I remember the first time this happened to me. It was at GD 219.
Arrive in system to see a small white star ahead. I see the yellow ring and think, "Gosh that star has a big corona for its siz-"
Prox warnings, red flashing lights, smashed out of supercruise.
What the hell? Tumbling, trying to work out what's happening with the stark white-hot light filling my entire cockpit, squinting against the glare.
"Warning, taking heat damage"
Glance across, heat is at 120% already (this was before the rework of the heat scale). Glance to my hull. It's at 84%. It drops to 83% a moment later.
I spent too long gawking and too long trying to work out what was happening.
I freeze in panic.
Heat is at 150%. Three modules fail in quick succession. I finally decide to act and my thrusters malfunction. I panic so much I forget this isn't the same as my frame shift drive, and I can still jump. I'm simply staring at my smoking console, the sparks flying everywhere.
For what feels like hours, my ship tumbles under the white-hot lance of GD 219. My heat reaches 180%.
The thrusters kick back in. I hammer the Frame Shift Drive. I just want to get away.
The Frame Shift Drive starts heating up the ship even more as it charges. I watch my heat climb to 200%. Then 210%. Then 220%. I always thought the FSD charge to supercruise was just a few seconds. I was wrong. It's taking months. It's taking years. The charging sequence almost seems to be teasing me as it adds each extra bar.
The charge completes. Nothing happens. "Align with escape vector". What? What? I drag the ship's nose around blindly, wondering where this thing is. It takes me a few moments that feel like centuries to think to check the nav compass. Behind me and above. I yank back and finally the FSD kicks in fully. I pray it doesn't fail due to damage.
I jump to supercruise at somewhere around 230% heat. To my horror, it keeps climbing. I need to get far enough from the star for the ship to start losing heat. I feel like I've seen every module failure message appear on screen at some point.
When the heat finally stabilises, wobbles and then starts coming down, I watch as damage keeps eating at my ship until it drops below 100%. By the time I'm out, my hull is at 30%. I look at my modules. Several are nearly completely destroyed. And I feel the most blazing, most adrenaline-fuelled surge of relief imaginable. It was the most expensive set of repairs I'd ever had up to that point. I didn't care.
Seriously, that's one of those gameplay memories burned into my mind - pardon the pun. Having my ship two-thirds melt around me is one hell of an experience.
And yeah, like others have said - you can zero your throttle while in witchspace during a jump... you don't see any change on the bar, because your ship is basically frozen and can't lose heat, charge power or change anything while there, but the moment you come out of the jump, your speed will drop to supercruise minimum almost immediately. You can also check your route for these kind of stars - they're DA class as far as I know. I've changed how I come out of jump at unknown systems and check my route now, in an attempt to learn from my own experience, heheh.
Bad luck... hope the repair bill wasn't too high!