There are Lovecraftian horrors, alien beyond mundane monstrosity, encountered by those most unlucky, where the vile beings have slipped from their cryptonic other-realms into our mundane universes. These beings are truly alien; they could not belong in any sane universe such as we mere mortals could comprehend. It is horrific enough to consider that there must exist universes, or rather dimensions stranger still, where such blasphemies do indeed belong, without our being forced to the mind-shattering realization that they may, upon apocalyptic occasion, be able to inflict a shadow-made-substantive of their inconceivably bizarre real selves on our all-too-vulnerable mundane universes.
In some of the more warped universes explored by the Empire, there are vast beasts, living monstrosities, which dance in orbit as planets might gods which seem to mortal eyes as suns emitting a black anti-light. The spawn and larvae of such horrors are launched through their dimensions, and occasionally seep through cracks into more mundane realities.
This has, upon occasions most ill-starred, given rise to races so horrific that the only rational reaction to the knowledge of their existence is to eradicate them where possible, and to flee and seal against all possible breaching all access to such realms lost irrevocably to unutterable corruption.
There are diaries and ships' logs better left unread which hint at entire planets being but acretions upon the shells of such beasts, of stars which are not simple balls of insindiary elements, blazing bright but harmlessly in the mundane universe, but rather are as pinpricks wrent through the oh-too-fragile membrane which separates our mundane reality from dimensions of unholy energies, stars whose very light corrupts.
Any artifacts, such as relict ships found adrift and somehow twisted in a manner unsetling beyond mere physical wrecking,any such artifact which might suggest that such horrors, or even lesser monsters merely tainted by the shadows of such imposible vileness, may have inhabited some mortal worlds, are better destroyed than understood.
Some have seen glimpses of their impossible reality during inter-dimensional travel. Such ravaged souls are kept safely confined, if death has not been merciful enough to spare them their visions.
If this is the effect of observing the shadow of a whisper, think how insensibly perverted must be those wretched minds which have turned to the persuit of actual knowledge of such blasphamy.