Move over, Evil Eye – astronomers have finally figured out the source of your sinister glare. The mysterious galaxy, also known as M64, is a strange and fascinating object in space, with its outer disk of hydrogen-rich material orbiting in the opposite direction to the inner disk of stars. But now, we know where that outer disk came from: a smaller, gas-rich satellite dwarf galaxy that M64 recently gobbled up and wrapped itself in.
This discovery sheds light on the process of galactic cannibalism, which is more common than you might think in our Universe. As galaxies merge and absorb smaller ones, they grow in mass and are infused with new material and gravitational interactions that keep the galaxy alive with new generations of stars. The Milky Way has experienced multiple mergers over its long, 13.6 billion-year history, and we can observe other galaxies at various stages of this process. But what's really exciting about the Evil Eye galaxy is that it could be giving us a glimpse into the future of our own Milky Way. The satellite dwarf galaxy that M64 absorbed was remarkably similar to the Small Magellanic Cloud, another Milky Way satellite that will one day be subsumed into our galaxy. By studying the absorption process in M64, we may gain valuable insight into the growth and evolution of our own galaxy, and how it will interact with the other galaxies around it.
The discoveries by astronomer Adam Smercina of the University of Washington and his team have been published in The Astrophysical Journal Letters, and they provide tantalizing clues about the evolution of M64 and other spiral galaxies like it. The researchers used the Subaru telescope's Hyper Suprime-Cam to study the space around M64 and found clear traces of a galactic merger, including a galactic halo and evidence of a shell produced by the gravitational interaction between two merging galaxies. They also used data from the Hubble telescope to estimate the mass and composition of the absorbed galaxy, which turned out to be around 500 million solar masses – consistent with what we know about the Small Magellanic Cloud. The motion of the gas suggests the satellite had a partially retrograde orbit around M64, and the ongoing merger is what's causing the dusty center and dark smudges of dust that give the galaxy its sinister appearance.
So, what can we learn from the Evil Eye galaxy? For starters, it's a fascinating object that's been capturing our imagination for decades. But more importantly, it's providing crucial insights into the process of galactic cannibalism, and how it shapes the growth and evolution of galaxies like our own Milky Way. As Smercina and his team note in their paper, "future observational and theoretical studies will help test this idea" and shed even more light on the mysteries of the Universe.