Free Astronomy Magazine March-April 2023

T he pair of merging galaxies known as UGC 4211 are har- boring one big se- cret: a pair of black holes that are dining to- gether, gobbling up the gas and dust around them. Scientists found and confirmed the existence of the pair — which are just 750 light-years apart — with observations from multiple research projects and telescopes: the Dark Energy Camera Legacy Survey (DECalS) on the Blanco 4 meter telescope at Cerro Tololo Inter-American Observatory (CTIO), the Multi- Unit Spectroscopic Explorer (MUSE) on ESO’s Very Large Telescope (VLT), the Keck Observatory, and the Atacama Large Millimeter/submillimeter Array (ALMA). Observing the galaxies in multiple wave- lengths helped scientists to see that there was more than a merger going on between the pair. [ALMA (ESO/NAOJ/NRAO), M. Koss et al (Eureka Scientific)] 50 MARCH-APRIL 2023 ASTRO PUBLISHING nucleus in the system,” said Treister. “And ALMA showed us the exact lo- cation of these two growing, hungry supermassive black holes. All of these data together have given us a clearer picture of how galaxies such as our own turned out to be the way they are, and what they will become in the fu- ture.” So far, scientists have mostly studied only the earliest stages of galaxy mergers. The new research could have a profound im- pact on our under- standing of the Milky Way Galaxy’s own im- pending merger with the nearby Androm- eda Galaxy. Koss said, “The Milky Way-An- dromeda collision is in its very early stages and is predicted to occur in about 4.5 bil- lion years. What we’ve just studied is a source in the very final stage of collision, so what we’re seeing presages that merger and also gives us insight into the connection be- tween black holes merging and growing and eventually producing gravitational waves.” “This fascinating discovery shows the power of ALMA and how multi- wavelength astronomy can generate important results that expand our understanding of the universe, including black holes, active galactic nuclei, gal- axy evolution and more,” says Joe Pesce, NSF program director for the Na- tional Radio Astron- omy Observatory. “With the advent of gravitational wave detectors, we have an opportunity to ex- pand our observa- tional powers even further by combining all these capabilities. I don’t think there’s really a limit to what we can learn.” T his video shows an illustration and ALMA images of two black holes having dinner together and greedily devouring the dust, gas and other material displaced by the collision. [ALMA (ESO/NAOJ/ NRAO), M. Koss et al (Eureka Scientific), S. Dagnello (NRAO/AUI/NSF)] !