Category: Astronomy

Image credit: NASA/JPL
Hidden behind a curtain of dusty darkness lurks one of the most violent pockets of star birth in our galaxy. Called DR21, this stellar nursery is so draped in cosmic dust that it appears invisible to the human eye.

By seeing in the infrared, NASA’s Spitzer Space Telescope has pulled this veil aside, revealing a fireworks-like display of massive stars. The biggest of these stars is estimated to be 100,000 times as bright as our own Sun.

The new image is available online at http://www.spitzer.caltech.edu and http://photojournal.jpl.nasa.gov/catalog/PIA05736.

“We’ve never seen anything like this before,” said Dr. William Reach, an investigator for the latest observations and an astronomer at the Spitzer Science Center, located at the California Institute of Technology, Pasadena, Calif. “The massive stars are ripping the cloud of gas and dust around them to shreds.” The principal investigator is Dr. Anthony Marston, a former Spitzer astronomer now at the European Space Research and Technology Centre, the Netherlands.

Located about 10,000 light-years away in the Cygnus constellation of our Milky Way galaxy, DR21 is a turbulent nest of giant newborn stars. The region is buried in so much space dust that no visible light escapes it. Previous images taken with radio and near-infrared bands of light reveal a powerful jet emanating from a huge, nebulous cloud. But these views are just the tip of the iceberg.

Spitzer’s highly sensitive infrared detectors were able to see past the obscuring dust to the stars behind. The new false-color image spans a vast expanse of space, with DR21 at the top center. Within DR21, a dense knot of massive stars can be seen surrounded by a wispy cloud of gas and dust. Red filaments containing organic compounds called polycyclic aromatic hydrocarbons stretch horizontally and vertically across this cloud. A green jet of gas shoots downward past the bulge of stars and represents fast-moving, hot gas being ejected from the region’s biggest star.

Below DR21 are distinct pockets of star formation, never captured in full detail before. The large swirling cloud to the lower left is thought to be a stellar nursery like DR21’s, but with smaller stars. A bubble possibly formed by a past generation of stars is visible within the lower rim of this cloud.

The new view testifies to the ability of massive newborn stars to destroy the cloud that blankets them. Astronomers plan to use these observations to determine precisely how such an energetic event occurs.

Launched on August 25, 2003, from Cape Canaveral, Florida, the Spitzer Space Telescope is the fourth of NASA?s Great Observatories, a program that also includes the Hubble Space Telescope, Compton Gamma Ray Observatory and Chandra X-ray Observatory.

JPL manages the Spitzer Space Telescope mission for NASA’s Office of Space Science, Washington. Science operations are conducted at the Spitzer Science Center. JPL is a division of Caltech. Spitzer’s infrared array camera, used to capture the new image of DR21, was built by NASA Goddard Space Flight Center, Greenbelt, Md. The development of the camera was led by Dr. Giovanni Fazio of Smithsonian Astrophysical Observatory, Cambridge, Mass.

Additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu.

Original Source: NASA/JPL News Release

Image credit: NASA
We are doomed. One day the Earth will be a burnt cinder orbiting a swollen red star.

This is the ultimate fate of any planet living close to a main sequence star like our sun. Main sequence stars run on hydrogen, and when this fuel runs out, they switch over to helium and become a red giant. While the sun’s transition into a red giant is sad news for Earth, the icy planets in the most distant regions of our solar system will bask in the sun’s warmth for the first time.

The sun has been slowly but steadily growing brighter and hotter over the course of its lifetime. When the sun becomes a red giant in about 4 billion years, our familiar yellow sun will turn a vivid red, as it mainly emits the lower frequency energy of infrared and visible red light. It will grow thousands of times brighter and yet have a cooler surface temperature, and its atmosphere will expand, slowly engulfing Mercury, Venus and possibly even the Earth.

While the sun’s atmosphere is predicted to reach Earth’s orbit of 1 AU, red giants tend to lose a lot of mass, and this wave of expelled gases could push Earth just out of range. But whether the Earth is consumed or merely singed, all life on Earth will have passed into oblivion.

Yet the conditions that make life possible could appear elsewhere in the solar system, according to a paper published in the journal Astrobiology by S. Alan Stern, Director of the Southwest Research Institute’s Department of Space Studies in Boulder, Colorado. He says that planets located 10 to 50 AU will be in the red giant sun’s habitable zone. The habitable zone of a solar system is the region where water can remain in a liquid state.

The habitable zone will shift gradually through the 10 to 50 AU region as the sun grows brighter and brighter, evolving through its red giant phase. Saturn, Uranus, Neptune and Pluto all lie within 10 to 50 AU, as do their icy moons and the Kuiper Belt Objects. But not all these worlds will have an equal chance at life.

The prospects for habitability on the gaseous planets Saturn, Neptune and Uranus may not be affected all that much by the red giant transition. Astronomers have discovered gaseous planets orbiting very close to their parent star in other solar systems, and these “hot Jupiters” seem to hold onto their gaseous atmospheres despite their proximity to the intense radiation. Life as we know it is not likely to appear on gaseous planets.

Stern thinks Neptune’s moon Triton, Pluto and its moon Charon, and the Kuiper Belt Objects will have the best chances for life. These bodies are rich in organic chemicals, and the heat of the red giant sun will melt their icy surfaces into oceans.

“When the sun is a red giant, the ice worlds of our solar system will melt and become ocean oases for tens to several hundreds of millions of years,” says Stern. “Our solar system will then harbor not one world with surface oceans, as it does now, but hundreds, for all of the icy moons of the giant planets, and the icy dwarf planets of the Kuiper Belt will also bear oceans then. Because temperature on Pluto will not be very different then, than Miami Beach’s temperature now, I like to call these worlds ‘warm Plutos,’ in analogy to the plethora of hot Jupiters found orbiting sun-like stars in recent years.”

