Published: Fri, June 02, 2017
Research | By Chelsea Rogers

LIGO detects gravitational waves for a third time

LIGO detects gravitational waves for a third time

The LIGO Scientific Collaboration has made another monumental announcement related to LIGO, the Laser Interferometer Gravitational-Wave Observatory - it has detected a gravitational wave event for the third time, a process that has been billions of years in the making. The new results, though quite similar to the first two detections, are an ebullient affirmation that the millions of dollars poured into these ultra-sensitive instruments is helping to open up a profound new window in the world of astrophysics.

The latest detection brought no surprise: it is more of the same - which is still a good thing, says Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics (MPIGP) in Hanover, Germany, which is part of the LIGO collaboration.

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses - objects we didn't know existed before LIGO detected them", David Shoemaker said in a news release about the discovery. Each detector has two L-shaped arms, extending out 2.5 miles in each direction. "And I want it to be a signal that no one has predicted, and for which no one has an explanation". What's more, black holes can also be tilted away from the orbital plane.

"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.

The group at IIT-Madras is involved in modelling the gravitational wave sources such as the ones which have been detected by the LIGO detectors so far as well as testing the consistency of the detected gravitational wave signals with the predictions of Einstein's general theory of relativity.

With the third detection, scientists are beginning to close in on their goal of using gravitational waves as a way of observing ancient events that would be invisible to optical or radio telescopes. The fact that this third merger happened at a distance of about 3 billion light-years gave scientists a chance to test yet another of Einstein's hypotheses. The black holes in the first and second detections were located 1.3 and 1.4 billion light-years away, respectively.

LIGO and the Virgo collaboration based in Europe published a paper Thursday on the latest detection in the journal Physical Review Letters.

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While it might be hard to picture, black holes can actually spin. But the LIGO team was also able to extract some information about the details of the collision and propagation of gravitational waves. LIGO has done a lot of work in a short amount of time; it's exciting to think about what might be ahead as the observatory turns its attention to other types of astronomical events, such as the collision of neutron stars.

It is possible that one of the black holes had a misaligned spin, which is to say that it was not spinning in the same direction as its overall spiral orbit. They can also be tilted.

"With the detection of GW170104, we are taking another important step toward gravitational-wave astronomy", Holz said. "This means they take longer to merge than if the spins are non-aligned", she said. They merged into a black hole whose size is in the middle of the other two merged black hole pairs. For the first time, researchers at the University of Toronto led the effort to characterize the properties of the colliding black holes - a task that rotates between participating teams in the collaboration in two-week shifts during the experiment's round-the-clock monitoring of the heavens. Physicist Albert Einstein said that they should be given off as a outcome of his general theory of relativity, but it took decades to nail down the evidence conclusively with LIGO. Einstein's theory indicates that gravitational waves do not disperse through a physical medium, unlike light through a prism. They collaborate with computer scientists at Northwestern's Image and Video Processing Laboratory, the Zooniverse team at Chicago's Adler Planetarium, human-computer interaction experts at Syracuse University and LIGO scientists at California State University, Fullerton.

"In Einstein's theory, no such dispersion is expected", said Sathyaprakash. That's because some of the mass gets converted into energy, via Einstein's famous equation, E=mc2.

Scientists detected them using laser beams fired through two perpendicular pipes, each four kilometres long, situated almost 2,000 miles apart in Hanford, Washington, and Livingston, Louisiana, in the US. 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.

Within tens of seconds, LIGO's search algorithms automatically analyzed the signal, comparing it to waveforms characteristic of gravitational waves. Virgo should go online sometime this summer. "We now have three solid detections, and these provide our first hints about the diversity of black hole systems in the universe".

As astronomer Duncan Brown told Mental Floss last June: "When a nuclear bomb explodes, you're converting about a gram of matter-about the weight of a thumb-tack-into energy".

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