Here’s the deal: You can’t understand astrology without understanding the Mythology of it.
Demon Swarbhanu was behaded by Vishnu when he cheated Vishu and took Amrit (necter of immortality) . However, by that time he had become an immortal thus he couldn’t die.
However, they are two archetypes representing to opposing sides of a man:
Rahu: a grossly materialistic side (ALL HEAD-NO HEART=Rahu) (Remember your empty suit of a boss who screams a lot and bullies the small guy and does nothing but plays politics, scheming and scamming all the time, That’s Rahu type for you )
They belong to the same person but never do they meet. A deep philosophical, astrological and psychological concept.