From the Super Mario Wiki
Purple Bombers are ghosts found in Luigi's Mansion. Purple Bombers are purple colored Ceiling Surprises and are usually found in the same places as them, but appear more often in later areas. One major difference between Ceiling Surprises and Purple Bombers is that Purple Bombers can attack with dropping a bomb. Purple Bombers have zero Heart Points and can be sucked up without effort. However, it will come back as long as the area that Luigi is in is dark.
Strangely enough, unlike their weaker counterparts, Purple Bombers are not always guaranteed to produce a heart once defeated.