The influence of the sun is not the whole story, however – the characteristics of a planetary body go a long way toward determining habitability. Such characteristics include a planet’s internal activity, the reflectivity, or “albedo” of a planet, and the thickness and composition of the atmosphere. Even if a planet has all the elements that favor habitability, life will not necessarily appear.

“We don’t know what is needed to start life,” says Don Brownlee, an astronomer with the University of Washington in Seattle and co-author of the book, “The Life and Death of Planet Earth.” Brownlee says that if warm wet interiors and organic materials are all that’s needed, then Pluto, Triton, and the Kuiper Belt Objects could harbor life.

“As a word of caution, however, the interiors of asteroids that produced the carbonaceous chondrite meteorites were warm and wet for perhaps millions of years in the early history of the solar system,” says Brownlee. “These bodies are extremely rich in both water and organic materials, and yet there is no compelling evidence that any asteroidal meteorite ever had living things in it.”

A planetary body’s orbit also will affect its chances for life. Pluto, for instance, doesn’t have a nice, regular orbit like the Earth. The orbit of Pluto is comparatively eccentric, varying in distance from the sun. From January 1979 through February 1999, Pluto was closer to the sun than Neptune, and in a hundred years, it’ll be almost twice as far out as Neptune. This type of orbit will cause Pluto to undergo extreme heating alternating with extreme cooling.

Triton’s orbit, too, is peculiar. Triton is the only large moon to orbit backwards, or “retrograde.” Triton may have this unusual orbit because it formed as a Kuiper Belt Object and then was captured by Neptune’s gravity. It’s an unstable alliance, since the retrograde orbit creates tidal interactions with Neptune. Scientists predict that someday Triton will either crash into Neptune, or break up into tiny pieces and form a ring around the planet.

“The timescale for the tidal decay of Triton’s orbit is uncertain, so it could be around, or it might have already crashed by the time the sun goes red giant,” says Stern. “If Triton is around, it’ll probably end up looking like the same kind of organic-rich ocean world as Pluto.”

The sun will burn as a red giant for about 250 million years, but is that enough time for life to get a foothold? During most of the red giant lifetime, the sun will be only 30 times brighter than its current state. Toward the end of the red giant phase the sun will grow more than 1,000 times brighter, and occasionally release pulses of energy reaching 6,000 times current brightness. But this period of intense brightness will last for a few million years, or tens of millions of years at most.

The brevity of the red giant’s brightest phases suggests to Brownlee that Pluto doesn’t hold much promise for life. Because of Pluto’s average orbit of 40 AU, the sun would have to be 1,600 times brighter for Pluto to get the same solar radiation we currently get on Earth.

“The sun will reach this brightness, but only for a very brief period of time – only a million years or so,” says Brownlee. “The surface and atmosphere of Pluto will be ‘improved’ from our point of view, but it won’t be a nice place for any significant period of time”.

After the red giant phase, the sun will become fainter, and will shrink to the size of the Earth, becoming a white dwarf. The distant planets that basked in the light of the red giant will become frozen ice worlds once again.

So if life is to appear in a red giant system, it will need a quick start. Life on Earth is thought to have originated 3.8 billion years ago, some 800 million years after our planet was born. But that is probably because the planets in the inner solar system experienced 800 million years of heavy asteroid bombardment. Even if life had gotten started immediately, the early rain of asteroids would’ve wiped the Earth clean of that life.

Brownlee says a new era of bombardment could begin for the outer planets, because the red giant sun could disturb the vast number of comets in the Kuiper Belt.

“When the red giant sun is 1,000 times brighter, it loses almost half of its mass to space,” says Brownlee. “This causes orbiting bodies to move outward. Gas loss and other effects might destabilize the Kuiper Belt and create another period of interesting bombardment.”

But Stern says that planets made habitable by a red giant sun won’t be bombarded as often as the early Earth was, because the ancient asteroid belt had much more material than the Kuiper Belt has today.

In addition, the outer planets won’t experience the same ultraviolet (UV) levels that Earth has had to endure, since red giants have very low UV radiation. The higher intensity UV of a main sequence star can be damaging to the delicate proteins and RNA strands needed for life’s origin. Life on Earth could only originate underwater, in depths protected from this light intensity. Life on Earth is therefore inextricably linked to liquid water. But who knows what sort of life might originate on planets that have no need for UV shielding?

Stern thinks we should look for evidence of life on Pluto-like worlds orbiting around red giants today. We currently know of 100 million solar-type stars in the Milky Way galaxy that burn as red giants, and Stern says that all of these systems could have habitable planets within 10 to 50 AU. “It would be a good test of the time required to create life on warm, water-rich worlds,” he says.

“The idea of organic-rich distant bodies getting baked by a red giant star is an intriguing one, and could provide very interesting if short-lived habitats for life,” adds Brownlee. “But I am glad that our sun has a good margin of time left.”

What’s Next
While much of what we know about the outer solar system is based on distant measurements made from Earth-based telescopes, on January 2, 2004, scientists caught a close-up glimpse of a Kuiper Belt Object. The Stardust spacecraft passed within 136 kilometers of comet Wild2, an enormous snowball that spent most of its 4.6 billion-year lifetime orbiting in the Kuiper Belt. Wild2 now orbits mostly inside the orbit of Jupiter. Brownlee, who is the Principle Investigator for the Stardust mission, says that the Stardust images show fantastic surface details of a body shaped both by its ancient and recent history. Stardust images show gas and dust jets shooting off the comet, as Wild2 rapidly disintegrates in the strong solar heat of the inner solar system.

