Astronomy and Cosmology

 1 Institute for Astronomy University of Hawaii
2 Astronomers Propose Searching For Life On Other Planets With A Plastic Telescope
3 UK Looks Forward to Next Generation Space Telescope
4 FIRST IMAGES FROM TELESCOPE LARGER THAN EARTH REVEAL ANCIENT QUASARS
5 ISO measures temperature variations of the surface of Pluto
6 University Of Washington Prepares First Graduate Program In Astrobiology
7 The European Southern Observatory (ESO)
8 ASTROPHYSICS: SUPERNOVA EXPLOSIONS


`1 Institute for Astronomy University of Hawaii, January 7, 1999

X-RAYS REVEAL PREVIOUSLY HIDDEN VIEW OF THE UNIVERSE'S SKELETON

Astronomers using X-rays to explore the universe have found a supercluster of galaxies to be much larger than anticipated. Superclusters, huge complexes of galaxies, are the largest objects in the universe and are key components of the universe's structural skeleton. The report is being made today to the American Astronomical Society meeting in Austin, TX by University of Hawaii astronomers Mr. Christopher Mullis and Drs. Patrick Henry and Isabella Gioia (also of Istituto di Radioastronomia del Consiglio Nazionale delle Ricerche, Bologna,Italy), and Drs. Hans Boehringer, Ulrich Briel, and Wolfgang Voges of the Max Planck Institute for Extraterrestrial Physics, Garching, Germany, and Dr. John Huchra of the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA. Locating collections of galaxies using their X-ray emission promises to reveal better the shapes of the very largest objects known thus providing clues to the origin of all structure in the universe.

The North Ecliptic Pole Supercluster (NEP Supercluster) is 1.3 billion light years from Earth (redshift of 0.0877) in the direction perpendicular to the Earth's orbit around the Sun. It is located in the constellation Draco. Drs. David Batuski and Jack Burns first discovered the NEP Supercluster in 1985 as an association of six clusters of galaxies (i.e. six groupings of several hundred galaxies each) originally found by Dr. George Abell in optical photographs of the sky. Dr. Richard Burg and colleagues reported X-rays coming from objects possibly related to this supercluster in 1992.

A much improved understanding of the NEP Supercluster's girth and content was provided by the X-ray All-Sky Survey conducted by astronomers at the Max Planck Institute using the Roentgen Satellit (ROSAT). This survey is the first of the entire X-ray sky using a telescope. A region around the NEP was surveyed by ROSAT to the faintest levels attained in the All-Sky Survey; comparable to the depth only previously achieved in isolated regions. "We realized that an X-ray survey of great depth over a contiguous area of the sky provides the essential combination required to find the largest structures in the universe," said Prof. Joachim Truemper, who is a Director of the Max Planck Institute and of the ROSAT satellite.

Clusters of galaxies which demark large superclusters are not the only objects in the X-ray sky, which also includes such high-energy phenomena as exploding stars and black holes. The reporting scientists came across the NEP Supercluster as a result of a larger program to determine the physical nature and distance of hundreds of X-ray sources discovered by ROSAT in the NEP study region. "Galaxy clusters are the hidden gems in the rough for us. We have spent many cold, high-altitude nights at the Mauna Kea observatories examining hundreds of X-ray sources to distill a very useful catalog of galaxy clusters. In terms of the NEP Supercluster, we hvve added 6 new objects and confirmed that the 5 reported previously by Dr. Burg also belong to it," said Mr. Mullis who is conducting this research for his Ph.D. thesis project at the University of Hawaii. The objects revealed by their X-ray emission approximately double the previously known size of the supercluster, which now extends 12 degrees over the northern sky, corresponding to a true physical size of 400 million light years.

The new view of the NEP Supercluster is shown in the figure. This picture shows that the massive Abell clusters that initially delineated it are linked together by less massive X-ray clusters and groups. The newly discovered X-ray sources bridge the region between the previously known NEP supercluster and another cluster of galaxies at the same distance, but not previously associated with it. If this supercluster is characteristic of others, then they can be substantially larger than what is shown by the Abell clusters. Further, Dr. Gioia an astronomer at the University of Hawaii and the IRA-CNR notes: "The area of sky we have examined in the NEP is not extremely large. The detection of a large scale structure in this small cone tells us that the universe may really be composed of a web of filaments and voids on scales of several hundred million light years, as has been indicated repeatedly by computer calculations of the growth of structure in the universe."

The small region of the sky examined in this study, while showing how common the structure found here is in the universe, leaves the door open for the supercluster being even bigger. "We have only examined one side of the original NEP Supercluster. It is possible that objects similar to those we have found are on its other side as well. A true reckoning of its size and shape requires another survey comparable to ours. And of course this is only one object. We really need to study many others in similar detail in order to understand better how the magnificent structure in the universe came to be," said Dr. Henry who is a Professor of Astronomy at the University of Hawaii in Honolulu.

This work is supported by the Extragalactic Astronomy Division of the U.S. National Science Foundation, the Office of Space Science of the U.S. National Aeronautics and Space Administration, the Deutsche Agentur fuer Raumfahrtangelegenheiten, and the Italian Consiglio Nazionale delle Ricerche.

For More Information:

Dr. Patrick Henry
(808-956-7598, henry@ifa.hawaii.edu)
Mr. Christopher Mullis
(808-956-8319, mullis@ifa.hawaii.edu)

FIGURE CAPTION: The top panel is the face-on view of the North Ecliptic Pole Supercluster. The large blue spheres represent the previously known Abell clusters of galaxies, all of which are X-ray sources as well. The yellow spheres are the clusters and groups of galaxies newly discovered because of their X-ray emission (along with three re-detected Abell clusters, the others were not in the NEP X-ray study area). The size of a sphere represents the mass of its associated object. Prior to this study, the NEP Supercluster was only known to comprise the six Abell clusters on the left. The newly discovered objects fill in the region between those previously known, linking the supercluster to another cluster and doubling its size. The bottom panel is the edge on view of the NEP Supercluster. The shape of the supercluster resembles a pancake, significantly thinner in one dimension compared to its other two dimensions. Each view is 500 million light years on a side. This figure was presented to the American Astronomical Society meeting in Austin.



