The Triple Helix @ UChicago

Winter 2018

"The New Astronomy: LIGO and Gravitational Waves" by Joshua Everts

 

Early astronomers were both curious and pragmatic. They would peer into the heavens at night, looking for signs of the future but also to guide travel and keep track of time. Some of the most well-known megalithic monuments, like Stonehenge, are linked to the seasons, suggesting that our ancient ancestors cared about and studied astronomical processes. Since then, much has changed. In 1608, Dutch lens-maker Hans Lippershey invented the first refracting telescope (King 1955, 30). Over the following centuries, many improvements were made, and we began utilizing other types of light, like radio waves and x-rays, to view the universe. We have even put telescopes into orbit to gain crisper images and better data. Yet, despite these advances, all of these technologies still relied on electromagnetic radiation to capture information.

All of this started to change, though, when the Laser Interferometer Gravitational Wave Observatory (LIGO) first went online in 2002. A joint partnership between the National Science Foundation, Caltech, and MIT, it was designed to give astronomers a new way of viewing the cosmos. LIGO is a detector that measures gravitational waves that emanate from the collisions and impacts of massive objects like black holes far away in space.  LIGO utilizes two separate locations, one in Washington, the other in Louisiana (Caltech n.d.). The wide geographical spacing of these two detectors allows astronomers to determine the direction from which a signal comes, which is vitally important since ripples in space-time, the ‘measuring stick’ of gravity, could come from any direction in space.

The LIGO detectors are marvels of modern scientific precision. They utilize finely-tuned 4-kilometer lasers arranged in an ‘L’ shape so that, when combined through a mirror, their wave frequencies are aligned (Caltech n.d.). This precise alignment allows tiny changes in the distance the laser travels to be detected.  Gravitational waves are astonishingly difficult to detect, and the LIGO interferometers are able to resolve lengths up to one ten-thousandth the width of a proton, an almost inconceivably tiny distance. This precision is only possible because natural distortion from air molecules is filtered out by creating an extreme vacuum. The LIGO detectors also feature both active and passive damping systems that prevent vibrations from entering the chambers (Caltech n.d.).  Once these features are coupled with an extremely precise, multi-stage laser and finely honed silica glass mirrors, LIGO is able to achieve its incredible precision. 

These massive technological developments with LIGO have led to astonishing discoveries about the nature of the universe. Albert Einstein first predicted gravitational waves with his theory of general relativity in 1915 (Finley 2013), and since then scientists have wanted to experimentally verify the nature of these waves and, more importantly, utilize them in scientific endeavours like astronomical research.

On September 14, 2015, LIGO made its first gravitational wave discovery, one that appeared to have come from two merging black holes (Caltech n.d.). This marked the first time that gravitational waves had been detected and utilized to provide astronomical information. After other detections, LIGO announced in August 2017 that they had detected the merging of two binary neutron stars (Abbot 2017). This event was particularly significant because, after identifying the location in the sky from which the waves had arrived, conventional telescopes across the world were able to identify light signatures that indicated the nature of the event (merging binary neutron stars) as well as further verify the accuracy of LIGO detectors (Abbot 2017). Because the gravitational wave signals arrived at nearly the same time as the light from the collision, this event provides direct evidence that gravitational waves do actually travel at the speed of light. Furthermore, the combined power of the LIGO detectors with more traditional light telescopes ushered in a new field known as multi-messenger astronomy, where information from one medium can be used to corroborate information from another.

These recent developments have radically changed astronomy, as the ability to look into the universe with an entirely different perspective is incredibly powerful. Some of astronomy’s greatest mysteries lie within the nature of the cosmos, including its accelerating expansion and the conditions of the very early universe. Because gravitational waves can be emitted by sources that have no light emission -- like certain black holes -- and are relatively unaffected by other bodies and dust in space, they offer a clearer insight into certain aspects of the universe than electromagnetic radiation has been able to provide in the past.

Gravitational waves have incredible scientific potential. Since their discovery, they have proven immensely valuable in both reaffirming scientific theory and furthering astronomical research. Gravitational waves and the success of the LIGO detectors represent much more than just another development in physics and astronomy. They are, in fact, a completely new way of investigating that endless, inky darkness that first captivated our ancestors thousands of years ago. 

References

[1] Abbot, B. P., Et al. "GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral." Physical Review Letters. October 16, 2017. Accessed March 06, 2018. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161101.

[2] "About." LIGO Lab | Caltech. Accessed March 06, 2018. https://www.ligo.caltech.edu/page/about.

[3] Finley, Dave. "Einstein's gravity theory passes toughest test yet: Bizarre binary star system pushes study of relativity to new limits." Phys.org - News and Articles on Science and

[4] King, Henry C. "The History of the Telescope." Google Books. Accessed March 06, 2018. https://books.google.com/books?id=KAWwzHlDVksC&pg=PA30&dq=Hans%2BLippershey%2Binventor%2Bof%2Bthe%2Btelescope.&hl=en&ei=uJKiTJvkIsP6lweQ4dHbAw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CD8Q6AEwBDgK#v=onepage&q=Hans%20Lippershey%20inventor%20of%20the%20telescope.&f=false.Technology. April 25, 2013. Accessed March 06, 2018. https://phys.org/news/2013-04-einstein-gravity-theory-toughest-bizarre.html.

[5] "LIGO Technology." LIGO Lab | Caltech. Accessed March 06, 2018. https://www.ligo.caltech.edu/page/ligo-technology.

[6] “Timeline.” LIGO lab | Caltech. Accessed March 08, 2018. https://www.ligo.caltech.edu/page/timeline

[7] "What is LIGO?" LIGO Lab | Caltech. Accessed March 06, 2018. https://www.ligo.caltech.edu/page/what-is-ligo.

 

 
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