The High Acuity Wide field K-band Imager (HAWK-I) on ESO’s Very Large Telescope (VLT) in Chile has taken the most detailed infrared image so far of a super star cluster called RCW 38.

A super star cluster is a very massive, young star cluster that is thought to be the precursor of a globular cluster. These clusters are referred to as ‘super’ due to the fact that they are more luminous and contain more mass than other young star clusters.

The super star cluster RCW 38 is the youngest (younger than one million years old) of the Milky Way’s 13 super star clusters, and the densest stellar system within 13,000 light-years of the Sun.

It contains hundreds of young, hot, massive stars and brown dwarfs, and lies approximately 5,500 light-years away in the constellation Vela.

RCW 38 is an ‘embedded’ cluster, in that the nascent cloud of dust and gas still envelops its stars.

The central area of the cluster is visible here as a bright, blue-tinted region.

The intense radiation pouring out from the newly-born stars causes the surrounding gas to glow brightly.

This is in stark contrast to the streams of cooler cosmic dust winding through the region, which glow gently in dark shades of red and orange.

Previous images of RCW 38 taken in optical wavelengths are strikingly different — optical images appear emptier of stars due to dust and gas blocking our view of the cluster.

Observations in the infrared, however, allow astronomers to peer through the dust that obscures the view in the optical and delve into the heart of this star cluster.

This image of RCW 38 was captured as part of a series of test observations — a process known as science verification — for the HAWK-I camera and its GRAAL adaptive optics system.

“HAWK-I is installed on Unit Telescope 4 (Yepun) of the VLT, and operates at near-infrared wavelengths,” explained ESO astronomer Bruno Leibundgut and colleagues.

“GRAAL is an adaptive optics module which helps HAWK-I to produce these spectacular images. It makes use of four laser beams projected into the night sky, which act as artificial reference stars, used to correct for the effects of atmospheric turbulence — providing a sharper image.”

“With HAWK-I/GRAAL data, we can directly study several key aspects of star formation: massive star birth; low-mass star and brown dwarf formation in a dense environment and under the influence of photoionization fronts from massive stars; the initial mass function; and mass segregation in young clusters.”

The science verification of the HAWK-I/GRAAL system was presented in a paper in The Messenger.

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Bruno Leibundgut et al. 2018. HAWK-I/GRAAL Science Verification. The Messenger 172: 8-12; doi: 10.18727/0722-6691/5074