By Gary Litt

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EFFORTS TO MEASURE OUR EXPANDING UNIVERSE

• By Gary Litt
• Astronomy 007

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Origins Einstein Static Universe

• According to general relativity, matter energy
  gravitate. Consequently, one would deduce that
  they would cause the universe to collapse upon
  itself, and this seemed physically unacceptable.
• Einsteins Solution Introduction of cosmological
  constant Additional term in equations of
  general relativity, which physically represents
  the possibility that there is a density and
  pressure associated with "empty" space. Suggests
  pervasive existence of mysterious dark energy.
• Einsteins Intention Balance the attractive
  force of gravity with pressure that tends to make
  the universe as a whole expand.
• Einstein proposed this to uphold the paradigm
  that the universe was indeed static (Newton).

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Repudiations of Static Universe

• Olberss Paradox The night sky is actually
  dark. If the universe was static, infinitely old
  filled uniformly with stars, the night sky
  should be ablaze with light.
• Edwin Hubble ? Einsteins greatest blunder
  Just 10 years after Einstein promulgated his
  relativity theories, Hubble observed that
  galaxies are receding from one another, thereby
  indicating that the universe is NOT static is
  expanding.
• Discovery of quasars Starlike objects with very
  large redshifts (distant past), which imply that
  the constitution of the universe was very
  different from what it is today.
• Cosmic Microwave Background
• Combined with other cosmological studies, reports
  of CMB studies, BOOMERANG MAXIMA, reported
  earlier this year strongly suggest that the
  universe is geometrically flat 2/3 of its
  density is due to unknown energy.

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Evolution of Universe

• Key Question Hubble proved the universe is
  expanding, but is this expansion occurring _at_ an
  increasing, constant, or decreasing rate?
• Cosmological Parameters
• Density Parameter (OT ?x / ?c)
• Critical Density Amount necessary to make
  space flat.
• Deceleration Parameter (qo) ? Rate _at_ which
  universe is slowing down (qolt0) or speeding up
  (qogt0)
• Universe underwent rapid expansion immediately
  following the BB Inflationary Period.
• Inflation acted to smooth out the universe,
  making it geometrically flat. OT 1
  (approximately).
• Standard Models OT 1 (Flat)
• OT Om O?
• Old Om 1 O? 0
• New Om 0.2-0.4 O? 0.6-0.8
• Shapes of the universe indicate matter energy
  content
• OT lt 1 Open ? Hyperbolic
• OT 1 Flat
• OT gt 1 Closed ? Spherical
• None of these universes has an edge or center.

Cosmic Geometry-Curvature 2D Representations of
Universe Shape
OT Combined average mass density of all forms
of matter energy
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What Dominates the Universe?

• Astronomers have only pinpointed 30-35 of the
  matter needed to validate the assumption of a
  flat universe. Cosmological constant (Vacuum
  Energy Density) accounts for the remaining
  matter.
• CC behaves gravitationally, like matter energy,
  except that it has a negative pressure. It
  creates a repulsive gravitational force, which
  acts to expand the universe.
• As the universe became more spread out, its
  density decreased its self-gravity weakened to
  the point that repulsive dark energy could take
  over and begin to accelerate the universes
  expansion. This balance tipped about 5 billion
  years ago.
• Radiation Dominated Universe ?rad gt ?m gt ??
• Matter Dominated Universe ?m gt ?rad gt ??
• Dark Energy Dominated Universe ?? gt ?m gt ?rad
• Return of ? ? Age Problem A universe with a lot
  of ? is older than we might otherwise think.
• Resurgence in 1980s
• Existence reconsidered for accelerating universe
  explanation in 1990s

Matter Budget of the Universe
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Supernova 1997ff
Universe has expanded at different rates at
different times in the past.

• SN1997ff comes from a time when gravity was still
  stronger than the repulsive force the universe
  was still decelerating ? Matter v. dark-energy
  dominated

• Nondescript 26th magnitude (apparent brightness
  measure) galaxy played a key role in cosmologys
  new dark energy developments, hosting the most
  distant Type IA Supernovae (SN1997ff) observed
  thus far.

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Measuring Cosmology with Supernovae
Type II Supernova

• Forces of electron degeneracy lose battle with
  gravity and material is ignited producing
  nuclear blast ? SN
• SN have emerged as powerful tools for measuring
  extragalactic distances.
• Type IA Empirical tools whose precision
  intrinsic brightness make them sensitive probes
  of cosmic expansion.
• Because they always explode _at_ minimum of 1.4
  solar masses, they all generally have the same
  qualities, namely how brightly they shine.
• Type IA explosions are typically 10-100 times
  brighter than a Type II Supernova.
• Powerful evidence for accelerating expansion At
  high redshifts, the most distant are dimmer than
  they would be if the expansion were slowing.
• Type II Used to measure distances independent of
  the extragalactic distance scale.
• The light from the explosion is 15 billion times
  brighter than the Sun, which is why they are
  visible from halfway across the universe.
• Unfortunately, they are very rare. The last one
  seen in our galaxy in 1006!

