Hydrogen in the universe exists in various states, including cold molecular clouds, warm diffuse clouds, and highly ionized regions. The appearance and visibility of hydrogen in different energy states depend on several factors, including its temperature and the specific wavelength of light being observed.
In cold molecular clouds, hydrogen can be in its lowest energy state, known as the ground state. At these low temperatures, hydrogen molecules tend to be in their most stable form, which is difficult to observe directly with optical telescopes. However, other wavelengths, such as radio waves, can penetrate these clouds and allow scientists to study the molecular composition and properties of these cold regions.
In warm diffuse clouds and ionized regions, hydrogen can exist in higher energy states. When excited by energy sources like stars or energetic events, hydrogen atoms can absorb or emit light at specific wavelengths, such as the Balmer series in the visible spectrum. This emission and absorption of light at characteristic wavelengths are used in various astronomical observations, such as spectroscopy, to study the properties and dynamics of ionized hydrogen.
It's worth noting that the detection and observation of different energy states of hydrogen depend on the sensitivity and capabilities of the instruments used for observation. Scientists employ a range of telescopes and detectors operating across different wavelengths to study different aspects of the universe.
In summary, while the majority of hydrogen in the universe may exist in a cold state that is not directly observable with visible light, it can still be studied through other wavelengths, such as radio waves or through the emission and absorption lines associated with higher energy states. Different observational techniques and instruments allow scientists to probe the diverse characteristics and behavior of hydrogen in the universe.