Prof. presents on worldwide cosmic collision discovery
Aug. 17 marked a landmark discovery in the field of astrophysics, in which a collective of scientists across the globe observed the first record of both gravitational waves and light from an ancient cosmic collision.
One of those scientists, Prof. Marcelle Soares-Santos (PHYS), spoke at an official press conference at the National Press Club in Washington, D.C. yesterday, together with other scientists representing the 70 ground- and space-based observatories that aided in confirming the unprecedented observation.
Approximately 130 million years ago, two neutron stars started spiraling together closer and closer, releasing high-energy gravitational waves that stretch and ripple spacetime. Their eventual collision led to a ‘kilonova,’ a fireball emitting gamma-rays that arrived to Earth as a distant and transient blue-to-red flash of light beginning on the morning of Aug. 17.
The U.S.-based Laser Interferometer Gravitational-Wave Observatory — the world’s largest gravitational wave observatory — and Europe-based interferometer Virgo were the first to detect gravitational waves produced by the colliding neutron stars.
Following this event, astronomers around the world collaborated to analyze the data from LIGO-Virgo, localize the optical source of the kilonova and track data of all the electromagnetic radiation forms that were observable for a few weeks. The overview paper published in the journal Physical Review Letters yesterday has over 3,500 authors.
The challenge with detecting optical sources “is the classical challenge of finding a needle in a haystack, … with the added complication that the needle is fading away and the haystack is moving,” said Soares-Santos during the press conference, livestreamed through National Science Foundation’s YouTube channel.
Neutron stars are the smallest and densest stars in the universe. The gravitational signal the collision released, named GW170817, only lasted for approximately 100 seconds. Two seconds later, gamma-rays emitted a visible flash of light that was observable to Earth for just a few days.
The more than 1,500 scientists part of the LIGO Scientific Collaboration and the Virgo Collaboration worked with each other from across the globe to analyze the results from the detectors.
Soares-Santos is part of one of the six teams that independently discovered the source of the event. Soares-Santos’s team used a dark energy camera (DECam), a wide field lens camera mounted on the 4-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in the Chilean Andes — an instrument Soares-Santos helped build.
LIGO-Virgo gravitational wave data was analyzed with optical detections from telescopes around the world, like Soares-Santos’s DECam in Chile, to confirm the event.
“This telescope and camera system allows us to search large areas in a short period of time. In other words, it allows us to search the entire localization area of an event and allows us to determine where the source is located,” said Soares-Santos.
Soares-Santos said her team’s strategy was to use the camera to map out the entire region and localize occurrence with overlapping exposures, explaining, “This enables us to determine what is the optical counterpoint and enables [us] ultimately to perform a number of scientific endeavors. ... the closest to my heart is cosmology, which is the goal of the dark energy survey and my own in terms of science.”
The first-ever detection of gravitational waves occurred in 2015, jumpstarting gravitational wave astronomy, according to the press release. In total, there have only been four previous confirmed detections of gravitational waves, with this being the first simultaneous light observance.
This combined gravitational and optical observation provides confirmation of Albert Einstein’s general theory of relativity from 1915, which predicted that gravitational waves travel at the same speed as light.
“Our strategy, as you know, paid off handsomely,” said Soares-Santos as she concluded her speech. Her team was not only able to localize the cosmic collision but also ruled out 1,500 candidates which “were present in that haystack.”
“Truth is, things that look like needles in this haystack are very common, and the problem here is not only to find a needle, but to make sure that we have the right one. And today, we are certain that we have.”
Soares-Santos became an assistant professor at the University in 2017. She is an associate scientist of the FERMI national accelerator laboratory. Soares-Santos leads the Blanco Images of the Southern Sky survey and campaigns of the Dark Energy Survey, with a focus in galaxy clusters and gravitational waves for cosmology.