Astrophysicists from Masaryk University contributed to research published in the journal Nature that first revealed intergalactic wind. Using the cutting-edge Resolve spectrometer onboard the Japanese XRISM satellite, they analysed the X-ray spectrum of the centre of the Centaurus cluster of galaxies. The research showed that the galaxy NGC4696 is exposed to winds with velocities ranging from 130 to 310 km/s, which prevent the cooling of gas and the formation of stars. This discovery brings new insights into the weather and the role of black holes in galactic atmospheres.
It is widely known in the scientific community that regular matter composed of atoms makes up only 5 percent of the Universe; the rest is mysterious dark matter and dark energy, about which we know very little. However, even from that 5 %, we only see a small fraction. The vast majority of normal matter does not form planets, stars, or galaxies, but exists in the form of tenuous matter that fills the space between galaxies. This rare and hot "gas" can be observed in the largest galaxies and galaxy clusters using X-ray space telescopes. Astrophysicists sometimes refer to this material, whose existence was revealed by space observatories fifty years ago, as galactic atmospheres. Up until now, astrophysicists have been able to measure their density, temperature, or pressure, but it was hitherto not known whether they are windy, turbulent, or quiet. This aspect of intergalactic weather in the Centaurus cluster was revealed by the X-Ray Imaging and Spectroscopy Mission (XRISM) satellite.
The Centaurus cluster, located approximately 100 million light-years from Earth, was one of the first targets that the XRISM satellite focused on with its Resolve spectrometer after launch. The Resolve instrument has about 30 times better resolution than spectrometers on previous missions, making it particularly suitable for measuring gas velocities with unprecedented precision. Observations revealed that the galaxy NGC4696, situated at the centre of this cluster, is subjected to winds blowing with velocities of 130 to 310 km/s. It appears that this gas in the middle of the cluster exhibits oscillatory motion, mixing the gas and thereby preventing its cooling and subsequent star formation.
Astrophysicists from Masaryk University are part of the scientific team of the XRISM mission as "guest scientists" nominated by the European Space Agency (ESA). Their contribution to this research primarily involved the analysis of imaging data from the Chandra X-ray satellite, which reveals signs of the interaction of outflows from the vicinity of the black hole at the centre of this galaxy cluster with the surrounding gas. "Plasma outflows from black holes in the centres of galaxy clusters create cavities in galactic atmospheres that are often larger than individual galaxies. Using a detection method I developed, we discovered three generations of these cavities in the centre of this cluster, allowing us to study the influence of the supermassive black hole on intergalactic weather," says Tomáš Plšek, a PhD student of astrophysics at the Faculty of Science of Masaryk University and a co-author of the article. "This observation suggests that intergalactic winds caused by previous galaxy cluster mergers may prevent the conversion of intergalactic material into stars and planets. Until now, we thought that star formation in the centres of galaxy clusters was primarily inhibited by black holes, but the XRISM satellite has just shown us the importance of 'intergalactic winds,'" adds Norbert Werner, a guest scientist in the scientific team of the XRISM mission, working at the Faculty of Science of Masaryk University. The research was supported by the GAČR EXPRO grant number 21-13491X.
Norbert Werner, Professor – Institute of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University
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