Feb. 11, 2016
SKA Organisation would like to congratulate colleagues at the Laser Interferometer Gravitational-Wave Observatory (LIGO) for their detection of gravitational waves – the ripples in the fabric of space-time predicted by Einstein in his theory of general relativity – announced earlier today.
“It’s a fantastic result !”, said Dr Robert Braun, Science Director at the Square Kilometre Array (SKA) Headquarters. “Today scientists have directly confirmed the solution to a 100-year-old physics mystery, building on the indirect detections honoured with a Nobel prize in 1993. It’s the dawn of an exciting time in physics, one in which the SKA will play an important role.”
The SKA, the world’s largest radio telescope due to start operation in 2020, will cover a large breadth of science, including among others, studying gravitational waves.
The SKA will look at gravitational waves coming from very different sources. While LIGO is sensitive to gravitational waves emitted by the merger of “small” (stellar-mass) orbiting black holes, the SKA will be sensitive to gravitational waves emitted by the merger of supermassive (more than one million times the mass of the Sun) black holes which are thought to reside in the centres of all large galaxies.
“This is because the gravitational waves caused by these events ripple at different frequencies, like the contrast between the small chop in a harbour and the long swell of the open ocean”, explained Dr Evan Keane, Project Scientist at the SKA. “In essence, it is like comparing the work of an optical telescope and an X-ray telescope, they are each sensitive to complementary phenomena.”Together with space-based experiments like eLISA and the proposed COrE, LIGO and the SKA will provide complete coverage of the gravitational wave spectrum.
LIGO has detected gravitational waves passing through Earth by precisely measuring how distances within the LIGO tunnels change, through the use of lasers. The SKA, meanwhile, will detect gravitational waves passing through our Galaxy by precisely measuring how the distances to pulsars change. Pulsars are fast-spinning neutron stars emitting beams of radio waves from their poles. Since some pulsars spin several hundred times per second they can be used as extremely accurate clocks. Small changes in the pulse arrival time can be used to measure the small changes in distance to these sources as a gravitational wave passes through the Galaxy.
The SKA is expected to detect all of the pulsars in the Galaxy, up to 30,000. “The more pulsars we detect, the better our chances of finding those that are the most precise clocks and with the exceptional sensitivity of the SKA we will be able to measure any changes in their “ticking” caused by gravitational waves”, said Dr Keane.
Beyond the first detection of the gravitational wave phenomenon, the SKA is expected to be able to conduct gravitational wave astronomy. “It’s a whole new field opening up today. Being able to study gravitational waves with LIGO, the SKA and other instruments will not only allow us to better understand gravity, but by confirming what we think about supermassive black holes at the centre of galaxies, it will also help confirm our model of the expansion of the Universe and the formation of galaxies themselves”, concluded Dr Keane.
Image: The Gravitational Waves Sky. The complete spectrum of gravitational wave astronomy is shown in this image. Ground-based laser interferometer systems, like LIGO and VIRGO, measure the most rapid variations of distance that have periods of only 10 milliseconds. Space-based laser interferometers, like eLISA, will be sensitive to periods of hours. Pulsar-based timing arrays using radio telescopes like the SKA will be sensitive to periods of years. While measurements of polarisation signatures within the Cosmic Microwave Background with systems like the proposed COrE will probe primordial gravitational waves with periods of many millions of years. The amplitude of the expected wave signature, a measure of how much the measured distance expands and contracts, is indicated by the vertical placement of the facilities in the Figure. The amplitude of the expected length changes, due to the passage of gravitational waves, can be as small as one part in 10 raised to the power of 21 (the number one followed by 21 zeroes).