ASTRONOMY

The Universe

Key Terms• Astronomy: The scientific study of the universe; it includes the observation and

interpretation of celestial bodies and phenomenon

• Big Bang: The theory that proposes that the universe originated as a infinitely

small mass which sub sequentially began to expand

• Cosmology: The study of the origins of the universe

• Doppler Effect / Red Shift: the wavelength of an object lengthens and shifts towards the red end of the spectrum as

it recedes from our position.

• Galaxy: A collection of stars, gas and dust held together by gravity

• Hubble’s Law: galaxies are receding from our galaxy at a speed that is proportional to their distance

• Universe: All matter and energy, including the earth, the galaxies, and the contents of intergalactic space, regarded as a whole

Origins

The Big Bang• The universe formed approximately 12 – 14 billion years ago

• Universe was condensed into an infinitesimally small point SINGULARITY

• For reasons still unknown, expansion of the singularity began

• All matter and space were created at this instant.

• In the first microseconds of expansion (Planck Era), the universe increased in sized at a faster than light rate Inflation theory: increased expansion rate due to an unknown and unstable form of energy

– The universe went from the size of an atom to the size of a grapefruit in 10 -43 sec.

• At 10 -32 sec. electrons, quarks and other subatomic particles formed

• 10 -6 sec. protons and neutrons form

• 300,000 years after the big bang the first atoms of H and He form Light

• 1 billion years after the big bang First Stars Form

BIG BANG

INFLATION AND BIG BANG EXPANSION

Evidence for the Big Bang Theory

The Big Bang Model is supported by a number of important observations.

• The expansion of the universe Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right.

• The abundance of the light elements H, He, Li The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang.

• The cosmic microwave background (CMB) radiation The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang. (COBE and WMAP)

The COBE satellite was developed by NASA's Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe to the limits set by our astrophysical environment.

Cosmic Background ExplorerThe COBE satellite carried three instruments1. Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared

background radiation (CIB).– The CIB represents a "core sample" of the Universe; it contains the cumulative emissions of stars and galaxies

dating back to the epoch when these objects first began to form. – The COBE CIB measurements constrain models of the cosmological history of star formation and the buildup

over time of dust and elements heavier than hydrogen, including those of which living organisms are composed. Dust has played an important role in star formation throughout much of cosmic history.

2. Differential Microwave Radiometer (DMR) to map the cosmic radiation sensitively• The CMB was found to have intrinsic "anisotropy“ or fluctuations for the first time, at a level of a part in 100,000.• These tiny variations in the intensity of the CMB over the sky show how matter and energy was distributed when

the Universe was still very young.• Later, through a process still poorly understood, the early structures seen by DMR developed into galaxies,

galaxy clusters, and the large scale structure that we see in the Universe today.

3. Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the

cosmic microwave background radiation with a precise blackbody.– The cosmic microwave background (CMB) spectrum is that of a nearly perfect blackbody with a temperature of

2.725 +/- 0.002 K.– This observation matches the predictions of the hot Big Bang theory extraordinarily well, and indicates that

nearly all of the radiant energy of the Universe was released within the first year after the Big Bang.

• WMAP has mapped the Cosmic Microwave Background (CMB) radiation (the oldest light in the universe) and produced the first fine-resolution (0.2 degree) full-sky map of the microwave sky

• WMAP determined the age of the universe to be 13.73 billion years old to within 1% (0.12 billion years)

WMAP (cont.)• WMAP nailed down the curvature of space to within 1% of "flat" Euclidean,

improving on the precision of previous award-winning measurements by over an order of magnitude

• WMAP's precision determination that ordinary atoms (also called baryons) make up only 4.6% of the universe (to within 0.1%)

• WMAP's complete census of the universe finds that dark matter (not made up of atoms) make up 23.3% (to within 1.3%)

• WMAP's accuracy and precision determined that dark energy makes up 72.1% of the universe (to within 1.5%), causing the expansion rate of the universe to speed up.

