Normally, most galaxies such as our Milky Way tend to be diffused. Sure, the Milky Way, for example has 400 billion stars, but it is spread out over 150,000 light years. Which means that the Milky Way has a moderate star density, and is not clumped together.
However, I read this article which talked about something that left me shocked.
The problem is, that this galaxy's 100 million stars are packed tightly into a region only about 300 light-years across. For reference, the Small Magellanic Cloud is about 3,500 ly across.
Even more baffling is the fact that this UCD3, despite having much less mass than our Milky Way, has a supermassive black hole that clocks in at about 3.5 million solar masses. For comparison, the Milky Way's supermassive black hole, only weighs about 4.1 million solar masses.
This means that UCD3's SMBH contains about 4% of the mass of its host galaxy. Typically, most SMBHs contain less than 1% of their galaxy's mass. This makes UCD3 an extremely baffling galaxy.
How could these ultracompact galaxies have formed in the first place?