Strömgren sphere

astronomy

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

A Strömgren sphere is a region of ionized hydrogen surrounding a hot star. Danish astrophysicist Bengt Strömgren discovered that these ionized hydrogen regions are confined to well-defined areas around luminous O- or B-type stars. The intense ultraviolet radiation from these stars is powerful enough to ionize the surrounding hydrogen, creating these spheres.12

These Strömgren spheres are significant because they are strong emitters of radio wavelengths, and their size is directly related to the luminosity of the central star. Astronomers can use the angular diameters of these spheres, even in distant galaxies, to help determine their great distances.2

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

2 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

astronomy
Investigations of interstellar matter
…II region, known as a Strömgren sphere. Such regions are strong and characteristic emitters of radiation at radio wavelengths, and their dimensions are well calibrated in terms of the luminosity of the central star. Using radio interferometers, astronomers are able to measure the angular diameters of H II regions even…
Read More
…II region, known as a Strömgren sphere. Such regions are strong and characteristic emitters of radiation at radio wavelengths, and their dimensions are well calibrated in terms of the luminosity of the central star. Using radio interferometers, astronomers are able to measure the angular diameters of H II regions even…
Read More