The rare object is known as NGC 4490, or the adjacent Cocoon Galaxy. Acknowledged in the Northern Hemisphere for its peculiar form, this twisted spiral galaxy seems to be covering an incredible rarity. In spite of its relatively small diameter, this object hosts not one, but two central cores.
Two Central Cores in a Small Galaxy
Allen Lawrence, an astronomer who first conducted the research at the University of Wisconsin-Madison before moving to Iowa State University, said: “I saw the double nucleus about seven years ago. It had never been observed – or nobody had ever done anything with it before.”
Observing both cores at the same time is rather difficult. The first can only be monitored by an optical telescope, and the other, which is hidden by dust, can only be identified using radio and infrared telescopes.
Back in 2013, while studying astronomy at the University of Wisconsin-Madison, Lawrence settled to analyze NGC 4490. Even though researchers had studied one nucleus using optical telescopes, and detected the other one with radio telescopes, not one scientist has compared observations and saw that there were two different cores in the galaxy.
Due to the fact that both cores appear to be of the approximate size, mass and brightness, Lawrence and his colleagues believe that the Cocoon Galaxy is in the late phases of a much-earlier crash between two galaxies.
Rarities Like This Keep Appearing
Currently, NGC 4490 has already branched out and is now on its way to engage with another galaxy, NGC 4485. This previous background of merging, though, might help researchers understand the reason why Cocoon Galaxy is hidden beneath a widespread hydrogen plume.
“The feature is particularly intriguing as a double nucleus morphology is not a common structure seen in low redshift spiral galaxies,” the authors explain. “For example, the Spitzer Infrared Nearby Galaxy Survey (SINGS) legacy project examined a sample of 75 nearby galaxies representing the full range of Hubble types. While this is not a complete survey, it is interesting to note that none of the spiral galaxies observed as part of SINGS show a double-nucleus morphology in the near and mid-infrared like we see in NGC 4490.”
Back in 2004, the Catalog of Double Nucleus Disk Galaxies listed only 107 cosmic objects, and the Seyfert galaxy Markarian 315 is one of these unique oddities. Similar to the Cocoon Galaxy, this spiral body also features two nuclei, about 6,000 light-years apart, and possibly fueled by massive black holes gathering matter.
As a matter of fact, one reason why researchers get so excited by double nuclei is that they might be one method of forcing gas deep into the core of a galaxy to power a gigantic black hole.
“This project demonstrates that using multiple wavelengths from space- and ground-based observations together can really help us understand a particular object,” says astrophysicist Charles Kerton.
The research pre-print has been published on arXiv and has also been issued in The Astrophysical Journal.