2 Jul 99 - Riess et al. report that distant, high redshift supernovae have significantly shorter rise times than the nearby supernovae used to calibrate the luminosity vs. decay time relationship. This is an indication of some kind of evolution in the supernova population, and if this evolution also affects the peak luminosity for a given decay rate it will directly affect the cosmological conclusions drawn from distant supernovae.
15 Apr 99 - Chen,
Lanzetta & Pascarelle report a galaxy with
redshift z =
The galaxy is indicated by the tickmark on the 2.3" by 22" image shown
above, taken with the STIS
instrument on the HST.
This report is based on a single emission line at 933.4
nm which they identify with the
Lyman alpha emission line of
hydrogen, which is emitted with a wavelength of 121.5 nm.
The spectrum taken with STIS in the slitless mode is shown at right.
also a break in the continuum
at 930 nm which they identify with the Lyman alpha forest.
The blue curve shows the smoothed spectrum which follows the continuum.
This is a more detailed article about the galaxy reported
on 24 Sep 98, and it appears in today's Nature.
26 Mar 99 - Nature has articles about the gamma-ray burst GRB990123 which was captured "live" by the Robotic Optical Transient Search Experiment (ROTSE) instrument reaching 9th magnitude in the optical, has a redshift > 1.6, and which had a gamma-ray fluence of 0.0003 erg/cm2. For Ho = 65 km/sec/Mpc, matter density OmegaM = 0.25 and cosmological constant lambda = 0.75, the luminosity distance of this source is 43 billion lightyears. [The value 9 billion light years reported in the newspapers seems to be some useless value like the light-travel distance.] The total energy released in the burst is
E = fluence*4*pi*DL2/(1+z) = 2.4*1054 ergswhich corresponds to the total annihilation and conversion into gamma rays of 1.35 solar masses of matter.
18 Dec 98 - Chen et al. report photometric redshifts for galaxies in the Hubble Deep Field South, including one galaxy with z = 10.56! This requires confirmation and followup, of course. The galaxy is so faint that spectroscopy will have to wait for the Next Generation Space Telescope.
11 Dec 98 -
The Sloan Digital Sky Survey
with redshifts greater than 4.9
in a tiny fraction of their planned survey area. The old quasar distance
record was a redshift of 4.897.
The spectrum of the new quasar with
redshift z = 5.0, seen at right, has three obvious
so the line identification is secure and thus the redshift is reliable.
Currently the most distant known objects are galaxies, including one
with a redshift of
24 Sep 98 - Lanzetta et al. report an object with a spectroscopic redshift of z = 6.68, based on only one emission line at 930 nm, assumed to be the Lyman alpha line, with a jump in the continuum at the line. This is the most distant known object, but confirmation of the distance will require spectroscopic observations in the infrared, which may be possible in 1999 using the NIRSPEC instrument on the Keck telescopes.
28 Aug 98 - Mather et al. (1998, ApJ in press), "Calibrator Design for the COBE FIRAS", give a slightly reduced value for the CMB temperature, To = 2.725 +/- 0.002 K, with 95% confidence. This important cosmological observable is now known to better than one part per thousand.
20 Jul 98 - A galaxy in the Hubble Deep Field which is very faint in the visible but relatively "bright" in the IR has an emission line at 803 nm, identified as Lyman alpha at z = 5.60.
5 Jun 98 - The Super-Kamiokande experiment released a press release tied to a presentation at the Neutrino'98 meeting, which announced that Super-K had confirmed that muon neutrinos produced in the Earth's atmosphere by cosmic rays were changing ("oscillating") into a different kind of neutrino during their passage through the Earth. It is an interesting commentary on science journalism that this press release generated front page headlines, while an article in the 29 May 98 Science by Joel Primack (v 280, pp 1398-1400), which states exactly the same properties of neutrinos based on preprints available at xxx.lanl.gov, did not.
The oscillation data do not determine the masses of neutrinos, but rather the difference between the squared masses of two neutrino types. The atmospheric muon data gives m22 - m12 = 0.001 to 0.01 eV2. Since the sum of the three neutrino masses has to be 5 to 7 eV to be cosmologically interesting, this result from Super-K is a mixed blessing for Mixed Dark Matter models, since is shows that
7 May 98 - GRB 971214 came from a galaxy with redshift z = 3.42 according to Kulkarni et al. (1998, Nature, 393, 35). This source was seen by BeppoSAX as a gamma ray burst and as a fading X-ray transient, and the fading optical transient was seen by observatories around the world. The BATSE gamma-ray fluence for this trigger (#6533) is 1.1*10-5 erg/cm2, and with H0 = 50 km/sec/Mpc and Omega = 1 this requires a gamma-ray emission in the source of 2.3*1053 ergs. This is about the same as the neutrino emission from a Type II supernova but it all has to come out as gamma-rays.
