A kink in one of its spiral arms suggests that the galaxy M66 recently staged a close encounter with a nearby companion galaxy. The kink is near the center of this image, and is marked by a bright red blob of newly forming stars. M66 is about the size of the Milky Way, as is its companion, M66. Gravitational interactions between the two galaxies may have distorted M66 and spurred the birth of many new stars. [NASA/ESA/Hubble Heritage]
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Our home galaxy, the Milky Way, and the Andromeda galaxy are the two largest members of the Local Group, a gathering of dozens of galaxies. They’re all gravitationally bound to one another, so even as the universe expands, their gravitational pull will keep them close together.
But the Local Group is hardly the only galaxy group in the universe. In fact, on spring nights the eastern sky features two large galaxies that resemble Andromeda and the Milky Way.
M65 and M66 are near Denebola, the bright star that marks the tail of Leo, the lion. Like Andromeda and the Milky Way, both are spiral galaxies. And also like the Milky Way, each is about a hundred thousand light-years across. M66 is a bit off-kilter, suggesting a fairly recent encounter with another galaxy. The encounter squeezed giant clouds of dust, causing them to give birth to millions of new stars.
M65 and M66 are a similar distance from us — a bit more than 30 million light-years. And they’re quite close to each other. In fact, they’re probably bound to each other just as the Milky Way and Andromeda are, so they’ll remain partners long into the cosmic future.
And you can see these two galaxies tonight. Look for Leo rising in the east as night falls. If you have a dark sky and a good pair of binoculars or a small telescope, the two galaxies should appear in the same field of view. They show us what our Local Group would look like if we could view it from afar.
Script by Ken Croswell, Copyright 2015