Herschel will allow us to measure unambiguously the stars born in the universe at every moment of its history, there are 10 billion years to the present day. Herschel will study in detail the composition of the interstellar medium of galaxies, focusing especially on interstellar dust that hides the birth of stars.
The different types of galaxies
A galaxy is a collection of stars, gas, dust and dark matter. Taken together, the dust and gas form what is called the interstellar medium. There is a wide range of sizes and shapes of galaxies:
- Elliptical galaxies, gas poor, who form a fairly regular ellipse.
- Spiral galaxies, which are made of a hard end filled with a mixture of gas, dust and stars, and a thicker bulb in the center mainly filled with stars. It is in the disk of spiral arms qu'apparaissent more or less numerous and more or less marked. The Milky Way belongs to this category.
- Irregular galaxies, often small and low-mass gas-rich and-poor stars.
These categories include the dwarf galaxies. The properties of dwarf galaxies are important because astronomers suggest that the most massive galaxies like ours come from the merger of small galaxies.
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