WELCOME

I am an associate professor of physics at the Open University of Israel and the head of ARCO. I work on a variety of theoretical topics in high energy astrophysics, a field of astrophysics dealing with some of the most extreme environments in nature, in which particles can be accelerated to within a fraction of the speed of light and the magnetic fields may be a hundred trillion times greater than those on Earth. In particular, my research focuses on Gamma ray bursts, fast radio bursts, magnetars, binary neutron stars, tidal disruption events and formation channels of heavy elements in the Universe.

MY MAIN RESEARCH INTERESTS

Gamma Ray Bursts

Gamma Ray Bursts (GRBs) are extremely bright and rapid explosions associated with the collapse of massive stars or with compact star mergers. An ultra-relativistic jet forms at the center of the explosion and due to internal dissipation emits gamma rays that are known as the “prompt" phase of the GRB. As the jet collides with the external environment, a smoother, longer-lived “afterglow" emission is produced. Although studied for almost 50 years, some major questions about GRBs remain unsolved. The recent discovery of a GRB counterpart to the gravitational wave signal observed from a binary neutron star merger was a spectacular milestone that has already helped address many of the open questions. Many other open questions will be similarly answered in the next few years, when more GRBs are detected as gravitational wave counterparts. I study many different aspects of GRBs, including radiation and dissipation mechanisms in the prompt and afterglow stages of GRBs, the central engines driving the explosions and the nature of the jets that they produce.

Fast Radio Bursts

Fast radio bursts are millisecond long radio pulses with a rate as high as 10,000 bursts per sky per day. These mysterious bursts have been discovered as recently as 2007. The understanding of this phenomena has been dramatically evolving in the last few years, and many surprising discoveries make this an incredibly dynamic and exciting research topic. The most recent of these discoveries include the recent detection of an FRB from a magnetar in own Galaxy and the discovery of periodicity in the signal of some FRBs. Understanding the conditions that lead to the formation of FRBs, their emission mechanism and the source of their potential repeatability and periodicity are among the driving theoretical questions of the moment.

Magnetars

Magnetars are neutron stars with the strongest magnetic fields in the Universe. They probe extreme physical conditions, such as strong field gravity, huge (nuclear) densities and extreme energy densities. The evolution and decay of their ultra-strong magnetic field powers a variety of X-ray bursting activity, ranging from relatively frequent short bursts to very rare and much more energetic giant flares. This makes magnetars relatively short lived objects, and is the reason why only a few dozen are known to exist in the Galaxy, despite the fact that a large fraction of neutron stars are thought to begin their lives in this state.
While typical Galactic magnetars spin around their axis once every several seconds, they might be born spinning as fast as a thousand times a second. Such newly born magnetars have been suggested as the fire-houses powering various astrophysical transients, and their are ongoing inquiries regarding the validity of these associations.
At the other extreme, recent discoveries of extremely long period Galactic objects hint at the existence of a large, and previously unknown population of ultra-long period magnetars whose periods could be hours long or more. This corroborates earlier suggestions based on FRB periodicities.

Compact binary systems

Binary neutron star systems are typically the result of two stellar collapses (i.e. supernovae). The fact that the two stars remain bound to one another after two such collapses strongly constrains the latter. As a result, the velocities of those systems, the amount of mass ejected by the collapsing star leading to the formation of the second neutron star in the system and the delay time between the formation of the binary neutron star and its eventual merger due to orbital energy losses by gravitational wave radiation, are all strongly constrained. These shed new light on the stellar evolution histories of those systems, the types of supernovae that are associated with their formation and exciting potential sources of gravitational wave radiation.

r-process nucleosynthesis

About half of the elements in the universe heavier than iron are created via the rapid neutron capture process (the r-process). Over the recent years our understanding of the formation sites of these elements has rapidly evolved with exciting observations such as the discovery of an r-process powered electromagnetic counterpart of a binary neutron star merger detected through gravitational waves and the observation of r-process enhanced stars in some of the smallest satellite galaxies of the Milky Way. Binary neutron star mergers have emerged as a leading site for the origin of r-process elements, although many uncertainties and mysteries remain, such as the role of turbulent mixing and the observed decline in deposition of r-process elements in the later stages of the Milky way's evolution. The next few years promise to bring big changes to our understanding of r-process formation in the Universe.