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Detecting Gravitational Waves from Massive Black Holes
Minute Motions from Massive Events
The merging of two black holes 1.3 billion years ago into a supermassive black hole created gravitational waves received at the LIGO detectors September 14, 2015. Courtesy LIGO. (Click for a larger version.)
Well folks, the physicists have done it: they’ve unambiguously detected gravitational waves using the two Laser Interferometry Gravitational Wave Observatory (LIGO) systems in Louisiana and Washington state. The detection took place on September 14, 2015 but it took scientists all these months to verify their findings. Now they’re sure — gravitational waves exist and they CAN be detected. And, the coolest part? This discovery opens the window on the science of gravitational astronomy. It will let us see how massive objects (like black holes and neutron stars) and their interactions can affect space-time. It’s also the first time that scientists have observed these gravitational ripples that spread out from titanic events in the cosmos.
The waves detected in September were generated by something really massive and cataclysmic that occurred about 1.3 billion years ago: the merger of black holes. Their action created a single black hole that contains the mass of about 62 Suns. That action created gravitational waves whose signal was picked up by LIGO. (You can get more details in the actual paper the scientists published.) This is pretty incredible news. And, as the folks at LIGO told us today, this finding fulfills Einstein’s prediction a hundred years ago that gravitational waves do exist.
How Do Scientists Detect Find Gravitational Waves?
I had a chance to visit the LIGO installation in Livingston, Louisiana some years ago. One of the things that our tour guide told us was that the instrument is SO sensitive that the rumbling of a passing dump truck could easily mask the incoming signal of a gravitational wave. That’s pretty darned sensitive. So, when physicists want to measure these things, they have to exclude any other sources. To put it another way, what the LIGO and other gravitational wave detectors actually sense has to be pretty darned unambiguously a gravitational wave.
Which is actually rather ironic, considering that these waves can be generated by interactions of some very, very massive objects in the universe. Things such as the collisions of neutron stars, or the merging of massive black holes at the hearts of galaxies. These are objects that stretch and squeeze the fabric of space-time.
So, how does the LIGO detector work? Both observatories (one in Louisiana, the other in Hanford, Washington) measure the wiggles of gravitational waves. LIGO has two “arms” that allow laser light to pass through them. The arms are four kilometers (almost 2.5 miles) long and are placed at right angles to each other. The light “guides” are vacuum tubes that guide the laser beams to bounce off of mirrors. When a gravitational wave passes by, it stretches one arm to be a little lonber. The other arm shortens by the same amount. Scientists measure the change using the laser beam. Really strong gravitational waves might stretch or shorten the arm by perhaps no more than 18 meters. That indicates waves generated by extremely massive objects. Both LIGO facilities operate together to get the best possible measurements of gravitational waves. This video gives you a fairly good idea of how it works.
At this point, future developments in LIGO will depend on funding. It has recently been retooled and Advanced LIGO (aLIGO) is operational. In the future, LIGO is partnering with India’s Initiative in Gravitational Observation (IndIGO) to create an advanced detector in India. This sort of collaborative is a big first step toward a global initiative to search out gravitational waves.
LIGO gets its funding from the National Science Foundation, and has partners in the United Kingdom, at the Max Planck Society of Germany, and the Australian Research Council.
LIGO isn’t the only detector looking for the faint traces of gravitational waves, although its news today may well be the first of many such announcements as installations around the world refine the techniques of observing these signals. Facilities in Britain and Italy are also searching out gravitational waves, and a new installation in Japan in the Kamiokande Mine will bring instruments onboard with increased sensitivity to this phenomenon.
Heading to Space
There’s also a push to get space-based interferometers out there to do the measuring away from potential sources of interference here on Earth. Two space missions called LISA and DECIGO are under development. DECIGO is a Japan-based project that will seek to detect gravitational waves from the earliest moments of the universe.
LISA Pathfinder was launched by the European Space Agency in late 2015 as a test concept not only in the search for gravitational waves, but also as a testbed for other technologies. The next step is an expanded LISA, called eLISA, which will use laser interferometry to aid in the hunt for these difficult-to-detect waves. LISA was originally a joint project between the U.S. and European Space Agency, but continued gutting of NASA’s science budget by Congress resulted in the U.S. having to pull out of the mission, a damage to U.S. prestige in this area.
However, today’s announcement puts the U.S. squarely in the center of a major new discovery, one that scientists have worked toward for decades. It will be interesting to see what comes out now that they have more sensitive detectors. It’s a whole new way of looking at the universe!
Learn more about today’s discovery here and here.
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Source: http://thespacewriter.com/wp/2016/02/11/detecting-gravitational-waves-from-massive-black-holes/
