dglobalnews.com LIGO bags its third black-hole merger
Published: Fri, June 02, 2017
Research | By Kayla Price

LIGO bags its third black-hole merger

LIGO bags its third black-hole merger

The three confirmed detections by LIGO (GW150914, GW151226, GW170104), and one lower-confidence detection (LVT151012), point to stellar-mass binary black holes that, once merged, are larger than 20 solar masses.

For a third time, scientists have detected the infinitesimal reverberations of spacetime: gravitational waves.

Most of the remaining mass - almost twice our sun's worth - cascaded out in a powerful burst of invisible energy: gravitational waves that took 3 billion earth years to reach us, and that passed right on by in a fraction of a second. LIGO partners with the Virgo Collaboration, which is supported by Centre National de la Recherche Scientifique (CNRS), Istituto Nazionale di Fisica Nucleare (INFN) and Nikhef, as well as Virgo's host institution, the European Gravitational Observatory, a consortium that includes 280 additional scientists throughout Europe.

"The entire Ligo and Virgo scientific collaborations worked to put all these pieces together". Its observations are carried out by twin detectors in the U.S. - one in Hanford, Washington, and the other in Livingston, Louisiana.

A major worldwide collaboration between the Laser Interferometer Gravitational-Wave Observatory in the US and a similar project in Europe named Virgo has confirmed the successful detection of gravitational waves for the third time in human history. A second detection was made in December 2015. But as these waves pass through LIGO's twin detectors, its enormous lasers can pick up on the truly tiny stretches and squeezes of space-time.

"Most of the gold we see in the solar system might have come from a binary neutron star collision that produced something like a Jupiter mass of gold and dispersed it in all directions", Creighton says. However, the black holes are spinning in a non-aligned fashion, which means they have different orientations relative to the overall orbital motion of the pair.

Black holes are some of the most massive objects in our known universe, which pull in anything that gets too close, including light. In the second detection (GW151226), recorded a year ago, there is some evidence that the spin of one of the black holes could be at an angle to the orbital angular momentum - but still have a component in the direction of the orbital angular momentum. "LIGO is making the most direct and pristine observations of black holes that have ever been made, and we're taking large strides in our understanding of how and where these black holes are formed". More observations with LIGO are needed to say anything definitive about the spins of binary black holes, but these early data offer clues about how these pairs may form. The new merger involved black holes with masses about 31 and 19 times the mass of the sun, the LIGO team reported.

An animation representing colliding black holes
What colliding black holes might look like to

With a star's mass packed into a radius of around 10 kilometres, and hundreds of rotations a second, even a bump just 10 centimetres high could be enough to throw detectable gravitational waves out into the Universe.

In the other model, massive black holes court each other in huge swarms of stars known as globular clusters. These binary pairs seem to sync up with one-another after they are born of a deceased star, rather than as the afterlife of two stars which were already paired up. As pairs of black holes spiral inwards, heading towards a collision, they also spin on their own axes. If they are formed in this manner, it's believed that the spins would be in the same direction. The second theory suggests that the black holes form independently within dense clusters of stars. It also confirms that a new era of scientific discovery is at hand, and with every new detection scientists will learn new information about the universe.

Einstein's version of relativity theory, however, rules out that kind of dispersion. The discovery will be published in the journal Physical Review Letters.

LIGO scientists' observations matched the first scenario, putting a new upper limit on the mass of the graviton-and letting general relativity live another day. LIGO did not find evidence for this effect.

"It looks like Einstein was right - even for this new event, which is about two times farther away than our first detection", says LIGO physicist Laura Cadonati of Georgia Tech. The great distance of this merger also provides the most rigorous test to date for a specific part of Einstein's general theory of relativity - the lack of dispersion in gravitational waves. The waves were detected first in Hanford, Washington, where LIGO's interferometer reacted, and yet again in Virginia, where another interferometer noted the energy a mere 3ms later. They are also working on technical upgrades for LIGO's next run, scheduled to begin in late 2018, during which the detectors' sensitivity will be improved.

This is an important detail that can teach us more about the dynamics of our universe, and so far we can only detect the spins of black holes using the brand new technique of gravitational wave measurements.

Although LIGO appears to be "uniquely suited" to observing these events, David Reitze, executive director of the LIGO Laboratory, said he hopes to see other types of astrophysical events soon.

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