Category: Hubble

The newly discovered pair of Uranus faint dusty rings. Image credit: NASA Click to enlarge
NASA’s Hubble Space Telescope photographed a new pair of rings around Uranus and two new, small moons orbiting the planet.

The largest ring is twice the diameter of the planet’s previously known rings. The rings are so far from the planet, they are being called Uranus’s “second ring system.” One of the new moons shares its orbit with one of the rings. Analysis of the Hubble data also reveals the orbits of Uranus’s family of inner moons have changed significantly over the past decade.

“The detection of these new interacting rings and moons will help us better understand how planetary systems are formed and sustained, which is of key importance to NASA’s scientific exploration goals,” said Dr. Jennifer Wiseman, program scientist for Hubble at NASA Headquarters.

Since dust orbiting Uranus is expected to be depleted by spiraling away, the planet’s rings must be continually replenished with fresh material. “The new discoveries demonstrate that Uranus has a youthful and dynamic system of rings and moons,” said Mark Showalter of the SETI Institute, Mountainview, California.

Showalter and Jack Lissauer of NASA’s Ames Research Center, Moffet Field, Calif., propose that the outermost ring is replenished by a 12-mile-wide newly discovered moon, named Mab, which they first observed using Hubble in 2003.

Meteoroid impacts continually blast dust off the surface of Mab. The dust then spreads out into a ring around Uranus. Mab’s ring receives a fresh infusion of dust from each impact. Nature keeps the ring supplied with new dust while older dust spirals away or bangs back into the moon.

Showalter and Lissauer have measured numerous changes to the orbits of Uranus’s inner moons since 1994. The moon’s motions were derived from earlier Hubble and Voyager observations. “This appears to be a random or chaotic process, where there is a continual exchange of energy and angular momentum between the moons,” Lissauer said. His calculations predict moons would begin to collide as often as every few million years, which is extraordinarily short compared to the 4.5 billion year age of the Uranian system.

Showalter and Lissauer believe the discovery of the second ring, which orbits closer to the planet than the outer ring, provides further evidence that collisions affect the evolution of the system. This second ring has no visible body to re-supply it with dust. The ring may be a telltale sign of an unseen belt of bodies a few feet to a few miles in size. Showalter proposes that a previous impact to one of Uranus’s moons could have produced the observed debris ring.

Hubble uncovered the rings in August 2004 during a series of 80, four-minute exposures of Uranus. The team later recognized the faint new rings in 24 similar images taken a year earlier. Images from September 2005 reveal the rings even more clearly.

Showalter also found the rings in archival images taken during Voyager 2’s flyby of Uranus in 1986. Uranus’s first nine rings were discovered in 1977 during observations of the planet’s atmosphere. During the Voyager encounters, two other inner rings and 10 moons were discovered. However, no one noticed the outer rings, because they are extremely faint and much farther from the planet than expected. Showalter was able to find them by a careful analysis of nearly 100 Voyager images.

Because the new rings are nearly transparent, they will be easier to see when they tilt edge-on. The new rings will increase in brightness every year as Uranus approaches its equinox, when the sun shines directly over the planet’s equator. When it happens in 2007, all of the rings will be tilted edge-on toward Earth and easier to study. These research data will appear in an upcoming issue of the journal Science.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington.

Original Source: NASA News Release

Sirius and its tiny companion. Image credit: Hubble. Click to enlarge
For astronomers, it’s always been a source of frustration that the nearest white-dwarf star is buried in the glow of the brightest star in the nighttime sky. This burned-out stellar remnant is a faint companion of the brilliant blue-white Dog Star, Sirius, located in the winter constellation Canis Major.

Now, an international team of astronomers has used the keen eye of NASA’s Hubble Space Telescope to isolate the light from the white dwarf, called Sirius B. The new results allow them to measure precisely the white dwarf’s mass based on how its intense gravitational field alters the wavelengths of light emitted by the star. Such spectroscopic measurements of Sirius B taken with a telescope looking through the Earth’s atmosphere have been severely contaminated by scattered light from the very bright Sirius.

“Studying Sirius B has challenged astronomers for more than 140 years,” said Martin Barstow of the University of Leicester, U.K., who is the leader of the observing team. “Only with Hubble have we at last been able to obtain the observations we need, uncontaminated by the light from Sirius, in order to measure its change in wavelengths.”

