Extremes of the Universe: Power and Phenomena

Jul 12, 2024

Lecture Notes: Extremes of the Universe

Key Theme

  • Power in the Universe: The lecture explores the most powerful objects in the universe, often driven by gravity and magnetism.

The Sun

  • Solar Eruptions: Solar prominences and flares, with the sun being relatively inactive compared to other stars.
  • Differential Rotation: Sun rotates at different speeds at the equator (26 days) and poles (30 days), causing magnetic field lines to spring out like rubber bands.
  • Historical Observation: Brightest solar flare recorded by Carrington in 1859, leading to auroras and telegraph disruptions.
  • Potential Impacts: Modern solar flares could disrupt transmission systems and satellites, including GPS.

Solar Flares

  • Energy and Frequency: Flares can range in energy and are plotted logarithmically to understand their occurrence rate and potential energy.
  • Kepler Satellite Observations: Continuation of solar flare patterns seen in thousands of stars similar to the sun.

Power Limits in the Universe

  • Maximum Power Equation: Maximum power derived from an object's mass using Einstein's E=mc^2 and light crossing time, resulting in a theoretical limit of 3.6 x 10^52 watts.
  • Eddington Limit: Limit to power due to radiation pressure opposing gravitational pull, demonstrated by comet tails.

Stars and their Fate

  • Life Cycle: Evolution of stars from hydrogen burning to potential endpoints as white dwarfs, neutron stars, or black holes.
  • Supernovae: Different types of supernovae (core collapse, binary mergers) and their contributions to heavy elements like iron and oxygen in the universe.

Neutron Stars and Pulsars

  • Crab Nebula: Remnant of a supernova in 1054 AD, containing a pulsar with highly magnetized spinning characteristics.
  • Magnetars: Neutron stars with extremely high magnetic fields, leading to intense flashes and ionization of Earth's atmosphere.

Black Holes

  • Observation: Evidence of black holes through the motion of stars and gravitational influences, including the supermassive black hole at the center of our galaxy.
  • Event Horizon: Concept of event horizon where gravity is so strong that not even light can escape, warping space-time.
  • Theoretical Predictions: Early theoretical predictions by John Mitchell and later advancements by Einstein and Schwarzschild.
  • Quasars: Extremely luminous objects powered by accretion of matter into black holes, visible even from great distances.

Gravitational Waves

  • Observations: Merging black holes observed through gravitational waves by instruments like LIGO, demonstrating extreme power outputs.
  • Implications of Mergers: Gravitational waves from mergers can be more powerful than the combined luminosity of all stars in the universe.

Feedback and Galaxy Evolution

  • AGN and Quasars: Influence of active galactic nuclei in shaping galaxies through radiation pressure and gas outflows.
  • Galaxy Structure: Correlation between black hole mass and galaxy mass, affecting star formation and evolution of galaxies.

Summary

  • Black holes and their associated phenomena demonstrate the most extreme manifestations of power in the universe, influencing the formation of elements, galaxy structures, and potentially playing a role in high-energy astrophysical events.