Numerical Simulations of
A Jet in a Star

The movies below present the results of relativistic hydrodynamic simulations.
Credit: Ore Gottlieb, Ehud Nakar

A jet that successfully breaks out from a star

The jet is launched into the stellar envelope following the collapse of the stellar core. The jet propagation inflates a hot pressurized bubble, known as "the cocoon". The jet-cocoon structure breaks out from the star. The cocoon spreads sideways while the jet remains narrowly collimated. The jet produces a luminous gamma-ray burst that can be seen only by an observer within the opening angle of the jet. The cocoon releases a wider and fainter gamma-ray flare upon breakout, followed by a cooling emission in X-ray, UV and optical bands. After breaking out, the cocoon spreads sideways and the supernova emission must go through the cocoon material on its way to the observer. As a result, broad absorption features can be seen in the supernova spectrum during the first several days.

Mass density colormap of a 3D simulation. Units are arbitrary and colorbar scale is logarithmic.

A choked jet with a cocoon breakout

The jet launching is terminated while the jet is still inside the star, and the jet is choked, depositing all its energy into the cocoon. The cocoon keeps propagating in the star until it breaks out. Since the jet is chocked, there is no luminous gamma-ray burst. Similarly to the successful jet, the cocoon radiates a faint flare of soft gamma rays upon breakout, followed by X-ray, UV and optical emission. After breaking out the cocoon spreads sideways in a similar way to the case where the jet is successful. The supernova emission must go through the cocoon material on its way to the observer, and broad absorption features can be seen in the supernova spectrum during the first several days. By detecting the signature of the cocoon, we can learn on the hidden jet that was launched following the core collapse. We can place constraints on the jet properties such as its energy and opening angle.

Mass density colormap of a 2D simulation. Units are arbitrary and colorbar scale is logarithmic.

For more videos of jets in various cosmic explosions,
including the double NS merger GW170817
click here

The simulations have been conducted with the public code PLUTO (Mignone et al. 2007)