Gravitational Waves detection: The new epoch of science's success

Salman Riaz

­On September 14, 2015, at 9:50:45 (Eastern Day light time at 5:51am) two L-shaped antennas (which are two observatories, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located on opposite sides of the United States blipped out of place. The displacement lasted just 0.2 seconds and moved a distance that is 1,000 times smaller than a proton. But this tiny event carried an enormous amount of information about the birth and nature of the universe and also the new epoch of Science’s success. The scientific milestone, announced at a news conference in Washington on 11 February, 2016 was achieved using a pair of giant laser detectors in the United States, located in Louisiana and Washington State, capping a long quest to confirm the existence of these waves. The cosmic dance took place more than a billion years ago.  And it came from a distance of about seven and a half billion trillion miles away.  Based on his General theory of Relativity (GR), Albert Einstein predicted the existence of these waves in 1916.  It has taken nearly a hundred years for the technology to advance enough to detect these waves directly.

The LIGOs detection is proved that Einstein was right from now 100 years ago. But the significance of GW detection is due to many reasons. There had been an ongoing controversy (from 1916 to 1957) as to whether GWs really exist, and if they carry energy in a manner that would make GWs detectable.  Einstein reversed himself twice on this issue; he first proposed it, then opposed it, and then strongly supported it again. One of his famous students (Nathan Rosen) continued to dispute the potential existence of GW as late as 1970s.  In the early ‘90s, the existence of GWs was confirmed indirectly by measuring the rate of energy loss by a pair of rotating pulsars.  However, even though this finding was rewarded with a Nobel Prize (1993, Hulse and Taylor), some people remained unconvinced.  The finding by LIGO is the first direct observation of GWs, and is therefore a very significant milestone in establishing the validity of GR. 

From many years ago, people have inferred the existence of many black holes based on indirect evidence.  But the result reported by LIGO is the first direct observation of black holes, and the merger of two black holes. In that context, LIGO imagined two monster black holes spinning down on each other in space. One has a mass which is about 35 times that of Sun, the other roughly 30. At the moment just before they coalesce, they're turning around each other several tens of times a second. And then, their event horizons merge and they become one - like two soap bubbles in a bath.

David Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatories (LIGO), described it thus: "Take something about 150km in diameter, and pack 30 times the mass of the Sun into that, and then accelerate it to half the speed of light. Now, take another thing that's 30 times the mass of the Sun, and accelerate that to half the speed of light. And then collide together. That's what we saw here. It's mind boggling."

What are Gravitational Waves?

Gravitational waves are distortions or 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. In 1916 Einstein's theory GR mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source. Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.

The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself. The gravitational waves were predicted by Einstein but the actual proof of their existence wouldn't arrive until 1974, 20 years after Einstein's death. In that year, two astronomers working at the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar--two extremely dense and heavy stars in orbit around each other. This was exactly the type of system that, according to general relativity, should radiate gravitational waves. Knowing that this discovery could be used to finally test Einstein's audacious prediction, astronomers began measuring how the period of the stars' orbits changed over time. After eight years of observations, it was determined that the stars were getting closer to each other at precisely the rate predicted by general relativity. Since then, more astronomers have studied the timing of pulsar radio emissions and found similar effects, further confirming the existence of gravitational waves.

What is LIGO and what is its contribution to detect GWs:

The LIGO is designed to open the field of gravitational-wave astrophysics through the direct detection of gravitational waves predicted by Einstein’s GR theory. Its multi-kilometer-scale gravitational wave detectors use laser interferometer to measure the minute ripples in space-time caused by passing gravitational waves from cataclysmic cosmic sources such as the mergers of pairs of neutron stars or black holes, or by supernovae. LIGO consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana, which are operated in unison to detect gravitational waves.

The design and construction of LIGO was carried out by LIGO Laboratory’s team of scientists, engineers, and staff at the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), and collaborators from the over 80 scientific institutions world-wide that are members of the LIGO Scientific Collaboration (LSC). There are more than 1 thousands scientists’ works as the team of LSC. LIGO is funded by the U.S. National Science Foundation and operated by Caltech and MIT.

LIGO's optics system consists of lasers, a series of mirrors, and a photo detector (a device that measures varying light levels). In order to measure a distance thousands of times smaller than a proton, LIGO's optical components must operate harmoniously and with unprecedented precision. It all begins with the main laser.

Scientists encounter lasers daily, in laser pointers, or cat toys, or in the scanners at grocery or other stores. The first thing to understand is that the word, "laser" is actually an acronym for “Light Amplification by the Stimulated Emission of Radiation”. The heart of LIGO is its 200 Watt laser beam. But the beam doesn't start out at 200 W. It actually takes four steps to amplify its power and refine its wavelength to a level of precision never before seen in a laser of this kind. The very first glimmer of light that ultimately becomes LIGO's powerful laser emerges from a laser diode, which uses electricity to generate an 808 nanometer (nm) near-infrared beam of about 4 Watts. This is the same kind of device that a typical laser pointer uses, but with one big difference: typical laser pointers generate less than 5 milli-watts of power. LIGO's initial 4 W beam is 800 times more powerful.

