Moore Foundation Awards $2.4M to ASAS-SN Astronomers

Humanity has always marveled at the night sky. Yet, even today, we do not monitor it fully. No existing survey images and records the entire celestial sphere nightly to seek out the transient, variable, and sometimes violent events that mark the evolution and transformation of our universe.

Now, a five-year, $2.4 million grant from the Gordon and Betty Moore Foundation is about to change that, making the critical difference for Ohio State’s All-Sky Automated Search for Supernovae (ASAS-SN) project. Led by Ohio State Astronomy Professors Krzysztof (Kris) Stanek (ASAS-SN principal investigator) and Co-PI’s Christopher Kochanek and Todd Thompson, this ambitious, reaching-for-the-sky project literally is like no other.

“Astronomers dream of watching everything at once, every night. Now we will,” said Stanek. He explained that the Gordon and Betty Moore Foundation grant makes it possible for ASAS-SN to add two new observatories, doubling the total number of ASAS-SN telescopes from 8 to 16. The complete system will observe the entire visible sky every night, providing real-time, public alerts of new astronomical transients of all types to both professional and amateur communities. As the telescopes will be distributed across the globe, “we’ll almost never be clouded-out; this minimizes the odds that we miss something truly incredible.” Stanek said.

“Equally important,” Kochanek adds, “the second piece of the grant will allow us to make the entire database of observations — now consisting of approximately 1,000 measurements of more than 50 million stars — and growing — publicly accessible, so that anyone can mine it for new science.

“It will have extraordinary legacy value,” he said.

In May 2014, ASAS-SN began its first observations with two sets of four telescopes located in Hawaii and Chile, hosted by the Las Cumbres Observatory based in Santa Barbara, California.

Using four, 14-centimeter diameter telescopes on a common robotic mount, these two sites cover about half of the visible sky to a depth of about 25,000 times fainter than the human eye can see. Thousands of images per night are compared with all previous images of each field, new sources are found, and data on known-sources are catalogued. All discoveries are made public.

Ohio State astronomy graduate students have played critical roles in ASAS-SN’s development. Former PhD students Benjamin Shappee (Hubble Postdoctoral Fellow at the Carnegie Observatories in Pasadena), José Prieto (professor at Universidad Diego Portales), and Subo Dong (professor at Peking University), as well as current students Thomas Holoien and Jonathan Brown, have developed the software that controls the survey and turns digital-camera images into scientifically useful data. Students also carry out many of the follow-up observations required to understand the transients found by ASAS-SN, turning new discoveries into published papers.

In just two years, ASAS-SN has become the world leader in the discovery of bright supernovae, detecting more than 150 events per year, including both the deaths of massive stars and the thermonuclear explosions of white dwarfs. ASAS-SN also discovered the most luminous supernova ever found, and the brightest example of a star shredded and eaten by a supermassive black hole.

 “Although many other telescopes survey the sky, no other project has the all-sky, all-science, and local-universe mindset of ASAS-SN,” Stanek said. As an example, he described the half-billion dollar, “Large Synoptic Survey Telescope,” planned for 2023 in Cerro Pachón, Chile. LSST will frequently cover large areas of the night sky, and because of its enormously larger aperture it will find many faint transients in the deepest reaches of space. Ironically, though, it is too powerful to survey the nearby universe because bright sources will saturate its light detectors — like trying to capture a cellphone image of our Sun.”

Other projects do not process their data in real time for bright, new sources, nor do others make their discoveries public.

With this new grant from the Gordon and Betty Moore Foundation, ASAS-SN will look everywhere, every night, finding the nearest, brightest transient sources that are easiest for scientists to study.

Additionally, by having multiple sites in each hemisphere, ASAS-SN is poised to capture the brightest once-in-a-decade events missed by other surveys, while providing a complete, unbiased sample of cosmic explosions.

“In essence, we will provide the first, time-lapse ‘movie of the universe’ — the first continuous, all-sky monitoring of the heavens ever undertaken,” Thompson said.