Category Archives: gravitational waves

Gravitational Waves Are Found Again!

Second Gravitational Waves Detection for LIGO

 When two black holes merge, gravitational waves ripple outward as the black holes spiral toward each other. The black holes — which represent those detected by LIGO on Dec. 26, 2015, formed a single black hole 21 times the mass of the Sun. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be too small to see. . Pyle/LIGO

When two black holes merge, gravitational waves ripple outward as the black holes spiral toward each other. The black holes — which represent those detected by LIGO on Dec. 26, 2015, formed a single black hole 21 times the mass of the Sun. In reality, the area near the black holes would appear highly warped, and the gravitational waves would be too small to see.
Artist’s concept by T Pyle/LIGO

They’ve done it again over at LIGO. Scientists  in the LIGO Scientific Collaboration and the Virgo Collaboration detected the faint, almost imperceptible gravitational waves from yet another black hole merger. Rumors have been flying the past few days about this (the first detection was announced earlier this year). Today, scientists using the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Hanford, Washington and Livingston, Louisiana made the news public: they detected a second gravitational wave signal on Christmas Day, 2015. It was a faint chirp generated by the cataclysmic collision of two massive black holes lying some 1.4 billion light-years away.

Here’s what the folks at Massachusetts Institute of Technology (who participated in the study) had to say about the discovery (which was formally announced today at the American Astronomical Society meeting in San Diego):

The researchers calculated that the gravitational wave arose from the collision of two black holes with masses of 14.2 and 7.5 times the mass of the Sun. The signal picked up by LIGO’s detectors encompasses the final moments before the black holes merged: For roughly the final second, while the signal was detectable, the black holes spun around each other 55 times, approaching half the speed of light, before merging in a collision that released a huge amount of energy in the form of gravitational waves, equivalent to the mass of the sun. This cataclysm, occurring 1.4 billion years ago, produced a more massive spinning black hole that is 20.8 times the mass of the Sun.

This second detection of gravitational waves, which once again confirms Einstein’s theory of general relativity, successfully tested LIGO’s ability to detect incredibly subtle gravitational signals.

The signal the scientists detected wasn’t like a loud “belch” of data. Indeed, it was the opposite: very faint — almost a “blip” in the data. It took quite a bit of data analysis to tease the signal out of the noise, but once the researchers figured it out, they knew they had another notch in their gravitational wave belts.

LIGO’s Gravitational Wave Mission

I got the chance to visit the Livingston, LA facility some years ago during a meeting. I was amazed at the painstaking care the scientists take to build an instrument capable of detecting these signals. Sorting them out from all the other “noise” in the universe is even more precise. They also have to deal withthe “noise” of things like gravel trucks and trains passing by here the facilities. That requires a lot of data analysis and a clear understanding of what they’re looking for in the data.

LIGO’s two interferometers, each four kilometers long (2.5 miles)  are designed so that each detector should stretch by an infinitesimal amount if a gravitational wave were to pass through. On Sept. 14, 2015, the detectors picked up the very first signal of a gravitational wave, It, too, was caused by a black hole merger. It stretched each detector by as little as a fraction of a proton’s diameter. Just four months later, on Dec. 26, LIGO recorded a second signal, which stretched the detectors by an even smaller amount. That may seem small, particularly when you think about the tremendous cataclysm that created the waves, but tiny wiggles of data such as these often provide some of the most profound insights into how objects work in the universe.

In particular, the detection of gravitational waves will help answer some important questions about how black holes merge, and even how the massive ones form in the first place. There are many theoretical scenarios, and data from LIGO will help scientists sort out which ones really help explain what we observe and know about these cosmic monsters.

Gravitational wave science is really just at the starting gate of what we will be able to discover about the universe when events and objects do interesting things. I look forward to further detections as the LIGO folk continue their search for their once-elusive prey.  (If you want to read more details about this second discovery, check out the MIT News source story and there’s a Youtube video of the “chirp” here and a very cool video animation of the merger, as well.)

Detecting Gravitational Waves from Massive Black Holes

Minute Motions from Massive Events

black holes and gravitational waves signals
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 came from 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, and created a gravitational “wiggle” that got 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 are 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. Objects this massive stretch and squeeze the fabric of space-time. So do their mergers.

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 longer. The other arm shortens by the same amount. Scientists measure the change using the laser beam. Both LIGO facilities operate together to get the best possible measurements of gravitational waves. This video gives you a fairly good idea of how the process 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 collaboration is a big first step toward a global initiative to search out gravitational waves across the spectrum of activity.

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.