Between stellar and supermassive black holes, intermediate-mass black holes (hundreds to hundreds of thousands of solar masses) are rare and hard to detect. They may form from dense star clusters or early universe conditions.
It matters because they could bridge our understanding of black hole growth and galaxy evolution.
It also informs searches for gravitational wave sources.
Intermediate-mass black holes are elusive cosmic objects with only a few candidates observed.
[NASA, nasa.gov]