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A105 Stars and Galaxies


Open Book Bring Text. Part I Multiple Choice. Part II News Articles ... SETI _at_ Home: a screensaver with a purpose. Visiting ET? ... – PowerPoint PPT presentation

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Title: A105 Stars and Galaxies

A105 Stars and Galaxies
Todays APOD
  • Final Exam
  • Tuesday, Dec. 12
  • 1230-230 PM
  • Swain West 119

Solar Lab after class today
Final Exam…
  • Open Book Bring Text
  • Part I Multiple Choice
  • Part II News Articles
  • Part III Short Written Summary
  • Comprehensive/emphasis on galaxies, cosmology,
    life elsewhere

Todays Topics
  • Planets around other stars
  • how do we find them
  • what are they like?
  • what kinds of stars have planets?
  • How likely it is that life exists elsewhere than
    Earth? (Drake Equation)
  • How would we detect life on other planets?

Our Solar System
Gas Giants
  • Terrestrial Planets

Ice Giants
Searching for Planets
  • Nearly 200 extra-solar planets have been
  • How are planets discovered?
  • Radial velocity
  • Transits
  • Gravitational lensing
  • Wobbles in stars positions

Discovering Planets from Spectra
  • Remember the Doppler Shift!
  • Absorption lines shift left or right if stars
    move toward or away from us
  • Planetary orbits cause stars radial velocities
    to change

Periodic velocity changes due to orbiting planet
Velocity vs. Time
VERY high precision is needed to measure these
very small velocity changes
Velocity of 51 Peg
About 7 orbits in 30 days P4.2 days
A Planet around e Eridani
  • A planet orbits the star e Eridani at a
    radius of 3.2 A.U.
  • e Eridani is similar to our Sun
  • e Eridani is only 10.5 light years away
  • The planet is similar to Jupiter
  • The planet orbits e Eridani in 7 years
  • e Eridani has at least one more planet

u And has at least 3 planets
terrestrial planets
Planetary Transits
If the Earth lies in the same plane as the orbit
of a planet we see a transit
  • The planet passes across the face of the star
  • Some of the starlight is blocked by planet and
    the star appears dimmer

Seeing planets near stars is hard
  • Looking for an Earthlike planet around a
    nearby star is like standing on the East Coast of
    the United States and looking for a pinhead on
    the West Coast with a VERY bright grapefruit
  • Very large telescopes will help

Imaging Planets?
  • This photo shows an image of the faint star GQ
    Lupi taken in the infrared. The faint object to
    the right of the star is a possible planetary
    companion. It is 250 times fainter than the star
    itself and it located 0.73 arcsecond west. At the
    distance of GQ Lupi, this corresponds to a
    distance of roughly 100 astronomical units. The
    planet probably has a mass of about 2 x Jupiter.

Another possible planet
  • Orbiting the brown dwarf 225 light years away
  • Young, about 1000K
  • Further from its sun than Pluto is from ours
  • (brown dwarf is blocked out)

Properties of KNOWN Extra-Solar Planets
  • All are gas giants like Jupiter and Saturn
  • Most are larger than Jupiter
  • Many orbit close to their parent stars
  • Some are in systems with multiple planets

Known Planets Are Close to Stars
Hot Jupiters
  • These hot Jupiters form further out, and
    migrate inward as they eject smaller bodies from
    their planetary systems

Selection Effects
  • Close-in, massive planets are easier to detect
  • Far-out planets and light-weight planets are MUCH
    HARDER to detect
  • So far, weve only been able to detect massive,
    close-in planets
  • Techniques, sensitivity are improving
  • Terrestrial planets soon!

The Habitable Zone
  • The planet needs to be the right distance from
    the star. WHY?
  • The star needs to have the right mass. WHY?

A planet needs the right star!
  • Constraints on star systems
  • Old enough to allow time for evolution (rules out
    high-mass stars - 1)
  • Need to have stable orbits (might rule out
    binary/multiple star systems - 50)
  • Size of habitable zone region in which a
    planet of the right size could have liquid water
    on its surface.

Even so… billions of stars in the Milky Way seem
at least to offer the possibility of habitable
You are here
There are 400 Billion Stars in our Galaxy. How
many harbor life?
How common is life of any kind in the Milky Way?
How common is intelligent, technological life?
The Drake Equation
  • Start with 1011 stars in the Milky Way…
  • What fraction of the stars are similar to the
  • What fraction of solar type stars have planets?
  • What fraction of solar type stars with planets
    have planets in the habitable zone?
  • On what fraction of these planets will life
  • On what fraction of these will intelligence
  • What fraction of these will develop technology?
  • What fraction of a stars life will a
    technological civilization survive (assume a
    solar-type star remains on the main sequence for
    1010 years)?

