…or at least star birth in the galaxies.
Observations of galaxies in the relatively nearby parts of the Universe show a wide variety of different morphologies. One style is that of a blob of old red stars in which no star birth is present. Studies into why there are these ‘dead’ galaxies and more active star nurseries about have normally focused on ways to get star birth going – big disruptions to the gas and dust in the galaxy. However, a team of scientists using the Hubble space telescope and the Chandra x-ray space telescope have looked at this another way – what could happen to switch off a galaxy? The answer, they believe, lurks in the very centre of every galaxy – a supermassive black hole.
Using the x-ray space telescope to infer the presence of an active black hole and then Hubble to investigate the optical galaxy itself, they conclude that the effect of massive radiation from an overactive accretion disc around the black hole is expulsion of light gas from the galaxy. With little gas to then form new stars, the galaxy will simply age with its stars. They believe that with a third or so of galaxies hosting these killers, the black holes can be made to perform this deadly feat when, for example, two galaxies merge. They also believe that some galaxies holding overly violent black holes may be warped by their activity, explaining lens shaped galaxies that show no signs of collisions with others.