2023-05-11 16:10:23
The name “quasar” stands for “quasi-stellar radio source”: quasi-stellar because they look like stars, radio source because they were discovered using radio emission.
Image: ESO/M. Grain fairs
Some galaxies have an active core: the black hole located there devours vast amounts of matter. Researchers are now trying to explain how these extreme objects form.
Abillions of galaxies populate the universe. Many of them harbor a massive black hole at their center. In most galaxies, stars and gas clouds revolve around it at a respectful distance. In the case of some galaxies, however, things are quite different: there, in a few tens of millions of years, the mass monsters eat up the masses of up to ten million suns. Before disappearing into the hole forever, this material heats up to unimaginable temperatures and shines many times brighter than the entire surrounding galaxy. Astronomers then speak of active galaxy nuclei, and in their most extreme form of “quasars”. The portmanteau stands for “quasi-stellar radio source”: quasi-stellar because they appear like stars, radio source because they were historically discovered in the radio domain. Quasars are the most luminous objects in the cosmos.
Now, 60 years after the discovery of the first quasar, astronomers seem to have found the answer to a central and long-debated question: what actually drives some galaxies to develop active galactic nuclei, while most lead completely unremarkable lives? The “galactic matchstick” that turns a quiet black hole into a fire-breathing quasar, is, according to a study published in the Monthly Notices of the Royal Astronomical Society publish a second galaxy: Around two thirds of the quasars examined there originated in galaxies that are in the process of merging with a second one. The resulting gravitational forces apparently drew additional material – gas and stars – into the vicinity of the black hole and fed it with it.
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