Transcript Instrumentation for Cosmology

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A new view of the Universe VII
Fred Watson, AAO
April 2005
In the Universe, things aren’t always
what they seem…
…in fact, they hardly ever are!
Building-blocks of illusion…
A 2-dimensional view of the sky
• Natural (stereoscopic) depth perception is
limited.
• Understanding Solar System dynamics
extends our perception of depth to more
than 10 billion km.
• Stellar parallax extends depth perception to
a thousand or so light-years.
Stellar parallax
Earth
Sun
Earth 6 months later
Star appears
to move against
background
Building-blocks of illusion…
A fixed vantage-point
You are
here
Building-blocks of illusion…
Natural sensitivity only to visible light
Building-blocks of illusion…
Finite speed of light
Lookback times:
• Moon… 1.3 seconds
• Sun… 8 minutes
• Jupiter (this evening)… 35 minutes
• Nearest star… 4.2 years
• Large Magellanic Cloud… 165,000 years
• Andromeda Galaxy… 2.2 million years
The Moon Illusion
Only my love
for you, my sweet.
What’s that beside
your head, Liam?
Spot the Moon…
Oh,
Yukkk!!!
Our perception of the sky—not a hemisphere,
but an inverted dish
Are we at the centre of
our Galaxy?
The Milky Way—
relatively uniform.
Are star-counts telling the truth?
No—they ignore the presence of dust
•
•
•
•
Globular clusters
About 150 known in
our Galaxy
Most are in one part of
the sky (Sagittarius)
Many are above or
below the plane of the
Galaxy—no dust
In 1919, Shapley
measured their
distances from the Sun
Deductions: we are in the galactic suburbs—
and the Galaxy is much bigger than anyone thought
The Galaxy’s halo
of globular clusters
We have a clearer view
of the halo than the disk
Supernovae
Vela supernova
remnant
Supernova 1987a
photographed
6 Feb 1989
Supernova Light Echo
Dust cloud
a
D
Earth
Supernova
D = 0.34 a2 / T
Supernova Light Echo
Supernova
Dust
sheets
Earth
What puts the spirals
into spiral galaxies?
What are the spiral arms?
Just strings of stars?
No, because they would be tightly wound up.
Suppose the age of the galaxy is 10 billion years.
Its inner regions rotate once in 200 million years…
Therefore, we’d expect about 50 turns.
The galaxy would look like a clock spring.
The spiral arms are an illusion.
They trace the passage of a ‘sound wave’
through the disk of the galaxy
This density wave triggers star-formation, producing
masses of hot bright stars that reveal its position.
Faster than light?
Many radio-objects
have expanding lobes
This is a double-lobed
radio galaxy, observed
with the ATNF, superimposed on a visiblelight photograph.
Twin jets of
material from a
binary star in our
Galaxy
The expansion took
place during the
course of a few days
in late-1997.
Faster than light…?
Jets moving outwards
at very nearly the
speed of light
To Earth
By the time
the jet reaches
HERE
light from the
outburst is only
HERE
giving the appearance from Earth of
material moving at
superluminal
velocity.
Gravity’s lens
The discovery of gravitational lenses
In the late 1970s, astronomers
started to discover
‘double quasars’
Shortly afterwards, strange arcs of
light were discovered, often
near faint galaxies.
Gravitational lensing
An Einstein Ring…
B0047-2808: zlens = 0.485; zsource = 3.595
Gravitational lens in Abell 2218
Is there a Cosmic
Illusionist?
The laws of physics create the
illusions…
but they also allow us to see
behind them!
The End