The New Era of Gravitational Wave Astrophysics

The New Era of Gravitational Wave Astrophysics

By Rebecca B. Andersen


   
OSA’s Centennial Light the Future speaker series was created during The Optical Society’s Centennial in 2016 to highlight the optical sciences in our everyday lives. Speakers have included visionaries, futurists and Nobel Laureates. The series continues in 2018 lead by Professor Nergis Mavalvala, Curtis and Kathleen Marble Professor of Astrophysics, Massachusetts Institute of Technology, USA.

Dr. Mavalvala is a longstanding member of the LIGO Scientific Collaboration, the scientific team that announced the first direct detection of gravitational waves from colliding black holes. She has also conducted pioneering experiments on generation and application of squeezed states of light, and on laser cooling and trapping of macroscopic objects to enable observation of quantum phenomena in human-scale systems.

Action at a Distance
Astrophysicists have sought to detect ripples in space-time called gravitational waves since they realized Albert Einstein’s 1916 theory of general relativity predicted their existence. Only some of the most massive astrophysical events, such as mergers of black holes and neutron stars, can produce gravitational waves strong enough to be detected on earth. Einstein, ‘the hero of gravity,’ went onto theorize gravitational waves and in turn wrote “one of the most beastly equations ever written” according to Mavalvala.

In 1916, Karl Schwarzschild obtained the exact solution to Einstein's field equations for the gravitational field outside a non-rotating, spherically symmetric body. The solution has come to be known as the Schwarzschild radius. The physical significance of this singularity, and whether this singularity could ever occur in nature, was debated for many decades; a general acceptance of the possibility of a black hole did not occur until the second half of the 20th century.

As Mavalvala explained, even Einstein was conflicted in his research of whether or not gravitational waves could exist. No matter what Einstein thought about his theory at the time – the equation was still accurate – capturing gravity, space-time and black holes.

The next step in gravitational wave astronomy was ushered in through the new field of numerical relativity. It emerged from the desire to construct and study more general solutions to the field equations by approximately solving the Einstein equations numerically. A necessary precursor to such attempts was a decomposition of space-time back into separated space and time.

A Meeting of the Minds
Nobel Laureates in Physics, Kip Thorne and Rai Wiess, began their research in the 1960’s and began to question what a gravitational wave would look like from the earth. Their scientific collaboration continued and in 1975, the team met in Washington DC to set into motion the development of one of the most complicated and risky scientific experiments ever conceived. With the guidance of Barry Barish and the financial support of the National Science Foundation, the LIGO Scientific Collaboration was formed. It was this team of international scientists that built the two LIGO facilities in the United States and now Italy with VIRGO. 

Beyond 100 Years of General Relativity
Gravitational waves went from a whisper to a shout when detected in October 2015. Using advanced optics-based systems, the research team was able to measure gravitational waves on Earth, enabling them to pinpoint the precise moments they were produced.  Unlike light, gravitational waves are not diminished by interstellar dust as they propagate through space. By detecting them, the research team is able to peer into the most energetic events of the universe and explore the cosmos in a completely new way.

On 17 August 2017, a team made another monumental detection. They were able to detect a bright spark of two neutron stars colliding, shedding light on the previously unknown origins of some of the universe's heavy elements. Named GW170817, the neutron star collision was detected for more than a minute and a half and covered the full acoustic frequency range sampled by the research team.

Dissimilar to the darkness viewed with two black holes colliding, Mavalvala noted that a neutron star collision gave astronomers a spectacular view of a technicolor light show visible around the world.
Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. As these neutron stars spiraled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves. In the days and weeks following the smashup, other forms of light, or electromagnetic radiation — including X-ray, ultraviolet, optical, infrared, and radio waves — were detected.

A Paradigm Shift in Astronomy
In 1610, Italian astronomer Galileo Galilei looked up at the heavens using a telescope of his making. And what he saw would forever revolutionize the field of astronomy, our understanding of the Universe, and our place in it. This Mavalava noted that this was a paradigm shift in astronomy – using optical instruments to peer even further into the cosmos.
 
     
   
    Ian Walmsley, Nergis Mavalvala and Liz Rogan

Optical telescopes first found a new point of light, resembling a new star but much brighter. Ultimately, about 70 observatories on the ground and in space observed the event on August 17 at their representative wavelengths. A 16-inch portable telescope was the first to make the optical discovery announced today. The research team noted, amateur astronomers on the earth may be able to ‘see’ more and more of these events in the future night sky.

From there, Mavalvala detailed the past 100 years of development in optical instrumentation for astronomy from George Ellery Hale’s 100-meter telescope on Mt. Wilson, to NASA’s Hubble and today’s Giant Magellan Telescope. As the optical instrumentation enabling these discoveries have grown in scope, so has opportunities to detect astrophysical events of all forms.

“Who knows where astronomy will be hundreds of years from now” but Nergis Mavalvala encouraged everyone at this Light the Future program to “dream big.”

About Nergis Mavalvala
With 129 papers published in gravitational wave astrophysics and quantum measurement science, Mavalvala is an accomplished researcher and explorer. In 2017, she was elected to the National Academy of Sciences.  She received the Special Breakthrough Prize in Fundamental Physics, as a member of the LIGO Scientific Collaboration in 2015. In addition to being an OSA Fellow, she is also MacArthur Fellow and an American Physical Society Fellow.

About the LIGO and Virgo Scientific Collaborations
LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project.

More than 1,200 scientists and some 100 institutions from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at http://ligo.org/partners.php.
   
The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.
 

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Posted: 11 April 2018 by Rebecca B. Andersen | with 0 comments

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