The Herschel Space Observatory’s lifespan ended in April 2013 when it ran out of coolant, just shy of a 4 year run orbiting the “second Lagrangian point (L2) of the Earth–Sun system,” a position in orbit behind the sun and Earth where the gravitational pull on objects is at its weakest point.
Operated by the European Space Agency (ESA), Herschel “specialised in collecting light from objects in the Solar System as well as the Milky Way and even extragalactic objects billions of light-years away.” But perhaps its greatest legacy is the completion of an exhaustive survey of cosmic dust that helps scientists distinguish the types of galaxies that exist in the universe.
This survey is almost akin to the periodic table of elements that provides an organized chart of all the known atoms and their properties.
A significant ingredient in the evolution of galaxies and in the formation of stars and planets, cosmic dust interacts with gas and other cosmic elements in ways scientists are only now beginning to understand. Using Herschel’s far-infrared and submillimetre wavelengths, scientists have been able to create a catalogue of 323 distinctive types of galaxies based in part on their cosmic dust composition.
Organized into a collage, galaxies that are rich in dust appear in the upper left of the graphic and galaxies with decreasing concentrations of dust appear in the bottom right. The graph provides intriguing insights into how varying amounts of dust influence the shape of galaxies. Irregular and spiral-shaped galaxies are often rich in dust, while elliptical-shaped galaxies are dust-poor.
The colors depicted in the chart are also revealing. Looking at the Herschel survey chart, galaxies whose dust is cooler due to a greater number of older stars assume hues of blue, while galaxies with hotter dust due to a greater number of young stars assume hues of red.
Thanks to Herschel’s data of cosmic dust, astronomers have plenty of information to sift through as they try to gain additional insights into the physical properties of cosmic dust and how they help form and shape stars, planets and galaxies.