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The Interstellar Medium

Jeffrey Linsky investigates clouds of warm gas in the interstellar medium close to the Sun, i.e., within 50 light years of Earth. Fifteen of these turbulent clouds have been identified thus far. The clouds were formed several million years ago by the winds from young, massive stars and supernova explosions in the Scorpio-Centaurus Association. Two of the nearest clouds, the Local Interstellar Cloud (LIC) and the G cloud, cover 70% of the sky as seen from Earth. Linsky recently determined that the solar system is still inside the LIC, but is moving toward the G cloud, which is a little cooler than Earth’s current space environment. Linsky and his collaborators are currently working on identifying the motions and other physical properties of the cloud in which the Sun is embedded.

In his studies of the motions and physical properties of the 15 nearby clouds, Linsky has been able to explain the phenomenon of scintillating quasars. Quasars twinkle relatively slowly, changing in intensity over several hours. They also twinkle at different rates, depending on the time of year. These twinkling patterns result from the interaction of Earth’s speed (30 km/s) around the Sun and its position with respect to the irregular shape of the turbulence in nearby interstellar clouds. If Earth didn’t move through space, quasars wouldn’t twinkle. In fact, the twinkling of quasars at radio wavelengths and the twinkling of stars at visible wavelengths in the night sky are essentially the same process. The only difference is that for the quasars, it’s the Earth that moves. For the stars, it’s the Earth’s atmosphere that moves around.