Astronomers using NASA’s James Webb Space Telescope have identified GLIMPSE-17775, a “little red dotthat provides multiple lines of evidence supporting the
black hole star” (BH*) model. The object, located behind galaxy cluster Abell S1063, consists of a supermassive black hole encased in a dense cocoon of partially ionized gas.
The discovery of GLIMPSE-17775 marks a turning point in the effort to understand little red dots,
a mysterious population of compact, red objects first spotted by the James Webb Space Telescope (JWST) in 2022. While scientists have explored multiple explanations for these little red dots, including the black hole star scenario, the spectrum of GLIMPSE-17775 suggests a black hole that is enveloped in a dense gas cocoon.
The Spectral Evidence of GLIMPSE-17775
A research team led by Vasily Kokorev at the University of Texas at Austin obtained the deepest spectrum of a little red dot to date by analyzing GLIMPSE-17775. The data revealed more than 40 spectral lines, a level of detail previously unavailable for this class of object. According to NASA, these lines support the BH* scenario, where a supermassive black hole is enveloped in a dense, ionized cocoon of gas.
Vasily Kokorev, lead author of the study, believes that a portion of the scientific community is reaching a consensus that little red dots can be explained by black hole star models, though he notes that no previous little red dots had provided all the necessary evidence in one place.
The object is located at a cosmological redshift of 3.5, placing its existence approximately 1.8 billion years after the Big Bang. The high resolution of the spectrum was made possible by a combination of JWST’s infrared sensitivity and gravitational lensing. GLIMPSE-17775 sits behind the galaxy cluster Abell S1063, which acted as a natural magnifying glass, amplifying the signal.
Gravitational Lensing and Telescope Efficiency
The discovery was an incidental find. The primary objective of the observations of Abell S1063 was to search for Population III stars and faint galaxies. However, the dataset included the spectrum of GLIMPSE-17775, which the team then analyzed in detail.
The efficiency of the observation was significantly boosted by the alignment of the celestial bodies. While Webb spent 30 hours capturing the spectrum, the effect of gravitational lensing made the data equivalent to 80 hours of telescope time. This amplification allowed Kokorev’s team to identify the specific markers of the BH* model that had remained elusive in other little red dots.
The BH* Model and Cosmic Dawn
The black hole star
model addresses a puzzle in astrophysics regarding little red dots, which emerged about 600 million years after the Big Bang.
In the BH* scenario, the black hole is shrouded in a dense, gas-reddened cocoon. This cocoon likely absorbs X-ray emission, explaining why most little red dots are faint in X-rays. The gas shroud reprocesses the light emitted from near the black hole and produces the features seen in the spectrum, leading to the black hole star
designation.
The findings were published in The Astrophysical Journal.
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