Cosmology 2005:a Tutorial

Roland E. Allen

All WMAP images and text from http://map.gsfc.nasa.gov/m_ig.html, with credit to NASA/WMAP Science Team.

Other credits given individually.Please inform me if any material or images are not properly credited.

From http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/Footprints.html

From Brian Schmidt’s web site, http://msowww.anu.edu.au/~brian/PUBLIC/public.html

From http://astron.berkeley.edu/~jcohn/lens.html

http://www.aip.org/history/einstein

Wendy Freedman was the leader of the Hubble Key Project, to determine how fast the universe is expanding. In 2000 the group concluded that the universe is expanding at a rate of 74 kilometers/second/megaparsec (one parcsec is 3.26 light-years) with a total uncertainty of 10%.

She is now leading the effort to build the Giant Magellan Telescope, a >20 meter instrument which will probably be the world’s largest when it is finished. Texas A&M is a founding partner for the GMT (together with Harvard University, the Massachusetts Institute of Technology, and several other institutions).

Leavitt discovered a direct correlation between the time it took a star to go from bright to dim and how bright it actually was.

During her career, Leavitt discovered more than 2,400 variable stars.

Henrietta Leavitt discovers a correlation between Cepheids' period and luminosity (1912).

http://www.pbs.org/wgbh/aso/databank/entries/baleav.html

The age of the universe as determined from the Hubble constant is nowconsistent with that determined from the oldest stars in globular clusters.

Cosmology becomes a science: Robert W. Wilson and Arno Penzias discover the cosmic background

radiation in 1964.

Robert W. Wilson

Nobel Prize, for what has been called “the greatest scientific discovery ever”.

Robert Woodrow Wilson – Autobiography [copied and edited from www.nobel.se]

During my pre-college years I went on many trips with my father into the oil fields to visit their operations. I puttered around the machine, electronics, and automobile shops while he went about his business.

I used to fix radios and later television sets for fun and spending money. I built my own hi-fi set and enjoyed helping friends with their amateur radio transmitters.

I did a senior thesis with C.F. Squire building a regulator for a magnet for use in low-temperature physics. Following that I had a summer job with Exxon and obtained my first patent.

Following Rice, I went to Caltech for a Ph.D in physics. David Dewhirst, a Cambridge astronomer, suggested that I see John Bolton and Gordon Stanley about radio astronomy. Maarten Schmidt, who had previously done galactic research and was currently working on quasars, saw me through the last months of thesis work.

I joined Bell Laboratories at Crawford Hill in 1963 as part of A.B. Crawford's Radio Research department in R. Kompfner's laboratory. I started working with the only other radio astronomer, Arno Penzias, who had been there about two years.

In early 1990’s, COBE sees inhomogeneities in cosmic background radiation (about one part in 100 000): the seeds of the structure seen in our present universe, and evidence for both quantum fluctuations and inflation in the extremely early universe. In addition, the peak associated with acoustic oscillations (more later) indicates that the universe is flat. [from http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/Footprints.html]

A bonus: COBE image of the Milky Way (credit to Ned Wright)

http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/Images/Geometry_lg.jpg

From Brian Schmidt’s web site, http://msowww.anu.edu.au/~brian/PUBLIC/public.html

Brian Schmidt

Saul Perlmutter

2 independent teams use Ia supernovae (white dwarf explosions) and discover in 1997 that the universe is accelerating!

Adam Riess Robert Kirshner

Nick Suntzeff Alex Filippenko

From Brian Schmidt’s web site, http://msowww.anu.edu.au/~brian/PUBLIC/public.html

Credit: Riess et al. 2004 and NASA

Evidence from Type Ia supernovae for a decelerating, then accelerating universe, and thus for dark energy.

Credit to Adam Riess et al. and NASA. Images from http://www-int.stsci.edu/~ariess and http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/12/image/a

These are images of three of the most distant supernovae known, discovered using the Hubble Space Telescope as a supernova search engine. The stars exploded back when the universe was approximately half its current age.

The light is just arriving at Earth now. Supernovae are so bright they can be seen far away and far back in time. This allows astronomers to trace the expansion rate of the universe, and to determine how it is affected by the repulsive push of dark energy, an unknown form of energy that pervades space.

Fritz Zwicky (1930’s) and Vera Rubin (see next page) discover dark matter.

http://www.swemorph.com/zwicky.html

http://www.dynamical-systems.org/zwicky/Zwicky-e.html

In the thirties, Zwicky and Smith both examined closely two relatively nearby clusters, the Coma cluster and the Virgo cluster. They looked at the individual galaxies making up the clusters individually, and the velocities of the clusters. What they found was that the velocities of the galaxies were about a factor of ten to one hundred larger than they expected. The velocities can indicate the total mass inside the cluster. The more mass in the cluster, the greater the forces acting on each galaxy, which accelerates the galaxies to higher velocities..

