Earlier model of Froggatt and Neilson proposed that dark matter should consist of cm-large white dwarf-like objects kept together by a skin separating two different sorts of vacua. Now in their recent paper, they proposed that these dark matter balls or pearls would collect in the middle of any star throughout it’s lifetime. At some stage during the development of a supernova the balls will begin to take in neutrons and then other surrounding material. By passing into a ball nucleons fall through a potential of order 10 MeV, causing a severe production of heat – of order 10 foe for a solar mass of material eaten by the balls. The temperature in the iron core will thereby be raised, splitting up the iron into smaller nuclei. This provides a mechanism for reviving the shock wave when it arrives and making the supernova explosion really occur.
A supernova explosion is supposed to originate from in-falling material of the progenitor star being reflected after having been stopped by the nuclear forces, when a neutron star is first formed and compressed to about double nuclear matter density. The re-expansion of the compressed neutron star in the center would then cause a shock wave to propagate outward. This shock wave is expected to cause what is seen as the supernova explosion. However, more detailed calculations suggest that, at least unless one includes convective or non-symmetric development, the shock wave tends to stall before reaching out far enough to expel the stellar envelope and provide sufficient energy for the observed magnitude of supernova explosions.
This conclusion that an insufficient amount of energy is deposited into the material expelled from the core remains true, even when the effect of a flux of neutrinos from the center is included in the calculations. Heating from these neutrinos does though not revive the shock wave sufficiently to provide the energy of 1 foe ≡ 10^51 ergs needed by the observed stellar remnants and radiation. It is not that there is insufficient energy available in the collapse, because the gravitational collapse to the neutron star easily releases 100 foe. Nevertheless the simulations show that the shock wave emitted runs out of force and cannot even provide the one foe needed.
It is still hoped that more detailed two dimensional or three dimensional simulations including convection could explain how, at least in some direction, enough energy would be brought to revive the shock wave so as to provide the observed explosion. Alternatively some extra source of energy providing this “revival” could help.
It is indeed such an extra energy source, which Froggatt and Nielsen proposed in this present work.
Froggatt and Neilson have previously speculated that dark matter consists of pearl-sized balls containing a different type of vacuum – one with a condensate of bound states of 6 top + 6 anti-top quarks – and very strongly compressed ordinary matter. They have here proposed that these dark matter balls can become active and suck in ordinary matter, if they become surrounded by material with a sufficient amount of free neutrons. The activity of these pearl-sized balls in a supernova consists in first of all taking in the free neutrons and thereby expanding themselves to a bigger and bigger size. Since the potential for nucleons in the vacuum inside the pearls is supposed to be 10 MeV lower for nucleons than outside, this expansion of the pearls liberates 10 MeV energy for each nucleon absorbed. The fast absorption of neutrons makes the expansion explosive and produces a large amount of energy in the region up to, say, 500 km from the center. This explosion is supposed to stop or rather postpone the usual Kelvin-Helmholtz gravitational collapse of the supernova, which begins at the end of the era of silicon burning to the iron peak elements. Before it is halted the Kelvin-Helmholtz collapse already begins to produce a bunch of neutrinos which, in the case of supernova SN1987A, was observed as the “first bunch” of neutrinos by the Mont Blanc experiment.
Then the interior of the star, heated by the explosion of the dark matter pearls, cools down by neutrino emission until the gravitational collapse can restart and generate a second bunch of neutrinos. “We estimated that this would happen a period of order 14 hours after the interruption of the first collapse. “, said Froggatt.
Support for their model is provided by the fact that, in the supernova SN1987A, there seemingly were indeed two bunches of strong neutrino bursts – each of a length of the order of 10 s. Furthermore there was an interval of 4 hours 43 minutes between the two neutrino bursts, which is perfectly consistent with their crude order of magnitude estimate of 14 hours for this delay time. A further important achievement of their model is the provision of an extra source of energy by the expansion of our dark matter pearls, which is well suited to revive the shock wave expelled by a newly formed neutron star. This extra energy is also able to deliver the observed 1 foe of energy needed by the stellar remnants to escape.
The dark matter pearls start out from cm-size with a density of order 10¹¹ g/cm³. However, they found that in the presence of a supply of free neutrons, the pearls rapidly expand until the (neutron) density in the surrounding material becomes sufficiently low.
“As the balls get larger the electric field surrounding the balls gets weaker – although more extended – which allows the balls more easily to glue together, finally forming one big ball surrounding the neutron star.”, said Neilsen.
Featured image: Artist impression of dark matter balls © gettyimages
Reference: C. D. Froggatt and H. B. Nielsen, “Dark matter balls help supernovae to explode”, Modern Physics Letters A, Vol. 30, No. 36, 1550195 (2015). https://www.worldscientific.com/doi/abs/10.1142/S0217732315501953 https://doi.org/10.1142/S0217732315501953
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