Download The Search for Low Mass Companions to White Dwarf Stars

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
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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.
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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!).
White Dwarf Stars
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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
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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 Earthlike 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?
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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
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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