Oh no! Another alien probe

[Anomalocaris]

The reason to believe this kind of object would be difficult to form in any environment other than around stars, or at least progenitors of stars, is random motion excerts a pressure on any collections of particles In interstellar space just as if they were a gas.  Small assembligaes of particles are therefore difficult to form because particle pressure prevent any over concentration from forming.  Any particles that touch and stick together are more likely to be blasted apart by the next extremely rare collision through random motion than to stick to form larger assemblagess.

The only time this condition change is if gravitational instability causes gas cloud to collapse.  This becomes a self reinforcing process and will eventually lead to formation of one or more collapse gas cores in the cloud that become progenitors of stars.   Only when the core is fairly massive and well on its way to becoming an infant star, would it excert enough gravity on the surrounding to create such an overbdensity of particles and gas can be sustained, and particles are likely to stick and grow rather than collide and then be blasted apart.

I've a calculation that suggest without gravitational help from a star or star progenitor,  the average time when particles in interstellar space can randomly accrete to asteriodal size is many orders of magnitude greater than the age of universe.