Number 109, January 8, 1993 by Phillip F. Schewe and Ben Stein THE TEMPERATURE OF THE UNIVERSE IS 2.726 K . New data from COBE's Far Infrared Absolute Spectrophotometer (FIRAS) presented at this week's meeting of the American Astronomical Society (AAS) in Phoenix show that the energy spectrum of the cosmic microwave background is extremely close to that of a perfect black body at 2.726 K. The agreement between the theoretical and observed spectra (consisting of measurements at 34 different wavelengths from 0.5 to 5 mm) is 30 times better than for the FIRAS data released 3 years ago. FIRAS leader John Mather of NASA/Goddard (301-286-8720) said the agreement is so good that constraints can be placed on the amount of radiant energy in the universe (no more than 0.03% of the total) that could have been emitted more than a year after the big bang. Some cosmologists have proposed that such energy might have been released by supermassive supernovas, by black holes, or by the decay of unstable particles. A DENSE CLUMP OF DARK MATTER apparently lurks within a small group of galaxies, the NGC 2300 group (containing only 3 galaxies), according to scientists using the German satellite Rosat. The mass of the dark matter was estimated to be 10 to 30 times that of the visible matter in the group, a ratio much higher than was expected for such a small group of galaxies. Dark matter cannot be observed directly of course; rather, Rosat measured x rays coming from a cloud of hot gas inside the group. The compact extent of the cloud (1.3 million light years across) and its high temperature (10 million K) cannot be accounted for by the constraining effects of the visible galaxies alone, but only by the additional shepherding presence of the dark matter. Richard Mushotzky of NASA/Goddard, one of the scientists to report on the Rosat results at the AAS meeting, suggested that if the density of dark matter inferred for NGC 2300 were typical of other areas in the universe---and small galaxy groups are more common than rich clusters (containing hundreds or thousands of galaxies) which, ironically, seem to have a lower-than-expected amount of dark matter---then there might be enough matter (dark plus visible) present to brake and reverse the expansion of the universe. A SOURCE OF INFRARED RADIATION HAS BEEN DISCOVERED NEAR THE GALACTIC CENTER at the location of the object called Sgr A*. The new IR results reinforce the idea, established by previous measurements of Sgr A* at radio, x-ray, and gamma wavelengths, that a black hole resides at the core of the Milky Way. At the AAS meeting, Laird Close of the University of Arizona (602-621-6523) presented pictures of the galactic core at wavelengths of 1.6 and 2.2 microns made using the 2.3-m telescope at Kitt Peak. The observations, employing adaptive-optics techniques in the infrared for the first time, had sufficient resolution to show that the IR source was no larger than 0.006 light years across. Arizona astronomer Joseph Haller presented separate IR studies of the velocities of stars as a function of distance out from Sgr A* showing that the velocities increased from nearly zero at a distance of 1.4 light years from Sgr A* to a velocity of nearly 100 km/sec at a distance of 0.7 light years. This pattern, plus the determination that there must be at least 100 times more mass inside the 0.7-light-year distance than can be accounted for by the observable stars alone, suggests to Haller that there should be a 900,000-solar-mass black hole at Sgr A*.