From http://www.astro.queensu.ca/~dursi/dm-tutorial/dm1.html

Vera Rubin determined the velocities as a function of distance from the galactic center of clouds of ionized hydrogen (in astrophysical terminology, HII regions). This was done by measurement of the Doppler shift of their H-alpha emission lines. The hydrogen clouds move with the stars and other visible matter in the galaxies. Their velocities are more easily and directly measured than other visible matter.

Rubin found that the velocities of the clouds did not decrease with increasing distance from the galactic center, and in some cases even increased a little. This is in striking contrast to the decrease in velocity with radius predicted by Keplerian motion, which would occur if all the mass of the galaxy were concentrated in the center of the galaxy.

Detailed observations were first made by Rubin and W.K. Ford of the Andromeda galaxy and published in "Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions," Astrophysical Journal 159, 379 (1970). They then made observations of over 60 other spiral galaxies which apparently confirmed that the presence of dark matter was a general phenomenon ["Rotation Velocities of 16 Sa Galaxies and a Comparison of Sa, Sb, and Sc Rotation Properties," Astrophys. J. 289, 81 (1985), with D. Burstein, W. K. Ford, Jr., and N. Thonnard].

by Benjamin Johnson

http://www.physics.ucla.edu/~cwp/articles/rubindm/rubindm.html

Photo credit: Mark Godfrey

From http://astron.berkeley.edu/~jcohn/lens.html

From http://astron.berkeley.edu/~jcohn/lens.html

http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/Images/CosmicTimeline_gr.jpg

Hubble Space Telescope (HST) being deployed during the STS 31 flight.

[National Space Science Data Center, http://nssdc.gsfc.nasa.gov/image]

Hubble Space Telescope (HST) being refurbished. Astronauts Story Musgrave and Jeffrey Hoffman are seen, with Australia's west coast in the background. [National Space Science Data Center, http://nssdc.gsfc.nasa.gov/image]

Hubble image of spiral galaxy NGC 4414. [http://nssdc.gsfc.nasa.gov/photo_gallery]

Resembling a gigantic hubcap in space, a 3,700-light-year-wide dust disk encircles a 300-million- solar-mass black hole in the center of the elliptical galaxy NGC 7052.The disk, possibly a remnant of an ancient galaxy collision, will be swallowed up by the black hole in several billion years. The black-and-white image on the left, taken by a ground-based telescope, shows the complete galaxy. The Hubble picture on the right is a close-up view of the dust disk surrounding the black hole.[http://hubblesite.org/newscenter/archive]

An international team of astronomers used the Hubble Space Telescope to help make a precise measurement of the mass of a planet outside our solar system. The Hubble results show that the planet is 1.89 to 2.4 times as massive as Jupiter, our solar system's largest orbiting body. Previous estimates, about which there are some uncertainties, place the planet's mass at a much wider range: between 1.9 and 100 times that of Jupiter's. The planet, called Gliese 876b, orbits the star Gliese 876. It is only the second planet outside our solar system for which astronomers have determined a precise mass. [http://hubblesite.org/newscenter/archive]

The First Image of an Extra Solar Planet Credit: NaCo, VLT, ESO

The white object is surely a brown dwarf star. The faint red object 2M1207b is 100 times fainter, intrinsically, than the bright white brown dwarf 2M1207a -- a characteristic well explained by a planet roughly five times the mass of Jupiter. The discovery - still subject to further confirmation - is considered a step toward the more ambitious goal of imaging Earth-like planets orbiting distant stars.

SIRTF - the Space Infrared Telescope Facility (now called the Spitzer Space Telescope) - launched into space by a Delta rocket from Cape Canaveral, Florida in September, 2003. SIRTF is the final mission in NASA's Great Observatories Program - a family of four orbiting observatories, each observing the Universe in a different kind of light (visible, gamma rays, X-rays, and infrared). Other missions in this program include the Hubble Space Telescope (HST), Compton Gamma-Ray Observatory (CGRO), and the Chandra X-Ray Observatory(CXO). Most of infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground. Also, many areas of space are filled with vast, dense clouds of gas and dust which block our view. Infrared light, however can penetrate these clouds, allowing us to peer into regions of star formation, the centers of galaxies, and into newly forming planetary systems. [http://sirtf.caltech.edu]

Lyman Spitzer (1914-1997) was one of the 20th century's great scientists. A renowned astrophysicist, he made major contributions in the areas of stellar dynamics, plasma physics, thermonuclear fusion, and space astronomy. He was the first person to propose the idea of placing a large telescope in space and was the driving force behind the development of the Hubble Space Telescope.

