What the Cosmos can teach us Brenna Flaugher Fermilab
Two Revelations of the past few decades: Dark Matter and Dark Energy 1) Most of the Mass in the Universe is DARK – we can’t see it 2) The expansion rate of the Universe is accelerating Dark Matter: any matter whose existence is inferred solely from its gravitational effects (i. e. , does not emit light) Dark Energy: defined as some sort of energy density that is pushing the universe apart. The existence of dark energy is inferred from the expansion rate of the universe The rest of this talk will cover what we know about dark matter and dark energy and describe the Dark Energy Camera project that is happening now at Fermilab
Cosmic Pie The results from WMAP, the supernova and the galaxy clusters all point to a Universe that is made up of 25% Dark Matter and 70% Dark Energy! 95% of the energy in the Universe is in stuff we can’t see! This was not expected. 2003 Science breakthrough of the year
Cosmology as we understand it now Models of Cosmology Us, Through the Ages Now
A picture of the young universe (~400, 000 yrs old) COBE and WMAP satellites measured the Cosmic Microwave Background (CMB) radiation density field (temperature) This is the farthest back we can see. Before that the photons could not escape. Temperature of the Universe is the same is all directions: Red: 2. 7+0. 00001 deg Kelvin Blue: 2. 7 -0. 00001 deg Kelvin 1 Kelvin = -458 deg. Fahrenheit Launched in 1990 Launched by NASA in 2001 The small differences in temperature (called CMB anisotropies) evolve into the structures (for example stars and galaxies) we see today WMAP Scale of the Observable Universe: Size ~ 1028 cm Mass ~ 1023 Msun
Cosmology as we understand it now Models of Cosmology Through the Ages Us, Now
Simulation of the evolution of Universe z>30 z=0 ~ conversion from redshift to years: [z/(1+z)]*13. 7 Byrs z = 30 is about 13. 2 billion years ago (in the “dark ages”) z = 0 is now The growth of the structures we see today (stars, galaxies, clusters of galaxies) is determined by the initial conditions (CMB), Gravity, the amount of mass, and by the expansion rate of the universe. The next few slides explain how we measure the mass in the universe.
Our galaxy, the Milky Way, is a spiral galaxy similar to this one (called M 81). M 81 is 12 Million light years away. Arrow shows where our sun would be if this were the (picture taken with HST) Milky Way Our solar system is 30, 000 light years from the galactic center, and is moving at 450, 000 mph
v 2 G MSun = R R 2 R v measure v & R R MSun v 2 G MGALAXY = R R 2 measure v & R MGalaxy
v (km/s) Galaxy rotation curves Observed Mass ~ R 100 Expected if the mass of the galaxy = the mass of the stars, v 2 ~ 1/R 50 5 10 R (kpc) Some sort of Mass must extend out ~10 times further than the stars! Vera Rubin
The Milky Way Galaxy as it actually is! The Milky Way Galaxy as we see it Dark Matter Halo
Einstein and General Relativity Idea: Matter affects the structure of Space. Time A massive object (star, galaxy, cluster of galaxies) attracts nearby objects by distorting spacetime Light follows lines of spacetime: Large clumps of Mass (dark and visible) curve spacetime and thus bend light like a lenses! Light rays coming from sources behind clumps of matter (such as a galaxy cluster) will be bent and distorted (lensed)
Gravitational Lensing Geometry Gravitational Lensing: multiple images or pronounced distortion of images Great book: Einstein’s Telescope: the hunt for Dark Matter and Dark Energy in the Universe by Evalyn Gates (U. Chicago)
Zoom in on a galaxy cluster – Gravity is bending light and there must be a lot of it beyond the visible galaxies in the cluster giant arcs are galaxies behind the cluster, gravitationally lensed
Many different experimental approaches to direct dark matter detection, but no luck, yet… Indirect Detection Direct Detection Try to find dark matter particles passing through earthly laboratories. For example CDMS, in Sodan Look for evidence of dark matter annihilations occurring in our galaxy Colliders Try to produce dark Astronomy matter particles in Gravitational evidence for dark accelerators. matter (lensed galaxies in background)
The previous slides showed the evidence for Dark Matter The next few slides explain what we know about Dark Energy
Big surprise of the 1990’s Two independent groups of astrophysicists measured the expansion rate of the universe using supernovae. Both groups found that the expansion was accelerating!
