[eesmith]

I thought it did talk about binary black hole merges as one source. Here's a quote from the article which seems to match what you describe:

> Inside a globular cluster, a 50-solar-mass black hole could merge with a 30-solar-mass one, for instance, and then the resulting giant could merge again. This second-generation merger is what LIGO/Virgo might have detected

[joemag]

Argh, you are right - the ad fold made it seem like the article ended, yet there were two more paragraphs below it.

Still, rereading the article, the main body seemed a bit coy. It kept talking about how such black holes should not exist, yet I kept thinking “hasn't LIGO detected formation of 60+ solar mass black holes via mergers?”

But perhaps I’m in an extra criticizing mood before my morning coffee.