To learn more about the outer solar system, we’ll need to send a spacecraft out there to investigate. In 2001, NASA selected the New Horizons mission for just such a purpose.

Stern, who is the Principal Investigator for the New Horizons mission, reports that the spacecraft assembly is scheduled to begin this summer. The spacecraft is due to launch in January 2006, and arrive at Pluto the summer of 2015.

The New Horizons mission will allow scientists to study the geology of Pluto and Charon, map their surfaces, and take their temperatures. Pluto’s atmosphere also will be studied in detail. In addition, the spacecraft will visit the icy bodies in the Kuiper Belt in order to make similar measurements.

Original Source: Astrobiology Magazine

Image credit: ESO
Home is the place we know best. But not so in the Milky Way – the galaxy in which we live. Our knowledge of our nearest stellar neighbours has long been seriously incomplete and – worse – skewed by prejudice concerning their behaviour. Stars were generally selected for observation because they were thought to be “interesting” in some sense, not because they were typical. This has resulted in a biased view of the evolution of our Galaxy.

The Milky Way started out just after the Big Bang as one or more diffuse blobs of gas of almost pure hydrogen and helium. With time, it assembled into the flattened spiral galaxy which we inhabit today. Meanwhile, generation after generation of stars were formed, including our Sun some 4,700 million years ago.

But how did all this really happen? Was it a rapid process? Was it violent or calm? When were all the heavier elements formed? How did the Milky Way change its composition and shape with time? Answers to these and many other questions are ‘hot’ topics for the astronomers who study the birth and evolution of the Milky Way and other galaxies.

Now the rich results of a 15 year-long marathon survey by a Danish-Swiss-Swedish research team [2] are providing some of the answers.

1,001 nights at the telescopes
The team spent more than 1,000 observing nights over 15 years at the Danish 1.5-m telescope of the European Southern Observatory at La Silla (Chile) and at the Swiss 1-m telescope of the Observatoire de Haute-Provence (France). Additional observations were made at the Harvard-Smithsonian Center for Astrophysics in the USA. A total of more than 14,000 solar-like stars (so-called F- and G-type stars) were observed at an average of four times each – a total of no less than 63,000 individual spectroscopic observations!

This now complete census of neighbourhood stars provides distances, ages, chemical analysis, space velocities and orbits in the general rotation of the Milky Way. It also identifies those stars (about 1/3 of them all) which the astronomers found to be double or multiple.

This very complete data set for the stars in the solar neighbourhood will provide food for thought by astronomers for years to come.

A dream come true
These observations provide the long-sought missing pieces of the puzzle to get a clear overview of the solar neighbourhood. They effectively mark the conclusion of a project started more than twenty years ago..

In fact, this work marks the fulfilment of an old dream by Danish astronomer Bengt Str?mgren (1908-1987), who pioneered the study of the history of the Milky Way through systematic studies of its stars. Already in the 1950’s he designed a special system of colour measurements to determine the chemical composition and ages of many stars very efficiently. And the Danish 50-cm and 1.5-m telescopes at the ESO La Silla Observatory (Chile) were constructed to make such projects possible.

Another Danish astronomer, Erik Heyn Olsen made the first step in the 1980’s by measuring the flux (light intensity) in several wavebands (in the “Str?mgren photometric system”) of 30,000 A, F and G stars over the whole sky to a fixed brightness limit. Next, ESA’s Hipparcos satellite determined precise distances and velocities in the plane of the sky for these and many other stars.

The missing link was the motions along the line of sight (the so-called radial velocities). They were then measured by the present team from the Doppler shift of spectral lines of the stars (the same technique that is used to detect planets around other stars), using the specialized CORAVEL instrument.

Stellar orbits in the Milky Way
With the velocity information completed, the astronomers can now compute how the stars have wandered around in the Galaxy in the past, and where they will go in the future, cf. PR Video Clip 04/04.

Birgitta Nordstr?m, leader of the team, explains: “For the first time we have a complete set of observed stars that is a fair representation of the stellar population in the Milky Way disc in general. It is large enough for a proper statistical analysis and also has complete velocity and binary star information. We have just started the analysis of this dataset ourselves, but we know that our colleagues worldwide will rush to join in the interpretation of this treasure trove of information.”

The team’s initial analysis indicates that objects like molecular clouds, spiral arms, black holes, or maybe a central bar in the Galaxy, have stirred up the motion of the stars throughout the entire history of the Milky Way disc.

This in turn reveals that the evolution of the Milky Way was far more complex and chaotic than traditional, simplified models have long so far assumed. Supernova explosions, galaxy collisions, and infall of huge gas clouds have made the Milky Way a very lively place indeed!

Original Source: ESO News Release

Image credit: RAS
An international team of astronomers has used the UK’s 2.5-m Isaac Newton Telescope on La Palma in the Canary Islands to map the Andromeda Galaxy (otherwise known as M31) and a large area of sky all around it. Their work over the last few years has created the most detailed image of a large spiral galaxy that currently exists. Dr Mike Irwin of the University of Cambridge, one of the team leaders, reports on some of the latest findings on Wednesday 31 March, when he will tell the RAS National Astronomy Meeting at the Open University about the first clear evidence that M31 is pulling one of its bright satellite galaxies apart, and the discovery of 14 previously unknown globular clusters orbiting far from the centre of M31 which could have been left behind when Andromeda devoured their parent galaxies.

Located around 2.5 million light years away, the Andromeda Galaxy is the most distant object visible to the naked eye, and is considered to be the sister galaxy of our own Milky Way. By studying this galactic neighbour, astronomers hope to understand more about the formation and evolution of many of the billions of spiral galaxies in the universe, including the Milky Way.

