Sparks in the Dark

NASA/ESA Hub­ble

Vio­lent things can come in small faint pack­ages as shown in this NASA/ESA Hub­ble Space Tele­scope image of the star­burst galaxy NGC 3738.

Explore the glow­ing red reser­voirs of hydro­gen gas, fil­a­ments of dust, and dif­fuse glow of thou­sands of stars in this faint irreg­u­lar galaxy. What shapes and sto­ries do you see? Leave a note in the com­ments below.

NGC 3738 is a dwarf galaxy in the mid­dle of extreme star for­ma­tion. The glow­ing red areas are full of hydro­gen, the stuff that helps make new stars. Grav­ity pulls together gas and dust in pock­ets within the cloud. As the pocket becomes more mas­sive, it begins to heat up until even­tu­ally it can become hot enough to fuse hydro­gen atoms in a sus­tain­able nuclear reac­tion. These new stars give off strong stel­lar winds and ultra­vi­o­let radi­a­tion that excites hydro­gen atoms in the rest of the cloud caus­ing it to glow a char­ac­ter­is­tic red.

This galaxy is rel­a­tively close to Earth; just 12 mil­lion light-years from the Sun; mean­ing light, trav­el­ing nearly 6 tril­lion miles per year, took 12 mil­lion years to cross the inter­galac­tic dis­tance. NGC 3738 is a com­pact bluish dwarf galaxy, the faintest of star­burst galax­ies. Blue com­pact dwarfs are gen­er­ally blue because of large clus­ters of hot, blue and young stars. These stars tend to be mas­sive, mean­ing they burn through their sup­ply of hydro­gen fuel within just a mil­lion years. If they are mas­sive enough, they will end their lives in cat­a­clysmic stel­lar explo­sions called super­novae. For a time, a sin­gle star can out­shine an entire galaxy, releas­ing more energy in a few moments than our Sun pro­duces in its entire expected lifes­pan of 8 bil­lion years.

As you explore NGC 3738, you may notice it seems jum­bled and dis­or­ga­nized. These galax­ies don’t have spi­ral arms nor bright cen­ter bulges. Some astronomers believe these galax­ies resem­ble some of the ear­li­est galax­ies that formed in the early Uni­verse and may pro­vide clues into how stars and galax­ies formed dur­ing that time. As you pan across the image, look for dozens of faint and far­away galax­ies scat­tered through­out this deep image of the cosmos.

NGC 3738, first observed by British astronomer William Her­schel in 1789, is found in the con­stel­la­tion Ursa Major, The Great Bear or Big Dip­per. It belongs to the Messier 81 group of galax­ies, a nearby galac­tic cluster.

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