My story opens with an old man who arrives at his "personal" asteroid somewhere out in space. When he arrives, everything is powered down and he has to bring systems online before he can take his suit off. He has left galactic society (perhaps there was a war) and he wants to live out his final days inside this rock. There is something in there he wants to see one last time. In years (or centuries) previous, he had significant resources to expend to hollow it out and create comfortable living space inside as well as a "workshop" for his pet project. Some sort of reactor (or collector) powers the whole thing, runs life support, etc.
Here are some ground rules of the story's universe:
No FTL - All travel is sublight, though much faster than what we can do in the present day. Some time dilation occurs and hibernation allows people to survive trips potentially spanning centuries.
No artificial gravity - Cylindrical colonies spin for centrifugal effect, but humanity has not figured out "gravitons" or whatever. We can fake it, but we can't make it.
Detection technology - In the present day, we look at the skies with radio telescopes, optical telescopes, etc. In this future scenario, there hasn't been significant advance other than increased resolution and clarity applied to the same principles of physics we understand now. I'm sure there are other present-day technologies that I am unaware of. If any of these might affect this question, I'd hate to be ignorant of them
So the nut of my question is this:
How can he "hide" this asteroid, yet still be able to find it later?
Most likely, nobody would even be looking for it, but our protagonist is paranoid or at least careful. He would want it to not stand out too much from any other asteroids due to heat, unusual EM output, or any other odd behavior that could be noticed from great distances (if someone happened to be observing that part of the sky, potentially from any angle). As for locating it later, other than just eyeballing whatever region of space it's in once he gets there, I imagined there could be some sort of doohickey made of a material that only reflects EM waves of a specific obscure frequency. Shoot a blast of that frequency out into that general region and get a "ping" back once it hits the rock. Not sure how feasible that is though.
The following aspects of the asteroid (and/or his ship) are flexible as needed to satisfy the requirements of the question:
Size of the asteroid - I don't know if it's the size of a house or the size of Texas, nor how this might affect not only its visibility, but its feasibility for hollowing out and inhabiting. Also, he doesn't have to use all the real estate. The inside could be the size of a house and the outside could be the size of Texas.
Composition of the asteroid - Rock. Haha, but seriously, we assume he searched long enough/got lucky enough and found the "perfect" asteroid that can remain obscure, yet could be mined for at least some resources.
Power source - Fusion? Fission? "Arc reactor" a la Iron Man? Some other magical McGuffin "future technology"? This might be the one place I'd have to apply some phlebotinum to make it work. Considerations would again include heat, EM waves, etc. that would affect how detectable it is.
Propulsion - The asteroid itself might have a similar propulsion system to his ship though not geared toward interstellar travel. It would be used for simple maneuverability and attitude adjustments. But what it is and how it works is up in the air. See "Power source" above. Otherwise, simple rockets could work, or even something that expels gases if it only needs to be nudged slightly. Again, how it would affect detectability is a consideration.
"Gravity" - Since we can't make gravity, the asteroid could spin for the aforementioned centrifuge effect. This might make docking his ship a bit more difficult unless he spins it up only after landing. But dependent on size, type of propulsion, power source, etc. it might be cost prohibitive to spin it up after landing, not to mention spinning it down upon his previous departure. And all that activity might make it more noticeable. I know the larger the rock, the more likely its own gravity would assert some force upon the man, but I imagine it would still be trivial. From the get-go I've been leaning toward magnetic boots. Staying in a non-spinning asteroid for long periods would likely lead to the usual microgravity symptoms such as atrophy, osteoporosis, etc. But he plans on dying here in peace, so this is not as much of a consideration.
Proximity to other heavenly bodies - Would it be better if the asteroid were near enough to a star to glean some energy from it? Would this make it more noticeable or less? Would it be better to orbit a planet which is itself in orbit around such a star? Or would it be better to be somewhere in the deep, away from the other cosmic "big boys"? Would being off in a relatively "dark" area of space make it more noticeable or less? This is assuming its power source can keep it warm enough inside to sustain a human life for possibly years.
Hopefully this is enough conditions (and not too many!) to help fill in any of my gaps in logic. I appreciate everyone's time and thoughts. Thanks!
Edit to address possible duplicate:
This is not a duplicate of the "stealth in space" question, as that seems to be geared toward an active cat-and-mouse type scenario involving a moving ship that is travelling hither and yon, trying to outsmart space pirates who also travel hither and yon.
In the case of the old man and the asteroid, the rock doesn't need much maneuverability nor sensor capability. EM and heat emissions would be shielded as much as possible and the whole thing wouldn't be going anywhere other than its existing orbital path.
Additionally, one of the requirements was that it could not hide behind or in front of things. No such restriction applies to my question. In fact, the allowance for hiding among other asteroids lent itself to part of the accepted answer.