Astronomers Find Planet Orbiting Nearby Star
Two teams of astronomers this week reported that one of the sun's nearest neighbors-a star just 15 light-years from Earth-possesses a planet 1.6 times as massive as Jupiter. As with other planets recently discovered, this object was not imaged, but betrayed its presence through its gravitational tug on its parent star. This story is reported in the June 27 issue of "Science News."
A leader of one of the teams, Geoffrey W. Marcy of San Francisco State University and the University of California, Berkeley, reported the finding on June 22 at a symposium of the International Astronomical Union in Victoria, British Columbia. Marcy and his colleagues used telescopes at Lick Observatory and the Keck I telescope atop Hawaii's Mauna Kea to detect a telltale wobble in the motion of the nearby star Gliese 876.
Just 2 hours after his presentation, a colleague presented him with an e-mail from a team led by Xavier Delfosse of Geneva and Grenoble observatories. The message said that the team had confirmed the finding. These astronomers used telescopes at the Haute-Provence Observatory in France and the European Southern Observatory in La Serena, Chile.
08:47 AM ET 07/08/98
Nearby star bears similarities to solar system
Release at 3 p.m. EDT
SANTA BARBARA, Calif. (Reuters) - Astronomers announced
Wednesday they have discovered a ring of dust around a nearby
star that could be similar to the solar system and may contain a
planet.
The ring around Epsilon Eridani is ``strikingly similar'' to
the inner comet zone in the solar system and shows an
''intriguing'' bright region that may be particles trapped
around a young planet, said Jane Greaves of the Joint Astronomy
Center in Hawaii (JAC).
``What we see looks just like the comet belt on the
outskirts of our planetary system, only younger,'' said Greaves
who led the research team that included astronomers from JAC,
the University of California, Los Angeles (UCLA) and the Royal
Observatory in Edinburgh, Scotland.
Greaves presented the team's findings Wednesday to the
Protostars and Planets conference in Santa Barbara.
``It's the first time we've seen anything like this around a
star similar to our sun,'' she said. ``In addition, we were
amazed to see a bright spot in the ring, which may be dust
trapped in orbit around a planet.''
UCLA's professor of physics and astronomy, Benjamin
Zuckerman, said: ``This is a star system that quite resembles
our solar system; it's one thing to suspect that another such
system exists, but another to actually see it and this is real
observational evidence.''
Zuckerman was enthusiastic about the observations. ``The
implication is that if there is one system similar to ours at
such a close star, presumably there are many others.
``In the search for life elsewhere in the universe, we have
never known where to look before. Now we are closing in on the
right candidates.''
Greaves was a member of an international team that reported
new images of dusty disks around the stars Fomalhaut and Vega in
April. But the new image of Epsilon Eridani is more significant,
she said.
``Epsilon Eridani is far more similar to our sun than either
Vega or Fomalhaut. This star system is a strong candidate for
planets.
``But if there are planets, it's unlikely there could be
life yet. When the Earth was this young, it was still getting
very heavily bombarded by comets and other debris.''
She said the new images were important also because ``this
is also a star in our neighborhood -- only about 10 light years
away -- which is why we can see so much detail in the new
image.''
Epsilon Eridani is in the constellation of Eridanus (the
river) and is among the 10 closest star systems to the Earth.
The research team also included astronomers from the
University of Arizona; University College, London, and the
Rutherford Appleton Laboratory.
The new image, from short-radio wavelengths and is not an
optical picture, was obtained by using the 15-meter James Clerk
Maxwell telescope at Mauna Kea Observatory in Hawaii.
Tuesday, 21 April 1998
Planet Construction Zone
NASA Astronomers, Keck II Telescope
Discover Best Evidence Yet of Solar System Beyond Our Own
WASHINGTON, D.C. - NASA astronomers using the new Keck II telescope in Hawaii have
discovered what appears to be the clearest evidence yet of a budding solar system around a nearby
star.
