Star Forming Regions

Since the '80s the $\mathit{\text{Einstein}}$ observatory has shown the Young Stellar Objects (YSOs), emit X-rays with luminosities, in the 0.3–8 keV bandpass, up to ${10}^3$–${10}^4$ times than the Sun and that the X-ray emission is highly variable. ROSAT has confirmed the pervasiveness of X-ray emission from YSOs and ASCA has provided evidence that the emission of Class I YSOs is largely originating from optical thin-plasma at temperature of 1-50 $\times {10}^6$ K. These intrinsic, unexpected, properties and the transformational capabilities of the $\mathit{\text{Chandra}}$ and $\mathit{\text{XMM-Newton}}$ observatories has made X-rays a powerful tool to trace the star formation process up to distance of a few kpc around the Sun. Starting from the early evidences of the '80s and the intriguing questions they raised, I will summarize the results obtained and how they have influenced our current understanding of physical processes at work and I will discuss some of the still open issues and some of the likely avenues that next generation X-ray observatory will open.