The bubbling Milky Way: An overview of infrared bubbles in our galaxy

Abstract

Infrared bubbles are cavity-like structures formed around OB-type star(s) or star clusters. They are detected primarily at mid-infrared wavelengths. They usually enclose ionized gas and hot dust, composed of very small grains. A combination of thermal pressure of the expanding HIIregion, powerful stellar winds, and radiation pressure associated with massive stars contribute to the formation of a bubble. Expanding bubbles could trigger star formation, either via the collect and collapse process or radiatively driven implosion. This can further provide a pathway for understanding the aspects related to triggered star formation. This article provides a brief overview on infrared bubbles, their association with the HIIregion,the massive and young stellar objects they enclose, and the mechanisms of triggered star formation when they expand to the interstellar medium. As a representative example, we present a multiwavelength investigation of the northern infrared bubble CN71. The physical environment of the bubble CN71 is investigated using Spitzer data. We have detected 29 Class I/II YSOs and 459 Class III YSOs by NIR-MIR photometric analysis. We have also detected the presence of 5 OB-type stars within the bubble boundary. Using the Gaia EDR3, we estimated the distance to the bubble to be 1.6 kpc. Our preliminary analysis suggests that CN71 shows the signature of triggered star formation.