`2 Astronomers Propose Searching For Life On Other Planets With A Plastic Telescope
Sender: owner-astro@brickbat12.mindspring.com Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov

News Services University of Arizona J. Roger Angel, 520-621-6541, rangel@as.arizona.edu Neville J. Woolf, 520-621-3234, nwoolf@as.arizona.edu James H. Burge, 520-626-7356, jburge@as.arizona.edu

January 9, 1999

Astronomers propose searching for life on other planets with a plastic telescope, By Mark Sincell

Two decades from now, astronomers may look for life on other planets using a telescope made of several sheets of reflective plastic in orbit around the Earth.

At least, that's the idea that Roger Angel, a professor at The University of Arizona's Steward Observatory, and co-workers Neville Woolf and James Burge, also of Steward Observatory, are presenting at today's meeting of the American Astronomical Society in Austin, Texas. Glass or metal telescopes large enough to make the first detection of life on planets outside our solar system are planned, but switching to lighter and cheaper plastic may be a crucial step towards a more detailed study of our extra-terrestrial neighbors.

The search for definitive evidence of life on planets orbiting other stars, called exoplanets, has become one of NASA's primary objectives. A primary goal of the Space Interferometry Mission (SIM), an orbiting telescope scheduled for launch in 2003, is to search for exoplanets. SIM is unlikely to detect planets similar to Earth, so a decade later, the Terrestrial PlanetFinder (TPF), will travel out past Jupiter's orbit with the goal of finding Earth-like planets and searching them for signs of life.

Angel sees his proposed telescope as the next step on the path. "PlanetFinder will give us a good first shot at finding evidence for life," says Angel, "but to study planets transformed by life, fecund life, you really need a larger telescope." The envisioned orbiting plastic telescope would have a total light collecting area of about 1,000 square meters.

But those expecting the new telescope to deliver snapshots of smiling extra- terrestrials on vacation will be disappointed. Angel's team estimates that even crudely resolved images of exoplanets would require an array of mirrors with a collecting area equivalent to a one kilometer diameter mirror, over a hundred times larger than the 8-meter primary mirror that will be used in the Next Generation Space Telescope (NGST).

Instead, astronomers plan to look for features in the exoplanets' thermal radiation spectrum left by oxygen and methane in the planet's atmosphere. Greenhouse gases such as oxygen and methane are a direct product of all the biological processes occurring on the Earth's surface. Although these molecules are common in the Earth's atmosphere, they are actually very unstable in combination and, if there were no life on Earth, they would rapidly combine. Finding evidence for both molecules is "the killer test" for life on other planets, says Angel.

Even with a large telescope, gathering enough light from the planet, and then separating it from the light radiated by the planet's own sun, is a formidable task. To accomplish this feat, planet-hunters plan to use a technique called interferometry, in which the light from the planet and its sun is reflected off different mirrors, forming two or more separate beams of light. These beams are then directed to a single detector where they are added up so that the light waves from the star cancel out and only the light from the planet remains.

The most straightforward way to perform space interferometry is to put several telescopes in orbit and combine their light. However, to detect exoplanetary greenhouse gases, each of these telescopes would have to be comparable in size to the NGST. Building and flying several copies of the NGST would be prohibitively expensive.

The idea proposed by Angel, Woolf, and Burge is to replace all but one of the telescopes with flat plastic mirrors, each about 10 meters square. The plastic reflecting surface is attached to a metal frame at several points that can be adjusted independently to preserve the planarity of the membrane.

Since the plastic mirrors are flat, they are relatively easy to build and maintain. "The main difficulty with curved mirrors is making them curved," says Angel, "Nature wants plastic to be flat." And micrometeorites, which periodically crash into satellites, pass right through the plastic.

To form the complete telescope, the plastic membrane mirrors are distributed in space over 100 meters apart, approximately 1 kilometer away from a central 10-meter space telescope, similar in design to the NGST. Light from the exoplanet is reflected off of the plastic mirrors and into the central telescope, where the different beams are "interfered" to remove the light from the star. "We can correct for the missing curvature of the flat mirrors inside the one telescope, in the same way that the optics in the Hubble Space Telescope were fixed", says Angel.

There are two main challenges to be met before plastic interferometric telescopes start scanning our cosmic neighborhood. First, the plastic surfaces have to be extremely smooth and uniform in thickness so that they reflect light very accurately. Learning how to manufacture plastic of such high smoothnesses will take "a lot of work", warns Angel.

Then, once the plastic is smooth, the entire array of mirrors, including the central telescope, must be kept in place, either by mounting the mirrors on a rigid carbon composite truss or by attaching small ion propulsion rockets to individual, free-flying, mirrors. Assembling and deploying such a network requires technology beyond that needed for even NGST.

Ultimately, how accurate will this telescope's design be? As a comparison, in recent demonstrations at The University of Arizona and the Jet Propulsion Laboratory in Pasadena, Calif., the light from two lasers has been made to cancel to one part in ten thousand. To remove the light from the star and observe the spectrum of a nearby planet, the light from the star must be canceled to one part in ten million. And it will all be done in a telescope orbiting thousands of miles from the Earth.


`3 UK Looks Forward to Next Generation Space Telescope

Royal Astronomical Society Press Notice, 25 January 1999

Peter Bond Space Science Advisor 10 Harrier Close, Cranleigh, Surrey, GU6 7BS, United Kingdom Phone: (0)1483-268672 Fax: (0)1483-274047 E-mail: 100604.1111@compuserve.com

Contacts for Further Information

Professor Martin Ward.
Tel: +44 (0)116-252-3494/3540. E-mail: mjw@star.le.ac.uk

Dr. Roger Davies.
Tel: +44 (0)191-374-2163 E-mail: roger.davies@durham.ac.uk

Dr. Gillian Wright.
Tel: +44 (0)131-668-8248. E-mail: gsw@roe.ac.uk

Illustrations are available from:
http://ngst.gsfc.nasa.gov/Hardware/designs.html

UK Looks Forward to Next Generation Space Telescope

As the Hubble Space Telescope (HST) continues to return a succession of staggering new images and data, astronomers on both sides of the Atlantic are preparing the next giant leap for orbital observatories. Three groups in the UK are playing a leading role in studies to decide which scientific instruments Europe will provide for HST's successor, the Next Generation Space Telescope (NGST).

The three studies involving UK groups are:

* The Multi-Object/Integral Field Spectrograph which includes the
University of Durham.
* The Visible Wavelength Camera/Spectrograph which is led by the
University of Leicester.
* The Telescope & Complete Payload Suite which includes the Astronomy
Technology Centre (Edinburgh), Durham University, Leicester University,
Rutherford Appleton Laboratory, and the University of Cambridge.

