Ronald Westra

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Introduction to Astrophysics Part 2 Our Amazing
Universe
Ronald Westra University Maastricht
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1. Gravity Revisited
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At large distances only the force of universal
gravity counts
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All movements are defined by Gravitation and
Kinetic Energy
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Example 1a two-body system
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Example 2a Formation of solar system from
accretion disk
This animation begins with a collapsing
interstellar cloud of gas and dust. Most of the
material becomes part of the young Sun, but some
debris forms a disk. Within this disk form the
planets, moons, comets, asteroids, and
meteoroids. Note that this process is repeated on
a smaller scale in the outer solar system, where
miniature disks form around the Jovian planets.
Within the Orion Nebulaa giant cloud of gas and
dust some 1500 light-years from Earthnew stars,
and perhaps new planets, are being formed. The
final closeup is a young star surrounded by a
dark disk of material within which planets may be
forming. (HST images).
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Example 2a Observations of stellar motions near
the central supermassive black hole of our
Galaxy
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Example 2b Observed stellar motions in the
centre of our galaxy M82 suggest a supermasive
black hole
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Example 3a Computer animation of two colliding
galaxies
The Merger of Two Disk Galaxies This
supercomputer simulation shows the collision and
merger of two disk-shaped galaxies. Stars in the
disk of each galaxy are colored blue, while stars
in their central bulges are shown in yellow. Red
indicates dark matter that surrounds each galaxy.
The total elapsed time for this simulation is one
billion years.
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Example 3b Computer animation of six colliding
galaxies
This supercomputer simulation shows six galaxies
merging to form a single giant galaxy. Toward the
end of the simulation a large galaxy forms that
"devours" other, smaller galaxies, a process
called galactic cannibalism. (In ordinary
galactic mergers, galaxies of about the same size
are involved.) Galactic cannibalism may explain
how giant elliptical galaxies form near the
centers of rich clusters of galaxies, where
galactic collisions are frequent.
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Computer animation of an active galaxy (Quasar)
based on a HST picture
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Animation of the two opposit jets of a Quasar
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2. Exotic Matter !!!
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The Enigmatic Dark Matter
90 of all matter is missing !!!
Brown Dwarfs? ... no
Old Pulsars? ... no
Black holes? ... no
MACHO's? ... no
WIMP's? ... ???
neutrino mass? ... no
Cosmical constant? ... ???
Gravitation adapted? ... ???
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Galactic Rotation Curve
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Supermassive Black Holes in Galactic Centres
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The centre of our Galaxy Sagitarius A
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3. History of the Universe
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Is the Universe Infinite and static?
Olbers Paradox
Newton Infinite uniformely distributed mass
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Hubble's Law of Redshift
Galaxies move aways from each
other (SlipherHubble)
Velocity proportional to distance (Hubble)
Proportionality Ho 70 km/s/Mpc
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Hubble's Law implies an Expanding Universe
Heliocentric position or Newtonian relativity ?
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Einstein's General Theory of Relativity
The laws of physics must be of such nature that
they apply to systems of reference in any kind
of motion
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GTR
Equivalence principle
gravity --gt accelarated motion --gt noninertial
frames --gt curved spacetime
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GTR
Equivalence principle
gravity --gt accelarated motion --gt noninertial
frames --gt curved spacetime
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Curved Spacetime
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The Big Bang Theory
Hubble's Law implies that the entire universe
started at one moment and in one point at 1/H0
14 billion yrs ago
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The Big Bang Theory
Physics can reconstruct the history of the
universe up to the Planck-time 1.35 .10-34
sec Before that time QM and RT contradict
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Models for the Evolution of the Universe

• 2D-Analogy inflation of a baloon
• All points move apart a la Hubble
• There is no centre of the universe
• Space itself expands

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Critical Density of the Universe
Critical density ?crit 2.10-27 kg/m3 ?
?/?crit
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Models for the evolution of the Universe
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Models for the evolution of the Universe
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The Early Universe
Up to 300,000 yrs Hot and opaque Matter and
radiation coupled
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Some fine day 300,000 yrs after the BB ...
Universe cooled by expansion matter and
radiation become suddenly decoupled Universe
becomes transparant This is the oldest radiation
and the farthest we can possibly see
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Models for the evolution of the Universe
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Cosmic Background Radiation
This radiation is the Cosmic Background Radiation
(CBR) Because of subsequent expansion the the
universe this is now cooled to 2.7
Kelvin Since january 2003 a entire map of the
CBR is available
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Isotropy Problem
CBR
Isotrope 110,000
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Universe is flat and isotrope
Newest measurements indicate that space is almost
flat and isotrope Solution inflation
theory Short after Plancktime space grew during
about 10-24 seconds a factor 1050
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Accelarating Universe and Anti-gravity
Newest measurements also indicate that redshift
grows stronger than Hubbles law The expansion is
accelerating !!! Possible solution
reintroduction of Cosmological Constant ?? What
would Einstein say ???
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Models for the evolution of the Universe
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Models for the evolution of the Universe
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Models for the evolution of the Universe
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The Fate of the Universe
Big Crunch not likely Big Sleep 1036 yrs
from now only low-energy radiation
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Models for the evolution of the Universe
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Is the Universe part of an infinite Multiverse
??? ...
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... only when physics becomes metaphysics ...
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... The End.