(455) HR diagrams [IB Physics SL/HL]

HR Diagram Overview

• Hertzsprung-Russell Diagram: Essential diagram for astronomers, akin to the periodic table.

• Axes:

  • Y-Axis: Luminosity (L) of stars.

  • X-Axis: Surface temperature (T) in Kelvin, reversely ordered (higher temperature on the left).

Star Classification

• Main Sequence Stars:

  • Predominantly located on the diagram.

  • Most stars convert hydrogen to helium in their cores.

  • Examples include blue stars (high luminosity, high temperature) and red stars (low luminosity, low temperature).

• Other Regions:

  • Red Giants: Located above main sequence; large and luminous.

  • White Dwarfs: Found below main sequence.

  • Red Supergiants: Located above red giants.

Distance Measurement Method

• Spectroscopic Parallax:

  • Uses the star's spectrum to determine its location on the H-R diagram.

  • After determining temperature and luminosity, distance can be calculated using the formula:B = \frac{L}{4\pi d^2}

  • Luminosity allows for distance estimations, with potential uncertainties.

Additional Insights

• Diagram Details:

  • Diagonal lines indicate star sizes; smaller stars are on the left and larger stars on the right.

    • Red dwarfs: nearly infinite lifespans (longer than the age of the universe).

    • Massive stars: short lifespans (burn fuel quickly, lead to rapid deaths).

• Lifespan Relation:

  • Young stars (high luminosity) burn fuel rapidly; older stars (dwarf varieties) last considerably longer.