Scientists spot rare gravity waves for the third time

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(As Albert Einstein figured out a century ago, pairs of dense, tightly orbiting objects are needed to generate ripples in the fabric of space-time, or gravitational waves.) But the three signals spotted by LIGO so far have all come from merging black holes, suggesting pairs of these ultradense, invisible objects abundantly populate the universe. The newly observed merger created a black hole of 49 solar masses, which sits nicely between the first detection (62 solar masses) and the second (21 solar masses).

Director France Córdova regarding news that researchers at the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves from a third pair of merging black holes 3 billion light-years away - the farthest distance yet. "It is remarkable that humans can put together a story, and test it, for such unusual and extreme events that took place billions of years ago and billions of light-years distant from us".

Shoemaker is an MIT scientist and newly-elected spokesman for the worldwide group of scientists who perform LIGO research together with the European-based Virgo Collaboration.

The fourth key area of significance was that the new detection occurred during LIGO's current observing run, which began November 30, 2016, and will continue through the summer. Another will be LIGO India, a collaboration with Indian scientists to create a third point in the LIGO system, now planned to commence operation in 2024. LIGO, operated by Caltech and MIT with hundreds of people working around the world, includes two detectors - one in Hanford, Wash., and the other in Livingston, La. - that are capable of measuring a ripple by as little as 1/1,000th of a proton. After detecting two gravitational-wave signals in September and December of 2015, the LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific and Virgo Collaborations are now reporting their third catch.

The third detection is described in a new paper accepted for publication in the journal Physical Review Letters.

Currently, there are only two detectors that can spot gravitational waves: the two LIGO detectors in Louisiana and Washington state.

That's when the ghosts of two dead stars - black holes dozens of times more massive than our sun - merged in a far-off corner of the universe. The wave was produced by two black holes that merged about 3 billion light-years from Earth. Georgia Tech astrophysicist Laura Cadonati on Wednesday likened the spinning black holes to a pair of tornadoes that dance around each other. Cadonati explained that while the two tornadoes may be rotating around each other, their individual spins may not be in the same direction.

There are two leading models for how these massive black holes are brought together. "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".

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That result fits neatly into a gap between the two earlier detections and suggests that "black holes exist in a variety of sizes", Dr. Pfeiffer said.

We knew, or at least strongly suspected, that gravitational waves existed long before their discovery in 2015.

She said the discovery was "a very significant advancement" because it provided some insight into how double black hole systems evolved. The black hole that resulted from the merger had a mass of 48.7 times that of the Sun.

There are now two primary theories about binary black hole formation: The first is that a pair of black holes is formed when a pair of stars explodes. It makes a lot of sense for the black holes to spin individually in the same direction they are spinning against each other, but as the new data shows, sometimes they spin in the opposite direction. That could reveal clues about the lives of the stars that formed them. "This clearly establishes a new population of black holes not known before LIGO discovered them", says LIGO scientist Bangalore Sathyaprakash of Penn State and Cardiff University.

Astronomers are particularly interested in determining how binary black holes are created.

"The new event also provides new opportunities to test Einstein's theory of general relativity".

Scientific and engineering teams at IPR Gandhinagar, IUCAA Pune and RRCAT Indore are actively engaged in the pre-construction activities of LIGO-India. 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. At that point, the instrument will undergo another round of sensitivity upgrades, including the swapping out of some mirrors for even more refined versions; additional improvements to laser power; and further efforts at noise reduction and improved computer control.

"The UChicago LIGO group has played an important role in this latest discovery, including helping to discern what emitted the gravitational waves, testing whether Einstein's theory of general relativity was correct, and exploring whether electromagnetic radiation-such as visible light, radio, or X-rays-were also emanated by the black hole collision", said Daniel Holz, associate professor in Physics and Astronomy & Astrophysics, and head of UChicago's LIGO group.