The Universe is expanding
Type Ia Supernovae are a type of Standard Candle These happen when a White dwarf star, accreting mass from a companion star, exceeds a critical mass (Chandrasekhar) and explodes. These explosions are billions of times brighter than our sun. The peak brightness of these type of explosions is standard and thus can be related to its distance. There is about 1 SN every 50 years in the Milky Way The explosions are usually visible for about 40 days.
Watch the same part of the sky for many days and look for changes
Our Universe’s Expansion is Accelerating! expansion accelerating open Now closed time
The Sloan Digital Sky Survey (SDSS) is a telescope Fermilab helped build and operate. It has a 2. 4 m mirror and no Dome Located in New Mexico • First started collecting images in 2000 • 120 Mega. Pixel digital camera • Spectrographs to measure the red shifts of over 600 galaxies at a time SDSS has measured ~ 1 million galaxies and over 500 type 1 a Supernova
Picture of the RECENT universe Sloan Digital Sky Survey (SDSS) has measured ~1 million galaxies Each galaxy is represented by a point in the figure Overdense regions are clusters of galaxies There also areas with no galaxies z=0 =now ~ conversion from redshift to years: [z/(1+z)]*13. 7 yrs z = 0 is Now z = 0. 14 ~ 1. 6 billion yrs ago
The Cosmic Web 1. 2 billion light years A simulation of the Universe from the big bang to now. Each point is a “Dark Matter particle”. This shows the same clusters and voids. The VIRGO Consortium
Cosmology as we understand it now Models of Cosmology Through the Ages Us, Now
Evidence for Dark Energy I. Direct Evidence for Acceleration Brightness of distant Type Ia supernovae: Standard candles measure luminosity distance d. L(z): sensitive to the expansion history H(z) Found that distant supernovae are not as bright as they should be: –> the universe is expanding faster than expected II. Evidence for `Missing Energy’ CMB Flat Universe: 0 = 1 Add up all the visible and Dark Matter Low matter density m 0. 3 missing = 1 – 0. 3 = 0. 7 = DE Can’t see it and it is pushing the universe apart so call it “dark energy” Dark Energy is either a new form of stress-energy with “negative pressure” or a breakdown of General Relativity (Gravity) at large distances
Multiple ways to measure the effects of Dark Energy z>30 z=0 The of growth of structure is determined by the initial conditions (CMB) and amount and distribution of dark matter, dark energy and by the expansion rate of the universe. The Dark Energy Survey will measure the effects of Dark Energy and Dark Matter 4 different ways and by combining the results we hope to get a better understanding of what they are Gravity and Expansion 1) Count the Galaxy Clusters as a function of red shift and cluster mass 2) Measure the distortion in the apparent shape of galaxies due to intervening galaxy clusters and associated clumps of dark matter (Lensing) 3) Measure the spatial clustering of galaxies as a function of red shift (Baryon Acoustic Oscillations) 4) Use Supernovae as standard candles to measure the expansion rate
The Dark Energy Survey (DES) The Deal: ¡ DES Collaboration provides a state-of-the-art instrument and data system for community use ¡ NOAO (NSF) allocates 525 nights of 4 m telescope time during Oct. –Feb. 2012 -2017 New Instrument (DECam): ¡ Replace the PF cage with a new 2. 2 FOV, 520 Mega pixel CCD camera + optics Collaboration Funding: ¡ DOE, NSF, STFC (UK), Ministry of Education and Science (Spain), FINEP (Brazil), Germany and the Collaborating Institutions Use the Blanco 4 m Telescope at the Cerro-Tololo Inter-American Observatory (CTIO)
Cerro Tololo Inter-American Observatory
The Blanco Telescope Built in the 1970’s A big solid telescope, ~ 15 tons at the top end People used to ride in the Prime Focus cage and aim/drive the telescope Pictures were taken on glass negatives In Mid-late 80’s digital camera technology (CCDs) started to be used on telescopes By mid 90’s these were the standard, but very expensive. The Blanco currently has a 64 MPixel Camera (8 2 k x 4 k CCDs)
