Identification of runaway stars and neutron stars from supernovae and dynamical ejection

• Applicant: Professor Dr. Ralph Neuhäuser
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437190647

Runaway stars are ejected from multiple stars or clusters by gravitational interaction or by a supernova (SN): former companions of core-collapse SN progenitors run away with their previous orbital velocity; if a neutron star is formed, it can obtain a high SN kick velocity. With highly precise Gaia data, we can now trace back the motion of runaway stars in 3D.Also, for neutron stars, often not only the 3D position is known, but also the proper motion (the radial velocity is often unknown for neutron stars, but can be drawn from the most likely 3D velocity distribution in a Monte Carlo simulation). Hence, we can trace back all runaway star to find systems which got ejected by dynamical ejection, and we can also trace back all neutron stars, to find pairs of runaways and pulsars, which were at the same time at the same place, i.e. that were ejected by a SN in a binary. Currently, some 400 neutron stars are known with position, proper motion, and distance. The main goals of this project are: (a) Compilation of a catalog of runaway stars from Gaia data and an investigation of the frequency of runaway stars around young clusters: Which percentage of runaway stars (or mass) get ejected? What is the mass and velocity distribution of the ejected stars ? (b) Search for runaway star-neutron star pairs indicating binary SN ejection. We can then estimate the progenitor mass from the lifetime (as difference between flight time and association age) as well as the SN kick velocity. (c) Search for pairs (or higher order multiples) of runaway stars which got ejected dynamically. A comparison of (b) with (c) will then also show how effective these two mechanisms areto produce runaway stars. With the newly available Gaia data, we can expect a large step forward in the understanding of the origin of runaway stars, SNe in binaries, and their dynamics.

• DFG Programme: Research Grants