Astr 5460 Wed., Jan. 29, 2003

Today: Textbook Check

Astro-ph (xxx.lanl.gov)

WIRO TBA

Assignment for Friday check

Longair, Chapter 1 (History)

Friday we’ll discuss Chapter 2

Note: This class will meet W&F, 5440 will be M&W

The Big Bang

George Gamow (late 1940s) realized that running the expansion backwards means a hot, dense early universe that was radiation dominated, and nucleosynthesis was possible.

With Alpher and Herman, predicted background radiation left over from this period, which would now have a temperature of about 5 K.

Penzias and Wilson discover the background radiation in 1965 by accident, win Nobel prize.

Prediction from Big Bang Model:
Abundance of the light elements

Big Bang Nucleosynthesis

T, r both high enough at start to fuse protons into heavier elements

T, r both dropping quickly so only have time enough to fuse a certain amount.

Simple models of expansion predict 24% abundance He

24% is the amount of He observed*

Abundance of ²H, ³He, ⁷Li depends on r_{normal matter}

Suggests r_{normal matter} is only 5% of r_critical

But we need to also consider “dark matter” and its gravity

Prediction from Big Bang model:
Cosmic Background Radiation

Look out (and back in time) to place where H became neutral

Beyond that the high density ionized H forms an opaque “wall”

Originally ~3000 K blackbody radiation

The material that emitted it was moving away from us at extreme speed

That v produces extreme redshift (z=1000), so photons all appear much redder, so T appears cooler

With red shift, get 2.7 K Planck blackbody

Should be same in all directions

Cosmic Microwave Background Observations

First detected by Wilson and Penzias in 1960’s

Serendipitous detection – thought is was noise in their radio telescope but couldn’t find cause. Only later heard of theoretical predictions

Best spectrum observed by COBE satellite

Red curve is theoretical prediction

43 Observed data points plotted there
error bars so small they are covered by curve.

it is covered by curve.

Isotropy also measured by COBE

T varies by less than 0.01 K across sky

Small “dipole” anisotropy seen

Blue = 2.721 Red = 2.729

Caused by motion of Milky Way falling towards the Virgo supercluster.

Critical points with time running forward

10^-45 sec Quantum gravity? Physics not understood

10^-34 sec 10²⁶ K Nuclear strong force/electro weak force separate
(inflation, matter/antimatter asymmetry)

10^-7 sec 10¹⁴K Protons, AntiprotonsÛphotons

10^-4 sec 10¹² K Number of protons frozen

    4   sec            10¹⁰ K                  Number of electrons frozen

    2   min Deuterium nuclei begins to survive

    3   min 10⁹ K Helium nuclei begin to survive

30   min           10⁸ K                     T, r too low for more nuclear reactions
(frozen number of D, He -- critical prediction)

300,000 yr 10⁴ K Neutral H atoms begin to survive
(frozen number of photons – critical prediction)

1 billion yr Galaxies begin to form

13 billion yr Present time

Big Bang Essentials

Hubble Expansion

Black Body Background Radiation

Light Element Abundances

Age of oldest stars consistent with Ho age

Galaxy Formation

Lots of theory here!

Jeans (1902), gravitational collapse in a stationary medium, depends on sound speed and density

Lifshitz (1946), general case including expanding medium, but collapse is not typically exponetial and structures grow very slowly – too slowly! Cannot start with infinitesimal perturbations.

Zeldovich, Novikov, Peebles (1960s) used finite perturbations (1 part in 10000).

Main test of all this is the cosmic microwave background radiation, since fluctations should leave imprints.

Galaxy Formation

Thermal history of pregalactic gas can be worked out in detail (and we will do so!).

Density fluctuations tied to temperature fluctuations, revealed finally by COBE, but small. Lots more details to go into here later in course.

Two main ideas: top-down vs. bottom-up.

Need for dark matter (hot or cold) became apparent – normal matter needs help to collapse into galaxies.

Very Early Universe

Isotropy – the universe looks the same in all directions, again strictly true on large scales

Small Baryon/Anti-baryon asymmetry

Close to critical (Omega = 1) (will be HW)

Initial fluctuations to seed structure growth

Very Early Universe

Inflation (Guth, others, early 1980s) resolves some of these properties. Inflation posits an early exponential expansion of the universe that leaves the curvature flat (close to omega = 1) and takes regions in causal contact and moves them far beyond their local horizons (isotropy). May help form the fluctuations leading to galaxies.


