Hubble and other telescopes have discovered that a peculiar little galaxy is one of the most incredible examples of extremely metal-poor (XMP) galaxies, meaning that its chemical composition has hardly changed in over 13 billion years. At 20 million light-years away, this is the closest XMP to Earth.
The object is 1,200 light-years across, tiny for a galaxy. There are nebulae in the Milky Way bigger than that. It is known as HIPASS J1131-31, but astronomers have given it another nickname: the Peekaboo Galaxy. The reason behind that is that it emerged over the last several decades from behind a bright, fast-moving star.
Following the Big Bang, only hydrogen and helium (with a dash of lithium) were present in the universe. All the other elements, colloquially called metals in astronomy, were formed after the very first stars went supernova. These supernovae polluted galaxies, and led to the formation of the stars and planetary systems we see today.
But the Peekaboo Galaxy has not experienced much of that, and for that reason has remained metal-poor for all this time.
"At first we did not realize how special this little galaxy is," co-author Professor Bärbel Koribalski, who is an astronomer at Australia's national science agency CSIRO, said in a statement. "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."
These telescopes were able to study the composition of 60 stars in this tiny galaxy. They are all relatively young, a few billion years old or younger, unlike many of the stars present in the galaxies in the local universe. Combining this with the scarcity of heavier elements in this galaxy makes for a puzzling object – one that ought to be studied more in the future.
"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," added co-author Dr Gagandeep Anand of the Space Telescope Science Institute in Baltimore, Maryland.
The study is published in the Monthly Notices of the Royal Astronomical Society.