Astronomers have discovered the Cocoon, a rare binary nucleus in the nearby Galaxy.
Recognized in the Northern Hemisphere for its distinctive shape, this distorted spiral galaxy, also known as NGC 4490, appears to hide true rarity.
Despite its relatively small size – its system is about a fifth of the Milky Way – this galaxy contains not one, but two central nuclei.
“I saw a double nucleus about seven years ago,” says astronomer Allen Lawrence, who began research at the University of Wisconsin-Madison.
“It has never been observed – or no one has ever done anything about it before.”
It is difficult to see both cores at the same time. The former can only be detected with optical telescopes, while the other, which is hidden by dust, can only be detected with radio and infrared telescopes.
In 2013, while studying astronomy at the University of Wisconsin-Madison, Lawrence decided to turn his attention to NGC 4490. Although scientists observed one nucleus with optical telescopes and the other with radio telescopes, no one compared the observations. So Lawrence discovered that there are two nuclei in the galaxy.
Lawrence et al., ArXiv, 2020
Since both nuclei are roughly the same size, mass and luminosity, Lawrence and his colleagues suspect that the Cocoon Galaxy is in the late stages of a collision between the two galaxies.
Today NGC 4490 is in the process of interacting with another galaxy, NGC 4485. However, this ancient history of the merger may explain why the Cocoon galaxy is covered with an extended hydrogen stream.
“This feature is intriguing, since the morphology of the double core is not the usual structure observed in spiral galaxies with low redshift,” the authors explain.
'For example, the Spitzer Infrared Nearby Galaxy Survey (SINGS) surveyed a sample of 75 nearby galaxies representing the full spectrum of Hubble types. While this is not a complete survey, it is interesting to note that none of the observed spiral galaxies exhibit the double morphology in the near and mid-infrared as we see in NGC 4490 '.
“This project demonstrates that sharing multiple wavelengths from space and ground-based observations can actually help us understand a particular object,” says astrophysicist Charles Curton.
A research preprint is available at arXiv and has been accepted for publication in the Astrophysical Journal.
Sources: Photo: Dataset from WISE / SAOimageDS9 software by A. Lawrence
