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CU-Boulder ASTR 1020 - Lecture Notes

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11ASTR 1020: Stars & GalaxiesApril 23, 2008• Reading: Chapter 23, sections 23.3-23.4 .• MasteringAstronomy Homework on The Fate of the Universe is due April 30th.• 2 more extra credit opportunities at FiskePlanetarium this week and next!• Meet at Fiske Planetarium next Monday.2Astronomy Picture of the DayMessier 63: The Sunflower GalaxyExplanation: A bright spiral galaxy of the northern sky, Messier 63 is about 25 million light-years distant in the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way.3Last TimeThe Creation of the Universe1.) Planck Era: before physics as we know it existed2.) GUT & Electroweak Eras: Four forces came into being3.) Particle Era: Origin of matter4.) Nucleosynthesis (fusion) Era: Helium is born45Today• From 3 minutes after the Big Bang Until Now• Cosmic Microwave Background• Evidence for the Big Bang Theory6Era of Nuclei• Dense clouds of protons (hydrogen nuclei), helium nuclei, electrons, neutrinos, photons• Temperatures too hot for electrons to combine with protons– electrons ionized by energetic photons• Universe is made of naked nuclei, not atoms with nuclei + electrons• Lasts for about 380,000 years27Era of Atoms• Finally cool enough for electrons combine with nuclei to form atoms• Photons now “decoupled”= free to fly• Universe becomes transparent to light8Light from the Beginning of Time• This light can be seen with telescopes- all around us!• Thermal spectrum at 3000 K at redshift ~10009The Cosmic Microwave Background• Discovered by accident by ArnoPenzias and Robert Wilson in 1965• Direct evidence forHOT early universe Æ Big Bang• 1978 Nobel Prize10Clicker Question: Remembering Wien’s Law• Wavelength maximum = 2,900,000 nm / T (K)If T = 2900 K, what is wavelength of the peak of the thermal spectrum?a) (pink) 100 nmb) (yellow) 1000 nmc) (green) 1,000,000 nm11• 2,900,000 nm / 2900 K = 1000 nmRemember that visible light is 400-700nmÆ Near infrared, spilling towards red/visible, similar to the coolest red stars.• We should see a red glow all around us?12Clicker Question: But why is the sky black?• The universe has expanded by a factor of 1000…• What is the current wavelength of the peak of this radiation?a) 1000 nmb) 1 nmc) 1,000,000 nm = 1 mm313• 1+z ~ 1000• Wavelength will be BIGGER because universe is now bigger:• Wavelength emitted x (1+z) = wavelength observed now1,000 nm x 1000 = 1,000,000 nm = 1 mmMicrowaves!14• Perfect thermal spectrum peaking at ~1 mm (Nobel prize in 2006 to Mather & Moot)• ~ 3 degrees K• Contributes to communications static (TV)15Cosmic Microwave Background (CMB)• Mapping of CMB shows TINY fluctuations: 1 part in 100,000• Seeds of galaxies, clusters that will collapse due to gravity?16Did the Big Bang Really Happen?• How can we tell what happened so long ago?• 14 billion years ago• Mostly unobservable, not repeatable• Some of it at temperatures beyond our ability to even understand how physics works!17 18Evidence for the Big Bang• 1) Expanding Universe• … run time


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