For their survey, the team have taken 150 individual images with a sensitive electronic CCD camera, which reveal millions of individual stars. It extends over an area 100 times greater than all earlier studies combined. The reason for scanning such a large area is that. around bright galaxies. there is a tenuous “halo” of stars which are leftovers from the formation of the galaxy billions of years ago. Studying this “fossil” information reveals evidence for how the halo, and hence the rest of the galaxy, has built up over cosmic history.

Traditionally, galaxy halos were thought to be relatively smooth and devoid of substructure. In fact the new survey shows that Andromeda’s halo is the exact opposite: it has a wealth of structure, indicating that it has ripped apart smaller galaxies that came too close and that the halo is built up from their remains. “Given that the disk of Andromeda appears so pristine, we were shocked to discover that its halo shows so much evidence for a history of interactions with other galaxies,” says Mike Irwin.

At this year’s National Astronomy Meeting, the Andromeda team report the discovery of a large stream of stars which appears to have been pulled out of one of Andromeda’s well-known satellite galaxies, NGC205. The visible part of the apparent stream extends nearly 50,000 light years from the main body of this small elliptical galaxy and was previously unknown despite the fact that NGC 205 has been well-studied.

“This is the first clear indication that one of Andromeda’s companion galaxies is being ripped apart as we watch,” commented team member Alan McConnachie, a doctoral student at Cambridge.

The 14 globular clusters the team has found orbiting far out from M31 may be evidence of Andromeda’s past cannibalism. Globular clusters are ancient systems of hundreds of thousands of stars, which are seen around many galaxies, and provide many clues to their evolutionary history. “Since the most distant of these globular clusters is some 250,000 light years from the centre of M31, our work shows that M31’s halo extends far beyond the edge of the bright part of the galaxy disk,” said Avon Huxor of the University of Hertfordshire.

“Both these discoveries will greatly aid in understanding the evolution of these nearby galaxies and should shed light on how our own Galaxy became what it is today,” commented Nial Tanvir, another team member from the University of Hertfordshire.

Original Source: RAS News Release

Image credit: NRAO
Thirty years after astronomers discovered the mysterious object at the exact center of our Milky Way Galaxy, an international team of scientists has finally succeeded in directly measuring the size of that object, which surrounds a black hole nearly four million times more massive than the Sun. This is the closest telescopic approach to a black hole so far and puts a major frontier of astrophysics within reach of future observations. The scientists used the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to make the breakthrough.

“This is a big step forward,” said Geoffrey Bower, of the University of California-Berkeley. “This is something that people have wanted to do for 30 years,” since the Galactic center object, called Sagittarius A* (pronounced “A-star”), was discovered in 1974. The astronomers reported their research in the April 1 edition of Science Express.

“Now we have a size for the object, but the mystery about its exact nature still remains,” Bower added. The next step, he explained, is to learn its shape, “so we can tell if it is jets, a thin disk, or a spherical cloud.”

The Milky Way’s center, 26,000 light-years from Earth, is obscured by dust, so visible-light telescopes cannot study the object. While radio waves from the Galaxy’s central region can penetrate the dust, they are scattered by turbulent charged plasma in the space along the line of sight to Earth. This scattering had frustrated earlier attempts to measure the size of the central object, just as fog blurs the glare of distant lighthouses.

“After 30 years, radio telescopes finally have lifted the fog and we can see what is going on,” said Heino Falcke, of the Westerbork Radio Observatory in the Netherlands, another member of the research team.

The bright, radio-emitting object would fit neatly just inside the path of the Earth’s orbit around the Sun, the astronomers said. The black hole itself, they calculate, is about 14 million miles across, and would fit easily inside the orbit of Mercury. Black holes are concentrations of matter so dense that not even light can escape their powerful gravity.

The new VLBA observations provided astronomers their best look yet at a black hole system. “We are much closer to seeing the effects of a black hole on its environment here than anywhere else,” Bower said.

The Milky Way’s central black hole, like its more-massive cousins in more-active galactic nuclei, is believed to be drawing in material from its surroundings, and in the process powering the emission of the radio waves. While the new VLBA observations have not provided a final answer on the nature of this process, they have helped rule out some theories, Bower said. Based on the latest work, he explained, the top remaining theories for the nature of the radio- emitting object are jets of subatomic particles, similar to those seen in radio galaxies; and some theories involving matter being accelerated near the edge of the black hole.

As the astronomers studied Sagittarius A* at higher and higher radio frequencies, the apparent size of the object became smaller. This fact, too, Bower said, helped rule out some ideas of the object’s nature. The decrease in observed size with increasing frequency, or shorter wavelength, also gives the astronomers a tantalizing target.

“We think we can eventually observe at short enough wavelengths that we will see a cutoff when we reach the size of the black hole itself,” Bower said. In addition, he said, “in future observations, we hope to see a ‘shadow’ cast by a gravitational lensing effect of the very strong gravity of the black hole.”

In 2000, Falcke and his colleagues proposed such an observation on theoretical grounds, and it now seems feasible. “Imaging the shadow of the black hole’s event horizon is now within our reach, if we work hard enough in the coming years,” Falcke added.

Another conclusion the scientists reached is that “the total mass of the black hole is very concentrated,” according to Bower. The new VLBA observations provide, he said, the “most precise localization of the mass of a supermassive black hole ever.” The precision of these observations allows the scientists to say that a mass of at least 40,000 Suns has to reside in a space corresponding to the size of the Earth’s orbit. However, that figure represents only a lower limit on the mass. Most likely, the scientists believe, all the black hole’s mass — equal to four million Suns — is concentrated well inside the area engulfed by the radio-emitting object.

