Starbursts represent a different style of star-forming activity: not only is star formation more intense, but it also tends to produce more stars in compact, massive star clusters. This concentration of stars into small regions and their influence on the surroundings sets a requirement for high angular resolution observations over a range of wavelengths that only HST can meet. These points are illustrated through a discussion of some of the current issues regarding the nature and impact of super star clusters in nearby starburst galaxies.
Starbursts are not simply scaled-up versions of the disks of normal spiral and irregular galaxies. The composite HST WFPC2 image of the classic starburst galaxy M82 in Figure 1 illustrates some of the differences. Star formation is localized in a well-defined central zone, where it is concentrated in clumps, beyond which there is virtually no star-forming activity (O'Connell & Mangano 1978). The well-known superwind extends above and below the plane out to kiloparsecs beyond the main starburst zone (Shopbell & Bland-Hawthorn 1998 and references therein). In M82 we can observe the combined effects of stellar feedback and a weak interaction with M81 in sufficient detail to test our models of galactic star formation. This is critical for understanding how the cycling of baryonic matter through stars relates to the overall structure of a galaxy, including its dark matter halo; e.g., through its influence in varying the luminosity part of the Tully–Fisher relationship (van Driel, van den Broek & Baan 1995).