In the video of the recent SpaceX Starlink launch, one view of the Falcon-9 2nd stage engine shows a cane-shaped tube that glows red hot at the "handle" end and seems to get hotter over time.
Question: What is the function of this tube, and why is it getting red hot?
The first two images are from
T+07:38, you can see here and in the video that as the tube heats up the red glow moves from the "handle" of the cane only and starts down the body.
The next two views are different lighting from the Sun to better understand the tubing and geometry.