NASA-JAXA’s XRISM Telescope Clocks Hot Wind of Galaxy M82

Astronomers have clocked gas hurtling out of a nearby galaxy at more than 3 million kilometers per hour — and the reading is making some old models look incomplete.

A team led by Erin Boettcher, an astrophysicist at the University of Maryland and NASA's Goddard Space Flight Center, used the XRISM space telescope to measure the velocity of superheated plasma streaming from M82, the starburst galaxy nicknamed the Cigar for its elongated shape. The hot wind came in at roughly 1,700 kilometers per second, the team reported in Nature on March 25 — faster than some prior models expected, and fast enough to carry gas well beyond the galaxy's gravitational reach. The escape velocity for M82 is around 450 km/s; the measured wind is roughly triple that.

"We see the gas moving even faster than some models predict, more than enough to drive the wind all the way to the edge of the galaxy," Boettcher said in a statement from NASA. M82 sits about 12 million light-years away in the constellation Ursa Major and is forming stars at roughly 10 times the Milky Way's rate — which is why it has enough supernovae and stellar winds to drive an outsized outflow in the first place.

What Resolve actually did

The measurement came from XRISM's Resolve instrument, a microcalorimeter spectrometer developed jointly by NASA and JAXA. XRISM (the X-ray Imaging and Spectroscopy Mission) launched from Tanegashima Space Center on September 6, 2023 — not a concept, not a roadmap, a working spacecraft in orbit. Resolve's 36-pixel detector array, chilled to roughly -270 degrees Celsius, resolves X-ray energies to about 7 electron-volts. For context, the CCD-based spectrometers on Chandra and XMM-Newton manage 100 to 150 eV. That difference in resolution is why older instruments could estimate velocities from M82's hot gas only indirectly; Resolve reads the Doppler broadening of iron emission lines directly, giving a genuine speed measurement rather than an inference.

The gas the team measured is not the visible wind. M82's extended cool wind, observable in optical and ultraviolet light, stretches roughly 40,000 light-years from the galaxy's disk. The hot wind traced by XRISM is a separate, inner-layer outflow at 45 million degrees Fahrenheit, thought to be powered by the collective energy of supernovae and stellar winds in the galaxy's densely packed core. "A fast starburst wind consumes most of the energy from supernovae," as the paper's title puts it — meaning the outflow is acting as a primary thermostat for the galaxy's star-forming engine.

Earlier work had pointed to this territory. A 2024 preprint by Boettcher and co-author Edmund Hodges-Kluck, based on XMM-Newton data, used OVIII spectral line broadening to estimate velocity dispersion in the hot gas at roughly 1,160 km/s — a measurement that reflected the range of velocities present in the turbulent plasma, not a direct read of bulk outflow speed. XRISM's Resolve instrument, with its superior energy resolution, confirmed that turbulent signature while adding a cleaner direct measurement of the overall wind velocity. The 1,700 km/s number is the new result; the 1,160 km/s context is from an earlier instrument answering a related but distinct question.

The missing gas problem

The result has a problem built into it. The team calculates that a wind moving at the measured speed can drive out about four solar masses of gas per year. But the total mass leaving M82's center — both the hot and cool components combined — is closer to seven solar masses per year. That leaves three solar masses per year unaccounted for.

"If the wind blows steadily at the speed we have measured, then we think it can power the larger, cooler wind by driving out four solar masses of gas a year," said Edmund Hodges-Kluck, a co-author and NASA Goddard astronomer on the XRISM team. "But XRISM tells us much more gas is moving outward."

Where's the rest? The paper doesn't say. The authors note that the discrepancy could reflect gas at temperatures between the hot and cool phases, or a time-variable wind that hasn't been sampled uniformly. It's an open question in a peer-reviewed paper, not a footnote.

What this is and isn't

This isn't a discovery of a new phenomenon. Starburst-driven galactic outflows have been observed for decades. What XRISM delivered is a precise velocity measurement of the hot wind component that powers those outflows — the mechanism that links supernova energy to large-scale gas removal. The instrument did its job. The universe still has questions the paper's authors haven't answered — which is how science works when the hardware is more capable than the models.

Sources: NASA Science press release | Nature paper (Boettcher et al., March 25, 2026) | arXiv preprint (Boettcher & Hodges-Kluck, 2024) | NASA XRISM spacecraft page