Hubble and NGST

Despite Hubble's success, a larger, more capable instrument is required to answer some of the questions raised by its discoveries. The NGST will be equipped with a much larger mirror than the HST -- probably 8 metres across compared to 2.4 metres. It will also operate for much of the time at infrared wavelengths (0.6-10+ microns). This will enable it to study the most remote galaxies whose light largely reaches us at infrared wavelengths.

The NGST has been chosen by NASA as an essential element of its Origins programme. NASA is currently undertaking definition and feasibility studies before deciding how best to proceed. The European Space Agency (ESA) and the UK Particle Physics and Astronomy Research Council (PPARC) are also keen to be involved. However, the telescope's final design and scientific payload have yet to be decided.

Although the HST was largely built and paid for by NASA, the European Space Agency has provided one science instrument (the Faint Object Camera) and various other pieces of hardware, such as solar panels, for the observatory. In return, European scientists have gained access to 15% of the available observing time on HST. ESA member states hope to continue this highly successful collaboration into the NGST programme.

Why do we need NGST?

Astronomers believe they have a good understanding of how the Universe has evolved in the last few billion years and what it was like when it was quite young (less than about 1 million years old). However, almost nothing is known about the events which took place between 1 million and a few billion years after the Big Bang. It is during this 'Dark Age' that the first stars and galaxies began to form.

'At the moment we can only see the tip of the iceberg. NGST will allow us to see the dwarf galaxies which we believe are the building blocks for the big ones, and the way they interact and grow into the giant galaxies we see today,' said Professor Martin Ward of Leicester University.

NGST is being designed with a number of fundamental questions about the age and nature of the Universe in mind:

1. What is the shape of the Universe?
2. How do galaxies evolve?
3. How do stars and planetary systems form and interact?
4. What are the life cycles of matter in the Universe?
5. What is dark matter?

Answers to most of these questions involve objects which formed extremely early in the history of the Universe. However, since such objects are moving away from us at tremendous speeds, the radiation we receive from them is stretched or redshifted. The best way to look at them is in the infrared portion of the spectrum.

Not only will the NGST be able to detect this infrared radiation, but it will also be able to see objects 400 times fainter than those currently studied with large ground-based infrared telescopes. At the same time, its spatial resolution (image sharpness) will be comparable to that of HST.

The UK and NGST

NGST is expected to operate along similar lines to Hubble, with NASA as the prime contributor and ESA as a major partner. ESA has accordingly assigned a number of technical assessments to groups throughout Europe in an effort to narrow down the options for its hardware contributions to NGST.

Roger Davies and his colleagues at Durham University are working with teams in France and Germany on a design study for a MULTI-OBJECT INFRARED SPECTROGRAPH. Since light from most distant galaxies is shifted towards the red end of the spectrum, this instrument is seen as an essential part of NGST's scientific payload.

The intention is to simultaneously study starlight from large numbers of distant galaxies. The spectrograph would be able to split and analyse light from numerous objects, much as a prism splits sunlight into different colours. This would enable astronomers to learn much more about the composition, distance, and speed of retreat of distant galaxies and quasars. Astronomers would then be able to 'map' the thousands of faint galaxies which lie in the depths of the Universe.

'At present we use spectrographs to analyse light from only a tiny area of sky ' said Dr. Davies. 'Telescopes have to be pointed very accurately to make sure the right object is in view, which is not so easy in space.'

'The new design developed at Durham allows the light from a much larger area of sky to analysed with the spectrograph. This means that we can study more objects at once and we don't have to point the telescope so accurately,' he explained.

Meanwhile, scientists at the University of Leicester heard in December 1998 that they had been chosen to study the implications of installing an OPTICAL CAMERA / SPECTROGRAPH on NGST. Other institutions taking part in the study come from France, Italy, Germany and Spain.

Although this new instrument would be similar to the Wide Field and Planetary Cameras which have been so successful on HST, the added spectrograph would give it the extra capability of dissecting and analysing starlight at optical wavelengths over a large area of sky.

Since NGST will use a mirror 10 times bigger in area than HST's (equivalent to the size of a large living room), the camera would provide even more detailed pictures than Hubble. In particular, it would reveal galaxies as they were when the Universe was young, and perhaps give us clues on how solar systems and planets are formed.

'NGST will be able to see galaxies which are only about 10% the age of the Universe -- they were born around 1 billion years after the Big Bang,' said Martin Ward, Scientific Principal Investigator for the ESA Visible Camera study.

'We will also be able to see dusty disks around other stars, and, perhaps, the gaps in these disks which astronomers predict are signatures of the formation of planetary systems,' he added.

In a third ESA study, the UK Astronomy Technology Centre (ATC) in Edinburgh leads a British team which is helping to define the most suitable telescope and instrument payload for NGST. Other participants include industry and astronomical institutes from Germany, France, Spain and the Netherlands.

'We are taking a broad perspective on the overall science case for the NGST and what Europe would like to see on NGST,' said the co-chair of the study science team, Gillian Wright. 'The study is concentrating on the telescope design, how to include all of the instruments astronomers would like, and the design of instruments not covered by the other studies. At the ATC we are particularly responsible for leading the study of an imaging spectrograph operating at mid-infrared wavelengths (5-30 microns).'

The results of these three studies are expected to be published June - September 1999.

Notes

The Hubble Space Telescope was launched from the Space Shuttle on 25 April 1990. A number of new instruments were added during the 1993 and 1997 Space Shuttle servicing missions.

Although the HST has been in orbit for almost nine years, the science community hopes that it will continue to operate until 2010. This means that it will be able to operate in parallel with the NGST, which is planned for launch in 2007.

One unusual aspect of the NGST mission will be its stable orbital location about 1.5 million km from Earth in the opposite direction from the Sun. Far from any heat radiated by the Earth and Moon, and protected by a sunshade, NGST will be able to remain very cool. This means that the faint infrared (heat) signatures of remote galaxies will not be swamped by the glow from the telescope itself.

The total cost for the mission including launch and ten years of operation is expected to be approximately $1.2 billion. ESA funding has yet to decided, but is likely to be approximately 15% of the total.

