  The massive stars end their lives by supernova explosions leaving central
compact objects that may evolve into neutron stars. Initially, after birth, the
star remains hot and gradually cools down. We explore the matter and star
properties during this initial stage of the compact stars considering the
possibility of the appearance of deconfined quark matter in the core of the
star. At the initial stage after the supernova explosion, the occurrence of
non-radial oscillation in the newly born compact object is highly possible.
Non-radial oscillations are an important source of GWs. There is a high chance
for GWs from these oscillations, especially the nodeless fundamental (f-) mode
to be detected by next-generation GW detectors. We study the evolution in
frequencies of non-radial oscillation after birth considering phase transition
and predicting the possible signature for different possibilities of
theoretical compact star models.
