Astronomers have discovered that a strange dwarf galaxy hidden for years in our cosmic neighborhood appears to belong to the early universe, even though it formed quite recently.
The small galaxy, only 1,200 light-years in diameter, earned the nickname “Pekkaboo” because it was hidden in the bright glow of a fast-moving foreground star and only appeared about 50 to 100 years ago.
The dwarf galaxy, officially named HIPASS J1131–31, is located about 22 million light-years from Earth in the constellation Hydra. Its strange appearance was confirmed with the Hubble Space Telescope after it appeared in observations from other space and ground-based telescopes.
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The galaxy’s pseudo-old appearance comes from the fact that it has a low abundance of elements heavier than hydrogen and helium, the lightest and oldest-forming elements of the universe. Astronomers call these heavier elements “metals” and they are usually found much further away; Thus, early galaxies that are commonly described as “extremely poor in minerals”.
As such, HIPASS J1131–31 represents the earliest example of a galaxy formed by processes that were present mostly 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 harsh environment and stars at a level of detail unattainable in the distant, distant universe,” said study co-author and astronomer at the Space Telescope Institute, Jagandip. Anand V.A statement (Opens in a new tab).
During the early universe, almost everything in the universe was made up of hydrogen and helium (Opens in a new tab). These light elements formed shortly after the Big Bang when the universe 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 lifetime formed heavier elements. When this very poor first generation of stars reached the end of their lives and exploded, they spread these heavy elements throughout the universe to become the building blocks for the next generation of stars.
As this process repeated throughout cosmic history, each subsequent generation of stars became richer in heavy elements and created the metal-rich universe we see throughout our cosmic neighborhood today.
These heavier building blocks that were forged in earlier stars—particularly carbon, oxygen, iron, and calcium—will also become the building blocks for life.
Although early and distant galaxies were hypothetically poor in metal, other examples of very poor metal galaxies have been discovered previously near our own Milky Way.
Peekaboo stands out from these galaxies because it apparently lacks an older star population and is therefore metal-poor. Additionally, at about 20 light-years from Earth, Peekaboo is much closer than other young, mineral-poor galaxies twice as far away.
The dwarf galaxy HIPASS J1131–31 was first discovered two decades ago by research co-author Professor Bärbel Koribalski in data collected in the HI Parkes All Sky Survey, and it didn’t immediately present itself as something special to astronomers. It took observations in far ultraviolet light by NASA’s now-defunct Galaxy Evolution Explorer (GALEX) mission to reveal the nature of Peekaboo as a strange compact blue dwarf galaxy.
“At first we didn’t realize how special this little galaxy is,” Koripalski said. “Now with data gathered from the Hubble Space Telescope, the South African Large Telescope (SALT), and others, we know that the Peekaboo Galaxy is one of the most mineral-poor galaxies ever discovered.”
Hubble was able to resolve approximately 60 stars in the dwarf galaxy that do not appear to be more than a few billion years old. Astronomers then used SALT to discover the metal-poor nature of Peekaboo, revealing it as one of the smallest and least chemically rich galaxies ever discovered in the local universe.
Since the local universe has more than 13 billion years to evolve, Peekaboo’s mineral-poor nature makes it very unusual and astronomers still have a lot to learn about this dwarf galaxy.
To improve on the snapshot of HIPASS J1131–31 collected by the Hubble observations, which was part of a survey of every known nearby galaxy, astronomers will now use the James Webb Space Telescope to observe the galaxy alongside Hubble.
Hopefully, this will reveal more about how many stars there are and how rich in metals they are.
“Because peekaboo is so close to us, we can make detailed observations, opening up the 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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