• WMAP discovered that the universe was reionized earlier than previously believed. By measuring the polarization in the CMB it is possible to look at the amplitude of the fluctuations of density in the universe that produced the first galaxies.

• WMAP has started to sort through the possibilities of what transpired in the first trillionth of a trillionth of a second

Large Scale Structures• Galactic Filaments

– Also known as Great walls , Supercluster

complexes or Sheets– Not gravitationally bound and therefore take part in

the Hubble expansion– Largest known cosmic structures in the universe– massive, thread-like structures with a typical length of 50

to 80 megaparsecs that form the boundaries between large voids in the universe.

– consist of gravitationally-bound galaxies; parts where a large number of galaxies are very close to each other are called superclusters.

• Voids– the empty spaces between filaments– contain very few, or no, galaxies– have a diameter of 11 to 150 Megaparsecs

• Great Attractor– a gravity anomaly in intergalactic space within the range of the Centauries Supercluster that reveals the existence of a localized concentration of mass equivalent to tens of thousands of Milky Ways– observable by its effect on the motion of galaxies and their associated clusters over a region hundreds of millions of light years across.

• Galactic cluster– A system of galaxies containing from several

to thousands of member galaxies

• Galaxy– A collection of stars, gas and dust held

together by gravity

Galactic Filaments of the Local Universe

11,000 Galaxieswith the Milky Way at the center

A Close up View of Home

It doesn’t add up.

• Data collected from COBE and WMAP indicates that the universe is too large and “lumpy” in structure to have formed in 13.7 billion years.

• More time was needed– Inflation theory: microseconds after expansion of the

universe began there was an inflated increase in the expansion rate of the early universe.

– This was due to the interaction of a mysterious form a matter and energy which accounts for the majority of matter and energy in the universe today

• Dark Matter• Dark Energy

Dark Matter

• matter that is inferred to exist from gravitational effects on visible matter and gravitational lensing of background radiation

• neither emits nor scatters light or other electromagnetic radiation (and so cannot be directly detected via optical or radio astronomy).

• Its existence was hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe and calculations based on the mass of the visible "luminous" matter these objects contain– stars and the gas and dust of the interstellar and intergalactic medium.

• Evidence– Galactic rotation curves: stars in galaxies move at different rates

– Velocity dispersions of galaxies: galaxies are being dispersed at different velocities from one another

– Galaxy clusters and gravitational lensing: the structure of clusters and the lensing effect of galaxies are caused by the gravitational effect of dark matter that surrounds galaxies in halo type structures

– Cosmic microwave background: CMB not uniform on a large scale (lumpy); fluctuations in the radiation caused by gravitational effect of dark matter

Dark Energy

• a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe.

• the most accepted theory to explain recent observations that the universe appears to be expanding at an accelerating rate.

• Evidence

– Supernovae: rate at which light reaches us is increased

– Cosmic Microwave Background: universe in nearly flat therefore mass/energy = critical density to have a flat universe; visible energy not enough

– Large Scale Structure: only accounts for 30% of total matter in universe– Late-time Integrated Sachs-Wolfe Effect: Accelerated cosmic expansion causes

gravitational potential wells and hills to flatten as photons pass through them, producing cold spots and hot spots on the CMB aligned with vast supervoids and superclusters. This so-called late-time Integrated Sachs-Wolfe effect (ISW) is a direct signal of dark energy in a flat universe

Composition of the Universe

Shape of the Universe

• Critical density ~ 6 H atoms/m3.• Density of the Universe is close to this amount,

therefore the Universe is probably infinite.

GALAXIES

A galaxy is collection of stars, gas and dust held together by gravity.

GALAXY FORMATION

STEP 1• About 1 billion years after the “big bang” dark matter and cooling

gas condense and collapses under its own gravity to form a PROTOGALAXY

STEP 2• Gravity separates out the protogalaxy into a core and a halo.

STEP 3• The subatomic particles that make up the gas interact to lose

energy and fall to the core of the protogalaxy.

STEP 4• The dark matter which only weakly interacts, remains in the halo.

