China’s powerful new telescope will search for exploding stars

High in the mountains on the remote Tibetan Plateau, a powerful new telescope has begun capturing the night sky in motion. Last week, China’s Wide Field Survey Telescope (WFST) released its first image: a high-resolution snapshot of Andromeda, the nearest major galaxy to the Milky Way.

The WFST, nicknamed ‘Mozi’, is set to be the Northern Hemisphere’s largest facility dedicated to time-domain surveys — studies that track cosmic objects that change during observation. It was developed by the University of Science and Technology of China in Hefei and the Chinese Academy of Sciences’ Purple Mountain Observatory in Nanjing.

Over six years, the 2.5-metre telescope will scan the skies for fast-moving phenomena, such as stellar explosions and the approach of near-Earth objects. It will also gain a deeper view of the Milky Way and its features. “It has the potential to map the Solar System in great depth and extent,” says Licai Deng, an astronomer at the Chinese Academy of Sciences’ National Astronomical Observatories in Beijing.

In October, the telescope will begin a three-month pilot survey that will lay the groundwork for its upcoming six-year mission, which is expected to begin in 2024. “We want to get some early science,” says team member Jian Jiang, an astronomer at the University of Science and Technology of China.

Supernova search

One of the WFST’s main goals is to find tens of thousands of exploding stars, known as supernovae. Among these, the team hopes to find around 100 each year within just days of their explosive deaths. Such events are difficult for smaller telescopes to detect, because in their early phase supernovae appear faint and behave differently from their more mature counterparts.

The WFST’s deep and wide gaze will be able to catch the beginnings of these stellar explosions by observing them at near-ultraviolet wavelengths, says Jiang. The ability to make observations at these wavelengths and others will also allow scientists to study other transient events in greater detail, including kilonovae — bursts of light that occur when pairs of neutron stars merge — and tidal disruption events, which happen when a star is pulled apart by a supermassive black hole.

“We want to discover these transients as early as possible,” says Jiang. “Then we can easily arrange follow-up observations to get their complete evolution.”

Capturing these phenomena as they unfold could help astronomers to unravel bigger questions about the Universe, such as how quickly it is expanding and how galaxies, black holes and chemical elements formed, says Anais Möller, an astronomer at Swinburne University of Technology in Melbourne, Australia. She adds that massive sky-survey facilities such as the WFST can also help researchers to better understand how often these time-sensitive events occur and the conditions that give rise to them. “The deeper we go and the wider images we can take, the more objects we can find,” says Möller. “If we take a lot of images, we are basically creating a video of these objects and how they evolve.”

Enhanced view

Over the past decade, astronomers have developed a number of wide-field telescopes that aim to track the shifting Universe, including the Zwicky Transient Facility (ZTF) in California, which covers an area of sky equal to that of more than 200 full Moons in a single image. The WFST will cast a narrower eye on the night sky, but will be able to look deeper into the Cosmos than the ZTF can and find objects that are fainter or farther away, says Matthew Graham, an astronomer at the California Institute of Technology in Pasadena. He adds that the WFST will complement the Legacy Survey of Space and Time (LSST) project planned for the Vera C. Rubin Observatory in Chile, another time-domain facility that is due to begin operations in 2024. The WFST will survey the Northern Hemisphere while the LSST covers the south.

“That really improves our ability to monitor things over the course of several nights,” says Graham, who is a project scientist at the ZTF. “It fills in that sampling space.”

The WFST will also cover the night sky in the East while the West is in daylight, says Colin Orion Chandler, an astronomer at the University of Washington in Seattle and a project scientist at the LSST. This is important for tracking fast-changing and potentially hazardous objects, such as asteroids that are veering close to Earth. “More eyes are definitely better,” says Chandler.

The telescope’s team also has its sights set on more precisely mapping the Milky Way and some of its features, such as understudied star clusters and dust, to unravel the Galaxy’s history. The WFST will be able to measure the chemical elements of different stars with its six optical filters. “There are many surveys that focus on the Milky Way,” says Jiang. “But we want to get much deeper.”