Welcome to Ned Wright's Cosmology Tutorial

News of the
Universe
Frequently Asked
Questions
Enter
the tutorial or the Italian
version    or the French
version

Cosmological fads
and fallacies

Cosmology and art

Cosmology, Religion
& Kansas
Send me your
comments

New on the tutorial:

A discussion
of the history of the CMB dipole discovery.

A history
of COBE, the COsmic Background Explorer, in pictures.

A cool rollover page
that blinks between a color image contructed from 3 WMAP bands and the WMAP
ILC reduced galaxy map

A calculator
that takes light travel time and computes the redshift.
There is also an advanced
version of my Cosmology
Calculator.

Cosmology is the study of the origin, current state, and future of our
Universe. This field has been revolutionized by many discoveries made during the
past century. My cosmology tutorial is an attempt to summarize these
discoveries. It will be "under construction" for the foreseeable future as new
discoveries are made. I will attempt to keep these pages up-to-date as a
resource for the cosmology courses I teach at UCLA. The tutorial is completely
non-commercial, but tax deductible
donations to UCLA are always welcome.

Astronomy and cosmology are very much mathematical sciences, but I have
attempted to avoid higher math in these pages. I do use high school algebra and
geometry - courses required for admission to UCLA - but I have also included
some animations [1, 2, 3, 4, 5,
6, 7], some Java
applets [1, 2], and many
illustrations in the tutorials, the ABC's of Distances,
and the answers to some of the Frequently Asked
Questions.

In addition to the cosmology tutorial,
there is also a relativity tutorial
and extensive discussions on the age, density and size of the Universe.
There is also a bibliography of books
at a range of levels, and a Javascript calculator of the many distances
involved in cosmology.

Slides for recent talks:

Colloquium
at the Geneva Observatory, 10 Nov 2006.

Public
talk at the 20 Oct 2006 meeting of the Ventura County Astronomical Society

27
Sep 2006 colloquium at the Arizona State University School of Earth and
Space Exploration.

24
Sep 2006 Talk at the Mt. Wilson Observatory
Association

Invited
talk at Einstein's Legacy:
Relativistic Astrophysics and Cosmology, 7-11 Nov 2005.

Presentation
at the International
Symposium on Particle Physics, Astrophysics and Cosmology

Lectures at the International Summer Institute on Particle physics,
Astrophysics and Cosmology, Hangzhou China, 2005 August 15, 16,
18.

"Fact
and Fiction in Cosmology", a public lecture at the Cal State Northridge
planetarium.

13
March 2005 AFHU Einstein Symposium Talk

3
March 2005 Director's Distinguished Lecture at LLNL

27
May 2004 Ohio State Colloquium

11 Oct 2003
UCLA Extension Course

September,
2003 NATO ASI in Cargese lectures (1, 2, 3)

lectures at
the July, 2003 winter school in
Argentina

"Are We
Likely to Be Alone" at the 4 April 2003 CSEOL Symposium

Astrophysics Fact
Sheet

The course
notes (130 pages, 398 equations, 51 figures) for the upper division
undergraduate Stellar Systems and Cosmology course, Astronomy
140, that I last taught in spring 2008 are available on the Web. And for a
much more technical discussion of cosmology see my graduate course Astro 275 lecture
notes (109 pages, 355 equations, 37 figures). This course was last taught in
the spring of 2007. If this course Web site gets closed, you can use a backup
Postscript copy of the A275 notes. Use
Ghostscript to view this file or save it to disk and send it to a Postscript
printer.

News of the Universe

Variable Constants?

20 Jun 2008 - Murphy, Flambaum,
Muller & Henkel (2008) show that the ratio of the proton mass to the
electron mass has varied by less than 1.8 parts per million (95% CL) since redshift z =
0.68466. They compared the radio inversion lines of ammonia to the pure
rotation lines of HCN and HCO+. All of these lines are measured very precisely
using radio astronomy techniques, and the redshifts are consistent. But the
ammonia lines are much more sensitive to the proton:electron mass ratio so this
quantity has not varied in the past 6 billion years. This report is an
improvement over previous
results using the same quasar absorption line cloud.