“Accurately determining the masses of white dwarfs is fundamentally important to understanding stellar evolution. Our Sun will eventually become a white dwarf. White dwarfs are also the source of Type Ia supernova explosions that are used to measure cosmological distances and the expansion rate of the universe. Measurements based on Type Ia supernovae are fundamental to understanding ‘dark energy,’ a dominant repulsive force stretching the universe apart. Also, the method used to determine the white dwarf’s mass relies on one of the key predictions of Einstein’s theory of General Relativity; that light loses energy when it attempts to escape the gravity of a compact star.”

Sirius B has a diameter of 7,500 miles (12,000 kilometers), less than the size of Earth, but is much denser. Its powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 150-pound person would weigh 50 million pounds standing on its surface. Light from the surface of the hot white dwarf has to climb out of this gravitational field and is stretched to longer, redder wavelengths of light in the process. This effect, predicted by Einstein’s theory of General Relativity in 1916, is called gravitational redshift, and is most easily seen in dense, massive, and hence compact objects whose intense gravitational fields warp space near their surfaces.

Based on the Hubble measurements of the redshift, made with the Space Telescope Imaging Spectrograph, the team found that Sirius B has a mass that is 98 percent that of our own Sun. Sirius itself has a mass of two times that of the Sun and a diameter of 1.5 million miles (2.4 million kilometers).

White dwarfs are the leftover remnants of stars similar to our Sun. They have exhausted their nuclear fuel sources and have collapsed down to a very small size. Sirius B is about 10,000 times fainter than Sirius itself, making it difficult to study with telescopes on the Earth’s surface because its light is swamped in the glare of its brighter companion. Astronomers have long relied on a fundamental theoretical relationship between the mass of a white dwarf and its diameter. The theory predicts that the more massive a white dwarf, the smaller its diameter. The precise measurement of Sirius B’s gravitational redshift allows an important observational test of this key relationship.

The Hubble observations have also refined the measurement of Sirius B’s surface temperature to be 44,900 degrees Fahrenheit, or 25,200 degrees Kelvin. Sirius itself has a surface temperature of 18,000 degrees Fahrenheit (10,500 degrees Kelvin).

At 8.6 light-years away, Sirius is one of the nearest known stars to Earth. Stargazers have watched Sirius since antiquity. Its diminutive companion, however, was not discovered until 1862, when it was first glimpsed by astronomers examining Sirius through one of the most powerful telescopes of that time.

Details of the work were reported in the October 2005 issue of the Monthly Notices of the Royal Astronomical Society. Other participants on the team include Howard Bond of the Space Telescope Science Institute, Baltimore, Md.; Matt Burleigh of the University of Leicester; Jay Holberg and Ivan Hubeny of the University of Arizona; and Detlev Koester of the University of Kiel, Germany.

Original Source: HubbleSite News Release

Stellar jets. Image credit: Hubble. Click to enlarge
Like traffic on a freeway, plasma spewing from the poles of newborn stars moves in clumps that travel at different speeds. When fast-moving particles run into slower material on these cosmic freeways, the resulting “traffic jams” create massive shock waves that travel trillions of miles.

Thanks to highly resolved images from the Hubble Space Telescope, a team of astronomers have created the first moving pictures of one of these cosmic freeways, which are known as stellar jets. The movies allow scientists to trace these stellar jet shock waves for the first time, gleaning important clues about a critical, yet poorly understood process of starbirth. The results appeared in the November issue of Astronomical Journal.

“When it comes to actually showing exactly what’s going on, there’s just nothing like a movie,” said study co-author Patrick Hartigan, associate professor of physics and astronomy at Rice University. “You can look at a still image and make up all kinds of stories, but they all go out the window when you see a movie.”

Hartigan and researchers from the Cerro Tololo Inter-American Observatory (CTIAO) in Chile, Arizona State University (ASU), the University of Hawaii and the University of Colorado at Boulder, made the movies using images taken in 1994 and 1999 of a newly formed star called HH 47 in the constellation Vela. Because Hubble flies above the Earth’s atmosphere, it can take much clearer images than Earth-based telescopes. As a result, Hartigan and his co-researchers were able to resolve objects in the Hubble images that were 20 times smaller than objects resolved in similar images taken on Earth. This extra resolution, and the five-year gap between Hubble surveys of HH 47, allowed them to make moving pictures of the stellar jet shock waves moving away from the new star.

