

Although Hubble-X and Hubble-V in the nearby galaxy NGC 6822 looks strikingly similiar to the nearby Orion Nebula in our Milky Way galaxy, they are much brighter and much bigger. In fact, if the Orion Nebula were placed at the distance of NGC 6822, it would be about the same brightness and size as the tiny bright knot visible just below Hubble-X in the Heritage image. Fascinating facts on the three objects: Orion is 450 pc distant and roughly 3 pc in diameter. Hubble-X in NGC 6822 is 500 kpc distant and 34 pc in diameter. The winner in size (by far) is Hubble-V, also at 500 kpc distant but nearly 60 parsecs in diameter!

Hubble-X in NGC 6822
HST - O'Dell
Orion Nebula
KPNO 4m- Bally
Hubble-V in NGC 6822
HST - O'Dell/Bianchi

Link to the Hubble Heritage Release on Hubble-X in NGC 6822


The giant clouds of hydrogen gas shown in the above NASA Hubble Space Telescope images contains a large number of hot, massive stars. Many are probably over 20 times more massive than our Sun (and thus over 100,000 times more luminous). All of the stars are very young, less than 10 million years old. They reside in star-forming regions called Hubble-V and Hubble-X.

Hubble's spectacular resolution allowed a group of European and American astronomers* to pinpoint individual stars in these crowded regions and measure their brightness and temperatures. They made their extensive analysis because of the telescope's ability to detect ultraviolet light, which is emitted by the hottest young stars. Their analysis has provided a better understanding of the populations of stars inside the cloud.

Hubble's sharp "eye" also allowed the astronomers to estimate the temperatures, brightness, ages, and masses of many stars. From this information, the astronomers determined that many of the stars formed at the same time.

The hot, massive stars emit a tremendous amount of radiation, which sculpted and illuminated the large gas cloud in which the stars were born. The cloud is actually composed of several "bubbles" of gas blown by the hefty stars. The hot radiation also energizes the gas, making it glow.

Besides unleashing powerful ultraviolet radiation, the massive stars also lose a significant amount of mass in "stellar winds." These winds travel at supersonic speeds (up to 6.7 million miles an hour or 10.8 million kilometers an hour), carrying away up to more than a solar mass per star every million years. The winds slam into the surrounding gas cloud, and may play a major role in triggering star formation of smaller-mass stars. The young stellar families in Hubble-V and Hubble-X are revealing the exact roles of all the stars in a stellar breeding ground. These two regions reside in a galaxy called NGC 6822, 1.6 million light-years away.

Why are these very massive stars so important? The interiors of massive stars - unlike those of most stars, including the Sun - reach high enough temperatures to transform through nuclear fusion great quantities of primordial elements, such as hydrogen and helium, into heavier elements. Therefore, they are responsible for producing all the existing oxygen, carbon, nitrogen, silicon, and calcium - just to name a few very familiar, life-sustaining elements. And they do so very effectively, too. A very massive star completes its life cycle in about 10 million years (1,000 times faster than the Sun). As a massive star reaches the end of its life, it releases most of its processed material back into space by exploding as a supernova or by shedding it more gently, forming the delicate shells of a planetary nebula.

* L. Bianchi, S. Scuderi, P. Massey and M. Romaniello - results appeared in the Astronomical Journal April 2001 issue.

Visit a Related Site of NGC 6822 at the NOAO Website