Are there any objects in space that are borderline dense where light can only partially excape?

Question

Can it leave these objects at a slower speed because they are not quite "dense enough"?

Answer 1

Of course there are such objects, but they are hard to discover. A neutron-star is a good example. Such a star is not visible with the eye or optical telescopes because there is no light, or better said only to be discovered by its emission of neutrons (that's why it is named neutron star). These are the densest objects in space after the black holes.
However, it cannot be answered whether you could escape at a speed slower than c, because we just don't know the real escape velocity for these neutron stars.
Scientist have calculated (by the mass of the stars), that some of the known objects are on the brink to become a black hole and some are not even worth to be mentioned, because their escape velocity is comparable to our sun. The only difference, a neutron star with an assumed escapevelocity of our sun is only about 20 km in diameter ... from that you can estimate its density.
Such thing you can indeed call "borderline dense".

Answer 2

Short answer: yes. Some black holes may, in fact, be (or once have been) much smaller than a basketball. Quantum black holes, produced during the Big Bang, would have been smaller than a proton at first. Stephen Hawking suggests that most of these may have 'evaporated', unable to sustain their own existence as space expanded because there were not enough nearby particles to absorb. According to the math, some mass DOES escape a black hole as the intense warping of space causes particle pairs to generate from the energies involved. One particle of each pair is thrown off radially. Should such a small black hole come within range of the sun's gravity field, the two would eventually be drawn together (a basketball sized hole would probably have a mass similar to that of the sun). Eventually they would collide. The masses involved might well produce a nova, in which case, 8 minutes later, the Earth would be subject to an enormous surge in photons. This would probably incinerate us. If not, a short while later the actual wavefront of hard radiation would reach us. It would, at least, strip the planet of its atmosphere and irradiate the surface, making it unliveable. If the shock wave were powerful enough, it might incinerate the surface, cause tectonic upheaval and even throw the planet out of its orbit. If the b-hole was not massive enough to cause a nova, it would orbit the sun, spiraling inward until it reached the center of mass, and growing in size. It would continue to orbit the center until it had absorbed the entire star. This process would take some time, possibly millennia. The ability of a black hole to absorb matter is a function of its mass, and also of its magnetic field. That field deflects some mass, just as the Earth's does. Mass falling into a black hole falls into a planar orbit, like the plane of the ecliptic within the solar system (There's a reason most of the planets travel in concentric orbits. The eccentric orbit of Pluto is one of the reasons astronomers not longer want to consider it a planet.). As the hole absorbs more mass, its ability to absorb increases. Toward the end, the sun would shrink very rapidly and its output in visible light and hard radiation would diminish.

Answer 3

No. Light travels at a constant speed, known as c, so it either escapes or does not, depending on what the escape velocity is for its environment. Black holes are the only known phenomena that have an escape velocity greater than c. Any "interesting" behavior of light would occur within the event horizon, and could never be observed. However, it might be possible for a phenomena to occur at the event horizon of a black hole, such that part of the phenomenon occurs inside the region where the escape velocity exceeds c, and part of it occurs outside of that region. Only the latter portion of the phenomenon would be observed, and so to an observer it would appear to emit less light or radiation than it actually releases.

Answer 4

The only black holes that I know of is in the middle of a Galaxy. That is the only dense thing That I know would have enough gravity to hold all the solar systems in orbit.