A new view of the Universe VI Fred WatsonApril 2005

A new view of the Universe VI Fred WatsonApril 2005

COSMOLOGYThe study of the origin and evolution

of the Universe as a whole…

What weneed is more money for cosmology

One will see what one

can do

Three microbes in Edinburgh…

Professor Malcolm Longair:“We are witnessing the dawn of a new realm

of precision cosmology…”August 2000

• Better described as “industrial-strength” cosmology because it is very robust…

• The robustness comes from advances in astronomical technology and theoretical physics in recent years…

Two kinds of observational cosmology…

• Near-field cosmology– History of nearby objects, e.g. stars, galaxies

• Far-field cosmology– Studies of the most distant objects: galaxies,

quasars, gamma-ray bursters etc.– Studies of gravitational lensing, the cosmic

microwave background, etc.

Both kinds tell us about the evolution of the Universe

The Nearby UniverseThe Nearby Universe

Tools of the trade

Astronomers don’t use light years.

(You can’t measure a light year.)

Astronomers use parsecs.

(Not to be confused with parsnips.)

What’s a parsec?

Earth

Earth 6 months later

Star appearsto move against

background

Sun

1 arcsecond

1 parsec = 3.27 light-years

1 parsec

Galaxies…

Basic building-blocks of the Universe

If this was our Galaxy,we’d be here •Around 100,000,000,000 stars

•Lots of gas and dust (in spirals)•Around 100,000 l.y. across (or 30 kiloparsecs)

Edge-on view of a spiral galaxy…

The gungy brown stuff is dust, which limitsthe view from the inside

The Eagle Nebula—stellar birthplace

In galaxies, stars are born…

The Vela supernova remnant

…and die

The Expanding UniverseThe Expanding Universe

The Hubble Deep Field—a core-sample of the Universe

Most of these galaxies have look-back times measured in billions of years…

But how do we know it’s expanding?

Tools of the trade

Telescopes can be used as celestial

speedometers for galaxies.

Astronomers record and measure

the spectra of the galaxies.

Blueend

Redend

A spectrum

(Not to be confusedwith a plectrum)

Spectra of about 100 galaxies arranged in order of increasing velocity

Blueend

Redend

Hubble’s Law (1929)

“The speed of recession of a galaxy, v, is proportional to its distance, d, from the observer.”

v = H0 d

The constant of proportionality, H0 is called the Hubble constant, and is in units of km/s per megaparsec. (1 Mpc = 3.27 million l.y.)

Accepted value today is H0 75 km/s/Mpc.

But what does “redshift” mean…?We now know the Hubble law comes about because space itself is expanding, stretching the

wavelength of light moving through it.

Rather than calculating a galaxy’s velocity, astronomers simply measure the fractional shift of its spectrum towards the red resulting from the expansion ( / emitted).

This is called the redshift, z

Tools of the trade

The Really Useful Quantity 1/(1 + z) tells us how big the Universe was when the light was emitted.

Remitted / Rnow = 1/(1 + z)

E.g., for a galaxy with z = 1, the Universe was half its present size when it emitted its light.

An Einstein Ring (B0047-2808)…

zforeground = 0.485; zbackground = 3.595

The Age of the UniverseThe Age of the Universe

How old is the Universe?

In 1927, Georges Lemaître realised that Hubble’s Law means the Universe itself is expanding.

He extrapolated back in time to when all the galaxies were at a single point.

The age of the Universe is then given by the “Hubble time” = 1/H0

If H0 = 75 km/s/Mpc, the Hubble time is 13 billion years.

13 billion years

The Universetoday

Origin of the Universe

Lemaître’s Picture:

Defining quantity: Hubble constant, H0 (uniform expansion)Problem: it only works if the Universe is completely empty.

About 9 billion years

The Universetoday

Origin of the Universe

Refined Model (1970s):

Defining quantities: Hubble constant, H0 (current expansion)cosmic density parameter,

Problem: the Universe is younger than most of its contents.

Dark matter and the composition of the Universe

~13 billion years

The Universetoday

Origin of the Universe

Current Model:

Defining quantities: Hubble constant, H0 (current expansion)cosmic density of all matter, m

cosmic density of ordinary matter, b

dark energy (cosmological constant, )(evidence from distant supernovae, etc.)

Age of the Universe

Mapping the UniverseMapping the Universe

Survey Regions

Pie-slice directions in the 2dF Galaxy Redshift Survey

The distribution of galaxies allows us to measure the“clumpiness” of the Universe

Then, of course, there are the quasars…

Spectra of 11,000 quasars from the 2dF surveyarranged in order of distance

The biggest survey to date—but it stillshows us only 0.1%of the Universe…

Quasars are also clumpy.

The hot Big BangThe hot Big Bang

The Hot Big Bang model

Modern equivalent of Lemaître’s picture.

It postulates a hot Big Bang—a unique event in which not only the matter in the Universe was created, but space and time as well…

Three vital pieces of evidence support it:

• the expansion of the Universe;

• the relative abundances of light elements;

• the cosmic microwave background radiation.

What’s the cosmic microwave background radiation?

• Faint background glow in the millimetre wavelength region of the radio spectrum.

• Almost perfectly uniform in all directions.

• It is the echo of the Big Bang fireball itself.

• We’re seeing back in time to a moment 300,000 years after the Big Bang when the Universe ceased to glow with brilliant white light— and became transparent…

Applause

You

Applause

Silence

YouR

R = 330 metres after 1 second; R = 660 metres after 2 seconds, etc.

i.e., R increases at the speed of sound.

Cosmic microwave background radiation • Why don’t we see a brilliant white back-ground in every direction?

• The radiation has been redshifted by the expansion of the Universe.

• The light waves have been s-t-r-e-t-c-h-e-d by about 1000 times to become longer wave- length microwaves. Thus, zCMBR 1000.

• The CMBR is easily the most ancient fossil remnant we can see…

COBE all-sky map showing 1-in-105 temperature fluctuationsThe hot-spots are the seeds of the structure we see

in the Universe today

What does the CMBR tell us about the Big Bang?

• The rippling in the CMBR (due to acoustic oscillations in the fireball) closely matches the clumpiness seen in the redshift surveys. It is the “baby face” of today’s Universe

• The radiation is very smooth—fluctuations in the early fireball must have been ironed out by an exceedingly short period of inflation.

• The rippling can tell us much, much more about both the Big Bang and the evolution of the Universe—hence NASA’s WMAP…

WilkinsonMicrowaveAnisotropyProbe

Launched30.6.2001

Notsucha badeffortfor a bunch ofmicrobes…

In summary…

Observing first-generation galaxies with the James Webb Space Telescope

There’s nothing wrong with a Dish – as long as it’s

not lamb casserole…