To make their measurement, the astronomers had to go to painstaking lengths to circumvent the scattering effect of the plasma “fog” between Sagittarius A* and Earth. “We had to push our technique really hard,” Bower said.

Bower likened the task to “trying to see your yellow rubber duckie through the frosted glass of the shower stall.” By making many observations, only keeping the highest-quality data, and mathematically removing the scattering effect of the plasma, the scientists succeeded in making the first-ever measurement of Sagittarius A*’s size.

In addition to Bower and Falcke, the research team includes Robin Herrnstein of Columbia University, Jun-Hui Zhao of the Harvard-Smithsonian Center for Astrophysics, Miller Goss of the National Radio Astronomy Observatory, and Donald Backer of the University of California-Berkeley. Falcke also is an adjunct professor at the University of Nijmegen and a visiting scientist at the Max-Planck Institute for Radioastronomy in Bonn, Germany.

Sagittarius A* was discovered in February of 1974 by Bruce Balick, now at the University of Washington, and Robert Brown, now director of the National Astronomy and Ionospheric Center at Cornell University. It has been shown conclusively to be the center of the Milky Way, around which the rest of the Galaxy rotates. In 1999, Mark Reid of the Harvard-Smithsonian Center for Astrophysics and his colleagues used VLBA observations of Sagittarius A* to detect the Earth’s motion in orbit around the Galaxy’s center and determined that our Solar System takes 226 million years to make one circuit around the Galaxy.

In March 2004, 55 astronomers gathered at the National Radio Astronomy Observatory facility in Green Bank, West Virginia, for a scientific conference celebrating the discovery of Sagittarius A* at Green Bank 30 years ago. At this conference, the scientists unveiled a commemorative plaque on one of the discovery telescopes.

The Very Long Baseline Array, part of the National Radio Astronomy Observatory, is a continent-wide radio-telescope system, with 10, 240-ton dish antennas ranging from Hawaii to the Caribbean. It provides the greatest resolving power, or ability to see fine detail, of any telescope in astronomy, on Earth or in space.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Image credit: Steve Phillipps
A new survey made with the Anglo-Australian Telescope (AAT) has revealed dozens of previously unsuspected miniature galaxies in the nearby Fornax galaxy cluster. They belong to a class of galaxies dubbed “ultra-compact dwarfs” (UCDs), which was unknown before the same team of astronomers discovered 6 of them in the Fornax cluster in 2000. Now they say the UCDs outnumber the “conventional” elliptical and spiral galaxies in the central region of the Fornax cluster and they have found some in the Virgo galaxy cluster too. It is possible that at least some are left-over examples of the primordial “building blocks” that formed large galaxies by merging together. It is likely that they are very common but have been overlooked because they resemble nearby stars at first sight. These results will be presented to the RAS National Astronomy Meeting at the Open University on Thursday 1 April by Dr Steven Phillips of Bristol University.

UCDs were discovered by chance when Dr Phillipps and his colleagues undertook a large survey of all the moderately bright objects they could see in the direction of the Fornax cluster. Only because they used a spectrograph (the Two Degree Field, or 2dF, system on the AAT) were they able to measure redshifts, which told them that 6 objects looking like local stars in our Galaxy were in fact in the Fornax cluster about 60 million light years away. Follow-up observations with the Hubble space Telescope and the European Southern Obervatory’s Very Large Telescope (VLT) revealed just how strange they are. Although their masses are similar to those of previously known dwarf galaxies, they are amazingly small – only about 120 light years across. Tens of millions of stars are squashed into what is a tiny volume by galaxy standards.

Favouring the idea that UCDs are the nuclei of galaxies that were originally larger and have been stripped of their outer stars, the team predicted that they would find them in other dense clusters where the stripping or ‘threshing’ process could go on. They also calculated how many more they would expect to find if they searched for fainter ones.

When they put their predictions to the test, 3 nights of observations uncovered a further 46 UCDs in Fornax – even more than the team had expected – and in just 4 hours they found 8 in the Virgo cluster, also around 60 million light years away. “These results indicate that UCDs are indeed common,” says Steve Phillipps, “and part of the standard population of galaxies we can expect in rich galaxy clusters. Given that we found so many, it is even possible that a proportion of them are the remnants of a population of primordial galaxies, remnants of the original building blocks of the large galaxies we find at the centres of clusters.”

Original Source: RAS News Release

Image credit: NASA
The Pleiades are elusive. You rarely find them on purpose. They’re best seen out of the corner of your eye, a pretty little surprise that pops out of the night sky when you’re staring elsewhere.

Venus is just the opposite. Dazzling, bright enough to cast faint shadows, it beams down from the heavens and grabs you, mesmerizing. You can’t take your eyes off it.

This weekend, Venus and the Pleiades are coming together. It happens every 8 years: Venus glides through the Pleiades star cluster and, while dissimilar things don’t always go well together, these do. It’s going to be a beautiful ensemble.

Step outside after dark on Thursday, April 1st and look west. Venus is the improbably-bright “star” about halfway up the sky. Just above Venus lies the Pleiades, often mistaken for the Little Dipper because the faint stars of the Pleiades trace the shape of ? a little dipper.

If you go outside and look several nights in a row, you can see how fast Venus travels across the sky. On Friday, April 2nd, Venus enters the Pleiades, just below the dipper’s bowl. On Saturday, April 3rd, Venus scoots upward to join the stars in the dipper’s handle. On Sunday, April 4th, Venus exits the cluster altogether. Compared to what you saw on April 1st, the two have switched places.

Here are a few things to think about while you’re watching the show:

The Pleiades are a clutch of baby stars. They formed barely 100 million years ago, during the age of dinosaurs on Earth, from a collapsing cloud of interstellar gas. The biggest and brightest of the cluster are blue-white and about five times wider than our own sun.

