Starship Asterisk*

Scientists using ALMA to look deep into the heart of UGC 4211 discovered two black
holes growing side by side, just 750 light-years apart. This artist’s conception shows
the late-stage galaxy merger and its two central black holes. The binary black holes
are the closest together ever observed in multiple wavelengths.
Credit: ALMA (ESO/NAOJ/NRAO); M. Weiss (NRAO/AUI/NSF)

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While studying a nearby pair of merging galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA)— an international observatory co-operated by the U.S. National Science Foundation’s National Radio Astronomy Observatory (NRAO)— scientists discovered two supermassive black holes growing simultaneously near the center of the newly coalescing galaxy. These super-hungry giants are the closest together that scientists have ever observed in multiple wavelengths. What’s more, the new research reveals that binary black holes and the galaxy mergers that create them may be surprisingly commonplace in the Universe. ...

At just 500 million light-years away from Earth in the constellation Cancer, UGC4211 is an ideal candidate for studying the end stages of galaxy mergers, which occur more frequently in the distant Universe, and as a result, can be difficult to observe. When scientists used the highly sensitive 1.3mm receivers at ALMA to look deep into the merger’s active galactic nuclei— compact, highly luminous areas in galaxies caused by the accretion of matter around central black holes— they found not one, but two black holes gluttonously devouring the byproducts of the merger. Surprisingly, they were dining side-by-side with just 750 light-years between them. ...

• Astrophysical Journal Letters 942(1):L42 (2023 Jan 01) DOI: 10.3847/2041-8213/aca8f0
  arXiv | astro-ph | arXiv:2301.03609 | 09 Jan 2023