Science & Technology (Commonwealth Union) – As data sets continue to shape the world as we know it, fast tracked advanced by technology we continue to see greater information to advance astronomy along with other science.
The Sloan Digital Sky Survey (SDSS) has unveiled Data Release 20 (DR20), representing a major milestone in research on accreting supermassive black holes (SMBHs). As part of the survey’s fifth phase, SDSS-V, the Black Hole Mapper (BHM) initiative is offering new levels of understanding into the size, evolution, and underlying processes of quasars and active galactic nuclei (AGN throughout the history of the universe.
DR20 introduces the first optical BOSS spectroscopic observations collected from the Southern Hemisphere at the Las Campanas Observatory (LCO) in Chile, while also adding a significant volume of new data from the Apache Point Observatory (APO) in New Mexico. The release includes more than 3.3 million optical spectra covering roughly 500,000 galaxies and 1.5 million stars, creating a powerful resource for multi-wavelength astronomy projects that combine ground-based observations with data from space telescopes.
One of the major achievements of the Black Hole Mapper program in DR20 is SPIDERS (SPectroscopic IDentification of ERosita Sources). This project combines SDSS optical spectroscopy with X-ray observations from the eROSITA space mission to identify sources in the X-ray sky and determine their precise cosmic distances through redshift measurements. SPIDERS provides detailed spectroscopic follow-up for around 200,000 X-ray sources, making it the largest and most consistent survey of its kind ever conducted.
Although SPIDERS detects a wide range of powerful X-ray sources, including galaxy clusters and highly energetic stellar systems, most of these intense cosmic emitters are powered by actively feeding supermassive black holes. These objects, known as active galactic nuclei (AGN) or quasars, provide crucial clues about how black holes grow and influence their surrounding galaxies.
X-ray radiation serves as a powerful window into the hearts of these enormous black holes, enabling astronomers to investigate their central regions and study the extremely hot X-ray coronae that surround them. By analyzing the “X-ray luminosity function”—a measurement that tracks the number of black holes at different energy outputs and throughout different stages of cosmic history—researchers can follow the evolution and growth of supermassive black holes from the nearby Universe to galaxies at redshifts approaching six, reaching back to the era known as the Universe’s “cosmic dawn.”
Combining the extensive sky coverage provided by SDSS and eROSITA has produced the most precise measurements yet of the Universe’s rarest and brightest quasars. The findings indicate that more massive black holes existed in the early Universe and that highly luminous active galactic nuclei (AGN) were more abundant at great distances than earlier models had predicted. These results suggest that rapidly expanding supermassive black holes were far more widespread in the early stages of cosmic evolution than previously believed.
The survey has also exposed a population of previously undetected or “hidden” black holes, showing that conventional optical and ultraviolet surveys overlook many actively feeding black holes, especially those with lower brightness levels or located at extreme distances. Furthermore, by estimating the total amount of black hole growth accumulated over cosmic time, scientists determined that black holes identified through soft X-ray observations represent only a small share of the overall mass growth seen in today’s Universe. The research suggests that between 70% and 90% of supermassive black hole growth took place while these objects were obscured by dense layers of gas and dust, or during periods when even X-ray emissions were heavily reduced.
“This release marks the culmination of more than a decade of joint planning and scientific exchange between the German eROSITA Consortium and the Sloan Digital Sky Survey”, explained Dr. Andrea Merloni, eROSITA Principal Investigator and BHM Survey Scientist. “With DR20, we demonstrate not only that combining the X-ray and optical spectroscopic data opens up new and original scientific perspectives in astrophysics, but also that large, international and diverse collaborations can effectively work together for years towards a common goal.”
