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Leo1 is a spheroidal dwarf galaxy in the constellation of Leo, located only 12arcmin away from Regulus (α Leo). With a distance of ~820000 lightyears it's the most distant satellite of the Milky Way.
It has a mass of ~20million solar masses and contains about 10milion stars, it's only 2000ly across. Recently evidence for a massive black hole in Leo1 with 3million solar masses has been found, see
https://iopscience.iop.org/article/10.3847/1538-4357/ac0c79/pdf. It is unexpected that a tiny galaxy like Leo1 hosts a black hole that is nearly as large as the one at the center of the Milky Way. So far it was believed that giant black holes grow from galaxy collisions and therefore their size should correspond with the galaxy's size.
Dwarf galaxies challenge more current theories. For example it is not explained yet why we only find so few dwarf galaxies while cosmological simulations predict way more (
https://en.wikipedia.org/wiki/Dwarf_galaxy_problem). (However, more and more dwarf galaxies and dwarf galaxy candidates are found.)
There are more problems:
Cusp/Core problem
https://en.wikipedia.org/wiki/Cuspy_halo_problemToo-Big-To-Fail problem (
https://arxiv.org/abs/1111.2048)
Planes-of-satellites problem (the mystery that observations have suggested that the Milky Way and Andromeda each have satellite galaxies generally within a plane, and each such plane is not the plane of the host galaxy, but tilted in relation to it which is unexpected when satellites are indeed formed together with the host galaxy).
Dwarf galaxies are indeed an interesting subject.
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