An active summoning beacon.
A summoning beacon is a device used by the Ankari to summon their "spirits of good fortune", nucleogenic lifeforms from another dimension.
After being stranded in the Delta Quadrant in 2371, the USS Equinox received supplies from the Ankari and witness the summoning beacon being used. The Equinox crew purchased their own beacon to summon the lifeforms for study, to accidentally discover that the beings could be used to enhance their warp drive.
In early 2376, after the Equinox escaped the USS Voyager, the Voyager crew contacted the Ankari for assistance. In Voyager's cargo bay, an Ankari used the summoning beacon and acted as an intermediary between Kathryn Janeway and the aliens. (VOY: "Equinox", "Equinox, Part II")