Bahram Mobasher. University of California,

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1 Acceleration of the Universe Bahram Mobasher University of California, Riverside

2 Beginning of the Universe (Big Bang) Expansion of the Universe Present state of the Universe Future of fth the Universe Distances to galaxies Motion of galaxies

3 Hubble s Law: In an expanding Universe, velocity= x distance

4 The Expanding Universe Hubble (1929) Velocities=Doppler shift=z Distances: Brightest stars One of the original reasons for building HST was to measure sets the scale of the Universe and its age

5 The Expansion Rate may be Slowing down or Speeding Up (Dark) Matter provides attractive gravity which should be decelerating Universe But Einstein thought Universe static, GR allowed for repulsive gravity, i.e., cosmological constant (Dark Energy), that could repel gravity and keep Universe static

6 Standard Candles How far away? We Need a Standard candle We can see Far away, Back in time Bright=near dim=far Receding how fast? Doppler Effect

7 Standard Candles Hubble sdiagram dust Bright=near dim=far dim & red=closer!

8 What we see

9 Measuring the Expansion History: g p y Changes in scale/changes in time

10 At the End of its Life, a Star is Reborn as bright as 4 billion Suns can be seen halfway across the Universe Subrahmanyan Chandrasekhar

11 Bang! A star explodes 1987: The galaxy next door

12 How (we think) Nature makes a SN Ia Type Ia Supernova White Dwarf An explosion resulting from the thermonuclear detonation of a White Dwarf Star Homogeneity: 1.4 M, ergs Negligible liibl hydrogen, hd lots lt of fime Mature progenitors Models (delayed-detonation) good fit to observations

13 Age: Four months in the life of a SN Ia -6 days On the Rise: Powered by radioactivity Maximum Vejecta=10-20,000 km/s +26 days +47 days +102 days Elements produced= Fe,Co,Ni,Si,Ca

14 How do we Find Supernovae?

15 Searching by Subtraction

16 Improving the Discovery Odds 1 SN per galaxy per 100 years = 1 SN per 100 galaxies per year = 10 SN per 1000 galaxies per year, if monitor them frequently enough.

17 The Dim, the Distant and the Dusty Improved SN Ia distances reveals motion of Local Group, and flows Riess et al 1995,1997

18 What can Supernovae tell us about the History of Cosmic Expansion? Disclaimer: The rest of this talk does not depend on H 0

observations) Homogeneous, isotropic on large scales Friedman Equation (Equation

19 Our Cosmological Framework Derives From Observations The Universe is Expanding CMB Hot Big Bang Theory General Relativity Pi Principles i (corroborated by observations) Homogeneous, isotropic on large scales Friedman Equation (Equation of Motion of the Universe) (Dark) Matter (Dark) Energy Einstein s Biggest Blunder Geometry

20 SN Ia Hubble Diagram (Riess et al 1998) (Perlmutter et al 1999) t ti ~25% Fainter than =0.3 =0.00 After Exhaustive tests for systematics: None significant

21 Why is The Universe Accelerating? (Honestly, we don t really know) Vacuum energy in QM (dark energy) right hand-side of Friedman eq We don t understand gravity on large scales left Mini-inflation iiifl i episode right ihhand-side of Friedman eq Superhorizon action, stringy effects, Chaplygin gas, etc Insert your idea here Important Prerequisite ( Sanity Check ): When was the Universe decelerating?

22 Search for cosmic deceleration SNe Ia at z > 1 provide an essential test of the transition between current cosmic acceleration and past deceleration Our current goal: 6-8 SNe Ia at 1.2<z<1.8

23 Searching for SNe Ia with ACS 5z-band epochs spaced by 45 days simultaneous v i band 120 tiles 5 z-band epochs, spaced by 45 days, simultaneous v,i band, 120 tiles CDFS HDFN

24 Finding High-z Sne We found 6 of the 7 highest redshift (z>1) supernovae currently known Search completed: 43 SNe identified ~25 Type Ia candidates at z>1 10 follow-ups by ToO program 12 spectroscopic confirmations so far 3 highest-z spectral confirmations (z>1.3) ~1 FTE with HST as is will yield ~100 Sne at z>1 Probe the nature of the dark energy HST+ground=SNAP-lite SNAP NOW! High-z SN Artemis from CDF-S ACS observations

