Astral Dimension

"What did you just do to me?" "I pushed your astral form out of your physical form."

- Stephen Strange and the Ancient One

The Astral Dimension, also referred as the Astral Plane or the Ancestral Plane, is a parallel dimension where the soul exists outside of the body.

Overview
The Astral Dimension, much like the Mirror Dimension, coexists alongside the Material Plane. However, to access it, one must successfully be separated from their physical form, existing in a state of pure energy. Time relative to the Material Plane is slowed down to a crawl when one enters the Astral Dimension, to the point that Doctor Strange was able to leave his body, speak with the Ancient One, and return in the time it took his body to fall to the floor.

Sorcerers are also able to peer into the Astral Dimension without leaving their bodies, as both the Ancient One and Doctor Strange were able to see each other's astral bodies while in the Material Plane. It is also demonstrated that sorcerers can learn to make their astral forms perceivable in the material world, with Strange forming a fractal-like portal from which he could appear to Christine Palmer, seemingly through the use of the Mirror Dimension. While speaking to her in his astral form, Strange was also able to see Lucian arrive. The Ancient One was able to project and return Strange's astral form to his body, suggesting that powerful sorcerers can control the Astral Dimension to some extent other than astral projecting.

Sorcerers have limited effect on the Material Plane while in the Astral Dimension, as during their Duel on the Astral Plane, Lucian and Doctor Strange were able to cause equipment to move around and lights to burst. Due to the astral form being energy, if a sorcerer's body is exposed to high amounts of energy, such as electricity, their astral form becomes charged to the point that Strange was able to kill Lucian by overloading his astral form after Palmer use a defibrillator on him.

One can simultaneously rest their bodies and perform other tasks using the Astral Dimension, as Doctor Strange was shown to be sleeping while studying a book in his astral form. Also, like the Mirror Dimension, the Astral Dimension is accessible without the use of the Sling Ring, as it occupies the same space as the real world while still being imperceptible.

For Black Panthers, after consuming the Heart-Shaped Herb, they are put into a slumber and buried, reawakening in the Astral Dimension by rising from the earth. The experience is shown to be extremely jarring, as both T'Challa and Erik Killmonger awoke from their visit visibly shaken and disoriented.

History
"In my culture, death is not the end. It's more of a stepping off point. You reach out with both hands to Bast and Sekhmet, they lead you into the green veld where... you can run forever."

- T'Challa

According to Wakandan lore, the Astral Dimension is where the soul settles after death. For Black Panthers, it is where they can go to commune with their ancestors after ingesting the Heart-Shaped Herb.

King T'Chaka's Death
"It sounds peaceful." "My father thought so. I am not my father."

- Natasha Romanoff and T'Challa

Following the death of T'Chaka, the King of Wakanda, Natasha Romanoff went to console his son, Prince T'Challa. He explained that, to Wakandans, death was not the end of a person's journey. Instead, they were brought by Bast and Sekhmet to the Ancestral Plane, where they would run through a green veld forever. Natasha stated that it sounded like a peaceful end, but T'Challa stated that it was a belief held by his father, but not him.

T'Chaka's Wisdom
"You're a good man, with a good heart, and it is hard for a good man to be king."

- T'Chaka to T'Challa

After his coronation, King T'Challa had his powers as the Black Panther returned, and was buried in the chamber where the Heart-Shaped Herb was cultivated. He awoke in the Astral Dimension, rising from the earth before the tree where his father and other ancestors rested in panther form. T'Challa went to greet his son, and they embraced as T'Challa mournfully remembered the events of his father's death in Vienna, exclaiming his sorrow for being unable to save him.

T'Chaka, however, exclaimed his pride in his son. As T'Challa confessed that he was unprepared to rule without his father, T'Chaka wistfully replied that a man who hadn't prepared his children for his death has failed them as a father.

Reunion with N'Jobu
"I fear you will not be welcomed there." "But why?" "They will say you are lost." "Maybe it's your people that's lost; that's why they can't find us."

- N'Jobu and Erik Killmonger To be added

End of Tradition
"You were wrong! All of you were wrong! To turn your backs on the rest of the world! We let the fear of discovery stop us from doing what is right. No more! I cannot stay here with you. I cannot rest while he sits on the throne. He is a monster of our own making. I must take the mantle back. I must! I must right these wrongs."

- Black Panther

Following his rescue by Jabari fishermen, T'Challa was given the last of the Heart-Shaped Herb by Nakia and Ramonda, who quickly buried him in the snow he'd been placed in.

Once again seeing his father, T'Challa questioned him why he'd left behind a Wakandan child to fend for himself after T'Chaka murdered his own brother, Prince N'Jobu. T'Chaka, ashamed, explained that it had been the actions of a king who wanted to bury his actions in the past.

When T'Chaka told his son to stay in the Ancestral Plane with their ancestors, T'Challa adamantly refused, calling out his predecessors for the flaws they've led Wakanda through. Unable to allow Erik Killmonger rule the country and prokove a war with the rest of the world, T'Challa denied his place among his ancestors.

Meeting the Ancient One
During Stephen Strange's first encounter with the Ancient One, he initially rejected the idea of souls and multiple universes along with all the other non-scientifically proven statements she made. To shut him up, the Ancient One pushed Strange's astral form out from his physical form, effectively forcing Strange briefly into the Astral Dimension.

Strange's Training
Upon starting his training in the Mystical Arts, Strange quickly became interested in the use of Astral Projections, despite Wong warning that he was not ready for it. Strange quickly became skilled in entering the Astral Dimension and frequently did so to keep studying while his physical body was sleeping.

Hospital Incident
When Stephen Strange was injured as a result of his conflict at the New York Sanctum, he stumbled through a portal into the Metro-General Hospital. There, Strange left his physical form by simultaneously assuming the astral form and entering the Astral Dimension, rendering his body unconscious. During this time, he helped Christine Palmer perform surgery on him by re-emerging in the regular universe in his astral form. Palmer was shocked by this stunt and assumed Strange was dead at first. However, he was followed by the astral form of Lucian, one of the enemies he had just overcome.

They battled it out in the Astral Dimension, and some of their actions had weak and muffled effects on the regular dimension. While they fought, Palmer continued her attempts to resuscitate Strange, using duel defibrillators. As it happened, this fact was able to energize Strange's astral form. Strange realized he could use that power against Lucian while in the Astral Dimension, so he asked Palmer to keep using the defibrillator. Strange forced the power through Lucian's astral form, completely incinerating him in the process.

Death in the Astral Dimension
Having been rushed to a hospital, the Ancient One left her physical body and entered the Astral Dimension, with Stephen Strange quickly following her. In her dying moments, the Ancient One witnessed a lightning strike New York alongside Strange. They stretched her dying moments into minutes in the Astral Dimension together. Her physical body then died, and her astral form faded at the same time.

Trivia

 * The Astral Dimension in Black Panther resembles the Djalia, or Great Veldt, from the comics, a place where the consciousness still exists after death in Wakandan lore.
 * It's unknown if the Ancient One's soul inhabits the Astral Dimension now since her astral form faded after her clinical death.
 * However, this could be explained as astral projection differing for the Masters of the Mystic Arts, as Black Panthers seem to fully depart into the Astral Dimension, whereas Masters still remain close to the Material Universe.
 * Interestingly, Doctor Strange was shown to be holding a book from the Kamar-Taj Library while in the Astral Dimension, and the book itself is translucent as though it existed in the astral plane as well.