Hundreds of 'little red dots' found in the early universe

Less than six months after beginning its science operations, the Webb Telescope (JWST) unveiled numerous red objects in the sky that puzzled scientists. These objects, initially dubbed “little red dots” (LRDs), appeared small but were abundant across the cosmos.

However, their exact nature, the reasons for their striking color, and their significance in understanding the early universe have left astronomers intrigued.

Little red dots and black holes

In a recent study, experts have compiled one of the largest samples of LRDs to date. Nearly all of these objects existed during the first 1.5 billion years after the Big Bang.

The findings are intriguing: a large fraction of these dots appear to harbor growing supermassive black holes.

“We’re confounded by this new population of objects that Webb has found. We don’t see analogs of them at lower redshifts, which is why we haven’t seen them prior to Webb,” said Dale Kocevski, lead author of the study and an astronomer at Colby College in Waterville, Maine.

“There’s a substantial amount of work being done to try to determine the nature of these little red dots and whether their light is dominated by accreting black holes.”

Discovery of the little red dots

The team of astronomers sifted through Webb’s data, compiled from multiple surveys, to analyze these peculiar objects.

The Cosmic Evolution Early Release Science (CEERS) survey, along with other major surveys like the JWST Advanced Deep Extragalactic Survey (JADES) and Next Generation Deep Extragalactic Exploratory Public (NGDEEP), provided a wealth of information.

Their work revealed that LRDs first emerged in large numbers around 600 million years after the Big Bang. Then, they underwent a rapid decline around 1.5 billion years after the Big Bang.

The images, such as the six Webb images in the CEERS survey, show these mysterious dots surrounded by fuzzy red halos, each containing a yellow-white core. The survey data provides a deeper understanding of the LRDs’ distribution and their link to cosmic history.

Early black hole growth

A significant discovery was the presence of rapidly orbiting gas, moving at speeds of up to 2 million miles per hour (1,000 km/s), around about 70% of the LRDs in the sample.

This is a sign of an accretion disk around a supermassive black hole. These findings suggest that many of the LRDs are in fact active galactic nuclei (AGN), where black holes are actively accreting matter.

“The most exciting thing for me is the redshift distributions. These really red, high-redshift sources basically stop existing at a certain point after the big bang,” explained Steven Finkelstein, a co-author of the study from the University of Texas at Austin.

“If they are growing black holes, and we think at least 70 percent of them are, this hints at an era of obscured black hole growth in the early universe.”

The universe isn’t broken, just evolving

When the little red dots were first discovered, some suggested that cosmology might be “broken” due to the unexpected size and rapid growth of these objects.

If the light from these dots came entirely from stars, it would imply that some galaxies had formed too quickly for existing models to explain. The team’s research, however, counters this.

The study supports the idea that much of the light from these objects comes from accreting black holes rather than stars. With fewer stars involved, the galaxies are likely smaller and more consistent with current cosmological theories.

“This is how you solve the universe-breaking problem,” said study co-author Anthony Taylor from the University of Texas at Austin.

New questions arise

Despite these breakthroughs, the nature of LRDs still raises many questions. One of the most pressing is why LRDs do not appear at lower redshifts. One possible explanation could be the process of inside-out growth.

As star formation spreads outward from the center of a galaxy, the gas feeding the accreting black hole may diminish, leading to less obscuration of the black hole. This process could cause the black hole to become bluer and lose its “red dot” status.

Another mystery is that LRDs do not emit much X-ray light, unlike most black holes at lower redshifts. This has led scientists to speculate that LRDs might be heavily obscured black holes, with X-ray photons trapped in dense gas regions.

“There’s always two or more potential ways to explain the confounding properties of little red dots. It’s a continuous exchange between models and observations, finding a balance between what aligns well between the two and what conflicts,” explained Kocevski.

Pushing the boundaries of space science

The team’s work has sparked a wave of new questions and possibilities, and further investigations are underway. Deep spectroscopic observations and mid-infrared property analysis of these objects will provide more clarity in the coming years.

These findings were presented at the 245th meeting of the American Astronomical Society and have been submitted for publication.

The James Webb Space Telescope continues to push the boundaries of space science, unveiling the mysteries of the universe. With its exceptional capabilities, Webb is helping to answer fundamental questions about the origins of the universe, the formation of galaxies, and the nature of black holes.

As the puzzle pieces slowly fall into place, the universe keeps revealing its secrets – one “little red dot” at a time.

The study is published in The Astrophysical Journal.

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