Peekaboo Galaxy HIPASS J1131–31 Is Extremely Metal-poor

By James Anderson •  Updated: 12/07/22 •  5 min read

Astronomers have discovered the most extraordinary example yet of a nearby galaxy with characteristics more akin to galaxies in the distant, early universe, peering out from behind the glare of a bright foreground star. The tiny galaxy HIPASS J1131-31 has been dubbed the Peekaboo galaxy because it emerged in the last 50-100 years from behind a fast-moving star that was obscuring astronomers’ ability to detect it.

The discovery was made with the help of telescopes on the ground and in space, including NASA’s Hubble Space Telescope. The research as a whole provides tantalizing evidence that the Peekaboo Galaxy is the closest example of the galaxy formation processes that were prevalent shortly after the big bang, 13.8 billion years ago.

“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,”

said co-author Gagandeep Anand, an astronomer at the Space Telescope Science Institute in Baltimore.

Extremely Metal-poor

Peekaboo galaxy - Tiny galaxy HIPASS J1131–31 peeks out from behind the glare of star TYC 7215-199-1, a Milky Way star positioned between Hubble and the galaxy. One hundred years ago, this fast-moving foreground star would have appeared directly in the line of sight, and the "Peekaboo" galaxy would not have been detectable at all.

Tiny galaxy HIPASS J1131–31 peeks out from behind the glare of star TYC 7215-199-1, a Milky Way star positioned between Hubble and the galaxy.
One hundred years ago, this fast-moving foreground star would have appeared directly in the line of sight, and the Peekaboo galaxy would not have been detectable at all.
The small galaxy presents astronomers with a unique opportunity for future in-depth analysis of a chemical environment typically only found in the very distant, early universe, where detailed study of individual stars’ chemical makeup is not possible. Peekaboo is, in effect, a direct portal into the past, allowing us to discover what the universe was like near the dawn of time.
Credit: NASA, ESA, and Igor Karachentsev (SAO RAS);Image Processing: Alyssa Pagan (STScI)

According to astronomers, galaxies like Peekaboo are “extremely metal-poor” (XMP). “Metals” refers to all elements heavier than hydrogen and helium in astronomy. Hydrogen and helium, made by the big bang, made up almost all of the early matter in the universe.

Throughout the universe’s history, stars have made heavier elements, which is why the universe is full of metals today. The building blocks of life as we know it are heavier elements such as carbon, oxygen, iron, and calcium.

While extremely metal-poor galaxies were the default for the universe’s earliest galaxies, similarly metal-poor galaxies have also been discovered in the local universe. Peekaboo drew the attention of astronomers not only because it is an XMP galaxy without a significant older stellar population, but also because it is only 20 million light-years from Earth, which is at least half the distance of previously identified young XMP galaxies.

Discovering The Peekaboo Galaxy

Professor Barbel Koribalski, an astronomer at Australia’s national science agency CSIRO and co-author of the latest research study on Peekaboo’s metallicity, found Peekaboo as a region of cold hydrogen with the Australian Parkes radio telescope Murriyang in the HI Parkes All Sky Survey more than 20 years ago. Using far-ultraviolet observations, NASA’s Galaxy Evolution Explorer mission in space found that it was a small blue dwarf galaxy.

“At first we did not realize how special this little galaxy is. 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,”

Koribalski said.

The Hubble Space Telescope was able to resolve approximately 60 stars in the tiny galaxy, nearly all of which appear to be a few billion years old or younger. SALT’s measurements of the Peekaboo Galaxy’s metallicity completed the picture.

These findings highlight the significant difference between Peekaboo and other galaxies in the local universe, which typically have stars that are billions of years old.

Data Still Incomplete

The stars in the Peekaboo Galaxy indicate that it is one of the youngest and least chemically-enriched galaxies ever discovered in the local universe. This is extremely unusual, given that the local universe has had approximately 13 billion years of cosmic history to develop.

However, Anand believes that the picture is still incomplete because the Hubble observations were made as part of a “snapshot” survey program called The Every Known Nearby Galaxy Survey, which aimed to collect Hubble data from as many neighbouring galaxies as possible.

Using Hubble and the James Webb Space Telescope, the research team plans to do more work on HIPASS J1131–31 to learn more about its star population and metal composition.

“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 said.

Reference: I D Karachentsev, L N Makarova, B S Koribalski, G S Anand, R B Tully, A Y Kniazev, Peekaboo: the extremely metal poor dwarf galaxy HIPASS J1131–31, Monthly Notices of the Royal Astronomical Society, 2022;, stac3284

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