X-ray Superbubbles  by David Burrows

Like supernova remnants, superbubbles are produced as large hot stars interact with the surrounding interstellar medium. Where a supernova remnant is produced by the explosion of a single star, a superbubble is produced by the combined stellar winds and supernova explosions of an entire stellar association containing dozens of stars in a relatively small region of space. An enormous amount of energy is dumped into the interstellar medium by such a cluster of stars during their lifetimes, with the result that the gas is pushed away from the association and large cavity filled with very tenous hot gas is left behind. This cavity can be hundreds or even thousands of light-years across. If the gas inside it is hot enough (several million degrees Celsius), it emits X-rays.

An example is the very old superbubble known as the Orion-Eridanus superbubble. This is a large cavity in the interstellar medium created by stellar winds from the Orion OB1 association and possibly reheated by supernova explosions from this same association. The superbubble is the bright (green/red/white) object near the center of this false-color soft X-ray map (from Snowden et al. 1995, ApJ, 439, 399) made by the ROSAT satellite (shown above, left).

In order to study this object in more detail, we have analyzed a large number of ROSAT pointed observations obtained by other astronomers for other purposes. Many of these fields contain apparent X-ray shadows correlated with dust filaments observed by the IRAS satellite. Followup 21 cm observations were made towards these filaments using the 140 foot telescope of the National Radio Astronomy Observatory (shown at right with PSU graduate student Zhiyu Guo, who collected and analyzed these data with Dr. David Burrows). The 21 cm data were used to identify the velocities of the dust filaments (by measuring their Doppler shift). Optical observations by Mr. Guo at Kitt Peak National Observatory allowed us to use the presence or absence of Na I absorption lines in stellar spectra at the velocities of the filaments to determine the distance to some of these dust clouds.

Click here for a postscript file (375K bytes) of a 4 page paper on the Orion-Eridanus superbubble presented at the conference "Roentgenstrahlung from the Universe" in Wuerzburg, Germany on September 27, 1995.

Click here for a compressed postscript file (20K bytes) of a 4 page paper on the size and pressure of the Local Bubble presented at the conference "The Local Bubble and Beyond" in Garching, Germany on April 22, 1997. (This paper is related to the one above on the Orion-Eridanus superbubble.)

Related work includes our study of X-ray emission from supernova remnants.   For more information, contact  David Burrows(burrows@astro.psu.edu).