HUBBLE DEEP FIELD SURVEY REVEALS GALAXIES NEAR THE BEGINNING OF TIME

Credit: Robert Williams and the Hubble Deep Field Team (STScI) and NASA.

Several hundred never-before-seen galaxies are visible in this deepest-ever view of the universe, called the Hubble Deep Field (HDF), made with the Hubble Space Telescope. Besides the classical spiral- and elliptical-shaped galaxies, there is an astonishing variety of other galaxy shapes and colors that are important clues to understanding the evolution of the universe. Some of the galaxies may have formed less than one billion years after the Big Bang.

Representing a narrow "keyhole" view all the way to the visible horizon of the universe, the HDF image covers a speck of sky 1/30 the diameter of the full Moon (about 25% of the entire HDF is shown here). This is so narrow that just a few foreground stars in our Milky Way galaxy are visible and are vastly outnumbered by the menagerie of far more distant galaxies, some nearly as faint as 30th magnitude, or nearly four billion times fainter than can be seen with the naked eye. (The relatively bright object with diffraction spikes just left of center may be a 20th magnitude star.) Though the field is a very small sample of sky area, it is considered representative of the typical distribution of galaxies in space because the universe, statistically, looks the same in all directions. Thus, based on these observations, the universe may contain roughly 50 billion galaxies rather than the 10 billion of previous estimates.

The image was assembled from many separate exposures (342 frames total were taken; 276 have been fully processed to date and used for this picture) made by the Wide Field and Planetary Camera 2 for 10 consecutive days, December 18-28, 1995.

"The variety of galaxies we see is amazing. In time these Hubble data could turn out to be the double helix of galaxy formation. We are clearly seeing some of the galaxies as they were more than ten billion years ago, in the process of formation," said Robert Williams, Director of the Space Telescope Science Institute. Williams and the STScI team he assembled to conduct the observations hope they will unlock clues to fundamental cosmological questions: Will the universe expand forever? How long ago did the first galaxies appear? How have galaxies evolved over the history of the universe? Though months of detailed research and analysis lie ahead, HDF team astronomers believe they see evidence for a significant population of galaxies that existed when the universe was less than a billion years old.

HUBBLE TELESCOPE CAPTURES FIRST DIRECT IMAGE OF A STAR

Credit: Andrea Dupree (Harvard-Smithsonian CfA). Ronald Gilliland (STScI). NASA, and ESA.

This is the first direct image of a star other than the Sun made with the Hubble Space Telescope. Called Alpha Orionis, or Betelgeuse, it is a red supergiant star marking the shoulder of the winter constellation Orion the Hunter. The Hubble image reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar surface. The enormous bright spot, more than 10 times the diameter of Earth, is at least 2000 K hotter than the surface of the star.

The image suggests that an unforeseen physical phenomenon may be affecting the atmospheres of some stars. Follow-up observations will be needed to help astronomers understand whether the spot is linked to oscillations previously detected in the giant star, or whether it moves systematically across the surface under the grip of powerful magnetic fields.

The observations were made by Andrea Dupree, Harvard Smithsonian Center for Astrophysics, and Ronald Gilliland, Space Telescope Science Institute, who announced their discovery at the American Astronomical Society annual meeting in January.

The image was taken in ultraviolet light with the Faint Object Camera on March 3, 1995. Hubble is able to resolve the star even though its apparent size is 20,000 times smaller than the width of the full Moon -- roughly equivalent to being able to resolve a car's headlights at a distance of 6000 miles. Betelgeuse is so large that, if it replaced the Sun at the center of our solar system, its outer atmosphere would extend past the orbit of Jupiter.

