* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Galaxies, Cosmology and the Accelera`ng Universe
Corona Borealis wikipedia , lookup
Nebular hypothesis wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Spitzer Space Telescope wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Constellation wikipedia , lookup
Gamma-ray burst wikipedia , lookup
Aries (constellation) wikipedia , lookup
Corona Australis wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Andromeda Galaxy wikipedia , lookup
Star catalogue wikipedia , lookup
Hubble Deep Field wikipedia , lookup
Stellar classification wikipedia , lookup
Observational astronomy wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Stellar evolution wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Galaxies, Cosmology and the Accelera6ng Universe Class 4: Mapping the Universe Steve Bryson h?p://stevepur.com/galaxies/ Ques6ons? Life Cycle of Stars • Most of the 6me in the “Main Sequence” – Burn Hydrogen to Helium • At the end, burn Helium to Carbon, then blow off outer atmosphere Size, Color and Life6me Depend on Mass • Heavier stars burn faster and ho?er – 10 x Sun: 32 million years, up to 1 million 6mes brighter – Sun: 10 billion years – 0.1 x Sun: 3 trillion years, 8% as bright Sun Heavier Stars Burn Beyond Carbon • Heavier stars are hot enough to keep burning – Carbon -‐> Neon, Calcium, Magnesium, Oxygen – Neon -‐> Oxygen and Magnesium – Oxygen -‐> Silicon and Phosphorous – Silicon -‐> Sulfur, Argon, Titanium, Chromium, Iron Later Stars Have Heavier Elements • Elements created in stars, which blow off their gas and spread the elements to clouds that create more stars… Measure the Composi6on of Stars with Spectra Distribu6on of Star Sizes • There are many more small, cool stars • Discovered by coun6ng the stars near the Sun Galaxies Made of Stars, Gas and Dust What Does it Mean to Map a Galaxy? • Where are the stars? – Are different types or ages of stars in different places? • What are the stars doing? • Where are the big gas clouds? • What is the overall shape? This is a Galaxy from the Outside This is a Galaxy From the Inside • How do we map our Galaxy? Like Mapping a Forest From the Inside • From a single loca6on This is a Galaxy From the Inside • Our view is obscured by lots of gas and dust But We’re Not Restricted to Visible Light • Longer wavelengths can get through dust be?er than visible light Different Views of the Milky Way • Using infrared and radio waves we can see through the dust Surveying the Galaxy • Stars – Distance • The first rungs of the Cosmic Distance Ladder – Composi6on • Spectra • Gas and dust clouds – Radio and infrared spectra Map of the Hydrogen Clouds • Mapped by radio telescopes The Milky Way Galaxy Barred spiral Much like many other galaxies The Milky Way is Big • 100,000 light years (30,000 parsecs) across – We’re about 26,000 light years from the center • If it were the size of a football field – The distance from the Sun to the nearest star would be just over 0.2 inches • Contains between 100 Billion and 400 Billion stars Map of the Milky Way Galaxy The Spiral Arms • Where the big Hydrogen clouds are – Regions of ac6ve star birth – Lit up by the newest, ho?est, largest stars • Up to a million 6mes brighter than the Sun Most Stars are Not In Spiral Arms • The spiral arms are where the big bright (and short-‐ lived) stars are • Most stars are dim and spread evenly throughout the Galaxy – These were also born in spiral arms much further in the past, and have drijed out of the spiral arms • Dim stars live a lot longer Distribu6on of Stars • Even though hot bright stars are rare, they make more light than all the other stars combined • In a cube 10 parsecs (32 light years) on a side – In the spiral arms • There are just a few hot young stars • There are 50 – 60 low-‐mass stars – Between the spiral arms • There are 50 – 60 low-‐mass stars Side View of the Milky Way Galaxy Thick vs. Thin Disk • The thin disk contains most of the stars – Mostly younger stars • Sun’s age and younger – All the Hydrogen and dust clouds for star forma6on – A few hundred parsecs thick • The thick disk contains fewer older stars – Fewer heavy elements than the Sun – A few thousand parsecs thick • Current thinking is that the thick disk stars were originally in the thin disk but were sca?ered • (some recent observa6ons suggest that there is not such a big difference between the thick and thin disks: there is one disk that just has fewer and fewer stars as you move above the Galaxy, but