Posted on by Fraser Cain

Searching for Gravity Waves

For almost 100 years, scientists have been searching for direct evidence of the existence of gravity waves faint ripples in the fabric of spacetime predicted in Albert Einsteins theory of General Relativity. Today, the hunt for gravity waves has become a worldwide effort involving hundreds of scientists. A number of large, ground-based facilities have been developed in Europe, the United States and Japan, but the most sophisticated search of all will soon take place in space.

Speaking on Tuesday 5 April at the RAS National Astronomy Meeting in Birmingham, Professor Mike Cruise will describe a joint ESA-NASA project called LISA (Laser Interferometric Space Antenna). Scheduled for launch in 2012, LISA will comprise three spacecraft flying in formation around the Sun, making it the largest scientific instrument ever placed in orbit.

LISA is expected to provide the best chance of success in the search for the exciting, low frequency gravity waves, said Professor Cruise. However, the mission is one of the most complex, technological challenges ever undertaken. According to Einsteins theory, gravity waves are caused by the motion of large masses (e.g. neutron stars or black holes) in the Universe. The gravitational influence between distant objects changes as the masses move, in the same way that moving electric charges create the electromagnetic waves that radio sets and TVs can detect.

In the case of a very light atomic particle such as the electron, the motion can be very fast, so generating waves at a wide range of frequencies, including the effects we call light and X-rays. Since the objects which generate gravity waves are much larger and more massive than electrons, scientists expect to detect much lower frequency waves with periods ranging from fractions of a second to several hours.

The waves are very weak indeed. They reveal themselves as an alternating stretching and contracting of the distance between test masses which are suspended in a way that allows them to move. If two such test masses were one metre apart, then the gravity waves of the strength currently being sought would change their separation by only 10e-22 of a metre, or one ten thousandth of a millionth of a millionth of a millionth of a metre.

This change in separation is so small that preventing the test masses being disturbed by the gravitational effect of local objects, and the seismic noise or trembling of the Earth itself, is a real problem that limits the sensitivity of the detectors. Since each metre length in the distance between the test masses gives rise separately to the tiny changes being searched for, increasing the length of the separation between the masses gives rise to a greater overall change that could be detected. As a consequence, gravity wave detectors are made as large as possible.

Current ground-based detectors cover distances of a few kilometres and should be able to measure the millisecond periods of fast-rotating objects such as neutron stars left over from stellar explosions, or the collisions between objects in our local galactic neighbourhood. There is, however, a strong interest in building detectors to search for the collisions between massive black holes that take place during mergers of complete galaxies. These violent events would generate signals with very low frequencies- too low to be observed above the random seismic noise of the Earth.

The answer is to go into space, away from such disturbances. In the case of LISA, the three spacecraft will fly in formation, 5 million kilometres apart. Laser beams travelling between them will measure the changes in separation caused by gravity waves with a precision of about 10 picometres (one hundred thousandth of a millionth of a metre). Since the test masses on each spacecraft will have to be protected from various disturbances that are caused by charged particles in space, they must be housed in a vacuum chamber in the spacecraft. The precision required is 1,000 times more demanding than has ever been achieved in space before and so ESA is preparing a test flight of the laser measurement system in a mission called LISA Pathfinder, due for launch in 2008.

Scientists from the University of Birmingham, the University of Glasgow and Imperial College London are currently preparing the instrumentation for LISA Pathfinder in collaboration with ESA and colleagues in Germany, Italy, Holland, France, Spain and Switzerland. When LISA is operating in orbit, we expect to observe the Universe through the new window offered by gravity waves, said Cruise. In addition to neutron stars and massive black holes, we may be able to detect the echoes of the Big Bang from gravity waves emitted tiny fractions of a second after the event that started our Universe on its current evolution.

Original Source: RAS News Release

Posted on by Fraser Cain

Starburst Galaxies Hide Black Holes

A team of European scientists has used Virtual Observatories to compare observations of distant “starburst” galaxies made at radio and X-ray wavelengths. This is the first study to combine the highest resolution and sensitivity radio and X-ray images which penetrate the dust hiding the centres of some of these distant galaxies.

The team focused on galaxies so far away that their radiation took more than six billion years to reach us. The galaxies are seen as they were when they were less than half the age that the Universe is today.

Speaking on Tuesday 5 April at the RAS National Astronomy Meeting in Birmingham, Dr. Anita Richards (Jodrell Bank Observatory, University of Manchester) will explain how the team used the UK?s MERLIN array of radio telescopes and the Very Large Array to investigate how galaxies in the early Universe differ from those nearby.

“The more remote starburst galaxies, so called because of their high rate of star formation, typically produce 1,000 or more solar masses of stars per year – at least 50 times more than the most active star-forming galaxies in the nearby Universe,” said Dr. Richards.

“Each distant starburst region is tens of thousands of light years across, equivalent to about the inner quarter of the Milky Way – also vastly larger than any such regions found in our part of the Universe.”

The radio search took place in an area known as the Hubble Space Telescope Deep Field North – a patch of sky smaller than the full Moon that contains tens of thousands of galaxies.

Apart from Hubble, radio telescope arrays are the only instruments that can see detailed structures within these galaxies. Moreover, only radio or X-ray emissions can penetrate the dense dust in the innermost regions of some of these galaxies.

The two main sources of radio waves and X-rays are star formation and emissions from Active Galactic Nuclei (AGN) that are generated when material is sucked into a massive black hole and ejected in jets. The team found about twice as many starbursts as AGN, where these could be distinguished in radio images.

