Neutron stars are city-size stellar objects with a mass about 1.4 times that of the sun. Neutron stars, known to be the smallest stars, pack their mass inside a 20-kilometer diameter. They are so dense that a single teaspoon of them would weigh a billion tons. On average, gravity on a neutron star is 2 billion times stronger than gravity on Earth. In fact, it's strong enough to significantly bend radiation from the star in a process known as gravitational lensing, allowing astronomers to see some of the back side of the star.
The power from the supernova that birthed it gives the star an extremely quick rotation, causing it to spin several times in a second. The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c (i.e. nearly a quarter the speed of light).
There are thought to be around 100 million neutron stars in the Milky Way, a figure obtained by estimating the number of stars that have undergone supernova explosions. 
Slow-rotating and non-accreting neutron stars are virtually undetectable; however, since the Hubble Space Telescope detection of RX J185635-3754, a few nearby neutron stars that appear to emit only thermal radiation have been detected.

PSR J1748-2446ad

The Kuiper Belt is a disc-shaped region of icy bodies - including dwarf planets such as Pluto - and comets beyond the orbit of Neptune. It extends from about 30 to 55 AU and is probably populated with hundreds of thousands of icy bodies larger than 100 km (62 miles) across and an estimated trillion or more comets. The first Kuiper Belt Object was discovered in 1992. The Kuiper belt was named after Dutch-American astronomer Gerard Kuiper, though he did not predict its existence.
It is similar to the asteroid belt, but is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. The Kuiper belt is home to three officially recognized dwarf planets: Pluto, Haumea and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, are thought to have originated in the region.

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