Story of the Universe Special theory of Relativity

Story of the Universe

Special theory of Relativity It is a basic property of Nature that: Velocity of Light in vacuum is constant. All inertial frames are identical so if two objects are moving with a constant velocity, it is impossible to do any test which allows to measure the velocities in absolute manner. This has significant consequences. Atoms to Astronomy 2

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Consequences • Because velocity of light is constant: – space and time must contract. – Acceleration must increase not just the velocity of an object but also its inertia and hence objects become heavier as they approach the velocity of light – No object with finite mass can move at velocity of light and no object of zero mass can move at a slower velocity! Atoms to Astronomy 4

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Gravity - 1 • 6

Gravity - 2 • It also defines Keplerian Velocity. In order for an object to remain in stable revolution around a star, it must have a velocity so that gravity and centrifugal force are balanced. • The inverse square law implies that in general, the orbit of an object experiencing the gravitational attraction of another body will undergo motion best explained by conic curves (ellipse, parabola or hyperbola) defined by initial conditions. • Also, the centre of mass of the two objects going around each other will be the stable point around which both the objects will revolve. 7

Problems • However, this is not fully satisfactory and cannot explain precession of orbits etc. • This led Einstein to expand it into a larger formulation called General Theory of Relativity. • Newton’s laws are a special case of General Theory of relativity when the masses and speeds are small. Atoms to Astronomy 9

General theory of Relativity General Theory of relativity states that: Influence of Gravity is identical to that of sitting in an accelerated frame. Identifying the curvature of space-time with Gravity It becomes important in the presence of Strong gravitational fields such as those existing near compact objects. Atoms to Astronomy 10

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Iron line in compact objects Super massive black hole in the galaxy NGC 4258 Quasi periodic oscillations of 0. 01 to 500 Hz and direct evidence of BH MCG-6 -30 -16 - 400 ks long XMM observation Atoms to Astronomy 12

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red yellow Doppler Shift Light from stationary star blue red yellow Light from star moving away from us (red shift) blue red yellow blue Light from object moving towards us (blue shift) Atoms to Astronomy 16

Southern Sky Northern Sky Atoms to Astronomy 17

Difference in brightness can arise because a) The stars are at different distances b) Stars are of different intrinsic brightness Atoms to Astronomy 18

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FOR NORMALISED AREA Atoms to Astronomy 20

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For stars at an angle, an additional cos( ) factor has to be considered Atoms to Astronomy 22

16 Dsun Atoms to Astronomy 23

1 AU 700 Dsun Atoms to Astronomy 24

Measuring distances to galaxies involves using some selected objects STANDARD CANDLES These are objects of known intrinsic brightness. Hence a ratio of their apparent brightness to their intrinsic (absolute) brightness gives their distance. For objects inside our galaxy an additional parameter comes from extinction where distance is measured by Atoms to Astronomy 26 parallax and ism by extinction.

Variable Stars as distance indicators The period-luminosity relation for Cepheids Note the logarithmic scale for the graph (type 1) Constant luminosity Atoms to Astronomy 27

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Redshift (z) is defined as z = / z = 1+[(c+vrec)/(c-vrec)]1/2 Depth of Universe Visible (a) is a = (1+ z)-1 30

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Planck Value: 67. 3 km/s/Mpc Atoms to Astronomy 32

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Gamma ray Atoms to Astronomy 36

WMAP Planck 37

Entropy A conspiracy of Gravity and Nuclear forces 3 min 380, 000 years Present Time 38

Cosmic time Star formation through time Madau plot (Cole et. Atoms to Astronomy al. 2001) 39

Wonders of the Universe 40

Gravity dominated Expansion dominated Atoms to Astronomy 41

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Inflation • It seems that the nascent universe passed through a phase of exponential expansion. • Inflation answers the following problems of the big bang cosmology: – Why does the universe appear flat, homogeneous and isotropic – Origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the universe. Atoms to Astronomy 43

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Proton formation: 1 sec The earliest galaxies we have seen are at z ~ 7. 51, i. e. about 10. 7 billion years since the birth of the Universe. The earliest stars were born 200 million years after the Universe was born! Inflation 10 -35 s 47

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String Theory? Theory of Vacuum fluctuations? ? ? Standard Model Abdul Salam’s Electrowea k Theory Maxwell’s Electromagnetic Theory 51

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This is an artist’s impression of the galaxy Z 8 -GND-5296. Image credit: V. Tilvi / S. L. Finkelstein / C. Papovich / the Hubble Heritage Team Z 8 -GND-5296 is forming stars extremely rapidly – producing each year about 300 times the mass of our Sun. By comparison, our Milky Way Galaxy forms only 2 – 3 stars per year. Even galaxies observed at a time when the Universe had reached only 5% of its current age may already be chemically enriched with dust and heavy elements, which must have been produced by an earlier generation of stars. Finkelstein, S. L. et al. Nature 502, 524– 527 (2013); see also Riecher 24 October 2013, Nature, 502, 459 Atoms to Astronomy 56

Cosmic clock Event H and He formation time 3 min. redshift 109 400, 000 yr 1, 500 The first stars 400 Myr 10 Reionization 400 Myr 9 The first galaxies 0. 7 Gyr 6. 5 Today 13. 7 Gyr 0 Recombination 57

Dark Energy 58

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~ 2 billion years ago Atoms to Astronomy 61

Matter Strength of the repulsive force in the Universe Atoms to Astronomy 62

75% 4% 21 % Atoms to Astronomy 63

Origin of elements in the Universe

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Synthesis of elements Atoms to Astronomy 67

Limits to production of heavy elements in the Universe: The Binding energy curve Atoms to Astronomy 68

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Abundance of matter in the Universe Atoms to Astronomy 71

How will the universe end?

Dark is more important than bright

Rotational velocity (km/s) Distance from Centre

Cosmic clock Event H and He formation time 3 min. redshift 109 400, 000 yr 1, 500 The first stars 400 Myr 10 Reionization 500 Myr 9 The first galaxies 0. 8 Gyr 6. 5 Today 13. 7 Gyr 0 Recombination

Star formation through time Cosmic time Madau plot (Cole et al. 2001)

~ 2 billion years ago

60% 4% 26 %

I should have stopped long back Atoms to Astronomy 87

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