Atop the summit of Haleakala on the Hawaiian island of Maui sits the Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS1 (PS1). As part of the Haleakala Observatory overseen by the University of Hawaii, Pan-STARRS1 relies on a system of cameras, telescopes, and a computing facility to conduct an optical imaging survey of the sky, as well as astrometry and photometry of know objects.
In 2018, the University of Hawaii at Manoa’s Institute for Astronomy (IfA) released the PS1 3pi survey, the world’s largest digital sky survey that spanned three-quarters of the sky and encompassed 3 billion objects. And now, a team of astronomers from the IfA have used this data to create the Pan-STARRS1 Source Types and Redshifts with Machine Learning (PS1-STRM), the world’s largest three-dimensional astronomical catalog.
The team began by taking publicly-available spectroscopic measurements of the 2,902,054,648 objects studied in the PS1 3pi survey, which provides them with definitive object classifications and distances. They then fed these to an artificial intelligence algorithm, which sorted them into stars, galaxies, quasars, or unsure (it also derived refined estimates for the galaxies’ distances).
As Beck described the process in a recent University of Hawaii News press release:
“Utilizing a state-of-the-art optimization algorithm, we leveraged the spectroscopic training set of almost 4 million light sources to teach the neural network to predict source types and galaxy distances, while at the same time correcting for light extinction by dust in the Milky Way.”
The most recent data release (DR16), the fourth release of the fourth phase of the SDSS (SDSS-IV), contains SDSS observations through to August 2018. The final release (DR17) is scheduled for July 2021 and will include all new spectra observations, as well as all final data products and catalogs. However, the SDSS catalog covers one-third of the sky and contains spectra for over 3 million objects.
In comparison, the PS1-STRM doubles the area surveyed, increases the number of objects tenfold, and covers specific areas that the SDSS missed. As István Szapudi, an IfA astronomer and co-author on the study, noted :
“Already, a preliminary version of this catalog, covering a much smaller area, facilitated the discovery of the largest void in the universe, the possible cause of the Cold Spot. The new, more accurate, and larger photometric redshift catalog will be the starting point for many future discoveries.”