In Star Wars Episode III Revenge Of The Sith, It is widly accepted that Darth Sidious killed Padmé. Many theorize that he siphoned the life/ force from Padmé to keep Darth Vader alive. I would like to debate this school of thought on both how he did this and the reason why.
I was recently listening to the audio book of Darth Plagueis.
The book accounts the history of Darth Plagueis and his apprentice, Palpatine AKA Darth Sidious. They are the beings who put everything into place for the clone war. Basically they are responsible for the direction of the universe in all the movies (1-6).
In the story, the first time Darth Sidious reveals himself as a Sith Lord to anyone, he reveals one of his great powers.
The first being to experience Darth Sidious is Nute Gunray. Sidious begins a relationship with him to ultimately position him at the head of the Trade Federation and control him through the future.
Darth Sidious initially sends a rare bird to Nute Gunray. Gunray has no idea who it is from. But he is the envy of his peers because he possesses the bird. When Sidious first reveals himself, he tells Gunray that the bird was a present. Nute Gunray attempts to dismiss the Sith Lord and end the communication stream. This is when Sidious threatens to kill the rare bird from across the universe, using the force. Within their conversation, he even goes as far as asking Nute Gunray if they scanned the bird for devices. So he can be sure to demonstrate his power in a believable manner.
In the end Sidious does not kill the bird. But we know he has this power.
Fast forward to Revenge of the Sith.
Darth Vader and Padmé get very close to death at the same time towards the end of the movie.
The story tells us Padmé died because she lost the will to live. At the same time Darth Vader is being put back together after his duel with Obi-Wan.
So we know that Darth Sidious can kill beings across the galaxy with the force. But can he transfer life/ the force from one being to another?
No, at least not in this situation.
Sidious knows how to control midichlorians and keep beings alive. He learned this from his Master, Plagueis. But there is no reason to siphon life from Padmé as she is not force sensitive. Her level of midichlorians would be useless to Darth Vader. Some theorize that she was Force sensitive while carrying the twins. But the twins survive obviously and remain force sensitive. Additionally Darth Vader is strong enough to climb up a hill with one arm while all his skin burns off and he has no legs. Watch the movie he gets pretty far. Both Jedi and Sith can use the force to heal themselves or prolong their death if they are dying.
Darth Vader doesn't need Padmé's life force. So why does Sidious kill her?
Because all great Sith must endure great pain to become more powerful in the dark side. They ultimately become stronger because of it. This is the case with Darth Bane, Darth Plagueis, Darth Sidious, and even Kylo Ren. Not to mention Darth Maul, who's entire existence was pure pain under Darth Sidious.
Darth Vader losing Padmé would be the best thing possible for his Sith career. Sidious knows this and acts accordingly.
Image Sources:
http://lucasfilm.com/star-wars-episode-3-revenge-of-the-sith
http://www.blastr.com/2016-5-4/star-wars-bloodline-shows-why-we%E2%80%99re-ready-prequel-era-padme-stories
http://starwars.wikia.com/wiki/Darth_Plagueis_(novel)
https://w-dog.net/wallpaper/palpatine-darth-sidious-star-wars/id/359209/
giphy.com
https://andrewpinkham.wordpress.com/2016/01/25/skyrim-character-build-sith/