The part where it's leaving a trail is material ablating (vaporizing) off the outside of the re-entry vehicle. It's still bright after that because it's still t

The part where it's leaving a trail is material ablating (vaporizing) off the outside of the re-entry vehicle. It's still bright after that because it's still traveling at mach 5-6 or so (very dense pointed entry vehicle that doesn't lose speed), so it maintains a superheated state where the surface is glowing white hot.