M64 has long perplexed astrophysicists, particularly because it looks like an evil eye. Now, researchers have discovered it takes its strange shape from a dwarf galaxy it recently cannibalized and wrapped itself in. That smaller galaxy is responsible for darkening M64’s outskirts.
The findings were led by astronomer Adam Smercina of the University of Washington and were reported by Science Alert on Tuesday.
“M64, often called the “Evil Eye” galaxy, is unique among local galaxies. Beyond its dramatic, dusty nucleus, it also hosts an outer gas disk that counter-rotates relative to its stars,” write Smercina and his colleagues in the new study abstract.
“The mass of this outer disk is comparable to the gas content of the Small Magellanic Cloud (SMC), prompting the idea that it was likely accreted in a recent minor merger. Yet, detailed follow-up studies of M64’s outer disk have shown no evidence of such an event, leading to other interpretations, such as a “flyby” interaction with the distant diffuse satellite Coma P.”
“We find evidence for a spectacular shell feature, and other tidal structures indicative of an ongoing, late-stage radial merger,” the researchers continue in their study.
“We estimate the stellar mass of the progenitor galaxy to be 500 million solar masses, with a metallicity of [M/H] ≃ −1 – very similar to the mass and metallicity of the Small Magellanic Cloud.
“The mass of M64’s counter-rotating outer gas disk is also comparable to the gas mass of the Small Magellanic Cloud, suggesting that the likeliest origin of M64’s unique counter-rotating disk was a recent merger with a gas-rich satellite very similar to the Small Magellanic Cloud.”
Therefore, their observations indicate what they say are clear traces of a galactic merger.
“The likely origins of the Evil Eye’s counter-rotating gas are at last revealed, after decades of curiosity,” the researchers conclude, according to Science Alert.
“We suggest that its outer gas disk was accreted recently during a 52:1 merger with a Small Magellanic Cloud-mass galaxy and is now colliding with an existing inner gas disk, fueling a burst of star formation at the disk–disk interface and driving the visible dust lanes from which it earns its name. Future observational and theoretical studies will help test this idea.”