Free Astronomy Magazine January-February 2024

27 JANUARY-FEBRUARY 2024 ASTRO PUBLISHING one measuring 154 million solar masses and the other 6.3 million solar masses, are approximately 1600 light-years apart. It is esti- mated that the two will eventually merge into one in about 250 million years to form an even more massive black hole while dispersing violent ripples of gravitational waves across spacetime. Because the galaxy is still reeling from the impact, most of the ten- drils we see are ablaze with bright young stars and active stellar nurs- eries. In fact, about 23 objects found in this system are considered candi- dates for young globular clusters. These collections of stars often form in areas where star formation is higher than usual and are especially common in interacting galaxies as we see here. Once the dust has settled, NGC 7727 is predicted to eventually become an elliptical galaxy composed of older stars and very little star formation. Similar to Messier 87, an elliptical galaxy with a supermassive black hole at its heart, this may be the fate of the Milky Way and the Androm- eda Galaxy when they fuse together in billions of years’ time. by NOIRLab Josie Fenske T he swirling arms of a spiral galaxy are among the most recognized features in the cos- mos: long sweeping bands spun off from a central core, each brimming with dust, gas, and dazzling pockets of newly formed stars. Yet this opu- lent figure can warp into a much more bizarre and amorphous shape during a merger with another gal- axy. The same sweeping arms are suddenly perturbed into disarray, and two supermassive black holes at their respective centers become en- tangled in a tidal dance. This is the case of NGC 7727, a peculiar galaxy located in the constellation of Aquarius about 90 million light- years from the Milky Way. Astronomers have captured an evocative image of this merger’s af- termath using the Gemini Multi-Ob- ject Spectrograph (GMOS) mounted on the Gemini South telescope in Chile, part of the International Gem- ini Observatory operated by NSF’s NOIRLab. The image reveals vast swirling bands of interstellar dust and gas resembling freshly-spun cot- ton candy as they wrap around the merging cores of the progenitor galaxies. From the aftermath has emerged a scattered mix of active starburst regions and sedentary dust lanes encircling the system. What is most noteworthy about NGC 7727 is undoubtedly its twin galactic nuclei, each of which houses a supermassive black hole, as con- firmed by astronomers using the Eu- ropean Southern Observatory’s Very Large Telescope (VLT). Astronomers now surmise the galaxy originated as a pair of spiral galaxies that be- came embroiled in a celestial dance about one billion years ago. Stars and nebulae spilled out and were pulled back together at the mercy of the black holes’ gravitational tug-of- war until the irregular tangled knots we see here were created. The two supermassive black holes, G emini South, one half of the In- ternational Gemini Observatory operated by NSF’s NOIRLab, captures the billion-year-old aftermath of a double spiral galaxy collision. At the heart of this chaotic interaction, en- twined and caught in the midst of the chaos, is a pair of supermassive black holes — the closest such pair ever recorded from Earth. [Interna- tional Gemini Observatory/NOIRLab/ NSF/AURA. Acknowledgment: PI: C. Onken (Australian National Univer- sity). Image processing: T.A. Rector (University of Alaska Anchorage/ NSF’s NOIRLab), J. Miller (Interna- tional Gemini Observatory/NSF’s NOIRLab), M. Rodriguez (Interna- tional Gemini Observatory/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab)] !