Tiny bright objects discovered at the dawn of the universe puzzle scientists

A recent discovery by NASA’s James Webb Space Telescope (JWST) confirmed that luminous, very red objects previously detected in the early universe are turning conventional ideas about the formation and evolution of galaxies and their supermassive black holes on their head.

An international team led by researchers from Penn State University used the NIRSpec instrument on board JWST as part of the RUBIES survey to identify three mysterious objects in the early universe, about 600–800 million years after the Big Bang, when the universe was only 5% of its current age. They announced the discovery today, June 27, in Letters from astrophysical journals.

The team examined spectral measurements, or the intensity of different wavelengths of light emitted by the objects. Their analysis revealed signatures of “old” stars that are hundreds of millions of years old, much older than would be expected in a young universe.

The researchers said they were also surprised to find signatures of giant supermassive black holes in the same objects. They estimated these to be 100 to 1,000 times more massive than the supermassive black hole in our own Milky Way. Neither of these are expected in current models of galaxy growth and supermassive black hole formation, which assume that galaxies and their black holes coalesce over billions of years of cosmic history.

“We confirmed that these appear to be full of old stars – hundreds of millions of years old – in a universe that is only 600 to 800 million years old. Remarkably, these objects hold the record for the earliest signatures of ancient starlight,” said Bingjie Wang, a postdoctoral fellow at Pennsylvania State University and lead author of the study.

“It was totally unexpected to find old stars in a very young universe. The standard models of cosmology and galaxy formation have been incredibly successful, but these luminous objects don’t quite fit into those theories.”

The researchers first discovered the massive objects in July 2022, when the first data set was released by JWST. The team published a paper in Nature Several months later, the existence of the objects was announced.

The researchers suspected at the time that the objects were galaxies, but following their analysis they conducted spectra to better understand the actual distances of the objects and the sources of their immense light.

The researchers then used the new data to paint a clearer picture of what the galaxies looked like and what was happening inside them. Not only did the team confirm that the objects were indeed early galaxies, but they also found evidence of surprisingly large supermassive black holes and a surprisingly old population of stars.

“It’s very puzzling,” said Joel Leja, assistant professor of astronomy and astrophysics at Penn State and co-author of both papers. “You can fit this uncomfortably into our current model of the universe, but only if we conjure up some exotic, insanely rapid formation at the beginning of time. This is without a doubt the strangest and most interesting collection of objects I’ve seen in my career.”

The JWST is equipped with infrared sensors that can detect light emitted by the oldest stars and galaxies. Essentially, the telescope allows scientists to look back about 13.5 billion years, to the beginning of the universe as we know it, Leja said.

One challenge in analyzing ancient light is that it can be difficult to distinguish between the types of objects that might have emitted the light. These early objects show clear features of both supermassive black holes and ancient stars.

However, it is not yet clear how much of the observed light comes from each individual galaxy, Wang explained. This means they could be early galaxies that are unexpectedly old and more massive than our own Milky Way and that formed much earlier than models predict. Or they could be normal-mass galaxies with “supermassive” black holes that are about 100 to 1,000 times more massive than such a galaxy is today.

“Distinguishing between the light from matter falling into a black hole and the light emitted by stars in these tiny, distant objects is challenging,” Wang said. “The inability to tell the difference in the current dataset leaves a lot of room for interpretation of these fascinating objects. Frankly, it’s exciting that there is still so much of this mystery to be solved.”

Aside from their unexplained mass and age, they are also not normal supermassive black holes, if some of the light is actually coming from them. They produce far more ultraviolet photons than expected, and similar objects studied with other instruments lack the hallmark features of supermassive black holes, such as hot dust and bright X-rays. But perhaps most surprising, the researchers say, is how massive they appear to be.

“Usually, supermassive black holes are paired with galaxies,” Leja said. “They grow up together and go through all the major life experiences together. But here we have a fully formed, adult black hole living in what should be a baby galaxy. That doesn’t make sense, because these things should grow together, or at least that’s what we thought.”

The researchers were also amazed by the incredibly small size of these systems, measuring just a few hundred light-years across, about 1,000 times smaller than our own Milky Way. The stars are about as numerous as in our own Milky Way—with somewhere between 10 billion and 1 trillion stars—but packed into a volume 1,000 times smaller than the Milky Way.

Leja explained that if the Milky Way were compressed to the size of the galaxies found, the closest star would be almost in our solar system. The supermassive black hole at the center of the Milky Way, about 26,000 light-years away, would be only about 26 light-years from Earth and would be visible in the sky as a giant pillar of light.

“These early galaxies were so full of stars – stars that must have formed in ways we’ve never seen before, under conditions we never expected, and at a time when we never expected to see them,” Leja said. “And for whatever reason, after just a few billion years, the universe stopped forming such objects. They are unique in the early universe.”

The researchers hope to make further observations, which they believe could help to clarify some of the objects’ mysteries. They plan to capture deeper spectra by pointing the telescope at the objects for longer periods of time. This will help to untangle the emissions from stars and the potential supermassive black hole by identifying the specific absorption signatures that would be present in each.

“There is another way we could make a breakthrough, and this is exactly the right idea,” Leja said. “We have all these puzzle pieces, and they only fit together if we ignore the fact that some of them are breaking. This problem is amenable to a stroke of genius that has so far eluded us, all of our collaborators, and the entire scientific community.”