The remarkable bright galaxies uncovered by the James Webb Space Telescope (JWST) may not be as brilliant as initially thought. These celestial bodies once posed a challenge to our cosmic understanding, implying they were home to supermassive black holes and an unexpected abundance of stars. However, new insights suggest these galaxies may harbor “baby” black holes.

During its initial years surveying the early Universe, JWST serendipitously discovered numerous bright and red galaxies, referred to as “little red dots” (LRDs).

The light emitted by these galaxies indicates the presence of far more mass than previously recognized in any other galaxy. They exhibit star densities that challenge existing models or host black holes larger than expected considering the size of their parent galaxies.

Both scenarios would necessitate a substantial overhaul of our galaxy formation and black hole growth theories in the early Universe.

Initial assumptions posited that the red hue of LRDs was due to copious dust surrounding the black holes or stars. This notion has come under scrutiny, as researchers find little evidence of dust in these extraordinary galaxies.

Jenny Green, a researcher at Princeton University, posits that this discovery warrants a reevaluation of LRD characteristics. “We were confident that if red coloration was due to dust, we’d detect dust emissions. However, we found none,” Green stated. “This suggests our initial assumption about their dust content was flawed.”

Previous analyses gauged the total brightness of the LRDs by assessing specific wavelengths of light linked to hydrogen, calibrated against a model of how dust impacts this light.

In their recent study, Green and her team measured the total light output from two LRD galaxies across various light frequencies, including X-rays and infrared. They discovered that, except for visible light, these galaxies emitted significantly less light than the typical galaxy—implying that LRDs are at least ten times dimmer than earlier estimates. This revelation holds critical implications for the nature of black holes within LRDs.

“If the emitted light is substantially less than we’ve believed, the mass of the black holes is likely much more modest,” Green remarked. “This reduces the tensions that have perplexed us since the black holes no longer need to be exceedingly massive or possess substantial mass initially.”

The new emission patterns imply the black holes may harbor less mass compared to standard black holes. Rohan Naidu from the Massachusetts Institute of Technology describes them as “baby black holes.” He further noted these findings align with the emerging perspective that LRD black holes could be categorized as black hole stars—a unique type of black hole encased in gas.

“In a typical black hole, what we observe is merely a fraction of the total energy emitted by the system. However, we should reconsider the little red dots as bulging black hole stars,” Naidu explained. “Most of their energy appears to be emitted at wavelengths we can detect, suggesting that what we see accurately reflects their output.”

Conversely, Roberto Maiorino from the University of Cambridge emphasizes that one cannot definitively ascertain the black hole’s mass within an LRD, as the emitted light reveals its growth rate rather than its total mass.

Green asserts that the notion of baby black holes holds merit. “If the photon count is significantly lower,” she noted, “this indicates a downward shift in the entire mass scale. On average, they possess lesser masses than previously assumed when we incorrectly categorized them as regular accreting black holes enshrouded in dust.”

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