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24 JULY-AUGUST 2022 ASTRO PUBLISHING Q uasar 3C273 observed by the Hubble Space Telescope (left). The exceeding brightness results in radial leaks of light cre- ated by light scattered by the telescope. At the lower right is a high-energy jet released by the gas around the central black hole. Radio image of 3C273 (right) observed by ALMA, showing the faint and extended radio emission (in blue-white color) around the nucleus. The bright central source has been subtracted from the image. The same jet as the image on the left can be seen in orange. [Komugi et al., NASA/ESA Hubble Space Telescope] jets emanating from the central nu- cleus. A synchrotron jet exists in 3C273 as well, seen in the lower right of the images. An essential characteristic of synchrotron emis- sion is its brightness changes with frequency, but the faint radio emis- sion discovered by the team had con- stant brightness irrespective of the radio frequency. After considering alternative mechanisms, the team found that this faint and extended radio emission came from hydrogen gas in the galaxy energized directly by the 3C273 nucleus. This is the first time that radio waves from such a mechanism are found to extend for tens of thousands of light-years in the host galaxy of a quasar. As- tronomers had overlooked this phe- nomenon for decades in this iconic cosmic lighthouse. So why is this dis- covery so important? It has been a big mystery in galactic astronomy whether the energy from a quasar nucleus can be strong enough to de- prive the galaxy’s ability to form stars. The faint radio emission may help to solve it. Hydrogen gas is an essential ingredient in creating stars, but if such an intense light shines on it that the gas is disassembled (ion- ized), no stars can be born. To study whether this process is happening around quasars, astronomers have used optical light emitted by ionized gas. The problem working with op- tical light is that cosmic dust absorbs the light along the way to the tele- scope, so it is difficult to know how much light the gas gives off. More- over, the mechanism responsible for giving off optical light is complex, forcing astronomers to make a lot of assumptions. The radio waves dis- covered in this study come from the same gas due to simple processes and are not absorbed by dust. Using radio waves makes measuring ion- ized gas created by 3C273’s nucleus much easier. In this study, the as- tronomers found that at least 7% of the light from 3C273 was absorbed by gas in the host galaxy, creating ionized gas amounting to 10-100 bil- lion times the sun’s mass. However, 3C273 had a lot of gas just before the formation of stars, so as a whole, it didn’t look like star formation was strongly suppressed by the nucleus. “This discovery provides a new av- enue to studying problems previ- ously tackled using observations by optical light,” says Shinya Komugi, an associate professor at Kogakuin University and lead author of the study published in The Astrophysical Journal . “By applying the same tech- nique to other quasars, we expect to understand how a galaxy evolves through its interaction with the cen- tral nucleus.” !