At a press conference held in Washington, D.C., on Tuesday, scientists released an image of the
probable site of planet formation around a star known as HR 4796, about 220 light-years from
Earth in the constellation Centaurus. The image, taken with a sensitive infrared camera developed at
NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, shows a swirling disk of dust around the
star. Within the disk is a telltale empty region that may have been swept clean when material was
pulled into newly formed planetary bodies, the scientists said.
"This may be what our solar system looked like at the end of its main planetary formation
phase," said Dr. Michael Werner of JPL, who co-discovered the region, along with Drs. David
Koerner and Michael Ressler, also of JPL, and Dana Backman of Franklin and Marshall College,
Lancaster, PA. "Comets may be forming right now in the disk's outer portion from remaining
debris."
The discovery was made on March 16 from the giant 33-foot (10-meter) Keck II telescope atop
Mauna Kea, Hawaii. Keck II and its twin, Keck I, are the world's largest optical and infrared
telescopes. Attached to the Keck II for this observation was the mid-infrared camera, developed by
Ressler at JPL and designed to measure heat radiation.
The four scientists reported their discovery in a submission to The Astrophysical Journal Letters.
The disk was discovered independently and contemporaneously at the Cerro Tololo Observatory in
Chile by another team of scientists, led by Ray Jayawardhana of the Harvard-Smithsonian Center for
Astrophysics (CfA), Cambridge, MA, and Dr. Charles Telesco of the University of Florida,
Gainesville.
Koerner of JPL said the finding represents a "missing link" in the study of how planetary systems
are born and evolve. "In a sense, we've already peeked into the stellar family album and seen baby
pictures and middle-aged photos," Koerner said. "With HR 4796, we're seeing a picture of a young
adult star starting its own family of planets. This is the link between disks around very young stars
and disks around mature stars, many with planets already orbiting them."
"This is the first infrared image where an entire inner planetary disk is clearly visible," Werner
said. "The planet-forming disk around the star Beta Pictoris was discovered in 1983 by the Infrared
Astronomical Satellite (IRAS), and also later imaged with the Hubble Space Telescope, but glaring
light from the star partially obscured its disk."
The apparent diameter of the dust disk around HR 4796 is about 200 astronomical units (one
astronomical unit is the distance from Earth to the Sun). The diameter of the cleared inner region is
about 100 astronomical units, slightly larger than our own solar system.
HR 4796 was originally identified as an interesting object for further study by Dr. Michael Jura,
an astronomy professor at the University of California, Los Angeles. The star, HR 4796, is about 10
million years old and is difficult to see in the continental United States, but is visible to telescopes in
Hawaii and the southern hemisphere.
The discovery of the HR 4796 disk was made in just one hour of observing time at Keck, but the
JPL team plans to return to Hawaii in June for further studies. They hope to learn more about the
structure, composition and size of this disk, and to determine how disks around stars in our galaxy
produce planets. They plan to study several other stars as well, including Vega, which was featured
prominently in the movie, "Contact."
The Harvard/Florida research team that also found the HR 4796 disk included Drs. Lee
Hartmann and Giovanni Fazio of Harvard-Smithsonian Center for Astrophysics, and Scott Fisher
and Dr. Robert Pina of the University of Florida. The Harvard-Florida research team's instrument,
OSCIR, will be attached to the Keck II telescope in early May.
JPL's use of the Keck telescope is supported by NASA's Origins program, a series of missions
to study the formation of galaxies, stars, planets and life, and to search for Earth-like planets around
other stars that might have the right conditions for life.
Said Keck observatory director Fred Chaffee, " It is very gratifying to see these new exciting
results from the Keck telescopes. They are a tribute to not only the astronomers who made
them, but to the engineers and technicians who have brought these marvelous telescopes into being
and keep them running night after night. The combination of the telescopes themselves and the rapid
development of new infrared-sensitive cameras such as MIRLIN and OSCIR opens, as these recent
findings dramatically illustrate, a whole new window on our search for
planets around nearby stars. We're only just now scratching the surface. These are exciting times."
