Brenna FlaugherFermilab

What the Cosmos can teach us

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

Models of Cosmology Models of Cosmology Through the AgesThrough the AgesUs,

Now

Cosmology as we understand it 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.

The small differences in temperature (called CMB anisotropies) evolve into the structures (for example stars and galaxies) we see today

Scale of the Observable Universe:

Size ~ 1028 cm

Mass ~ 1023 Msun

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

WMAP

Launched in 1990

Launched by NASA in 2001

Models of Cosmology Models of Cosmology Through the AgesThrough the AgesUs,

Now

Cosmology as we understand it now

Simulation of the evolution of Universe

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.

z>30 z=0

~ conversion from redshift to years: [z/(1+z)]*13.7 Byrsz = 30 is about 13.2 billion years ago (in the “dark ages”)z = 0 is now

Our solar system is 30,000 light years from the galactic center, and is moving at 450,000 mph

(picture taken with HST)

Our galaxy, the Milky Way, is a spiral galaxy similar to this one (called M81). M81 is 12 Million light years away.

Arrow shows where our sun would be if this were the Milky Way

Rv

MSunmeasure v & R

v2 G MSun

R R2=

MGalaxymeasure v & R

v2 G MGALAXY

R R2=

R

Galaxy rotation curves

105

100

50

Expected if the mass of the galaxy = the mass of the stars, v2 ~ 1/R

Observed Mass ~ R

Some sort of Mass must extend out ~10 times further than the stars!

v (k

m/s

)

R (kpc)

Vera Rubin

The Milky Way Galaxy as we see itThe Milky Way Galaxy as it actually is!

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)

giant arcs are galaxies behind the cluster, gravitationally lensed

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

Many different experimental approaches to direct dark matter detection, but no luck, yet…

Direct DetectionTry to find dark matter particles passing through earthly laboratories. For example CDMS, in Sodan

Indirect DetectionLook for evidence of dark matter annihilations occurring in our galaxy

CollidersTry to produce dark matter particles in accelerators.

AstronomyGravitational evidence for dark 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!

time

exp

ansi

on open

closed

accelerating

Now

The Sloan Digital Sky Survey (SDSS) is a telescope Fermilab helped build and operate.It has a 2.4m mirror and no Dome

Located in New Mexico• First started collecting images in 2000•120 MegaPixel digital camera•Spectrographs to measure the red shifts of over 600 galaxies at a time

SDSShas measured

~ 1 million galaxies and over 500 type 1a 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 are also areas with no galaxies

z=0 =now

~ conversion from redshift to years:[z/(1+z)]*13.7 yrsz = 0 is Now

z = 0.14 ~ 1.6 billion yrs ago

The The

CosmicCosmic

WebWebA simulation A simulation

of the of the Universe from Universe from the big bang the big bang to now. Each to now. Each

point is a point is a “Dark Matter “Dark Matter

particle” .particle” .

This shows This shows the same the same

clusters and clusters and voids .voids .

The VIRGO Consortium

1.2 billion light years

Models of Cosmology Models of Cosmology Through the AgesThrough the AgesUs,

Now

Cosmology as we understand it now

Evidence for Dark Energy

I. Direct Evidence for Acceleration

Brightness of distant Type Ia supernovae: Standard candles measure luminosity distance dL(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

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

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

z>30 z=0

Gravity and

Expansion

Expansion

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 4m 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

4m 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 64MPixel Camera (8 2k x 4k CCDs)

The DES Instrument: DECam DECam Focal Plane

3 sq. deg. field of view (~ 0.5 meter diameter focal plane)

62 2kx4k Image CCDs: 520 MPix8 2kx2k Alignment/focus CCDs

4 2kx2k Guide CCDs

Full size prototype imager used for integration testing out at SiDet

Optics Fabrication is in Progress in Europe

C2

C1 blank inspection

C1

Design: 5 lenses

Largest is~ 1m diameter

Smallest is ~ 0.5m

Polishing started in May 2008 Est. Delivery Dec. 2010

Cost of all 5 lenses ~ $3M

DES Image Simulation

DECam will be the largest CCD camera of its time.

Each image3 sq. deg.~ 20 Galaxy clusters~ 200,000 Galaxies520 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

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

Conclusions

QUESTIONS?

Cosmology 90 years ago

Hubble also looked at other “nebulae”.

By the end of the 1920s, 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)

Telescopes in Space!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 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 Modern Ground Based Telescopes

Large Binocular Telescope 2006

Two 8 meter mirrorsGemini Telescope 2000; 8 meter

Blanco Telescope 1975; 4 meter

Future telescopes are planning to have

30 meter diameter segmented mirrors by ~ 2018 Artist

conception

Orion NebulaOver 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

BigDipper

Sun

Earth

1/30 MoondiameterAim the Hubble telescope at the same location for

400 orbits around earth, 800 exposures,

A total of 11.3 days of exposure time

HubbleHubble Deep FieldDeep Field

160 billion over entire sky

10,000here

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!

The Hubble Ultra Deep FieldThe Hubble Ultra Deep FieldThe Hubble Ultra Deep FieldThe Hubble Ultra Deep Field

300,000years

3minutes

4-picoseconds

1-microsecond

atomsform

nucleiform

neutronsprotons

form

primordialsoup

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 1Recession 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

Cosmic Scale Factor

radius a(t1):

radius a(t2)

Redshift = z

1+z = a(t0)/a(te)

= (t0)/ (te)

t0 = age of Universe

today

te = age of the

Universe when light was emitted

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 Newton1643-1727

Principia

Albert Einstein1879-1955

Nobel prize in Physics 1921

1920-1980’s the big cosmological question was

What is The Ultimate Fate of Our Universe?

time

exp

ansi

on

open

closed

Big

BangBig

Crunch

Big

Chill

Now

Supernova 1987A in the Large Magellanic Cloud

Dark Energy Survey Collaboration ~ 140 scientists, 4 PhD students

International collaborationFermilabUniversity of Illinois at Urbana-ChampaignUniversity of ChicagoLawrence Berkeley National LaboratoryUniversity of MichiganNOAO/CTIOSpain-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 PennsylvaniaBrazil-DES ConsortiumThe Ohio State UniversityArgonne National LaboratorySouth Bay Group: Santa

Cruz/SLAC/Stanford

DES Collaboration meeting in La Serena, Chile

The same is true for clusters of galaxies: ~ 90% of the mass of the cluster is not visible

SDSS data

Cluster of Galaxies: Largest gravitationally bound objects

Size ~ 1025 cm ~ Megaparsec (Mpc) ~ 3.2 Million light years

1917 Einstein proposedcosmological constant.

1929 Hubble discoveredexpansion of the Universe.

1934 Einstein called it“my biggest blunder.”

1998 Astronomers foundevidence for it.

CosmologicalCosmologicalconstantconstant

CosmologicalCosmologicalconstantconstant

the weight of spacethe weight of space

(Dark energy)(Dark energy)

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

$35M Total Project Cost to DOE; $30M spent so far (Nov.05-present)

$10M contributed by NSF, Universities, foreign governments

Cerro Tololo Inter-American Observatory