Hunting for Planets around Dead Stars

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Hunting for Planets around Dead Stars

• Richard Ignace
• Department of Physics, Astronomy, and Geology
• East Tennessee State University

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The Earth as Seen from Space
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Extrasolar Planets

• They exist! We now know of about 100 examples,
  plus 100s 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.

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• 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!).

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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!

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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.

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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
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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

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