Hot Interstellar Medium

Normal spiral galaxies such as our own Milky Way contain immense volumes of very hot gas, with temperatures of millions of degrees. We are beginning to understand the sources and life cycle of this gas, heated by supernova explosions and the winds from young, hot stars. It is still not clear, for example, how this gas, rich in newly synthesized elements such as carbon, oxygen, and iron, cools and is recycled into future generations of stars and planets (e.g. in starbursts and galaxy mergers). Gas at these temperatures is a potent source of x-rays, smoothly distributed over large areas of the sky.

We have used Chandra and other x-ray observatories to survey our own and other galaxies for bubbles of hot gas. Teasing apart the foreground heliospheric x-ray emission from Galactic hot gas, and from extragalactic x-ray sources, is tricky, but can be approached due to the superb angular resolution of the Chandra X-ray Observatory.

This hot gas fills voids in cooler gas, which can be seen in absorption with satellites such as HST and FUSE. Five-times ionized Oxygen in the boundaries of hot regions can be studied with FUSE, and combined with x-ray observations of six- and seven-times ionized oxygen to provide a more complete picture of the hot interstellar medium.