“Imagine taking a photo at a football game that shows the quarterback throwing the ball at the start of a play,” Hartigan said. “There is no way to know what happened in the play without a second photograph at the end of the play that shows a touchdown, incomplete pass, interception, or whatever occurs. If you take a series of photos, with enough resolution to make out the ball, you could determine whether someone ran with the ball or caught a pass, and you could determine the relative position of all of the players to one another at any time during the play.

“Like the time-lapse images of the game, our movies give us the ability to track the movement of individual features within the stellar jet, both relative to stationary objects and relative to other objects that are moving within the jet at a different speed,” Hartigan said.

New stars form out of giant clouds of gas and dust. Within these clouds, strong gravitational forces pull material together into a tight ball surrounded by a large spinning disk. The new star forms out of the ball, and any planets that might form do so in the disk. Through processes not well-understood, much of the disk material gradually spirals into the star, and the resulting energy from this process drives stellar jets of plasma that erupt from the star at perpendicular angles to the spinning accretion disk. The material thrown away from the star in the jets acts as a brake on disk, slowing its rotation and allowing more material to fall into the growing star. Scientists know stellar jets play an integral role in star formation, but they have yet to determine the specifics of their role, or how it is carried out.

The research was funded by NASA. Co-authors on the study include CTIO’s Steve Heathcote, ASU’s Jon A. Morse, University of Hawaii’s Bo Reipurth and University of Colorado at Boulder’s John Bally.

Original Source: Rice University

Crab Nebula. Image credit: Hubble. Click to enlarge
This is a mosaic image, one of the largest ever taken by NASA’s Hubble Space Telescope of the Crab Nebula, a six-light-year-wide expanding remnant of a star’s supernova explosion. Japanese and Chinese astronomers recorded this violent event nearly 1,000 years ago in 1054, as did, almost certainly, Native Americans.

The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula’s eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star’s rotation. A neutron star is the crushed ultra-dense core of the exploded star.

The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory’s Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.

Original Source:HubbleSite News Release

Einstein ring gravitational lens: SDSS J163028.15+452036.2. Image credit: Hubble. Click to enlarge
As Albert Einstein developed his theory of general relativity nearly a century ago, he proposed that the gravitational field from massive objects could dramatically warp space and deflect light.

The optical illusion created by this effect is called gravitational lensing. It is nature’s equivalent of having a giant magnifying lens in space that distorts and amplifies the light of more distant objects. Einstein described gravitational lensing in a paper published in 1936. But he thought the effect was unobservable because the optical distortions produced by foreground stars warping space would be too small to ever be measurable by the largest telescopes of his time.

Now, almost a century later, astronomers have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA’s Hubble Space Telescope, to identify 19 new “gravitationally lensed” galaxies, adding significantly to the approximately 100 gravitational lenses previously known. Among these 19, they have found eight new so-called “Einstein rings”, which are perhaps the most elegant manifestation of the lensing phenomenon. Only three such rings had previously been seen in visible light.

In gravitational lensing, light from distant galaxies can be deflected on its way to Earth by the gravitational field of any massive object that lies in the way. Because of this, we see the galaxy distorted into an arc or multiple separate images. When both galaxies are exactly lined up, the light forms a bull’s-eye pattern, called an Einstein ring, around the foreground galaxy.

The newly discovered lenses come from an ongoing project called the Sloan Lens ACS Survey (SLACS). A team of astronomers, led by Adam Bolton of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Leon Koopmans of the Kapteyn Astronomical Institute in the Netherlands, selected the candidate lenses from among several hundred thousand optical spectra of elliptical galaxies in the Sloan Digital Sky Survey. They then used the sharp eyes of Hubble’s Advanced Camera for Surveys to make the confirmation.

“The massive scale of the SDSS, together with the imaging quality of the Hubble telescope, has opened up this unprecedented opportunity for the discovery of new gravitational lenses,” Bolton explained. “We’ve succeeded in identifying the one out of every 1,000 galaxies that show these signs of gravitational lensing of another galaxy.”

The SLACS team scanned the spectra of approximately 200,000 galaxies 2 to 4 billion light-years away. The team was looking for clear evidence of emission from galaxies twice as far from Earth and directly behind the closer galaxies. They then used Hubble’s Advanced Camera for Surveys to snap images of 28 of these candidate lensing galaxies. By studying the arcs and rings produced by 19 of these candidates, the astronomers can precisely measure the mass of the foreground galaxies.

