A superbubble scene

This sprawling cosmic vista and subject of today’s ESA/Hubble Picture of the Month comes from the Large Magellanic Cloud, or LMC. The LMC is the largest of the small galaxies that orbit our Milky Way galaxy. At just 160 000 light-years away, the LMC offers a close look at highly active stellar birthsites like the nebula shown here. This nebula is named LHA 120-N44, or N44 for short, and it’s located in the constellation Dorado.

The appearance of this photogenic nebula is dominated by two features: a vast central void and a shell of dense, dusty gas. The central void is a ‘superbubble’ spanning roughly 210 by 140 light-years. The glittering stars at the centre of the void are responsible for its creation; through their powerful stellar winds and explosive supernovae, these stars have expelled much of the gas from which they were born.

When the stars of N44’s central star cluster swept away this gas, the expelled gas formed a shell around the superbubble. New stars are forming in this compressed gas shell, making N44 an interesting target for researchers studying the process of star formation. In particular, astronomers have turned to this nebula as an ideal place to time this process from start to finish. Their goal is to understand how long it takes from the collapse of cold gas clouds into dense knots to the moment nuclear fusion ignites in the heart of a newborn star.

Researchers used Hubble to survey N44 and take a census of its stars, cataloguing nearly half a million stars within the cluster as well as interlopers drifting in front of it. Of the stars surveyed, nearly 30 000 are what astronomers call pre-main-sequence stars, which have yet to begin fusing hydrogen into helium in their cores. This treasure trove of baby stars was discoverable thanks to the high sensitivity and fine spatial resolution of Hubble’s instruments that can pick out faint objects in crowded clusters.

The gas shell surrounding the superbubble is energised by ultraviolet radiation from massive stars, causing it to glow and highlighting several distinct features. Each feature within the broader N44 star-forming complex was catalogued by astronomer Karl Henize in the 1950s. One feature is a smaller bubble, catalogued as N44F, that is located near the upper-right corner of this image. N44F is an interstellar bubble blown by the intense stellar winds of a single hot and massive star. As this previously released Hubble closeup shows, the star’s furious winds and radiation have sculpted the surrounding bubble and created pillars of dusty gas.

The data used to create this image come from an observing programme (#14689; PI: Gouliermis) that aimed to probe stars in the N44 complex that have not yet begun fusing hydrogen into heavier elements in their cores. These data help to determine how long the process of star formation takes, as well as what masses newborn stars typically have. Hubble's sensitive observations of the lowest-mass stars in this region open a new window onto star formation in regions that, like the LMC or the galaxies of the early Universe, are poor in elements heavier than helium.