The Role of Dark Matter in Galactic Formation

Formation of Protogalaxy

Actual Image of a Protogalaxy

A protogalaxy candidate. The blue galaxy in the image is located approximately 10 billion light years away from us

and about four times farther away than the yellower galaxies in the image. The spectrum of the galaxy indicates it is

only about 10 million years old--a relative baby in terms of galaxy evolution.

PROTOGALAXY

Galaxy EvolutionGalaxy evolution is process of gravitational

interaction between dark and visible matter

and collisions between large galaxies.1. Irregular galaxies condense to form globular clusters.

2. Globular cluster collide to form spirals which collide to form ellipticals.

Types of Galaxies

Galactic Structure

ACTIVE GALACTIC NUCLEI

• Seyfret galaxies, Quasars and Blazars1. All three are associated with super massive black holes.2. Many astronomers think they are the same object viewed

from different angles.3. They shine brighter than any other objects in the universe

4. They all emit great amounts of energy in the form of …• Infrared radiation• Radio waves• UV radiation• X-ray radiation• Gamma radiation

Seyfert Galaxies

• Spiral shaped galaxies• low-energy gamma-ray sources

• Rotating super massive black hole releases gamma ray jets from either pole as matter is

destroy

BLAZARS

• A class of active galaxy characterized by strong, compact, flat-spectrum radio emission

• Extremely bright• Strong gamma ray emissions• Believed to be active galactic

nuclei whose jets are aligned

within 10° of our line of sight

QUASARS

• Quasi-stellar objects of small angular size and immense power output.

• Strong radio sources• Because they are so bright, quasars are some of

the most distant objects we can see in the universe.

• Huge power output is believed to be fueled by interactions between the central black hole and a surrounding "accretion disk": – a disk of matter that gathers around the black hole in

the galactic nucleus.

Infrared Imaging of Quasar Radio Jets

Infrared Imaging of Quasar Radio Jets

QUASAR

THE FORMATION STARS

STAR FORMATION• Stars form inside relatively dense concentrations of interstellar gas and

dust known as molecular clouds.

• These regions are extremely cold (temperature about 10 to 20K, just above absolute zero). At these temperatures, gases become molecular meaning that atoms bind together.

• CO and H2 are the most common molecules in interstellar gas clouds. The deep cold also causes the gas to clump to high densities. When the density reaches a certain point, stars form.

• Since the regions are dense, they are opaque to visible light and are known as dark nebula. Since they don't shine by optical light, we must use infrared radiation and radio telescopes to investigate them.

1. Star formation begins when the interstellar dust and gas is disturbed by some nearby phenomenon (supernova, galactic collision, etc.)

2. The denser parts of the cloud core collapse under their own weight/gravity.

3. These cores typically have masses around 104 solar masses in the form of gas and dust.

4. The cores are denser than the outer cloud, so they collapse first. As the cores collapse they

fragment into clumps around 0.1 parsecs in size and 10 to 50 solar masses in mass.

5. These clumps then form into protostars and the whole process takes about 10 millions years.

STAR FORMATION

Protostars: • Once a clump has broken free from the other

parts of the cloud core, it has its own unique gravity and identity and we call it a protostar. 1. As the protostar forms, loose gas falls into its center. 2. The infalling gas releases kinetic energy in the form of heat

and the temperature and pressure in the center of the protostar goes up.

3. As its temperature approaches thousands of degrees, it becomes a infrared radiation source.

STAR FORMATION• During the initial collapse, the clump is transparent to radiation

and the collapse proceeds fairly quickly.

• As the clump becomes more dense, it becomes opaque. 1. Escaping infrared radiation is trapped, and the temperature and pressure in the center

begin to increase.

• At some point, the pressure stops the infall of more gas into the core and the object becomes stable as a protostar.

• The protostar, at first, only has about 1% of its final mass. But the envelope of the star continues to grow as infalling material is accreted.

• After a few million years, thermonuclear fusion begins in its core, then a strong stellar wind is produced which stops the infall of new mass.

• The protostar is now considered a young star since its mass is fixed, and its future evolution is now set.

PROTOSTAR