The heating occurs due to the object compressing the atmosphere (air) in front of it. A fast moving object (over Mach 3) compresses air because the air can't move out of the way, which causes the compressed air to heat up.
Anytime you compress a gas in an enclosed space it heats up. (the opposite is also true)
It is the very hot air that glows, (it actually becomes a plasma), and the heat from that heats up the object.
This plasma is electromagnetic, and blocks radio waves, so there used to be a "dead air time" while returning spacecraft were creating the plasma. (see the movie Apollo 13). Modern spacecraft bounce the signals off a satellite, above the craft, avoiding this radio silence.
Anyone explaining it by saying it is "friction with the air" is wrong
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