What wavelengths must astronomers use to penetrate dense cores where stars form?

Longer wavelengths like infrared or radio waves, which can penetrate the obscuring dust.

The densest regions of cosmic clouds, particularly molecular nebulae where gravitational collapse is actively occurring, are optically thick to visible light due to the high concentration of obscuring dust. To gain insight into the processes happening deep within these stellar nurseries, astronomers must employ techniques that allow radiation to pass through this dust layer unimpeded. Longer wavelengths, such as those found in the infrared and radio portions of the electromagnetic spectrum, have longer paths that allow them to penetrate the obscuring material, revealing crucial information about temperature, density, and the formation of protostars.