New names and old puzzles

The next-generation successor to the Hubble Space Telescope will be known as the James Webb Space Telescope, in honour of James E Webb, NASA's second administrator, who led the agency during a major era of expansion from February 1961 to October 1968. Although Webb is best known for leading Apollo and the series of lunar exploration programmes that culminated in the first human landings on the Moon, he also initiated a space-science programme that included America's first missions to Venus and Mars. The Webb Telescope is scheduled for launch in 2010 aboard an expendable launch vehicle. It will take about three months for the spacecraft to reach its destination, the second Lagrange Point (L2), 1.5 million km from Earth. At this distance, it will be too far away for servicing by space shuttle astronauts, but a shield on only one side of the observatory can protect the instruments from the light and heat of both the Sun and Earth. As a result, the observatory can be cooled to –200 °C without complicated refrigeration equipment, making infrared observation possible. Webb will carry a segmented primary mirror at least 6 m in diameter, folded during the launch. The new telescope will carry a near-infrared camera, a multi-object spectrometer and a mid-infrared camera/spectrometer. The UK Astronomy Technology Centre at the Royal Observatory, Edinburgh, will help to construct the mid-infrared camera/spectrometer as part of a European collaboration. The Goddard Space Flight Center manages the James Webb Space Telescope for NASA's Office of Space Science. The programme has several industry, academic and government partners, as well as the European Space Agency and the Canadian Space Agency (www.ngst.nasa.gov). New evidence from NASA's Chandra X-ray Observatory supports the existence of cold dark matter. The Advanced CCD Imaging Spectrometer on Chandra was used to observe NGC 720, which is about 80 million light years from Earth, for 11 hours. The data show that it is enveloped in a slightly flattened, or ellipsoidal cloud of hot gas whose orientation differs from that of the visible galaxy. The shape of the hot gas cloud requires a flattened dark matter halo about five to ten times the mass of the stars in the galaxy. “The shape and orientation of the hot gas cloud require it to be confined by an egg-shaped dark matter halo,” said David Buote (University of California, Irvine), lead author of a report in the 20 September issue of The Astrophysical Journal. “This means that dark matter is not just an illusion due to a shortcoming of the standard theory of gravity – it is real.” The researchers also found that the Chandra data fit predictions of the cold dark matter theories, according to which dark matter consists of slowly moving particles that interact with each other and “normal” matter only through gravity. “Chandra's ability to identify precisely and locate the point-like sources contaminating the diffuse emission in the X-ray image was essential,” said Buote. “Only then could we make accurate measurements of the shape and orientation of the X-ray image contours” (chandra.harvard.edu and chandra.nasa.gov). Scientists at the Carnegie Observatories in Pasadena, California, have uncovered six times the expected number of active, supermassive black holes in a single viewing of a cluster of galaxies, a finding that has profound implications for theories as to how elderly galaxies fuel the growth of their central black holes. The finding suggests that voracious, central black holes might be as common in old, red galaxies as they are in younger, blue galaxies, a surprise to many astronomers. The team found six red galaxies with high X-ray activity during a nearly 14-hour Chandra observation of a galaxy cluster named Abell 2104, over 700 million light years from Earth. Only one active galaxy was expected. Previous surveys of galaxy clusters at optical wavelengths have found that about only 1% of the constituent galaxies have Active Galactic Nuclei (AGN). However, this latest Chandra observation, if typical, raises the proportion to about 5%. Follow-up optical observations were made with the 6.5 m Walter Baade Telescope at the Las Campanas Observatory in Chile. “With Chandra, we have found that even ancient galaxies with 10-billion-year-old stars can have central black holes still actively pulling in copious amounts of interstellar gas. This activity has simply been hidden from us all this time. This means these galaxies aren't over the hill after all and our theories need to be revised,” said Dan Kelson, co-author of a paper in the 10 September issue of The Astrophysical Journal Letters. The question now is, how do these black holes produce bright X-ray sources, similar to those observed in much younger galaxies? It may be that galaxies are better at holding on to a supply of gas and dust than previously thought, particularly near their central, supermassive black holes. The presence of so many AGN could also contribute to the radio and infrared radiation from the clusters, which until now was thought to be almost exclusively a product of star formation. Estimates of the amount of star formation taking place in galaxy clusters may be too large. Medium-size black holes really do exist, according to the latest findings from the Hubble Space Telescope, but scientists had to look in some unexpected places to find them. A team led by Roeland Van Der Marel (Space Telescope Science Institute) has uncovered a black hole in the centre of the M15 globular cluster, 32 000 light years away in the constellation Pegasus. His collaborator Joris Gerssen, also of the Space Telescope Science Institute, calculated that the black hole had 4000 times the mass of our Sun. In a separate observing programme, a team led by Michael Rich (UCLA) found a 20 000-solar-mass black hole in the giant G1 globular cluster, located 2.2 million light years away in the Andromeda galaxy. Both of these discoveries lie mid-way between previously recognized small black holes only a few times the mass of our Sun, and supermassive black holes in galactic centres that are millions or billions of times more massive than the Sun. The findings also seem to indicate that some yet-to-be-discovered underlying process makes a black hole's mass proportional to the mass of the star system it inhabits. Supermassive black holes in the centres of galaxies typically represent about 0.5% of the galaxies' mass, and the black holes now found in globular clusters, which are 10 000 times less massive than a galaxy, also seem to obey this trend. “The intermediate-mass black holes that have now been found with Hubble may be the building blocks of the supermassive black holes that dwell in the centres of most