The Drake Equation
What are the odds that there are intelligent,
advanced, communicative civilizations out there?
How many can we expect to exist in all of the
Milky Way Galaxy?
Make your own calculation of the number of
intelligent, communicative, technologically
advanced civilizations in the Milky Way.
We do not know the values for the Drake Equation
NHP ? flife ? fciv ? fnow
  • NHP probably billions.
  • flife ??? Hard to say (near 0 or near 1)
  • fciv ??? It took 4 billion years on Earth
  • fnow ??? Can civilizations survive long-term?

Search for Extra-Terrestrial Intelligence
SETI experiments look for deliberate signals from
Can We Find Extra-Terrestrial Intelligence?
  • Looking for SIGNALS is the easiest way
  • We can also transmit a signal (but its a long
    wait for the answer...)
  • Different kinds of signals to listen for
  • local communication signals on Earth, this
    includes TV, radio, etc.
  • communication between the planet and another
    site, such as satellites and spacecraft
  • A BEACON signal used to try to communicate with
    other civilizations.

Can Earth Be Heard from Space?
  • YES! Earth has been broadcasting TV and radio
    communications for the last 50 years. ET
    civilizations up to 50 light years away could be
    picking us up.
  • We can listen but radio wavelengths may be best
  • Biggest collecting area - Arecibo telescope.
  • The background sky is the quietest at wavelengths
    of about 0.1 mm. At shorter wavelengths, emission
    from the galaxy is loud, and at longer
    wavelengths, interstellar clouds absorb the

Message to M13 Nov 1974
  • Message was beamed from the Arecibo radio
  • toward the M13 star cluster
  • 24,000 light-years away
  • a 1679 (23 x 73) pulses and spaces
  • The message was transmitted only once and was
    intended to serve as a exercise in how we might
    go about trying to contact extra-terrestrials.

Message to M13
  • Formed a picture showing when arranged in a
  • numbers 1-10
  • elements, chemicals of life
  • a DNA molecule
  • a stick figure of a human
  • solar system
  • diagram of radio telescope

Searching for ET
  • NASA funded SETI until 1993
  • Present efforts all privately funded
  • SETI Institute (Frank Drake)
  • seti_at_home -- help analyze SETI data
  • Planetary Society
  • META (million channel extraterrestrial assay) --
    scans one million channels in the band
  • BETA (billion channel version of META)
  • 84 ft. dish antenna at Harvard Univ.
  • connected to supercomputers that look for
    non-random patterns in the signals (most of the
    signals come from natural sources such as stars)
  • 250 megabytes of data each second

Your computer can help! SETI _at_ Home a
screensaver with a purpose.
Visiting ET?
  • With foreseeable technology, we can achieve
    speeds of 10 of the speed of light
  • We can travel 10 light years in 100 years
  • We can reach the nearest star in 43 years
  • Allow each new colony 5000 years to duplicate the
  • Colonies could spread out about 50 light years
    every 25,000 years

How long to colonize?
Assume 100,000 years per 20 parsec hop
30,000 pc
Total time to cover the Galaxy 1500 hops x
100,000 years 150,000,000 years
The Fermi Paradox
  • Enrico Fermi
  • Edward Teller
  • Herbert York
  • Emil Konopinski

Emil Konopinski
LANL Tech Area
Enrico Fermi
LANL Fuller Lodge Cafeteria
The Fermi Paradox
The Drake Equation A few hundred technical
150,000,000 million years to colonize the Galaxy
Where is Everyone?
  • Some factors in Drake equation may be much
    smaller than we believe is life, or intelligent
    life, very rare?
  • Do civilizations hide to avoid a galactic
  • Do technological civilizations self-destruct?
  • Is no one more advanced than we are?
  • The Zoo hypothesis…

Possible solutions to the paradox
  • Civilizations are common but interstellar travel
    is not. Perhaps…
  • Interstellar travel more difficult than we think
  • Desire to explore is rare
  • Civilizations destroy themselves before achieving
    interstellar travel

These are all possibilities, but not very
Possible solutions to the paradox
  • We are alone life/civilizations much rarer
    than we might have guessed.
  • Our own planet/civilization looks all the more

OR - There IS a galactic civilization… …
and some day well meet them…
Difficulties of Interstellar Travel
  • Far more efficient engines are needed
  • Energy requirements are enormous
  • Ordinary interstellar particles become like
    cosmic rays
  • Social complications of time dilation

Traveling to Another Star?
  • Distances between stars are much greater than we
    can imagine
  • Sci-fi books and movies have dramatized space
    travel to make it seem possible
  • Interstellar travel may never happen
  • Even the Voyager spacecraft (some of the fastest
    ever flown) traveled at only 20 km/s through
    space - not even 1 of the speed of light. They
    would take 60,000 years to reach even the nearest

Maximum Speed Achieved
Can we travel to new worlds?
  • Within the lifetime of todays children we will
    be able to send robotic spacecraft to visit our
    nearest neighbors
  • At 10 of the speed of light (30,000 km/sec)
    travel time will be about 100 years
  • Then wait another 10-20 years for the data to

SOLAR LAB! Kirkwood Obs. NOW!
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