Astro Reaps Stellar Data, Helps Confirm Theories
BOSTON — TECHNICAL glitches kept the Astro observatory from getting all its planned data when it orbited Earth on board the space shuttle Columbia last month. But as scientists begin to extract their findings from the data it did return, they are calling the mission an outstanding success. For Theodore P. Stecher of the Goddard Space Flight Center in Greenbelt, Md., it's also a double-barreled personal triumph.
Goddard's Ultraviolet Imaging Telescope, for which Dr. Stecher is principal investigator, spotted emissions that confirm Stecher's 1967 proposed theory of how hydrogen breaks up into atoms when hit by radiation and then recombines into molecules in the interstellar medium. It's part of the basic knowledge needed to understand the nature of material that permeates our galaxy.
University of Wisconsin astronomer Arthur D. Code says that the ultraviolet telescope for which he is principal investigator has confirmed another Stecher theory. Stecher suggested 25 years ago that graphite could account for certain optical characteristics of some interstellar dust clouds. Dr. Code says that a quick look at data from the Wisconsin instrument, which measures polarization of ultraviolet light, indicates that Stecher's graphite does, indeed, exist.
``That was very gratifying,'' says Stecher. He relates that Astro has brought in a data harvest that ``gives us a whole different perspective on things.'' He calls the mission ``a pinnacle of my career.''
Two-thirds was a lot
Arthur F. Davidson, principal investigator for the Johns Hopkins University ultraviolet telescope, agrees that ``it was a spectacular mission.'' Astro missed a third of its 200 observation targets. Yet, Dr. Davidson says, ``we got enough data to call the mission a success.''
Theodore R. Gull, who heads the Astro scientific program at Goddard, is ``enormously proud'' of the entire mission team. He considers Astro to be ``the most successful attached payload yet flown'' on a shuttle. Astro's four telescopes - three ultraviolet detectors plus an X-ray instrument - worked flawlessly. It was auxiliary control equipment that malfunctioned.
Furthermore, Dr. Gull forecasts that Astro's data ``will spark the most scientific papers'' yet produced from a space astronomy project. He anticipates at least 100 papers. Also, to judge from the very early results, he expects a number of them to deal with fundamental scientific matters.
For example, he cites data Davidson gathered that bear on so-called dark matter. There are indications that as much as 99 percent of cosmic matter is invisible. No one knows what forms such dark matter may take. One speculation is that much if it consists of neutrinos.
These are electrically neutral particles that travel at the speed of light and zip through other matter, such as our massive Earth, as though it were not there. Physicists once believed the particles had no inherent mass. But they have speculated for over a decade now that they in fact do. They noted that, if neutrinos have even a little inherent mass, they should be numerous enough to account for much of the dark matter.
One theory shot down
Cosmologist Dennis W. Sciama of the International Centre for Theoretical Physics in Trieste, Italy, published a speculative theory along this line last month in the journal Nature. He predicted neutrino masses and the energy of ultraviolet photons that would be emitted when they change from one form of neutrino to another.
``We tackled that immediately,'' Davidson says. He explains that the photon prediction called for a ``yes'' (they exist) or ``no'' (they don't exist) answer. Astro's answer was ``no.''
``We basically have ruled out the theory in the form it was presented,'' Davidson says. He adds, however, that massive numbers of neutrinos may still exist, but they may decay at a rate different from that assumed by Dr. Sciama. So the question of whether or not neutrinos have mass and constitute dark cosmic matter remains open.
Gull notes that Goddard's X-ray telescope in the Astro battery has also turned in results of basic importance. He explains that principal investigator Peter J. Serlemitsos and his group already have results that help clarify star formation in galaxy clusters.
Theorists had thought that stars might form and grow faster in the core galaxy of the cluster. But Astro data show a more or less uniform abundance of star births across the cluster studied.
Gull further notes that Code's confirmation of Stecher's interstellar graphite is yet another early finding with basic significance. Stars form when clouds of dust and gas contract under their own gravity. As the clouds shrink, however, their gas heats up and expands. This tends to resist the gravitational contraction. How a star-forming cloud overcomes this resistance is an open astronomical question.
Code explains: ``You've got to get rid of the heat. Dust grains provide one mechanism to both reduce heating [by absorbing heat] and to radiate it away. Thus dust is an important element in the formation of stars.'' Knowing that graphite, which would be a cooling agent, is present in interstellar clouds will help astronomers understand better how stars form.
While early insights, such as these, encourage Astro scientists, Code echoes their consensus when he says: ``There's going to be a lot of work ahead of us. Data analysis will be a long process.''