Philosophical Society of Washington

Minutes of the 2052nd Meeting


Speaker: Christopher Burroughs, European Space Agency and Space Science Telescope Institute
Topic: “Recent Results from the Hubble on Star and Planet Formation”

The President Mr. Ohlmacher called the 2052nd meeting to order at 8:21 p.m. on December 15, 1995. The Recording Secretary read the minutes of the 2051st meeting and they were approved. The President then read a portion of the minutes of the 444th meeting December 1895.

The President introduced Mr. Christopher Burroughs of the European Space Agency and Space Science Telescope Institute to discuss “Recent Results from the Hubble on Star and Planet Formation”.


Mr. Burroughs traced the original concept for the Hubble space telescope to a 1946 Rand report written by Lewin Spitzer. That report proposed that one objective for a space research program should be the construction of an orbiting observatory. It was argued that an orbiting telescope of moderate size should be able to resolve details comparable to ground-based telescopes many times larger because a telescope in space would not have its performance degraded by atmospheric turbulence. After a long, unfortunate delay caused by the Challenger disaster, the Hubble Space telescope was finally placed in orbit in April 1990. It was designed to make observations using visible and ultraviolet light with an estimated operational life of 15 years. Eventually it will be one of four orbiting telescopes including the gamma ray observatory placed in orbit in 1991 and X-ray and infrared observatories yet to be orbited.

Soon after the Hubble telescope began operation it was found that the large primary mirror although extremely precise, was not accurate. The largest deviation in the smoothness of the surface was not more than the equivalent of 3 inches in the width of the United States. But on the same scale, there was the equivalent of a 3 mile error in the height of the mirror at its edge. This error resulted in a spherical aberration which caused objects “in focus” to have a fuzzy halo. For the first five years of its operation it was necessary to use computer image processing to attempt to make corrections for this defect, an approach which worked well enough for bright or near-field objects. Replacement of the primary mirror was not feasible, but studies indicated that a package of corrective optics could be installed during the first scheduled shuttle maintenance mission at the cost of displacing one of the detector packages.

In 1995 the corrective optics were installed at the same time some of the other experimental detectors were replaced. The effectiveness of the corrective optics was illustrated with photographs of a recent supernova. The ground-based telescope images show an unresolved, fuzzy patch of light. The image produced by the Hubble telescope without corrective optics appeared like a fuzzy star with a large pair of lobes on opposite sides. With the corrective optics a pair of glowing rings on opposite sides of the central nova are resolved and clearly visible. Now knowing that they have best image they are likely to have for some time, the theorists can ponder how to explain this very strange and beautiful phenomenon.

Some spectacular Hubble telescope photographs have recently been released of the M16 nebula that show the process of star formation. In these images new stars can be seen boiling away the gas and dust clouds that had collapsed to form them. The gas clouds appear as dark columns like elephants' trunks and the hot new stars studding the surface are pushing back the cloud with light and stellar winds of ejected plasma. Objects that are thought to be black holes have produced images of rapidly spinning accretion disks and of jets of luminous matter being ejected at opposite poles. It is still difficult to produce models that predict jets that are as compact as the jets in these images. Another photograph was of what is though to be a black hole with 109 solar masses contained within the diameter of the solar system. Not only black holes but also more normal star formation may proceed with accretion disks and jets. In one image of what is possibly a binary protostar there were arcs and distorted jets. Other photographs depicted more quiescent star formation one with a stellar accretion disk about the same size as the solar system and another of beta pictoris a normal star with a disk seen almost edge on.

Another recent photograph is the first image of what is thought to be a brown dwarf, a gas supergiant planet that is too small to initiate nuclear fusion in its core. The object in this photograph may have a surface temperature of about 900°C.



Mr. Burroughs kindly answered questions from the audience. The President thanked the speaker on behalf of the Society, announced the speaker for the next meeting, restated the parking policy, and adjourned the 2052nd meeting to the 126th annual business meeting at 9:23 p.m.

Attendance:52
Temperature:7.8°C
Weather:raining

Respectfully submitted,
 
John S. Garavelli
Recording Secretary


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