Further Information and Photos of the proposed NGST designs are available on the Web at: http://ngst.gsfc.nasa.gov/Hardware/designs.html
ESA's NGST page is: http://astro.estec.esa.nl/SA-general/Projects/NGST/

Contacts

Professor Martin Ward, Director X-Ray Astronomy Group, University of
Leicester, University Road, Leicester LE1 7RH.
Tel: +44 (0)116-252-3494/3540. Fax: +44 (0)116-252-3311
E-mail: mjw@star.le.ac.uk

Dr. Roger Davies, Physics Dept, Rochester Laboratory, Durham
University,
South Road, Durham, DH1 3LE. Tel: +44 (0)191-374-2163
Fax: +44 (0)191-374-7465 or 3749) E-mail: roger.davies@durham.ac.uk

Dr. Gillian Wright, UK Astronomy Technology Centre, The Royal
Observatory,
Edinburgh, Blackford Hill, Edinburgh EH9 3HJ.
Tel: +44 (0)131-668-8248. Fax: +44 (0)131-662-1668.
E-mail: gsw@roe.ac.uk

Spacecraft that will help answer some of the biggest questions in space science have been chosen as candidates for NASA's medium-class Explorer (MIDEX) program. The spacecraft will observe the largest explosions and brightest galaxies in the Universe; study the link between the Earth's aurora and the solar wind; search for planetary systems around 40 million stars; and investigate magnetic eruptions in the Sun's corona. The five proposals will undergo detailed study over the next five months in the first step of a two-step process. NASA will select two of the missions for flight under the MIDEX program, designed to foster lower-cost, highly focused, rapidly developed scientific spacecraft.

"Once launched, these missions will provide insights into some of the biggest questions in space science," said Dr. Ed Weiler, Associate Administrator for Space Science at NASA Headquarters. "However, MIDEX missions not only return impressive science results, they continue NASA's trend toward greatly lowering mission costs with innovative mission planning and operations."

Following detailed mission concept studies, which are due for submission by June18, 1999, NASA intends to select two of the mission proposals in September 1999 for full development as the third and fourth MIDEX flights. The two missions developed for flight will be launched in 2003 and 2004.

The selected proposals were judged to have the best science value among 35 proposals submitted to NASA in August 1998 in response to an Explorer Program Announcement of Opportunity. Each will now receive $350,000 to conduct a four month implementation feasibility study focused on cost, management, and technical plans, including educational outreach and small business involvement.

The selected MIDEX proposals are:

* The Swift Gamma Ray Burst Explorer, a three-telescope space observatory for studying the position, brightness, and physical properties of gamma ray bursts. Although gamma ray bursts are the largest known explosions in the Universe, outshining the rest of the Universe when they explode unpredictably in distant galaxies, their underlying nature and the cause of the explosion are true mysteries of astrophysics. Swift would use its gamma ray telescope, X-ray telescope, and ultraviolet/optical telescope to determine the nature of gamma ray bursts by probing distant regions of the Universe. Swift would be led by Dr. Neil Gehrels of NASA's Goddard Space Flight Center in Greenbelt, MD, at a total mission cost to NASA of $135 million.

* The Next Generation Sky Survey (NGSS), a four-channel, supercooled infrared telescope designed to survey the entire sky with 1,000 times more sensitivity than previous missions. This infrared survey should discover millions of new cosmic sources of infrared radiation including the brightest galaxy in the Universe, the closest star to the Sun, every asteroid between Mars and Jupiter that is larger than two miles across, and protoplanetary discs in the process of forming planetary systems around nearby stars. NGSS would be led by Dr. Edward L. Wright of the University of California, Los Angeles, at a total mission cost to NASA of $139 million.

* The Full-sky Astrometric Mapping Explorer (FAME), a space telescope designed to obtain highly precise position and brightness measurements of 40 million stars. This rich database would enable numerous science investigations, including accurately determining the distance to all of the stars on this side of the Milky Way galaxy, detecting large planets and planetary systems around stars within 1,000 light years of the Sun, and measuring the amount of dark matter in the galaxy from its influence on stellar motion. FAME would be led by Dr. Kenneth J. Johnston of the U.S. Naval Observatory, Washington, DC, at a total mission cost to NASA of $138 million.

* The Auroral Multiscale Midex Mission (AMM), a formation of four identically instrumented small satellites in a near-polar, highly elliptical orbit. AMM would study the electrical connection between Earth's ionosphere and the distant magnetosphere and how that connection gives rise to the occurrence, structure, and rapid variations of the northern and southern lights. The four-satellite constellation will, for the first time, permit observations to be interpreted unambiguously in terms of variations in space or time. AMM would be led by Dr. Barry H. Mauk of the Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, at a total mission cost to NASA of $130 million.

* The Advanced Solar Coronal Explorer (ASCE), a powerful solar telescope which would reveal the physical processes in the Sun that lead to the solar wind and explosive coronal mass ejections. ASCE would carry two solar instruments that are 100 times better than previous solar coronographs. It would be deployed on a recoverable satellite from the Space Shuttle and retrieved two years later. ASCE would be led by Dr. John L. Kohl of the Harvard- Smithsonian Center for Astrophysics, Cambridge, MA, at a total mission cost to NASA of $131 million.

NASA has also selected instruments from two proposed MIDEX missions for technology development funding. Dr. Richard Rothschild of the University of California at San Diego will develop an X-ray detector for studying black holes of all sizes. Dr. Gary Swenson of the University of Illinois at Urbana-Champaign will develop detectors for studying waves in the Earth's upper atmosphere. Both researchers will receive $700,000 over the next two years for their work.

The Explorer Program is designed to provide frequent, low- cost access to space for physics and astronomy missions with small to mid-sized spacecraft. Explorer missions are required to advance the goals and objectives of the Structure and Evolution of the Universe, Sun-Earth Connection, and Astronomical Search for Origins science themes within the Office of Space Science. The selected MIDEX science missions must be ready for launch before June 30, 2004, within the Explorer Program's NASA cost cap of $140 million. The Explorer Program is managed by NASA's Goddard Space Flight Center, Greenbelt, MD, for the Office of Space Science, Washington, DC.



`4 FIRST IMAGES FROM TELESCOPE LARGER THAN EARTH REVEAL ANCIENT QUASARS

Images of quasars billions of light-years away are among the striking initial results of the Very Long Base Interferometry (VLBI) Space Observatory Program, a new type of astronomy mission that uses a combination of satellite- and Earth-based radio antennas to create a telescope larger than Earth.

Initial results of the radio interferometry mission, launched in February 1997 by Japan's Institute of Space and Astronautical Science (ISAS), are reported in the September 18, 1998, issue of Science magazine.