The Pleiades didn’t exist when Venus first emerged from the protosolar nebula 4.5 billion years ago. No one knows what Venus was like in those early days of the solar system. It might have been lush, verdant, Earth-like. Today, though, it’s hellish. A runaway greenhouse effect on Venus has super-heated the planet to nearly 900? F, hot enough to melt lead. Dense gray clouds laced with sulfuric acid completely hide Venus’ surface from telescopes on Earth. The smothering clouds, it turns out, are excellent reflectors of sunlight, and that’s why Venus looks so bright.

As seen from Earth, Venus shines about 600 times brighter than Alcyone, the most luminous star in the Pleiades. During the weekend try scanning the group with binoculars. You’ll see dozens of faint Pleiades invisible to the unaided eye. Among them, bright Venus looks like a supernova.

But, really, it’s just an ancient planet gliding in front of some baby stars–a dissimilar ensemble that you won’t want to miss.

Original Source: NASA Science

Image credit: ESO
Detecting or constraining the possible time variations of fundamental physical constants is an important step toward a complete understanding of basic physics and hence the world in which we live. A step in which astrophysics proves most useful.

Previous astronomical measurements of the fine structure constant – the dimensionless number that determines the strength of interactions between charged particles and electromagnetic fields – suggested that this particular constant is increasing very slightly with time. If confirmed, this would have very profound implications for our understanding of fundamental physics.

New studies, conducted using the UVES spectrograph on Kueyen, one of the 8.2-m telescopes of ESO’s Very Large Telescope array at Paranal (Chile), secured new data with unprecedented quality. These data, combined with a very careful analysis, have provided the strongest astronomical constraints to date on the possible variation of the fine structure constant. They show that, contrary to previous claims, no evidence exist for assuming a time variation of this fundamental constant.

A fine constant
To explain the Universe and to represent it mathematically, scientists rely on so-called fundamental constants or fixed numbers. The fundamental laws of physics, as we presently understand them, depend on about 25 such constants. Well-known examples are the gravitational constant, which defines the strength of the force acting between two bodies, such as the Earth and the Moon, and the speed of light.

One of these constants is the so-called “fine structure constant”, alpha = 1/137.03599958, a combination of electrical charge of the electron, the Planck constant and the speed of light. The fine structure constant describes how electromagnetic forces hold atoms together and the way light interacts with atoms.

But are these fundamental physical constants really constant? Are those numbers always the same, everywhere in the Universe and at all times? This is not as naive a question as it may seem. Contemporary theories of fundamental interactions, such as the Grand Unification Theory or super-string theories that treat gravity and quantum mechanics in a consistent way, not only predict a dependence of fundamental physical constants with energy – particle physics experiments have shown the fine structure constant to grow to a value of about 1/128 at high collision energies – but allow for their cosmological time and space variations. A time dependence of the fundamental constants could also easily arise if, besides the three space dimensions, there exist more hidden dimensions.

Already in 1955, the Russian physicist Lev Landau considered the possibility of a time dependence of alpha. In the late 1960s, George Gamow in the United States suggested that the charge of the electron, and therefore also alpha, may vary. It is clear however that such changes, if any, cannot be large or they would already have been detected in comparatively simple experiments. Tracking these possible changes thus requires the most sophisticated and precise techniques.

Looking back in time
In fact, quite strong constraints are already known to exist for the possible variation of the fine structure constant alpha. One such constraint is of geological nature. It is based on measures taken in the ancient natural fission reactor located near Oklo (Gabon, West Africa) and which was active roughly 2,000 million years ago. By studying the distribution of a given set of elements – isotopes of the rare earths, for example of samarium – which were produced by the fission of uranium, one can estimate whether the physical process happened at a faster or slower pace than we would expect it nowadays. Thus we can measure a possible change of the value of the fundamental constant at play here, alpha. However, the observed distribution of the elements is consistent with calculations assuming that the value of alpha at that time was precisely the same as the value today. Over the 2 billion years, the change of alpha has therefore to be smaller than about 2 parts per 100 millions. If present at all, this is a rather small change indeed.

But what about changes much earlier in the history of the Universe?

To measure this we must find means to probe still further into the past. And this is where astronomy can help. Because, even though astronomers can’t generally do experiments, the Universe itself is a huge atomic physics laboratory. By studying very remote objects, astronomers can look back over a long time span. In this way it becomes possible to test the values of the physical constants when the Universe had only 25% of is present age, that is, about 10,000 million years ago.

Very far beacons
To do so, astronomers rely on spectroscopy – the measurement of the properties of light emitted or absorbed by matter. When the light from a flame is observed through a prism, a rainbow is visible. When sprinkling salt on the flame, distinct yellow lines are superimposed on the usual colours of the rainbow, so-called emission lines. Putting a gas cell between the flame and the prism, one sees however dark lines onto the rainbow: these are absorption lines. The wavelength of these emission and absorption spectra lines is directly related to the energy levels of the atoms in the salt or in the gas. Spectroscopy thus allows us to study atomic structure.

The fine structure of atoms can be observed spectroscopically as the splitting of certain energy levels in those atoms. So if alpha were to change over time, the emission and absorption spectra of these atoms would change as well. One way to look for any changes in the value of alpha over the history of the Universe is therefore to measure the spectra of distant quasars, and compare the wavelengths of certain spectral lines with present-day values.

Quasars are here only used as a beacon – the flame – in the very distant Universe. Interstellar clouds of gas in galaxies, located between the quasars and us on the same line of sight and at distances varying from six to eleven thousand of million light years, absorb parts of the light emitted by the quasars. The resulting spectrum consequently presents dark “valleys” that can be attributed to well-known elements.

