In the dense, star-forming gas cloud W44, the ALMA telescope has spotted eight tiny clumps racing at enormous speeds. In position–velocity maps, each one looks like the letter V, just like the previously discovered 'Bullet'. This resemblance hints at a common origin.
Most likely, it wasn't a single object that dove into the cloud at high speed, but an entire small cluster of compact objects — possibly the remnants of an old star cluster. Their total mass, estimated from the velocity dispersion, is about one hundred thousand solar masses — roughly that of a typical globular cluster. Momentum analysis suggests the main 'Bullet' could have been created by a lone black hole that punched straight through the gas.
Such 'bullets' offer a rare glimpse of how invisible dense objects interact with the gas in the Galactic disk. They leave behind not only a hole but also a hot trail that radio telescopes can detect.
The line widths of the 'bullets' correspond to speeds up to tens of kilometers per second — faster than a rifle bullet.