Another Bullet Cluster

17 Jun 2008 - Bradac et al.
(2008) have found another bullet
cluster where two clusters of galaxies have collided, leaving the hot gas in
between the clumps of galaxies, but the source of gravity has passed right
through the collision, staying with the galaxies. Since the hot gas is most of
the normal matter, this shows that the source of gravity is not the normal
matter, but rather dark matter. This is a problem for alternative
models that modify gravity to eliminate the need for dark matter.

Supernova Initial Flash

22 May 2008 - Soderberg et
al. report an observation of a soft X-ray flare from a spot that later
turned out to be a Type Ibc supernova. The peak flux was about 7 x
10-10 erg/cm2/sec for about 400 seconds. At the 27 Mpc
distance of the host galaxy NGC 2770 this is about 2 x 1046 ergs in
X-rays produced when the shockwave breaks out of the massive star whose core has
collapsed. The UV peaked a day later, and the optical 20 days later as the
remains of the star expanded and cooled.

This was quite an interesting result when it appeared three months ago on arxiv.org, but it was embargoed by Nature until publication so I didn't
post this news item until now.

New High Redshift CMB Measurement

13 May 2008 - Srianand et
al. have announced
a measurement of TCMB at a redshift of 2.418. Absorption
lines from carbon monoxide (CO) molecules were seen in the spectrum of a
distant quasar, and showed rotational excitation in the CO ground vibrational
state. The temperature seen is 9.15 +/- 0.7 K, while the Big Bang model predicts
9.315 K. So this observation is consistent with the Big Bang, but contradicts
the Steady
State model.

New Union Supernova Catalog

28 Apr 2008 - Kowalski et al. (2008) of the
Supernova Cosmology Project present a union catalog of supernovae. The catalog
contains 332 SNe that pass all cuts when the low redshift SNe are
included. Click on the thumbnail at right for binned ΔDM vs. redshift tables and
plots. ΔDM is the difference in the distance
modulus between the data or model and an empty Universe model. A higher
distance modulus means the supernovae are fainter than expected in an empty
Universe.

Tired Light is Still Dead

24 Apr 2008 - Blondin et
al. (2008) studied distant
supernovae using spectra to judge the age of the object during each
observation. They found an aging rate that varied with redshift z
like
1/(1+z)(0.97 +/- 0.10),
compatible with the expected
1/(1+z) for expanding Universes, but 9.7 standard deviations away from the
constant aging rate expected in the tired light model.

Dark Matter Detected?

17 Apr 2008 - The DAMA/LIBRA experiment
announced a confirmation of their
previously found annual modulation signal in the count rate of a deep
underground CsI detector. They see a modulation of +/-0.027 counts/kg/keV/day in
the 2.5 to 3.5 keV band, but since the amplitude of modulation is supposed to be
at most 7% of the dark matter signal this implies a dark matter generated event
rate of 0.38 cts/kg/keV/day or more. The total rate in the experiment is 1.24
cts/kg/keV/day in this 2.5-3.5 keV band, so the dark matter rate is at least 31%
of the total. With such a large fraction of the total rate coming from dark
matter events in this 3 keV bump one would expect to see a corresponding bump in
the total rate spectrum and it is actually present. But the CDMS experiment in the Soudan mine saw no counts in 397.8 kg-days of
exposure, so the high DAMA/LIBRA rate seems unlikely - but not impossible given
the differences in the detector materials and methods. However, it is peculiar
that the annual modulation technique is being used when the ratio of dark matter
to background counts is this large.

Naked Eye Visible Gamma Ray Burst Afterglow from z=1!

19 Mar 2008 - The NASA satellite Swift has
detected the most
luminous explosion yet seen. Gamma Ray Burst
GRB080219B got slightly brighter than optical magnitude
6, the limit of naked-eye visibility, and has a redshift greater than
or probably equal to 0.937, the higher
of two absorption line redshifts. The absolute magnitude is then -38! The press
is catching up to this story: the New
York Times, the Associated
Press, and the Agence
France Presse all have articles on this. Here is the NASA
press release.

WMAP 5 year Data Released

5 Mar 2008 - WMAP released its five year dataset today,
with 7 papers and new maps and power spectra posted to LAMBDA. Highlights of the new results
include:

Definite evidence for light neutrinos. The presence of the neutrino
background was necessary from Big Bang
Nucleosynthesis results, but now the CMB requires their presence at 99.5%
confidence.

The epoch of reionization is now more than 3 sigma earlier than the redshift z=6.2 where
the Gunn-Peterson
effect blackens quasar
spectra.

