Primordial Black Hole
These atom-sized mini black holes formed during the early stages of the Big Bang. Despite their tiny size, they mass a few billion tons, about the same as a mid-sized asteroid. Most primordial black holes evaporated in a storm of energy a few billion years ago, but a few were large enough to survive. Some appear to have had close encounters with other celestial bodies (mostly the many billions of chunks of rock and ice in the Kuiper Belt or Oort Cloud). Braked by tidal forces as they interpenetrated, they slowed down enough to be gravitationally bound within them. Their slow decay produces enough heat and gamma radiation to be noticed.
As early as the late 20th century, the theoretical existence of primordial black holes had been postulated by Steven Hawking, and Robert Forward had proposed a mechanic for their survival inside minor planets. Nevertheless, no one expected to find any, especially inside our solar system, as theory predicted less than one per cubic light year. After Muldoon went public with her discoveries and people knew what to look for, a half-dozen were found using sensitive infrared and gamma-ray telescopes. With the exception of Shezbeth, all were scattered about the Oort Cloud, separated by hundreds of AU.
One primordial black hole, occupying the Kuiper Belt Object 112434 Shezbeth, has been recovered. The next nearest one is inside comet 2098 D2, an ice-and-rock body about 12 miles in diameter. 2098 D2 is in an eccentric orbit and is currently passing “relatively” close to the sun, at a distance of 1,100 AU.
The other five mini black holes detected to date are all in the Oort Cloud, 40,000+ AU away.