The W. M. Keck Observatory is owned and operated by the California Association for
Research in Astronomy, a joint venture between the University of California, California Institute of
Technology (Caltech), Pasadena, CA, and NASA. Use of the Keck Observatory for Origins
research is managed by JPL for NASA's Office of Space Science, Washington, DC. JPL is a
division of Caltech. The research of both teams was supported in large part by the NASA Origins
Program, with additional support to the CfA-Florida team from the National Science Foundation,
the National Optical Astronomy Observatories, and the Smithsonian Institution; and with additional
NASA support for the CalTech/JPL-Franklin & Marshall team, including use of the Keck
Observatory.
- end press release text -
NOTE TO EDITORS: The Keck II image of HR 4796 and information on the MIRLIN camera
are available on the World Wide Web at: http://cougar.jpl.nasa.gov/HR4796/hr4796.html
(If this server has reached capacity or is unable to be accessed, go through the JPL homepage at:
http://jpl.nasa.gov and enter the news release sub-directory)
A false-color image of the HR 4796A disk is available at:
http://www.astro.ufl.edu/news/
Information on the Keck Observatory is available at:
http://www2.keck.hawaii.edu:3636
Information on the Origins program is available at:
http://origins.jpl.nasa.gov
March, 1998 - Galaxies at High Redshift Discovery Pushes Back Boundaries of the KnownUniverse Astronomers using the largest optical and infrared telescopes in the world have found the most distant known object in the cosmos, a young galaxy in existence when the universe was only 6 percent of its present age, and nearly 90 million light-years farther than any previously discovered. The serendipitous discovery is raising realistic hopes that the emerging generation of large ground-based telescopes will unveil the formative stages of galaxies, allowing astronomers to resolve two of the central questions facing contemporary astrophysics: How and when did galaxies form? The findings will be detailed in a scientific paper to be published in an upcoming issue of the Astrophysical Journal Letters. The paper was written by Arjun Dey, a Hubble Postdoctoral Fellow at The Johns Hopkins University, astronomers Hyron Spinrad, Daniel Stern and James R. Graham at the University of California, Berkeley, and Frederic H. Chaffee at the W.M. Keck Observatory in Hawaii. "It is an extremely exciting discovery, since so little is known about this stage of the universe, in terms of the objects that lived there, or how galaxies -- giant collections of stars -- might form," Dey said. "We are trying to find baby galaxies. These are galaxies that would eventually turn into something like the one we live in, but would be undergoing their first episode of star formation. In other words ... they are essentially collapsing from a large gas cloud and forming their first generation of stars." Because of its great distance and the constant speed of light, astronomers now see the galaxy as it was when the universe was only 6 percent of its present age, about 820 million years after the Big Bang. Astrophysicists need to observe embryonic galaxies to test, refine and/or refute theories about how galaxies form. Without direct, observational evidence, specific theories cannot be substantiated. "The problem is that, although people have looked for many, many years, they have never been able to find galaxies that are truly primeval," said Dey. Astronomers don't yet know whether they have now discovered one such primeval galaxy, but it is their best candidate to date. Scientists can determine the distance to a galaxy by measuring the speed with which it is moving away from us as the universe expands. More distant galaxies are receding faster, a phenomenon observed in the late 1920s by American astronomer Edwin Hubble. The faster a galaxy is moving, the more its light is shifted to the longer (or redder) wavelengths. The light is said to be "red shifted." The farther away a galaxy is, the faster it appears to be receding from us, and the greater its redshift. The newly discovered galaxy, called 0140+326RD1 (or RD1), has a redshift of 5.34, marking the first time the 5.0 redshift barrier has been broken. "We've never had any glimpse of what might be at redshifts beyond 5," said Dey, the team leader. "But now that we know what to look for, I'm sure this record will be broken in a matter of months." The astronomers discovered RD1 while they were observing distant galaxies with the 10-meter Keck II Telescope located atop Mauna Kea, a dormant volcano on