Free Astronomy Magazine July-August 2023

17 JULY-AUGUST 2023 ASTRO PUBLISHING T he Gemini North telescope, one half of the International Gemini Observatory, operated by NSF’s NOIRLab, captured this dazzling image (previous page) of the so-called Taffy Galaxies — UGC 12914 and UGC 12915. Their twisted appear- ance is the result of a head-on collision that occurred about 25 million years prior to their appearance in this image. A bridge of highly turbulent gas devoid of significant star formation spans the gap between the two galaxies. The video above describes the bridge. [International Gemini Observatory/NOIRLab/DOE/ NSF/AURA, T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Rodriguez (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab), ESA/Hubble/L. Calcada, D. Munizaga, N. Bartmann] Galaxy collisions can happen out of a variety of different scenarios, often involving a larger galaxy and a smaller satellite galaxy. As they drift near one another, the satellite galaxy can attract one of the larger galaxy’s primary spiral arms, pulling it out of its orbit. Or the satellite galaxy can actually intersect with the larger gal- axy, causing significant distortions to its own structure. In other cases, a collision can lead to a merger if nei- ther member has enough momen- tum to continue on after colliding. In all these scenarios, stellar material from both galaxies mixes through a gradual combining and redistribu- tion of gas, like two puddles of liq- uid that are slowly bleeding into each other. The resulting collecting and compression of the gas can then trigger star formation. A head-on collision, however, would be more like pouring liquid from two sepa- rate cups into a shared bowl. When the Taffy Galaxies’ collided, their galactic disks and gaseous compo- nents smashed right into each other. This resulted in a massive injection of energy into the gas, causing it to be- come highly turbulent. As the pair emerged from their collision, high- velocity gas was pulled from each galaxy, creating a massive gas bridge between them. The turbulence of the stellar material throughout the bridge is now prohibiting the collec- tion and compression of gas that are required to form new stars. The Gemini North observations of this object were led by Analía Smith Castelli, an astronomer with the In- stituto de Astrofísica de La Plata in Argentina. Argentina is one of the partners in the International Gemini Observatory. !