NASA's Jet Propulsion Laboratory, Pasadena, CA, is part of an international consortium of organizations that support the mission, that creates the largest astronomical "instrument" ever built -- a radio telescope more than two-and-a-half times the diameter of the Earth. One of the most complex space missions ever attempted, Space VLBI has given astronomers one of their sharpest views yet of the universe.

The Science article releases four new images, all depicting quasars whose emissions are estimated to have traveled billions of years to reach Earth. "These images probe some of the most distant and ancient objects in the universe, giving us a glimpse of quasars as they existed billions of years ago," said co-author Dr. Robert Preston, project scientist for the mission at JPL. "These powerful objects exist at the center of many galaxies, including our own familiar Milky Way, which has a weak version of a quasar."

Key results detailed in the article revolve around images of extremely distant objects created through a combination of raw data from the space radio telescope and an array of ground radio telescopes, along with highly sophisticated digital imaging techniques. Of special note is the value of such images in clearly resolving individual components in the observed quasars' jets, which are composed of material rushing away from quasars at nearly the speed of light. The four quasar images are available at http://www.jpl.nasa.gov/releases/98/spacevlbi.html.

Quasars are enormously bright point-like optical objects, often shining with an intensity many hundreds of times that of an entire galaxy. It is believed that quasars are powered by gas and the remnants of stars spiraling into black holes that have masses of millions to billions of times that of our Sun. Black holes are objects that are so massive that no light or matter can escape from them. Some of the material rushing into the black hole is thought to be thrown away at enormous speeds to form the observed narrow, radio-emitting jets. By studying these jets, astronomers hope to learn more about the black holes that power them.

Very long baseline interferometry is a technique used by radio astronomers that electronically links widely separated radio telescopes together to form a single instrument with extraordinarily sharp "vision," or resolving power. The wider the distance between the telescopes, the greater the resolving power. By taking this technique into space for the first time, astronomers have approximately tripled the resolving power previously available with only ground-based telescopes. The Space VLBI satellite system has resolving power more than 100 times greater than the Hubble Space Telescope has at optical wavelengths. In fact, its resolving power is almost equivalent to being able to see a grain of rice in Tokyo from Los Angeles.

The project, a major international undertaking, is led by Japan's ISAS, backed by the National Astronomical Observatory of Japan. Collaborators include JPL; the National Science Foundation's National Radio Astronomy Observatory (NRAO); the Canadian Space Agency; the Australia Telescope National Facility; the European VLBI Network and the Joint Institute for Very Long Baseline Interferometry in Europe. More than 50 scientists associated with these and other collaborating institutions contributed to report published in Science magazine overview paper.

The Space VLBI project's eight meter (26-foot)-diameter orbiting radio telescope observes celestial radio sources in concert with a number of the world's ground-based radio telescopes. It is in an elliptical orbit, varying between 1,000 and 20,000 kilometers (620 to 12,400 miles) above the Earth's surface. This orbit provides a wide range of distances between the satellite and ground-based telescopes, which is important for producing a high-quality image of the radio source being observed. One orbit of the Earth takes about six hours.

Approximately 40 radio telescopes from more than 15 countries have committed time to co-observe with the satellite. These telescopes include NASA's Deep Space Network antennas in California, Spain, and Australia; the National Science Foundation's Very Long Baseline Array (VLBA), an array of 10 telescopes spanning the United States from Hawaii to Saint Croix; the European VLBI Network, more than a dozen telescopes ranging from the United Kingdom to China; a Southern Hemisphere array of telescopes stretching from eastern Australia to South Africa; and Japan's network of domestic radio telescopes.

JPL manages the U.S. Space Very Long Baseline Interferometry project for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology.


`5 ISO measures temperature variations of the surface of Pluto

ESA Science News http://sci.esa.int - 29 May 2000

A team from the Observatoire de Paris using ESA's infrared space telescope ISO has measured variations in the thermal flux of the Pluto-Charon system, which prove that the temperature of Pluto's surface is not uniform. The coldest regions have a temperature of about -235 degrees Centigrade, while the warmest may reach -210 degrees. The measurements provide indications about its physical nature.

Pluto along with its satellite Charon is the outermost planet of the Solar System, at a mean distance from the Sun of 5900 million kilometres. The two bodies, of similar sizes (respective diametres 2320 and 1180 km), form a unique system: they orbit around their common centre of gravity with a 6.4 day period, a time interval that also corresponds to the rotation of each body about its polar axis; therefore, Pluto and Charon permanently show the same side to each other.

Observations performed by a team led by Emmanuel Lellouch (Observatoire de Paris, DESPA), including Dutch astronomer Rene Laureijs from the ISO Data Centre in Spain, used the ISOPHOT instrument on board ESA's ISO to provide the first unambiguous detection of the 'light curve' of the Pluto-Charon system at thermal wavelengths (Fig. 1). The light curve of a rotating body indicates how its brightness changes depending on which of its faces is being measured. In this case astronomers were detecting infrared light, which is actually 'thermal' energy, the light curve measured in the Pluto-Charon system is a temperature curve.

At some orbital positions, the system emits more thermal energy than at others, implying that the regions seen from the Earth at that time are warmer.

It has been known for a long time that Pluto's surface is not uniform. In particular, the visible solar light reflected by Pluto reproducibly varies with the 6.4-day period. Thus the visual brightness of Pluto varies with its position on its orbit. But ISO data show now that Pluto's infrared brightness does not match its visual brightness. More precisely, the orbital positions in which Pluto shines more in the visible are also those in which Pluto's thermal flux is lower, i.e., where Pluto is colder.

The position of Pluto on its 6.4-day orbit is measured by its longitude, ranging from 0 to 360 degrees. Pluto emits a maximum of visible light at a longitude L 3D 220 degrees and a minimum near L 3D 100. Conversely, the measurements made by the ISOPHOT camera on board ISO show (Fig. 2) a maximum thermal flux of the Pluto-Charon system around L 3D 80, and a minimum around L 3D 240.

This general anti-correlation with the visible light curve is normal: it is expected that the darker regions of Pluto are warmer that the brighter ones. Indeed, the darker regions absorb more the solar energy, they warm up more and therefore emit a larger infrared flux.

The coldest regions have a temperature of 35-40 degrees Kelvin (-238 to -233 degrees Centigrade), while the warmest may reach 55-65 degrees Kelvin (-218 degrees Centigrade to -208 degrees Centigrade).

The detailed analysis of the ISO measurements shows, in addition, that the anti-correlation is not perfect. The thermal 'light curve' is actually slightly delayed relative to the visible light curve. This shift allows the thermal inertia of Pluto's surface to be measured, suggesting that the material of the darkest regions is probably porous.