$700 million Space Infrared Telescope Facility (SIRTF), or Spitzer Space

Telescope, the last of NASA's Great Observatories. [http://sirtf.caltech.edu]

Four days after its launch on August 25, 2003, NASA's Spitzer Space Telescope opened its infrared eyes for the first time and immediately performed beyond all expectations by providing the world with one of the deepest infrared images ever taken. Two years later, Spitzer continues to surpass expectations by uncovering a hidden universe teeming with warm stellar embryos, chaotic planet-forming disks, majestic galaxies, hidden black holes, remnants of dead stars, and much more.

This Chandra X-Ray Observatory image of the supermassive black hole at the Milky Way's center, Sagittarius A* was made from the longest X-ray exposure of that region to date. More than two thousand other X-ray sources were detected in the region, making this one of the richest fields ever observed.Credit: NASA/CXC/MIT/F.K.Baganoff et al. [http://chandra.harvard.edu]

Compton Gamma-Ray Observatory (CGRO)

http://cossc.gsfc.nasa.gov/cgro/egret_pulsars.html

Wilkinson Microwave Anisotropy Probe (WMAP)Artist's Conception: The composite/aluminum spacecraft is 150 inches (3.8 meters) high by 198 inches (5 meters) wide. WMAP weighs 1,850 pounds (840 kilograms) and is supplied with 419 Watts of power. The original WMAP mission lifetime was 27 months: three months of transit to L2 and 24 months of observing time. WMAP is still functioning, so its mission has been extended to improve the already great results.

[All WMAP images and text fromhttp://map.gsfc.nasa.gov/m_ig.html, with credit to NASA/WMAP Science Team]

The Wilkinson Microwave Anisotropy Probe (WMAP) is named in honor of David Wilkinson of Princeton University, a world-renown cosmologist and WMAP team member who died in September 2002.

Charles Bennett presenting Wilkinson Microwave Anisotropy Probe (WMAP) results at a press conference in Feb. 2003. He is the principal investigator for WMAP, which recently determined the age, content, history, and other key properties of the universe with unprecedented accuracy.

The Wilkinson Microwave Anisotropy Probe (WMAP) uses differential microwave radiometers that measure temperature differences between two points on the sky. [http://map.gsfc.nasa.gov]

The Wilkinson Microwave Anisotropy Probe (WMAP) observes the sky from an orbit about the L2 Sun-Earth Lagrange point, 1.5 million km from Earth. The observatory can always point away from the Sun, Earth and Moon while maintaining an unobstructed view to deep space. WMAP orbits L2 in an oval pattern every six months, and requires occasional maneuvers (usually about every 3 months) to remain in position. [http://map.gsfc.nasa.gov]

In the above contour plot we see that L4 and L5 correspond to hilltops and L1, L2 and L3 correspond to saddles (i.e. points where the potential is curving up in one direction and down in the other). This Suggests that satellites placed at the Lagrange points will have a tendency to wander off (try sitting a marble on top of a watermelon or on top of a real saddle and you get the idea). A detailed analysis confirms our expectations for L1, L2 and L3, but not for L4 and L5. When a satellite parked at L4 or L5 starts to roll off the hill it picks up speed. At this point the Coriolis force comes into play - the same force that causes hurricanes to spin up on the earth - and sends the satellite into a stable orbit around the Lagrange point. [http://map.gsfc.nasa.gov]

The easiest way to see how Lagrange made his discovery is to adopt a frame of reference that rotates with the system. The forces exerted on a body at rest in this frame can be derived from an effective potential in much the same way that wind speeds can be inferred from a weather map. The forces are strongest when the contours of the effective potential are closest together and weakest when the contours are far apart.

The Sun is a bubbling ball of extremely hot gas. In this false-color picture, light blue regions are extremely hot - over 1 million degrees, while dark blue regions are slightly cooler. The camera filter used was highly sensitive to the emission of highly charged iron ions, which trace the magnetic field of the Sun. This picture was taken in ultraviolet (extremely blue) light by the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft, which is orbiting the Sun just ahead of the Earth, at the L1 point. [http://sohowww.nascom.nasa.gov]

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

http://sohowww.nascom.nasa.gov

WMAP has made the first detailed full-sky map of the oldest light in the universe. It is a "baby picture" of the universe. Colors indicate "warmer" (red) and "cooler" (blue) spots. (The oval shape is a projection to display the whole sky.) The microwave light captured in this picture is from 380,000 years after the Big Bang, over 13 billion years ago. The data brings into sharp focus the seeds that generated the cosmic structure we see today. These patterns are tiny temperature differences within an extraordinarily evenly dispersed microwave light bathing the Universe, which now averages a frigid 2.73 degrees above absolute zero temperature. WMAP resolves slight temperature fluctuations, which vary by only millionths of a degree. These data support and strengthen the Big Bang and Inflation Theories. [http://map.gsfc.nasa.gov]

Power Spectrum (Fingerprint of the Universe)The "angular spectrum" of the fluctuations in the WMAP full-sky map. The shapes of these two curves contain a wealth of information about the age and content of the universe and about the source of the fluctuations seen in the picture. The rise in the bottom curve at large angles (~90 degrees) is the indication that the first stars in the universe formed very quickly.