	Today: Textbook Check
	Astro-ph (xxx.lanl.gov)
	WIRO TBA
	Assignment for Friday check
	Longair, Chapter 1 (History)
	Friday we’ll discuss Chapter 2


	Note: This class will meet W&F, 5440 will be M&W


	George Gamow (late 1940s) realized that running the expansion backwards means a hot, dense early universe that was radiation dominated, and nucleosynthesis was possible.

	With Alpher and Herman, predicted background radiation left over from this period, which would now have a temperature of about 5 K.

	Penzias and Wilson discover the background radiation in 1965 by accident, win Nobel prize.


Big Bang Nucleosynthesis
	T, r both high enough at start to fuse protons into heavier elements
	T, r both dropping quickly so only have time enough to fuse a certain amount.

	Simple models of expansion predict 24% abundance He
		24% is the amount of He observed*
	Abundance of ²H, ³He, ⁷Li depends on r_{normal matter}
		Suggests r_{normal matter} is only 5% of r_critical
		But we need to also consider “dark matter” and its gravity


	Look out (and back in time) to place where H became neutral
	Beyond that the high density ionized H forms an opaque “wall”
	Originally ~3000 K blackbody radiation
	The material that emitted it was moving away from us at extreme speed
	That v produces extreme redshift (z=1000), so photons all appear much redder, so T appears cooler
	With red shift, get 2.7 K Planck blackbody
	Should be same in all directions


First detected by Wilson and Penzias in 1960’s
	Serendipitous detection – thought is was noise in their radio telescope but couldn’t find cause. Only later heard of theoretical predictions

Best spectrum observed by COBE satellite
	Red curve is theoretical prediction
	43 Observed data points plotted there error bars so small they are covered by curve.
	it is covered by curve.

Isotropy also measured by COBE
	T varies by less than 0.01 K across sky
	Small “dipole” anisotropy seen
		Blue = 2.721 Red = 2.729
		Caused by motion of Milky Way falling towards the Virgo supercluster.


	10^-45 sec Quantum gravity? Physics not understood
	10^-34 sec 10²⁶ K Nuclear strong force/electro weak force separate (inflation, matter/antimatter asymmetry)
	10^-7 sec 10¹⁴K Protons, AntiprotonsÛphotons
	10^-4 sec 10¹² K Number of protons frozen
	4 sec 10¹⁰ K Number of electrons frozen
	2 min Deuterium nuclei begins to survive
	3 min 10⁹ K Helium nuclei begin to survive
	30 min 10⁸ K T, r too low for more nuclear reactions (frozen number of D, He -- critical prediction)
	300,000 yr 10⁴ K Neutral H atoms begin to survive (frozen number of photons – critical prediction)
	1 billion yr Galaxies begin to form
	13 billion yr Present time


	Hubble Expansion

	Black Body Background Radiation

	Light Element Abundances

	Age of oldest stars consistent with Ho age


	Lots of theory here!

	Jeans (1902), gravitational collapse in a stationary medium, depends on sound speed and density

	Lifshitz (1946), general case including expanding medium, but collapse is not typically exponetial and structures grow very slowly – too slowly! Cannot start with infinitesimal perturbations.

	Zeldovich, Novikov, Peebles (1960s) used finite perturbations (1 part in 10000).

	Main test of all this is the cosmic microwave background radiation, since fluctations should leave imprints.


	Thermal history of pregalactic gas can be worked out in detail (and we will do so!).

	Density fluctuations tied to temperature fluctuations, revealed finally by COBE, but small. Lots more details to go into here later in course.

	Two main ideas: top-down vs. bottom-up.

	Need for dark matter (hot or cold) became apparent – normal matter needs help to collapse into galaxies.


	Isotropy – the universe looks the same in all directions, again strictly true on large scales

	Small Baryon/Anti-baryon asymmetry

	Close to critical (Omega = 1) (will be HW)

	Initial fluctuations to seed structure growth


	Inflation (Guth, others, early 1980s) resolves some of these properties. Inflation posits an early exponential expansion of the universe that leaves the curvature flat (close to omega = 1) and takes regions in causal contact and moves them far beyond their local horizons (isotropy). May help form the fluctuations leading to galaxies.