http://www.latimes.com/science/sciencenow/la-sci-sn-ligo-gravity-waves-20170601-story.html

Scientists with the Laser Interferometer Gravitational-wave Observatory, or LIGO, have detected the signal from a cataclysmic collision between two black holes that lie 3 billion light-years away – much farther than the previous two discoveries.

The findings, described in a paper accepted to Physical Review Letters, cement the idea that gravitational-wave astronomy – a whole new way to observe some of the most powerful events in the universe – is here to stay.

“We’re really moving from novelty to new observational science — a new astronomy of gravitational waves,” said MIT’s David Shoemaker, spokesman for the LIGO scientific collaboration.

Astronomers document the universe in different wavelengths of light, from visible and infrared all the way to X-rays and gamma rays. But black holes do not emit light as far as we know — making them very difficult to study. By picking up deformations in space-time, LIGO allows scientists to “hear” these mysterious phenomena, even if they can’t see them with telescopes.

“We’re entering a whole new kind of astronomy,” said Clifford Johnson, a theoretical physicist at USC who was not involved in the work. “Every time we find a new way of looking in the sky … we understand our universe in a whole new way, at a whole new level.”

The new signal, called GW170104, was picked up in the early morning hours of Jan. 4 by the twin L-shaped detectors in Hanford, Wash., and Livingston, La. The ripple was triggered as two black holes, spinning around slowly toward one another, finally succumbed to each other’s gravitational tug — and merged. The collision resulted in the creation of a new, single black hole.
This merger between a binary pair of black holes happened around 3 billion light-years away—much farther than the first two finds (which lay around 1.3 and 1.4 billion light-years from us, respectively). The two black holes appear to have held 31.2 and 19.4 solar masses respectively, and when they coalesced the new singularity weighed in at 48.7 solar masses. (The remaining two suns or so of mass were transformed into gravitational waves.)

This puts the merger right in the middle of the same weight class as the previous two black hole mergers – a class that scientists had not originally expected to encounter. Most black holes, they had figured, were the corpses of dead stars and significantly smaller, on the order of a few times the mass of the sun. Others were supermassive, holding millions or even billions of solar masses, and anchored the hearts of galaxies (just as one does at the center of our Milky Way). Many LIGO researchers thought they’d start to see some of those smaller singularities.

These intermediate black holes, however, are starting to look increasingly common.

“It clearly establishes a new population of black holes that were not known before LIGO discovered them,” said LIGO scientific collaboration member Bangalore Sathyaprakash of Penn State and Cardiff University.

The new merger does have one key difference, however. In the previous two events, the paired black holes seemed to have spins that were aligned with their orbital axis. This is consistent with one theory of their formation, the isolated binaries formation mechanism, which assumes that the stars that became these black holes are born, and die, in pairs.

But in the new find, the black holes’ spins were apparently not aligned – favoring another theory, the dynamical capture mechanism, that says the black holes may actually pair up much later in their life histories.