The Evolution of the Universe

Nicola Loaring

The Big Bang

• According to scientists the Universe began ~15 billion years ago in a hot Big Bang.

• At creation the Universe was infinitely hot and infinitely small.

• Time started when the Universe began- there is no before the Big Bang!

10-34 seconds : Matter forms Scores of different building block particles - quarks, leptons, photons, and neutrinos flood the universe (the size of a melon).

10-6 seconds : Protons and Neutrons formQuarks combine to form protons and neutrons. Each is made of 3 quarks

3 minutes : Nuclei formProtons and neutrons combine to form the atomic nuclei of the lightest elements hydrogen, helium and lithium.

~ 700,000 years : Atoms formThe temperature has fallen to a few 1000K, electrons and protons can hold together to begin forming hydrogen atoms.

The early Universe

• As the Universe cools sufficiently for all the electrons to be soaked up into atoms the matter and radiation stop interacting

• Light is free to travel to us.

• We see this as the Cosmic Microwave background radiation.

The Cosmic microwave background

The cosmic microwave background

• The earth is bathed in CMB at a temperature of 2.73K

• Very smooth in all directions , temperature variations of only 1 part in 105 -tiny temperature fluctuations

WMAP probe currently measuring the CMB

The Universe is expanding: Hubble’s Law

• In 1929 Hubble noted that speed of recession of galaxies is proportional to their distance from us

• Newton realised that a falling apple is attracted to the Earth via a force called gravity.

• Newton’s third law states that every force has an equal and opposite reaction – so that every object attracts every other object

• Leads to build up of structure

How does structure form?Gravity

F = G m1 m2

r2

Stellar evolution• Stars shine by nuclear burning

of fuel

• Gravity is balanced by radiation pressure

• Evolution depends on initial mass of the star

• Initial masses of less than 8 solar masses end their lives by ejecting planetary nebulae (White dwarf remnants)

• Initial masses greater than 8 solar masses end their lives by exploding as supernovae. Remnants are neutron stars or black holes

Size is the same as the orbit of Mars

Star formation• As Universe cooled further

giant molecular clouds formed

• Gravity collapses them until they are so dense that nuclei begin to fuse - a star is born

Supernovae• Needed to form very heavy elements • Nuclei thrown into the galaxy and pick up elections forming

heavy atoms which are used in next round of star formation• All the atoms in your body except hydrogen were made in a

supernova ~5 billion years ago or more

Formation of the solar system• Formed when a cloud of gas

and dust in space was disturbed

• Gravity pulled the gas and dust together, forming a solar nebula

• The cloud began to spin as it collapsed

• As the disk got thinner particles began to stick together and form clumps eventually forming planets or moons

• As the cloud continued to fall in, the center eventually got so hot that it became a star, the Sun

Galaxies1pc =3x1013 km = 3.2 light

years = 206,000AU

• Have billions of stars

• Stars gather together by mutual gravitational attraction

• Gas and dust are intermixed with the stars

• 70% spiral, 30% elliptical

• Size ~9kpc

M33 spiral galaxy M83 – Spiral galaxy

M32 - Elliptical galaxy

Peering at the earliest Galaxies• The further away from the Earth we look, the further back

in time we are looking due to the finite speed of light.

The Hubble Space telescope deep field

• Distant galaxies as they were nearly 13 million years ago• Still busy forming and interacting

Galaxy clusters• Sizes 1-10 Mpc

• Irregular Virgo Galactic Cluster

• 50 million light-years from Earth

• Contains roughly 2,000 galaxies

• The dominant (largest) galaxy is the elliptical M87 (Virgo A)

Super-structuresFrom 2QZ

Simulations of structure formation

Virgo consortium simulation

The matter density of the Universe and dark matter

• Evidence for dark matter on a range of scales: from galaxy rotation curves

• Gravitational lensing

• Most of the matter in the Universe is ‘dark’

The fate of the Universe• Dark energy introduced by Einstein, anti-gravity energy to stop collapse• Appears to dominate the total mass-energy content of the Universe• Universe expansion is accelerating at the moment