the Big Island of Hawaii. Keck II is an identical twin to the 10-meter Keck I; they are the largest optical and infrared telescopes in the world. In September 1997, Dey, Spinrad, Stern and Graham were using the Keck Low-Resolution Imaging Spectrograph to analyze the light from a very distant and faint galaxy in the constellation of Triangulum, when they spotted something unexpected: the spectral signature of another even fainter galaxy which had not been seen on existing images of that patch of sky. In December, the team took deeper images by increasing the exposure time of their observations. "And sure enough, we began to see something show up: a faint blob," Dey said. Keck Observatory director Frederic Chaffee joined the team, and they studied the object's light again, confirming the discovery of the new, extremely distant galaxy. The astronomers are continuing follow-up observations with Keck, and they hope to observe the object with the Hubble Space Telescope. "Astronomers the world over have spent years devising clever techniques to find galaxies beyond redshift 5, but so far have come up empty," said Chaffee, who has watched numerous teams search for such ultra-distant objects. "We had assumed this was because such objects are extremely rare and faint -- rather like seeking out the needle in a 10,000,000-straw haystack. But here, one was found serendipitously by observing only one tiny area of sky." The previous most-distant known object was a galaxy at redshift 4.92, discovered by astronomers using the Keck and Hubble telescopes. "How galaxies formed in the early universe is one of the most exciting puzzles in astronomy today," said Hugh Van Horn, director of the National Science Foundation's Division of Astronomical Sciences. "This record-breaking observation will give us new information about a galaxy in its youth." The actual age of the universe is a matter of debate. However, if astronomers use 13 billion years as the age of the universe, then light from RD1 was emitted when the universe was 820 million years old. The light has traveled a distance of about 12.22 billion light-years. The previous most-distant galaxy is about 12.13 billion light-years from Earth, nearly 90 million light-years closer than RD1. RD1 is a fairly average galaxy, with a mass and luminosity less than that of the Milky Way, Dey said. That finding gives astronomers hope that the embryonic stages of galaxies similar to today's large spiral and elliptical galaxies might be bright enough to be seen with greater ease by the Kecks and other large telescopes now being built. Presently, the two 10-meter Keck telescopes are unrivaled. But within a decade, about a dozen 8-meter class telescopes will join the hunt for answers to some of the most pressing questions facing cosmology today. "We are sort of at a watershed in observational cosmology, in terms of understanding how galaxies form and evolve," Dey said. The astronomers hope to find other primeval galaxy candidates at even larger distances. "Deep targeted searches with the new generation of large ground-based telescopes will soon uncover more nascent galaxies," said Spinrad. The Hopkins/UC-Berkeley/Keck research has been funded by NASA and the National Science Foundation.
Jan, 1998 - Black hole that periodically ejects its inner disk as jets discovered by Caltech, MIT, and NASA astrophysicists
WASHINGTON-Astronomers observing a disk of matter spiralling into a black hole in our galaxy have discovered that the black hole periodically hurls the inner portion of the disk into space as jets travelling at near the speed of light.
According to Stephen Eikenberry, an astrophysicist at the California Institute of Technology, the superhot gas in the inner disk shines brightly in X-rays, and dramatic dips in the X-ray emission suggest that the inner disk vanishes every 20 to 40 minutes. Infrared and radio observations at the same time show huge flares which indicate that matter is being thrown out of the system.
Eikenberry and colleagues from the Massachusetts Institute of Technology and NASA's Goddard Space Flight Center will discuss their findings at a 9:30 a.m. press conference on Wednesday, January 7, during the winter meeting of the American Astronomical Society.
The scientists observed the disappearance of the inner portion of the disk, known as an accretion disk, at the same time that glowing plasma is ejected from the black hole system. In August, Eikenberry and his collaborators at Caltech observed infrared flares from the black hole system, known as GRS 1915+105, using the Mt. Palomar 200-inch telescope.
