![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheQyirIbh0616g8JOYqPWACiB4G1ZSikJheHaZ5kkdlIsexAPLb5jqt53eNbS0ESUOoQjwyY3p0wKbXC0SDBO4kPEqqLw7gF5-KKnfx7_wpOx0aWuK6ywEq2QwABsMd8qSc4gwSo1cu96k/s200/Ultra+luminous+Infrared+Galaxies.jpg)
Ultra luminous
Infrared Galaxies (ULIRGs)
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The satellite IRAS discovered a class of ultra
luminous galaxies that radiate more than 90% of infrared light. Studies
show that optical and infrared most of these objects are in systems of galaxies
in collision or interaction. The study of the nature of ULIRGs and their
relation to active galaxies (see next paragraph) is one of the most important
problems in astrophysics.