Webb discovers ancient galaxies that defy explanation

NASA‘S James Webb Space Telescope has revealed mysterious objects in the early universe that challenge current theories about galaxies and supermassive stars black hole evolution.

These objects contain old stars and massive black holes, much larger than expected, suggesting a rapid and unconventional form of early galaxy formation. The findings highlight significant discrepancies with existing models, and the unique properties of the objects point to a complex early cosmic history.

Breakthrough in the early universe

A recent discovery by NASA’s James Webb Space Telescope (JWST) confirms that luminous, very red objects previously observed in the early universe challenge existing ideas about the origin and evolution of galaxies and their supermassive black holes.

Led by researchers from Penn State and using the NIRSpec instrument on JWST as part of the RUBIES survey, the international team identified three enigmatic objects dating to 600-800 million years after the Big Banga time when the universe was only 5% of its current age. They announced the discovery on June 27 in the journal Astrophysical Journal Letters.

The scientists analyzed spectral measurements, or intensities of different wavelengths of light emitted by the objects. Their analysis found signatures of “old” stars, hundreds of millions of years old, much older than expected in a young universe.

Unexpected discoveries in galactic evolution

The researchers said they were also surprised to find traces of massive supermassive black holes in the same objects, which they estimate are 100 to 1,000 times more massive than the supermassive black hole in our own space. Milky WayNeither is expected in current models of galaxy growth and supermassive black hole formation, which assume that galaxies and their black holes grow together over billions of years of cosmic history.

“We’ve confirmed that these appear to be chock full of old stars — hundreds of millions of years old — in a universe that’s only 600-800 million years old. Remarkably, these objects hold the record for the earliest signatures of ancient starlight,” said Bingjie Wang, a postdoctoral researcher at Penn State and lead author of the paper. “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 fit comfortably into those theories.”

The researchers first spotted the massive objects in July 2022, when the first dataset from JWST was released. The team published a paper in Nature A few months later, the existence of the objects was announced.

Challenges in cosmic observation

At the time, the researchers suspected the objects were galaxies, but they conducted their analysis by measuring spectra to better understand the objects’ true distances and the sources producing their immense light.

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

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

Mysteries of Ancient Galactic Structures

The JWST is equipped with infrared sensing instruments that can detect light emitted by the oldest stars and galaxies. In essence, the telescope allows scientists to peer back in time about 13.5 billion years, near 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 could have emitted the light. In the case of these early objects, they have clear signatures of both supermassive black holes and ancient stars. However, Wang explained that it’s not yet clear how much of the observed light comes from each. This means that these could be early galaxies that are unexpectedly old and even more massive than our own Milky Way, and that formed much earlier than models predict. They could also be more normal-mass galaxies with “overmassive” black holes, which are about 100 to 1,000 times more massive than such a galaxy would be today.

“It’s challenging to distinguish between light from material falling into a black hole and light emitted by stars in these small, distant objects,” Wang said. “That inability to tell the difference in the current dataset leaves plenty of room for interpretation of these intriguing objects. Frankly, it’s exciting to have so much of this mystery to unravel.”

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

“Normally, supermassive black holes are paired with galaxies,” Leja said. “They grow up together and have all their important life experiences together. But here we have a fully formed adult black hole living in what should be a baby galaxy. That doesn’t really make sense, because these things should grow together, or so we thought.”

The researchers were also baffled by the incredibly small size of these systems, 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 — somewhere between 10 billion and 1 trillion stars — but they are contained in a volume 1,000 times smaller than the Milky Way.

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

“These early galaxies would be so full of stars — stars that would have formed in a way that we’ve never seen before, under conditions that we would never expect at a time when we would never expect them,” Leja said. “And for whatever reason, the universe stopped making objects like these after just a few billion years. They’re unique to the early universe.”

The researchers hope to make more observations, which they said could help explain some of the objects’ mysteries. They plan to take deeper spectra by pointing the telescope at the objects for longer periods of time, which will help tease apart emission from stars and the potential supermassive black hole by identifying the specific absorption signatures that would be present in each.

“There’s another way we can have a breakthrough, and that’s just the right idea,” Leja said. “We have all these pieces of the puzzle, and they only fit if we ignore the fact that some of them are going to break. This problem lends itself to a stroke of genius that has eluded us, all of our collaborators, and the entire scientific community.”

Reference: “RUBIES: Evolved Stellar Populations with Extended Formation Histories at z ∼ 7–8 in Candidate Massive Galaxies Identified with JWST/NIRSpec” by Bingjie Wang, 冰洁王, Joel Leja, Anna de Graaff, Gabriel B. Brammer, Andrea Weibel, Pieter van Dokkum, Josephine F. W. Baggen, Katherine A. Suess, Jenny E. Greene, Rachel Bezanson, Nikko J. Cleri, Michaela Hirschmann, Ivo Labbé, Jorryt Matthee, Ian McConachie, Rohan P. Naidu, Erica Nelson, Pascal A. Oesch, David J. Setton, and Christina C. Williams, June 26, 2024, The letters of the astrophysical journal.
DOI file: 10.3847/2041-8213/ad55f7

Wang and Leja received funding from NASA’s General Observers program. The research was also supported by the International Space Science Institute in Bern. The work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. Calculations for the research were performed on Penn State’s Institute for Computational and Data Sciences’ Roar supercomputer.

Other co-authors of the paper are Anna de Graaff of the Max Planck Institute for Astronomy in Germany; Gabriel Brammer of the Cosmic Dawn Center and the Niels Bohr Institute; Andrea Weibel and Pascal Oesch of the University of Geneva; Nikko Cleri, Michaela Hirschmann, Pieter van Dokkum and Rohan Naidu of Yale University; Ivo Labbé of Stanford University; Jorryt Matthee and Jenny Greene from Princeton University; Ian McConachie and Rachel Bezanson of the University of Pittsburgh; Josephine Baggen of Texas A&M University; Katherine Suess of the Observatoire de Sauverny in Switzerland; David Setton of the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology; Erica Nelson of the University of Colorado; Christina Williams of the U.S. National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory and the University of Arizona.