The James Webb Space Telescope has made a groundbreaking discovery, spotting a bizarre object just 660 million years after the Big Bang. This object, named MoM-BH*-1, appears as a red point in images but emits an astonishing amount of energy, equivalent to around 100 billion Suns. What makes this finding even more intriguing is the proposed explanation for its power source: an accreting black hole buried within a dense gas cocoon, rather than a conventional star powered by nuclear fusion.
The object's spectrum, analyzed using Webb's NIRCam and NIRSpec instruments, reveals a peculiar sequence of colors and a strong Balmer break, indicating a significant change in brightness. This break, caused by the absorption of photons by hydrogen atoms, is much stronger than what is typically observed in ordinary stars. The researchers found that the Balmer break strength was measured at 7.7, which is far beyond the expected limit for standard dust-free stellar populations.
The team's preferred model suggests that MoM-BH*-1 hosts an active galactic nucleus within metal-poor gas with extremely high density. This gas cocoon, with a hydrogen density of around 10^11 particles per cubic centimeter and a column density near 10^25.8 particles per square centimeter, reprocesses the radiation emitted by the accreting black hole, giving the object a star-like appearance. The black hole's accretion flow heats and emits radiation, which is then absorbed and re-emitted by the surrounding gas, creating a larger effective surface.
The term 'black hole star' is used to describe this configuration, but it's important to note that it refers to the object's appearance and radiative physics, not a star with a conventional fusion-burning core. The object's power output, estimated at around 10^45 ergs per second, is an order of magnitude higher than what would be expected from a star of similar mass.
The black hole mass is still uncertain, with estimates ranging from one million to ten million solar masses. The authors caution that standard relations derived from nearby active galaxies may not accurately represent these early sources. Webb did not directly observe the black hole due to its distance and the dense gas cocoon, but the spectral evidence strongly supports the presence of a central high-energy source and a highly dense, opaque gas environment.
This discovery adds a missing piece to the puzzle of 'little red dots,' a phenomenon observed by Webb in the early universe. These dots are compact and red in visible light, often associated with accreting black holes, but they tend to be faint in X-rays. The gas cocoon model can explain several of these dots' characteristics, including their red color, broad hydrogen lines, and faint X-ray emissions.
MoM-BH*-1 is particularly valuable because it appears to be a black hole star with minimal contribution from a bright host galaxy. The object is located near a young galaxy at the same redshift, but the two are distinct. By including the host galaxy's light, the team could reproduce the mixed appearance of more familiar little red dots. A similar extreme break has been observed in a lower-redshift source, further supporting the gas cocoon interpretation.
While the evidence strongly suggests a black hole star, the internal geometry remains uncertain. The authors acknowledge that their model is simplified, and various factors, such as accretion spectrum, gas shape, turbulence, and energy transport, can influence the results. Future observations, including time monitoring, deeper spectra, and longer-wavelength studies, will help test the validity of this interpretation.
If the black hole star interpretation is correct, it could explain a brief stage in the early universe where young black holes grew rapidly due to a dense gas cocoon. This cocoon can trap or redistribute accretion energy, allowing the black hole to grow faster than conventional radiation pressure would permit. As the cocoon thins, the black hole may reveal a more conventional active galactic nucleus or quasar.
This discovery highlights the James Webb Space Telescope's ability to isolate and study the buried phases of early universe objects. MoM-BH*-1 demonstrates that Webb can reveal the extraordinary head start a massive seed black hole may have acquired, addressing one of the most challenging timing problems in early-universe astronomy.
