ASTR 101 Scale Of The Universe: An Overview

ASTR 101Scale of the Universe: an OverviewJanuary 23, 20151

Universe – An outline of what we knowEarth – our home in the universe– Is a planet – 3rd from the Sun in the solar system– Spherical in shape – somewhat flattened diameter 12756 km at equator 12715 km pole to pole mass 6x1024 kg12712 km– It spins: period 23h 56m 4.098s– and revolves around Sun12756 km period 365.25 days (24 hour days) mean distance to Sun 150 million (1.5x108) km (1AU) wikipedia.org/wiki/Earth 27s rotation Earth has a companion – a satellite – the Moon– diameter 3476 km ( ¼ of earth)– mass 7.2x1022 kg ( 1/80 mass of earth)– Moon revolves around earth period 27 d 7 h 43.1 m at a mean distance 384,000 km from earth(30 times the Earth diameter)2

The Solar System Earth is only one of the planet in the solar systemThere are 7 other major planets, most of them havesatellitesDwarf planets, asteroids, comets All orbiting the Sun.Sun is a star:–––––A huge ball of hot gas - 1,390,000 km in diameter110 times earthmainly hydrogen (H 75%) and helium(He 25%)Mass 2x1030 kg 280,000 M produces energyconverting H to He in its core by nuclear reactions,like in a hydrogen bomb 4 million tons of H (4x109kg ) converted into Heeach second,100 billion H bombs each second – Surface temperature 6000K, core 20 million K3

Solar system: some factsSun: diameter 1,390,000kmmass: 2x1030kgdistance from Earth: 150,000,000 kmspace is mostly empty!Nearest other star is4.3 light years away!!planetDistancetosun(AU)Diameter(Earth 1)mass(Earth 1)Orbitalperiodrotationperiodnumber ofmoonsMercury0.3870.380.05587.9 d58.6 d0Venus0.7230.950.82225 d243 d0Earth1.0011.001.00 y23.93 h1Mars1.520.530.11687 d24.6 h2Jupiter5.2011.231811.9 y9.93 h67Saturn9.549.4495.229.5 y10.6 h62Uranus19.24.0114.583.8 y17.2 h27Neptune30.13.8817.1165 y16.1 h13Pluto39.50.180.0022248 y6.39 d5(dwarf planet)4

The Milky Way Galaxy Sun is just one star of a large stellarsystem, which has over 100 billionstars – A galaxy Our galaxy: Milky way. Shape of a flattened disk with acentral spherical bulge. 100,000 light years in diameter Sun is located half way out from thecenter. All objects in the Milky way are orbitingaround the center of the Milky way. Sun (and the solar system) moves at aspeed about 230 km/s, and takesabout 225 million years to completeone orbit. It is called a Galactic year (or a Cosmicyear).Sunan illustration of the Milky way: credit NASA5

A galaxy contains, stars, gas clouds, debris ofdead stars . Many stars are associated with star clusters, ratherthan isolated Two types of star clusters:––globular clusters (up to few million stars)open clusters (100-1000s stars)globular cluster NGC 6388open cluster : M36globular cluster: M4globular cluster: M13 300,000 stars, size 160 lymass 6 105 M ,distance 25 klyPladies6

Orion nebula. A gas cloud 20 light years across.Horse head nebula, a dust cloudCrab Nebula M11.A supernovaruminant(exploded star)planetaryNebula M57, gasescaped (shed)from a star. Most of the material in galaxies are in the from of interstellar gasclouds, they could be gas clouds yet to form stars or debris of old stars In addition, neutron stars, black holes (all debris of dead stars)7

Milky way Galaxy All stars we see in the night sky are in the Milky way. Since we are in the milky way galaxy, we can not see its actual shape Like the view of a large stadium from a seat there.– See near by individual people, see their faces, can recognize them.– Hard to see individual people seated other side of the stadium, only see alarge crowd.

looking awayfewer starsSUNlooking towards theouter edge, sparselooking towardsthe center, dense Our view of the milky way is somewhat similar to that view of the stadium. Most of the stars we see in the night sky are nearby stars, within few thousandlight yearsTo the naked eye, stars far away do not appear as separate stars, there are somany of them we see all of them together as a luminous cloud stretchingacross the sky.Towards the center of galaxy more stars, so brighter in that direction. Alsomany dust clouds appear as dark patches.Center is so dense, it obstructs the view beyond, so we can not see what isbeyond the center. 9

Milky way stretching across the sky(arc shape due to wide field lens)looking towardsthe center, denselooking towards theouter edge, sparseSun10

Credit: http://astrophoto.com/JonTalbotandMilkyWay.htmView of the Milky way towards the center. Dark areas are dust clouds

galactic centerSagittariusby Derek Rowley.