The tensor:scalar ratio is now shown to be less than 0.2.

More than 400 radio sources are seen by WMAP.

The image at right
is a new combined CMB
power spectrum showing that a 6 parameter ΛCDM model still fits all the CMB
data as well as the Baryon Acoustic Oscillation signal and the supernova data.
Click on the image for a larger version.

The NASA
press release finally came out late on March 7. Coverage at Science
Daily, the New
Scientist, and the New
York Times, quoting me.

Supernova Progenitor Seen? - Probably Not

15 Feb 2008 - Roelofs, Bassa, Voss
& Nelemans (2008) comment on the claimed detection by Voss & Nelemans (2008, Nature, 451,
802) of an X-ray binary progenitor at the position of the Type Ia supernova
SN 2007on. They find that the X-ray source is probably still present, although
significantly fainter. Furthermore, with better astrometry the X-ray position is
slightly offset from the position of the supernova, by 1.18+/-0.27 arc-seconds.
Since a Type Ia supernova completely disrupts the white dwarf that explodes, a
surviving X-ray source is very unlikely. So the putative progenitor was quite
possibly a chance coincidence with a variable X-ray source.

Highest Redshift Galaxy? but no lines

12 Feb 2008 - The HST and the Spitzer Space Telescope have issued a
press
release claiming the detection of a galaxy at redshift
z=7.6. However, NO lines have been observed. Based on previous
z=10 galaxies, we should require two lines before believing any story like
this. The NASA budget must be tight.

Very Precise Distance to a Cepheid

11 Feb 2008 - Kervella et
al. report a distance to the Cepheid variable RS Puppis of 1992 +/- 28
parsecs. This distance was obtained geometrically using a light echo technique.
Cepheids are used to calibrate the Hubble constant
that determines the age and size of the Universe. ESO has issued a press
release. The paper will be published in Astronomy & Astrophysics.

Quasi-Steady State Cosmology Fails Again

18 Jan 2008 - Narlikar, Burbidge and
Vishwakarma (2007, J. Astr. & Ap., 28, 67) claim to fit the CMB
anisotropy data with the QSSC model. Not surprisingly, this claim is false.

Crafoord Prize to Sunyaev

17 Jan 2008 - the Crafoord Prize in Astronomy
and Mathematics was split between Rashid Sunyaev and two
string theorists. Sunyaev is famous for the Sunyaev-Zeldovich
effect and other studies of the Cosmic Microwave
Background. Born and raised in the Soviet Union, Sunyaev is now director of the Max Planck
Institute for Astrophysics in Garching near Munich.

Not Much Evidence for Cosmic Texture

07 Dec 07 - What is essentially a 1.4 standard deviation result is in today's
Science: Cruz et al. (2007, Science,
318,1612), a paper that explains the giant hole
in space by an unwinding texture event. A texture is a topological defect
like a cosmic string, and the model that cosmic structures were created by
topological defects was ruled out by COBE. But it is always
possible that a small fraction of cosmic structures are created by topological
defects, and Cruz et al. consider a model where that small fraction is just one
cosmic defect matched to the "cold spot" in the Cosmic Microwave Background
(CMB) found by WMAP. They find a
likelihood ratio of 2.5 to 1, which is normally considered to be
exp(n2/2) where n is the number of standard
deviations.

Cruz et al. do not consider the giant
void found in the direction of the cold spot. If both the cold spot and the
void can be explained by texture their model would gain in credibility. This
void has always been claimed to be evidence of a bridge
to another Universe, so it has certainly been a magnet for unusual theories.

Giant Hole in Space?

23 Aug 2007 - There is a widely picked up press
release about results by Rudnick
et al. (2007, ApJ in press) on explaining a WMAP cold spot reported
earlier. The original report on the WMAP cold spot was statistically weak since
the authors searched through roughly 100,000 combinations of position and
resolution, so finding an oddly cold spot was not too surprising. But the new
result shows that the WMAP cold spot coincides with an anomalous spot in the
radio survey NVSS. Rudnick et
al. have interpreted this as a very large void in the distribution of
matter in this direction, causing the cold spot via the late-integrated Sachs-Wolfe
effect. However, they have no distance information on the sources in the spot so
the interpretation is still uncertain. But the coincidence between the WMAP cold
spot and the NVSS low source count spot is intriguing.

