Life on the Edge

Credit: ESA/Hub­ble & NASA

An ancient ball of stars, known as NGC 6934, lies at the outer reaches our galaxy in this image from NASA’s Hub­ble Space Tele­scope.

Explore this great clus­ter of a few hun­dred thou­sand stars. Glob­u­lar clus­ters are groups of stars that are born together from great clouds of gas and dust. Usu­ally star clus­ters drift apart over time, but grav­ity holds these clus­ters together. NGC 6934 lies about 50,000 light-years from Earth toward the dim con­stel­la­tion Del­phi­nus, the Dol­phin. The glob­u­lar clus­ter is home to some of the most remote stars in our galaxy. NGC 6934 was first seen by William Her­schel in the late 18th cen­tury. The clus­ter is just one of about 150 other glob­u­lar clus­ters that form a dis­tant halo around the core of the Milky Way.

The col­ors in the image are a bit mis­lead­ing how­ever. New stars are usu­ally blue in color. Big, blue stars don’t usu­ally live very long before explod­ing as super­novae. Glob­u­lar clus­ters are incred­i­bly ancient. So why all the blue stars in the image? Astronomers some­times take images of stars through col­ored fil­ters to learn more about the stars. The red-colored stars are glow­ing brightly in infrared mean­ing they are prob­a­bly red giants. The blue stars are actu­ally yellow-orange in color. Many of the stars in this clus­ter are prob­a­bly sim­i­lar to our Sun, although much older.

Astronomers use glob­u­lar clus­ters as a key to under­stand­ing how stars form. Since all of the stars are born at about the same time from the same cloud, astronomers can focus on other details of the stars par­tic­u­larly about how they age and die.