Hunting for Planets around Dead Stars Richard Ignace Department of Physics, Astronomy, and Geology East Tennessee State University

The Earth as Seen from Space

Extrasolar Planets They exist! We now know of about 100 examples, plus 100’s of star systems that have swirling disks of gas that may produce planets in the future. Most of the planets so far discovered orbit stars similar to our sun. A handful have been discovered that orbit giant stars.

Most of the planets have been inferred from motion observed in the central star. Doppler shift explains the effect of changing pitch of sound from a passing train. A related effect operates for light. The motions detected are like 10-100 meters per second (this is just 20 to 300 mph!).

White Dwarf Stars We think that stars are born out of large clouds of gas that collapse to make star clusters The protostars become stars when they initiate nuclear fussion in their cores Eventually, fussion stops and the outer stellar atmosphere bloats up - a giant star! This atmosphere is blown away revealing a hot stellar core remnant called a White Dwarf - a body with the mass of a star but only ther size of the Earth!

Planetary Companions to White Dwarf Stars What happens to a planetary system as a star moves from something like the Sun to a White Dwarf? Some closer planets may be swallowed. More distant planets may drift into bigger orbits. The orbits of some might even shrink. However, it may be that the atmospheres of Earth-like planets may be stripped away because of the strong giant star winds. We want to find planets around White Dwarfs to better understand the interaction between a star and its companions.

How to Look? Finding planets is hard, because they are faint. Brightness is related to how hot and how big. A major advantage of targeting White Dwarfs is that they are small stars. The best approach is to search in the Infrared (or “heat light”), because the planets are relatively bright, but the stars are relatively dim. In fact, White Dwarfs are so small that in the Infrared, a planet can be brighter than the star! The recently launched Spitzer Infrared space telescope

A Really Bizarre System A Jovian planet in a neutron star – white dwarf system System lies in the Globular cluster M4, over 5000 LY away It is about 13 Billion years old