Going underground to detect gravitational waves in space

21 June 2019

Since 2015, astrophysicists have opened fresh realms of exploration in physics and astronomy to boost our understanding of the universe through groundbreaking direct detection of gravitational waves.

These ripples in time and space have been located using ground-based observational facilities in the US and Europe. Now Professor Albert Kong (Croucher Fellowship 2000), Institute of Astronomy at National Tsing Hua University in Taiwan, is looking forward to adding stellar insights from Asia through a novel, soon-to-be deployed, underground gravitational wave detector, located in Japan.

To date, gravitational wave data on space convulsions such as collisions of black holes has mainly been collected using twin detectors in Washington and Louisiana and a third near Pisa in Italy. The detectors come under the Laser Interferometer Gravitational-Wave Observatory (LIGO) global scientific collaboration and European Virgo network respectively.

The Japan-based interferometer, known as the Kamioka Gravitational Wave Detector (KAGRA), is due to launch its first observational run in late 2019. The innovative telescope should enable regional researchers to make pioneering contributions to astrophysics through its special ultra-low temperature feature and underground location.

The so-called 2.5-generation detector was introduced by the KAGRA network of scientists in a January 2019 paper in Nature Astronomy. Participating researchers include those from Taiwan, South Korea, China and Japan. Kong, a leading gravitational wave astrophysicist, is steering the Taiwanese team involved in the collaboration.

“KAGRA will help to identify the physical properties of black holes and neutron stars,” he said. “This may also help to identify how heavy elements such as gold and silver are formed.” In coming on stream at the end of 2019, KAGRA aims to join the LIGO and Virgo networks’ third observational run, which began on 1 April 2019 and will scan the skies for around a year.

KAGRA’s design is based on laser interferometry, with two three-kilometre baseline arms positioned in an L-shape, similar to the second-generation Advanced LIGO and Advanced Virgo facilities. However, being underground will help to reduce noise from ground vibrations. It is also expected to cut down thermal noise by using sapphire mirrors cooled to cryogenic temperatures.

The two features combined should provide improved sensitivity at around 100Hz, allowing KAGRA to detect gravitational waves at lower frequencies. This is an important advantage over LIGO and Virgo facilities, which are situated above ground.

Indeed, it is anticipated that KAGRA could have the capacity to detect a binary neutron-star at a range of more than 150 megaparsecs (Mpc). A megaparsec represents a million parsecs, with one parsec being equal to 3.26 light years or around 31 trillion kilometres.

Constructing KAGRA has had its challenges. During initial tests, designers and scientists had to overcome ground vibration interference with sensors’ detection capability, and the disruption of a series of large earthquakes in the region.

Nevertheless, the launch is now in view and Kong finds it tremendously exciting to be at the forefront of an emerging field of knowledge. With gravitational waves viewed as an important key to revealing more of the cosmic cataclysmic explosions and collisions, KAGRA can hopefully inspire a new generation of scientists from Asia to look to the universe.

Professor Albert Kong is an astrophysicist focusing on multi-wavelength astrophysics research of compact objects, using space and ground-based telescopes. He received his DPhil in Astrophysics from the University of Oxford. He started his postdoctoral fellowship in 2000 at the Harvard-Smithsonian Center for Astrophysics working on multi-wavelength studies of X-ray binaries. He then moved to MIT in 2005 before joining National Tsing Hua University in Taiwan in 2007. He is now a Distinguished Professor at the University’s Institute of Astronomy, working on multi-messenger astrophysics. He also leads the Taiwanese team in the KAGRA collaboration. Professor Kong received a Croucher Fellowship in 2000. 

To view Professor Kong’s Croucher profile, please click here.

To read one of his latest articles, please click here