NGC 4395 is one of the nearest dwarf galaxies with an active nucleus. At its center sits an intermediate-mass black hole — a rare class of objects between ordinary stellar black holes and the supermassive giants in large galaxies. This makes NGC 4395 an ideal laboratory for studying how smaller black holes interact with their surrounding gas.
A team of astronomers targeted NGC 4395 with three powerful instruments simultaneously: JWST (NIRSpec and MIRI spectrographs), the ALMA radio interferometer, and the Gemini optical telescope. JWST alone detected 134 emission lines in the galaxy's nucleus — a detailed chemical fingerprint of the gas around the black hole.
The key finding: the outflows from the active nucleus have a complex layered structure, like an onion. The hottest ionized gas (velocities up to 716 km/s) flies closest to the black hole. Further out — warm molecular hydrogen at temperatures from 580 to 2,900 K. And on the outside — cold gas (below 50 K), traced via the CO molecule by ALMA.
Paradoxically, the cold gas carries the most mass — 1–2 orders of magnitude more than the hot phases. Yet the kinetic coupling efficiency is very low (0.003%–1.4%), and only the low-ionization gas significantly impacts the galaxy's interstellar medium.
These data help explain how intermediate-mass black holes regulate the evolution of dwarf galaxies — a process that remains one of the open puzzles in astrophysics.