The timing of the press release is a bit unusual, since the paper was
released on the preprint server in April, and has not yet appeared in print, so
neither of the usual hooks for timing press releases was used.

UPDATE: 19 May 2008 - Smith and
Huterer find no evidence for the void in the NVSS.

Big Bang Pioneer Passes

12 Aug 2007 - Ralph
Alpher who, along with his thesis adviser George Gamow and colleague Robert
Herman developed the hot Big Bang model, died today. Alpher and Herman's paper
(1949, Phys. Rev., 75, 1089-1095) gave two versions of the hot Big Bang, one
with To = 1 K and one with To = 5 K.
Fred Hoyle ignored
these results when he used the T(CN) = 2.3 K observed by McKellar (1939) as
evidence against the Big Bang in a 1950
book review.

Redshift 10 Galaxies?

12 Jul 07 - Stark et al. claim to
have detected Lyman alpha emission from
6 candidate objects with redshifts between 8.5
and 10.2. These are very faint sources which have been magnified by the gravitational
lensing of a foreground cluster of galaxies, and even then barely detected
with very long exposures on the Keck
telescopes. The negative image at right shows a near infrared image taken
with the Hubble Space Telescope,
and it is clear that whatever there is in the center of the circle is very
faint. But when the light coming from the center of the circle is spread out
into a spectrum using the NIRSPEC instrument built at
UCLA there is an easily visible clump in the spectral image, shown at left. This
is also a negative image, so the dark spot in the center of the circle is an
emission line. This spectral line is at a wavelength of 1.355 microns, which is
11.1 times longer than the rest wavelength of Lyman alpha, so if it really is
Lyman alpha, the redshift of this source is 10.1. Using my cosmology
calculator, one finds that the age of the Universe was 475 million years
when this galaxy emitted the light that we see. That light took 13.190 billion
years to reach us, and the galaxy is now 31.578 billion light years away from us
due to the expansion of the Universe.

One note of caution: a previous claimed
redshift 10 galaxy based on the same kind of evidence was not
confirmed.

Variable Constants?

21 Jun 2007 - A new
study of ammonia and carbon monoxide lines in a distant quasar shows that
the electron to proton mass ratio has remained quite constant. Earlier work with
ultraviolet lines of molecular hydrogen, redshifted into the optical, suggested
a small change in this ratio, but this new study uses radio astronomy which
allows much more precise measurements of line ratios.

Underground Laboratory Cosmology

09 Jun 2007 - Today I visited the Soudan Underground Laboratory near Tower,
MN. This is in an old iron mine in the Mesabi Iron Range, where hematite (70
percent iron by weight) was brought up from nearly 0.8 km underground. It is run
as a state historical park, so you can tour the engine house and see the antique
hoist, then hear the antique hoist crank up and lift the previous tourists out
of the mine. Then you put on your hard hat, get in the 1.2 meter square cage and
go down into the Earth. In the physics lab the lights and air handling system let you
forget you are so deep underground, and you find the MINOS far detector. MINOS
stands for Main Injector Neutrino Oscillation Search, and is an experiment that
generates a neutrino beam at Fermilab near Chicago, and send the neutrinos
through 800 km of rocks to the Soudan Underground Laboratory. There the 6000 ton
MINOS far detector sees about 2 or 3 neutrinos per day. Everything you see in
the physics laboratory had to go down in the 1.2 meter square cage! The MINOS
detector sees many cosmic ray muons and you can see the latest event on
the Web.

The MINOS experiment has confirmed the earlier results of the Super-Kamiokande
experiment that used atmospheric neutrinos. It appears that muon neutrinos
oscillate into tau neutrinos indicating a difference in mass squared of about
0.0025 eV2. While neutrino oscillation experiments only measure delta
mass squared values, this result indicates that neutrinos are probably not the
cosmological dark
matter, since if the tau neutrino has a mass of 0.05 eV, and the muon and
electron neutrinos are much lighter, then neutrinos make up only 0.1 percent of
the critical
density of the Universe, and the current model has 23 percent of the
critical density in dark matter.

The other cosmological experiment in the Soudan lab is the Cryogenic Dark Matter Search (CDMS). This
experiment is searching for dark matter made up of WIMPs. So far it
only has measured upper limits.

News of the
Universe Archive

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© 1996-2008 Edward
L. Wright. Last modified 20 Jun 2008