The second step in generating LIGO's 200 W beam occurs when the 4 W beams enters a device called a Non-Planar Ring Oscillator (NPRO) containing a remarkably small boat-shaped crystal--the crystal is only about the size of a pinky fingernail! While the 4 W beam bounces around inside the crystal, it stimulates the emission of a 2 W beam with a wavelength of 1064 nm (in the infrared part of the spectrum).

Step three in LIGO's laser amplification occurs when this 2 W beam enters another amplifying device that boosts the 1064 nm beam from 2 to 35 W. Getting from 35 W to 200 W requires a different kind of device, however. So the 35 W beams is sent through a High Powered Oscillator (HPO), which performs further amplification and refinement, generating a 200 W, 1064 nm beam of pristine "lased" light. This is the beam that ultimately enters LIGO's interferometer. This multi-stage amplified laser is required for LIGO because of its ability to continually produce a pristine single wavelength of light. In fact, LIGO's laser is the most stable ever made to produce light at this wavelength. This stability is one of several factors critical for LIGO's ability to detect gravitational waves.

Gravitational Waves detection and Bangladesh:

Bangladeshis are proud of Selim Shahriar and Dipankar Talukder to be engaged as detecting Gravitational Waves and be proud participants of proving Einstein’s famous ‘General theory of Relitivity’. Selim was the US-based Bangladeshi professor and LIGO Collaboration led the team of scientists at Northwestern University in the historic event of detecting the gravitational waves, a discovery that confirms GR. Professor Selim Shahriar, who leads the experimental portion of Northwestern University’s chapter of the LIGO Scientific Collaboration, the international consortium that made the groundbreaking discovery, comes from Bera, Pabna, in Bangladesh. Born in 1964, Selim grabbed board places both in SSC examination from Bihari High School and in the HSC from Dhaka College. His father Azim Uddin Ahmed was a mathematics teacher in the same school where from Selim SSC passed. After that, Selim went to the US to study at the Massachusetts Institute of Technology (MIT). He is now professor of Department of Electrical Engineering and Computer Science and also Department of Physics and Astronomy, Northwestern University in Evanston, Illinois, USA. He is director of Laboratory for Atomic and Photonic Technology under Northwestern University, which works for detecting GVs.

Selim searches for ways to improve the sensitivity of the LIGO detectors and broaden the spectrum over which the detectors are sensitive. His group has identified a technique that improves sensitivity by a factor of nearly 20; a tweak could allow the instrument to probe a volume that is about 8,000 times larger than is now possible. Implementation of Selim’s technique would enable the detection of a much larger number of events in a given period. Selim is also working on a second technique that uses atomic clocks in the form of artificial pulsars that are placed on other planets and celestial bodies to enable the detection of gravitational waves in a different and very important part of the spectrum. Up until now, astronomers have only been able to explore the universe using light. Detecting gravitational waves gives them another tool for astronomical exploration that could potentially reveal what happened within the very moments that the universe was born.

Another Bangladeshi physicist is on the team of scientists who act to prove GVs expecting by Einstein. He born in 1977 in Barguna, Dipankar had spent his school days in acute poverty. He spent his childhood in Barguna studying in Barguna Adarsha School, Government Primary School and Barguna Zila School. Passing HSC from Barguna Government College, Dipankar got enrolled in the University of Dhaka. He acheive first class fifth from physics Department. Completing graduation (2002) in physics, Dipankar started teaching in Mastermind and Oxford schools for some days. Then, he received the commonwealth scholarship from UK and started studying higher mathematics in Cambridge (2003).

After that, he joined Washington State University as one of his professors told him that he would get an opportunity to study gravitational waves. He completed Master of Science in Physics in 2008 and Doctor of Philosophy (physics) in 2012 from the same university as one of the best students. The topic of his PhD research was also about black holes and gravitational waves. Dipankar started studying gravitational waves back in 2007 and became a member of LIGO in 2008.  Right now, he is working for Oregon University’s LIGO collaboration team. When he first started working for the LIGO, 400 scientists used to work there. Now around 1,000 scientists from 15 countries across the world work for the LIGO.

Since 2007 he has been working 100% for the LIGO Scientific Collaboration. Like many others, his work include practical aspects of detection and understanding of gravitational waves from modeled and unmodeled sources i.e, extract a signal from inherently noisy data and use the signal to obtain useful information about the source parameters.

Then, What next?

"We can observe the universe in this new way; not using light, but using gravity," physicist Brian Greene told after the announcement of GVs detection news. The most important target to find out— how does matter behave in extreme environment and how is the gamma-ray bursts produced. 

As one LIGO scientist pointed out, the discovery is akin to astrophysicists gaining a new sense: hearing. "Now we set to work to use that tool to examine astrophysical phenomena: the merger of black holes, the motion of neutron stars, the formation of massive black holes, the nature of space and time. All of that now is open to us in a sparkling new way." Before this discovery, researchers explored the universe using infrared, ultraviolet and visible light, with optical and radio telescopes, but now they have a new way to probe the depths of the cosmos: by using gravity as a way to observe what would otherwise be invisible.  Gravitational waves propagate through space-time, the malleable structure that surrounds cosmic objects like planets, stars and black holes.  Everything that happens in the universe, a bit of light traveling from one place to another, or mass moving around that’s happening in space-time, and it’s affecting space-time and it’s being affected by space-time.

Salman Riaz is Journalist and international affairs analyst.