Besides producing odd shapes, gravitational lensing gives astronomers the most direct probe of the distribution of dark matter in elliptical galaxies. Dark matter is an invisible and exotic form of matter that has not yet been directly observed. Astronomers infer its existence by measuring its gravitational influence. Dark matter is pervasive within galaxies and makes up most of the total mass of the universe. By searching for dark matter in galaxies, astronomers hope to gain insight into galaxy formation, which must have started around lumpy concentrations of dark matter in the early universe.

“Our results indicate that, on average, these ‘elliptical lensing galaxies’ have the same special mass-density structure as that observed in spiral galaxies,” Bolton continued. “This corresponds to an increase in the proportion of dark matter relative to stars as one moves away from the center of the lensing galaxy and into its fainter outskirts. And since these lensing gelaxies are relatively bright, we can solidify this result with further ground-based spectroscopic observations of the stellar motions in the lenses.”

“Being able to study these and other gravitational lenses as far back in time as several billion years allows us to see directly whether the distribution of dark [invisible] and visible mass changes with cosmic time,” Dr. Koopmans added. “With this information, we can test the commonly held idea that galaxies form from collision and mergers of smaller galaxies.”

The Sloan Digital Sky Survey, from which the SLACS lens-candidate sample was selected, was begun in 1998 with a custom-built ground-based telescope to measure the colors and brightnesses of more than 100 million objects over a quarter of the sky and map the distances to a million galaxies and quasars. “This type of gravitational-lens survey was not an original goal of the SDSS, but was made possible by the excellent quality of the SDSS data,” said Scott Burles of the Massachusetts Institute of Technology in Cambridge, Mass., a SLACS team member and one of the creators of the SDSS.

“An additional bonus of the large size of the SDSS database is that we can design our search criteria so as to find the lenses that are most suitable for specific science goals,” said SLACS team member Tommaso Treu of the University of California, Santa Barbara. “Whereas until now we have selected the largest galaxies as our targets, in the next stages of the survey we are targeting smaller lens galaxies. There have been suggestions that the structure of galaxies changes with galaxy size. By identifying these rare objects ‘on demand,’ we will soon be able for the first time to test whether this is true.”

Added SLACS team member Leonidas Moustakas of the NASA Jet Propulsion Laboratory and the California Institute of Technology in Pasadena, Calif.: “These Einstein rings also give an unrivaled magnified view of the lensed galaxies, allowing us to study the stars and the formation histories of these distant galaxies.”

The SLACS Survey is continuing, and so far the team has used Hubble to study almost 50 of their candidate lensing galaxies. The eventual total is expected to be more than 100, with many more new lenses among them. The initial findings of the survey will appear in the February 2006 issue of the Astrophysical Journal and in two other papers that have been submitted to that journal.

Original Source: Hubblesite News Release

NGC 346 in the Small Magellenic Cloud. Image credit: Hubble. Click to enlarge.
This is a Hubble Space Telescope view of one of the most dynamic and intricately detailed star-forming regions in space, located 210,000 light-years away in the Small Magellanic Cloud (SMC), a satellite galaxy of our Milky Way. At the center of the region is a brilliant star cluster called NGC 346. A dramatic structure of arched, ragged filaments with a distinct ridge surrounds the cluster.

A torrent of radiation from the cluster’s hot stars eats into denser areas creating a fantasy sculpture of dust and gas. The dark, intricately beaded edge of the ridge, seen in silhouette by Hubble, is particularly dramatic. It contains several small dust globules that point back towards the central cluster, like windsocks caught in a gale.

Energetic outflows and radiation from hot young stars are eroding the dense outer portions of the star-forming region, formally known as N66, exposing new stellar nurseries. The diffuse fringes of the nebula prevent the energetic outflows from streaming directly away from the cluster, leaving instead a trail of filaments marking the swirling path of the outflows.

The NGC 346 cluster, at the center of this Hubble image, is resolved into at least three sub-clusters and collectively contains dozens of hot, blue, high-mass stars, more than half of the known high-mass stars in the entire SMC galaxy. A myriad of smaller, compact clusters is also visible throughout the region.

