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Cosmology and art |
New on the tutorial:
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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© 1996-2008 Edward L. Wright. Last modified 20 Jun 2008