Webb Telescope Spots "Black Hole Star" 660 Million Years Post-Big Bang

Astronomers using the James Webb Space Telescope (JWST) have identified a peculiar object, cataloged as MoM-BH*-1, which existed approximately 660 million years after the Big Bang. Despite appearing as a mere red point in Webb's images, its spectrum reveals an energy output comparable to 100 billion Suns. Researchers propose that this immense energy is not generated by nuclear fusion, as in typical stars, but rather by a black hole actively accreting matter, hidden within a dense gaseous cocoon.

The object, first detected in the PRIMER extragalactic field, stood out due to its extreme redness. Webb's Near-Infrared Camera (NIRCam) captured it in specific filters, but it vanished at wavelengths shorter than two micrometers. Spectroscopic analysis by JWST's Near-Infrared Spectrograph (NIRSpec) provided crucial data, fixing its redshift at 7.7569. This redshift places the object in the early universe, about 660 million years after the Big Bang, according to the standard cosmological model.

An unusual spectral signature

What truly baffled scientists was the object's spectrum. A detailed analysis revealed an unusually strong "Balmer break," a feature related to hydrogen absorption around 364.6 nanometers. Standard stellar populations, even those rich in A-type stars, typically exhibit a Balmer break strength of around 3. MoM-BH*-1, however, showed a break strength of 7.7. Furthermore, the flux increased by more than 20 times from one Webb band to another, and the object displayed broad hydrogen-beta emission lines, suggesting rapid gas movement.

"The combination of broad emission, deep absorption, and the extreme break gave the researchers more than an unusual colour; it provided a set of physical constraints that a successful model had to reproduce," stated a report detailing the findings. The researchers explored nearly a million radiative-transfer models to explain these anomalies. Their leading hypothesis involves an active galactic nucleus, powered by a black hole, embedded within extremely dense, metal-poor gas. This gas, with a density around 10^11 particles per cubic centimeter and a column density near 10^25.8 particles per square centimeter, acts as a "gaseous photosphere."

This dense envelope is largely dust-free. Instead, the hydrogen gas itself absorbs and reprocesses short-wavelength radiation from the accreting black hole, effectively creating the star-like appearance and the extreme Balmer break. This process differs significantly from explanations involving ordinary dust reddening a quasar's spectrum. The findings align with emerging research suggesting that many "little red dots" observed in the early universe might be young black holes enveloped in dense, ionized cocoons. This interpretation offers a solution to several puzzles, including why these objects are often faint in X-rays and why they appear to imply rapid galaxy formation when treated as stars.

The immense energy output, described as roughly 100 billion Suns' worth of luminosity, refers to the total power radiated across all wavelengths, not the object's mass or size. Estimates for the black hole's mass itself, based on these early universe models, are uncertain but broadly range from one million to ten million solar masses. The authors caution that standard methods for estimating black hole mass from nearby galaxies might not apply accurately to these early, exotic objects.

While the "black hole star" model provides a compelling explanation, the researchers acknowledge that the internal geometry is not definitively proven. The model represents a simplification, and future observations with JWST, including longer-duration monitoring and deeper spectra at various wavelengths, will be crucial for testing the variability and behavior of the gaseous cocoon. If this interpretation holds, MoM-BH*-1 could represent a brief but critical phase in the evolution of early black holes, showcasing how a dense shroud can influence the observable characteristics of accretion processes in the nascent universe. The evidence is spectral, indicating a central high-energy source obscured by extremely dense and opaque gas that shapes the observable light.