Some of these mini-clusters appear to be embedded in dust and nebulosity, and are sites of recent or ongoing star formation. Much of the starlight from these clusters is reddened by local dust concentrations that are the remnants of the original molecular cloud that collapsed to form N66.

An international team of astronomers, led by Dr. Antonella Nota of the Space Telescope Science Institute/European Space Agency in Baltimore, has been studying the Hubble data. In an upcoming issue of Astrophysical Journal Letters the team reports the discovery of a rich population of infant stars scattered around the young cluster NGC 346. These stars are likely to have formed 3 to 5 million years ago, together with the other stars in the NGC 346 cluster. These infant stars are particularly interesting as they have not yet contracted to the point where their interiors are hot enough to convert hydrogen to helium.

The Small and Large Magellanic Clouds are diffuse irregular galaxies visible to the naked eye in the southern hemisphere. They are two smallish satellite galaxies that orbit our own Milky Way Galaxy on a long slow journey inwards towards a future union with the Milky Way. Hubble has resolved many star formation regions in both of these neighboring galaxies that provide astronomers with laboratories other than our own Milky Way Galaxy to study how young stars interact with and shape their environments. The two satellites are named after the Portuguese seafarer Ferdinand Magellan (1480-1521) who sailed from Europe to Asia and is best known as the first person to lead an expedition to circumnavigate the globe.

This image of NGC 346 and its surrounding star formation region was taken with Hubble’s Advanced Camera for Surveys in July 2004. Two broadband filters that contribute starlight from visible and near-infrared wavelengths (shown in blue and green, respectively) have been combined with light from the nebulosity that has passed though a narrow-band hydrogen-alpha filter (shown in red).

Original Source: Hubble News Release

Hubble’s view of the Moon. Image credit: Hubble. Click to enlarge.
NASA is using the unique capabilities of the Hubble Space Telescope for a new class of scientific observations of the Earth’s moon.

Hubble’s resolution and sensitivity to ultraviolet light have allowed the telescope to search for important oxygen-bearing minerals on the moon. Since the moon does not have a breathable atmosphere, minerals, such as ilmenite (titanium and iron oxide), may be critical for a sustained human lunar presence. Ilmenite is a potential source of oxygen for breathing or to power rockets.

The new Hubble observations are the first high-resolution, ultraviolet images ever acquired of the moon. The images provide scientists with a new tool to study mineral variations within the lunar crust. As NASA plans future expeditions to the moon, such data, in combination with other measurements, will help ensure the most valuable sites are targeted for robotic and human missions.

“These observations of the moon have been a challenging and highly successful technological achievement for NASA and the Hubble team, since the telescope was not originally designed for lunar observations,” said Jennifer Wiseman, program scientist for the Hubble at NASA Headquarters. “The images will inform both scientific studies of lunar geology and future decisions on further lunar exploration,” she said.

Hubble’s Advanced Camera for Surveys snapped ultraviolet and visible light images of known geologically diverse areas on the side of the moon nearest Earth. These included the Aristarchus impact crater and the adjacent Schroter’s Valley. Hubble also photographed the Apollo 15 and 17 landing sites, where astronauts collected rock and soil samples in 1971 and 1972.

Scientists are comparing the properties of the rock and soil samples from the Apollo sites with the new Hubble images, and the Aristarchus region, which neither humans nor robotic spacecraft have visited. The Hubble observations of Aristarchus crater and Schroter’s Valley will help refine researchers’ understanding of the diverse, scientifically interesting materials in the region and to unravel their full resource potential.

“Our initial findings support the potential existence of some unique varieties of oxygen-rich glassy soils in both the Aristarchus and Apollo 17 regions. They could be well-suited for visits by robots and human explorers in efforts to learn how to live off the land on the moon,” said Jim Garvin, chief scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md. Garvin is principal investigator for the project.

“While it will require many months before fully quantitative results can be developed, we already have evidence that these new observations will improve the precision by which we can understand materials such as ilmenite to help better inform exploration decisions,” Garvin said.

Hubble’s lunar observation analysis team included colleagues from Goddard and Cornell University, Ithaca, N.Y.; Brown University, Providence, R.I.; Northwestern University, Evanston, Ill.; the University of Pittsburgh.; and the University of Hawaii, Manoa.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. It is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington, under contract with Goddard.

