Welcome to MAE 87 Freshman Seminar

New Observations and Ideas about Cosmology

Carl H. Gibson

Fall Quarter: October 1 to December 3, 2003

Course outline

EBU2: 479 is on the fourth floor facing the main UCSD campus library (West).

WebSites of interest:
Space Telescope Science Institute

This image taken with the Hubble Space Telescope shows galaxies of stars in a small dark part of the Big Dipper. Because it is dark we know the age of the universe is finite. Because all the galaxies are moving away and because the view is the same in all directions, most scientists believe they all started at once about 13 billion years ago with a big bang.

Most of the matter (99.9%) in this image is not in the form of luminous stars, and is therefore termed "dark matter". The percentage is a subject of debate, as is the form of the dark matter. Even the big bang origin of the universe is debatable. One purpose of the class is to urge students to keep their minds open to new ideas about cosmology. Information is flooding in at a rate never before seen in astronomy. Old ideas are evaporating faster than new ideas can form to replace them. Another purpose of the class is to alert students to sources of the new information and ideas about astronomy and to give them some tools needed to appreciate the significance of the information as it arrives. First tool: Don't believe everything people say. Second tool: Listen anyway. Look through the HST webpages carefully to see the range of new information available from that source alone, but be skeptical about the explanations. Notice that the first images from HST began arriving in 1994, when the revolution in astronomy and cosmology began.

This is the Hubble Space Telescope (HST). It was placed into orbit 380 miles above the earth in 1990. Remarkably, its pictures are available almost immediately to everyone through the internet, and a fabulous archive of these pictures is maintained.

SIRTF Space Infrared Telescope Facility Launched August 25, 2003

This telescope promises to give much new information about objects that are cooler than stars like large planets. The telescope is in a three month check-out period now, but clearly is working well as shown by the engineering image below.

This engineering image is a quick look at the sky through the Infrared Array Camera (IRAC), one of three scientific instruments aboard SIRTF. The 5 arcmin x 5 arcmin image was taken in a low Galactic latitude region in the constellation Perseus. It results from 100 seconds of exposure time with the short-wavelength (3.6 micron) array. The visible band is at about 0.5 micron wavelength, so this view would be quite invisible to the naked eye of humans.

National Aeronautics and Space Administration (NASA) "Origins" program

Look through these pages to see the conventional wisdom about the origins of the universe and its components. Many of the assumptions are questionable, and will be discussed in class. Gives a good summary of our present space program in astronomy and astrophysics.

Other telescopes investigate the ultraviolet and X-ray bands, which generally originate from superhot objects like black hole accretion disks and quasars. Gamma rays appear in random directions as localized bursts. Many theories have been advanced to explain this phenomenon, but no concensus has emerged about the correct explanation except that "gamma-ray bursts" must come from outside our Milky Way galaxy.

The first observations by telescope were by Galileo in 1609. The sketches were made in ink from his observations of the moon, and clearly showed the moon was not smooth as previously thought. Galileo also saw four of the moons of Jupiter with his telescope. The Next Generation Space Telescope (NGST) will be larger than the HST and have better infrared sensitivity to see back further in time toward the big bang. The launch date is 2008, nearly 400 years after Galileo's pioneering sketches.

The most distant and earliest information comes to us with red-shift of more than 1000 in the microwave frequency band. By a trick of general relativity theory the big bang does not appear as a distant point in some particular direction, but as a sphere stretched uniformly about us. The "cosmic microwave background radiation" (CMB-Wayne Hu website) is also a surrounding sphere reflecting the universe at a time about 300,000 years after the big bang at the time when the opaque primordial plasma of hydrogen and helium cooled enough so that it turned into a transparent gas.

A huge effort has been expended to study the CMBR in detail, since this is the earliest data available about the universe. Telescopes have been attached to balloons to avoid the absorption of microwave radiation by the atmosphere, and another (WMAP) has been in orbit for nearly two years about the neutral point beyond the earth where gravity and centrifugal forces balance for the earth-sun system (the second Lagrange point).

One result of this effort is evidence that the big bang is the result of a period of strong turbulence. The evidence is circumstantial. Turbulence causes very special statistical patterns in quantities the turbulence mixes, like temperature. The temperature patterns of the CMB precisely match the patterns that occur for strong turbulence. The question is, "When was the universe before 300,000 years turbulent?". The answer appears to be that it was turbulent from the beginning.

You will not find much information about turbulence in cosmology if you search the literature. One reason is that turbulence was claimed to be important by early cosmologists such as George Gamov in ways that have been shown to be unlikely by modern observations. Gamov thought primordial turbulence caused galaxies to precipitate on the density maxima produced by the turbulence. However, the CMB observations show the primordial universe was much too uniform to be turbulent; that is, the temperature fluctuations were only 1/100,000 compared to 1/10 expected for turbulence. This just means that the universe was not turbulent at the time of the CMB, not that the universe was never turbulent. The most important question is, "Why was the universe at the time of the CMB not turbulent?". Fluids in motion at large scales tend to become turbulent unless something prevents the turbulence from forming, such as viscosity (molasses), buoyancy forces (the ocean and atmosphere) or strong rotation (Jupiter). It turns out that all of these factors probably acted to inhibit turbulence at various stages in the fluid mechanical history of the universe. At the time of the CMB (300,000 years after the big bang beginning) the only forces available to prevent turbulence were viscous forces and buoyancy forces. The viscosity required is enormous (10^30 m^2 s^-1) compared to that of the plasma (10^25 m^2 s^-1) so we are left only with buoyancy forces, but this means gravitational structure formation must have begun in the primordial plasma. When did this happen? All evidence points to a time about 30,000 years after the big bang when the mass of the matter within the scale of causal connection ct matched the known mass of superclusters of galaxies 10^47 kg, where c is light speed and t is time. These large structures fragmented to galaxy masses of 10^43 kg before turning to gas.

