Astronomy 1143 – Spring 2014 Lecture 17: Matter! It matters!

Key Ideas: Temperature of matter is important! Measures energy of particles “Normal Matter” in the Universe hydrogen and helium in atomic/ionized form Make-up of ordinary matter: electrons, protons, and neutrons Stable particles that exist at low temperatures Atoms Elements Isotopes

Key Ideas: Radioactive particles are unstable – decay to other particles Showed that the atom was divisible Experiments have shown the existence of other types of particles Anti-matter Same mass, opposite charge Annihilates when meets its matter counterpart Fundamental particles – quarks, leptons, neutrinos, force- carrying bosons At high temperatures, many more massive fundamental particles present

State of Matter Depends on Conditions HOT COLD High Temperatures – Fast moving particles Emission of high-energy radiation

Temperature Temperature is a measurement of the internal energy content of an object. Solids: Higher temperature means higher average vibrational energy per atom or molecule. Gases: Higher temperature means more average kinetic energy (faster speeds) per atom or molecule.

Kelvin Temperature Scale An absolute temperature system: Developed by Lord Kelvin (19th century) Uses the Celsius temperature scale Absolute Kelvin Scale (K): 0 K = Absolute Zero (all motion stops) 273 K = pure water freezes (0º Celsius) 373 K = pure water boils (100º C) Advantage: The total internal energy is directly proportional to the temperature in Kelvins.

Hot Gas Faster Average Speeds Cool Gas Slow Average Speeds

Effects of High Temperature Particles are moving very fast, so they have high energy collisions Energetic photons or high-energy collisions between particles break bonds Matter becomes dominated by fundamental particles Energetic photons can create matter-antimatter pairs, so long as energy is greater than the rest mass energy of particle

Einstein’s Famous Formula Einstein famously unified matter and energy Particles with lots of mass can be converted into lots of energy – pair annihilation Energy can turn into mass – photons turning into electron-positron pairs Most famous example: Hydrogen fusing to He Mass 1 He nucleus=6.664x kg Mass of 4 H nuclei =6.690x kg 4.6x kg turned into energy

Where do we have high energies? Supernova Disks around Black Holes Early Universe

Experimental Results (Many of) the crazy ideas of particle physics are accepted because they have been verified by experiment Experimental techniques Particle accelerators Bubble chambers Energy detectors – large vats of xenon, water, etc, providing lots of targets Observations of early Universe

Bubble Chambers Particle beam is sent through a chamber filled with superheated fluid. Chamber also has magnetic field running through it. Charged beam particles pass through the liquid Deposit energy by ionizing atoms Energy causes liquid to boil along their paths. Beam particles may also collide with atomic nuclei Produce new particles New particles also deposit energy, creating more bubble Flash photographs taken from several angles

Bubble Chambers

Atoms Ordinary matter is found primarily in the form of atoms. To make people, rocks (and rocky planets), plants, animals, etc, nature forms complex structures with atoms called molecules Molecules are found in interstellar space and in the “cool” atmospheres of stars, but most of the current Universe is in atoms (or ionized atoms)

The Divisible Atom Ironically, the word “atom” is derived from the Greek word atomos, meaning "indivisible” Atoms are indivisible chemically, unlike molecules But radioactivity revealed that the atom is actually divisible and added new particles to the particle zoo

Atomic Structure Nucleus of heavy subatomic particles: proton: positively charged neutron: uncharged (neutral) Electrons orbiting the nucleus: negatively charged particles 1/1836 th the mass of a proton Atoms are mostly empty space: Only 1 part in of space is occupied The rest of the volume is threaded by electromagnetic fields 1H1H + 4 He

Elements Distinguish atoms into Elements by the number of protons in the nucleus. Atomic Number: 1 proton = Hydrogen 2 protons = Helium 3 protons = Lithium... and so on Number of electrons = Number of protons All elements are Chemically Distinct

Top Ten Most Abundant Elements in the Universe 10) Sulfur 9) Magnesium 8) Iron 7) Silicon 6) Nitrogen 5) Neon 4) Carbon 3) Oxygen 2) Helium 1) Hydrogen

Known Elements 118 elements are currently known: 87 are metals 11 are gasses 2 occur as liquids (Bromine & Mercury) 26 are natural radioactive elements 25 are made only in particle accelerators In addition, each element can have a number of different isotopes.

Isotopes A given element can have many Isotopes Same number of protons. Different number of neutrons. Example: 12 C has 6 protons and 6 neutrons 13 C has 6 protons and 7 neutrons 14 C has 6 protons and 8 neutrons Chemically identical, but different masses.

Hydrogen 1 proton Helium 2 protons Lithium 3 protons Proton:Neutron: 1H1H 3 He 2H2H 3H3H 4 He 6 Li 7 Li Deuterium Tritium

Ionization Electrons absorb enough energy to escape the atom completely This ionizes the atom. Example: To ionize from the ground state of hydrogen requires 13.6 eV of energy. This is a photon of 91.2 nm (ultraviolet) In the center of the Sun, over % of the material is ionized – sea of nuclei and free electrons

Recombination Free electrons (electrons not bound to an atom) can be captured by an atom, particularly an atom that has been ionized. This process is called recombination. Energy is released when the electron recombines Free electrons can interact with any wavelength of light – not confined to certain quantized levels Much tougher for a photon to make it through free electrons than atoms

Radioactivity If a nucleus has too many or too few neutrons, it is unstable to radioactive decay Examples: 3 H (1p+2n)  3 He (2p+1n) + e  + e 14 C (6p+8n)  14 N (7p+7n) + e  + e (basis of radioactive carbon dating) Free neutrons are also unstable: n  p + e  + e Who ordered this?

Discovery of Neutrino Proposed in 1930 by Wolfgang Pauli to explain what happened to the energy in radioactive decay that seemed to “disappear” Detected in Found to be extremely weakly interacting, as expected 300 billion neutrinos are passing through my hand per second, mostly thanks to the Sun A new particle was added to our understanding of the Universe

Neutrino Interaction in Bubble Chamber

Fundamental Particles

Stable and Unstable Particles Heavier fundamental particles decay into lighter fundamental particles So ordinary matter is composed of the “Generation One” particles Heavier particles continually being created by energetic events

Matter & Antimatter Each particle has an anti-particle Same mass, but opposite charge (if possible) If a particle and anti-particle meet, they annihilate each other, leaving behind a burst of energy It is possible, but unlikely, that there are pockets of anti-matter in the Universe Why the Universe has a surplus of matter is something that needs to be explained.

Anti-Particles

Quarks Elementary particles that form hadrons Free quarks do not exist in normal conditions Held together by the strong force

The Particle Zoo Atoms – not indivisible! protons, neutrons, electrons quarks Hadrons Baryons (3 quarks) Mesons (2 quarks)

Particle Physics View of World The modern view of forces is that they are carried by particles Choice in the way you think about things – what matters is what you can predict Very successful at predicting the interaction between particles and light

The Four Fundamental Forces

History of the Universe The Big Bang theory states that the observable Universe started out in an extremely hot and dense state Expanded and cooled since then Early in the Universe, temperatures are so high that only fundamental particles can exist – e.g., quarks, leptons and bosons High enough energy that many massive particles being formed Nature of dominant form of matter has changed over the history of the Universe