35: Professor Lewin’s Early days at MIT

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Topics covered: Professor Lewin talks about some of the highlights from his early days at MIT. It began with balloon flights at very high altitude to make observations of the stars in X-rays. This led to discoveries of X-ray flaring events and a periodic X-ray source (GX 1+4). In the seventies and eighties he made important contributions to our understanding of X-ray bursts (thermo-nuclear fusion episodes on neutron stars).

Instructor/speaker: Prof. Walter Lewin

Date recorded: December 8, 1999

Video Index

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  • X-ray Astronomy from Balloon Flights
    Professor Lewin takes us back to 1966 when Professor George Clark and he pioneered X-ray observations from balloon-borne telescopes at altitudes of 145,000 ft.

  • Slides of High Altitude Ballooning Expeditions
    A series of slides are shown of the construction of an X-ray telescope, the manufacturing of the balloons, and balloon launches in both Alice Springs, Australia and Palestine, Texas. The risks that arise during launch and during flight are shown, as are some interesting encounters during payload recovery.

  • X-ray Observations
    The science gained from the balloon-borne telescopes is described, such as the first ever flaring event and the 2.3 minute periodicity observed from a previously unknown source (GX 1+4). We now know of hundreds of binary star systems where gas from a "donor" swirls onto a neutron star (the accretor). The gas reaches the neutron star's surface with about 1/3 the speed of light. It heats up its surface to a few million degrees Kelvin which is why the neutron star emits large amounts of X-rays.

  • Binary Stars and X-ray Bursts
    Professor Lewin reviews the Doppler shift of the neutron star's pulsar period and of the donor star's spectral lines in X-ray binaries. He then talks about X-ray bursts. These are thermonuclear flashes (nuclear bomb explosions) on the surface of neutron stars. The X-rays from these flashes temporarily excite the matter in the accretion disk, resulting in delayed optical flashes. This delay provided the first measurement of the size of an accretion disk.

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