Looking Back In Time. WMAP, in the present era, looks back to the first light to break free in the Universe, the afterglow of the Big Bang that emerged 380,000 years after the Big Bang. This light, seen today, has taken over 13 billion years to reach us. During that time, giant clouds of gas in the early Universe condensed under the force of gravity to form the first stars (200 million years after the Big Bang). Then, galaxies and galaxy clusters formed into the vast structure we see today. The temperature fluctuations seen today correspond to the seeds that grew to become galaxies.

The First Stars. The first stars in the Universe turn on. WMAP data reveals that this era occurred 200 million years after the Big Bang, much earlier that many scientists had suspected.

Content of the Universe. The Universe is much more than what meets the eye. The contents of the Universe include 4% atoms. This is ordinary matter, the stuff from which stars and everything we see and touch is made. WMAP data reveals that 23% of the Universe is unseen dark matter, a mysterious form of matter intrinsically different from atoms. This matter does not radiate light like ordinary matter, but is detected only indirectly by its gravity. Most of the Universe, 73%, is a mysterious form of energy, dubbed dark energy, that acts as sort of an anti-gravity force and is responsible for accelerating the expansion of the Universe.

The light that is reaching us has been stretched out as the universe has stretched, so light that was once beyond gamma rays is now reaching us in the form of microwaves. Microwaves are the same kind of electromagnetic radiation as the light we see with our eyes, but stretched out to a longer wavelength.

Map showing an asymmetry (light and dark gray tones), called the "dipole", due to the motion of the spacecraft.The foreground signal of the Milky Way can be separated from the cosmic background because they are different colors.

WMAP Conclusions

The new WMAP data has been combined with other diverse cosmic measurements (galaxy clustering, Lyman-alpha cloud clustering, supernovae, etc.) to yield a new unified understanding of the universe:*Universe is 13.7 billion years old with a margin of error of close to 1%.*First stars ignited 200 million years after the Big Bang.*Light in WMAP picture from 379,000 years after the Big Bang.*Content of the Universe: 4% Atoms, 23% Cold Dark Matter, 73% Dark energy. *The data places new constraints on the dark energy. It seems more like a "cosmological constant" than a negative-pressure energy field called "quintessence". But quintessence is not ruled out.*Fast moving neutrinos do not play any major role in the evolution of structure in the universe. They would have prevented the early clumping of gas in the universe, delaying the emergence of the first stars, in conflict with the new WMAP data.*Expansion rate (Hubble constant) value: Ho= 71 km/sec/Mpc (with a margin of error of about 5%)*New evidence for Inflation (in polarized signal)*For the theory that fits our data, the Universe will expand forever. (The nature of the dark energy is still a mystery. If it changes with time, or if other unknown and unexpected things happen in the universe, this conclusion could change.)

The Sloan Digital Sky Survey is the most ambitious astronomical survey project ever undertaken. The survey will map in detail one-quarter of the entire sky, determining the positions and absolute brightnesses of more than 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars.

Credit and copyright: Sloan Digital Sky Survey Team, NASA, NSF, DOE

Evidence for a mysterious dark energy in the universe:

Gazing to the far reaches of space and time, NASA's Hubble Space Telescope identified the farthest stellar explosion ever seen, a supernova that erupted 10 billion years ago. By examining the glow from this dying star, astronomers have amassed more evidence that a mysterious, repulsive force is at work in the cosmos, making galaxies rush ever faster away from each other.

[http://hubblesite.org/newscenter/archive]

From Brian Schmidt’s web site, http://msowww.anu.edu.au/~brian/PUBLIC/public.html

This and several following slides fromhttp://www-supernova.lbl.gov

The predicted abundance of elements heavier than hydrogen, as a function of the density of baryons in the universe (expressed in terms of the fraction of critical and the Hubble parameter). From http://astron.berkeley.edu/%7emwhite/darkmatter/dm.html

The Four Pillars of the Standard Cosmology

"The evolution of the world can be compared to a display of fireworks that has just ended; some few red wisps, ashes and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanishing brilliance of the origin of the worlds." Lemaitre.

The four key observational successes of the standard Hot Big Bang model are the following:

Expansion of the Universe Origin of the cosmic background radiation Nucleosynthesis of the light elements Formation of galaxies and large-scale structure

The Big Bang model makes accurate and scientifically testable hypotheses in each of these areas and there is remarkable agreement with the observational data. from http://www.damtp.cam.ac.uk/user/gr/public/bb_pillars.html