Megamaser
Astrophysical masers with luminosities 100 million times brighter than Milky Way masers.
A megamaser is a type of astrophysical maser, a naturally occurring source of stimulated spectral line emission, distinguished from other astrophysical masers by its large isotropic luminosity. Megamasers have typical luminosities of 10³ solar luminosities (L☉), which is 100 million times brighter than masers in the Milky Way, hence the prefix 'mega.' Most known extragalactic masers are megamasers, and the majority of megamasers are hydroxyl (OH) megamasers, though megamasers are also known for water (H₂O), formaldehyde (H₂CO), and methine (CH).
- first discovered
- 1979 (water megamaser in NGC 4945)
- first hydroxyl megamaser
- 1982 (Arp 220)
- typical luminosity
- 10³ L☉
- common molecule
- hydroxyl (OH)
- other molecules
- water (H₂O), formaldehyde (H₂CO), methine (CH)
- known hydroxyl megamasers (as of 2007)
- 109
- known water megamasers (as of 2007)
- 65
Lore & Background
The first megamaser discovered was a water megamaser in 1979 in NGC 4945, a galaxy in the nearby Centaurus A/M83 Group. The first hydroxyl megamaser was found in 1982 in Arp 220, the nearest ultraluminous infrared galaxy to the Milky Way. All subsequent OH megamasers have been found in luminous infrared galaxies, most of which have recently merged or interacted with another galaxy and are undergoing a burst of star formation. Water megamasers and kilomasers are found primarily associated with active galactic nuclei, while galactic and weaker extragalactic water masers are found in star forming regions.
Reader's Guide
Megamasers are significant because they provide a powerful tool for studying extragalactic environments and physical processes. Hydroxyl megamasers, for instance, are hosted in luminous infrared galaxies that often show signs of recent mergers and star formation bursts. The population inversion in hydroxyl molecules is produced by far infrared radiation from forming stars, and Zeeman splitting of hydroxyl megamaser lines may be used to measure magnetic fields in the masing regions, representing the first detection of Zeeman splitting in a galaxy other than the Milky Way. Water megamasers have been used to make accurate measurements of distances to galaxies, providing constraints on the Hubble constant. The study of megamasers also reveals differences between extragalactic and galactic masers, such as the amplification of background radiation and distinct line ratios in hydroxyl megamasers. As of 2007, 109 hydroxyl megamaser sources were known, and over 100 extragalactic water masers were known, with 65 bright enough to be considered megamasers.
Did You Know?
- The first megamaser discovered was a water megamaser in 1979 in NGC 4945.
- The first hydroxyl megamaser was found in 1982 in Arp 220, the nearest ultraluminous infrared galaxy.
- Zeeman splitting of hydroxyl megamaser lines provided the first detection of Zeeman splitting in a galaxy other than the Milky Way.
- Observations of water megamasers have been used to make accurate measurements of distances to galaxies to constrain the Hubble constant.
More in Astronomical radio sources 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record