4 solar masses mass the fuel amount is fixed so the

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Unformatted text preview: it of 1.4 solar masses mass The fuel amount is fixed so the brightness is predictable brightness Distance Ladder Distance These methods extend distance measurements to 200,000,000 parsecs (200 Mpc) Mpc Note that each level depends on the accuracy of shorter range distance measures measures The Local Group of Galaxies The The Milky Way and Andromeda are the two large galaxies in the local group local The local group is mostly dwarf ellipticals and ellipticals and irregular galaxies Galaxy Clusters Galaxy Galaxy tend to group together on the sky sky A subset of galaxies sit in large concentrations called galaxy clusters galaxy Virgo Cluster Nearby galaxy Nearby groupings groupings Clusters of clusters Clusters Galaxy clusters also group together in superGalaxy clusters We see structure in the galaxy distribution out to the largest scales out Survey Simulation Galaxy Clusters Galaxy Are Galaxy clusters just chance arrangements on the sky? arrangements Are galaxies in galaxy clusters different to other galaxies? to YES: There are more elliptical galaxies YES: in clusters in Galaxy Clusters: Distinct entities Distinct Cluster galaxies gravitationally interact gravitationally The relative speeds of cluster galaxies indicate this (more than 1000 km/s) km/s) Much faster than other spatially nearby galaxies spatially Galaxy Clusters: Galaxy Distinct entities Galaxy clusters are full of hot gas at 100 million degrees held in by gravity 100 This gas emits X-rays This Chandra Image Hubble’s Law Hubble Slipher (1912) found spectral lines in Slipher (1912) galaxies galaxies The spectral lines are Doppler shifted – this indicates the relative motion of the this galaxies galaxies Slipher found most galaxies are Slipher found redshifted (moving away) redshifted Hubble’s Law: Hubble Redshift The spectra are moved to the red moved The fraction the wavelengths must move back to have the lines at the regular wavelength is the redshift z redshift Hubble’s Law Hubble Hubble measured distances to galaxies using Cepheid variable stars stars He discovered a strong correlation between redshift (velocity) and redshift (velocity) distance from us distance Hubble’s Law Hubble The straight line fit between distance and velocity is called Hubble’s Law and The constant is Hubble’s Constant H0 The velocity v = H0 d H0=70 km/s per Million parsecs H0=70 Twice as far implies twice the speed and twice the redshift twice redshift Hubble’s Law Hubble The Univer...
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