This work is described in a paper accepted for publication by the international journal Icarus.

Contacts: Emmanuel Lellouch (Observatoire de Paris) lellouch@megasx.obspm.fr Tel: +33 1 45077672

RenE9 Laureijs (ESA, ISO Data Centre) rlaureij@iso.vilspa.esa.es Tel: +34 91 8131367

Martin Kessler, ESA, ISO project scientist mkessler@iso.vilspa.esa.es Tel: +34 91 8131253

USEFUL LINKS FOR THIS STORY

* ISO Science website
http://www.iso.vilspa.esa.es/

* ISOPHOT Data Centre
http://www.mpia-hd.mpg.de/ISO/welcome.html

* ICARUS journal
http://www.academicpress.com/icarus

* Observatoire de Paris
http://www.obspm.fr/

IMAGE CAPTIONS:

[Fig 1: http://sci.esa.int/content/image/index.cfm?aid3D1&cid3D1&oid3D19710&ob jecttypename3Dnews&ooid3D19705]

Detection of Pluto/Charon with 60 and 100 micron obtained by ISOPHOT on March 17, 1997. The level of flow is approximately 0.40 Jansky with 60 micron and 0.53 Jansky at 100 micron.

[Fig 2: http://sci.esa.int/content/image/index.cfm?aid3D1&cid3D1&oid3D19740&ob jecttypename3Dnews&ooid3D19705]

The curve of light of Pluton/Charon at 60 micron. The system emits approximately 60% of more flow to orbital longitude L3D100 than with longitude L3D240. The curve is a fascinating model illustratingt an effect of delay related to thermal inertia.



`6 University Of Washington Prepares First Graduate Program In Astrobiology

FROM: Vince Stricherz, 206-935-7430, vinces@u.washington.edu
Contacts: James Staley: (206) 543-0461 or 543-6646 jstaley@u.washington.edu.
Woodruff Sullivan: (206) 543-7773 or 543-2888 woody@astro.washington.edu.
Conway Leovy: (206) 543-4952 leovy@atmos.washington.edu.
Richard Gammon: (206) 543-1609 or (206) 543-4301 gammon@u.washington.edu.
Sept. 30, 1998

UW prepares for first graduate program in astrobiology to train those who will hunt for life in outer space

The University of Washington is poised to become the first institution anywhere to launch a doctoral program specifically geared to train scientists to search for life on celestial bodies such as Mars or Europa, an icy moon of Jupiter.

The astrobiology program will be financed by a 5-year, $2 million grant announced today by the National Science Foundation and supplemented by $500,000 from the university.

The highly interdisciplinary curriculum will involve 11 UW degree programs -- Oceanography, Astronomy, Aeronautics & Astronautics, Genetics, Chemistry, Biochemistry, Microbiology, Atmospheric Sciences, Geophysics, Geological Sciences and History. Graduates can receive degrees in any of those areas, with an endorsement noting an emphasis in astrobiology.

The School of Oceanography will provide dedicated laboratory space for students to study organisms that live in extreme conditions. Oceanography professors John Delaney and Jody Deming and associate professor John Baross have closely studied organisms living in high-temperature, high-pressure conditions in ocean environments where little light penetrates.
Baross is trying to relate the conditions in which those organisms live now to conditions when life began on Earth 3.5 billion years ago.

Two entities outside the university also are participating. The Pacific Northwest National Laboratory in Richland will offer students a chance to study microbial life in the subterranean basalt formations in Eastern Washington. ZymoGenetics Inc. of Seattle, a subsidiary of Novo Nordisk A/S of Denmark that is interested in enzymes from unusual bacteria, is offering summer internships so students can pursue that work.

"We recognize that there is a good possibility that life exists in the solar system outside Earth, but if that life does exist it would be microbial, not the higher forms," said James Staley, a UW microbiology professor who is the principal investigator for astrobiology.

Likely sites for such life are Mars, where there is evidence of water, or the ice-clad moon Europa. The key to finding life in such forbidding environments is understanding how life exists in extreme conditions on Earth -- such as hot springs in Yellowstone National Park, undersea vents where no sunlight penetrates and temperatures reach several hundred degrees, pools of brine within polar sea ice, and volcanic basalt formations.

"We have microbial systems on Earth that are good models for those on Mars or Europa, and those systems are poorly studied," Staley said. He added that such life forms were the precursor to advanced life on Earth, so their presence on other planets could signal the eventual evolution of advanced life there, as well.

The idea for an astrobiology program grew out of a special seminar, Planets and Life, offered at the university in 1996 shortly after the discovery of planets orbiting nearby stars and an announcement that NASA scientists possibly had found microbial fossils inside a Martian rock. That claim since has drawn much scientific skepticism, but the success of the seminar -- it was attended by 30 graduate students and 20 post-doctoral researchers and faculty, and it sparked much campus excitement -- laid a foundation for a program in astrobiology.

Woodruff Sullivan, a UW astronomy professor and adjunct history professor, spearheaded the seminar and is an astrobiology co-investigator. He expects about a dozen students when the program begins in the fall quarter of 1999.

But there is much to be done before then. Five new courses must be designed to complement existing courses that will be included in the curriculum, Sullivan said. Departments involved will have to devise different ways of testing and grading students involved in astrobiology, since an astrobiology student pursuing a degree in astronomy, for instance, will have significantly different course demands than other astronomy students.
One-third of astrobiology course work will be in areas not closely related to the student's home department, so an astronomy astrobiology student might spend a great deal of time studying microbiology.

Students also must take part in an annual workshop, three days of work in the field. It could be looking for microbes at the Hanford Nuclear Reservation, Sullivan said, or using an electron microscope to study comet dust. "Everyone will have to get their hands dirty."

Conway Leovy, a UW atmospheric sciences professor and also a co-investigator, expects the program to be an education for faculty members as well as students. But he said the students will be particularly challenged as they blaze a new path, and it will be some time before the first doctoral degrees in astrobiology are awarded.

"Astrobiology students will have to learn rigorously as well as more broadly than most other science graduate students," Leovy said. "We probably can't expect to see the fruits of our efforts in the form of many Ph. D. graduates sooner than five years from now."

Richard Gammon, who is a UW chemistry and oceanography professor and also is an adjunct professor of atmospheric sciences, helped write a financing proposal for the astrobiology degree program. He believes the approach of breaching traditional barriers between different science disciplines was a key to National Science Foundation support.