9 Apr 98 - Yahoo reports bigger than expected profits. Given the sorry state of its cosmology listings, one has to ask why?
12 Mar 98 - Dey et al. report a galaxy at redshift z = 5.34 based on a single line in the spectrum at 771.7 nm wavelength which they assume is Lyman alpha. Even though this is based on only one line, the line profile and continuum dropoff on the blue side look very much like Lyman alpha lines in other high redshift objects. Esther Hu et al claim an object at z = 5.64 but the spectrum is much weaker because of the strong night sky emission.
4 Mar 98 -
Results reported at the DM98 meeting sponsored by UCLA
are coming out in the popular press: the 3 Mar 98 New York Times
and the 27 Feb 98 issue of Science (1998, 279, 1298).
These stories both cover the High-Z SN Team results on
distant supernovae, which are in accordance with the LBL results
reported below for 6 Feb 98.
Both groups support a non-zero cosmological
constant, a term Einstein added to general relativity which allows
a static Universe because it gives a repulsive gravity.
More about the cosmological constant.
Redshift-distance plot of the distant supernovae, and a plot showing the error ellipses of the two groups.
6 Feb 98 - The 30 Jan 98 issue of Science (1998, 279, 651-652) has a News article with a graph from the LBL (Perlmutter) group with many more SNe included, which indicates that OmegaM - 0.863*lambda = -0.40 +/- 0.15(stat) +/- 0.81(sys) and 0.863*OmegaM + lambda = 0.97 +/- 1.92. A more detailed write-up gives 0.8*OmegaM - 0.6*lambda = -0.2 +/- 0.1 (stat), and OmegaM = 0.28+0.09-0.08 for a flat OmegaM + lambda = 1 model. The potential systematic errors could be large, but this is good evidence for a non-zero lambda (cosmological constant). [The High-z SN Team results (see 4 Mar 98 above) can be written as OmegaM - 0.823*lambda = -0.31 +/- 0.14 and 0.823*OmegaM + lambda = 0.95 +/- 1.92 which are remarkably similar to the LBL results.]
9 Jan 98 -
(Diffuse InfraRed Background Experiment) team on the
satellite announce that they have detected a Far InfraRed Background
(FIRB) at 140 and 240
Images of the sky before and after foreground removal are on the Astronomy Picture of the Day Web site.
This FIRB is very small: if you put an IR detector in your refrigerator, and closed the door so the light went out, the detector would still see 7 billion times more power than the far IR background.
Five papers: Hauser et al. giving the FIRB conclusions, Kelsall et al. describing the zodiacal light foreground removal, Arendt et al. describing the galactic foreground removal, Dwek et al. giving a theoretical interpretation, and Fixsen et al. comparing the FIRAS data to the DIRBE data have been submitted to The Astrophysical Journal. Previously posted or published papers by Schlegel, Finkbeiner & Davis (1998) found a similar FIRB using DIRBE data, and by Puget et al. (1996, A&A, 308, 5) found a similar background level using FIRAS data.
The detections reported by Hauser et al. are 25.0 +/- 6.9 nW/m2/sr at 140 microns and 13.6 +/- 2.5 nW/m2/sr at 240 microns. Fixsen et al. give 14 nW/m2/sr for the total intensity longer than 125 microns. These values are 1-2% of the Cosmic Microwave Background (CMB) radiation (the 2.725 K blackbody). In the S10 notation often used for sky brightness, 14 nW/m2/sr is about 1.4 mbol=10th magnitude stars per square degree.
16 Dec 97 - Perlmutter et al.(1998, Nature, 391, 51-54) get data on a supernova at z = 0.83. It shows a time dilation factor of 1.86+0.31-0.09 compared to the expected 1+z = 1.83, and agrees with Garnavich et al. (1998, ApJL, 493, L53-L57) that the density is less than the critical density, with Omega = 0.2 +/- 0.4 for no cosmological constant. This new point has been added to my large redshift magnitude-redshift diagram.
