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All posts for the month April, 2012

What They Say About Themselves

Last week, I was a guest speaker at StarFest, a Denver-based Sci-Fi Con that regularly draws several thousand folks. I usually talk about astronomy topics and this year was no exception.  My main talk was about Pluto (and its dwarf planet status), and I also participated in a panel discussion about hoaxes — astronomical, planetary, and paranormal.  The Pluto talk went really well, and the crowd was really into the whole story of  its meandering progress through planetary status.

Pluto is a dwarf planet, a status that is not a bad thing. I’ve said before that giving it the “dwarf” nomenclature tells us something about its evolution, its place in the solar system hierarchy, and even gives us a clue about our own understanding (or lack thereof) about the details of Pluto’s composition and history.  It’s not terribly different from looking at a dwarf galaxy and wondering what that “dwarf-ness” means. A dwarf galaxy is NOT a wanna-be galaxy. It’s not a consolation prize. It’s a status that helps astronomers understand the evolutionary state of such collections of stars, as well as other characteristics such as the metal content of their constituent stars (and the materials those stars formed from). Dwarf galaxies are small, usually containing up to a few billion stars, and they are implicated in the evolutionary process that forms larger galaxies.  Right now, dwarf spheroidal galaxies are being sucked into our own Milky Way Galaxy or are orbiting nearby.

There are also dwarf stars which comprise the main sequence (a classification scheme that lumps stars together by their color and brightness). The Sun is a dwarf star, for example.  There are red dwarfs, yellow dwarfs (the Sun), blue dwarfs, white dwarfs, and so on.  The most fascinating ones (to me, anyway) are the brown dwarfs.  These are not actually stars like the Sun, but are really sub-stellar objects. They’re not massive enough to fuse hydrogen into helium as most other stars do, but they do have enough  mass to fuse deuterium (an isotope of hydrogen) in their cores.  The masses of brown dwarfs range from about 0.08 solar masses and more than about 13 Jupiter masses.

Where do brown dwarfs come from?  Their origins are still really not well understood. Whereas astronomers can trace the beginnings of dwarf galaxies in the early universe, and we think we kind of know where dwarf planets come from in the evolutionary history of the solar system, the formation of brown dwarf substellar objects is still a hot topic in astronomy.  Some astronomers think that they are born much like stars are born, through the collapse of interstellar gas clouds. Low-mass clouds might be yielding l0w-mass objects.  Others suspect that brown dwarfs form in larger clouds along with stars of various masses, and that the brown dwarfs are ejected from their birth places in gravitational interactions with their higher-mass siblings.

Only a few hundred brown dwarfs have actually been observed, so as astronomers find more of these objects that are too cool to be stars and too hot to be planets, they should get a better handle on the environments in which they formed.  And that will tell them more about brown dwarf formation throughout the history of the cosmos. So, as with Pluto — which is going to help planetary scientists understand the worlds of the extreme outer solar system — brown dwarfs may help shed light (no pun intended) on what is still a little-understood population of objects that form in interstellar gas clouds.

Hubble Space Telescope’s 22nd Anniversary and Me

This past week marked the 22nd anniversary of the launch of the Hubble Space Telescope.  It really is hard to believe all that time has passed, but the solid record of science achievements from this famous orbiting telescope is proof that even if you start out with a problematic telescope, you can still do good science. Of course, making Hubble DO that good science took squads of astronauts, ground-based technicians and scientists years of problem-solving to do.  But, they did it.

I was not quite in graduate school when Hubble went up on April 24, 1990. I’d been part of a science team at the University of Colorado for just over a year and a half, led by Dr. John C. Brandt, who was (at that time, among his many responsibilities) the co-Principal Investigator for the Goddard High-Resolution Spectrograph instrument onboard HST.  I was working on a project analyzing Comet Halley images; specifically, I was doing astrometry on images of the comet’s tail so that we could analyze how the tail was being affected by the solar wind as the comet rounded the Sun during its last close approach in 1985 and 1986.

Not long after launch, Jack came back from Goddard Space Flight Center and warned us that there could be some problems with the telescope.  I think that only a few people knew how bad the problems were, mostly because they were still analyzing the images and calibrating the telescope. But, in June 1990, the full news broke and people were devastated by the idea that HST was flawed. I know we at the university were.

But, even as early as August of that year, we were seeing images that didn’t look awful, and I knew from talking with Jack that there was good science to be had — even if it took a bit longer to analyze the images. Our instrument, however, was pretty badly affected, as was the Faint Object Spectrograph.  I started to make notes about the problems with the telescope, and paying attention to the images it was producing. I think I had some idea that I’d write a book about the project someday and I knew it would be good practice to keep notes from the early days. In the meantime, I plugged away on the Comet Halley project, which eventually got published in 1992 as the International Halley Watch Atlas of Large-Scale Phenomena (Brandt, Niedner, and Rahe, with mucho work done by me in a small-credit role).

This Hubble image of the Egg Nebula shows one of the best views to date of this brief but dramatic phase in a star’s life. This is the site of a star in its death throes. At the center of this image, and hidden in a thick cloud of dust, is the nebula’s central star. While we can’t see the star directly, four searchlight beams of light coming from it shine out through the nebula. It is thought that ring-shaped holes in the thick cocoon of dust, carved by jets coming from the star, let the beams of light emerge through the otherwise opaque cloud. The precise mechanism by which stellar jets produce these holes is not known for certain, but one possible explanation is that a binary star system, rather than a single star, exists at the center of the nebula. The onion-like layered structure of the more diffuse cloud surrounding the central cocoon is caused by periodic bursts of material being ejected from the dying star. The bursts typically occur every few hundred years.Courtesy NASA/STScI.

Well, after that one thing led to another—I studied MORE comets as part of the Ulysses Comet Watch, and  I entered graduate school and joined Jack’s GHRS team (albeit as a very junior member).  The science flowing from HST was getting better and better, and the first servicing mission proved that the telescope could be brought “up to spec”.  So, I decided to shop around the book idea, and took Jack on as a co-author.  After a false start or two, we ended up signing a contract with Cambridge University Press, and in 1995, we published Hubble Vision, which was updated a few years later. I also did a planetarium show by the same name, which has been a mainstay of my company’s repertoire ever since (read more about that show here).

I feel like I kind of grew up with Hubble, or maybe we grew up together. I feel privileged to have worked on an instrument team for HST, and to have written about it as extensively has I have.  The telescope has for me–and I hope for all people who follow astronomy exploration–expanded the horizons of cosmic understanding. And that’s a great tribute to its 22 years (and counting) legacy!

If you haven’t taken time to browse the images at Hubblesite.org, take some time to do so. The very act of exploring those pages is a voyage of exploration of the universe.

Check it out!