"All of these efforts are to meet the needs of students of the future, who are going to need training across fields," Gammon said.

The UW is one of 17 universities sharing in $40.5 million in National Science Foundation graduate education and research training grants. For more information about the NSF program, visit http://www.nsf.gov/igert/


`7 The European Southern Observatory (ESO) is an intergovernmental organisation supported by Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden and Switzerland. Portugal has an agreement with ESO aiming at full membership. ESO is a major driving force in European astronomy, performing tasks that are beyond the capabilities of the individual member countries. The ESO La Silla observatory (Chile) is one of the largest and best-equipped in the world. ESO's Very Large Telescope Array (VLT) is under construction at Cerro Paranal (Chile). When completed in 2001, the VLT will be the largest optical telescope in the world.

Useful Physics On Stage addresses

"Physics on Stage" webaddress: http://www.estec.esa.nl/outreach/pos

International Steering Committee (ISC) Clovis de Matos (Executive Coordinator) ESA/ESTEC European Space Research and Technology Centre Office for Educational Outreach Activities Keplerlaan 1 Postbus 299 NL-2200 AG Noordwijk The Netherlands
cdematos@estec.esa.nl Telephone: +31-71-565- 5518 Fax: +31-71-565 5590

National Steering Committees (NSC) (current status):
Prof. Christian Gottfried Theobaldgasse 16/13 A-1060 Wien Austria Tel: +43.1.587.46.02 Fax: +43.1.586.20.90 e-mail: christian.gottfried@cern.ch

Belgium: Dr. Petra Rudolf email: Petra.Rudolf@fundp.ac.be
Prof. Ivan Lalov Chairman of the NSC /PoS - Bulgaria Union of the Physicists in Bulgaria Blvd. James Bourchier 5 Sofia - 1164, Bulgaria

Dr. Jiri Dolejsi Faculty of Mathematics and Physics Charles University V Holesovickach 2 CZ-180 00 Prague 8 Czech Republic e-mail: dolejsi@hp02.troja.mff.cuni.cz

Dr. Brigitte Sode-Morgensen Ministry of Research and Information Technology Bredgade 43 DK-1260 Copenhagen K Denmark

Physics on Stage National Steering Committee in Finland c/o Markku Sarimaa Ursa Astronomical Association Raatimiehenkatu 3 A 2 FIN-00140 Helsinki Finland

France: Mr. Pierre-Louis Contreras email: pierre-louis.contreras@cnes.fr

Prof. Michael Kobel Physikalisches Institut, Universitaet Bonn Nussallee 12 D-53115 Bonn Germany Phone: +49 228 73-3532 Fax: +49 228 73-3220 e-mail: kobel@physik.uni-bonn.de

Physics on Stage c/o N.D. Tracas Physics Department National Technical University Zografou Campus 157 73 Zografou Athens GREECE Tel: +30 1 772 3047 Fax:+30 1 772 2906 email: pos@lattice.physics.gsd.ntua.gr

Dr. Adam Kovach Inst. of Nuclear Research, P.O.B. No.51 H-4001 Debrecen Hungary

Dr. Ian Elliott Dublin Institue for Advanced studies School of Cosmic Physics Dunsink Observatory Dublin 15 Ireland

The official mailing address of the Italian NSC is: pos@sif.it.

Luxembourg: Dr. Fernand Wagner fernand.wagner@ci.educ.lu

Prof. Dr Aart W. Kleyn Leiden Institute of Chemistry Gorlaeus Laboratories Leiden University Einsteinweg 55 P.O. Box 9502 2300 RA Leiden The Netherlands

Norway: Dr. Heidi Bruvoll heidi.bruvoll@fys.uio.no

Poland: Dr Tadeusz Skoskiewicz skosk@ifpan.edu.pl

Dra. Ana Noronha Ciencia Viva Ministerio da Ciencia e da Tecnologia Unidade Ciencia Viva Av. dos Combatentes, 43 A-10B 1600 Lisboa Portugal

Dalibor Krupa Slovak Physical Society c/o Slovak Academy of Sciences Stefanikova 49 SK-814 38 Bratislava Slovak Republic

Rosa M. Ros Real sociedad Espanola de Fisica Facultad de Ciencias Fisicas Universidad Complutense 28040 Madrid Spain

Sweden: Dr. Thomas Lindblad indblad@particle.kth.se

Prof. Claude Joseph Institut de Physique des Hautes Energies Universit=E9 de Lausanne CH-1015 Lausanne Tel.: +41-21-692 37 01 Fax: +41-21-692 36 05 e-mail: Claude.Joseph@iphe.unil.ch

Dr Steven Chapman Secretary, Physics on Stage United Kingdom National Steering Committee Institute of Physics 76 Portland Place London W1N 3DH Tel: +44 20 7 470 4924 Fax: +44 20 7 470 4848 e-mail: Steven.Chapman@iop.org


`8 ASTROPHYSICS: SUPERNOVA EXPLOSIONS

Supernovae are violent explosions marking the terminal stage of certain stars. They are classified into two broad types, Type I and Type II. A Type II supernova shows hydrogen in its spectrum, while a Type I supernova shows no hydrogen in its spectrum. Type I supernovae are further classified as Type 1a, Type 1b, and Type Ic. A Type 1a supernova is believed to be due to the explosion of a *white dwarf star in a binary star system, the result of matter falling onto it from the companion star. When the mass of the white dwarf exceeds the *Chandrasekhar limit, the white dwarf undergoes runaway carbon burning and explodes. Type Ib and Ic supernovae are thought to result from the collapse of the cores of massive stars which have lost their hydrogen envelopes. Type II supernovae arise from the explosion of stars of more than 8 solar masses. In this case, the explosion involves a violent blow-off of outer-layer material after the massive star has collapsed into a *neutron star or a *black hole. Despite the existing classification scheme, Type Ib and Type Ic supernovae are more closely related to Type II supernovae than to Type Ia supernovae. Gamma ray bursts are intense flashes of *gamma rays detected at energies up to 10^(6) *electronvolts. They were discovered by US Air Force satellites in 1967 but not declassified until 1973. The detection of these bursts averages about 1 per day, and measurements indicate the distribution of bursts is isotropic, i.e., they are uniformly distributed across the sky. The current consensus is that gamma ray bursts are produced by the merger of two neutron stars, and up to this point, the bursts that have been noted apparently originate outside our own galaxy.

