You and up to eight willing creatures within range project your astral bodies into the Astral Plane (the spell ends instantly if you are already on that plane). Each target’s body is left behind in a state of suspended animation; it has the Unconscious condition, doesn’t need food or air, and doesn’t age.
A target’s astral form resembles its body in almost every way, replicating its game statistics and possessions. The principal difference is the addition of a silvery cord that trails from between the shoulder blades of the astral form. The cord fades from view after 1 foot. If the cord is cut—which happens only when an effect states that it does so—the target’s body and astral form both die.
A target’s astral form can travel through the Astral Plane. The moment an astral form leaves that plane, the target’s body and possessions travel along the silver cord, causing the target to re-enter its body on the new plane.
Any damage or other effects that apply to an astral form have no effect on the target’s body and vice versa. If a target’s body or astral form drops to 0 Hit Points, the spell ends for that target. The spell ends for all the targets if you take a Magic action to dismiss it.
When the spell ends for a target who isn’t dead, the target reappears in its body and exits the state of suspended animation.
* - (for each of the spell’s targets, one jacinth worth 1,000+ GP and one silver bar worth 100+ GP, all of which the spell consumes)
What known things cut the cord?
An Astral Dreadnought's attack, the Greater Silver Sword, and probably a Wish Spell
This is such a pointless spell in 5e. If you enter another plane from the Astral Sea (otherwise known as, the entire point of the spell) your real body appears in that plane with you? So, if you enter Acheron or the Abyss, you might as well end the spell and re-enter your physical body, as the only alternative is to just leave it, unattended, in a hostile plane you may have never been to before while you continue to float around as a ghost.
What makes this spell at all worthwhile as opposed to gate or plane shift? I'd hoped that they would have maybe addressed that possibility of extreme danger if you use this spell for its intended purpose or polished up the wording of the actual spell, but they removed the line in the 2014 DMG that implies that, somehow, being killed in your real body while in another plane wouldn't actually kill you if you got there by use of this spell. Better yet, explain, like every previous version of this spell did, that the physical body you inhabit on the new plane is not your original, and if you die you'll be returned to your true body which is still on your plane of origin. Color pools are opaque, so you can't see where you'll wind up ahead of time like you can with gate. And it's a 9th level spell that consumes its costly components, unlike plane shift which is only 7th level and lets you keep the components which are far cheaper. The only upside is you may get to see githyanki dommy mommies while traveling the Astral, but even then, they'll just kill you with their silver swords.