Tsvi Piran

Tsvi Piran (Hebrew: צבי פיראן; born May 6, 1949) is an Israeli theoretical physicist and astrophysicist, best known for his work on Gamma-ray Bursts (GRBs) and on numerical relativity. The recipient of the 2019 EMET prize award in Physics and Space Research. At a time when most astronomers believed that GRBs were galactic (see however an earlier suggestion by Bohdan Paczynski ) with Eichler, Livio and Schramm, Piran proposed that GRBs originate from cosmological neutron star binary mergers, a model that is generally accepted today. During the early nineties when the cosmological vs. galactic debate took place, Piran was a prominent proponent of a cosmological origin, which was confirmed in 1997 with the discovery of cosmological redshifts from GRB's afterglow. Before the cosmological origin of GRBs was confirmed, Piran co-developed the cosmic fireball model. He suggested that GRBs indicate the formation of a black hole. Later on, together with Re'em Sari and other collaborators, Piran further developed the theory of GRB afterglows, and of GRB jets. Before working on GRBs, Piran worked on 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 and the resulting gravitational radiation waveform. This waveform shows relaxation towards the quasinormal modes of the black hole that forms. Detection of this waveform by advanced gravitational radiation detectors may provide evidence for 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) and, in particular, that this is so...