Astennu first came to notice as the guitarist and songwriter for the Australian black metal band Lord Kaos.

Astennu stayed in Norway and reworked some music he had written for Lord Kaos into songs for a solo project called Carpe Tenebrum.

[1] The first Carpe Tenebrum album Majestic Nothingness featured Astennu on all instruments with vocals from Nagash of Dimmu Borgir and The Kovenant.

He also contributed some guitar solos to the Aggressor album and the Triumph of the Blasphemer EP by Nocturnal Breed, a band that also featured Dimmu Borgir's other guitarist Silenoz.

In 2002 he recorded and released a third Carpe Tenebrum album, Dreaded Chaotic Reign, this time performing vocals himself.