Unless someone is watching 100% of the sky for even the slightest miniscule changes, I imagine you could get mighty close (granted, close is Pluto) without being detected.
Isn't most of the information we have about newly discovered far away objects is how they interacted with other known far away objects?
But, of course, there's the given that if we've advanced far enough to engage in space combat then we've likely created technology to help in detection.
Ships CAN be bright, we have the tech now to make them dark.
True, burning fuel is a big problem. Especially if they were traveling rather fast towards us and they flipped over to reverse thrust to slow down. But what if you don't burn fuel as a means of propulsion?
I'm going with the assumption if that if someone wished to do something bad, say invading a neighboring solar system, they would take precautions in being detected.
The article was also operating within the realm of theoretically available technology. There are very few propulsion systems that don't emit hot matter out the back (like solar sails) and the article addressed them suitably.
-You can do a full survey in about 5 hours with one telescope these days.
-Ships are very bright, don't look anything like stars and CCDs are very sensitive.
http://www.projectrho.com/rocket/spacewardetect.php has a good break down.
This tells me that 6 years ago we did not know all of the +300m asteroids within the orbit of Mars. How much better are we now? I read the page you linked to, but that didn't list actual numbers based on asteroid searches.
There's an estimated 4,000,000 asteroids in the solar system of size 300m or larger. I sincerely doubt that a telescope survey of 5 hours finds 1 million+ asteroids each night, otherwise that number would be pinned down a lot better. (It can't find all 4 million because at 5 hours there's still substantial portions of the sky unseen.)
Using the formula in the "Refrigeration" section of the page linked to by Avshalom, the "maximum range a ship running silent with engines shut down" (assuming diameter = 500 m and temperature = 290K is about 500 million km, or about 3.3 AU. That's well within the orbital radius of Jupiter.
That's assuming the entire asteroid is at 290K. Pluto averages about 40 AU out, given a 0.056% chance that a room-temperature asteroid would be detectable.
I'm also uncertain about the reasoning in the page linked to by Avshalom. I think that assumes a 3K background, and I think you also think there's a big heat differential. However, the average temperature of the moon is something like -25C, and if an asteroid were closer to the sun, then the difference in surface temperature between an internally heated vs. sun heated asteroid is well within the errors in measuring the physical properties of the asteroid.
You can even work it out for yourself, using the equation at http://en.wikipedia.org/wiki/Standard_asteroid_physical_char... . I worked it out to:
166C at Mercury orbit: http://www.google.com/search?&q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(0.3+*+150000000+km)**2)))+**+(1%2F4)
90C at Venus orbit: http://www.google.com/search?q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(0.6+*+150000000+km)**2)))+**+(1%2F4)
5C at Earth orbit: http://www.google.com/search?q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(1.0+*+150000000+km)**2)))+**+(1%2F4)
Still, that's enough to show that the heat differentials inside of the Earth's orbit are not that big.
I should restate what I said: instead of "that's assuming the entire asteroid is at 290K", I mean, "except the insulation layer", which you need anyway to keep the near-surface area livable.
If you need 20 meters for that, then your living volume is 21 million cubic meters, or a reduction of about 20%.
That's not to say that there's no contribution. More that I believe the calculations from that linked-to page ignore the difficulties of differentiating between the internal heat (cooled through black-body radiation) from surface heat from the sun.
For example, from Stefan-Boltman, cooling goes as T * * 4, which means if you have a cooling radiator on the sun-side which is at 150C, or 20C above "normal", then it's about 6 times more effective than a -90C radiator on the cold side. I suspect it's easier to stop the 20C delta on the cold side than the warm side.
Otherwise, I just don't see interstellar space warfare as being that practical if it takes years to launch an attack.
What about a neutron star? It's probably too exotic to consider how a wormhole would interact with a black hole.
I don't know how much density is in a 5,000 kg chunk of the sun.