Starship Asterisk*

LIGO is thrilled to announce that it has nabbed its third gravitational wave in 18 months!

[img3="Schematic showing the relative 'sizes' (in Rs) of the black holes before and after merging. Credit: LIGO"]https://www.ligo.caltech.edu/system/med ... 1496264615[/img3][hr][/hr]

At 2:11:58 a.m. on January 4th 2017 the arms of LIGO’s Hanford, WA interferometer shivered. Three milliseconds later, Livingston’s interferometer followed suit. Even though parts of the U.S. were experiencing record cold temperatures, the trembling wasn’t caused by the frigid air of that winter morning. Rather, it was the shudder of space-time itself generated by the merger of two massive black holes in the distant universe: a gravitational wave had washed over the Earth, passing successively through the two detectors while most people in the U.S. were still asleep.

LIGO researchers quickly determined that the black holes were around 3 billion light years away from Earth when they collided, making this merger the farthest one yet observed (3 billion light years is about one-fifth of the way out to the ‘edge’ of the visible Universe). These waves had been traveling for around 3 billion years by the time they reached us.

Since learning of the detection, LIGO scientists have also determined that the two black holes involved in the merger were about 19 times and 32 times the mass of the Sun (with these masses, these objects add to a mysterious ‘new’ population of black holes with masses not known to astronomers prior to LIGO’s first detection). The resultant merged black hole is estimated to weigh about 49 times that of the Sun. ...

• Physical Review Letters 118(22):1101 (02 Jun 2017) DOI: 10.1103/PhysRevLett.118.221101

Gravitational wave astronomy sheds light on supernova explosions

New information gleaned from gravitational wave observations is helping scientists understand what happens when massive stars die and transform into black holes.

Rochester Institute of Technology researcher Richard O’Shaughnessy and collaborators reanalyzed the merging black holes detected by LIGO (Laser Interferometer Gravitational Wave Observatory) on Dec. 26, 2016.

“Using essentially freshman physics, we drew new insights about the most violent events in the universe,” said O’Shaughnessy ...

The current study reanalyzed the binary black holes, known as GW151226. It has been the only time LIGO has reported binary black holes must be spinning, O’Shaughnessy said. LIGO’s previous measurements suggested that the larger mass orbited the other at a slightly tilted angle.

O’Shaughnessy and his team link the black hole’s misalignment to when it formed from the death of a massive star. The force of the stellar explosion and collapse expelled the newborn black hole with a “natal kick,” causing this misalignment, the authors suggest. ...

• arXiv.org > astro-ph > arXiv:1704.03879 > 12 Apr 2017