At the same time, Ronald Remillard and his collaborators at MIT monitored X-ray dips from the same black hole using NASA's Rossi X-ray Timing Explorer (RXTE) satellite. Jean Swank and her collaborators at NASA/GSFC observed similar dips, and in September saw them again at the same time that Felix Mirabel (Center d'Etudes de Saclay, France) measured infrared and radio flares from GRS 1915+105.
"Since the X-rays come from the parts of the disk closest to the black hole, when we saw the X-ray dips every half hour it seemed that the inner disk was disappearing," Remillard says. "In fact, similar behavior had been studied and modelled extensively over the last year by a team led by Tomaso Belloni in the Netherlands and by Jean Swank's team at Goddard.
"The real excitement came when we saw the infrared flares," Remillard adds. "This showed that the black hole was throwing matter out of the system at the same time the disk disappears."
"These results are fascinating," says Eikenberry. "Scientists have studied the accretion disks and high-speed jets around black hole systems for decades, and many theoretical models have predicted that the jets are linked to the inner accretion disk.
"However, the direct connection between the disappearance of the inner disk and the jet ejection has never been seen until now."
"This work is also exciting because it may help us understand many other types of systems with jets," notes Robert Nelson, who works with Eikenberry at Caltech. "Astronomers have found jets in a wide range of objects, from quasars incredibly powerful objects seen out to the edge of the observable universe to young protostars."
The half-hour spacing between the ejections may be telling researchers that what they had thought were smooth, continuous outflows may in fact be intermittent explosions.
"There are many fine details in the X-ray dips that we may now seriously investigate to better understand the ejection mechanism," adds Edward R. Morgan, who works with Remillard at MIT. "In particular, there is a very unusual X-ray flash at the bottom of these dips in which the X-ray spectrum changes significantly. This may be the trigger for the rapid acceleration of the disk material."
The black hole in GRS 1915+105 became known to astronomers in 1992 as an X-ray nova, which is believed to signify the sudden flow of hot gases into a black hole from a companion star in a binary system. The black hole in GRS 1915+105 is thought to have a mass equal to ten Suns or more, all crushed by its own gravity into a tiny sphere contained within an "event horizon," which itself has a radius of about 20 km.
When a black hole pulls gas from the atmosphere of a companion star, the matter spirals in toward the event horizon like water going down a drain, and the swirling disk created by the flow is known to astronomers as an "accretion disk." The gas in the disk heats up dramatically due to the large acceleration and friction. Just before entering the event horizon, the gas reaches temperatures of millions of degrees, causing it to glow in X-rays.
In 1994, Mirabel and Luis Rodriguez observed radio emission from jets in GRS 1915+105, and they determined that the speed of the jets was greater than 90 percent of the speed of light, or roughly 600 million miles per hour. Since RXTE began observing the X-ray sky in early 1996, the exceptionally chaotic behavior of GRS 1915+105 in X-rays has been chronicled on many occasions.
The new results gained by Eikenberry's team brings together these phenomena by showing that modest jet ejections and the pattern of X-ray variations are synchronized in an organized way.
"The repeated ejections are really amazing," says Craig Markwardt, a member of the NASA/GSFC team. "The system behaves like a celestial version of Old Faithful. At fairly regular intervals, the accretion disk is disrupted and a fast-moving jet is produced."
"This jet is staggeringly more powerful than a geyser," adds Swank. "Every half hour, the black hole GRS 1915+105 throws off the mass of an asteroid at near the speed of light. This process clearly requires a lot of energy; each cycle is equivalent to 6 trillion times the annual energy consumption of the entire United States."
"Since the disk-jet interaction is so poorly understood, we're hoping that further analysis of these observations will show us more details of what is happening so close to the black hole," Eikenberry says. "We're planning more detailed studies for the coming year which should give us even more clues as to the nature of these incredibly powerful events.