Because the time, temperature, density, composition, and rate-of-strain of the cooling plasma at its transition to gas are all precisely known, the fluid mechanics of gravitational structure formation when the plasma universe turned to gas is easy. The gas was unstable to fragmentation at two length scales, one determined by the speed of sound and one determined by the viscosity. The viscosity of the H-He gas reduced by a trillion from that of the plasma so the gravitational fragmentation mass became that of a small planet (10^25 kg). The sound speed reduced from c/3^.5 for the plasma (2x10^8 m/s) to < 10^5 m/s so the acoustic fragmentation mass became that of a globular cluster of stars (10^36 kg). Within a gravitational free-fall time of less than a million years after the plasma-gas transition at 300,000 years the plasma turned to a fog of earth-mass fragments within million-sun mass clumps, within trillion-sun mass proto-galaxies...and stars appeared. The baryonic dark matter consists of proto-globular-star-cluster clumps (PGCs) of primordial-fog-particles (PFPs) that have frozen to form Jovian (ie: like Jupiter...gassy vs. rocky) planets rather than merging to form stars. These Earth-mass Jovian planets dominate the density of the interstellar medium. They are revealed only if something very hot appears in their near vicinity to cause their frozen hydrogen and helium gasses to evaporate. This occurs in planetary nebula, which are solar mass dying stars that become very hot when they have nothing left but carbon, which crushes itself to become a white dwarf star. An example is the Helix planetary nebula, the closest one to the earth. With the Hubble Space Telescope we see it is surrounded by thousands of "cometary globules", which are likely these primordial-fog-particle (PFP) Jovian planets coming out of cold storage. Each of the comets is 10^13 m in diameter, the size of the solar system out to Pluto. For details, see the HST archives. The comets (PFPs) are separated by about 10^14 m, and weigh 10^24 to 10^25 kg (some of the ones close to the hot star are much heavier, say 10^27 kg like Jupiter because they are ancient aggregates of thousands of the smaller PFPs). Stars are formed by gravitational accretion of millions of PFPs forming thousands of such Jupiters that form hundreds of brown dwarfs, etc.

Not all of the big-bang matter could turn into gas....only the hydrogen and helium. The remainder is called the "non-baryonic dark matter" and is probably something like neutrinos or is an unfamiliar neutrino species. Neutrino species were formed in vast quantities during the hot stages after the big bang when the protons and neutrons of the hydrogen and helium atoms were formed, and only recently (1998) have been discovered to have mass. Neutrino-species are difficult to study because they interact very weakly with other particles and are formed at temperatures too hot to produce on Earth. Gravitational fragmentation of the "neutrino-fluid" was much later than the fragmentation of the plasma and gas of baryons because it is so diffusive. Neutrino-fluid forms outer halos of galaxies and galaxy clusters in fluid-cosmology modeling. The total mass of the neutrino-fluid halos of galaxies is about 30 times larger than that of the stars or dark-matter PFPs that form the inner galaxy halos, but its density is less.

Strange pictures emerge from the HST archives such as this picture of two merging galaxies called the Mice because of the star tails. We will see that the standard explanations of such galaxies in terms of collisionless interactions and tidal ejections of the stars along the tails have difficulties when confronted with high resolution images that show young globular clusters (YGCs) and new stars forming along the tails. The ages of the YGCs are smaller than the time it takes to form the tail, so they must be formed in place. Where do they get the matter for their million stars, and how is it concentrated to densities millions of times larger than the ambient density? The answer is that the matter was dark (PFPs in PGCsc) before the galaxy passage and the star and star-cluster formation was triggered due to agitations of the dark matter caused by the passage of the galaxy. As the merging galaxies pass through each other's inner halos, the PFP planets are evaporated and their accretion rate increases. The new stars and new globular clusters of stars appear as luminous wakes of the passing galaxies. Only the inner dark-matter halos of the two galaxies are included in this picture (3 10^21 m)...the outer neutrino-fluid halos are much larger (3 10^22 m).

Have a look at the recent HST composite image of the Sombrero galaxy. The bright objects are not stars but globular clusters of stars...thousands of them out of the million protogalaxy original supply of dark PGCs (there is a bright foreground star at 4 o'clock and a double galaxy at 7 o'clock). Stars look like smoke at these distances, even to the HST. The Milky Way galaxy only has a couple of hundred luminous globular clusters from its PGC supply. Sombrero's black hole is a thousand times larger than the million sun black hole in Milky Way. The larger luminous "core" of field stars for Sombrero is apparently related to the black hole formation process. Like the Milky Way, all the globular star clusters in Somrero are very old...13 billion years, not like in Mice where they are young...only a million.

Picture of the week. See the pictures NASA scientists found most interesting during 2003. Read the explanations, but don't believe everything you read (for example, ignore everything about cold dark matter, dark energy, dark halos, the accelerating universe and dark ages). If you want more, see the Astronomy picture of the day.



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Last edited: Sept. 23, 2003