Magellanic CloudsPhoto credit: sguisard.astrosurf.com Companion galaxies of the Milky way, Irregular shaped dwarfgalaxies.Nearest extragalactic (outside milky way) objects–– Large Magellanic Cloud: nearest galaxy 170,000 ly away, 14,000lyin sizeSmall Magellanic Cloud : second nearest 240,000 ly away,7,000ly in sizeLocated in the southern sky,not visible from the US, have to be at least in the tropics to seethem. Named after Magellan:–Who saw them on his voyage (not the first European to see them)13

Galaxies: Building blocks of the universe Milky way is just one of the galaxies. Universe is full of Galaxies, over100 billion of them in the observable universe.Galaxies come in different shapes and sizes:– spherical, elliptical, spiral, irregular– Dwarf galaxies hundreds of million stars to giants with hundreds of trillionsstarts– Tens of thousand light years to millions of light years in diameterNGC 4150NGC 1232NGC 4449

Neighborhood of the Milky way Many large galaxies have smaller galaxies accompanying them Milky way has many ( 20) satellite galaxies Nearest large galaxy – Andromeda galaxy– Like satellites (moons) of planets, gravitationally bound together orbitingthem– Largest of them are Large and small Maglenic clouds(visible to the naked eye)–2.5 million light years away

Andromeda Galaxy Nearest large galaxy is the Andromeda galaxy, 2.5 million ly awaylarger than the Milky way– 220,000 ly in diameter, 1trillion (1012) stars– Many small satellite galaxies– Visible to the naked eye,– most distant object visible without a telescopeMilky way and Andromeda galaxy are moving towards each other ( 120km/s). Theare expected to collide in 3.75 billion years and merge to form a large ellipticalgalaxy.16

Two Other nearby GalaxiesPinwheel galaxy– Next nearest large galaxy– 21 million light years away– 170,000 light years in diameterWhirlpool galaxy– 25 million light years away

Clustering of Galaxies Milky way, Andromeda, Pinwheel and their companion galaxies forma group of galaxies called the local group This way of galaxies forming groups is common Some groups are large, clusters consisting of thousands of galaxies Which in turn form even larger structures like super clusters ofgalaxies, filaments, walls They together form the large scale structure of the universe.galaxies clusters of galaxies super clusters of galaxies cosmic web

Nearest large cluster to us is the Virgo cluster of galaxies––––20 million light years in size, not much larger than local group but1000-2000 galaxies1014 solar massesSo many galaxies are close together, some are colliding(as seen in the image)

Neighborhood of the Virgo Cluster - Virgo super cluster The enormous size (gravity) of the Virgo Cluster makes it the center ofa larger structure Virgo super cluster.––––A collection of nearly 100 clustersconsisting thousands of galaxiesstretches across a 100 million light-years.1015 solar masses

Our neighborhood of 500 million light years

10 billion lyCosmic Webcluster of galaxies (Virgo) This would be the view of the universe in the largest scales, filaments, walls,super clusters and voids of galaxiesNo further hierarchical structures.It is uniform on scales larger than 500 million light years– homogeneous (same everywhere)– and isotropic (same in all directions)

Slices through the Sloan Digital Sky Survey 3-dimensional map of thedistribution of galaxies with the Earth at the center.23

Hubble eXtreme Field –– Image of a tiny patch ofthe sky, 2 arc minutes insize35 millionth of the sky11500area of a quarter at 3’Over 5000 galaxiesFarthest galaxies inthe image 13 billion lyaway, almost at theedge of the observableuniverse.(age of the universe13.8 billion years, firstgalaxies 400M yearsafter that).24

Virgo ClusterCosmic WebSolar system Cosmic address of the Earth: Cosmic Web Virgo super cluster Local group of clusters Milky way Solar System EarthOur ancestors thought Earth was the center of the universe and rest of theuniverse revolved around it.Now we know we are so insignificant compared to the Universe!25

Evolution of the universe Observational evidence suggests that universe was originated about 13.8billion years ago. This event, in which universe (space and time) emerged is called the BigBang. At the beginning, size of the universe was extremely small, smaller thana single atom, and extremely hot over 1032K Universe expanded from this initial state of Big Bang to the currentstate, and it continue expanding.26

newly formed starsin a nebulaHL-Tauri : a newly formedstar with a planetarysystem still undergoing.Crab-nebulaa star exploded1000 years ago.150 lya star exploded40,000 years ago. Early universe was filled with a mixture of Hydrogen(75%) and Helium (25%). As the universe expanded it cooled, stars and galaxies formed from gasclouds. All the elements other than hydrogen and helium were formed by nuclearreactions in stars. Those elements were dispersed in space when stars exploded at the end oftheir lives. From those debris new stars and planets formed, and the cycle continues.27

Observable Universe Since universe is only 13.8 billion years old, we can only see regions ofthe universe where light can reach us in 13.8 billion years.– Light from regions of the universe beyond that has not reached us, so we cannot see them.– This part of the universe where light had time to reach us is called“the observable universe”– As time goes by, in principle we will be able to more distant parts of of theuniverse.28

Review Questions According to the information in page 3, size (diameter) of the Sun is 110 times theEarth.– What is the volume of the Sun in terms of Earth’s volume.– What you can say about the density of the Sun compared to the density of Earth.What is the shape of the milky way? Where is the Sun’s location in it?What is the estimated number of stars in the Milky way, what is its diameter?Can we see all of the Milky way galaxy from Earth?What is the reason we see Milky way as a luminous cloud?What is most distant object in the universe one can see without a telescope?What are the dark areas in the Milky way we see, devoid of any stars?What are the Magellanic clouds?What is the size of the Andromeda galaxy compared to our galaxy?What are the dark areas we see in the images of galaxies.What are the largest structures in the universe?How old is the universe?What is the observable universe?From the information in page 23 (Hubble deep field) make a rough estimate ofthe total number of galaxies in the universe. How realistic is this estimate forthe number of galaxies in the universe today?29

Scale of the Universe: an Overview January 23, 2015 1. Universe –An outline of what we know Earth –our home in the universe – Is a planet –3rd from the Sun in the solar system – Spherical in shape –somewhat flatten