Three years ago, astronomers stumbled upon peculiar galaxies known informally as “little red dots.” A recent study suggests that these mysterious features might be young supermassive black holes hiding under a cloak of gas.
Using NASA’s $10 billion James Webb Space Telescope, researchers first identified these dots in late 2022. They emerged shortly after the Big Bang, about 1 billion years in, and started to vanish after 2 billion years. Currently, our universe is about 13.8 billion years old.
This discovery sparked a heated debate among scientists. Some proposed that the little red dots were not just star-rich galaxies but rather havens for supermassive black holes. The idea is that gas rushing toward these black holes could heat up, creating the bright light we observe. However, both hypotheses faced challenges. They were deemed too massive to have formed so early in cosmic history. Plus, supermassive black holes typically emit X-rays and radio waves, which haven’t been detected in these dots.
A recent study examined 12 of these ancient galaxies, some appearing while the universe was just 840 million years old. The results showed the dots were too compact and bright to simply be star clusters. Instead, the findings indicated that the light sources were as bright as more than 250 billion suns but crammed into a space less than a third of a light-year across—far smaller than an entire galaxy. This compact nature hints they might indeed be young supermassive black holes.
Research revealed that the light emitted from the little red dots bounced off electrons in dense gas clouds. These clouds act like cocoons, hiding the usual signals from black holes, such as X-rays and radio emissions. “These objects turned out to be supermassive black holes despite their disguise,” said Vadim Rusakov, the study’s lead author from the University of Manchester.
The study also estimated the gas swirling around these black holes was moving at around 670,000 miles per hour (1.08 million kilometers per hour). This led to the conclusion that these black holes likely hold a mass between 100,000 and 10 million times that of our sun—a much smaller size than previously thought. This discovery aligns more closely with expectations for early black holes.
Rusakov pointed out that this might be our first glimpse into the formative stages of supermassive black holes. He noted, “If we’re fortunate, little red dots may still hold clues about their origins—whether from smaller black holes or as larger entities formed from collapsing gas.” Understanding how these black holes came to be remains a significant question in astrophysics.
Recent statistics from a 2022 survey found that nearly 60% of astrophysicists consider the formation of supermassive black holes among the top unsolved mysteries in the field. As research continues, little red dots could provide valuable insights into the universe’s early days, making them a focal point for future studies.
The study’s findings appeared in the Jan. 15 issue of Nature.
