A dwarf galaxy in our neighborhood universe appears to belong in a different epoch, the early stages of galactic evolution itself, similar to someone living without contemporary amenities. The “very metal-poor” galaxy, which has a dearth of the chemical components, or “metals,” that stars make and enrich their galaxies with over time, has been confirmed by NASA’s Hubble Space Telescope. Its stars most intriguingly show that it is also one of the newest galaxies ever discovered in the nearby cosmos. The galaxy was largely obscured by the brilliance of a foreground star, earning it the moniker Peekaboo, but Hubble was still able to distinguish specific stars for research. The find offers the enticing chance to examine a historical artifact in great detail, as though shaking hands with a prehistoric ancestor.
Astronomers have discovered the most spectacular example of a neighboring galaxy with properties that are more similar to galaxies in the distant, early cosmos by peering out from behind the glare of a bright foreground star. The tiny galaxy HIPASS J1131-31, which measures just 1,200 light-years across, has earned the moniker “Peekaboo” due to its recent appearance from behind a fast-moving star that had previously prevented researchers from seeing it.
The finding was confirmed by NASA’s Hubble Orbit Telescope and was made possible by a collaboration of telescopes on the ground and in space. Together, the studies provide tantalizing proof that the Peekaboo Galaxy is the closest illustration of the galaxy formation processes that frequently occurred not long after the big bang, 13.8 billion years ago.
According to astronomer Gagandeep Anand of the Space Telescope Science Institute in Baltimore, Maryland, and co-author of the recent study on the intriguing characteristics of Peekaboo, “discovering 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.”
Galaxies like Peekaboo are described by astronomers as being “very metal-poor” (XMP). In astronomy, any elements heavier than hydrogen and helium are referred to as “metals.” The elements created in the big bang, primordial hydrogen and helium, made up practically the entire very early cosmos. Over the course of cosmic history, heavier metals were created by stars, leading to the primarily metal-rich cosmos we inhabit today. The “building blocks” of life as we know it are composed of heavier elements like calcium, iron, carbon, and oxygen.
Although XMP galaxies were the default for the first galaxies in the universe, similar metal-poor galaxies have also been discovered in the nearby cosmos. Peekaboo attracted astronomers’ interest because, in addition to being an XMP galaxy without a significant older stellar population, it is also positioned at least half as far from Earth as other young XMP galaxies, at a distance of only 20 million light-years.
Professor Bärbel Koribalski, an astronomer at Australia’s national science agency CSIRO and a co-author of the most recent study on Peekaboo’s metallicity, discovered Peekaboo as a region of cold hydrogen more than 20 years ago with the Australian Parkes radio telescope Murriyang in the HI Parkes All Sky Survey. It was identified as a compact blue dwarf galaxy by NASA’s space-based Galaxy Evolution Explorer mission’s observations in the far ultraviolet.
Koribalski remarked of Peekaboo, “At first we did not grasp how unique this little galaxy is.” We now know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever found thanks to the combination of data from the Hubble Space Telescope, the Southern African Large Telescope (SALT), and other observatories.
About 60 stars in the tiny galaxy were resolved by NASA’s Hubble Space Telescope, and almost all of them appeared to be a few billion years old or younger. SALT’s metallicity measurements of Peekaboo completed the picture. Together, these results highlight the key distinction between Peekaboo and other local universe galaxies, which often include elderly stars with billions of years of age. Peekaboo is one of the youngest and least chemically loaded galaxies ever discovered in the nearby universe, according to the stars in the galaxy. Given that the local universe has had around 13 billion years to form, this is quite exceptional.
The picture is still limited, according to Anand, because the Hubble observations were made as part of the Every Known Nearby Galaxy Survey, a “snapshot” survey program that aimed to collect Hubble data from as many nearby galaxies as possible. To learn more about Peekaboo’s star populations and their metal compositions, the research team intends to do additional research using Hubble and the James Webb Space Telescope.
As a result of Peekaboo’s closeness to Earth, Anand added, “we can undertake in-depth studies, creating opportunities to study an environment mimicking the early cosmos in unparalleled detail.”
The findings have been approved for publication in the Royal Astronomical Society’s Monthly Notices.
NASA and ESA collaborated internationally on the Hubble Space Telescope project. The telescope is run by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Hubble science operations are carried out by the Space Telescope Science Institute (STScI) in Baltimore. The Association of Universities for Research in Astronomy, based in Washington, D.C., runs STScI for NASA.NASA
