What exactly is the difference between the ninth jhana and enlightenment?
The Ninth Jhana: Cessation
When you reach the limits of perception, you realize that lesser mental activity is better for your calm and peaceful state. You enter a state of “cessation” of consciousness where there is only a very sublte form of perception. The meditator may appear to be unconscious. There have been reports of meditators having heart beats as low as 20 to 40 beats per minute at this jhanic level. The nearest way to describe this state is something like a very deep sleep. The eight and ninth jhanas are not full enlightenment, but very close stepping stones to full awakening. Only those who are very close to being fully enlightened can enter the eighth and especially, the ninth jhana.
That is just a quote from wikipedia about it, but I am curious, once all perception disappears, what is essentially left is awareness with no object, or a non-dual form of awareness, correct?
I am curious how that differs from from enlightenment as a Buddha would experience it (At least theoretically)
The ninth jhana (the cessation of apperception and feelings) is a state of non-analytical cessation, whereas Nirvana is a state of analytical cessation.
Cessation (Wyl.‘gog pa; Skt. nirodha) — generally the word refers to the absence or extinction of a given entity. As the third of the four noble truths, it refers specifically to the pacification of suffering and its causes, and is therefore a synonym of nirvana.
Cessation is of two kinds:
analytical (so sor brtags pa'i 'gog pa) and
non-analytical (brtags min 'gog pa).
In his commentary to Mipham Rinpoche’s Khenjuk, Khenpo Nüden writes:
This is the unconditioned aspect of the permanent elimination of destructive emotions and other factors to be eliminated, through the force of developing realization of the undefiling path, such as the wisdom of discernment, within the mind.
This does not refer to the ceasing of latent habitual tendencies as a result of analysis and investigation, but rather to the absence of a given thing in a particular place due to an incompleteness of necessary causes and conditions, as in the case of horns on a horse’s head, for instance. Another example which is mentioned in the commentaries is the fact that other types of consciousness do not arise when the eye-consciousness is distracted by a visual form. This also includes all the various forms of non-existence (or absence), such as the absence of a vase in a particular place.
Also jnana wrote:
Firstly, nibbāna isn't a "state." Secondly, nibbāna is the cessation of passion, aggression, and delusion. For a learner it is the cessation of the fetters extinguished on each path. The waking states where "suddenly all sensations and six senses stop functioning" are (1) mundane perceptionless samādhis, and (2) cessation of apperception and feeling. Neither of these are supramundane and neither of these are synonymous with experiencing nibbāna.
All the best,
Nibbāna is a negation. It means extinguishment. With the fruition of each of the four paths one knows the termination of the fetters which are eliminated by that path. This termination is nibbāna appropriate to that path. The Paṭisambhidāmagga:
How is it that the discernment of the termination of continuance in one who is fully aware is gnosis of full extinguishment (parinibbāna ñāṇa)?
Through the stream-entry path he terminates identity view (sakkāyadiṭṭhi), doubt (vicikicchā), and mistaken adherence to rules and duty (sīlabbataparāmāsa).... This discernment of the termination of continuance in one who is fully aware is gnosis of full extinguishment....
He causes the cessation of identity view, doubt, and mistaken adherence to rules and duty through the stream-entry path.
And so on for the fetters which are terminated on the remaining three paths. The once-returner path terminates the gross fetters of desire for sensual pleasure (kāmacchanda) and aversion (vyāpāda/byāpāda). The non-returner path terminates the secondary fetters of desire for sensual pleasure (kāmacchanda) and aversion (vyāpāda/byāpāda). The arahant path terminates the fetters of passion for form [existence] (rūparāga), passion for formless [existence] (arūparāga), conceit (māna), restlessness (uddhacca), and ignorance (avijjā).
All the best,