Welcome

• Sean Tulin (York University)
• Laura Sagunski (Goethe University)

Invited talk on "Neutron Stars: Astrophysical Probes of Extreme Matter"

• Debarati Chatterjee (IUCAA, Pune, India & Chair LIGO-India EPO)

Chair: Laura Sagunski Neutron stars are among the most fascinating and intriguing objects in the Universe. These compact objects contain matter in the densest and coldest form, possess ultrastrong magnetic fields and display ultrahigh velocities. These astrophysical laboratories effectively allow us to investigate properties of matter under the most extreme conditions, far beyond the reach of terrestrial experiments. While multi-wavelength astronomical observations provide us a wealth of data about them, the recent detection of gravitational waves emitted by neutron stars is allowing us for the first time to probe their interior composition directly. Together, these tools of multi-messenger astronomy of neutron stars have opened up a window to an unforeseen Universe.

Discussion round with the speaker

• Debarati Chatterjee (Pune University)

EXPLORE project: "Probing Dark Matter with Gravitational Waves " (Dark Matter Team)

• Majd Noel (York University)
• Romina Ghasemidzadeh (Goethe University)
• Ethar Mansour (Goethe University)
• Johannes Pöplau (Goethe University)

Chair: Edwin Genoud-Prachex Co-Chair: Nassim Borzognia Mentors: Laura Sagunski, Saeed Rastgoo Junior mentors: Adam Smith-Orlik, Niklas Becker On Sep 14, 2015, a dramatic event has taken place. LIGO has detected the first graviational waves of a binary black hole merger and thus started the era of gravitational wave astronomy. Seeing the universe with these new eyes opens up countless possibilties to test our theories and make new detections. One of the most intriguing detections would be dark matter! Massive black holes at the centers of clusters or galaxies are surrounded by gigantic dark matter halos. Near these black holes, the dark matter density can be extremely high and form a so-called dark matter density spike. Due to its extremely high density, the dark matter density spike creates a violent environment around the black hole. If the black hole then merges with a smaller companion object, the presence of the dark matter density spike will drastically affect the binary merger dynamics. In particular, it will leave an imprint on the emitted gravitational wave signal. If we detect such a signal, we can thus probe the nature of dark matter with gravitational waves! Main tasks: 1. Model the profile of the dark matter density spike around the black hole for different dark matter models (cold dark matter, self-interacting dark matter) in Newtonian gravity and then include relativistic effects. (Dark Matter Group) 2. Model the merger dynamics and the gravitational wave signal including post-Newtonian corrections. (Gravity Group) 3. Compute the gravitational wave signal for different dark matter models, check its detectability with current and future gravitational wave detectors (LIGO, LISA) and constrain the particle nature of dark matter with gravitational waves. (Gravity Group)

Discussion session for EXPLORE students

• Laura Sagunski (Goethe University)
• Nassim Bozorgnia (York University)
• Saeed Rastgoo (York University)
• Sean Tulin (York University)
• Jürgen Schaffner-Bielich (Goethe University)

Chair: Nassim Bozorgnia

Announcements (visit at Goethe University, prize)

• Jürgen Schaffner-Bielich (Goethe University)
• Laura Sagunski (Goethe University)
• Nassim Bozorgnia (York University)
• Saeed Rastgoo (York University)
• Sean Tulin (York University)

EXPLORE project: "Probing Dark Matter with Gravitational Waves " (Gravity Group)

• Nifia Garg (York University)
• Hazkeel Khan (York University)

Chair: Jürgen Schaffner-Bielich Mentors: Saeed Rastgoo, Laura Sagunski Junior mentors: Robin Diedrichs, Niklas Becker On Sep 14, 2015, a dramatic event has taken place. LIGO has detected the first graviational waves of a binary black hole merger and thus started the era of gravitational wave astronomy. Seeing the universe with these new eyes opens up countless possibilties to test our theories and make new detections. One of the most intriguing detections would be dark matter! Massive black holes at the centers of clusters or galaxies are surrounded by gigantic dark matter halos. Near these black holes, the dark matter density can be extremely high and form a so-called dark matter density spike. Due to its extremely high density, the dark matter density spike creates a violent environment around the black hole. If the black hole then merges with a smaller companion object, the presence of the dark matter density spike will drastically affect the binary merger dynamics. In particular, it will leave an imprint on the emitted gravitational wave signal. If we detect such a signal, we can thus probe the nature of dark matter with gravitational waves! Main tasks: 1. Model the profile of the dark matter density spike around the black hole for different dark matter models (cold dark matter, self-interacting dark matter) in Newtonian gravity and then include relativistic effects. (Dark Matter Group) 2. Model the merger dynamics and the gravitational wave signal including post-Newtonian corrections. (Gravity Group) 3. Compute the gravitational wave signal for different dark matter models, check its detectability with current and future gravitational wave detectors (LIGO, LISA) and constrain the particle nature of dark matter with gravitational waves. (Gravity Group)

EXPLORE project: "Dark Stars"

• Subbashivani Ganesa Moorthy (York University)
• Dhyan Thakkar (York University)
• Eyosyas Andarge (York University)
• Joshua Parsons (York University)

Chair: Robin Diedrichs Co-Chair: Saeed Rastgoo Mentors: Jürgen Schaffner-Bielich, Nassim Bozorgnia, Sean Tulin Junior mentors: Daniel Schmitt, Edwin Genoud-Prachex Dark matter structures are known to span from dwarf galaxies to the large scale structure of the cosmic web. But there is an uncharted territory: Do dark matter structures exist on (much) smaller scales? The research goals are divided in • Study of dark star properties • Derive observational constraints on dark stars from tidal streams Dark stars properties are investigated along these lines: • What are the properties of dark matter stars? • Solve the Tolman-Oppenheimer-Volkoff equations and derive mass-radius relations • Calculate the I-Love-Q relations of dark stars and compare to the one of neutron stars Dark stars passing through the stream cause dynamical heating. The gravitational encounters impart random kicks to stream stars. A limit on dark stars using observed velocity dispersion of GD-1 stream can be derived. The constraint is not just for dark stars, but for any compact dark object as primordial black holes and MACHOs (Massive Compact Halo Objects). The goal is to derive (and publish) new general exclusion limit. Phase 1: Analytic calculation • Compute dynamical heating of streams from compact objects • Point-like objects (black holes), finite objects (dark stars) →Use mass-radius relation Phase 2: Numerical simulation • Simulation of tidal stream + encounters from compact objects • Goal: numerical validation of analytic results Phase 3: Data analysis • Explore Gaia data for calculating GD-1 stream velocity dispersion (reproducing known results)

Social event

• Daniel Schmitt (Goethe University)
• Adam Smith-Orlik (York University)
• Robin Diedrichs (Goethe University)
• Niklas Becker (Goethe University)
• Edwin Genoud-Prachex (Goethe University)