these have not been confirmed) The Galac6c Halo • Oldest stars in highly ellip6cal orbits – As much as 10 billion years old – Possibly relics of the forma6on of the Milky Way • Size of halo not well known The Galac6c Center • Un6l about 20 years ago was thought to be a spherical bulge • Now we believe it is a bar The Galac6c Center • Very ac6ve star forma6on – Lots of bright, hot, young stars – Average distance between stars is about 12 6mes the size of the Solar System – The night sky there contains more than a million stars brighter than Sirius, the brightest star in our sky Infrared picture of the Galac6c Center from the Spitzer Space Telescope How Do Stars Move in the Milky Way? • We want to understand – How do stars near the Sun orbit the Milky Way? – How do stars at the center of the Milky Way move? – What do these orbits tell us about mass in the Milky Way? Mo6on from the Spectrum: the Doppler Effect • Just like for sound waves, if the source is moving towards you it sounds like a higher frequency – Sound: higher pitch – Light: more blue • Moving away: lower frequency – Sound: lower pitch – Light: more red Doppler Effect • Something moving away looks redder • Something moving closer looks bluer We See a Shij in the Spectral Lines • The size of the shij tells you the speed of the source towards or away from you (Radial Velocity) (away) (towards) Star’s Mo6on in the Sky • We also see a star’s mo6on across the sky (Tangen6al Velocity) – May have to wait many years • Combining the tangen6al and radial gives us the star’s true mo6on Orbits in the Spiral Arms • The Sun orbits the center of the Galaxy in nearly a circle once every 240 million years – so the Sun has completed over 18 orbits since its birth • Stars in the thin disk all orbit at about the same speed – This is a surprise, and indicates that most mass is in the disk, not in the center The Sun’s Orbit Stars Orbi6ng the Galac6c Center • We can observe stars at the very center of the Galaxy The Black Hole at the Center of the Galaxy • The stars at the center of the Galaxy are moving so fast that they must be orbi6ng something very massive – About 4 million 6mes the mass of the Sun • This must be a supermassive Black Hole – Gravity is so strong that when you are too close even light cannot escape – All that mass is concentrated in an infinitely small volume • Or so says theory, but theory is probably wrong when the volume is very very small (10-‐35 meters across) – Material falling in forms an “accrea6on disk” that emits a large amount of energy The Galac6c Center is Very Ac6ve • The central black hole blasts out large amounts of energy • We observe very high-‐energy gas above and below the Galac6c Center The Virgo Stream • There is a stream of stars high above the Galac6c disk – Indicates a past collision with a smaller Galaxy – We’ll discuss galaxy collisions when we discuss galaxy forma6on Missing Mass • When we compute the speed that stars should orbit based on the stars, gas and dust that we see, we get a speed very different from what we observe • The simplest explana6on is that there is stuff in the Galaxy that we do not see – Mass of this stuff is more than the mass of the stars, gas and dust • Our first encounter with the Dark Ma?er problem – Much more about that in two or three weeks Looking Out We See Many Many Galaxies Besides Spiral Galaxies • But we see two types of other shapes – Ellip6cal, ojen very large, very li?le gas and dust – Irregular, typically smaller Galaxy Demographics • About 20% of all galaxies are spiral – But they are the brightest, so they make up the majority of visible galaxies – About 2/3 have bars • About 60% are ellip6cal – Most are small • The rest (20%) are irregular • Most spirals and large ellip6cals have central supermassive black holes Hubble’s Classifica6on of Galaxies Colliding Galaxies • We see some galaxies colliding – The stars just go through each other, too far apart to collide – The gas collides, and creates new stars – Typical result: long streams of new stars, large gravita6onal distor6on of the galaxies Galaxies Come in Clusters Our local group Galaxy cluster Galaxy supercluster More about this when we talk about large-‐scale structure in a couple weeks The Expanding Universe • Most surprising of all: most galaxies have a red shij – Indica6ng that they are moving away from us • The more distant the galaxy the larger the red shij • Simplest explana6on: the universe is expanding! – We’ll see next week that we have other reasons to believe this