Original Source: Hubble News Release

Supernova remnant N132D. Image credit: Hubble. Click to enlarge.
Intricate wisps of glowing gas float amid a myriad of stars in this image created by combining data from NASA’s Hubble Space Telescope and Chandra X-ray Observatory. The gas is a supernova remnant, cataloged as N132D, ejected from the explosion of a massive star that occurred some 3,000 years ago. This titanic explosion took place in the Large Magellanic Cloud, a nearby neighbor galaxy of our own Milky Way.

The complex structure of N132D is due to the expanding supersonic shock wave from the explosion impacting the interstellar gas of the LMC. Deep within the remnant, the Hubble visible light image reveals a crescent-shaped cloud of pink emission from hydrogen gas, and soft purple wisps that correspond to regions of glowing oxygen emission. A dense background of colorful stars in the LMC is also shown in the Hubble image.

The large horseshoe-shaped gas cloud on the left-hand side of the remnant is glowing in X-rays, as imaged by Chandra. In order to emit X-rays, the gas must have been heated to a temperature of about 18 million degrees Fahrenheit (10 million degrees Celsius). A supernova-generated shock wave traveling at a velocity of more than four million miles per hour (2,000 kilometers per second) is continuing to propagate through the low-density medium today. The shock front where the material from the supernova collides with ambient interstellar material in the LMC is responsible for these high temperatures.

It is estimated that the star that exploded as a supernova to produce the N132D remnant was 10 to 15 times more massive than our own Sun. As fast-moving ejecta from the explosion slam into the cool, dense interstellar clouds in the LMC, complex shock fronts are created.

A supernova remnant like N132D provides a rare opportunity for direct observation of stellar material, because it is made of gas that was recently hidden deep inside a star. Thus it provides information on stellar evolution and the creation of chemical elements such as oxygen through nuclear reactions in their cores. Such observations also help reveal how the interstellar medium (the gas that occupies the vast spaces between the stars) is enriched with chemical elements because of supernova explosions. Later on, these elements are incorporated into new generations of stars and their accompanying planets.

Visible only from Earth’s southern hemisphere, the LMC is an irregular galaxy lying about 160,000 light-years from the Milky Way. The supernova remnant appears to be about 3,000 years old, but since its light took 160,000 years to reach us, the explosion actually occurred some 163,000 years ago.

This composite image of N132D was created by the Hubble Heritage team from visible-light data taken in January 2004 with Hubble’s Advanced Camera for Surveys, and X-ray images obtained in July 2000 by Chandra’s Advanced CCD Imaging Spectrometer. This marks the first Hubble Heritage image that combines pictures taken by two separate space observatories. The Hubble data include color filters that sample starlight in the blue, green, and red portions of the spectrum, as well as the pink emission from glowing hydrogen gas. The Chandra data are assigned blue in the color composite, in accordance with the much higher energy of the X-rays, emitted from extremely hot gas. This gas does not emit a significant amount of optical light, and was only detected by Chandra.

Original Source: Hubble News Release

Distant galaxy in a Hubble Ultra Deep Field image. Image credit: Hubble. Click to enlarge.
Two of NASA’s Great Observatories, the Spitzer and Hubble Space Telescopes, have teamed up to “weigh” the stars in several distant galaxies. One of these galaxies, among the most distant ever seen, appears to be unusually massive and mature for its place in the young universe.

This came as a surprise to astronomers, as the earliest galaxies in the universe are commonly thought to have been much smaller associations of stars that gradually merged to build large galaxies like our Milky Way.

“This galaxy, named HUDF-JD2, appears to have bulked up quickly, within the first few hundred million years after the big bang. It made about eight times more mass in stars than are found in our own Milky Way, and then, just as suddenly, it stopped forming new stars,” said Bahram Mobasher of the Space Telescope Science Institute, Baltimore and the European Space Agency, Paris.

The galaxy was pinpointed among approximately 10,000 others in a small patch of sky called the Hubble Ultra Deep Field (UDF). The galaxy is believed to be about as far away as the most distant known galaxies. It represents an era when the universe was only 800 million years old. That is about five percent of the universe’s age of 14 billion years.

Scientists studying the UDF found this galaxy in Hubble’s infrared images. They expected it to be young and small, like other known galaxies at similar distances. Instead, they found evidence the galaxy is remarkably mature and much more massive, and its stars appear to have been in place for a long time.

