Nunk's Marauder creates a geodesic fold.
A geodesic fold is a portal created inside a red giant by firing a geodesic pulse. This results in a temporary "wormhole" that opened in another red giant.
However, a geodesic fold emits high levels of geodesic radiation. Normal shields won't withstand this. With adapted shielding it is possible to get a ship through. But the radiation is still too powerful for a crew to survive. As the radiation will liquify organic material.
It is also impossible to send any transmission through a geodesic fold.
DaiMon Nunk created such a phenomena in the northern hemisphere of a red giant in 2377, during his attempt to kidnap Seven of Nine from the USS Voyager, in the Delta Quadrant, in order to return her supply of nanoprobes to his ship located in the Alpha Quadrant. (VOY "Inside Man")