While observing data from the Hubble Space Telescope (HST) and long-slit spectroscopy using the Southern African Large Telescope (SALT), scientists discovered the Peekaboo dwarf galaxy (HIPASS J1131–31) is exceptionally metal-poor. Detailed in the recently published Monthly Notices of the  Royal Astronomical Society collaborators and the South African Astronomical Observatory’s (SAAO) Astronomer Alexei Kniazev, the team named the dwarf galaxy, Peekaboo due to its shy nature and its potential importance. As the team specifies, Peekaboo hides in the halo of a bright foreground star of magnitude 10.4.

In Astronomers’ standard picture of galaxy formation, stars started forming in the first billion years after the Big Bang, when the universe was dense with cooled hydrogen and helium gas. After which, these groups of stars came together to form big galaxies and dwarf galaxies.

More than 13 billion years after the Big Bang, stars’ life and death cycle have transformed some primordial gas into the heavier chemical elements present today. Moreover, the process is more sophisticatedly observed in big galaxies than dwarf galaxies. Thus, of importance is that almost all galaxies studied by astronomers have old stars as essential components.

However, there is a small group of dwarf galaxies with common and perplexing properties; interestingly, accounting for ten times their normal matter (discounting mysterious dark matter) is hydrogen and helium gas rather than stars. In addition, the fraction of heavier elements is the smallest ever seen in galaxies. 

Furthermore, all the stars that can be observed in HST images are less than a billion years old, begging the question, “Where are the 13-billion-year-old stars we see in almost all other galaxies”? The Peekaboo galaxy is the closest example of these unusual systems, which makes it fascinating because it can be studied in greater detail as unearthed through a search for sources of hydrogen gas using the Parkes Radio Telescope in Australia. 

The Doppler shift of the hydrogen spectral line disclosed what had to be a nearby galaxy. Peekaboo became visible using HST imaging; it was 15 arc seconds away from a bright star.  Astronomers used SALT and found extremely poor amounts of chemical elements in this galaxy.

According to Alexei Kniazev, “A 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.” Hence, resulting in a compromised existing image of the Peekaboo galaxy by the glare of the bright star. 

Nonetheless, examining deeper images will be possible with proper masking. In addition, future observations with the HST and James Webb Space Telescope (JWST) should expose if stars began forming in Peekaboo early in the universe, as expected according to galaxy formation theory, or whether Peekaboo is inconsistent with this theory and can be called ‘young’.

“We are going to continue our studies of this galaxy with SALT, as well as extend our spectral analysis to understand Peekaboo’s evolution in more detail,” commented Alexei Kniazev.