"Right now, we still aren't even sure why these dips and ejections occur every half hour or so why not every week or every 30 seconds, for instance?"
17 Sept 1997 - Gamma Rays and Cosmic Fireball Astronomers detect relativistically expanding clouds around the May 8, 1997 gamma-ray burst PASADENA - Astrophysicists still don't know what caused the gamma-ray burst of May 8, but they now have a size and rate of expansion for its remnant "fireball" to add to the location and distance. New measurements by researchers at the California Institute of Technology and the National Radio Astronomy Observatory (NRAO) indicate that the fireball is now 85 times larger in diameter than our own solar system. Further, the researchers have determined that the fireball is expanding at an extremely high rate of speed-perhaps as fast as 99.99 percent of the speed of light when the explosion first occured, and currently about 85 percent of light speed. "This has all helped us to understand the mechanics of gamma-ray bursts once they take place," said Shrinivas Kulkarni, a Caltech astrophysicist who is coprincipal investigator of the work, which is reported in the September 18 issue of the journal Nature. A few months ago the Caltech team, using the Palomar and the Keck telescopes, decisively showed that this gamma-ray burst occurred in a distant galaxy, settling one of the major controversies about the origin of these enigmatic objects. Coprincipal investigator Dale Frail of NRAO added, "If you ask me what caused the burst, I'd still have to say it's pure speculation. It could have been a black hole smothering a neutron star, or maybe two neutron stars colliding, or perhaps even two black holes colliding. "What we do know is that this was a spectacular cosmic event-far more energetic than a supernova explosion." Gamma-ray bursters were first discovered by military satellites almost 30 years ago. The field has advanced rapidly, thanks to the precise localization of the bursts offered by the Italian-Dutch satellite BeppoSAX. Astrophysicists have now found, rapidly in succession, that gamma-ray bursts occur at cosmological distances and are probably the most energetic events in the universe. This particular burst was first reported by BeppoSAX on May 8, 1997. Before the advent of BeppoSAX, astrophysicists had no idea whether gamma bursts originated in our own galaxy or across the universe, and, in fact, had formulated competing theories accounting for either scenario. The measurements were obtained at the Very Large Array, a radio telescope array operated by NRAO with funding from the National Science Foundation. Other authors of the paper include Greg Taylor of NRAO and two BeppoSAX team members, Luciano Nicastro and Marco Feroci. Kulkarni and the other researchers obtained the new information when they observed that the radio emission from the fireball showed considerable fluctuations over the first three weeks following the burst. These subsequently died down. The astronomers attribute this to "twinkling." As amateur astronomers probably know, a star twinkles because it is a tiny point source of light whose image is displaced by atmospheric disturbances. A planet does not twinkle, however, because its disk is actually big enough in the sky to smear out the disturbances. At visible wavelengths, an object in outer space must appear to be at least several arc-seconds in diameter-about the size of a pinhead held at arm's length-to avoid twinkling. A similar twinkling phenomenon occurs at radio wavelengths, but in this case is caused by clouds of gas in the interstellar medium, the space between stars. At radio wavelengths, the disk of an object can be approximately a thousand times smaller in apparent diameter without twinkling. Thus, when the researchers observed that the twinkling had ceased some three weeks after the initial gamma burst, they could infer the actual size and expansion rate of the fireball because they knew the apparent size of the object in the sky and its distance from Earth. "In just six months we have come a long way from having no understanding of these objects to making measurements," said Kulkarni. The gamma-ray emission actually lasted only about 15 seconds. After that, the event continued to emit lower-energy radiation at other frequencies. It was detected by ground-based telescopes and the Hubble Space Telescope for a couple of weeks. The radio emission is still visible today. Kulkarni added, "Probably, the bulk of the radio emissions will slowly decay over the next few months. However, the fireball will be visible at meter wavelengths for probably another year. The radio emission is indeed the embers of this explosive event."