6 Nov 97 - This is the 6000'th birthday of the Universe, according to the Archbishop Ussher.
13 May 97 - GRB970508 has an associated optical transient source that shows absorption lines with a redshift of z = 0.835. From the absence of the Lyman alpha forest it is likely that the object itself is at z < 2.1, and it must have z > 0.835. Somehow the LA Times 15 May 1997 story converted these redshifts into distances between 2 and 7 billion light years. They must have been using Hubble's original value for Ho.
So we welcome a new class of objects to the field of cosmology. And we still don't know how to radiate 1051 ergs of gamma rays in a few seconds. This energy is all the energy the Sun will radiate in its entire 10 billion year lifetime.
18 Apr 97 - Nodland and Ralston claim an intrinsic rotation rate for polarized light that varies with the cosine of the angle relative to a preferred axis. But Eisenstein and Bunn point out statistical flaws in Nodland and Ralston's work. I have found that using Eisenstein and Bunn's null hypothesis increases the probability of producing Nodland and Ralston's result by pure chance by more than a factor of 100(!) for the case where the axis is specified, and a factor of 60 when the axis is found from the data. As a result, the probability of getting the Nodland and Ralston work by chance is 30 percent, which means that their result is not statistically significant. Carroll and Field have done similar calculations and also find that there is no detectable intrinsic rotation. Leahy has made detailed studies of sources where the polarization angle can be predicted accurately, and finds that any rotation is at least 30 times smaller than that predicted by Nodland and Ralston. Even though the effect is clearly not present, Professor J. W. Moffat and net-kooks Ray Tomes and Archimedes Plutonium have each announced that the anisotropic rotation supports their theories.
10 Apr 97 - Most distant object record broken! Redshift z = 4.92 (Franx et al.)
10 Apr 97 - HIPPARCOS parallax data on subdwarfs puts globular cluster further away -- their stars more luminous and younger. (Reid)
1997 - HIPPARCOS Cepheid parallaxes increase distance scale by ten percent (Feast & Catchpole, 1997, MNRAS, in press)
1994 - Wendy Freedman et al. (1994, Nature, 371, 757-762) announce Ho = 80 +/- 17 km/sec/Mpc based on HST observations of Cepheids in the Viro Cluster, producing a major flap over "the Universe is younger than the oldest stars". But the Universe has gotten older and the oldest stars have gotten younger since then.
1992 - Smoot et al. (1992, ApJL, 396, L1) announce the discovery of intrinsic anisotropy of the microwave background. See Bennett et al. (1996, ApJL, 464,L1) for a summary of the final COBE DMR results.
1990 - Mather et al. (1990, ApJL, 354, L37) show microwave background spectrum is within 1% of a blackbody. Later Fixsen et al. (1996, ApJ, 473, 576) show that it is within 0.005% (RMS) of a 2.728 K blackbody.
1969 - Conklin (1969, Nature, 222, 971) discovers the dipole anisotropy in the microwave background. This was confirmed by Henry (1971, Nature, 231, 516) and reconfirmed by Corey & Wilkinson (1976, BAAS, 8, 351) before the first flight of the U-2 experiment, so it is clear that Smoot, Gorenstein & Muller (1977, PRL, 39, 898) did not discover the dipole, but they did make a good measurement of it.
1965 - Penzias & Wilson discover the microwave background: "A Measurement of Excess Antenna Temperature at 4080 Mc/s" (1965, ApJ, 142, 419).
1948 - Alpher & Herman (1948, Nature, 162, 774) predict T = 5 K for Universe.
1941 - Adams (1941, ApJ, 93, 11) reports on the CN R(1) line - first evidence of microwave background.
1933 - Zwicky finds that 90% or more of the matter in clusters of galaxies is dark.
1929 - Hubble discovers the expanding Universe: "A Relation between Distance and Radial Velocity among Extragalactic Nebulae" (1929, PNAS, 15, 168).
1922 - Alexander Friedmann finds solutions of General Relativity representing homogeneous isotropic Universes expanding from a singularity - the Big Bang models.
1917 - de Sitter (1917, MNRAS, 78, 3) constructs a cosmological model which shows a redshift. [Now we usually change variables to put the de Sitter metric into the metric of the Steady State model with exponential expansion and flat spatial sections.]
1917 - Einstein models the Universe as a static homogeneous isotropic solution of General Relativity by introducing the cosmological constant.
Tutorial: Part 1 | Part 2 | Part 3 | Part 4 | Age | Distances | Bibliography | Relativity
© 1997-2000 Edward L. Wright. Last modified 20-Jul-2000