Download Detecting individual argon atoms

Detecting individual argon
atoms
Neutrinos produces a
radioactive argon with a
half-life of 35 days
The argon gas bubbles
up when purged with
helium gas.
Helium is cooled to
separate out argon, and
resulting argon atoms
counted individually by
a geiger counter!
Saturday, February 5, 2011
Neutrino Flavors
Electrons have massive “cousins”: muons
and taus.
Neutrinos are the neutral pairing of these
three.
The “Standard model” of particle physics
incorporates these.
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Photons from sun
Very slow to escape via a random walk
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Neutrinos from sun
Saturday, February 5, 2011
Why Study Neutrinos
“Neutrino Astrophysics”: Detect high
energy neutrinos from galactic and extragalactic sources (like supernova and gamma
ray bursts!)
Saturday, February 5, 2011
Hot Dark Matter
Neutrinos as dark matter candidates:
✔ Invisible
✔ Weakly interacting
✔ Abundant
✘ Able to clump together
Ultra-relativistic particles which could
explain “missing mass”
“Sterile” Neutrinos hypothesized may help
the case.
Saturday, February 5, 2011
Other Worlds
Saturday, February 5, 2011
Are Earth-Like
Planets common?
Saturday, February 5, 2011
Finding an exoplanet
Planets glow in the
reflected light of
their host stars, and
are incredibly faint
compared.
very difficult to “see”
a planet.
Indirect methods are
required.
Saturday, February 5, 2011
Extrasolar planets
Planetary Science, and study of solar
system formation: Major problem — Only
one case to study!
15 years ago, we could only speculate if
other stars harbored planets.
Today we have over 500 and counting.
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History
1989: HD 114762: “A probable Brown Dwarf” (in
hindsight a planet)
1992: PSR 1257: Pulsar Planet (and then two more!)
1995: 51 Peg b: First normal star conclusively shown to
have a planet
2002: Exoplanet atmosphere detected (absorption
features in starlight)
2003: 100th exo-planet found.
2005: Subtracted light signal of planet in the infrared
2007: Subtracted light spectrum of planet in IR
2008: First direct image of extrasolar planet
2010: First direct spectrum of extrasolar planet
Saturday, February 5, 2011
Brown Dwarf vs. Planet
Brown Dwarfs are
“Failed Stars”... never
hot enough to burn
Hydrogen
(<0.072M⨀=75MJ)
“Electron degeneracy
pressure” supports
them
Brown Dwarfs can burn
Deuterium (>13MJ),
which is used as their
(somewhat arbitrary)
defining feature.
Saturday, February 5, 2011
Detecting Exo-Planets
Timing (e.g. of pulsar pulses)
Astrometry
Radial Velocity of parent star
transiting planet Photometry
“MicroLensing” of gravity
Direct imaging (!)
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Micro-Lensing
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A Lensing Detection
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Astrometry
Measure precise position of star as it
wobbles.
Rarely used.
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RV techniques
Doppler shift of lines as
planet “tugs” the star
back and forth.
Highly precise
measurements required
(~m/s)!
By far the most used
technique.
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Transits
Best possible
situation
planet size
precisely
constrained
Learn about
planet’s density,
structure, etc
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Figure 8-2 shows one aspect of recent scientific results f
empirical mass-radius relation for exoplanets down to th
2007, Deming et al. 2007). As noted on Figure 8-2, the
radii too large for their mass is currently a major open q
Mass Radius Relation
Figur
transi
dashe
Bode
(solid
heavy
giant
the co
than t
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Structure
Transits gives you radius, orbit gives you
mass... density!
Planet structure can be inferred from
density using models.
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First Differential Spectrum
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First Direct Image
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First Direct Spectrum
Saturday, February 5, 2011
Which stars have planets?
We now have enough exoplanets to consider
them as a group, and ask questions about
planet formation.
What fraction of stars have planets? Does
it depend on mass or other properties?
Are earth-like planets common?
Are they commonly found in the “habitable
zone” where liquid water exists?
Saturday, February 5, 2011
Mass Distribution
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Discovery Rate
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MZ = (60 ME) x 10 ([Fe/H]-0.8)
“Metal”
Effects
f [Fe/H] < -0.1" (?!)
(P < 4 years)
s
More
Metals:
More
planets!
s
Fe/H)!]
2
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Bias
Not all planets
equally
detectable by
all methods
“Hot Jupiters” –
large planets in
tight orbits –
are best for
doppler based
detection
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SuperEarths
Planets <10× Earth’s mass.
Pulsar planet was the first.
GL876d: 7.5 ME.
GL581b: (almost) in habitable zone!
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Not so fast?
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Not so fast?
“Gregory’s model finds the probability
that the six-planet model is a false alarm
is 99.9978 percent”
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Ongoing Efforts
Searching 100,000 stars for earth-like planets
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Kepler
Just announced:
1235 new
candidates
54 in the
habitable zone(!)
68 Earth-sized
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The 1st Five
Saturday, February 5, 2011
Early Kepler results
Kepler 11 has 6 transiting planets!
5 closer than mercury!
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Assignments
Read: Interview with Geoff Marcy: http://
www.wired.com/wiredscience/2011/02/geoffmarcy-qa/
Explore the site expolanet.eu, bring an
interesting correlation diagram with a
question to the next class.
Saturday, February 5, 2011