Well that's a good theory, and I'll take those into account once I've become a more popular theorist. But my counter to the star being associated with the traveler is one, the way they say the machine in this grimoire, and that stars are used widely for any being that is allied with the traveler(check ghost fragment ghosts and ghost fragment darkness 3) I will make more of these once I hit a certain number and have many ideas on all of the cards

I had been assuming that the references to stars in those two cards had been referring to actual stars. Giant balls of gas burning billions of miles away and what-not. Ghosts reminds me of the shield worlds of Halo lore in which a planet sized sphere contained within itself a dyson sphere (like the everted Earth mentioned in Mysteries 2) inside a pocket of subspace (how a 1AU construct can fit inside such a relatively small thing). I had assumed that Ghosts was describing the inside of the Traveler (that particular Ghosts memory of the time before it became a Ghost). Which I suppose also meant that I was assuming that Ghosts are like Monitors from Halo lore which are digitized minds of the formerly living. Thus my theory has been that the Traveler is an artificial construct (I don't see how it could possibly be naturally occurring) that contains a massive Dyson Sphere like habitation for some hyper-advanced alien race (contained within a pocket of subspace of course). Upon or near death these aliens digitize their minds and become Ghosts. The Traveler (as we know it) has been traveling around looking for new worlds for these aliens to call home, going as far as attempting to terraform them. Or perhaps it has been searching for new inhabitants because all that is left of the aliens are the Ghosts, the rest having been wiped out by whatever the Darkness is. When the Traveler became damaged it released a number of these Ghosts to coopt the local fauna to help protect and repair itself. In this case the Darkness would be the Queen of Armies and the Traveler would be the Queens of Mixed Ideologies (the one that Toland thinks is the dream of small minds and cannot hold out against the Queen of Armies). It is always possible that Bungie didn't use their previous work as a starting point and all of my assumptions are false, but they seemed to have used Marathon and ONI (at least) as sources of ideas for Halo so I'm not going to count that possibility out just yet.

Great theory, but I think he garden is the inside of the traveler If you look around you see a huge dome around you while inside. A ghost was found being born inside the garden in a grimoire card Look at mysteries 1, it looks like the darkness met Rasputin at the garden and turned it black

So when you defeat the Heart of Darkness in the Black Garden and your Ghost tells you, "We're back, on Mars." you think it is lying to you and you are actually inside of the Traveler and not just an underground cavern on the planet from which you entered that garden? As for Mysteries, I believe the gardener to be the Traveler, but the garden is the Sol system. The Traveler tended the whole system (at least the inner planets) and made life to prosper. Rasputin attempted to fight the darkness when it arrived in system but got "schooled". It only survived by shutting down and avoiding any further conflict; saving itself but condemning humanity to die. In another card we see it instructing other warminds to do the same. The Traveler did not make this choice, instead opting to sacrifice itself (or nearly so) to save at least some small part of humanity from the onrushing darkness (the giant fighting against the onrushing waterfall to reach a "lever" to cut off the flow? (Mysteries 2)) That "Ghost" in the garden was a flower grown in the shape of a Ghost in Pujari's vision/dream after having leapt from the Shores of Time (a crucible map filled with Vex ruins). I believe that he saw it as a Ghost in his vision because as a Guardian he views Ghosts as trusted sources of information and understanding and whatever power was attempting to plant that seed of doubt knew its words would carry added weight if delivered in that form. In that card (Legend: The Black Garden) Pujari seems to me to be calling the Vex gardeners ("There are gardeners now. They came into the garden in vessels of bronze and they move through the groves in rivers of thought."); there are certainly plenty of Vex in the Black Garden. I'm doubtful that the two garden references are connected.