SpaceTime

Image: Artist's concept of a "hot Jupiter" - Credit: NASA/JPL-Caltech Gas giants orbiting their host star within the ice line are thought to have migrated to their current locations from farther out. In a recent paper (Antonini et al 2016) the authors consider the origin and dynamical evolution of observed Jupiters, focusing on hot and warm Jupiters with outer friends. They show that the majority of the observed Jupiter pairs (twenty out of twenty-four) will be dynamically unstable if the inner planet was placed at >~1AU distance from the stellar host. This finding is at odds with formation theories that invoke the migration of such planets from semi-major axes >~1AU due to secular dynamical processes (e.g., secular chaos, Lidov-Kozai oscillations) coupled with tidal dissipation. In fact, the results of N-body integrations show that the evolution of dynamically unstable systems does not lead to tidal migration but rather to planet ejections and collisions wi...

Image: Quasar Pair Captured in Galaxy Collision. Credits: X-ray: NASA/CXC/SAO/P. Green et al. Optical: Carnegie Obs./Magellan/W. Baade Telescope/J.S. Mulchaey et al. Strong observational evidence suggests that every massive galaxy hosts a supermassive black hole in its nucleus. The central black hole (BH) is an important component of the galaxy, since the BH mass is correlated with the global properties of the host galaxy, e.g., dispersion velocity, bulge luminosity, or bulge mass.

Fujita et al. (2016) explore the possibility that Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, significantly contributes to the observed TeV-PeV cosmic rays (CRs) as a Galactic PeV particle accelerator ("Pevatron").

The scenario consistent with a wealth of observations for the missing mass problem is that of weakly interacting dark matter particles. However, arguments or proposals for a Newtonian or relativistic modified gravity scenario continue to be made.

Image Credit: NASA/Dana Berry Long and precise follow-up measurements of the X-ray afterglow (AG) of very intense gamma ray bursts (GRBs) provide a critical test of GRB afterglow theories.

Image: Illustration of a warm Jupiter planet. Credit: X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS Most warm Jupiters have pericenter distances that are too large for significant orbital migration by tidal friction.