Speak to Ikora at the Tower about the data you collected in the Black Garden.
Ikora has analyzed the data you collected, and it all points to a single conclusion: the Vex have resurrected the Undying Mind, a Hydra built to seize control of the Black Garden. It appears to be hiding itself in multiple co-occurrent timelines. Ikora intends to devise a plan to deal with this new threat but needs time to sort out the details.
Continue your efforts in the Vex Offensive activity while Ikora develops her plan.