The sky has just gained an immense amount of new data.
The Sloan Digital Sky Survey, or SDSS, publishes more than three million spectra of stars, galaxies and quasars. For the first time in this phase of the program, a significant part of these observations also covers the southern sky. Astronomers thus have a much more uniform dataset to compare the two hemispheres.
A spectrum is the light of an object broken down according to its different wavelengths. This decomposition acts a bit like a fingerprint: it provides information about a star's composition, temperature or motion. For a distant galaxy, it can also help measure its distance through the shift of its light.
Screenshot of LVMvis showing an observation of the Helix Nebula included in the DR20 data release (expnum=4297).
The twentieth SDSS data release, called DR20, brings together observations from two 2.5-meter telescopes. One is located at Apache Point, New Mexico, and the other at Las Campanas, Chile. Their location makes it possible to observe different regions of the sky and combine them in a single survey.
In total, DR20 contains more than three million spectra, corresponding in particular to about 1.5 million stars. About 500,000 galaxies and quasars are also covered. A quasar is the extremely bright nucleus of a galaxy, powered by matter falling toward a supermassive black hole.
This mass of data is not only used to count objects. The program devoted to the Milky Way, for example, tracks stars very far from the galactic disk. Some are located more than 65,000 light-years away. Their motion and chemical composition retain traces of the small galaxies absorbed by our own over the course of its history.
Another set concerns 49,000 white dwarfs, the very dense remains of stars comparable to the Sun after the end of their nuclear activity. More than 80% of these objects had never been observed before by SDSS. Their atmospheres can sometimes contain traces of materials from ancient planetary systems.
The release also includes observations coordinated with the eROSITA X-ray space telescope. Nearly 48,000 X-ray sources thus have a visible spectrum obtained by SDSS. These associations make it possible to more precisely identify active stars, binary systems where matter falls onto a compact object, and other energetic sources.
DR20 is already publicly available with its catalogs and consultation tools. SDSS is also preparing the DR21 and DR22 releases, which will incorporate new observations. Astronomers will therefore be able to compare this vast inventory with additional data as the SDSS-V survey progresses.
The tool is publicly accessible at https://dr20.sdss.org/lvmvis/