Week 4: Astrophysics Predictions

Astrophysics Predictions: Origins and Models

Guest Lecturer: Blakesley Burhart: Harvard-Smithsonian Center for Astrophysic (CfA) Institute for Theory and Computation

Google Docs Notes


Astronomy/astrophysics: humans seek to understand our universe and our place in it and predict the future based on the past and on models.

For much of 19th century, astronomy was focused on charting positions and computing the motions of celestial objects.

Astrophysics began to emerge when William Hyde Wollaston and Joseph von Fraunhofer discovered that when light was decomposed from the Sun, black lines were observed in the spectrum
  • Eventually deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere.

September 2, 1859: Earth hit by the largest solar storm in history.


Early models for the heavens: astrology,  epicycles

Based on this course, how are astrology/modern astronomy different?  What is similar?

How do both seek to make predictions?

  • Astrology is the more ancient study of celestial positions, with the charting of the planets and stars.

    • Pyramids in Egypt and Americas (Mayan culture)

    • Thought that Stonehenge in England served as a calendar in order to mark positions of the Sun and the moon

    • Thought to be used as an aid for planting or harvesting crops or to aid in religious ceremonies for eternal life

    • Generally follows idea that either celestial bodies are signs of events or that they are the actual causes of events

  • Astronomy is a more recent development, and marks its beginning at about the time of the Renaissance.

    • Astronomy follows idea that celestial bodies have no influence upon human behavior but can be scientifically measured using natural laws of physics


Astronomy (Western)

  • Copernicus
  • Giodarno Bruno
  • Tycho Brache
  • Galileo
  • Kepler
  • Isaac Newton
  • Einstein
  • Hubble

Astrology (Western)

  • Nostradamus
  • Tycho Brache
  • William Lilly
  • Llewellyn George
  • Marc Edmond Jones
  • Jonathan Cainer
  • Jeane Dixon
Fundamental Ideas



Use of constellations

Use of signs of the zodiac

States that stars have no significance in regard to human behavior

States that stars predict fae or provide advice for human behavior

Planets have no significance in regard to human behavior

Planets predict fate or provide advice for human behavior

Claims moon has no significance in regard to providing advice to human behavior

Moon predicts the fate of or provides advice for normal human behavior

Does not predict human behavior, and therefore has no measurement of human behavior

Attempts to predict human behavior, but makes no attempt to verify or measure the results

Typical results are repeatable, and requires equipment (such as a telescope) for measurement or verification

Typical results for behavior are not repeatable and does not require equipment for measurement or verification

Can obtain an accredited college degree in astronomy

Cannot obtain an accredited college degree in astrology

Not generally used to advice farmers beyond use of calendar

Used to hatch chickens, butcher hogs, cure meat, or can food

Follows rigorous standards of other sciences, particularly physics

No scientific standard, considered to be an “art”


Model of Epicycles:  


Historical predictive models worked sometimes and changed history!



Modern astronomy: classical physics and determinism.


How does this deterministic view apply to modern astrophysics?
  • Representation according to which a particular future state (B) will arise from a particular past one (A)

How do stochastic or random models apply to modern astrophysics?

Emergence of Models
  • First stellar evolution code written in the fifties and first stellar dynamics code in the sixties
  • By seventies, first simulations of stellar collisions carried out

-Turbulent Star formation  simulations: do these sorts of simulations make predictions or are they totally random?

Can star formation ever be predictive?


Explanation of Video


-Large scale simulations in astronomy

-Illustris simulations: combine classical predictability of gravity with ‘randomness’ of hydrodynamics…

  • A set of large-scale cosmological simulations, including most ambitious simulation of galaxy formation yet performed

  • Calculation tracks the expansion of the universe, the gravitational pull of matter onto itself, the motion of cosmic gas, as well as the formation of stars and black holes



What sort of predictions can be make with these simulations?

-Particle astrophysics: study smallest things to learn about universe.


Here quantum mechanics becomes important for astrophysics.

In Quantum mechanics, determinism is thrown out the window


Quantum mechanics is probabilistic, famous example of Double Slit Experiment


Double Slit Experiment Explained


These effects can become important when dealing with astroparticle physics including the hunt for particle associates with dark matter, i.e. detection of WIMPS


  • Weakly Interacting Massive Particles (WIMPs) represent one hypothesized class of particles to explain dark matter. They neither absorb nor emit light and don’t react strongly to other particles, but when they come across each other, they annihilate and create gamma rays

  • https://www.youtube.com/watch?v=fec8DEGsxY4

NBODY6 Simulation
  • Helps to obtain detailed information about the dynamical evolution of star clusters


Kira (N-body integration program)


Python n-body simulator

Millennium Simulation Project

Used more than 10 billion particles to trace evolution of matter distribution in a cubic region of universe  over 2 billion light-years



Maya Open Lab
  • Project directed toward construction of an open laboratory for dense stellar systems, such as star clusters, star forming regions, and galactic nuclei containing one or more massive black holes
  • http://www.artcompsci.org
The GRAPE Family
  • Stands for GRAvity PipE and is hardware specialized for stellar dynamics calculations


The Hertzsprung-Russell Diagram



Methods of observation (http://www.theguardian.com/science/2008/apr/26/spaceexploration.particlephysics)The naked eye

    • “Tycho Brahe, who lived before the invention of the telescope by Galileo in 1609, was able to measure the angular movement of planets to an accuracy of one 60th of a degree.”

    • Venus, Jupiter, Saturn and Mars are all visible without instruments.

    • Used by the ancients

  • Radio telescopes

  • Refractive/reflective telescopes

    • Refractive lenses become impractical at larger sizes, where chromatic aberrations occur and the weight becomes too much.

    • Hubble uses reflective mirrors.

  • Infrared/ultraviolet telescopes

    • “Useful for detecting heat radiated by objects and dust in space that may not show up in the visible light spectrum”

    • Exoplanets can be detected by measuring changes in the infrared given off by a star as the planet passes by it

    • Red shift/Blue shift

      • Objects moving away give off radiation toward the red end of the spectrum, object moving closer give off radiation toward the blue end

  • Gamma rays

    • Highest energy form of radiation, so is therefore useful in detecting violent phenomena, such as neutron stars and black holes

  • Neutrinos

  • Testing in astrophysics done to assess hypotheses
  • Technological advances allow for increased observables and phenomena
    • Wide fields, low fluxes, fast timing, multi wavelengths
  • Using independent sets of observations to confirm hypotheses
    • Testing existence of dark matter: big bang nucleosynthesis, rotation curves of galaxies, confinement of hot gas in clusters
  • Then tested through high energy physics
    • Large Hadron Colliders
  • Astronomical observations must be used too
    • Gamma-ray emission during dark matter particle decay
  • Observation can be a way of testing hypotheses without direct experimentation
  • Use of statistical models to assess hypotheses is also common
  • Our evidence for black hole comes from observation of the movement of stars
    • However, proving is very difficult -> it could be an exotic object
  • Cosmic Rays also used for observation and testing
  • In astrophysics, observations are very important bases for testing hypotheses