The Search for Exoplanets

An exoplanet is a planet orbiting a star outside of our solar system

The first proven exoplanet was 51 Pegasi, announced in 1995. To date, 1918 planets

have been identified.

Ways of Discovering ExoplanetsStars are so much bigger and brighter (+1,000,000x)

than planets, it is nearly impossible to just point a telescope at a star and see its planets

Radial VelocityAs a planet goes around its star, they both orbit the same center of gravity. The gravity of the planet cause the star to wobble.

This back forth wobble is detectable as a back and forth redshift and blueshift of the star

Radial Velocity only works on very large planets, bigger than Jupiter. It also appears to be most effective if the planet is very close to

the star.

51 Pegasi, the first exoplanet, is 3 times closer to its star than Mercury.

As of May 2015, 601 exoplanets have been discovered using Radial Velocity

Imaging

Recently, telescopes have made huge technologicaladvances. Telescopes and interferometers (a bunchof small telescopes mimicking a giant one) have become advanced enough to take actual pictures ofexoplanets. 53 planets have been discovered by imaging.

Gravitational Microlensing

Gravity from a star or planet causes light to bend. If a star has a planet going around it, this “lensing” will cause it to periodically become brighter and dimmer.

This technique is only being done by the University of Warsaw in Poland. They have discovered 35

exoplanets

Pulsar Timing

When very massive stars run out of nuclear fuel, they explode, leaving a small dense core, called a

neutron star.

These remnants usually spin, sending out “blips” of radiation, this is called a “pulsar”.

A planet can form out of the debris of the dead star, which can gravitationally alter the spin of the pulsar,

which can be measured.

19 exoplanets, with a pulsar as the central star, have been discovered.

Transit PhotometryThe total light from a star can be measured. If you

continuously watch a star, and note that it gets dimmer periodically, that is caused by a planet

blocking the light. 1206 planets have been discovered.

The Kepler space telescope (launched 2009), is looking at a tiny patch of sky with powerful enough optics to detect these miniscule differences in light

1020 planets have been confirmed.

Kepler is looking at 150,000 medium to small stars for changes in the light curve of the star.

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If you were watching a star, and a planet passed in front….what would happen to the light curve?