This is probably nutty, but something like adiabatic magnetic refrigeration might work. https://en.wikipedia.org/wiki/Magnetic_refrigeration
Imagine taking the iron core of a dead star. Apply a mind-bogglingly large external magnetic field, using something like solar-system-wide Helmholtz coils. Maybe Magneto could do it. Anyway, once the system equilibrates to the new high field, the iron core will be magnetized, meaning all of its magnetic domains are aligned along the field.
Now start to lower the externally applied magnetic field. I'm not sure how to estimate over what timescale it can be lowered, but there would be an incredible amount of energy stored in a stellar core sized chunk of iron, so I would guess centuries just comparing that mass to a standard adiabetic magnetization refrigerator mass.
As the magnetic field decreases, the core's magnetic domains will start to randomize by absorption of thermal energy. But until the magnetic field is zero, the domains will reorient themselves to this lower energy state, resulting in a "spontaneous" decrease in entropy, cooling the body. So over whatever time scale you lower the magnetic field, the body would overall be colder than surrounding space, with the cooling power equal to the decrease in stored magnetic energy over time.
It would be artificial to set up, but in principle it could be a relic from an older hyper-advanced civilization, with the magnetic field machinery just now decaying when we find it.