbuit it is spread out and so has little effect except I guess to background radiation.

The recent NS-NS merger deteted by Ligo coincided with a GRB and the spectra obtained from it analysed.

How do they measure the magnetic fields of a star quite a few light years away accurate enough to determine exactly what it's structure is?

[The Admiral]

Indeed fission is the breaking apart of the fissile nucleus, but what happens is that in the high neutron flux some fissile nuclei can acquire neutrons and through a series of interactions and decays, the actinides can be built up. For example, Plutonium-239 is created when U-238 acquires a neutron to become U-239, which then decays to Np-239, which then decays to Pu-239. I think that the presence of elements with a mass greater than iron is a reflection of the material which formed the star, created from other stellar evolution processes. My point about there being fissile material on earth is that it is present in sufficient quantities, and will also be present in other stellar bodies too. The concentration of fissile elements in Przbylski's Star will have come about by the magnetic separation that apparently happens in this type of star, and crucial to my postulation is that this is the very process by which sufficient fissile material could be confined to give rise to a chain reaction.

It always amazes me how so much information about other bodies can be garnered so remotely!

Ian

[Dave In Vermont]

Well, we have high-end spectroscopes for analysis of stellar elements from starlight. So perhaps a tunable scintillation-counter/meter would be of interest?

Hmmm..... Curses, Ian - now you've gotten me doing it, too!

Oh my neurons!

Dave