Forget ‘little green men’ – it’s the ‘little red dots’ in the baby universe that caught the eye of the James Webb Space Telescope (JWST).
The strange red bodies, scientists say, hide stars that models predict are “too old” to have lived in the early cosmic ages, and black holes that are up to a thousand times larger than the supermassive black hole at the heart of the Milky Way. Scientists believe that these objects must have been born in a way unique to the early universe—a method that appears to have ceased in the cosmos after about 1 billion years of its existence.
The three small red dots are seen as they were when the universe was 600 million to 800 million years old. While this may seem like an extremely long time after the Big Bang, the fact that the universe is 13.8 billion years old means that it was no more than 5% of its current age when these objects existed.
By confirming the existence of these dots in the early universe, these JWST findings could challenge what we know about the evolution of galaxies and the supermassive black holes that sit at their hearts.
Related: The James Webb Space Telescope observes the never-before-seen behavior of stars in a distant nebula (video, photo)
A team led by Penn State University scientists saw these mysterious crimson cosmic oddities while probing the early universe with JWST’s Near Infrared Spectrograph (NIRSpec) instrument as part of the RUBIES survey.
“It’s very confusing,” team member Joel Leja, an assistant professor of astronomy and astrophysics at Penn State, said in a statement. “You can fit it uncomfortably into our current model of the universe, but only if we conjure up some exotic, insanely fast entity at the beginning of time.
“This is without a doubt the most unique and interesting collection of objects I have seen in my career.”
What’s behind the dots?
Scientists studied the intensity of different wavelengths of light emanating from the tiny red dots. This revealed signs that the stars are hundreds of millions of years old – much older than expected for stars at this early stage of the cosmos.
Scientists have also seen traces of supermassive black holes in regions of small red dots with masses equivalent to millions, sometimes even billions of suns. These black holes are 100 to 1000 times more massive than Sagittarius A* (Sgr A*), the supermassive black hole at the heart of the Milky Way, located just 26,000 light-years from Earth.
Both of these discoveries are not expected according to current models of cosmic evolution, galaxy growth or supermassive black hole formation. All these theories suggest that galaxies and supermassive black holes grow gradually – but this growth takes billions of years.
“We confirmed that they appear to be full of ancient stars – hundreds of millions of years old – in a universe that is only [600 million to 800 million years] old. It’s remarkable that these objects hold the record for the first signs of old starlight,” said lead researcher Bingjie Wang, a postdoctoral fellow at Penn State. “It was completely 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 very comfortably into those theories.”
The team first spotted the tiny red dots while using JWST in July. At the time, scientists immediately suspected that these objects were actually galaxies that existed about 13.5 billion years ago.
A deeper examination of the light spectra of these objects confirmed that they were galaxies that lived at the very dawn of time, and also revealed that “overgrown” supermassive black holes and impossibly “old” stars are driving the impressive light output of the red dots.
The team is not yet sure how much of the light from the tiny red dots comes from each of these sources. This means that these galaxies are either unexpectedly old and more massive than the Milky Way, having formed much earlier than the models predict, or they have a normal amount of mass, but somehow overmass black holes—empty spaces that are much more massive than a similar galaxy during the present epoch of the cosmos.
“Distinguishing between light from material falling into a black hole and light emitted from stars in these small, distant objects is challenging,” Wang said. “This inability to tell the difference in the current data set leaves plenty of room for interpretation of these interesting objects.”
This is no ordinary supermassive black hole!
Of course, all black holes have light-trapping boundaries called “event horizons,” meaning that however much light they contribute to the little red dots must come from the material surrounding them, rather than from within.
The enormous gravitational influence of black holes creates turbulent conditions in this material, which also feed the black hole over time, heating it up and causing it to glow brightly. Regions powered by supermassive black holes in this way are called “quasars” and the regions of their galaxies in which they reside are known as “active galactic nuclei (AGNs).
These newly found “red dot” black hole regions could be different from other quasars, even those JWST has already seen in the early universe. For example, black holes with red dots appear to produce much more ultraviolet light than expected. But the most shocking thing about these supermassive black holes remains how massive they look.
“Normally, supermassive black holes are paired with galaxies,” Leja said. “They grow up together and go through all their major life experiences together. But here we have a fully formed adult black hole living inside what should be a baby galaxy.”
“That doesn’t really make sense because these things are supposed to come together, or so we thought.
The red dot galaxies themselves are also surprising. They appear to be much smaller than other galaxies despite having nearly as many stars. This means that red dot galaxies appear to consist of 10 billion to 1 trillion stars crammed into a galaxy a few hundred light-years across with a volume 1,000 times smaller than the Milky Way.
To put this into context, if the Milky Way were shrunk to the size of one of these red dot galaxies, then the closest star to the Sun (Proxima Centauri, which is 4.2 light years away) would be in the Solar System. Additionally, the distance between Earth and the Milky Way’s supermassive black hole, Sgr A*, would shrink from 26,000 light-years to just 26 light-years. This would see it and its surroundings appear in the night sky above Earth.
“These early galaxies would have been so dense with stars — stars that must have formed in a way we’ve never seen, under conditions we’d never expect during a period we’d never expect to see,” Leja said. “And for whatever reason, the universe stopped producing objects like these after a few billion years. They’re unique to the early universe.”
The team intends to follow up on their findings with further observations of these puzzling little red dots to better understand the mysteries of the dots. This will involve obtaining deeper spectra by pointing JWST at red objects for longer periods of time to obtain the emission spectra of light associated with different elements. This could help reveal the contributions of ancient stars and supermassive black holes in galaxies.
“There’s another way we could make a breakthrough, and that’s just [having] right idea,” concluded Leja. “We have all these pieces of the puzzle and they only fit if you ignore the fact that some of them break. This problem is open to a touch of genius that has so far eluded us, all our collaborators, and the entire scientific community.
“Honestly, it’s exciting to have so much of this mystery to solve.
The team’s research was published June 26 in the Astrophysical Journal Letters.