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Understanding the Hubble Diagram and Cosmic Distances: Redshift, Standard Candles, and More

This article delves into the Hubble Diagram, exploring how redshift and blueshift provide insights into the motion of galaxies. We examine the concepts of standard candles, including Cepheid variable stars and supernovae, which allow astronomers to determine cosmic distances through the inverse square law of light. The implications of galactic velocities, measured via wavelength shifts, are detailed, alongside interpretations of the Hubble constant and potential future scenarios for the universe, including the Big Rip theory and dark energy considerations.

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Understanding the Hubble Diagram and Cosmic Distances: Redshift, Standard Candles, and More

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  1. CZ (km/s) Δy Δx Slope = Δy/Δx = H0 D (Mpc) The Hubble Diagram

  2. Redshift when λo λe Redshift & Blueshift

  3. λo Absorption lines can be blue-shifted (galaxy is moving toward us) or redshifted (galaxy is moving away). The velocity can be measured by the shift in the wavelength: v = cz = (λo - λe)/λo λe

  4. Standard Candles A standard candle is an astrophysical object whose absolute magnitude is well known. By comparing the relative intensity of light observed from the object, with that based on its known absolute magnitude, the inverse square law for light intensity can be used to determine the distance to the object. Cepheids & Supernovae

  5. The Inverse Square Law of Light … relates the absolute luminosity, M of an objectto its apparent luminosity m by m = M / r^2 where r is the distance.

  6. Cepheid Variable Stars

  7. Supernova 1994D Supernovae

  8. 4 Z4 CZ (km/s) 3 Z3 Z2 2 1 Z1 Z0 0 D1 D2 D3 D4 D D0 (Mpc) Original Hubble Diagram

  9. Interpretation • H4 > H3 Decelerating Universe • H3>H2Decelerating Universe • H2 < H1 Accelerating Universe • H1 < H0 Accelerating Universe H = kilometres per second per Megaparsec

  10. What next? Cosmological constant or Quintessence?

  11. Only one option!!!

  12. The Big Rip At last: proton decay

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