If the fine-structure constant happens to change over the duration of the light’s journey, the energy levels in the atoms would be affected and the wavelengths of the absorption lines would be shifted by different amounts. By comparing the relative gaps between the valleys with the laboratory values, it is possible to calculate alpha as a function of distance from us, that is, as a function of the age of the Universe.

These measures are however extremely delicate and require a very good modelling of the absorption lines. They also put exceedingly strong requirements on the quality of the astronomical spectra. They must have enough resolution to allow very precise measurement of minuscule shifts in the spectra. And a sufficient number of photons must be captured in order to provide a statistically unambiguous result.

For this, astronomers have to turn to the most advanced spectral instruments on the largest telescopes. This is where the Ultra-violet and Visible Echelle Spectrograph (UVES) and ESO’s Kueyen 8.2-m telescope at the Paranal Observatory is unbeatable, thanks to the unequalled spectral quality and large collecting mirror area of this combination.

Constant or not?
A team of astronomers [1], led by Patrick Petitjean (Institut d’Astrophysique de Paris and Observatoire de Paris, France) and Raghunathan Srianand (IUCAA Pune, India) very carefully studied a homogeneous sample of 50 absorption systems observed with UVES and Kueyen along 18 distant quasars lines of sight. They recorded the spectra of quasars over a total of 34 nights to achieve the highest possible spectral resolution and the best signal-to-noise ratio. Sophisticated automatic procedures specially designed for this programme were applied.

In addition, the astronomers used extensive simulations to show that they can correctly model the line profiles to recover a possible variation of alpha.

The result of this extensive study is that over the last 10,000 million years, the relative variation of alpha must be less than 0.6 part per million. This is the strongest constraint from quasar absorption lines studies to date. More importantly, this new result does not support previous claims of a statistically significant change of alpha with time.

Interestingly, this result is supported by another – less extensive – analysis, also conducted with the UVES spectrometer on the VLT [2]. Even though those observations were only concerned with one of the brightest known quasar HE 0515-4414, this independent study lends further support to the hypothesis of no variation of alpha.

Even though these new results represent a significant improvement in our knowledge of the possible (non-) variation of one of the fundamental physical constants, the present set of data would in principle still allow variations that are comparatively large compared to those resulting from the measurements from the Oklo natural reactor. Nevertheless, further progress in this field is expected with the new very-high-accuracy radial velocity spectrometer HARPS on ESO’s 3.6-m telescope at the La Silla Observatory (Chile). This spectrograph works at the limit of modern technology and is mostly used to detect new planets around stars other than the Sun – it may provide an order of magnitude improvement on the determination of the variation of alpha.

Other fundamental constants can be probed using quasars. In particular, by studying the wavelengths of molecular hydrogen in the remote Universe, one can probe the variations of the ratio between the masses of the proton and the electron. The same team is now engaged in such a large survey with the Very Large Telescope that should lead to unprecedented constraints on this ratio.

Original Source: ESO News Release

Image credit: Chandra
The Chandra image of N49B, left, the remains of an exploded star, shows a cloud of multimillion-degree gas that has been expanding for about 10,000 years. A specially processed version of this image, right, reveals unexpectedly large concentrations of the element magnesium, shown in blue.

Magnesium, created deep inside the star and ejected in the supernova explosion, is usually associated with correspondingly high concentrations of oxygen. However, the Chandra data indicate that the amount of oxygen in N49B is not exceptional. This poses a puzzle as to how the excess magnesium was created, or, alternatively, how the excess oxygen has escaped detection.

The amount of magnesium in N49B is estimated to be about equal to the total mass of the Sun. Since the Sun contains only about 0.1 percent of magnesium by mass, the total mass of magnesium N49B is about a thousand times that in the Sun and its planets.

Magnesium, the eighth most abundant material in the Earth’s crust, is a mineral needed by every cell of our bodies. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, and bones strong. It is also involved in energy metabolism and protein synthesis. Fortunately for us, and thanks to stars such as the one that produced N49B, there is an abundant supply of magnesium in the Universe.

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. ( NASA/CXC/Penn State/S. Park et al. )

Original Source: Chandra News Release

Image credit: Hubble
WIMPs speeding at 670,000 mph on a “highway” in space may be raining onto Earth ? a phenomenon that might prove the existence of “dark matter” that makes up most our galaxy and one-fourth of the universe, says a study co-authored by a University of Utah physicist.

Many researchers have long suspected that dark matter may be made of WIMPS or Weakly Interacting Massive Particles, which are theorized subatomic particles. More than 20 groups of physicists worldwide are building or have built devices to detect them.

Scientists who run a WIMP detector named DAMA (Dark Matter) in Italy claimed in 1998 that the underground device sensed WIMPs reaching Earth from an unseen halo of dark matter surrounding our Milky Way galaxy. The claim was doubted by scientists who run other WIMP detectors, which are designed differently than DAMA and have not found WIMPs.

The new study ? published in the March 19 issue of the journal Physical Review Letters ? advises how the DAMA scientists might prove their claim.

“We?re suggesting a way to check if what DAMA claimed to have seen are really WIMPs,” says study co-author Paolo Gondolo, an assistant professor of physics at the University of Utah. “This is about finding out what 90 percent of our galaxy is made of.”

Gondolo and colleagues say that in addition to the WIMPs pouring into our Milky Way galaxy from the surrounding halo, a dark matter “highway” of WIMPS may be raining onto our solar system after flying out of Sagittarius, a dwarf galaxy that slowly is being gobbled up and torn apart by gravity from the Milky Way.

