Free Astronomy Magazine March-April 2024

MARCH-APRIL 2024 smear out into a disk shape. And this is where the story gets interesting. Steiman-Cameron and his team found that a phenomenon known as differential precession is respon- sible for NGC 4753’s entangled dust lanes. Precession occurs when a ro- tating object’s axis of rotation changes orientation, like a spinning top that wobbles as it loses momen- tum. And differential means that the rate of precession varies de- pending on the radius. In the case of a dusty accretion disk orbiting a galactic nucleus, the rate of preces- sion is faster toward the center and slower near the edges. This varying, wobble-like motion results from the angle at which NGC 4753 and its former dwarf companion collided and is the cause of the strongly twisted dust lanes we see wrapped around the galaxy’s luminous nu- cleus today. “For a long time nobody knew what to make of this peculiar galaxy,” said Steiman-Cameron. “But by starting with the idea of accreted material smeared out into a disk, and then analyzing the three-di- mensional geometry, the mystery was solved. It’s now incredibly excit- ing to see this highly-detailed image by Gemini South 30 years later.” Though NGC 4753 appears to be ex- ceptionally unique, this may be a misconception. According to Steiman-Cameron, if one were to view the twisted dusty disk from directly above it likely would look no different than a stan- dard spiral galaxy. It’s due only to our fortuitous, nearly edge-on view that we are able to see the full scope of its tangled dust lanes, meaning these peculiar features may not be as rare in the Universe as they seem. [International Gemini Observatory/NOIRLab/NSF/AURA. Image processing: J. Miller (International Gemini Observa- tory/NSF’s NOIRLab), M. Rodriguez (International Gemini Observatory/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab)] !