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A new view of the Universe VII Fred Watson, AAO

April 2005

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…

• 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.

A 2-dimensional view of the sky

Stellar parallax

Earth

Earth 6 months later

Star appearsto move against

background

Sun

Building-blocks of illusion…

A fixed vantage-point

You arehere

Building-blocks of illusion…

Natural sensitivity only to visible light

Building-blocks of illusion…

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

Finite speed of light

The Moon IllusionThe Moon Illusion

Spot the Moon…

What’s that besideyour head, Liam?

Only my lovefor you, my sweet.

Oh, Yukkk!!!

Our perception of the sky—not a hemisphere, but an inverted dish

Are we at the centre of our Galaxy?

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 haloof globular clusters

We have a clearer viewof the halo than the disk

SupernovaeSupernovae

Vela supernova remnant

Supernova 1987aphotographed 6 Feb 1989

Supernova Light Echo

Earth

Dust cloud

SupernovaD

a

D = 0.34 a2 / T

Supernova Light Echo

Earth

Supernova

Dust

sheets

What puts the spirals into spiral galaxies?

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.

This density wave triggers star-formation, producing masses of hot bright stars that reveal its position.

The spiral arms are an illusion.They trace the passage of a ‘sound wave’ through the disk of the galaxy

Faster than light?Faster than light?

Many radio-objects have expanding lobes

This is a double-lobed radio galaxy, observed with the ATNF, super-imposed on a visible-light 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 outwardsat very nearly the speed of light

To Earth

By the time the jet reachesHERElight from the outburst is onlyHEREgiving the appear-ance from Earth of material moving atsuperluminalvelocity.

Gravity’s lensGravity’s lens

The discovery of gravitational lenses

In the late 1970s, astronomersstarted 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?

Is there a Cosmic Illusionist?

The laws of physics create the illusions…

but they also allow us to see behind them!

The EndThe End