The smallest spherical objects in the known universe are subatomic particles, specifically elementary particles. Elementary particles are the building blocks of matter and are not composed of smaller constituents. They are considered point-like particles, meaning they have no internal structure or size.
The Standard Model of particle physics describes several types of elementary particles, including quarks, leptons, and gauge bosons. Quarks are the fundamental particles that combine to form protons and neutrons, which are found in the nucleus of atoms. Leptons include electrons and neutrinos, which are the constituents of matter outside the atomic nucleus. Gauge bosons are responsible for mediating the fundamental forces in the universe, such as photons for electromagnetism and W and Z bosons for weak nuclear interactions.
These elementary particles are incredibly small, with sizes on the order of 10^(-19) to 10^(-17) meters. Keep in mind that they are point-like in nature, so they don't have a physical extent like macroscopic objects. The concept of "size" in particle physics refers to the range over which the particle's influence is felt or the region within which the particle's probability distribution is concentrated.
Regarding the composition of elementary particles, they are not made up of smaller components. Instead, they are considered fundamental and indivisible entities. However, they do possess various properties, such as mass, electric charge, and spin, which are used to characterize and distinguish them.