Scientists are striving to understand how supermassive black holes-those enormous gravitational sinks found at the centers of galaxies-form and evolve over cosmic time. A key to unlocking this mystery lies in detecting these black holes as they existed in the distant past, billions of years ago. New research indicates that NASA's upcoming Nancy Grace Roman Space Telescope, scheduled for launch on August 30, 2026, will significantly advance this pursuit by detecting ancient supermassive black holes up to 11 billion years old.
Supermassive black holes are typically studied by observing the luminous matter swirling around them in an accretion disk. This matter heats up and emits light before ultimately being consumed by the black hole. However, lighter supermassive black holes-those with masses ranging from about 100,000 to 100 million times that of the Sun-are difficult to observe because their accretion disks tend to be less luminous due to lower accretion rates. Occasionally, these lighter black holes reveal themselves through dramatic events known as tidal disruption events (TDEs). In a TDE, a star ventures too close to the black hole and is torn apart by its intense gravitational forces. This process causes a sudden and intense flare of light that can outshine the entire host galaxy for weeks, providing a unique beacon that signals the black hole's presence.
The Nancy Grace Roman Space Telescope (referred to as Roman) is poised to revolutionize the study of these transient phenomena. According to lead author Mitchell Karmen, a graduate student at Johns Hopkins University and a National Science Foundation Graduate Research Fellow, Roman's high sensitivity will enable astronomers to detect multiple TDEs occurring at greater distances and earlier epochs than ever before. This advancement will allow researchers to characterize the population of early supermassive black holes and track how they grow and evolve over billions of years-offering vital clues to their ultimate origins.
Roman's capability to detect TDEs arises largely from one of its primary observation programs, the High-Latitude Time-Domain Survey. This survey will repeatedly scan approximately 18 square degrees of the sky-an area equivalent to about 90 full moons-at regular intervals. By revisiting the same regions multiple times, astronomers can identify transient events such as TDEs as they brighten and fade.
TDEs are phenomena that mainly occur around lighter supermassive black holes. Very massive black holes, those exceeding a billion solar masses, tend to swallow stars whole without producing the bright flares typical of TDEs. In contrast, lighter black holes can rip stars apart, creating a luminous flare that brightens over a few weeks before gradually fading away. Understanding the rate at which TDEs occur over cosmic time is crucial in tracing the growth and properties of these black holes.
Previous studies predicted that the rate of TDEs would decline with increasing distance from Earth, as the earliest black holes were thought to be too small or faint to produce observable TDEs. However, the new research led by Karmen incorporates a more detailed model that considers how various factors evolve over time. These factors include the frequency of galaxy mergers-which can trigger black hole growth-the density and number of stars in galactic cores, and how tightly packed these stars are. By integrating these elements, the researchers generated predictions for how many TDEs Roman and other observatories might detect.
In addition to Roman, other major observatories such as the ground-based Vera C. Rubin Observatory and NASA's James Webb Space Telescope (JWST) will contribute to observing TDEs. The Rubin Observatory, with its wide field of view and ability to scan large portions of the sky in visible light, is expected to detect thousands to tens of thousands of TDEs annually.
However, its observations will primarily capture relatively nearby TDEs because visible light from more distant events is redshifted into the infrared. Roman, optimized for near-infrared wavelengths, is uniquely suited to detect TDEs whose light has traveled between 8 and 11 billion years, corresponding to the universe's earlier epochs. Although Roman will detect fewer TDEs per year-up to about 100-it will observe events from a much earlier cosmic era, particularly around "cosmic noon," the time approximately 11 to 12 billion years ago when star formation in the universe peaked.
This capability is significant because by measuring the number of TDEs as a function of redshift (a proxy for distance and cosmic time), astronomers can impose meaningful constraints on the population of supermassive black holes, especially those with masses near a million times that of the Sun. Co-author Suvi Gezari, an associate professor of astronomy at the University of Maryland, emphasizes that Roman's observations will transform our understanding by probing these events at greater distances and across a wide span of cosmic history, thereby revealing how TDE rates-and by extension, black hole populations-evolve over time.
One of the enduring puzzles in astrophysics is how gargantuan black holes existed so early in the universe's history. Observations have revealed supermassive black holes that had already reached enormous sizes less than a billion years after the Big Bang, challenging existing models of black hole growth. Since such colossal black holes must have started out smaller, understanding their initial masses and growth mechanisms is critical.
Two main theories attempt to explain the origins of supermassive black holes. The first, known as the "light seeds" model, proposes that black holes form from the deaths of massive stars, producing initial black holes weighing up to a few hundred times the mass of the Sun. These seed black holes then grow by merging with others and by rapidly accreting surrounding gas. This model implies that nearly every young galaxy should host a massive black hole at its center.
The second theory, called the "heavy seeds" model, suggests that some black holes form directly with much larger masses-up to a million solar masses-through processes such as the direct collapse of massive gas clouds. This scenario would be less common, resulting in fewer supermassive black holes in early galaxies.
TDEs provide a unique observational tool to test these theories because they preferentially occur around lighter supermassive black holes. By studying the frequency and distribution of TDEs over cosmic time, astronomers can distinguish between the light and heavy seed scenarios. As Karmen explains, analyzing TDEs helps probe the population of lighter supermassive black holes, thereby discriminating between models of black hole formation.
Ultimately, the data collected by Roman will allow researchers to track how global processes-like galaxy mergers and star formation-impact black hole populations throughout the universe's history. Once Roman and Rubin begin their regular science operations, astronomers look forward to comparing actual observations with current predictions, refining their understanding of black hole growth.
As Gezari notes, just as the James Webb Space Telescope has transformed our view of distant galaxies, Roman is expected to revolutionize our knowledge of transient phenomena at high redshifts, including tidal disruption events.
The Nancy Grace Roman Space Telescope is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, with contributions from NASA's Jet Propulsion Laboratory in California, Caltech/IPAC, the Space Telescope Science Institute, and a science team from various institutions. Industrial partners include BAE Systems, L3Harris Technologies, and Teledyne Scientific & Imaging.
In summary, Roman's upcoming mission will enable astronomers to peer back billions of years to observe the dynamic interactions between stars and supermassive black holes. By detecting and characterizing tidal disruption events in the early universe, it will provide unprecedented insight into the origins, growth, and evolution of the most massive black holes, shedding light on some of the most fundamental questions in astrophysics.