Forget “little green men”; it was the “little red dots” in the infant universe that caught the eye of the James Webb Space Telescope (JWST).
Scientists say the strange red objects hide stars that models suggest are “too old” to have existed in early cosmic times, as well as black holes thousands of times more massive than the supermassive black hole at the heart of the Milky Way. Scientists believe these objects must have been born in a way unique to the early universe – a method that appears to have ended in the cosmos after about 1 billion years of existence.
The three small red dots are seen as the universe was between 600 million and 800 million years old. While that may seem like a long time after the Big Bang, the fact that the universe is 13.8 billion years old means that when these objects existed, the universe was no more than 5% of its current age.
By confirming the existence of these dots in the early universe, the JWST findings could challenge what we know about the evolution of galaxies and the supermassive black holes at their centers.
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The team, led by scientists from Penn State University, spotted these mysterious red 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 this uncomfortably into our current model of the universe, but only if we invoke an exotic, crazy-fast formation at the beginning of time.
“This is the strangest and most interesting set of objects I have ever seen in my career.”
What’s behind the dots?
The researchers studied the intensity of different wavelengths of light coming from the tiny red dots, which revealed signs that the stars were hundreds of millions of years old – much older than expected for stars at this early stage in the cosmos.
The researchers also saw traces of supermassive black holes with masses equal to millions, sometimes even billions, of suns in the regions of the small red dots. These black holes are 100 to 1,000 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.
Neither of these discoveries are expected under current models of cosmic evolution, galaxy growth, or supermassive black hole formation. All of these theories suggest that galaxies and supermassive black holes are growing simultaneously — but this growth takes billions of years.
“We confirmed that these are full of old stars, in a universe that formed only a few million years ago. [600 million to 800 million years] “They are old. Surprisingly, these objects record the earliest traces of ancient starlight,” said study leader Bingjie Wang, a postdoctoral researcher at Penn State. “Finding old stars in a very young universe was completely unexpected. Standard models of cosmology and galaxy formation have been incredibly successful, but these bright objects don’t fit those theories very well.”
The team first noticed the tiny red dots while using JWST in July. At the time, researchers immediately suspected that the objects were actually galaxies that existed about 13.5 billion years ago.
A deeper look at the light spectra of these objects confirmed that they were galaxies that lived at the dawn of time, and also revealed that “overgrown” supermassive black holes and impossibly “old” stars were powering the red spots’ impressive light output.
The team isn’t 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, forming much earlier than models predict, or that they have normal amounts of mass but somehow contain extremely large black holes — voids much larger than a similar galaxy in the current era of the cosmos would have.
“It is difficult to distinguish between light from matter falling into the black hole and light emitted from stars in these small, distant objects,” Wang said. “The inability to distinguish the difference in the current dataset leaves plenty of room for interpretation of these intriguing objects.”
This is no ordinary supermassive black hole!
Of course, all black holes have light-trapping boundaries called “event horizons,” which means that whatever light they send to the little red dots must come from the matter surrounding them, not from within them.
The immense gravitational pull of black holes creates turbulent conditions in this matter, which over time feed the black hole, heating it up and causing it to shine brightly. Regions powered by supermassive black holes in this way are called “quasars”, and the regions of galaxies where they are located are called “active galactic nuclei (AGNs)”.
These newly found “red spot” black hole regions may even be different from the quasars that JWST has seen in the early universe. For example, red spot black holes appear to produce much more ultraviolet light than expected. Still, the most shocking thing about these supermassive black holes remains how massive they appear to be.
“Normally, supermassive black holes are paired with galaxies,” Leja said. “They grow up together and experience all the 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 make sense because these things are supposed to grow together, or at least that’s what we thought.”
Red dot galaxies themselves are also surprising. They appear to be much smaller than other galaxies, despite having almost the same number of stars. This means that red dot galaxies are made up of between 10 billion and 1 trillion stars, packed into a galaxy a few hundred light-years across, 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, 4.2 light-years away) would be within the solar system. Also, 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 make it and its surroundings visible in the night sky above Earth.
“These early galaxies would have been very dense with stars — stars that had formed in a way we’d never seen before, under conditions we’d never expected at a time we’d never expect to see,” Leja said. “And for whatever reason, the universe stopped producing such objects after just a few billion years. They’re unique to the early universe.”
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The team aims to follow up their findings with more observations to better understand the mysteries of these puzzling little red dots. This will involve pointing JWST at red objects for longer periods of time to obtain deeper spectra, to obtain emission spectra of light associated with various elements. This could help unravel the contributions of ancient stars and supermassive black holes in galaxies.
“There is another way we can make a breakthrough and that is just [having] “It’s the right idea,” Leja concluded. “We have all these puzzle pieces, and they fit together only if we ignore the fact that some of them are broken. This problem is a stroke of genius that has eluded us, all our collaborators, and the entire scientific community until now.
“It’s honestly exciting how much of this mystery is still waiting to be solved.”
The team’s research was published June 26 in the Astrophysical Journal Letters.