Dr. Andrew Cooper _ Exploring the first science results from the DESI Milky Way Survey
Introduction to the event
In the past year, Dr. Cooper’s Galaxy Formation and Galactic Archaeology research group at the NTHU Institute of Astronomy has grown quickly. It now includes 5 students: two PhDs, one MS and three undergraduates, all supported by Dr. Cooper’s Yushan fund. Their aim is to understand how galaxies have evolved over the 13 billion year history of the cosmos. Their work is focused on a large international project called DESI (Dark Energy Spectroscopic Instrument). Over the next 5 years, DESI will start its main mission to take the optical spectra of 8 million stars and 30 million galaxies. This will be the largest project of its kind. Each spectrum will measure the light from a star or galaxy at thousands of different wavelengths, from which we can learn about its chemical composition and how fast it is moving towards or away from us. The massive number of these observations DESI will make will help us understand the history of the Universe and the behaviour of the mysterious dark matter. Dr. Cooper is sharing his work on these topics with students at NTHU through two lecture courses on Cosmology and Galaxy Astrophysics.
The start of the main DESI survey was delayed until the summer of 2021 by the coronavirus outbreak, but test observations from January to March have already provided Dr. Cooper and his group with more than 300,000 spectra to study. They will use this data to investigate the origin of our galaxy’s oldest and most unusual stars, working alongside 29 collaborators from 8 countries as part of DESI’s Milky Way Survey project. An important task that will be carried out by Dr. Cooper and his group at NTHU will be to compare these observations to predictions from supercomputer simulations. To help to create and analyze these simulations, Dr. Cooper and his colleagues at the Institute of Astronomy have continued to expand the computing resources of the Centre for Informatics and Computation in Astronomy (CICA), which are shared by all students and faculty at the institute. The CICA computing cluster is now one of the most powerful and versatile computing facilities dedicated to astronomy research in Taiwan.
An image of the night sky above Hsinchu taken by the NTHU Observatory all-sky camera in January 2021, showing the Orion constellation (lower right).
The ‘shoulders’ of Orion are marked by two very bright stars, Betelgeuse (red) and Bellatrix (blue).
Dr. Cooper, his group and their colleagues in the DESI Milky Way Survey team want to learn about the underlying physical properties of stars that give them their different colors, including their temperatures, sizes, ages and mixtures of chemical elements. Instead of an image of the sky, instruments like DESI observe spectra, the amount of light each star emits at thousands of discrete wavelengths.
The inset panels show spectra from a random selection of the 300,000 test observations carried out by DESI in January and February 2021. Red stars like Betelgeuse (left) have spectra that peak at long wavelengths, blue stars like Bellatrix (right) have spectra that peak at short wavelengths. The detailed shape of each spectrum contains a huge amount of scientific information. Over the next five years, DESI will measure spectra for up to 8 million very distant stars, the faintest of which will be almost 100 million times dimmer than Betelgeuse. From these data, we hope to learn about the different types of stars in the Milky Way, the 13-billion-year history of our galaxy, and the nature of the mysterious Dark Matter. [ DESI is a project of the US Department of Energy Office of Science and its institutional partners, led by Lawrence Berkeley National Laboratory. ]