The Nancy Grace Roman Space Telescope, set to launch on August 30, 2026, will be able to detect supermassive black holes that existed up to 11 billion years ago. This is described in a new study published in The Astrophysical Journal.
Lighter black holes are hard to observe directly — they are faint. But sometimes such a hole shreds and consumes an entire star. This is called a tidal disruption event (TDE). The region around the hole brightens for a few weeks so intensely that it outshines an entire galaxy, then gradually fades.
Tidal disruptions are possible only for lighter supermassive holes — from 100,000 to 100 million solar masses. Those heavier than a billion solar masses swallow a star whole, with no flare.
Roman will observe in near-infrared. Light from distant TDEs is stretched to longer wavelengths by the expansion of the universe, so the telescope is well suited to catch events whose light traveled 8 to 11 billion years to reach us. In a year it should record about 100 such flares — distant but important ones. The ground-based Vera C. Rubin Observatory will see thousands to tens of thousands of TDEs, but only closer ones.
Counting tidal disruptions at different distances will help test two ideas about how supermassive holes formed. The "light seeds" theory starts them from remnants of massive stars, a few hundred solar masses. The "heavy seeds" theory has them born at once with a million solar masses through the direct collapse of a gas cloud.