This week we continue our month-long journey through the world of galaxies, but this time, we move beyond what galaxies are and explore what galaxies actually do. It turns out these vast islands of stars are anything but static. They collide, merge, exchange gas and dust, fling stars into deep space, and sometimes grow by consuming smaller neighbors in a process astronomers call galactic cannibalism.

We begin close to home with the Sagittarius Dwarf Spheroidal Galaxy, a hidden companion galaxy currently being torn apart by the gravity of our own Milky Way. From there, we travel some 70 million light-years away to the spectacular Antennae Galaxies, where two spiral galaxies are locked in a slow-motion collision that is both destructive, and strangely creative.

Along the way, we recall my recent conversation with astrophysicist Enrique López Rodríguez to explore the possibility of magnetic bridges and “superhighways” carrying gas, dust, and charged particles between galaxies, raising the astonishing possibility that the raw ingredients of future planets may sometimes originate far beyond their home galaxy.

And finally, we return to the question we teased last week: What about us? Is the long-predicted collision between the Milky Way and the Andromeda Galaxy still inevitable? New observations from Hubble Space Telescope and Gaia suggest the answer may be far less certain than we once believed.

We'll also check in with this week's night sky, and wrap up our discussion of NightWatch.

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