Astronomers Propose New Origin Theory for Mysterious ‘Little Red Dot’ Galaxies
A new study by Harvard astronomers has shed light on the enigmatic “little red dot” galaxies—compact, ruddy celestial bodies that populated the early universe. These galaxies, first revealed by the James Webb Space Telescope (JWST), may have formed in slowly spinning dark matter halos, allowing gas to funnel directly into their centers and ignite rapid star formation.
The research, conducted by astrophysicists Fabio Pacucci and Avi Loeb, suggests that these galaxies were born with minimal angular momentum, a condition that prevented them from expanding outward like typical spiral galaxies. Instead, the gas collapsed inward, creating dense, luminous cores that appear as red dots in JWST imagery.
Discovered in galaxies dating back 640 million to 1.5 billion years after the Big Bang, these little red dots are remarkably compact—emitting half their light from regions just 1,000 light-years across, a fraction of the Milky Way’s size. Their red hue is attributed to a combination of dust, gas, and ancient red giant stars, with their light further reddened by cosmic expansion over 12 billion years.
Two competing theories have attempted to explain their nature: one posits that they host supermassive black holes actively accreting gas, while the other suggests they are densely packed with billions of stars. However, both models face challenges—such as the absence of expected X-ray emissions in the black hole scenario, and the implausibly high stellar densities required by the latter.
Rather than resolving this debate, Pacucci and Loeb’s work focuses on the formation mechanism, proposing that the lack of spin in their dark matter halos is the key to their compact structure. “They are really, really remarkable,” Pacucci noted, emphasizing their potential role in understanding early galaxy evolution.
As astronomers continue to analyze JWST data, these little red dots may offer critical insights into how the first galaxies formed and evolved in the nascent universe.