galaxies,” said Karl Gebhardt (University of Texas at Austin). Previous X-ray observations with ROSAT and Chandra identified ultra-bright X-ray sources that could also be interpreted as intermediate-mass black holes in star-forming galaxies. However, alternative interpretations for these X-ray sources continue to exist. By contrast, Hubble's measurements are based on the velocities of stars in the cores of globular clusters, which yield a direct measurement of the black hole masses. Although the M15 globular star cluster is close enough for individual star speeds to be measured, the G1 observations rely on measurements of the collective properties of many stars. In both cases, the black hole can be identified by searching for a rise in velocities toward the cluster's centre. Stars close to the black hole orbit at a faster rate (oposite.stsci.edu/pubinfo/pr/2002/18). Observations by the Hubble Space Telescope indicate that Kuiper Belt Object 2002 LM60 is the largest object found in the solar system since the discovery of Pluto 72 years ago. Approximately half the diameter of Pluto, the icy world called “Quaoar” (pronounced kwa-whar) by its discoverers, is the most distant solar system object ever to be resolved by a telescope. The object was initially detected by Michael Brown and Chadwick Trujillo (California Institute of Technology) earlier this year, with the aid of the ground-based Palomar Oschin Schmidt telescope, where 2002 LM60 appeared as an 18.5 magnitude object creeping across the constellation Ophiuchus. Trujillo and Brown have proposed the name Quaoar after a creation god of the Native American Tongva tribe, the original inhabitants of the Los Angeles basin. According to legend, Quaoar “came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals, and then mankind.” Follow-up observations using Hubble's new Advanced Camera for Surveys on 5 July and 1 August led to the first-ever direct measurement of a Kuiper Belt Object's disc. The HST revealed an angular size of 40 milliarcseconds, corresponding to a diameter of about 1300 km. Quaoar is about 43 AU (about 6.5 billion km) from the Sun, well over a billion km beyond Pluto. Its orbit around the Sun is circular, so that it is sometimes closer in than Pluto, and sometimes more remote. Although considerably smaller than Pluto, Quaoar is greater in volume than all the asteroids combined – though it probably has only one third the mass of the asteroid belt, because it is a mixture of ice and rock (oposite.stsci.edu/pubinfo/pr/2002/17). The ESA's INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) spacecraft was launched from Baikonur on 17 October and placed in a preliminary orbit. Some of the first telemetry received showed the satellite's passages through the Earth's electron and proton radiation belts. A first test of the optical monitor provided sharp views of a region of sky in the constellation Triangulum Australe. Over the following two months INTEGRAL should manoeuvre into its final orbit of 9000–155 000 km above Earth and then undergo tests to verify that its instruments work correctly. INTEGRAL is the second medium-size mission carried out under ESA's Horizon 2000 science programme. During its planned lifetime of at least two years, its main instruments, the SPI spectrometer and IBIS imager, will explore the gamma-ray universe in great detail. Developed by a Franco-German-led team, the spectrometer will analyse isolated sources and regions of gamma-ray activity with unprecedented energy resolution (40 times better than previous satellites), using germanium detectors cooled to 85 K. The SPI uses the “coded-mask imaging” technique to form its images from very faint radiation. The imager, designed by an Italian-led team, has a poorer energy resolution but an angular resolution 12 times sharper. INTEGRAL also carries a Danish X-ray imager (JEM-X), with twin detectors each fitted with coded masks, and a Spanish CCD imager (OMC) operating in the visible waveband. By combining the data collected by these four instruments it will be possible, for the first time, to make simultaneous observations of high-energy phenomena from visible to gamma-ray wavelengths. INTEGRAL will primarily study dense objects, such as neutron stars and black holes, enabling astrophysicists to confirm the presence of supermassive black holes at the centres of distant galaxies. Other areas of interest will include nova and supernova events and gamma-ray bursts. • MARSINSTITUTECREATED. A new organization aimed at furthering the scientific study, exploration, and public understanding of Mars was unveiled at the World Space Congress on 15 October. The California-based Mars Institute is an independent, non-profit organization whose purpose is “to focus on advancing the scientific study and exploration of Mars, with a central commitment to conducting high-quality peer-reviewed research, and on sharing knowledge and experiences of Mars exploration with students and the general public worldwide. The Mars Institute will strive to provide leadership as the premier international non-governmental organization for the peaceful advancement of these goals.” It will be funded through public and private sources. The founding Board of Directors includes Pascal Lee of the SETI Institute (Principal Investigator of the NASA Haughton-Mars Project), Charles Cockell of the British Antarctic Survey, and Marc Boucher of SpaceRef Interactive, Inc (www.marsinstitute.info). • BEFOREANDAFTERANOVA. Spanish researchers have discovered a white-dwarf star that exploded in a nova outburst in 1998 then returned to normal surprisingly quickly (in just 2.7 years). After observing the nova with the European Space Agency's XMM-Newton observatory, Margarita Hernanz and Glòria Sala reported in the 11 October issue of Science that the nova's position matches that of a star recorded in 1990, making these the first “before and after” X-ray observations of a nova. Nova Ophiuchi 1998 (V2487 Oph) was discovered optically on 15 June 1998 with a visual magnitude of 9.5, and was confirmed as a nova by spectral observations three days later. Hernanz and Sala observed V2487 Oph twice with the EPIC camera on XMM-Newton, first on 25 February 2001 (986 days after outburst) and later on 5 September 2001 (1178 days after outburst). They later found that the nova is in the same position as the X-ray source 1RXS J173200.0-1934, which was detected by the ROSAT All-Sky Survey in September 1990. They conclude the nova's precursor may have been seen eight years before the explosion took place, thanks to the X-rays emitted in the accretion flow around the white dwarf. This supports the cataclysmic variable scenario for nova explosions.

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