The DES Instrument: DECam Focal Plane 3 sq. deg. field of view (~ 0. 5 meter diameter focal plane) 62 2 kx 4 k Image CCDs: 520 MPix 8 2 kx 2 k Alignment/focus CCDs 4 2 kx 2 k Guide CCDs
Full size prototype imager used for integration testing out at Si. Det
Optics Fabrication is in Progress in Europe C 2 Design: 5 lenses Largest is~ 1 m diameter Smallest is ~ 0. 5 m Polishing started in May 2008 Est. Delivery Dec. 2010 Cost of all 5 lenses ~ $3 M C 1 blank inspection
DES Image Simulation DECam will be the largest CCD camera of its time. Each image ¡ ¡ 3 sq. deg. ~ 20 Galaxy clusters ~ 200, 000 Galaxies 520 Mega pixels (62 CCDs) Each night ~ 300 GB of image data courtesy of F. Valdes/NOAO
DECam Telescope Simulator in Lab A We will put everything (except the lenses) together in Lab A and test it in all orientations before shipping to Chile.
Cage hexapod and barrel on Telescope Simulator, at Zenith
Conclusions Dark Energy and Dark Matter make up 95% of the energy density in the Universe and yet their properties are mysterious The theorists are stumped It is up to the observers to make new measurements Improved technology, bigger cameras, better CCDs, hold great promise for beginning to reveal these secrets
QUESTIONS?
Cosmology 90 years ago Hubble also looked at other “nebulae”. By the end of the 1920 s, most astronomers were convinced that our Milky Way galaxy was but one of millions of galaxies in the universe! The Universe = MANY galaxies! Edwin Hubble's greatest discovery came in 1929. He measured the velocities of the other galaxies relative to our own Milky Way galaxy, and determined that the farther a galaxy is from Earth, the faster it appears to move away. This relationship is called Hubble's Law. Supports the Big Bang Theory In the 1980’s NASA named the first space telescope after him. One of the goals was to measure the expansion rate of the universe to better precision than was possible from the ground. Edwin P. Hubble (1884 -1953) (Grew up in Wheaton, IL U of C graduate, also played basketball)
Talk of a space telescope began as early as 1923, but it wasn’t until 1975 that NASA began seriously considering one. In 1977 Congress approved funding for the project and it really began. Hubble Space Telescope (HST): Scheduled for Launch Oct. 1986. Jan. 1986 Challenger Space Shuttle exploded on launch Hubble finally launched in 1990 Optics repaired in 1993. Final servicing mission May 2009 Expected lifetime 2014 (24 years in space!) Telescopes in Space!
Telescopes throughout the ages Main advantage of putting a telescope in space is so you don’t have to look through the atmosphere! This improves the resolving power – the ability to see and separate very small objects The Hubble space telescope mirror is 94 inches (2. 4 meters) diameter, about the size of the telescope used by Edwin Hubble in the 1920’s and much smaller than the largest ground based telescopes today. Main disadvantage of putting a telescope in space is that it is very expensive (Billions of $$) The full moon is 1800 arc sec (0. 5 deg)
Modern Ground Based Telescopes Blanco Telescope 1975; 4 meter Future telescopes are planning to have 30 meter diameter segmented mirrors by ~ 2018 Gemini Telescope 2000; 8 meter Artist conception Large Binocular Telescope 2006 Two 8 meter mirrors
Orion Nebula Over 3000 Stars plus gas and dust forming new stars Only 1500 light years away! This is the closest star forming region to Earth
With Hubble we can even see galaxy collisions in progress
Hubble Deep Field 1/30 Moon diameter Aim the Hubble telescope at the same location for 400 orbits around earth, 800 exposures, A total of 11. 3 days of exposure time Big Dipper Earth Sun
The Hubble Ultra Deep Field Aim the Hubble telescope at the same location for 400 orbits around earth, 800 exposures. A total of 11. 3 days of exposure: UNIVERSE OF GALAXIES! 10, 000 here 160 billion over entire sky
300, 000 years atoms form 3 minutes nuclei form 1 -micro second neutrons protons form 4 -pico seconds primordial soup BANG!