MILLIMETER OBSERVATIONS SUGGEST GLOBAL DUST ACTIVITY ON MARS VISUAL CONFIRMATION SOUGHT

Todd Clancy, University of Colorado/Laboratory for Atmospheric and Space Physics, reported January 5 that observations from Kitt Peak suggest that a large-scale dust storm is probably occurring on Mars. Clancy is observing Mars with the 12-meter NRAO telescope, measuring atmospheric CO absorption lines at millimeter wavelengths. Normally, under clear atmospheric conditions, there is enough of a temperature difference between the martian surface and atmosphere to result in the formation of absorption features with high contrast. However, under dusty conditions, the surface-atmospheric temperature difference is smaller, and the absorption feature contrast is substantially decreased.

Observations from Kitt Peak in early January (at Ls=222) revealed lower CO absorption band contrast than usual, indicating an estimated 320K elevation in the atmospheric temperature above the 10-20- kilometer level. This amount of atmospheric heating is consistent with a global-scale dust storm, similar to, though not as large as, events reported by Clancy, Grossman, and Muhleman during April 1994 and April 1992. The storm has apparently just begun (atmospheric heating was not detected in this year's observations prior to Ls=222), and is probably only in the early to middle stages of the dust buildup. Additional millimeter observations were planned later in January in order to confirm the storm and to more accurately quantify the dust opacity.

It would be highly desirable to obtain visual confirmation of this dust event and scrutinize the storm itself, as well as to practice making groundbased support observations that are needed by the upcoming Mars Pathfinder mission. However, this is a difficult task, as Mars is currently only 4.0 arcsec in apparent diameter and only 13 from the Sun (and approaching conjunction). Both professional and amateur observers who can observe Mars are encouraged to do so to try to provide visual verification and additional information about the character of the dust storm. Unfortunately, the Hubble Space Telescope will not be able to observe Mars until September because of solar phase angle limitations. Interested colleagues should send questions, comments, or observing progress reports to Jim Bell, Cornell University, Department of Astronomy, Center for Radiophysics and Space Research, 424 Space Sciences Building, Ithaca NY 14853- 6801. Phone: 607-255-5911; fax: 607-255-9002.
E-mail: jimbo@marswatch.tn.cornell.edu
WWW: http://marswatch.tn.cornell.edu

MORE EXTRASOLAR PLANETS?

Geoffrey Marcy, San Francisco State University, and Paul Butler, University of California at Berkeley and San Francisco State, announced evidence for planets orbiting two Sun-like stars at the American Astronomical Society annual meeting in January. Using the Lick Observatory 3-meter telescope, they compiled radial velocity data by measuring the Doppler shift of each star's spectrum; this data represents the tug exerted by the companion object as it orbits the star.

Data from 47 Ursae Majoris, a fifth-magnitude G0-type star 46 light years away, suggest a companion 3.5 times Jupiter's mass in a circular orbit at 2.1 AU (roughly twice the Earth's distance from the Sun). The orbital period is about three years.The fifth magnitude, G4-type star 70 Virginis, about 78 light years away, has a radial velocity of up to 311 meters per second, which suggests a companion between 8 and 9 times Jupiter's mass orbiting at 0.43 AU (slightly larger than Mercury's orbit) every 117 days. The orbit is eccentric (e = 0.35) rather than circular, which suggests that the companion could be a brown dwarf rather than a true planet.

This detection technique only provides a minimum mass for a companion, however. The true mass is larger than this minimum by a factor of 1/sin i, where i is the angle between our line-of- sight to the star and the perpendicular to the orbital plane of the companion (i = 0 degrees means we are directly above or below the orbital plane; i = 90 degrees means that we are in the orbital plane).

According to David C. Black, Lunar and Planetary Institute, the jury is still out as to whether any extrasolar planets have been discovered. He considers the companion to 47 Ursae Majoris the only likely candidate with all others being brown dwarfs. Black notes that most people still use 10-20 Jupiter masses as the lower limit to the mass of a brown dwarf (thus anything less massive is deemed a planet), but that this number is based on what is probably the wrong mechanism for brown dwarf formation. When new theories on formation are taken into account, Black believes there could be planets more massive than brown dwarfs.