The combination of the Milky Way WIMPS and those from the Sagittarius dwarf galaxy should produce a distinct pattern in the Italian data that “would be a smoking gun for WIMP detection,” the new study says.

Gondolo conducted the research with physicist Katherine Freese and graduate student Matthew Lewis of the University of Michigan, and astronomer Heidi Jo Newberg of Rensselaer Polytechnic Institute in Troy, N.Y.

The Dark Side of the Universe
Scientists realized a few decades ago that the motions of galaxies within the universe could not be explained by the gravitational pull of visible galaxies, stars and gases. For a long time, scientists said that 10 percent of the universe was visible matter and 90 percent was unseen dark matter filling the voids among stars and galaxies.

In recent years, however, astronomers determined that the universe and its galaxies were flying apart at an accelerating rate, a phenomenon consistent with the existence of an anti-gravitational force known as “dark energy.”

Gondolo says scientists now believe the universe is about 5 percent visible matter, 25 percent dark matter and 70 percent dark energy.

Unlike dark matter, which is subject to gravity, dark energy is not pulled into our galaxy, so the Milky Way is about 10 percent matter and 90 percent dark matter, Gondolo says.

The spinning motion of the flattened, spiral disk-shaped Milky Way is too fast to be explained merely by the gravity of its visible stars and gases, so scientists believe it is surrounded by a much larger “halo” ? actually a flattened sphere ? that contains some stars but mostly unseen dark matter.

Over the years, numerous theories were proposed as to the nature of the dark matter: from dim brown dwarf stars that never ignited to the whimsically named MACHOs (Massive Compact Halo Objects) and subatomic WIMPs.

Gondolo says WIMPs and other subatomic particles called axions now are considered the most likely candidates to be dark matter.

The DAMA detector, located at Italy?s Gran Sasso National Laboratory, is run by an international collaboration of physicists led by the University of Rome. The DAMA group announced in 1998 that it found evidence for WIMPS.

Because DAMA is underground, overlying rock filters out particles created when cosmic rays hit Earth?s atmosphere and produce showers of smaller particles. WIMPs are “weakly interacting” particles, so they pass through Earth. But they can hit sodium iodide crystals inside DAMA, causing flashes of light and making sodium or iodine ions recoil.

If WIMPs do exist, they flow toward our solar system from the halo around our galaxy. As the Earth orbits around the sun, it sometimes moves “upstream” against the flow of oncoming WIMPs, and sometimes moves with the flow. The DAMA scientists believe this explains the up-and-down pattern in the number of particles detected by DAMA, and supports the assertion those particles are WIMPs.

Other physicists, however, remain unconvinced. Their detectors, which use germanium as a sensor instead of sodium iodide, should be equally sensitive, but have not “seen” WIMPs. They argue the annual fluctuation in the number of particles detected by DAMA may be caused by seasonal changes in the atmosphere, the DAMA detector or DAMA?s environment, so that the particles have not been proven to be WIMPs.

The New Study: A Solution from Sagittarius?
The visible Milky Way is vast, about 100,000 light years across, or about 588 million billion miles (588 times 10 to the 15th power). For eons, the Milky Way has been absorbing and tearing apart the Sagittarius dwarf galaxy, which is one-tenth the Milky Way?s diameter.

Newberg and other astronomers recently discovered two arc-shaped “tails” or streams of stars flowing from Sagittarius. The streams are believed to also contain WIMPs ? if they exist. Our solar system sits in one of these streams, which Gondolo and Freese describe as a possible “dark matter ?highway? raining down upon the solar system.”

In the new study, Gondolo and colleagues suggest how the combination of WIMPs from the Milky Way?s halo and from the Sagittarius stream would register on the DAMA detector:

— The dates of the maximum and minimum number of WIMPs detected by DAMA would shift when dark matter from Sagittarius is considered. That is because the Sagittarius WIMPs hit Earth from a different angle than Milky Way halo WIMPS, changing the dates when the most and the fewest WIMPs hit Earth and thus DAMA. Gondolo says the peak should be May 25 instead of June 2 if Sagittarius WIMPs and halo WIMPs both hit Earth. DAMA found the maximum was
May 21, plus or minus 22 days.

— The “smoking gun” that would prove WIMPS exist is more complicated to explain. When particles hit sodium iodide in DAMA, the ions recoil in proportion to the mass and speed of the incoming particle. Gondolo says WIMPs from the Milky Way halo move at speeds of zero to 600 kilometers per second (1.34 million mph), with an average speed of 220 kilometers per second (about 492,000 mph). WIMPs in the Sagittarius stream or highway all move at 300 kilometers per second (about 671,000 mph). When the recoil energies of the two kinds of WIMPs are combined and plotted on a graph, there should be a steep “step” or drop in the number of collisions with higher recoil energies, reflecting the fact that Sagittarius WIMPs do not exceed 671,000 mph.

If DAMA scientists find that “step” in their data, it should be the smoking gun to prove dark matter exists in the form of WIMPs, Gondolo says.

“This would be a corroboration of their result,” he adds. “As way to check if they really have seen WIMPs, they could look for the specific signature of WIMPs in the Sagittarius stream.”

Scientists at DAMA are aware of the new study and are rechecking their data to determine if it contains the evidence that could prove the detector found WIMPs. The process could take months, and it will take a few years for newer detectors to confirm the finding, Gondolo says.

He and his colleagues suspect other detectors have not found WIMPs because the particles may be lighter and smaller than expected, so germanium does not recoil much when hit by an incoming WIMP, while DAMA?s ions have measurable recoil.

Gondolo says he studies dark matter because “I want to know what the universe is made of. I was unsatisfied when I learned most of the universe is not made of atoms.”

Original Source: University of Utah News Release