Barnard’s Galaxy as seen by ESO
What do you get when you point a powerful telescope at a tiny, irregular dwarf galaxy that just so happens to be a neighbor of the Milky Way Galaxy? The folks at the European Southern Observatory did just that and created an amazing image of a tough little galactic neighbor brimming with star formation regions, interesting bubble-shaped nebulae,and scads of hot, blue stars.
Now, you may look at this image and think to yourself, “It doesn’t look like a galaxy — don’t all galaxies have spiral arms?”
Well, not always. There are many in the universe that look like this — oddly misshapen, dwarf-sized collections of stars. Yet, even though Barnard’s Galaxy doesn’t have that spiral-armed grace and large central bulge that the Milky Way and Andromeda have, it plays an important role in stellar and galaxy evolution. In addition, its reddish nebulae are the same kinds of active star-formation regions that we see in larger galaxies. These regions glow because their hot young stars are heating the surrounding gas clouds. Also prominent in the upper left of this new image is a striking bubble-shaped nebula.
At its heart (if you zoom in closely), you can make out a collection of massive, superhot stars that are sending waves of matter smashing into the material in nearby regions. The interaction has created what looks like a glowing ring around the central region. Look closely enough and you’ll see other regions where hot young stars are heating up their neighborhoods.
This tough, tiny little galaxy comes in at about a tenth of the size of the Milky Way and has about 10 million stars. Yet, as part of the Local Group, it’s in the majority of galaxy types because the Local Group dwarfs outnumber the “normal” spirals. This kind of begs the questions, “What’s the norm?” And “How do these galaxies fit in the hierarchy of other galaxies?
Irregular dwarf galaxies are blobby and not very well-defined. They get these amorphous shapes from close encounters of the galactic kind that go on for millions of years.
How does that work?. Like everything else in the universe, galaxies are in motion, and this means that at some point, a given galaxy will encounter at least one other one during its lifetime. They often make close passes or even go through one another. The density of stars in galaxies is quite low, meaning that few stars physically collide. But, the gravitational effect that each galaxy has on the other will warp and twist their shapes. When this happens, huge collections of stars are pushed or pulled in new directions, or even flung out away from the galaxy where they formerly “lived.” After the encounters, the resulting galaxies look a lot like Barnard’s Galaxy — irregular, with regions of star formation and star death studded among their other stars. They have to be tough to survive the close encounters of the galactic kind!