Ultra-fast black hole winds detected for the first time in a ‘dead’ galaxy

Supermassive black holes lie at the centres of most galaxies. When they accrete matter, they can launch powerful winds that may heat or remove the gas needed to form stars, shaping the evolution of their host galaxies. A team led by researchers from the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) at the Institute of Space Sciences (ICE-CSIC) detected for the first time an ultra-fast wind in a galaxy near the Milky Way that stopped forming stars about nine billion years ago. The results have been published by Astronomy & Astrophysics.

Winds moving faster than about 10,000 km/s are known as ‘ultra-fast outflows’. They arise very close to actively feeding supermassive black holes and can carry enough energy to affect the gas from which stars form. Until now, these winds had been found almost exclusively in active galaxies that are still forming stars or are in the process of shutting down their star formation. 

However, the galaxy studied, called KUG 1208+386, is fundamentally different. Its stellar population indicates that the galaxy stopped forming stars around nine billion years ago, yet its central black hole remains active and launches a wind at approximately 7% of the speed of light, about 21,000 km/s. At this velocity, the wind travels over 200,000 times faster than an F-1 car at full speed and could circle the Earth in less than two seconds. In addition, X-ray observations reveal dense material surrounding the black hole, showing that a gas-rich environment can survive in the nucleus of an apparently ‘dead’ galaxy.

“What surprised us is the strong contrast between the galaxy and its nucleus. The galaxy has been quiescent for billions of years, but its central black hole is still accreting material and driving a powerful wind,” says Yerong Xu, first author and IEEC postdoctoral fellow at ICE-CSIC. “It shows that a galaxy can look ‘dead’ on large scales while remaining remarkably active at its very centre,” he adds.  

The ultra-fast wind was detected using archival X-ray observations obtained with XMM-Newton observatory of the European Space Agency (ESA) in 2009 and NASA’s NuSTAR observatory in 2019, combined with optical spectra obtained by the Dark Energy Spectroscopic Instrument (DESI)–in which the IEEC is involved–in 2022 and released as part of DESI Data Release 1.  

“The discovery of ultra-fast outflows in a quiescent galaxy challenges the convention that these winds are exclusive to gas-rich or active star-forming galaxies. Both discoveries of a global quiescent galaxy and a gas-rich nuclear region imply that they are not directly related to the galaxy properties but depends more on the nuclear environment,” says Mar Mezcua, IEEC researcher at the ICE-CSIC. 

Astronomers generally think that black holes can influence their galaxies in two broad ways. During powerful phases of accretion, radiation and winds can heat or remove gas, thereby suppressing star formation. In galaxies that are already quiescent, radio jets are often thought to provide a longer-lasting “maintenance” feedback by preventing gas from cooling and forming new stars. The discovery raises the possibility that black-hole winds could also contribute to this maintenance phase.

“Our results point to a possible wind-driven form of maintenance feedback,” says Víctor Rodríguez, ICE-CSIC PhD researcher. “Rather than shutting down star formation, these winds may help an already-quiescent galaxy remain quiescent by preventing gas from cooling and forming new stars again.” 

This study advances our understanding of how galaxies stop forming stars and remain quiescent over billions of years, which is one of the central questions in modern astrophysics. 

The next step is to determine whether KUG 1208+386 is an exceptional case or part of a larger population of quiescent galaxies with powerful black-hole winds. By studying more galaxies with ultra-fast outflows, the researchers aim to understand which physical conditions favor the launching of these winds and whether host-galaxy properties can influence wind characteristics.

Lead Researcher at the IEEC

Yerong Xu

Institute of Space Studies of Catalonia (IEEC)
Institute of Space Sciences (ICE-CSIC)
E-mail: yerong@ieec.cat

Mar Mezcua

Institute of Space Studies of Catalonia (IEEC)
Institute of Space Sciences (ICE-CSIC)
E-mail: mezcua@ieec.cat, mezcua@ice.csic