ARE THE TWO BLACK HOLES OBSERVED BY LIGO PRODUCED FROM THE COLLAPSE OF A SINGLE STAR?

Image: Simulation of two colliding black holes. Animation created by SXS, the Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org) - Caltech LIGO

If the GW signal observed by LIGO is due to the merger of two isolated black holes (BHs) in vacuum, no electromagnetic counterparts are expected. However, Fermi observed a signal 0.4 s after LIGO in a region of space compatible with the GW source.

A recent paper (Loeb 2016) suggests that the two black holes could be the result of the collapse of a single massive and rapidly rotating star. In this scenario the GRB is produced from a jet generated in the accretion disk of residual debris around the black hole or from an outflow generating by the BHs' merging.

The detection of a GRB afterglow in the future could be used to determine the precise localization of the electromagnetic source and eventually confirm the association to the GW source.

Loeb 2016 (accepted for publication in ApJ Letters) - Electromagnetic Counterparts to Black Hole Mergers Detected by LIGO (arXiv)

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ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

NEW WATER MASER IN S0 GALAXY IRAS 15480-0344

Image: Colour composite image of Centaurus A, revealing the lobes and jets emanating from the active galaxy’s central black hole. This is a composite of images obtained with three instruments, operating at very different wavelengths. The 870-micron submillimetre data, from LABOCA on APEX, are shown in orange. X-ray data from the Chandra X-ray Observatory are shown in blue. Visible light data from the Wide Field Imager (WFI) on the MPG/ESO 2.2 m telescope located at La Silla, Chile, show the background stars and the galaxy’s characteristic dust lane in close to "true colour". Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray) A maser, an acronym for 'microwave amplification by stimulated emission of radiation', is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The maser was the forerunner of the laser: they work by the same principle. The difference is

THE HITCHCHIKER'S GUIDE TO THE LOCAL SUPERCLUSTER

Image: Virgo Supercluster. Credit: Andrew Z. Colvin The Virgo Supercluster is a region with a diameter of 33 megaparsecs (~1000 times larger the Milky Way's diameter) containing at least 100 galaxy groups and clusters.

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