A galaxy that has taunted astronomers since they first detected a hint of its presence more than 20 years ago has finally come out of hiding.
It’s called HIPASS J1131-31, or Peekaboo, and it’s located just 22 million light-years away. And it was so hard to see because it’s tiny and obscured by a bright Milky Way star that’s almost directly ahead.
Through a collaborative effort involving space and ground telescopes, scientists have learned that the extremely small Peekaboo is also extremely young and close – providing a snapshot of galactic childhood.
“Discovering the Peekaboo Galaxy is like discovering a direct window into the past, allowing us to study its extreme environment and stars in a level of detail unattainable in the distant, early Universe,” says astronomer Gagandeep Anand. from the Space Telescope Science Institute. in Baltimore.
Given the absolute preponderance of things in the Universe, it’s quite common for objects in the foreground to sit in front of more distant objects. So when the HI Parkes All Sky Survey spotted the galaxy behind the bright star TYC 7215-199-1 in the early 2000s, it wasn’t a huge surprise.
Ultraviolet observations revealed that Peekaboo is what is called a compact blue dwarf galaxy: a small galaxy bursting with the formation of young stars, the brightest of which appear to be blue.
But light from star TYC 7215-199-1 and its diffraction artifacts obscured the galaxy from clear view.
That may be it, except it turned out that the star was moving fast and the direction it is moving is moving away from the galaxy. If we had looked 100 years ago, we might not have seen the galaxy at all. Over the past two decades, this gap has continued to widen. And our space observation technology has become more and more powerful.
So an international team led by astronomer Igor Karachentsev of the Russian Academy of Sciences revisited Peekaboo for further examination. They used the Hubble Space Telescope for optical observations, the Large Southern African Telescope for optical spectra, and the Australia Telescope Compact Array (ATCA) for radio observations.
These observations not only resolved about 60 individual stars in Peekaboo, but helped researchers determine what the stars are made of.
“At first we didn’t realize how special this little galaxy was,” says astronomer Bärbel Koribalski of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia and the researcher who detected for the first time the presence of HIPASS J1131-31.
“Now, with combined data from the Hubble Space Telescope, the Large Southern African Telescope and others, we know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever detected.”
All of the stars resolved by Hubble appear to be less than a few billion years old, at most, which means that Peekaboo appears to be very young in the scheme of the Universe.
And Peekaboo has a surprisingly low abundance of metals. Generally, a low metallicity indicates that an object formed at the beginning of the Universe; newer objects have higher heavy element content.
That’s because there wasn’t a lot of metal in the very early Universe. In the era after the Big Bang 13.8 billion years ago, the Universe was mostly made up of hydrogen and helium. It is from these elements that the first stars were formed, fusing hydrogen and helium into heavier elements, up to iron.
Metals heavier than iron were forged in the violent supernova explosions when stars died, scattering across the Universe where they could be incorporated into the formation of new stars.
In addition to its population of young stars, the researchers made only faint detections of signatures from older stars, suggesting that star formation at Peekaboo only began a few billion years ago. .
This means it could be an example of what the first generation of galaxies and the star populations within looked like.
It’s basically a time capsule and practically right next to it, cosmically speaking. Because Hubble’s observations weren’t particularly detailed, researchers hope to revisit the galaxy with JWST to make a more detailed catalog of its chemistry.
“Due to Peekaboo’s proximity to us, we can make detailed observations, opening up the possibility of seeing an environment resembling the early Universe in unprecedented detail,” Anand said.
The research was accepted in the Royal Astronomical Society Monthly Notices.
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