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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 (125 pages, 397 equations, 50 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 these course Web sites get closed, you can use these backup Postscript copies of the A140 or the A275 notes. Use Ghostscript to view these files or save them to disk and send them to a Postscript printer.
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.
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.
14 Apr 2007 - Preliminary results from the GP-B mission were reported at the APS meeting in Jacksonville, FL today. Everything is consistent with the predictions of General Relativity, but the accuracy achieved to date is disappointing. There is a good post on this at Cosmic Variance.
There were two major glitches in the GP-B experiment:
Further data analysis may reduce this uncertainty. But Murphy, Nortvedt & Turyshev claim that lunar ranging has already verified the frame dragging effect to 1 part per thousand, and GP-B is very unlikely to get a final accuracy close to this precision.
05 Mar 2007 - A new preprint gives results on the change in the fine structure constant alpha. for a quasar at z = 1.84. The change is insignificant and in the opposite direction to earlier reports. The fine structure constant is probably constant. Here is a graph of all the results.
04 Jan 2007 - Wood-Vasey
et al. (2007) and
Miknaitis
et al. (2007) present data from the ESSENCE supernova project.
I found that their distance moduli were 0.106 mag higher than those in
Riess et al. (2007) on the low redshift calibration set
in common, so I subtracted this constant and added the ESSENCE supernovae
to the Riess etal (2007)
dataset.
There is enough scatter in this ΔDM to make me think that this
combination of datasets
will have to done again by someone in one of the supernova teams, but I give
it here for a first look analysis.
Click on the small plot at right to see the resulting
plot, and find the binned data table toward the bottom of my
supernova cosmology page.
There is no great change to the picture, but it is good to see another
group getting consistent results on supernovae.
Of course some of the parameter estimates reported in
Wood-Vasey
et al. (2007) are absurd. Figure 13 showing the limits
on the dark energy equation of state
shows w(z) = w0 +wa(1-a) with (w0,
wa) = (-1.7,3) as being within the 1 sigma contour. But
this combination gives a dark energy density much larger than the matter
density at last scattering. This is a consequence of not having enough
data to constrain the variable w. But the take home message,
"A w = -1, flat-Universe model is consistent with our data" makes perfect
sense.
18 Dec 06 - Kashlinsky et al. issued a press release claiming that fluctuations in the background of deep infrared images from the Spitzer Space Telescope are due to very distant objects with high redshifts, z > 7. But Cooray et al. show that masking faint galaxies visible in HST images eliminates the fluctuations seen by Kashlinsky et al. These HST galaxies have photometric redshifts in the range 1 < z < 2. This redshift range corresponds to the well known peak in star formation, so there is nothing surprising or newsworthy in the IR fluctuations. Full disclosure: I am a co-author on Cooray et al.
So the answer to the question in the title is: NO! As is always must be, according to Hinchliffe's rule: if the title is a question, the answer is `no'.
12 Dec 06 - Brad Schaefer has posted
his paper about the
gamma-ray burst (GRB) Hubble diagram. I have binned data from
the table in this paper to compute the
luminosity distance
vs. redshift and used it to
extend my plot based on supernovae.
While the GRB distances derived by Schaefer are quite imprecise
relative to the accuracy obtained with supernovae,
they extend to much higher redshifts.
This new data is consistent with the consensus flat
vacuum energy dominated
ΛCDM model, but it is not consistent with the closed
vacuum dominated model that fit the supernova data alone.
Click on the small graph at right for a
larger version. It shows
that the high redshift data is useful for constraining the geometry
of the Universe. Both an equation of state
different than w=-1 or a non-flat Universe with
Ω
not equal to 1 affect the distance
vs redshift starting at order z3, so these parameters are
hard to separate at low and moderate redshifts. Getting high z
data helps considerably.
16 Nov 06 - NASA held a press telecon today about dark energy, but neither the
press release nor the
images accompanying it contained any useful information.
UPDATE: 20 Nov 06 - The Riess et al. paper has reached the preprint server and provides the information the press office stripped out. The paper assumes that the Universe is flat when trying to find the properties of the dark energy, and bases this assumption on the fact that a flat Universe with a cosmological constant fits all the available data. Therefore the conclusion of this paper, which is that the dark energy looks like a cosmological constant, is built into the assumptions. This analysis is not sound logic. But the data are sound, and everything remains reasonably consistent with a flat Universe with a cosmological constant. I have updated my supernova cosmology page using these new results.
14 Nov 2006 - Two preprints describing the instrument and the data analysis for the MAXIPOL balloon-borne polarization experiment were posted today. The data were taken 3.5 years ago, and the final results are an E-mode polarization amplitude of 55+51-45 μK2 in the range of angular scales from 0.3 to 1.2 degrees. The prediction from the standard flat vacuum-dominated ΛCDM cosmology with accelerating expansion is 14 μK2. This result is consistent with the standard model but also consistent with zero. The South Pole-based experiment DASIPOL got better results earlier
03 Oct 2006 - John Mather and George Smoot have won the 2006 Nobel Prize in Physics for their work on COBE. Mather was the PI on FIRAS, the instrument to measure the spectrum of the Cosmic Microwave Background (CMB). Smoot was the PI on the DMR, the instrument to measure the anisotropy of the CMB. Of course many others including myself worked on COBE. See my E-mail to the COBE team announcing the discovery of the DMR signal, which is part of my view of the history of the CMB up until WMAP which is still observing. John Mather mentioned the October 1991 draft paper I presented to the COBE Science Working Group in his book, "The Very First Light".
