hydrogen line



physics, mathematical physics, philosophy of physics

Surveys, textbooks and lecture notes

theory (physics), model (physics)

experiment, measurement, computable physics




What is called the 21cm hydrogen line or just hydrogen line is the signature of the electromagnetic radiation of wavelength about 21cm which is emitted by hydrogen atoms when the electrons in their shell change quantum state from the “triplet” to the singlet ground state.

In astrononmy

In astronomy, the Tully-Fisher relation is a relation between the asymptotic behaviour of galaxy rotation curves, witnessed by the width of their 21cm hydrogen line, and the total visible baryonic mass of the galaxies.

In cosmology

In the context of cosmology it has been argued (Higan-Rees 79) that observation of a absorption at the 21cm hydrogen line in the cosmic microwave background would be a signal from the time when the first stars? formed and ignited, a cosmological epoch not otherwise accessible to observation. A claim of detection of this signal by the EDGES experiment appeared in BRMMM 18.



In astrophysics and cosmology

The suggestion that the 21cm hydrogen absorption line in the cosmic microwave background should be an interesting probe for early universe cosmology goes back to

Review includes

A claim of detection of the cosmological signal by the EDGES experiment is due to

Discussion incluces

Calling this argument into question:

Arguments that this detection of the 21cm line rules out substantial contributions of fuzzy dark matter: