Category: Astronomy

Image credit: Hubble

The new Advanced Camera for Surveys (ACS) on the Hubble Space Telescope has revealed a clear disk of dust around a young, 5 million year old star. Astronomers believe these disks are the birthplaces of planets. The star, called HD 141569A is part of a triple star system located 320 light-years away in the constellation of Libra.

NASA Hubble Space Telescope’s new Advanced Camera for Surveys (ACS) has given astronomers their clearest view yet of the dust disk around a young, 5-million-year-old star. Such disks are expected to be the birthplace of planets. The star, called HD 141569A, lies 320 light-years away in the constellation Libra and appears to be a member of a triple-star system.

The star HD 141569A was first identified as a candidate for a circumstellar disk in 1986, from observations done with the NASA/Netherlands/United Kingdom Infrared Astronomy Satellite (IRAS). An excess of infrared radiation associated with the star provides telltale evidence for the presence of a dust disk. Hubble’s Near Infrared Camera and Multi-Object Spectrometer photographed the disk in 1999 and revealed two concentric rings divided by a dark lane. This was interpreted as evidence of dynamical sculpting by one or more planets.

The ACS reveals that the disk’s structure is much more complex than previously thought. The disk is actually a tightly wound spiral structure. The outer regions of the disk reveal two diffuse spiral arms, one of which appears to be associated with the nearby double star system (HD 141569BC) seen at the upper left. The apparent connection between the disk and the double star suggest that an interaction with the double star may be responsible for the structures seen in the disk.

However, previous mid-IR images of the disk show that it is relatively clear of dust within approximately 2.8 billion miles of the star. This inner region may have been swept clear by one or more unseen planets.

These observations of the disk were obtained with the ACS’s High Resolution Camera (HRC) coronagraph. The photo on the left is a processed visible light image. In the photo on the right, the disk has been geometrically altered to simulate a face-on view, and false-color has been applied to enhance the disk structure. The black center marks regions where light from the star has been masked out. These images are the first results of a survey of disks around young main-sequence stars being conducted by the ACS science team.

Original Source: Hubble News Release

Image credit: NASA

A team of astronomers from the California Institute of Technology in Pasadena presented images today of a rare Hyper Extremely Red Object (Hero). This dim object, located near a galaxy 10 billion light years away is traveling away from us at almost the speed of light. In fact, it’s so far, and moving so fast, it has gone way past being red-shifted – it’s only visible in infrared light.

Heroes are usually confined to comic books and movies, but as the saying goes, we all need one. So astronomers have turned to the deep, dark cosmos to find their heroic figure — the “Hyper Extremely Red Object,” or “Hero.”

At the American Astronomical Society winter meeting in Seattle today, an astronomer from the California Institute of Technology in Pasadena reports the discovery of a Hero near the radio galaxy 53W002, more than 10 billion light years away. This marks the first time a Hero has been found near a radio galaxy, suggesting that radio galaxies — which are optically dim but have strong radio emissions — may provide a guidepost for scouting out other Hero objects.

“Hero objects are intriguing. Like comic book heroes, they travel really fast — almost at the speed of light. They are virtually invisible to our eyes and they are very mysterious. Most importantly, this type of Hero may hold a key for understanding how the first galaxies formed and evolved in the universe,” said Dr. Myungshin Im, a staff research scientist at the Space Infrared Telescope Facility Science Center, located at Caltech.

So far, the astronomical version of a hero has taken on the unassuming guise of a small, glowing, red patch in deep space. More advanced infrared telescopes like NASA’s Space Infrared Telescope Facility, managed by the Jet Propulsion Laboratory, Pasadena, Calif., and launching in spring 2003, may, among other things, lift this red veil and reveal these remote objects for what they really are — quite possibly the universe’s earliest stars and galaxies.

Due to expansion of the universe after the Big Bang, a distant object in the universe races away from us so fast that any visible light from it “redshifts” — in other words, a light source becomes redder when it recedes from observers on Earth, and, conversely, bluer when it approaches. So when a visible light source moves away from us at nearly the speed of light, it often appears in infrared wavelengths. Big Bang theory also implies that the farther away an object is, the faster it moves away from us.

53W002_HERO1, the designation for the newly found Hero, is so far away and moves so fast it appears as a faint infrared source. In fact, it took two powerful telescopes equipped with infrared cameras to spot it in the deep sky. Im discovered 53W002_HERO1 from images taken by the near-infrared camera and multi-object spectrometer on NASA’s Hubble Space Telescope and the cooled infrared spectrograph and camera attached to the Subaru 8-meter (26-feet) telescope atop Mauna Kea in Hawaii. Dr. Toru Yamada and collaborators at the National Astronomical Observatory of Japan provided Im with the Subaru data.

The more distant a cosmic object is, the further in the past we see it. But for Im and colleagues to glean information about the early universe from 53W002_HERO1, they first need to determine its intrinsic color — that is, how would this astronomical hero appear to a human observer nearby?

It could be red, indicating either dust-obscured galaxies cocooning intense star formation, or older galaxies filled with an overabundance of elderly, reddish stars, both of which would lie about 10 billion light-years away. If the former condition exists, astronomers will appreciate the degree to which dust hid star formation during that epoch. However, if the latter holds then scientists can trace back to a time when a significant population of stars were born.

Another possibility is that a Hero might really be blue — a very young galaxy populated with fresh, super-hot blue stars at a distant 13 to 14 billion light years. In this instance, we may be witnessing the formation of the universe’s very first galaxies.

To determine whether 53W002_HERO1 is intrinsically red or blue, Im and his colleagues will peer at these mysterious objects in the redder part of infrared, a feat that requires a view from above Earth’s infrared-absorbing atmosphere. This will be accomplished with the Space Infrared Telescope Facility.

Original Source: NASA/JPL News Release

Image credit: Rensselaer Polytechnic Institute

Astronomers announced today that they have discovered a giant ring of stars circling the Milky Way. They believe this ring could contain as many as 500 million stars, and was formed when our galaxy collided with a smaller, dwarf galaxy several billion years ago. Other galaxies have been seen with a halo of stars, including Andromeda.

A previously unseen band of stars beyond the edge of the Milky Way galaxy has been discovered by a team of scientists from Rensselaer Polytechnic Institute, Fermi National Accelerator Laboratory, and the Sloan Digital Sky Survey (SDSS). The discovery could help to explain how the galaxy was assembled 10 billion years ago.

This ring around the Milky Way galaxy discovered by the Sloan Digital Sky Survey may be what’s left of a collision between our galaxy and a smaller, dwarf galaxy that occurred billions of years ago. It’s an indication that at least part of our galaxy was formed by many smaller or dwarf galaxies mixing together, explained investigators Heidi Jo Newberg of Rensselaer Polytechnic Institute and Brian Yanny of the Fermi National Accelerator Laboratory’s Experimental Astrophysics Group. For illustration purposes, the sun is approximately 30,000 light years from the center of the galaxy. Traveling from Earth at the speed of light, it would take 40,000 light years to reach the newly-discovered ring of stars.

Hidden from view behind stars and gas on the same visual plane as the Milky Way, this ring of stars is approximately 120,000 light years in diameter, says Heidi Newberg, associate professor of physics and astronomy at Rensselaer and a co-lead investigator on the project. Traveling from Earth at the speed of light, it would take 40,000 light years to reach the ring.

“These stars may be what’s left of a collision between our galaxy and a smaller, dwarf galaxy that occurred billions of years ago,” says Newberg. “It’s an indication that at least part of our galaxy was formed by many smaller or dwarf galaxies mixing together.”

The ring of stars is probably the largest of a series of similar structures being found around the galaxy. Investigators believe that as smaller galaxies are pulled apart, the remnants dissolve into streams of stars around larger galaxies. Gravity, primarily from unseen dark matter, holds the ring in a nearly circular orbit around the Milky Way.

“What’s new is the position of the star belt on the outskirts of the Milky Way, an ideal position to study the distribution and amount of dark and light mass within the band,” said Brian Yanny, a scientist at Fermilab’s Experimental Astrophysics Group and a co-lead investigator on the project.

Newberg and Yanny presented their findings today at the American Astronomical Society meeting in Seattle, Washington.

Evidence of this new unexpected band of stars hidden by the Milky Way comes from multi-color photo imagery of hundreds of square degrees of sky and hundreds of spectroscopic exposures from the Sloan Digital Sky Survey, the largest international collaborative astronomical survey ever undertaken.

For four years Newberg, Yanny, and a collaboration of SDSS scientists have been examining the distribution of stars in the Milky Way. At the outer edge of the galaxy in the direction of the constellation Monoceros (the Unicorn) they found tens of thousands of unexpected stars that altered then-standard galactic models.

Three-dimensional mapping from the SDSS revealed the excess stars were actually parts of a separate structure outside the Milky Way.

“The large area covered by the Sloan Survey and the accuracy of the multi-colored observations has allowed us to revisit some classic questions, questions from 50 to 100 years ago,” Yanny said. “What does our Milky Way look like as a whole? How did it form? Did it form in one ‘whoosh,’ or was it built up slowly via mergers of collapsing dwarf galaxies? And how does the mysterious dark (invisible) matter affect the distribution of stars?”

Original Source: SDSS News Release

Image credit: Hubble

A new paper published by Dartmouth university researcher Brian Chaboyer reports that our universe might be dominated by “dark energy”; a mysterious force that seems to be causing objects in the universe to accelerate away from each other. The researchers came to this conclusion by calculating the age of distant globular clusters, and matching it to the expansion age of the universe. The numbers only match if the universe has been accelerating up until now.

A Dartmouth researcher is building a case for a “dark energy”-dominated universe. Dark energy, the mysterious energy with unusual anti-gravitational properties, has been the subject of great debate among cosmologists.

Brian Chaboyer, Assistant Professor of Physics and Astronomy at Dartmouth, with his collaborator Lawrence Krauss, Professor of Physics and Astronomy at Case Western Reserve University, have reported their finding in the January 3, 2003, issue of Science. Combining their calculations of the ages of the oldest stars with measurements of the expansion rate and geometry of the universe lead them to conclude that dark energy dominates the energy density of the universe.

?This finding provides strong support for a universe which is dominated by a kind of energy we?ve never directly observed,? says Chaboyer. ?Observations of distant supernova have suggested for a few years that dark energy dominates the universe, and our finding provides independent evidence that the universe is dominated by this type of energy we do not understand.?

The researchers came to this conclusion as they were refining their calculations for the age of globular clusters, which are groups of about 100,000 or more stars found in the outskirts of the Milky Way, our galaxy. Because this age (about 12 billion years old) is inconsistent with the expansion age for a flat universe (only about 9 billion years old), Krauss and Chaboyer came to the conclusion that the universe is expanding more quickly now than it did in the past.

The only explanation, according to Chaboyer and Krauss, for an accelerating universe is that the energy content of a vacuum is non-zero with a negative pressure, in other words, dark energy. This negative pressure of the vacuum grows in importance as the universe expands and causes the expansion to accelerate.

Original Source: Dartmouth College News Release

Image credit: ESA

Shortly after the Big Bang, it’s believed that all the matter in the Universe was broken up into its smallest components. But astronomers believe that some of this original material may be created again inside very dense neutron starts. Using the XMM-Newton space telescope, a team of astronomers are attempting to calculate the “compactness” of several neutron stars – to see if they go beyond the density of normal matter.

A fraction of a second after the Big Bang, all the primordial soup of matter in the Universe was ‘broken’ into its most fundamental constituents. It was thought to have disappeared forever. However scientists strongly suspect that the exotic soup of dissolved matter can still be found in today’s Universe, in the core of certain very dense objects called neutron stars.

With ESA’s space telescope XMM-Newton, they are now closer to testing this idea. For the first time, XMM-Newton has been able to measure the influence of the gravitational field of a neutron star on the light it emits. This measurement provides much better insight into these objects.

Neutron stars are among the densest objects in the Universe. They pack the mass of the sun inside a sphere 10 kilometres across. A sugar cube-sized piece of neutron star weighs over a billion tonnes. Neutron stars are the remnants of exploding stars up to eight times more massive than our Sun. They end their life in a supernova explosion and then collapse under their own gravity. Their interiors may therefore contain a very exotic form of matter.

Scientists believe that in a neutron star, the density and the temperatures are similar to those existing a fraction of a second after the Big Bang. They assume that when matter is tightly packed as it is in a neutron star, it goes through important changes. Protons, electrons, and neutrons ? the components of atoms – fuse together. It is possible that even the building-blocks of protons and neutrons, the so-called quarks, get crushed together, giving rise to a kind of exotic plasma of ‘dissolved’ matter.

How to find out? Scientists have spent decades trying to identify the nature of matter in neutron stars. To do this, they need to know some important parameters very precisely: if you know a star?s mass and radius, or the relationship between them, you can obtain its compactness. However, no instrument has been advanced enough to perform the measurements needed, until now. Thanks to ESA’s XMM-Newton observatory, astronomers have been able for the first time to measure the mass-to-radius ratio of a neutron star and obtain the first clues to its composition. These suggest that the neutron star contains normal, non-exotic matter, although they are not conclusive. The authors say this is a ?key first step? and they will keep on with the search.

The way they got this measurement is a first in astronomical observations and it is considered a huge achievement. The method consists of determining the compactness of the neutron star in an indirect way. The gravitational pull of a neutron star is immense – thousands of million times stronger than the Earth?s. This makes the light particles emitted by the neutron star lose energy. This energy loss is called a gravitational ‘red shift’. The measurement of this red shift by XMM-Newton indicated the strength of the gravitational pull, and revealed the star?s compactness.

“This is a highly precise measurement that we could not have made without both the high sensitivity of XMM-Newton and its ability to distinguish details,” says Fred Jansen, ESA’s XMM-Newton Project Scientist.

According to the main author of the discovery, Jean Cottam of NASA?s Goddard Space Flight Center, “attempts to measure the gravitational red shift were made right after Einstein published the General Theory of Relativity, but no one had ever been able to measure the effect in a neutron star, where it was supposed to be huge. This has now been confirmed.”

Original Source: ESA News Release

Image credit: Hubble

Astronomers have discovered a new object far past the orbit of Pluto. Dubbed Quaoar, the object is 1,200 km across (approximately 1/10th the size of the Earth), and orbits the sun once every 288 years. Although the object is half the size of the Pluto, it probably won’t be considered a new planet ? even Pluto’s planetness is hotly debated. Ironically, Quaoar was caught in images taken as far back as 20 years ago; astronomers just didn’t realize what they were looking at.

NASA’s Hubble Space Telescope has measured the largest object discovered in the solar system since the discovery of Pluto 72 years ago.

Approximately half the size of Pluto, the icy world 2002 LM60, dubbed “Quaoar” (pronounced kwa-whar) by its discoverers, is the farthest object in the solar system ever to be resolved by a telescope. It was initially detected by a ground-based telescope, as simply a dot of light, until astronomers aimed the powerful Hubble telescope at it.

Quaoar is about 4 billion miles away from Earth, well over a billion miles farther away than Pluto. Unlike Pluto, its orbit around the Sun is very circular, even more so than most of the planetary-class bodies in the solar system.

Although smaller than Pluto, Quaoar is greater in volume than all the asteroids combined (though probably only one-third the mass of the asteroid belt, because it’s icy rather than rocky). Quaoar’s composition is theorized to be largely ices mixed with rock, not unlike that of a comet, though 100 million times greater in volume.

This finding yields important new insights into the origin and dynamics of the planets, and the mysterious population of bodies dwelling in the solar system’s final frontier: the elusive, icy Kuiper belt beyond Neptune.

Michael Brown and Chadwick Trujillo of Caltech are reporting the findings today at the 34th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Birmingham, Ala.

Earlier this year, Trujillo and Brown used the Palomar Oschin Schmidt telescope to discover Quaoar as an 18.5-magnitude object creeping across the summer constellation Ophiuchus (it’s less than 1/10,000th the brightness of the faintest star seen by the human eye). Brown had to do follow-up observations using Hubble’s new Advanced Camera for Surveys on July 5 and August 1, 2002, to measure the object’s true angular size of 40 milliarcseconds, corresponding to a diameter of about 800 miles (1300 kilometers). Only Hubble has the sharpness needed to actually resolve the disk of the distant world, leading to the first-ever direct measurement of the true size of a Kuiper belt object (KBO).

Like Pluto, Quaoar dwells in the Kuiper belt, an icy debris field of comet-like bodies extending 7 billion miles beyond Neptune’s orbit. Over the past decade more than 500 icy worlds have been found in the Kuiper belt. With a few exceptions all have been significantly smaller than Pluto.

Previous record holders are a KBO called Varuna, and an object called 2002 AW197, each approximately 540 miles across (900 kilometers). Unlike Hubble’s direct observations, these diameters are deduced from measuring the objects’ temperatures and calculating a size based on assumptions about the KBOs’ reflectivity, so the uncertainty in true size is much greater.

This latest large KBO is too new to have been officially named by the International Astronomical Union. Trujillo and Brown have proposed naming it after a creation god of the Tongva native American 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.”

Quaoar’s “icy dwarf” cousin, Pluto, was discovered in 1930 in the course of a 15-year search for trans-Neptunian planets. It wasn’t realized until much later that Pluto actually was the largest of the known Kuiper belt objects. The Kuiper belt wasn’t theorized until 1950, after comet orbits provided telltale evidence of a vast nesting ground for comets just beyond Neptune. The first recognized Kuiper belt objects were not discovered until the early 1990s. This new object is by far the “biggest fish” astronomers have snagged in KBO surveys. Brown predicts that within a few years even larger KBOs will be found, and Hubble will be invaluable for follow-up observations to pin down sizes.

Original Source: Hubble News Release

What is the biggest telescope in the world?

Image credit: NASA

A team of astronomers have taken the highest resolution mid-infrared picture ever taken of the center of our Milky Way galaxy. The image is so detailed, you can actually see dust swirling around the giant black hole located at the centre of the galaxy. The camera, called the Mid-Infrared Large-Well Imager, or Mirlin, is attached to the enormous Keck observatory in Hawaii.

The highest resolution mid-infrared picture ever taken of the center of our Milky Way galaxy reveals details about dust swirling into the black hole that dominates the region.

The image was taken by a team led by Dr. Mark Morris of the University of California, Los Angeles, at the Keck II telescope in Hawaii, with an infrared camera built at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. The camera, called the Mid-Infrared Large-Well Imager, or Mirlin, used three different infrared wavelengths to build the color composite image available online at http://irastro.jpl.nasa.gov/GalCen/galcen.html.

The mid-infrared part of the electromagnetic spectrum comprises the wavelengths at which room temperature objects glow most brightly. Everything on Earth, including the telescope, the astronomers, and even the atmosphere, emits a bright glow in the mid-infrared. Seeing celestial objects though this glow is like trying to see stars during daylight; special techniques are needed to tease the stars from this glow to build a recognizable picture.

Near the center of the image, but not apparent at these wavelengths, is a black hole three million times heavier than our Sun. Its gravitational pull, so powerful that not even light can escape from its surface, affects the motion of dust, gas and even stars, throughout the region.

A veil of dust absorbs the visible light emitted by most of the stars near the Galactic Center. The light warms the dust, which then radiates in the infrared and becomes visible to the mid-infrared camera.

The image shows this dusty material spiraling toward the black hole, most notably the stream of gas and dust called the Northern Arm. When this material eventually falls into the black hole, it will release energy that affects everything in its vicinity. This event, which astronomers are certain has happened many times in the history of the Milky Way, may trigger the formation of a new generation of stars by causing other nearby dust clouds to collapse, or it may actually inhibit the formation of new stars if the released energy destroys those clouds. Either way, the black hole continues to grow larger as new material falls into it.

Astronomers know that the stars in this image are all very luminous, because less luminous stars appear very faint to a mid-infrared camera. A massive star nearing the last stages of its life, the red supergiant IRS7, is visible in this image as the smallish, bright spot just above the center. IRS7 is simply so luminous — more than 100,000 times as bright as our Sun — that we can see its starlight directly.

The “mini-cavity” in the center is a bubble that has apparently been evacuated of dust and gas. A star located at the center of the mini-cavity (not visible in this image) apparently blows this bubble with its powerful stellar wind. The “bullet” is a mysterious, fast-moving feature pointing roughly away from the mini-cavity, just below and to the right of the center. It may be a jet composed of gas and dust.

Other members of the Mirlin imaging team, along with Morris, are Dr. Andrea Ghez, Dr. Eric Becklin and Angelle Tanner of UCLA; Drs. Michael Ressler and Michael Werner of JPL; and Dr. Angela Cotera Hulet of the Arizona State University, Tempe, Ariz. The camera was built at JPL by Ressler and Werner. Operation of Mirlin is supported by a grant from NASA’s Office of Space Science, Washington, D.C. Some findings based on this image have been published in the Astrophysical Journal.

Studying processes in the center of our own galaxy may teach astronomers more about much more active, more distant galactic nuclei — objects like quasars and Seyfert galaxies, which are the most violent places known in the universe. More information about both the center of our Milky Way and the centers of other galaxies may be obtained with future instruments that have higher resolution and greater sensitivity.

For example, NASA is planning a similar infrared camera, the Mid-Infrared Instrument, one of three instruments that will fly aboard the James Webb Space Telescope, launching in 2010. This camera will achieve resolution roughly equivalent to the Keck images, but because it will orbit above the warm glow emitted by Earth’s atmosphere, it will be 1,000 times more sensitive. Using this instrument, astronomers will be able to study the centers of galaxies all the way to the edge of the observable universe.

JPL, in conjunction with a consortium of European countries and the European Space Agency, is developing the Mid-Infrared Instrument. The James Webb Space Telescope is managed by the Goddard Space Flight Center, Greenbelt, Md.

JPL is a division of the California Institute of Technology in Pasadena.

Original Source: NASA/JPL News Release

An amateur astronomer has discovered what could be a new object orbiting the Earth; maybe it’s a recently captured space rock, or maybe it’s just a remnant from the Apollo program. Whatever it is, the object, dubbed J002E2, seems to orbit the Earth every 50-days in a wide orbit. If it turns out to be natural, the object will become the Earth’s 3rd moon (and you only thought we had one), after Cruithne which was discovered in 1986 in a long erratic orbit. (BBC News Story)

Image credit: SWRI

Although the Kuiper Belt, a region of icy objects located past the orbit of Neptune, was only discovered in 1992, it’s already presented a host of mysteries. One mystery is why an unusually large number of these objects have small satellites orbiting them – 8 out of the 500 objects discovered so far have had satellites. The high number brings into question the traditional theory that they’re caused by collisions.

The Kuiper Belt region of the solar system, which stretches from just past Neptune to beyond the farthest reaches of Pluto?s orbit, was only discovered in 1992, but continues to reveal new knowledge into the formation processes of the planets. Now, in a paper to be published in the October issue of The Astronomical Journal, a Southwest Research Institute? (SwRI?) scientist reveals a new mystery about Kuiper Belt Objects (KBOs).

The study examined the formation of KBO satellites, which have been observed only since 2001 and continue to be discovered around an unexpectedly large number of the more than 500 known KBOs.

?In just over a year since the first satellite of a KBO was found, scientists have discovered a total of seven KBO satellites. Surprisingly, observations by both ground-based telescopes and the Hubble Space Telescope have indicated that, in many cases, the KBO satellites are as large or nearly as large as the KBOs around which they orbit,? says Dr. S. Alan Stern, director of the SwRI Space Studies Department. ?That so many binary or quasi-binary KBOs exist came as a real surprise to the research community.?

The focus of Stern?s work was not observational in nature, but rather it sought to understand how such large KBO-satellite pairs could form. The standard model for large satellite formation is based on collisions between an interloping body and the parent object around which the satellite orbits. This model has successfully explained binary systems around asteroids and the Pluto-Charon system, and also has direct relevance to the formation of the Earth-moon system.

Stern?s findings call into question the formation of KBO satellites by standard collisional processes. Collisions of the magnitude required, Stern found, appear to be energetically improbable, given the number and masses of potential impactors in both the ancient (more massive) and modern day (eroded) Kuiper Belts.

This likely implies one of two alternatives: Either KBO satellites were not formed by collisions, as has been commonly assumed, or the surface reflectivities (which help determine size) of KBOs with satellites, or the reflectivity of the satellites themselves, have been significantly underestimated.

?If the surfaces of KBOs with satellites, or the satellites themselves, are more reflective than previously thought,? says Stern, ?these objects would be smaller and less massive, and would therefore require smaller, less energetic impacts to create the satellite systems we see.?

NASA?s new Space Infrared Telescope Facility (SIRTF), set for launch early next year, will help resolve these two alternatives, Stern says, by directly measuring the reflectivities and sizes of numerous KBOs, including those with satellites.

In addition to this work, Stern serves as principal investigator of the NASA New Horizons mission to Pluto and the Kuiper Belt. Expected to launch in January 2006, this spacecraft will make the first ever flyby reconnaissance of the Pluto and Charon system and then go on to explore KBOs as it leaves the solar system. New Horizons is the only NASA mission planned to study Kuiper Belt Objects at close range.

The NASA Origins of Solar Systems program provided funding for this research.

Original Source: SWRI News Release

Image credit: Hubble

Astronomers have spotted a number of young stellar clusters dotted around a very old elliptical galaxy – this disputes the established theory that old galaxies contain only older stars. The team used the Hubble Space Telescope and the ESO Very Large Telescope to take a series of images of galaxy NGC 4365, and they were able to identify star clusters that were only a few billion years old, while the majority were over 12 billion years old. Why the galaxy contains such a combination of young and old stars is still a mystery.

Combining data from the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT), a group of European and American astronomers have made a major discovery. They have identified a huge number of ‘young’ stellar clusters, in an old elliptical galaxy.

For the first time, it has been possible to identify several distinct periods of star formation in a galaxy as old as this one. Elliptical galaxies have always been considered to have undergone one early star-forming period and thereafter to be devoid of star formation. However, the combination of the best and largest telescopes in space and on the ground has now clearly shown that there is more than meets the eye.

Do elliptical galaxies only contain old stars?
One of the challenges of modern astronomy is to understand how galaxies – large systems of stars, gas and dust – form and evolve. When did most of the stars in the Universe form? Did this happen at a very early stage, within a few billion years of the Big Bang? Have a significant number of the stars we now observe formed much more recently?

Spectacular collisions between galaxies take place all the time, triggering the formation of thousands or even millions of stars. However, when looking at the Universe as a whole, most of its stars are found in elliptical galaxies whose overall appearance has so far led us to believe that they, and their stars and as well, are old.

These elliptical galaxies do shine with the diffuse, reddish glow normally associated with stars that are many thousand million years old. However, what is the underlying mix of stars that produces this elderly appearance? Could a significant number of much younger stars be ‘hiding’ among the older ones?

Detailed observations with the world’s premier telescopes have now cast new light on this central question about the behaviour of some of the major building blocks of the Universe.

Cosmic paleonthology
To break the stellar ‘cocktail’ in elliptical galaxies down into its different constituents, a team of European and American astronomers observed massive stellar clusters in and around nearby galaxies. These “globular” clusters, so called because of their shape, exist in large numbers around all observed galaxies and form a kind of ‘skeleton’ within their host galaxies. These ‘bones’ receive an imprint for every episode of star formation they undergo. By reading the ages of the globular clusters in a galaxy, it is possible to identify the past epoch(s) of active star formation in a galaxy.

Reading the imprints and deducing the distribution of ages of the globular clusters, astronomers can reveal when many of the stars in elliptical galaxies formed. This is similar to the way a palaeontologist uses the skeletons of dinosaurs to deduce information about the era in which they lived.

A surprising discovery
The team combined images of a number of galaxies from Hubble’s Wide Field and Planetary Camera 2 with infrared images obtained from the multi-mode ISAAC instrument on the 8.2m VLT Antu telescope at the ESO Paranal Observatory (Chile). To their great surprise, they discovered that many of the globular clusters in one of these galaxies, NGC 4365, a member of the large Virgo cluster of galaxies, were only a few thousand million years old, much younger than most of the other stars in this galaxy (roughly 12 thousand million years old).

The astronomers were able to identify three major groups of stellar clusters. There is an old population of clusters of metal-poor stars, some clusters of old but metal-rich stars and now, seen for the first time, a population of clusters with young and metal-rich stars.

These results have been fully confirmed by spectroscopic observations made with another of the world’s giant telescopes, the 10-metre Keck on Hawaii.

“It is a great pleasure to see two projects wholly or partly funded by Europe – VLT and Hubble – work in concert to produce such an important scientific result”, says Piero Benvenuti, ESA Hubble Project Scientist. “The synergy between the most advanced ground and space telescopes continues to prove its effectiveness, paving the way to impressive new discoveries that would not otherwise be possible.”

The discovery of young globular clusters within old galaxies is surprising since the stars in the giant elliptical galaxies were until now believed to have formed during a single period early in the history of the Universe. It is now clear that some of the galaxies may be hiding their true nature and have indeed experienced much more recent periods of major star formation.

Original Source: ESA News Release