25 Our first higher-z SN Ia, Aphrodite Aphrodite (z=1.3) ACS F850lp ACS grism spectrum Highest z spectrum of a SN NICMOS F110W viz

26 HST Found SN Ia in Early-type yp Hosts, 0.9<z<1.7 Lancaster z=1.2 Thoth z=1.3 Sasquatch z=1.4 97ff z=1.7 Vilas z=0.9 Thames z=1.0 Ramone z=1.0 Ferguson z=1.0 Redford z=1.2

27 The HST Advantage HST-ACS z=1.30 Highest 2 Groundbased z=1.06 ToO z=1.30 z=1.20

28 Measuring Distances D 2 L = (L/4π F) μ 0 = m M = 5 log D L + 25 μ (z; H 0 ;q; 0 ; dq/dz)

29 Deceleration vs. Acceleration We minimize the difference μ(z i ;H 0 ; q 0 ; dq/dz) μ 0, ι By optimizing q 0 and dq/dz μ,0,i,, using χ 2 statistics. i,0,i : distance from SNe μ(z i ; H 0 ; q 0 ; dq/dz): predicted distance q(z) = q0 + z dq/dz Calculate the probability density e χ2/2 q 0 < 0 Recent acceleration dq/dz > 0 Past deceleration

30 Expansion Kinematics (How Long Has This Been Going On?) q(z) = q0 + z dq/dz z t = -q 0 /(dq/dz) eceleration past de present acceleration z~ , ~5 GYR ago

31 High Redshift SN and Expansion History Taylor Expansion of the left handside of the Friedman Eq: a(t)=f(t,h,q,j, ) Fai inter 1.0 H(z)=f(z,H 0,q 0,dq/dz) =f(z,h 0,q 0,j 0 ) q 0 =-, dq/dz=0 (j 0 =0) Constant acceleration Brighter Relative Bri ightness (Δ Δm) q 0 =-, dq/dz=+ (j 0 =+) Acceleration/ Deceleration Freely yexpanding p g q(z)=0 ()0 Constant deceleration q 0 =+, dq/dz=0 (j 0 =0) present Redshift z past

32 Dark Matter pulls Dark Energy pushes

33 Is Cosmic Acceleration Real??

34 (If the Dark Energy is Lambda), Updated Constraints factor of 7 improvement! New Riess et al 1998; High-z Team See also Perlmutter et al d L (Ω M ; Ω Λ )-d L0 L,0

35 SNe Ia If Dark Energy is Real CMB(WMAP) + ISW, X-ray Clusters LSS What is it?

36 Dark Energy is repulsive Gravity (how strong is it?) In GR, gravitational force Cosmological Constant (vacuum) (mini-inflation) +1/3 0-1/3 <w<-1-1 If w<-1/3 the Universe accelerates

37 Before Acceleration there was Deceleration If the Universe was always accelerating apart, how did the galaxies, stars, and planets form? Hubble Space Telescope

38 Probing Dark Energy Two fundamental properties/clues of dark energy: its strength, w0, AND is it dynamic or static, i.e. is w =0? We have doubled our knowledge of w0 and w in 1 year with HST Einstein s s model now looks better than ever, a way to go W Einstein s w w0

39 Dark Energy: Static or Dynamic? (ultimately, w(z) )

40 Dark kenergy: Future Studies 1. Observe more SNe at z > /08 2. HST/WFC3 to get Sne at z > 1.5 HST servicing mission JitD 3. Joint Dark ke Energy Mission i (JDEM) and SNAP 2014

41 Joint Dark Energy Mission (JDEM) ~2015??? SDT just 1000 s formed SNe Ia Systematics: we will need to control them to ~1%

42 The physics of Dark Energy will determine the fate of the Universe.

43 Dark Matter pulls Dark Energy pushes

45 T-minus 10 minutes to Rip

46 The End

Supernovae Observations of the Accelerating Universe. K Twedt Department of Physics, University of Maryland, College Park, MD, 20740, USA

Supernovae Observations of the Accelerating Universe K Twedt Department of Physics, University of Maryland, College Park, MD, 20740, USA Over the past three decades, supernovae observations have been the