30 Sep 2006 - The Los Angeles Times has a story today about the paper that suggests the Universe might be egg-shaped, and that this might explain the low quadrupole seen in the WMAP (and COBE DMR) CMB anisotropy maps. This was a silly paper and I said as much to the reporter John Johnson. Adding an additional quadrupole from the ellipsoidal Universe will make the probability of the low observed quadrupole even smaller, unless there is a reason that the quadrupole from the ellipticity will be equal and nearly opposite to the quadrupole from inflation. No such reason is given in this paper. Unfortunately the referees for the Physical Review Letters missed this, and the American Institute of Physics issued a press release (subscription) about the paper.
14 Sep 2006 - Kramer et al. report on an analysis of 2.5 years of timing data on the double pulsar in a paper published in Science Express (subscription) online on 14 Sep 2006. The printed version will appear in Science. The neutron stars masses are now 1.3381 +/- 0.0007 and 1.2489 +/- 0.0007 solar masses. Four post-Keplerian parameters of the binary are determined and all agree with GR, to accuracies of 0.3 +/- 1.4%, 0.36 +/- 0.68%, 0.013 +/- 0.05%, and 0.9 +/- 0.55%.
14 Sep 2006 - Iye et al. report a galaxy at z=6.96 with a one line redshift. Since the reported z=10 galaxy fell apart, this is the highest redshift spectroscopically measured to date.
6 Sep 2006 - Andrew Lange and Paolo de Bernardis have won the Balzan Prize for their work with the CMB anisotropy experiment BOOMERanG. Of course the first BOOMERanG results were miscalibrated, giving a 10% error in the acoustic scale, but this was corrected in 2001.
21 Aug 2006 -
NASA announced updated information about the "bullet cluster"
1E0657-56 today.
Two clusters of galaxies have recently collided in this X-ray source.
This cluster is filled with hot gas so X-ray observations by the
Chandra X-ray Observatory
show where the ordinary matter is located.
90% of the ordinary matter (the "baryonic" matter) is hot gas.
The new results
[Clowe et al.,
Bradac et al.]
use gravitational
lensing of background galaxies to
show where the sources of gravity are located.
The sources of gravity in the cluster are not located where the ordinary
matter is located, so this cluster is a counter-example to
MOND.
All of this was known in 2003
but with less precision. Sean Carroll has a
nice
post about this at
Cosmic Variance.
I have set up a
page that blinks back and forth among different views of this
cluster.
15 Aug 2006 - The Gruber Prize in Cosmology was awarded to the COBE team at the IAU meeting in Prague today. That includes Ned Wright. [Physics Web, Yahoo]
11 Aug 2006 - Macri et al. give a Cepheid distance to NGC 4258, where Herrnstein et al. found a distance of 7.2 Mpc based on observing the velocity and angular radius of a disk of masers around the nucleus, and both the angular velocity and the centripetal acceleration of the masers. Cepheids in NGC 4258 were 10.88 magnitudes fainter than Cepheids of the same period in the LMC giving a distance of 48 +/- 2 (random) +/- 3 (systematic) kpc for the LMC. This agrees very well with the light echo distance of 47 +/- 1 kpc for the LMC based on SN 1987A.
The final value for the Hubble constant is Ho = 74 +/- 3 (random) +/- 6 (systematic) km/sec/Mpc which agrees very well with the current concordance models. Oddly enough, the second author on this paper is also the second author on another recent result that claims a significantly lower value for Ho. But none of the recent differences in Ho determinations come close to the old Hubble constant wars between the Sandage and de Vaucouleurs camps.
05 Aug 2006 - Ohio State astronomers have measured a new precise distance to the nearby galaxy M33 based on a spectroscopic eclipsing binary. Their value is 15% larger than the old Cepheid based distance. By itself this says nothing about the Hubble constant because M33 is so close to the Milky Way that its radial velocity is dominated by random motions, not the expansion of the Universe. But it could indicate that Cepheid distances are incorrect by 15%.
If so, the Hubble constant would be smaller: about 61 instead of 72 km/sec/Mpc. But the claim in the OSU press release that "the universe could be [...] 15 percent older" is incorrect. If the Hubble constant is lower, then CMB anisotropy data require that OmegaM, the ratio of the matter density to the critical density, be higher, so the vacuum energy is lower, and the change in the age of the universe is considerably smaller, as shown in graph at right above [click on the graph to enlarge] which shows the age vs. Ho for CMB consistent models as the solid curve, and the 1/Ho behavior assumed by the OSU press release as the dashed curve. So the Universe would not be 15% older but perhaps 7% older.
The claim that the Universe would be 15% larger is partially incorrect. Even though relatively nearby galaxies would be 15% further away the actual size of the Universe would go from infinite (flat) to finite (closed) but very big, which is a smaller Universe. The distance to distant quasars at redshift z=6 would increase by only 4%, and the distance to the last scattering surface changes less than 0.5% because this is what is fixed by the CMB.
CNN quoting space.com and
John Johnson of the
LA Times accepted the press release's claims of
a 15% older and larger Universe uncritically.
The real news is that a new method for precision distance measurements
has achieved its first result. It will be averaged in with other
methods used to calibrate the Cepheid period-luminosity relation and
lead to a few percent decrease in the Hubble constant.
One of the methods to be averaged will be the Sunyaev-Zeldovich effect which gives Ho = 77 +/- 10 km/sec/Mpc according to a recent paper. This agrees with the values of Ho from WMAP and HST quite well.
31 Jul 2006 - Today's Space News has a graph of launches to Earth orbit or beyond per year since 1957. 2005 had the fewest launches since 1961. If you think this is a bad thing, write your Congressman and Senators! Competitively selected small unmanned science missions like the Explorer and Discovery programs have been particularly hard hit by the underfunding of the Vision for Space Exploration.
Click on the thumbnail at right for a larger version.
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