‘Tiny Red Spots’ in the Early Universe Could Be Black Holes Pushing Their Limits
The James Webb Space Telescope has provided an unprecedented glimpse into the earliest stages of galaxy formation. Alongside these discoveries, it has also unveiled a few unexpected phenomena—among them, the appearance of small, highly redshifted objects known as “little red dots” (LRDs).
While their exact nature remains uncertain, a new study offers a compelling explanation. One key observation is that their spectra are significantly broadened by motional Doppler effects, indicating that gas is orbiting at astonishing speeds—over 1,000 kilometers per second—around a central region. This suggests the presence of a supermassive black hole, a defining characteristic of active galactic nuclei (AGN).
However, the AGN model presents some challenges. Unlike typical AGNs, LRDs exhibit an unusually flat infrared spectrum and emit very little in the X-ray and radio ranges. To investigate further, researchers analyzed high-resolution spectra from 12 LRDs observed by JWST and compared the data to supermassive black hole models.
The models assumed a rapidly spinning accretion disk surrounded by a dense, ionized galactic cloud. This would absorb most X-ray and radio emissions, explaining their absence in the data.
Black Holes in LRDs May Be Growing at the Maximum Possible Rate
If this shroud effectively blocks X-rays and radio waves, the black hole must be generating energy at an extraordinary rate to maintain the LRDs’ brightness in red and infrared wavelengths. Observations suggest that these black holes are accreting mass at nearly the Eddington Limit—the theoretical maximum at which a black hole can accumulate matter. Beyond this limit, the intense radiation would overpower gravitational forces, preventing further accretion.
This paints a picture of LRDs as newly formed supermassive black holes in the early stages of rapid growth. Their estimated masses, ranging between 10,000 and 1,000,000 solar masses, are significantly smaller than fully developed supermassive black holes, further supporting this idea.
Moreover, this model helps explain why LRDs are not observed at lower redshifts. As they accumulate matter at the Eddington Limit, they eventually clear away the ionized clouds surrounding them. Once this happens, they begin to resemble the more familiar active galactic nuclei seen throughout the cosmos.
Read Original Article: Science Alert
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