We see radiation today from last scattering surface when the universe was just 400, 000 years old Right after the Big Bang the photons, protons, and electrons were in thermal equilibrium - a big hot cloud Once things expanded and cooled off a bit, Hydrogen formed and the photon interactions slowed way down – meaning the photons got away – these are the Cosmic Microwave Background photons or the CMB The Universe has been expanding since then and is now really cold – measuring the CMB is measuring the temperature of the universe
Measuring astronomical distances part 1 Recession Velocity (similar to the Doppler shift): As you move away from light source (or the source moves away from you) the wavelength of the light stretches out The Universe is expanding – this stretches out the light from distant objects. We use the term “redshift” to refer to the amount the light is stretched
Redshift = z 1+z = a(t 0)/a(te) = (t 0)/ (te) Cosmic Scale Factor radius a(t 1): t 0 = age of Universe today te = age of the Universe when light was emitted radius a(t 2) The redshift is an indication of age and distance: z = 0 here and now z = 1000 for the oldest photons, originating from the most distant place we can see (CMB)
The Big Bang and Future of the Universe The Universe has been expanding isotropically from a hot, dense `beginning’ (aka the Big Bang) for about 13. 7 billion years Newton & Einstein: the expansion of the Universe should be slowing down over time, due to the gravitational attraction of all matter in the Universe If there is enough matter in the Universe, we would expect the expansion to eventually halt, and the Universe to recollapse in a big crunch. If there is too little matter, we expect the Universe will continue to expand forever. Which of these Universes do we inhabit?
Isaac Newton 1643 -1727 Principia Albert Einstein 1879 -1955 Nobel prize in Physics 1921
expansion 1920 -1980’s the big cosmological question was What is The Ultimate Fate of Our Universe? open Big Chill Now closed Big Bang time Big Crunch
Supernova 1987 A in the Large Magellanic Cloud
Dark Energy Survey Collaboration ~ 140 scientists, 4 Ph. D students DES Collaboration meeting in La Serena, Chile International collaboration Fermilab University of Illinois at Urbana-Champaign University of Chicago Lawrence Berkeley National Laboratory University of Michigan NOAO/CTIO Spain-DES Collaboration: Institut d'Estudis Espacials de Catalunya (IEEC/ICE), Institut de Fisica d'Altes Energies (IFAE), CIEMAT-Madrid: United Kingdom-DES Collaboration: University College London, University of Cambridge, University of Edinburgh, University of Portsmouth, University of Sussex The University of Pennsylvania Brazil-DES Consortium The Ohio State University Argonne National Laboratory South Bay Group: Santa Cruz/SLAC/Stanford
The same is true for clusters of galaxies: ~ 90% of the mass of the cluster is not visible Cluster of Galaxies: Largest gravitationally bound objects Size ~ 1025 cm ~ Megaparsec (Mpc) ~ 3. 2 Million light years SDSS data
the weight of space Cosmological constant (Dark energy) 1917 Einstein proposed cosmological constant. 1929 Hubble discovered expansion of the Universe. 1934 Einstein called it “my biggest blunder. ” 1998 Astronomers found evidence for it.
How long and how much does it cost to build a 520 Mpixel camera? We started talking about it and requesting funding in 2004 Fully approved and funded in 2008 (CD-3) First light expected in 2011 $35 M Total Project Cost to DOE; $30 M spent so far (Nov. 05 -present) $10 M contributed by NSF, Universities, foreign governments Cerro Tololo Inter-American Observatory
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