The Hot Corona of the Milky

As early as 1956 Lyman Spitzer showed that the Milky Way has to be surrounded by a large envelope of very hot gas (Fig. 15.26). Almost two decades later the Copernicus satellite, whose scientific program was directed by Spitzer, found evidence for this kind of gas, which began to be called galactic coronal gas, in analogy with the solar corona. The satellite observed emission lines of e. g. five times ionized oxygen (O VI), four times ionized nitrogen (NV) and triply ionized carbon (CIV). The formation of these lines requires a high temperature (100,000-1,000,000 K), and a high temperature is also indicated by the broadening of the lines.

Galactic coronal gas is distributed through the whole Milky Way and extends several thousand parsecs from the galactic plane. Its density is only of the order of 10-3 atoms/cm3 (recall that the mean density in the galactic plane is 1 atom/cm3). Thus coronal gas forms a kind of background sea, from which the denser and cooler forms of interstellar matter, such as neutral hy-

Fig. 15.26. Galaxy's hot corona. NGC 2403 is a spiral galaxy, is seen around the galaxy. Large holes created by supernova similar to our Milky Way. On the right, it is photographed explosions are seen in the gas corona. (Image NRAO/AUI and in visual light. On the left, in a VLA radio image, on the Tom Oosterloo, Astron, The Netherlands) same scale with the optical image, a large hydrogen corona

Fig. 15.26. Galaxy's hot corona. NGC 2403 is a spiral galaxy, is seen around the galaxy. Large holes created by supernova similar to our Milky Way. On the right, it is photographed explosions are seen in the gas corona. (Image NRAO/AUI and in visual light. On the left, in a VLA radio image, on the Tom Oosterloo, Astron, The Netherlands) same scale with the optical image, a large hydrogen corona

drogen and molecular clouds, rise as islands. In the early 1980's the IUE satellite also detected similar coronae in the Large Magellanic Cloud and in the spiral galaxy M100. Coronal gas is probably quite a common and important form of matter in galaxies.

Supernova explosions are probably the source of both coronal gas and its energy. When a supernova explodes, it forms a hot bubble in the surrounding medium. The bubbles from neighbouring supernovae will expand and merge, forming a foamlike structure. In addition to supernovae, stellar winds from hot stars may provide some of the energy of the coronal gas.

Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment