Until our gravitational observatories become sensitive enough, the best way to learn about supermassive black holes is to look at how they affect their surroundings.

An international team of astronomers has used the ALMA observatory to discover a unique, swirling, cool jet of dense gas in NGC 1377, a galaxy 70 million light-years away. The researchers are hopeful that this finding will shed some light on how supermassive black holes grow.

“We were curious about this galaxy because of its bright, dust-enshrouded center. What we weren’t expecting was this: a long, narrow jet streaming out from the galaxy nucleus,” said team-leader Susanne Aalto in a statement.

The observations, presented in Astronomy & Astrophysics, show a jet 500 light-years long traveling at a speed between 240 and 850 kilometers per second (500,000 to 1.9 million mph). Usually, jets emitted by black holes are narrow, straight, and hot. But NGC 1377’s jet, with its twisted cool clumpy gas, is something else entirely.

“The jet’s unusual swirling could be due to an uneven flow of gas towards the central black hole. Another possibility is that the galaxy’s center contains two supermassive black holes in orbit around each other” said Sebastien Muller, also a member of the team, in the statement.

^{Alma’s close-up view of the center of galaxy NGC 1377 (upper left) reveals a swirling jet. Aalto et al./ALMA}

The jet formed very quickly, in about half a million years, but it is surprisingly big, with researchers estimating the gas content to weigh about two million times the mass of the Sun. This rapid accretion indicates that whatever growing mechanism is happening around the black hole is happening very fast.

“Black holes that cause powerful narrow jets can grow slowly by accreting hot plasma. The black hole in NGC 1377, on the other hand, is on a diet of cold gas and dust, and can, therefore, grow – at least for now – at a much faster rate,” explained team member Jay Gallagher from the University of Wisconsin-Madison in the statement.

The hot jets are usually quite destructive for star formation in galaxies, as they generate galaxy-wide winds that snuff out new stars. But black holes have also been observed helping new stars being born, and what’s happening in NGC 1377 might be in the latter category.

All these findings combined suggest the supermassive black hole is going through a quick accretion phase, another clue in the mystery that surrounds galaxy evolution.