Tsvi Piran

Tsvi Piran

Tsvi Piran
Born (1949-05-06) May 6, 1949
Tel Aviv, Israel
Fields Theoretical Physics and Astrophysics
Institutions The Hebrew University of Jerusalem
Alma mater The Hebrew University of Jerusalem
Doctoral advisor Jacob Shaham and Joseph Katz
Notable students Amos Ori, Eli Waxman, Ehud Cohen, Re'em Sari, Shai Ayal, Ehud Nakar, Jonathan Granot

Tsvi Piran (born May 6, 1949 in Tel Aviv, Israel) is an Israeli theoretical physicist and astrophysicist, best known for his work on Gamma-ray Bursts (GRBs) and on numerical relativity.

At a time when most astronomers believed that GRBs were galactic (see however an earlier suggestion by Bohdan Paczynski [1]) with Eichler, Livio and Schramm, Piran proposed that GRBs originate from cosmological neutron star binary mergers,[2] a model that is generally accepted today. During the early nineties when the cosmological vs. galactic debate took place, Piran was one of the strongest and most vocal proponents of cosmological origin,[3] which was confirmed in 1997 with the discovery of cosmological redshifts from GRB's afterglow. Even before the cosmological origin of GRBs was discovered Piran laid the foundation to the generally accepted cosmic fireball model.[4] He suggested that GRBs herald the formation of a newborn black hole.[5][6] Later on, together with Re'em Sari and other collaborators, Piran further developed the theory of GRB afterglows,[7] in a paper which has by now more than 1000 citations, and of GRB jets.[8] His review papers[9][10] are the standard literature on this subject.

Before working on GRBs, Piran made important contributions to numerical relativity, the numerical solution of Einstein's equations. In 1985 he wrote the first numerical code calculating the collapse and formation of a rotating black hole[11] and the resulting gravitational radiation waveform. This waveform shows relaxation towards the quasinormal modes of the black hole that forms. Detection of this waveform in the future by advanced gravitational radiation detectors might provide the ultimate proof of the existence of a black hole.

In addition to these works, Piran's contributions range over a selection of problems in Relativistic Astrophysics. He demonstrated the critical dependence of the stability of accretion disks on the cooling and heating mechanisms. Piran was the first to point out that inflation is a generic phenomenon involving any scalar field (without requiring a specific potential)[12] and, in particular, that this is so for a free massive scalar field. He went on later to show that, in fact, the onset of inflation is not fully generic and it requires specific initial conditions,[13] a concept whose full implications have not been addressed up to now. He was the first to suggest and show that cosmic biasing depends on galaxy types and that different galaxies are distributed differently in the Universe. This is a concept that seems obvious today but was controversial when proposed in the late eighties.[14] Piran's work includes also contributions to the general theory of relativity such as one of the strongest counter examples to the cosmic censorship hypothesis[15] and the demonstration of the instability of the inner structure of a black hole.[16]

In addition to Piran's work as an astrophysicist, he has served from 2005 until 2009 as the dean of the Hebrew University School of Business Administration. During this term he has made revisions in the school.

Chronology

Honors

Landau Prize for a distinguished PhD thesis - 1976

Distinguished Moore Fellowship Caltech - 2005

ERC Advanced Research Grant - 2009

References

  1. ↑ Paczynski, Bohdan (1986). "Gamma-ray bursters at cosmological distances". Astrophysical Journal Letters 305: L43–L46. Bibcode:1996ApJ...365L..55S. doi:10.1086/18740.
  2. ↑ Eichler, D.; Livio, M.; Piran, T. & Schramm, D. (1988). "Nucleosynthesis, neutrino bursts and gamma-rays from coalescing neutron stars". Nature 340: 126–128. Bibcode:1989Natur.340..126E. doi:10.1038/340126a0.
  3. ↑ Piran, T. (1995). Bahcall, J.; Ostriker J., eds. "Towards Understanding Gamma-Ray Bursts". Nature 340: 126–128. Bibcode:1989Natur.340..126E. doi:10.1038/340126a0.
  4. ↑ Shemi, Amotz; Piran, Tsvi (1990). "The appearance of cosmic fireballs". Astrophysical Journal Letters 365: 55–88. Bibcode:1990ApJ...365L..55S. doi:10.1086/185887.
  5. ↑ Piran, T. (1994). Gerald J. Fishman, ed. "Fireballs". in Proceedings of the 2nd Workshop held in Huntsville, Alabama, October 1993, New York: American Institute of Physics (AIP), AIP Conference Proceedings 307: 495. Bibcode:1994AIPC..307..495P.
  6. ↑ NYT article 1999
  7. ↑ Sari, Re'em; Piran, Tsvi; Narayan, Ramesh (1998). "Spectra and Light Curves of Gamma-Ray Burst Afterglows". Astrophysical Journal Letters 497: 17–20. arXiv:astro-ph/9712005. Bibcode:1998ApJ...497L..17S. doi:10.1086/311269.
  8. ↑ Sari, Re'em; Piran, Tsvi; Halpern, J. P. (1999). "Nucleosynthesis, neutrino bursts and gamma-rays from coalescing neutron stars". Astrophysical Journal Letters 519: 17–20. arXiv:astro-ph/9903339. Bibcode:1999ApJ...308L..17S. doi:10.1086/312109.
  9. ↑ Piran, Tsvi (1999). "Gamma-ray bursts and the fireball model". Physics Reports 314: 575–667. arXiv:astro-ph/9810256. Bibcode:1999PhR...314..575P. doi:10.1016/S0370-1573(98)00127-6.
  10. ↑ Piran, Tsvi (1999). "The physics of gamma-ray bursts". Reviews of Modern Physics 76: 1143–1210. arXiv:astro-ph/0405503. Bibcode:2004RvMP...76.1143P. doi:10.1103/RevModPhys.76.1143.
  11. ↑ Stark, R. F. & Piran, T. (1985). "Gravitational-wave emission from rotating gravitational collapse". Physical Review Letters 55: 891–894. Bibcode:1985PhRvL..55..891S. doi:10.1103/PhysRevLett.55.891.
  12. ↑ Piran, Tsvi & Williams, Ruth M. (1985). "Inflation in universes with a massive scalar field". Physics Letters B 163: 331–335. Bibcode:1985PhLB..163..331P. doi:10.1016/0370-2693(85)90291-6.
  13. ↑ Goldwirth, Dalia S. & Piran, Tsvi (1992). "Initial conditions for inflation". Physics Reports 214: 223–292. Bibcode:1992PhR...214..223G. doi:10.1016/0370-1573(92)90073-9.
  14. ↑ Lahav, Ofer; Nemiroff; Robert J. & Piran, Tsvi (1990). "Relative bias parameters from angular correlations of optical and IRAS galaxies". Astrophysical Journal 350: 119–124. Bibcode:1990ApJ...350..119L. doi:10.1086/168366.
  15. ↑ Ori, Amos & Piran, Tsvi (1990). "Naked singularities and other features of self-similar general-relativistic gravitational collapse". Physical Review D 42: 1068–1090. Bibcode:1990PhRvD..42.1068O. doi:10.1103/PhysRevD.42.1068.
  16. ↑ Hod, Shahar & Piran, Tsvi (1998). "Mass Inflation in Dynamical Gravitational Collapse of a Charged Scalar Field". Physical Review Letters 81: 1554–1557. arXiv:gr-qc/9803004. Bibcode:1998PhRvL..81.1554H. doi:10.1103/PhysRevLett.81.1554.
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