Bruce Balick

Department of Astronomy
PO Box 351580
University of Washington
Seattle, WA 98195
(206) 543-7683

  

Bruce Balick at the launch pad at Cape Canaveral, December 1999.
   Left: Balick and the Hubble Wide-Field Camera 3 design team in front of shuttle "Discovery" on the launch pad, December 1999.
  Right: Bruce is standing in front of the astronauts' port of entry
into the shuttle a week before STS101's launch to repair the Hubble Space Telescope. Bruce would have flown,
but declined because he had a cheap, nonrefundable airline ticket back home to Seattle for a flight that left Orlando before launch.
The silly looking, ill fitting white paper suit that Bruce is wearing is to keep hair out of the shuttle. Oddly, sneezing is allowed.
              --Thanks to Jay Frogel for the picture!

I joined the faculty in 1975 and became the Chair of the Department in 2001. My primary research interest areas are late phases of stellar evolution and the hydrodynamical evolution of the gas that is ejected in these phases. The study of such gas provides important historical insights into the manner in which an evolving star sheds its outer layers. In turn, this provides clues to the mechanical properties of a star, much as the sound made by a bell provides some indication of its size and structure.

The objects that my collaborators* and I study are classified as "Planetary Nebulae" (PNs) because the astronomers who discovered them over a century ago saw that they are small, look round, and appear greenish in color, and reminded them of Uranus.

The strikingly structured nebula (or cloud) of glowing gas surrounds an old, rapidly dying central star, or nucleus. These nuclei have all but run out of fuel to burn -- their brightness comes largely from residual heat left from earlier years.

Nuclei have already shed most of their outer layers by the time we see the nebula. The star we see today is the remnant of the stellar core whose remaining mass is about 55-75% that of the Sun today. (Theories predict that the Sun is destined to become a PN in another 5 billion years.)



These are 3-color images of planetary nebulae coded so that emission
from low-ionization ions is shown in red (N+), moderate-ionization ions
(O++) is shown in green, and high-ionization ions (He++) is shown in blue.
The full set of jpeg color images, along with other images showing faint
halos of gas from previous episodes of mass loss, can be seen by clicking here.

In the past few years I have been analyzing some spectacular images of planetaries from the Hubble Space Telescope. My work is compiled and described on a separate WWW page written in a non technical style.
We used to think that nuclei simply shed their outermost layer, producing a bubble of slowly expanding material that eventually dissapated into the background interstellar medium. However, pictures like those below indicate that the process is far more interesting. Although none of these nebulae look like an expanding bubble, all have round outlines. Also, within these outlines is complex but symmetric structure, suggesting that whatever the process that shapes nebulae, it is a coherent one involving ejection mechanisms that act over size scales of the dying star, or larger.

The cartoon to the left shows a model of a PN which is surrounded by a donut of ejected material has been assumed to be expelled earlier. The nucleus (ligh blue) now ejects a wind (yellow) which flowsfreely until it rams in to the disk along the equator. In other directions the outflowing stellar wind is less inhibited. A hot bubble (orange) of expanding gas is formed. The nebula tends to grow slowest along the equator where the dense torus inhibits its growth, and fastes t along the polar (up-down) direction. The detailed models show that a crucial parameter in foverning the evolving shapes of PNs is the original disk-to-polar density ratio.

My former students, collaborators and I have been making models of gas ejection which, we hope, might account for the appearances of the nebulae. We use essentially the same types of computational methods used to study air flows around airplane wings, though in our case the gas speeds are 10-100 miles per second, not 500 MPH, and the gas temperatures are close to 15,000 deg F, not -50 to 50F.

So how well do the models account for the structures of PNs? The answer is seen visually in the collage to the right. Here Dr. Adam Frank extracted just one frame in time from one of his many models. He then tilted it at six different angles with respect to our viewing line. Its the same model, seen by six astronomers from six different vantage points. The images of six famous nebulae are shown for comparison. Draw your own conclusions.

Adam Frank and his students have been running some two-dimensional hydro models for these objects. You can see their lovely results by clicking here. For some of the details of a bipolar nebula, look at this monster model by Prof. Icke.

However, there are peculiar small structures in planetary nebulae. Most of them are very low in ionization, being seen best in singly ionized lines such as nitrogen and sulfur or the neutral lines of oxygen. Some of these are moving at very high velocities. These are called "FLIERs". They can be seen in the color images above as red knots in the images of NGC3242, 6826, 7009, 7662, and some of the other nebulae. The models fail entirely to account for the formation of such small, symmetrically located, and high speed "spit balls".

Our work continues. We are extending the computational models to very young stellar objects, perhaps the most famous of which is the eta Carinae nebula. This may be the youngest and most massive star forming in the Milky Way at the present moment. Between 1820 and 1840 eta Car was a second magnitude bright red star which has now faded by a factor of a million. Chances are that during its eruption it lost about as much mass as our Sun now has, and there is ample evidence of prior eruptions of similar magnitudes! We think the star trying to form at the center is 100x more massive than the solar system. In any case, the nebula being formed appears to be replicated quite well by our models.

I am also actively involved in the design of a new camera for the Huble Space Telescope, called Wide-Field Camera 3 ("WFC3"). WFC3 will replace the aging but venerable imaging workhorse, WFPC2, perhaps in 2006. It will be the last new instrument for the Hubble Telescope until its return to Earth in 2010. I also serve on the Board of Governors of the Astrophysical Research Corp. which owns and operates the 3.5-m telescope and the Sloan Digital Sky Survey facilit at Apache Point New Mexico.

* In our theory collaboration, I do much of the observing and my colleagues -
Prof. Vincent Icke, Leiden Univ. in the Netherlands,
Prof. Adam Frank, U. Rochester,
Dr. Garrelt Mellema, Dwineloo Observatoryin the Netherlands and
Dr. Romano Corradi, Isaac Newton Group of Telescopes -
do the cool stuff: generate lovely computer models. We all participate in the generation of new ideas.

Thanks to my dear wife Della, progeny Charlene and Marshall, and Lulu (our cat) for tolerating my absences, bletherings, daydreams, and bad jokes for so many years! Their tolerance and support have made my mad career possible.

Teaching is an important part of my professional life. If you're interested in highly recommended WWW-based teaching activities, be sure to visit this terrific compilation by Andy Fraknoi: www.aspsky.org/html/astro/instsites.html

Going to Florence, Andalucia, or other places where I've been? Here are some tips.

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Lat updates March 2005, all minor