Starburst galaxies often host multiphase, galaxy-scale winds thought to enrich the circumgalactic medium and limit further star formation by disrupting interstellar gas clouds1–3. These winds are primarily powered by supernovae4–6, but it remains unclear how supernova energy forms an organized flow. Here we use the Resolve spectrometer on the X-ray Imaging and Spectroscopy Mission to show that the hot (T = 2 × 107 K) gas in the nucleus of the starburst galaxy M82 is moving quickly, with a line-of-sight velocity dispersion \(\sigma =59{5}_{-128}^{+464}\,\mathrm{km}\,{{\rm{s}}}^{-1}\) . This is consistent with a hot, nuclear wind generated by thermal pressure. We show that a free-wind model reproduces the measured temperature but underpredicts the velocity. The inferred mass and energy outflow rates from the nucleus, about 7 M⊙ yr−1 and 4 × 1042 erg s−1, require that most supernova energy is thermalized. These outflow rates provide enough energy to power the ≳30 M⊙ yr−1 cool outflow and still transport up to 3 M⊙ yr−1 to the intergalactic medium, suggesting that thermal gas pressure is sufficient to power the multiphase wind without additional support from cosmic rays7. We also show that the nuclear gas is hotter and faster than the plasma seen on larger scales ( \(kT\,=\,{0.72}_{-0.08}^{+0.10}\,\mathrm{keV}\) , \(\sigma =17{5}_{-73}^{+86}\,\mathrm{km}\,{{\rm{s}}}^{-1}\) ), suggesting a distinct origin for the latter.
