Since its deployment in late 2021, the James Webb Space Telescope (JWST) has been unveiling glimpses into the earliest stages of the universe. Its data has prompted astrophysicists to push back their estimates for when galaxies first began forming. Most recently, the telescope has captured images of blue ultraviolet light from a time period previously thought to be devoid of stars.

These latest findings include nine new sources of light, six of which are at a redshift of 17 and three at a redshift of 25, dating back to when the universe was merely 200 million to 100 million years old. “This discovery goes deeper by a significant margin than any other we’ve obtained throughout the JWST mission,” explains Pablo Pérez-González, an astrophysicist at the Center for Astrobiology in Madrid and lead author of a study now accepted for publication in the Astrophysical Journal.

Pérez-González notes, “If these observations are correct, it suggests that the universe was far more active within its first 200 million years than we previously believed.”

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If these observations hold true, the newly discovered objects not only extend the timeline of galaxy formation but also challenge the existing cosmological models about the dawn of star formation. As a result, another team of astronomers has suggested a theory to explain these enigmatic findings. They propose that “primordial black holes,” formed shortly after the big bang, might have illuminated the universe before the formation of the first stars. This hypothesis is detailed in a study accepted for publication in Astronomy & Astrophysics.

“If the light and its intensity cannot be accounted for by stars, then another phenomenon must be responsible,” remarks Andrea Ferrara, a co-author of the hypothesis and an astrophysicist at the Superior Normal School in Pisa, Italy. “This could likely be a primordial black hole.”

In essence, it’s conceivable that the universe’s initial luminous bodies were not stars, but rather voracious black holes that came into existence seconds after the big bang.

Challenges with Ancient Galaxies

The more distant the celestial object, the further back in time we are observing. Due to the universe’s expansion, light from these far-off objects stretches to the infrared end of the light spectrum, a phenomenon known as redshift. A higher redshift thus signifies a glimpse further back in time.

Prior to JWST, the highest redshift galaxy confirmed by astronomers was at redshift 9, corresponding to a universe aged between 600 million and 500 million years. Initially, JWST’s mission involved verifying galaxies previously spotted by the Hubble Space Telescope (HST).

Factors such as the distribution of dark matter and conditions necessary for star formation help astrophysicists estimate the timeline for galaxy development in the early universe. However, since mid-2022, as JWST started identifying galaxy candidates from even earlier periods, astronomers began questioning their earlier understanding.

“JWST is discovering too many massive galaxies too soon in the cosmic timeline,” states Allison Kirkpatrick, an astrophysicist specializing in galaxy evolution at the University of Kansas, not involved in the new research.

To date, the oldest confirmed galaxies observed by JWST are at redshift 14, corresponding to a universe approximately 300 million years old. “The goal now was to push beyond that, to redshift 15 and above,” says Pérez-González.

His team’s identification of nine new objects at higher redshifts requires further verification. To confirm the distance of these objects, astronomers must analyze their light at specific wavelengths through a process called spectroscopy.

Utilizing data from JWST’s Near Infrared Camera (NIRCam) across two imaging surveys, Pérez-González and his colleagues selected these new galaxy candidates from a pool of over 80,000. After more than 100 hours of filtering and imaging a section of the sky, they were able to pinpoint galaxies varying in brightness and select the most promising ones for further study. This broad approach reduces bias before focusing on the most intriguing distant objects.

The candidate galaxies identified emit a bright blue light in the ultraviolet spectrum—suggestive of the light expected from massive early stars. However, according to galaxy evolution models, forming stars at such an early stage in the universe’s history seems highly unlikely. The models suggest there wouldn’t have been enough time for gas to cool and clump together into clouds dense enough to collapse under gravity into stars.

“Galaxies can’t form quickly because the gas in the early universe is too hot, which prevents it from collapsing into galaxies and stars,” explains Kirkpatrick. “Instead, the structure of dark matter develops first, and its intense gravity pulls gas towards the center to form the earliest stars and galaxies. This process takes more than 100 million years.”

Primordial Black Holes as Early Light Sources

To address this issue, Ferrara and his team suggest that primordial black holes—unique black holes theorized to have formed within seconds after the big bang—were consuming gas in the early universe. This activity could have emitted light, now observable with JWST, from a period preceding star formation. Interestingly, the first significant light sources in the early universe might have been black holes, not stars.

Typically, black holes are formed when massive stars exhaust their fuel and collapse or when a large gas cloud collapses directly into a black hole, skipping the star phase. Primordial black holes, however, are thought to be different. “We propose that primordial black holes formed within one to five seconds after the big bang,” Ferrara explains. “They have essentially been around since the beginning.”

Initially, these black holes would have been minuscule, “no larger than an atom,” according to Kirkpatrick. In the first second of the universe’s existence, a rapid period of expansion known as inflation caused space to expand by 35 orders of magnitude, akin to stretching an atom to the size of the solar system. “This rapid expansion could have led to the creation of very small black holes,” Kirkpatrick notes. These black holes may have grown to 10,000 times the mass of the sun after 100 million years, the team suspects.

When gas approaches a black hole, it heats up to extremely high temperatures, causing the superheated matter to emit light. From afar, this might resemble the glow of a star. Thus, distinguishing between light from primordial black holes and stars based on current imagery is challenging. However, other indicators might help.

One method to determine if these light sources are primordial black holes or first-generation stars is to examine the sizes of galaxies. If they appear more point-like, then the primordial black hole theory might be more plausible because a massive black hole is still relatively small compared to an entire galaxy. However, if the light sources are more diffuse and spread out, they are likely to be stars.

“We’ve measured the sizes, and some of the candidates appear point-like based on our current data, but not all of them. Some are more extended. So maybe 30 percent of them could be what a primordial black hole would resemble,” Pérez-González explains.

At this point, the data are far from conclusive. Since primordial black holes are hypothesized to have existed since the dawn of the universe, they should also leave imprints in the cosmic microwave background (CMB), a relic of the universe from 380,000 years after the big bang. “Our current images of the CMB are still slightly too coarse to detect the detailed structures that primordial black holes might have introduced,” Ferrara states.

For now, a definitive answer remains elusive. Nonetheless, the potential existence of primordial black holes could help explain another cosmic mystery: the presence of supermassive black holes at the centers of early galaxies. “We still lack a proven explanation for how the initial seeds of supermassive black holes formed, and this could be one possible pathway. It might help resolve some discrepancies between JWST observations and existing cosmological models,” Kirkpatrick suggests.

“These observations are challenging, and we are pushing the JWST to its limits,” Ferrara notes. “We must proceed with caution, as these galaxies could ultimately be contaminants, lower-redshift galaxies, or something else entirely.” Whether these enigmatic black beacons outshone the earliest stars remains a question that may soon be answered.