A transformation in progress

A visually striking collection of interstellar gas and dust is the focus of this week's Hubble Picture of the Week. Named RCW 7, the nebula is located just over 5300 light-years from Earth in the constellation Puppis.

Nebulae are areas of space that are rich in the raw material needed to form new stars. Under the influence of gravity, parts of these molecular clouds collapse until they coalesce into protostars, surrounded by spinning discs of leftover gas and dust. In the case of RCW 7, the protostars forming here are particularly massive, giving off strongly ionising radiation and fierce stellar winds that have transformed it into what is known as a H II region.

H II regions are filled with hydrogen ions — where H I refers to a normal hydrogen atom, H II is hydrogen that has lost its electron. The ultraviolet radiation from the massive protostars excites the hydrogen, causing it to emit light and giving this nebula its soft pinkish glow. Here Hubble is studying a particular massive protostellar binary named IRAS 07299-1651, still in its glowing cocoon of gas in the curling clouds towards the top of the nebula. To expose this star and its siblings, this image was captured using the Wide Field Camera 3 in near-infrared light. The massive protostars here are brightest in ultraviolet light, but they emit plenty of infrared light which can pass through much of the gas and dust around them and be seen by Hubble. Many of the other, larger-looking stars in this image are not part of the nebula, but sit between it and our Solar System.

The creation of an H II region marks the beginning of the end for a molecular cloud. Over only a few million years, the radiation and winds from the massive stars gradually disperse the gas — even more so as the most massive stars come to the end of their lives in supernova explosions. Only a fraction of the gas will be incorporated into new stars in this nebula, with the rest being spread throughout the galaxy to eventually form new molecular clouds.

[Image Description: Clouds of gas and dust with many stars. The clouds form a flat blue background towards the bottom, and become more thick and smoky towards the top. They are lit on one side by stars in the nebula. A thick arc of gas and dust reaches around from the top, where it is brightly lit by many stars in and around it, to the bottom where it is dark and obscuring. Other large stars lie between the clouds and the viewer.]

Links

• Science paper in Nature Astronomy
• Pan of RCW 7