Map of supermassive black holes. Click for original.

The Sloan Digital Sky Survey (SDSS) has now released a new map of the universe, showing the location of more 200,000 suspected supermassive black holes, almost all of which are located at the center of galaxies, identified by matching the X-ray emissions detected by the eROSITA instrument on Spektr-RG orbiting space telescope with their optical spectra collected by Sloan.

This new dataset provides the tightest constraints to date on the rarest, most luminous quasars. The survey reveals more giant black holes early on and higher space densities of the most luminous AGN at high redshifts than previously expected. This reveals that rapidly growing giant black holes were surprisingly common in the early Universe. More “hidden” black holes have been uncovered,where traditional optical and UV sky surveys miss a substantial fraction of accreting black holes, particularly at lower luminosities and extreme distances.

Also, by calculating total accumulated black hole growth over time, researchers found that soft X-ray-selected black holes account for only a minority of total black hole mass in the local Universe. This implies that 70% to 90% of all supermassive black hole growth occurred behind heavy veils of dust and gas, or during phases where even X-rays were suppressed.

The real discoveries from this survey data will come later, as astronomers pour through it over the coming years.

It is not likely that this particular dataset will be expanded by Sloan in the near future. Because of Russia’s invasion of the Ukraine in 2022, the partnership with Russia on Spektr-RG ended in 2022. No data from the eROSITA instrument has been gathered since.