Presentation on theme: "Chapter 5: Cosmic foundations for origins of life."— Presentation transcript:
Chapter 5: Cosmic foundations for origins of life
Is life a natural consequence of cosmology? - Evidence for origin of evolution by Big Bang becoming very secure… - expansion of the universe, - cosmic microwave background radiation, - synthesis of simple elements - hydrogen, helium, lithium. - Galaxies are a consequence of small fluctuations produced during the Big Bang… - Stars form in galaxies … first stars created first carbon in universe; life not possible before this? - Stars produce all the heavier elements (dubbed “metals”) produced by fusion in stellar interiors (eg. O, C, N, ….) - Synthesis of carbon “finely tuned”… a slight change in strength of forces could result in universe with *no* heavy elements, so no life.
Our Milky Way Galaxy is a spiral galaxy much like Andromeda – our most massive partner in the Local Group of Galaxies. Note this spiral galaxy has a galactic bulge, halo, and disk. There are also 2 dwarf galaxies visible that orbit Andromeda.
THE EXPANDING UNIVESE Edwin Hubble: At the 48 inch on Mt. Palomar
Cepheid variable stars in M100 – galaxy in the Virgo cluster: used by Hubble to measure the distance to galaxies. P vs. L relation:
Hubble Diagram (1929): all galaxies receed from us. Speed of separation (v) is measured from the red shift of some typical well-observed line. - Hubble founds that v is proportional to the distance to the galaxy – HUBBLE’S LAW: Hubble’s original data and graph.
Red-shift distance relation for galaxies enormously more distant than in Hubble’s original study. Galaxies studied here are members of galactic clusters (eg. Virgo, Hydra, etc)
Galaxies move away from us - the same for observers in any other galaxy: at some past time, all the matter must have been at one point – a “Big Bang must have occurred!
Best measured value for Hubble’s constant: - Good distance measurements from 1. HST observations of Cepheids in other galaxies and 2. “Tully-Fischer” relations Hubble constant has units of 1/time – so a good estimate of age of the universe is: 1/Ho = 15 billion years!
CFA survey of galaxies – out to 200 MPC covering 6 deg. thick slice of sky galaxies shown.
Cosmological Model – a homogenous and isotropic universe Probe structure in the universe on ever larger scales – there is a largest scale seen: Great Wall of about 200 Mpc in scale. On scales > 300 Mpc – universe appears to be homogenous (same everywhere). Universe is same in every direction on these largest scales – isotropic. 23,697 galaxies within 1000 Mpc (Las Campanas survey). Voids and walls no larger than 100 – 200 Mpc.
Picturing the Expansion of the Universe: It is spacetime that expands – the distance between galaxies grows! The Big-Bang is not like a bomb going off inside some space – it is spacetime itself that “explodes” – about 15 billion yrs ago. Picture dots on a balloon (galaxies). As balloon expands (ie spacetime), galaxies carried away from one another. Every observer on every dot sees all the other dots recede – ie, Hubble’s law is measured by all observers in the universe
General relativity and cosmology : Cosmological model: assume homogenous and isotropic distribution of matter on largest scales General relativity shows space-time is dynamic! Evolution of universe depends on its density. Critical density for universe: at greater than the critical density, the expansion of the universe will ultimately cease and it will re-collapse. At densities lower that critical value, the universe will continue to expand forever. Critical density in general relativity can be accurately calculated using Hubble’s law, and Newtonian gravity to find:
General relativity: The fate of the universe depends on how dense it is. A low density universe (open) will continue to expand forever. A critical density universe will coast to a stop after an infinite time. A high density universe (closed) will expand to a maximum size in a finite time – and collapse into a singularity again: the “Big Crunch” Distance between galaxies as a function of time: model with critical density labelled “marginally bound”
Geometry of the universe in four dimensions: Closed Universe Critical Open Universe (sphere) (flat) (saddle)
Predicted in 1948 (Alpher, Bethe, and Gamow) Discovered in 1964 by Penzias and Wilson – Nobel prize
Cosmic Microwave Background Radiation (CMBR) Major prediction of the Big Bang is that the universe started very dense and hot, and then cooled with time. CMBR pervades all space, and should be black- body. Explanation: Wien’s law for black body radiation: increasing wavelength implies that temperature decreases:
Expansion of universe stretches out the wavelength of a photon – like wave drawn on a balloon that is stretched with time: This is why galaxies appear to be redshifted! NOT that galaxies move relative to one another – but that universe expands during the time it takes light to travel from another galaxy to us. Temperature varies inversely as scale factor of universe:
COBE measurement of CMBR spectrum: T=2.735 K Experimental errors are smaller than size of dots in figure. Blue line is best fit black-body spectrum
COBE map (1989): – fluctuations in temperature; one part in a hundred thousand
WMAP (2003): 45 times more sensitive, and 33 times the spatial resolution of COBE Data from WMAP gives age of universe of 13.7 billion yrs; to accuracy of 1%! *Fluctuations are the seeds of galaxy formation*
Inflation and CMBR (Alan Guth, 1981) At a time when the age of the universe was; -Universe underwent a brief(!) epoch during which exponentially fast expansion occurred - increasing its size by 50 orders of magnitude! (before and after this episode, the size of the universe grows as a power-law function of time – much slower!). - Universe grew out of a single “fluctuation” of this new phase – solving problems
During first 3 minutes; in time that universe cools from 10 billion to 1 billion deg. K; nucleosynthesis is possible. Elements fabricated are Helium-3, Helium-4, Deuterium, and a trace of Lithium. Deuterium and Helium isotopes produced using neutrons – unlike proton- proton chain. Big Bang Nucleosynthesis
Producing simplest elements in the Big Bang: Observations of Helium 3 & 4, + deuterium, -> specific density and temperature conditions -> strongly constrain the cosmological model – fraction of matter in baryons. Deuterium is not produced significantly in stars – so are seeing primordial abundance. Best fit: baryon density that is a few % of critical.
Supernovae Type Ia’s; mapping the cosmos to furthest distances… discovery of dark energy
Composition of universe Measure density in units of the critical density – define density parameter: Contribution of baryonic (ordinary) matter: Contribution of all matter (baryonic + dark): Contribution of “dark energy” (cosmological constant) from CMBR and supernova measurements: Key result:
Text History of our universe
Origin of Galaxies Density fluctuations arise at earliest moments when universe is still a quantum- mechanical object. This is the “Planck scale”: Quantum fluctuations in Planck era are ultimate density fluctuations that grow to be galaxies! This spectrum of fluctuations is preserved in the CMBR fluctuations - predicts many aspects of galaxies such as their size distribution, evolution with time (“hierarchical”), etc. Computer simulation – courtesy Hugh Couchman (McMaster University)
Formation of the first star Physics is much simpler – no magnetic fields, no dust or complex molecules, primordial gas contains hydrogen and helium. Start with a small, cold, dark matter halo – about a million times mass of the Sun. Gas within it cools down to 200 K, (molecular hydrogen is the coolant) A 100 solar mass core forms inside a filamentary “molecular cloud”
The very first star… 100 times the mass of our Sun - a single star forms Abel et al (2002), Science
First stars turned on perhaps 200 million years after the Big Bang… they started to make the elements out of which planets, and living things, are made.
Stellar evolution – forming the elements for biolmolecules and planets….