Dark Energy and How to Find It: The SNAP Experiment

1. Dark Energyand How to Find It:The SNAP Experiment Stuart Mufson IU Astronomy June 2007

2. Energy Content of the Universe Astronomical Observations: • vis = 0.007 Super-K: •  = 0.006† WMAP + SNIa + SDSS: • baryons = 0.047 • dark matter = 0.24‡ • dark energy = 0.70‡ † no  mass degeneracy ‡h = 0.70  + baryons + dark matter + dark energy = crit = 1  k = 0

3. Fundamental Principle of Cosmology: • The Copernican Hypothesis is valid • except for local irregularities, the Universe presents the same aspect from every place in it no matter where you are in the Universe, IT LOOKS THE SAME! (on cosmological scales) • the laws of physics as seen on Earth apply throughout the Universe

4. Copernican Principle: Universe is homgeneous & isotropic nonisotropic homogeneous nonisotropic nonhomogeneous isotropic homogeneous

5. 1 billion light years Copernican Principle: looks ok Universe uniform on a scale of approx. 1 billion light years every dot represents a galaxy Earth

6. Rules of the Game: • Universe must be described by 4-dimensional space-time • 3 dimensions of space (length, width, height) • 4th dimension is time • Gravity is the force that governs the Universe on • cosmological scales Einstein’s Theory of Gravity (General Relativity) is the correct theory of gravity

7. General Relativity: the Universe can have only one of three possible “shapes” Shape #1: “spherical”, closed geometry k = +1 finite, unbound  l

8. Shape #2: “saddle-shaped”, open geometry k = -1  l infinite, unbound

9. But the Universe has “shape” #3 Shape #3: “flat” or Euclidean geometry k = 0  l infinite, unbound (unbound = no edge)

10. Worse! It has precisely the “right amount” of Dark Energy to make it happen! Astronomical Observations: • vis = 0.007 Super-K: •  = 0.006† WMAP + SNIa + SDSS: • baryons = 0.047 • dark matter = 0.24‡ • dark energy = 0.70‡ † no  mass degeneracy ‡h = 0.70  + baryons + dark matter + dark energy = crit = 1  k = 0

11. One more thing: the Universe is Expanding How the universe expands from time t1 to time t2 is described by the “expansion factor” R(t) time = t2 time = t1 * * R(t1) R(t2) * *

12. The Friedmann Equation: • distance formula + General Relativity Put it all together/mix well/add a bunch of astrophysicsts expansion/contraction/ of the Universe strength of gravity in the Universe geometry of the Universe  plus

13. R(t) k= -1 solutions to Friedmann’s equation k=0 scale factor k= +1 time t Big Bang Big Crunch now Solutions without Dark Energy

14. (2) the Universe then speeds up forever (accelerates) because of Dark Energy R(t) scale factor (1) the Universe first slows down (decelerates) because of gravity time t Big Bang now Big Crunch When astronomers went looking, this is what they found

15. Two “Outstanding” issues: • What is the “stuff” that makes the Universe “flat”? • What is the “stuff” that is causing the Universe to expand at an ever increasing rate? A Possible answer: the “stuff” is Dark Energy • What is Dark Energy? Good question

16. Dark Energy • FRW distance + General Relativity + Dark Energy  Modified Friedmann’s Equation: geometry of the Universe expansion/contraction of the Universe strength of gravity in the Universe modified by Dark Energy

17.                 Dark Energy Dark Energy: acts like negative gravity but does not get weaker as the Universe expands! matter density gets smaller (1/R3) as the Universe expands  Dark Energy Dark Energy  Eventually Dark Energy must rule!

18.                 time As the Universe expands, the galaxies do not grow in size but space gets filled up uniformly with more and more Dark Energy It’s like Jello that just keeps filling up space as it expands

19. Dark Energy Causes the Universe to Accelerate Forever! (2) the Universe then speeds up forever (accelerates) because of Dark Energy R(t) scale factor (1) the Universe first slows down (decelerates) because of gravity time t Big Bang now Big Crunch

20. SuperNova Acceleration Probe SNAP

21. Standard Candles In the early 1990’s, a new type of standard candle was discovered – a kind of supernova technically called SNIa These supernovae are immune from evolutionary effects because their brightness only depends on the unchanging parameters of nuclear physics super (this kind of supernova had been discovered long ago – that it could be used as a standard candle was what was recognized in the early 1990’s)

22. Bright, SNe Ia SNIa Milky Way-like galaxy A supernova can outshine an entire galaxy! and so be seen from very far away

23. SNe Ia are similar throughout the Universe Nearby SNe Ia Distant SNe Ia

24. SNAP Mission • Telescope: 1.8 meter aperture sensitive to light from distant SNe and galaxies.

25. Mission Design

26. Mission Design

27. Mission Design

28. Mission Design

29. Mission Design

30. Mission Design

31. Instrument Design Cables/ FE elec Cold plate Radiator Thermal links Spectrograph Guiders Particle/ Thermal/ Light shield Shutter CCDs/ HgCdTe Near electronics Filters

32. 6.5° * 1.2° Observing Concept • Step across survey field in a predetermined pattern. • Fields revisited every four days. • All objects see all 9 filters. • Four exposures per position • To implement dithering pattern • This improves the spatial and photometric resolution • To eliminate cosmic ray pollution. • Defects in the image are eliminated by this procedure • 300 sec fixed length exposures determined by a shutter. • After the set of four exposures shift over by 0.05O – half the pitch of a detector. • Follow-up spectroscopy on SNe at peak brightness.

33. Launch Vehicle 1600 kg satellite can be lifted by a Delta IV [recent first flight] to our orbit with margin. Can use equivalent Delta IV, Atlas, or Sea Launch.

34. Mission Orbit L2 Lagrange point ~1,500,000 km L2 ~374,000 km ~1,500,000 km