Astronomers have discovered a rare pairing of a quasar and a dusty star-forming galaxy.

In the grand scheme of the Universe, only a relatively short time has passed since the first stars emerged and the cosmic web of galaxy clusters formed. Within just a few hundred million years, the Universe developed a large-scale structure. Enormous galaxies, supermassive black holes, and an inconceivable number of stars formed rapidly. It is believed that major catalysts for this rapid development were galaxy mergers, which triggered active star formation and the growth of supermassive black holes.

Quasars are the active cores of galaxies, distinguished by their incredible brightness, which arises from the intense absorption of matter by the central black hole. Scientists associate about half of the quasars found in the young Universe with merger events. It is challenging to identify objects in the young Universe that illustrate the tumultuous development of that era. Fortunately, researchers got lucky.

An international team of astronomers from the USA, Sweden, and Japan studied 21 promising quasars from a time when the Universe was around one billion years old using the ALMA radio telescope array. Their observations focused on the spectral line of ionized carbon (C II), which serves as an indicator of star formation and gas dynamics in interstellar and intergalactic space.

The scientists discovered a rare pair. It turned out that quasar J1133+1603 is connected by a "bridge" of gas to a compact and dust-obscured star-forming galaxy, which has been named J1133c. The article detailing this discovery is available in open access on the arXiv.org website.

The galaxy J1133c is located approximately 32,600 light-years away from the quasar. The presence of the “bridge” and the “stretched” emission to the north of the quasar indicates active merging. In other similar pairs, the distance between the objects is significantly greater. For instance, in the pair of the quasar and the submillimeter galaxy BRI 1202-0725, it reaches 81,500 light-years.

The authors of the study also noted the extraordinarily compact size of the galaxy. It is possible that the quasar has already pulled in an external "shell," or that an active core is located at the center of this galaxy.

Star formation in J1133c is also occurring at an extremely active rate. Over the course of a year on Earth, the galaxy forms stars with a total mass of around one thousand solar masses. In comparison, the star formation rate in the Milky Way is approximately three solar masses per year. Scientists speculate that both the active core and the rapid star formation may result from the merger with the quasar.

The activity of the quasar and the star-forming galaxy, along with the presence of a "bridge" of gas between them, serves as a valuable illustration of the significant role that mergers and gas "exchange" played in the formation of galaxies and the rapid growth of supermassive black holes in the young Universe.