Hubble’s optical-light UDF image is the deepest image ever taken, yet this galaxy was not evident. This indicates much of the galaxy’s optical light has been absorbed by traveling billions of light-years through intervening hydrogen gas. The galaxy was detected using Hubble’s Near Infrared Camera and Multi-Object Spectrometer. It was also detected by an infrared camera on the Very Large Telescope (VLT) at the European Southern Observatory. At those longer infrared wavelengths, it is very faint and red.

The big surprise is how much brighter the galaxy is in even longer- wavelength infrared images from the Spitzer Space Telescope. Spitzer is sensitive to the light from older, redder stars, which should make up most of the mass in a galaxy. The infrared brightness of the galaxy suggests it is massive. “This would be quite a big galaxy even today,” said Mark Dickinson of the National Optical Astronomy Observatory, Tucson, Ariz. “At a time when the universe was only 800 million years old, it’s positively gigantic,” he added.

Spitzer observations were also independently reported by Laurence Eyles from the University of Exeter in the United Kingdom and Haojing Yan of the Spitzer Science Center, Pasadena, Calif. They also revealed evidence for mature stars in more ordinary, less massive galaxies at similar distances, when the universe was less than one billion years old.

The new observations reported by Mobasher extend this notion of surprisingly mature “baby galaxies” to an object which is perhaps 10 times more massive, and which seemed to form its stars even earlier in the history of the universe.

Mobasher’s team estimated the distance to this galaxy by combining information provided by the Hubble, Spitzer, and VLT observations. The relative brightness of the galaxy at different wavelengths is influenced by the expanding universe and allows astronomers to estimate its distance. They can also get an idea of the make-up of the galaxy in terms of the mass and age of its stars. It will take the next generation of telescopes, such as the infrared James Webb Space Telescope, to confirm the galaxy’s distance.

While astronomers generally believe most galaxies were built piecewise by mergers of smaller galaxies, the discovery of this object suggests at least a few galaxies formed quickly long ago. For such a large galaxy, this would have been a tremendously explosive event of star birth. Mobasher’s results will appear in the Astrophysical Journal on Dec. 20.

For electronic images from the research and information on the Web, visit: http://hubblesite.org/news/2005/28

Original Source: Hubble News Release

Artist illustration of the heart of galaxy M31. Image credit: NASA. Click to enlarge.
Astronomers using NASA’s Hubble Space Telescope have identified the source of a mysterious blue light surrounding a supermassive black hole in our neighboring Andromeda Galaxy (M31). Though the light has puzzled astronomers for more than a decade, the new discovery makes the story even more mysterious.

The blue light is coming from a disk of hot, young stars. These stars are whipping around the black hole in much the same way as planets in our solar system are revolving around the Sun. Astronomers are perplexed about how the pancake-shaped disk of stars could form so close to a giant black hole. In such a hostile environment, the black hole’s tidal forces should tear matter apart, making it difficult for gas and dust to collapse and form stars. The observations, astronomers say, may provide clues to the activities in the cores of more distant galaxies.

By finding the disk of stars, astronomers also have collected what they say is ironclad evidence for the existence of the monster black hole. The evidence has helped astronomers rule out all alternative theories for the dark mass in Andromeda’s core, which scientists have long suspected was a black hole.

“Seeing these stars is like watching a magician pulling a rabbit out of a hat. You know it happened but you don’t know how it happened,” said Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona. He and a team of astronomers, led by Ralf Bender of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and John Kormendy of the University of Texas in Austin, made the Hubble observations. The team’s results will be published in the Sept. 20, 2005 issue of the Astrophysical Journal.

Hubble Probes Strange Blue Light
Astronomer Ivan King of the University of Washington and colleagues first spotted the strange blue light in 1995 with the Hubble telescope. He thought the light might have come from a single, bright blue star or perhaps from a more exotic energetic process. Three years later, Lauer and Sandra Faber of the University of California at Santa Cruz used Hubble again to study the blue light. Their observations indicated that the blue light was a cluster of blue stars.

Now, new spectroscopic observations by Hubble’s Space Telescope Imaging Spectrograph (STIS) reveal that the blue light consists of more than 400 stars that formed in a burst of activity about 200 million years ago. The stars are tightly packed in a disk that is only a light-year across. The disk is nested inside an elliptical ring of older, cooler, redder stars, which was seen in previous Hubble observations.

