Astronomers have discovered that a strange dwarf galaxy hidden for years in our cosmic neighborhood looks like it belongs in the early universe, despite having formed more recently.
The tiny galaxy measuring just 1,200 light-years across earned the nickname 'Peekaboo' because it was hidden in the bright glare of a fast-moving foreground star and only emerged between 50 and 100 years ago.
The dwarf galaxy, bearing the official name HIPASS J1131–31, is located around 22 million light-years from Earth in the constellation of Hydra. Its strange appearance was confirmed using the Hubble Space Telescope after it showed up in observations from other space and ground-based telescopes.
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The galaxy's faux-ancient appearance comes from the fact that it has low abundances of elements that are heavier than hydrogen and helium, the universe's lightest and earliest-formed elements. Astronomers describe these heavier elements as 'metals' and are usually found in much more distant locations; thus, early galaxies that are typically described as 'extremely metal-poor.'
As such, HIPASS J1131–31 represents the closest example of a galaxy formed by processes that existed predominantly throughout the universe shortly after the Big Bang.
"Uncovering the Peekaboo Galaxy is like discovering a direct window into the past, allowing us to study its extreme environment and stars at a level of detail that is inaccessible in the distant, early universe," study co-author and Space Telescope Science Institute astronomer, Gagandeep Anand, said in a statement.
During the earliest era of the universe, almost everything in the cosmos was composed of hydrogen and helium. These light elements were formed shortly after the Big Bang when the universe had expanded and cooled enough to allow electrons and protons to bond and form the first atoms and thus the first chemical elements.
These elements formed the first stars, which during their lifetimes forged heavier elements. When this first generation of extremely metal-poor stars reached the end of their lives and exploded, they spread these heavy elements throughout the universe to become the building blocks of the next generation of stars.
As this process repeated throughout cosmic history, each subsequent generation of stars became more and more enriched with heavy elements and created the metal-rich universe that we see throughout our cosmic neighborhood today.
These heavier building blocks forged in earlier stars — particularly carbon, oxygen, iron, and calcium — would also become the foundational elements of life.
Though early and distant galaxies were by default metal-poor, other examples of extremely metal-poor galaxies have previously been discovered closer to the Milky Way, our galaxy.
Peekaboo stands out from these galaxies because it seems to lack an older stellar population of ancient and thus metal-poor stars. Additionally, at just around 20 light-years from Earth, Peekaboo is much closer than other young metal-poor galaxies which are twice as distant.
First discovered two decades ago by research co-author professor Bärbel Koribalski in data collected in the HI Parkes All Sky Survey, the dwarf galaxy HIPASS J1131–31 didn't immediately present itself as anything special to astronomers. It took observations in far-ultraviolet light by NASA's now-defunct space-based Galaxy Evolution Explorer (GALEX) mission to reveal Peekaboo's nature as a strange compact blue dwarf galaxy.
"At first we did not realize how special this little galaxy is," Koribalski said. "Now with combined data from the Hubble Space Telescope, the Southern African Large Telescope (SALT), and others, we know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever detected."
Hubble was able to resolve around 60 stars in the dwarf galaxy which all appear to be no older than a few billion years. Astronomers then used SALT to discover Peekaboo's metal-poor nature, revealing it as one of the youngest and least-chemically-enriched galaxies ever detected in the local universe.
As the local universe has had over 13 billion years to evolve, the metal-poor nature of Peekaboo marks it as extremely unusual and astronomers still have much to learn about this dwarf galaxy.
To improve the snapshot of HIPASS J1131–31 collected by the Hubble observations, which were part of the Every Known Nearby Galaxy Survey, astronomers will now use the James Webb Space Telescope to observe the galaxy alongside Hubble.
Hopefully, this will reveal more about its population of stars and how enriched with metals they are.
"Due to Peekaboo's proximity to us, we can conduct detailed observations, opening up possibilities of seeing an environment resembling the early universe in unprecedented detail," Anand concluded.
The team's research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
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