Solid hydrogen at 342 GPa: no evidence for an alkali metal

Abstract

Thus the inferred isotropic energy loss in g-rays is E G ϳ3 ϫ 10 53 erg: This is remarkably coincident with the gravitational binding energy released during the merger of two neutron stars 24 .Even though E G is much greater than E A , the afterglow measurements pose a clear problem to GRB models. At the time the ␥-rays are emitted, the shocked gas is moving with very large Lorentz factor (Γ). The initial Γ is assumed to be 10 2 -10 3 and expected to evolve as t −3/8 . Due to relativistic beaming, only a small portion, solid angle ϳΓ −2 , of the fireball is visible to us. Hence we remain ignorant of the true shape of the fireball. The estimate of E G can be reduced by assuming that the emitting surface is a narrow jet directed towards the observer. However, Γ is smaller during the optical afterglow emission than during the ␥-ray emission. Relativistic beaming is less of a limitation, and the full extent of the fireball is gradually revealed to the observer. The monotonic power-law decay at optical wavelengths seen in the OTs of previous transients 13-15 is not consistent with the narrow jet-like emitting surfaces. We recognize that more complicated models (in which energy is injected non-spherically) could account for such monotonic decays whilst having nonspherical geometry. However, the main issue that we discuss here is the inferred energetics. It is by no means clear that the energy requirements inferred from afterglow observations (when the Lorentz factor is small) is any lower than the simplest case considered here.According to the models discussed here, the afterglow emission is supposed to arise from non-radiative shocks; that is, the efficiency of the shock in converting E 0 (the total energy in the GRB event) to afterglow radiation is low. Thus, E 0 is significantly larger than the E A reported above. This finding is in direct contrast to the assumptions made by most practitioners in this field, namely E 0 ¼ 10 51 erg. As an aside we note that equation (1) predicts that the break frequency should evolve with time as t −3/2 . Measurement of the break frequency at successive epochs for future bursts offers the possibility of directly confirming or refuting the non-radiative shock assumption.The evidence presented here favours GRB models which produce energy vastly in excess of 10 51 erg; see for example, refs 24, 25, 29. The afterglow emission is similar in nature to the emission from supernovae but is more energetic by two orders of magnitude. Following the naming sequence, nova and supernova, it is only appropriate to refer to GRB afterglow as hypernova 29 .Ⅺ

The ruby pressure standard to 150GPa

“…A striking example of the need comes from studies of hydrogen at high pressures. Narayana et al 11 studied hydrogen in a DAC to 342 GPa and observed that the sample remained transparent to this pressure ͑the only measurement made on the sample was this visual one͒. Later, Loubeyre et al 12 studied hydrogen and observed it to become black at a lower pressure, 320 GPa.…”

Superconducting high-pressure phase of platinum hydride from first principles

“…1,2 However, hydrogen remained an insulator even up to the pressure of 342 GPa. 3 Recently, it was suggested that hydrogen-rich group IV hydrides can be metalized at much lower pressures because of the "chemical precompression" caused by the group IV atoms. [4][5][6][7][8][9][10][11] Therefore, much theoretical and experimental effort has focused on the possibility of attaining high-temperature superconductivity in group IV hydrides.…”

Selected results and open problems in a semiclassical theory of dense matter

“…Static experiments performed at values of pressure P ≤ 342 GPa have not shown signs of metallization of hydrogen [12],so the problem seems (at present)to be completely open.The literature on this topic is huge,but for examples of interesting recent papers see [13] and [14].One of these papers , [13],invokes the influence of disorder as a possible reason why metallization was not observed at the theoretically predicted value of the pressure.…”