... ... Adam Burrows (University of Arizona Tucson, US) presents a review of current research on supernova explosions, the author making the following points:

1) Supernovae are crucial to the dynamical and morphological development of the Universe, and they are also the focus of many of the important debates now current among astronomers. The author suggests that type 1a supernovae are "now arguably astronomy's most accurate probe of the scale and geometry of the Universe." An unknown fraction of another supernova subtype, the core-collapse supernovae, may be the source of gamma-ray bursts. The author suggests that as major sources of the chemical elements of existence, supernovae themselves are primary agents of stellar and galactic evolution, and supernovae and gamma-ray bursts share the distinction of being the most powerful explosions in the Cosmos. Recent observational and theoretical breakthroughs and a renewed appreciation of the manifold roles of supernovae have inaugurated a new era in their study.

2) The light curve and spectra of a supernova reflect more its progenitor's radius, chemical makeup, and expansion velocities than the mechanism by which the explosion of the supernova came into being. To the theorist, the achievement of the critical Chandrasekhar limiting mass unites the various types of supernovae: the supernova mechanism is either an implosion to an object of the density of an atomic nucleus and subsequent hydrodynamic ejection of material (core-collapse supernovae), or an explosive incineration produced by a thermonuclear runaway (type 1a white dwarf supernovae).

3) There is approximately 1 supernova explosion in the Universe every second. In our Galaxy, there is one supernova approximately every 30 to 50 years, and one type 1a supernova approximately every 300 years. Astronomers using only modest telescopes can now capture a dozen extragalactic supernovae per night, mostly the bright type 1a. Approximately 200 supernova remnant shells are known in our Galaxy, and these are radio, optical, and x-ray echoes of only the most recent Galactic supernova explosions. Within the last millennium, humans have witnessed and recorded 6 supernovas in our Galaxy.

3) The brightness of supernovae suggests their use in surveying the Universe. If supernovae were *standard candles, a comparison between their apparent brightness and their intrinsic (absolute) brightness would yield their distance. A spectrum taken with a large-aperture telescope capable of precision measurements of dim objects made dim by distance would yield the spectral *redshift (z) of the host galaxy of the supernova in the *Hubble flow of the expanding Universe. A selection of these measurements would provide redshift-distance and redshift- magnitude relations which can be used to distinguish different models of the Cosmos, to determine the geometry and mass-energy content of the Cosmos, and to help determine the ultimate fate of the Cosmos.

4) The author concludes: "In important ways, the histories of star and galaxy formation and of supernovae are inextricably linked. Progress in understanding one demands progress in understanding the other. Today, as we attempt to fathom the mechanisms of supernova explosions, the origin of the elements, the death of stars, and the birth of neutron stars and black holes, we are simultaneously advancing the means by which we can comprehend our origins. Crucial to the development of the Universe, supernovae tell a story that goes beyond the exotic physics, the state of the art numerical technique, and their role in surveying the Universe, to the heart of mankind's ability to comprehend its home."

----------- Adam Burrows: Supernova explosions in the Universe. (Nature 17 Jan 00 403:727) QY: Adam Burrows [aburrows@as.arizona.edu]

----------- Text Notes:

... ... *white dwarf star: White dwarf stars are extremely dense and compact stars that have undergone gravitational collapse. They are the final stage in the evolution of low-mass stars after they have lost their outer layers. White dwarf stars are about the size of Earth, but with a mass about that of the Sun.

... ... *Chandrasekhar limit: The remnant mass after the blow-off during the terminal stage of the life of a star determines the ultimate fate of the star. If the remnant mass is less than 1.44 solar masses (the Chandrasekhar limit for a star with no hydrogen content), the star collapses into a white dwarf. If the remnant mass is greater than 1.44 solar masses, depending on the remnant mass, the star collapses into either a neutron star or a black hole. Named after Subrahmanyan Chandrasekhar (1910-1995), who first proposed the modern theory of stellar gravitational collapse, and who received the Nobel Prize in Physics 1983.

... ... *neutron star: If, following its terminal stages, the remnant mass of a star is between 1.4 and 2 to 3 solar masses, the star will collapse into a neutron star, a body with a radius of 10 to 15 kilometers, with a core so dense that its component protons and electrons have merged into neutrons. The average density of a neutron star is 10^(15) grams per cubic centimeter, and the weight of an object on the surface of a neutron star would be 10^(11) its weight on the surface of the Earth. Neutron stars apparently have an outer shell of iron, but it is iron like no Earth iron, an iron of 4 orders of magnitude greater density.

... ... *black hole: If the terminal stages of star death leave a remnant star mass greater than 3 solar-masses, the ultimate gravitational collapse will produce a black hole, a relativistic singularity. A black hole is a localized region of space from which neither matter nor radiation can escape. The "trapping" occurs because the requisite escape velocity, which can be calculated from the relevant equations, exceeds the velocity of light and is therefore unattainable. Another view of a black hole

... ... *gamma rays: Gamma rays are radiation of high energy, from about 10^(5) electronvolts to more than 10^(14) electronvolts -- radiation with the shortest wavelengths and highest frequencies, the gamma ray region of the electromagnetic spectrum merging into the adjacent lower energy x-ray region.

... ... *electronvolts: (eV) A unit of energy defined as the energy acquired by an electron in falling through a potential difference of 1 volt. 1 electronvolt =3D 1.602 x 10^(-19) joule.

... ... *standard candles: In general, in this context, the term "standard candles" refers to astronomical objects whose intrinsic brightness is known and whose distance can therefore be calculated from apparent brightness.=20

... ... *redshift (z): Redshift (symbol: z) is a lengthening of the wavelengths of electromagnetic radiation from a source caused either by the movement of the source (Doppler effect) or by the expansion of the universe (cosmological redshift). Redshift is defined as the change in wavelength of a particular spectral line divided by the unshifted wavelength of that line. Large redshifts imply large radial velocities (which imply large distances, according to current cosmological theory), but at redshifts greater than about 0.2 there is a relativistic divergence from a linear relation. A redshift of 4.0 corresponds to an object receding with a radial velocity 92% that of the velocity of light. The largest astrophysical redshifts so far observed are of the order of z =3D 4.9.

... ... *Hubble flow: In general, the outward motion of galaxies resulting from the uniform expansion of the Universe, with all motions lying in a radial direction from the observer, and with velocities proportional to the distance of the galaxies. (Because of mutual gravitational interactions between galaxies, the actual pattern of galaxy motions is not precisely of this form.)