An international team of astronomers has found a distant galaxy slowly being strangled by a bigger companion. This “gruesome” display is actually helping astronomers understand the evolution of dwarf galaxies.
The object is nicknamed "Little Cub" since it’s in the constellation of Ursa Major, the Great Bear. It’s 50 million light-years from Earth and considered a primitive galaxy, which means its composition hasn’t changed much since its formation.
An intriguing detail about Little Cub is that it’s losing its gas, as reported in a paper submitted for publication in the Astrophysical Journal Letters. The culprit of this gas theft is a much larger companion, known as NGC 3359, located between 200,000 and 300,000 light-years away. Without this gas, the star formation in Little Cub will soon be quenched.
“We may be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way-like galaxy,” lead author Tiffany Hsyu, a graduate student in the Department of Astronomy and Astrophysics at UC Santa Cruz, said in a statement. “It is rare for such a tiny galaxy to still contain gas and be forming stars when it is in close proximity to a much larger galaxy, so this is a great opportunity to see just how this process works. Essentially, the larger galaxy is removing the fuel that the Little Cub needs to form stars, which will eventually shut down star formation and lead to the smaller galaxy's demise.”
But its death is only one of many characteristics worth noting. Its chemistry matters as well. Little Cub has not changed much over the last 13 billion years, so we are looking at a large and (moderately) nearby object like it’s a relic from the dawn of the universe. Studying Little Cub can provide new insight into how galaxies have evolved.
The research is being presented this week at the National Astronomy Meeting at the University of Hull.
“We know by studying the chemistry of the Little Cub that it is one of the most primitive objects currently known in our cosmic neighborhood,” co-author Ryan Cooke, Royal Society University research fellow in Durham University's Centre for Extragalactic Astronomy, added. “Such galaxies, which have remained dormant for most of their lives, are believed to contain the chemical elements forged a few minutes after the Big Bang. By measuring the relative number of hydrogen and helium atoms in the Little Cub, we might be able to learn more about what made up the Universe in the moments after it began 13.7 billion years ago.”
Little Cub is a galaxy that time forgot, and now we have a front row seat to its eventual demise.