The astronomers also used STIS to measure the velocities of those stars. They obtained the stars’ speeds by calculating how much their light waves are stretched and compressed as they travel around the black hole. Under the black hole’s gravitational grip, the stars are traveling very fast: 2.2 million miles an hour (3.6 million kilometers an hour, or 1,000 kilometers a second). They are moving so fast that it would take them 40 seconds to circle the Earth and six minutes to arrive at the Moon. The fastest stars complete an orbit in 100 years.

Andromeda’s active core probably made similar disks of stars in the past and may continue to make them.

“The blue stars in the disk are so short-lived that it is unlikely in the long 12-billion-year history of Andromeda that such a short-lived disk would appear now,” Lauer said. “That’s why we think that the mechanism that formed this disk of stars probably formed other stellar disks in the past and will trigger them again in the future. We still don’t know, however, how such a disk could form in the first place. It still remains an enigma.”

The astronomers credit Hubble’s superb vision for finding the disk.

“Only Hubble has the resolution in blue light to observe this disk,” said team member Richard Green of the National Optical Astronomy Observatory in Tucson. “It is so small and so distinct from the surrounding red stars that we were able to use it to probe into the very dynamical heart of Andromeda. These observations were taken by the members of our team that built STIS. We designed its visible channel specifically to seize such an opportunity ? to measure starlight closer to a black hole than in any other galaxy outside our own.”

Solid Evidence for a Monster Black Hole
In addition to the discovery of the disk of stars, the astronomers used this uniquely close look at Andromeda to prove unambiguously that the galaxy hosts a central black hole. In 1988, in independent ground-based studies, John Kormendy and the team of Alan Dressler and Douglas Richstone discovered a central dark object in Andromeda that they believed was a supermassive black hole. This was the first strong case for what are now 40 detections of black holes, most of them made by Hubble. Those observations, however, did not definitively rule out other, very exotic, and far less likely, alternatives.

“There are compelling reasons to believe that these are supermassive black holes,” Kormendy said. “But extreme claims require extraordinarily strong evidence. We have to be sure that these are black holes and not dark clusters of dead stars.”

The STIS observations of Andromeda are so precise that astronomers have eliminated all other possibilities for what the central, dark object could be. They also calculated that the black hole’s mass is 140 million Suns, which is three times more massive than once thought.

So far, dark clusters have definitively been ruled out in only two galaxies, NGC 4258 and our galaxy, the Milky Way. “These two galaxies give us unambiguous proof that black holes exist,” Kormendy added. “But both are special cases ? NGC 4258 contains a disk of water masers that we observe with radio telescopes, and our galactic center is so close that we can follow individual stellar orbits. Andromeda is the first galaxy in which we can exclude all exotic alternatives to a black hole using Hubble and using the same techniques by which we find almost all supermassive black holes.”

“Studying black holes always was a primary mission of Hubble,” Kormendy said. “Nailing the black hole in Andromeda is without a doubt an important part of its legacy. It makes us much more confidant that the other central dark objects detected in galaxies are black holes, too.”

“Now that we have proven that the black hole is at the center of the disk of blue stars, the formation of these stars becomes hard to understand,” Bender added. “Gas that might form stars must spin around the black hole so quickly ? and so much more quickly near the black hole than farther out ? that star formation looks almost impossible. But the stars are there.”

A Galaxy’s Active Core
The black hole and the disk of stars are not the only pieces of architecture in Andromeda’s core. A team led by Lauer and Faber used Hubble in 1993 to discover that the galaxy appears to have a double cluster of stars at its center. This finding was a surprise, because two clusters should merge into one in only a few hundred thousand years. Scott Tremaine of Princeton University solved this problem by suggesting that the “double nucleus” was actually a ring of old, red stars. The ring looked like two star clusters because astronomers were only seeing the stars on the opposite ends of the ring. The ring is about five light-years from the black hole and its surrounding disk of blue stars. The disk and the ring are tilted at the same angle as viewed from Earth, suggesting that they may be related.

Although astronomers are surprised to find a blue disk of stars swirling around a supermassive black hole, they also say the puzzling architecture may not be that unusual.

“The dynamics within the core of this neighboring galaxy may be more common than we think,” Lauer explained. “Our own Milky Way apparently has even younger stars close to its own black hole. It seems unlikely that only the closest two big galaxies should have this odd activity. So this behavior may not be the exception but the rule. And we have found other galaxies that have a double nucleus.”

Original Source: Hubble News Release