Number 63, January 17, 1992 by Phillip F. Schewe and Ben Stein|
GAMMA RAY ASTROPHYSICS IS VIOLENT . In one single-week interval, for example, quasar 3C279 emitted about 1054 ergs of energy in gamma rays, roughly the same energy you would get if all the particles in our Sun were to be annihilated into radiation. Although scientists don't yet know the nature of the engine which produces such stupendous supplies of gammas, the sources of gamma radiation can at least be inventoried and studied by the Compton Gamma Ray Observatory (GRO), launched in April 1991. GRO has now discovered, in addition to 3C279, three new quasars that emit gamma rays (although not on a continuous basis) at a rate of 1048 ergs/sec. Other GRO results: The observation of gammas with energies as high as 1 GeV from solar flares. More than 200 gamma bursters have now been found, and their distribution across the sky remains isotropic, almost surely ruling out the notion that they originate in the plane of our galaxy. Two leading explanations for the isotropy entail interesting problems of their own: If the bursters sit in the galactic halo, then the halo would have to be much larger than thought before, more than 150,000 light years in radius. If the bursters are extra-galactic, how could it be that so many gammas had traveled so far? A third gamma pulsar, Circinius, has been discovered; the other two are the Crab and the Vela pulsars and, unlike these two, Circinius beams gammas only once for each pulsar rotation instead of twice. Finally, GRO has monitored the electron-positron annihilation radiation from the center of our galaxy and found that, unlike previous, less-sensitive measurements by other detectors, the radiation does not seem to vary with time.
BEST EVIDENCE YET FOR A NEARBY BLACK HOLE . New Hubble Space Telescope (HST) images of galaxy M87 show a bright concentration of light at the core of the galaxy. The density of the light is some 300 times higher than what you would expect for a galaxy of this type. This and the presence of an energetic, collimated jet of material extending out more than 4000 light years from the core can best be explained by supposing that a black hole with a mass of 2 to 3 billion solar masses sits at the galactic hole, according to Tod R. Lauer of the National Optical Astronomical Observatories. Upcoming spectroscopic studies will test this hypothesis by measuring the velocities of stars near the galactic nucleus.
YOUNG STAR CLUSTERS IN GALAXY NGC1275 . Jon Holtzman of the Lowell Observatory released high-resolution HST images of galaxy NGC1275 which show 50 bright objects believed to be massive, blue (and therefore very young, perhaps only hundreds of millions of years old) globular clusters. This is surprising because globular clusters in our own galaxy are among the oldest stars (typically 10 billion years old) in the Milky Way. Holtzman said that not only are these clusters blue, but almost precisely the same shade of blue, suggesting that the stars there formed at about the same time; this, Holtzman believes, may have been the result of two galaxies colliding or merging to form the present NGC1275.