SN 1987A (Before After). Discovery date
February 23, 1987. Although its light took
170,000 years to reach Earth, it became easily
visible to the naked eye. To date, it was the
closest and brightest SN as seen from the Earth
in the past 350 years.
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Discovering Cosmic Explosions

• Must discover both nearby distant supernovae
  accurately in order to provide some basis of
  comparison.
• Greater apparent magnitude corresponds to a
  dimmer supernova, thereby indicating the SN is
  farther away.
• Cosmology projects used instruments that enabled
  them to scan a piece of the sky larger than the
  size of the moon every 5 minutes to a faintness
  level that allows us to locate IA-SN halfway
  across the universe.
• Each image taken contains 50,000 galaxies.
• Able to survey gt 1 million galaxies in 1 night
  find tens of SN.
• Typically find up to 4 SN in 1 patch of sky ½ the
  size of full moon.

Hubble Space Telescope
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Supernova Cosmology Project

• Goal Measure changes in the expansion rate of
  the universe, which in turn would yield clues to
  the origin, structure fate of the cosmos
• Methodology
• Track Type IA Supernovae Standard Candles
• Visible over distances of 5 billion light years ?
  Explosions are brighter than entire galaxies
• Measuring their redshift and brightness
• Intrinsic brightness serves as dependable gauge
  for determining distance via tools of apparent
  absolute magnitude.
• Findings based on data from gt 3 dozen Type IA
  Supernovae corroborated by additional results
  from High-Z Supernova Search Team, an independent
  group.
• Type IA supernovae appear dimmer than they would
  if the universes expansion was constant or
  slowing down because they are moving away from
  us.
• Conclusion Breakthrough of the year (1998)
• Accelerating expansion of the universe is due to
  a mysterious, dark energy that pervades all space.

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Wheres Waldo?Find the Missing Supernova
Bright New Spot
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Wheres Waldo?Find the Missing Supernova
Computer software that subtracts the images
facilitates the process of locating supernova.
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SNAP (Supernova Acceleration Probe)
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What is SNAP?

• Proposed space-based telescope that seeks to
  discover several extremely distant supernovae
• Will cover wavelength range from 400-1700 nm with
  spectro-photometry supernovae from redshifts of
  0.3-1.7.
• In measuring these supernovae, SNAP will
  effectually map out, in detail, the expansion
  rate of the universe at epochs varying from the
  present to 10 billion years in the past.
• Lawrence Berkeley National Lab University of
  California at Berkeley
• SNAP would orbit a 3-mirror, 2-meter reflecting
  telescope in a high orbit over the Earths poles,
  circling the globe every 1 or 2 weeks.
• Will use radiation-tolerant, high-resistivity
  CCDs. Most have poor responses to red infrared
  light.

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Purpose of SNAP

• Objective Provide greater understanding of the
  mechanism driving the acceleration of the
  universe cosmological constant ? dark energy or
  perhaps some other fundamental particle or force
  yet to be discovered.
• Gives several experimental measurements of
  cosmological parameters statistical
  uncertainties, but more importantly, will put
  strong constraints on known hypothesized
  cosmological models
• SNAP would discover thousands of Type IA-SN at
  redshifts greater than any yet found will cover
  a much larger range, much more precisely!
• Technical Challenges Manufacture of a wide field
  instrument with 1 billion pixels, the detectors
  associated electronics, the operation of the
  detectors in a space environment.
• High precision in a high-radiation environment is
  an ongoing technological development.
• SNAP will shed light on phenomena such as galaxy
  clusters, gamma-ray bursters, cold dark matter,
  weak lensing, asteroids, astronomical transients.

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SNAP Satellite Strategy

• Observing strategy Will monitor repeatedly
  image a 20-square-degree region of sky near the
  north or south ecliptic poles, discovering and
  following supernovae that explode in that region.
• Measures SN spectra their light curves from
  their earliest moments, through their maximum
  brightness, until their light has died away
  with unprecedented precision.
• Type IA Supernovae (up to 2,000/year x 3 year
  mission lifetime).
• Type II Supernovae Expected to provide an
  independent precision measurement of the
  cosmological parameters using the blackbody
  emission from the hot type II photosphere to
  obtain a luminosity-distance scale (light
  curves).
• Precision Instruments
• 1 billion-pixel CCD camera with a 1-square-degree
  field of view and quantum efficiency gt 80, with
  wavelength coverage from 350 nm to 1 micrometer
• Infrared imager with field of view of up to 10 x
  10 arcminutes
• A 3-arm spectrograph sensitive to wavelengths
  from the near ultraviolet to the near infrared

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Future Goals

• Helpful Additions
• Access to more supernovae of both high low
  redshifts.
• Use of Cepheids (pulsating stars) to assist in
  calibration.
• Plans Hopes with this Method
• More carefully control systematic errors to
  ensure future conclusions are NOT dominated by
  effects unrelated to cosmology.
• Better characterize the equation of the state of
  the dark energy leading to the observed
  acceleration of objects.
• Lingering Questions
• Has ? been constant over the history of the
  universe?
• Exactly how old is the universe?

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SOURCES

• Davies, Paul. The Last Three Minutes.
• Hawking, Stephen. Black Holes Baby Universes.
• http//cfa-www.harvard.edu/cfa/oir/Research/supern
  ova/HighZ.html
• http//snap.lbl.gov
• http//super.colorado.edu/michaele/Lambda/lambda.
  html
• http//www.pbs.org/wgbh/nova/universe
• Kaufmann Freedman. Universe.
• Parker, Barry. Invisible Matter the Fate of the
  Universe.
• Perlmutter, Saul.Supernovae, Dark Energy, and
  the Accelerating Universe. Physics Today.