The UK AstroGrid and the European AVO ? parts of the international Virtual Observatory – were used to find counterparts for the radio sources from a variety of other data held by archives and observatories around the world. In this way it was discovered that 50 distant X-ray sources with measured redshifts had also been detected by the Chandra space observatory.

Virtual Observatory tools made it easy to calculate the intrinsic brightness of the sources, corrected for distance and redshift. However, the team found that there was no obvious relationship between radio and X-ray luminosity. This was a surprise since there is such a link in most local starburst galaxies.

Some of the faintest radio sources were found to emit the most X-rays and vice versa – suggesting that two separate mechanisms within each galaxy were generating powerful emissions at opposite extremes of the spectrum.

Members of the European Virtual Observatory team had earlier used the Chandra X-ray data and Hubble images to find 47 AGN in the Hubble Deep Field North. These appeared to be seen sideways on, so that the dusty torus surrounding the black hole blocked all but the most energetic X-rays from emerging in our direction.

“Astonishingly, only 4 of these looked like AGN in the radio observations,” said Richards. “10 had radio emissions characteristic of starbursts, 4 could not be classified, and the rest went undetected by radio telescopes.”

The 10 super-starburst/AGN hybrids tended to be at a higher redshift ? indicating that they are much further away from Earth than the rest of the radio galaxies. Over half of them were among the enigmatic ?SCUBA sources?. These objects are very bright at wavelengths just under a millimetre, probably as a result of dust being strongly heated by violent star formation, but almost invisible to most other instruments.

“We concluded that, not only were these young galaxies undergoing much more violent and extended star formation than we see today, but they were simultaneously feeding active, supermassive black holes responsible for the X-ray emission,” said Richards.

“One clue to the origin of this phenomenon is that the Hubble Space Telescope often reveals two or more distorted galaxies associated with these sources, suggesting that galaxy interactions were commoner when the Universe was young. The ensuing collisions of gas and dust clouds trigger star formation and also feed the central black hole.

“Modern starburst galaxies are not only slower at star formation, but mostly have much quieter AGN, if any. This is not surprising as the super-starbursts must run out of fuel quite quickly (by cosmological standards), when all the available material has either turned into stars or fallen into the black hole.”

Original Source: RAS News Release

Posted on by Fraser Cain

How Many Habitable Planets Could Be Out There?

How many planets like the Earth are there among the 130 or so known planetary systems beyond our own? How many of these ?Earths? could be habitable?

Recent theoretical work by Barrie Jones, Nick Sleep, and David Underwood at the Open University in Milton Keynes indicates that as many as half of the known systems could be harbouring habitable ?Earths? today.

Unfortunately, existing telescopes are not powerful enough to see these relatively small, distant ?Earths?. Orbiting close to a much brighter star, these very faint worlds resemble glow-worms hidden in the glare of a searchlight.

All of the planets that have been detected so far are giants the mass of Neptune or larger. Even so, they cannot be directly seen with ground-based instruments. Almost all of the known exoplanets have been found through the ?wobbling? motion they induce in their star as they orbit it, like a twirling dumb-bell in which the mass at one end (the star) is much greater than the mass at the other end (the giant planet).

Speaking today at the RAS National Astronomy Meeting in Birmingham, Professor Jones explained how his team used computer models to see if ?Earths? could be present in any of the currently known exoplanetary systems, and whether the gravitational buffeting from one or more giant planets in those systems would have torn them out of their orbits.

?We were particularly interested in the possible survival of ?Earths? in the habitable zone,? said Professor Jones. ?This is often called the ?Goldilocks zone?, where the temperature of an ?Earth? is just right for water to be liquid at its surface. If liquid water can exist, so could life as we know it.?

The Open University team created a mathematical model of a known exoplanetary system, with its star and giant planet(s), then launched an Earth-sized planet at some distance from the star to see if it survived.

By detailed study of a few representative exoplanetary systems, they found that each giant planet is accompanied by two ?disaster zones? – one exterior to the giant, and one interior. Within these zones, the giant?s gravity will cause a catastrophic change in the Earth-like planet?s orbit. The dramatic outcome is a collision with either the giant planet or the star, or ejection into the cold outer reaches of the system.

The team found that the locations of these disaster zones depend not only on the mass of the giant planet (a well known result) but also on the eccentricity of its orbit. They thus established rules for determining the extent of the disaster zone.

Having found the rules, they applied them to all of the known exoplanetary systems – a much quicker method than studying each system in detail. The range of distances from the star covered by its habitable zone was compared to the locations of the disaster zones to see if there was a full or partial safe haven for an Earth-like planet.

They discovered that about half of the known exoplanetary systems offer a safe haven for a period extending from the present into the past that is at least long enough for life to have developed on any such planets. This assumes that ?Earths? could have formed in the first place, which seems quite likely.

However, the situation is complicated by the fact that the habitable zone migrates outwards as the star ages, and in some cases this changes the potential for life to evolve. Thus, in some cases a safe haven might have been available only in the past, while in other cases it might exist only in the future.

These scenarios of past extinction and future birth increase to about two-thirds the proportion of the known exoplanetary systems that are potentially habitable at some time during the main-sequence lifetime of their central star.

Original Source: RAS News Release

Posted on by Fraser Cain

What’s Up This Week – Apr 4 – Apr 10, 2005

Monday, April 4 – Tonight our binocular and telescope study will take us to a place of intrigue… An interacting pair of galaxies that are easily observed in Ursa Major. Start by drawing an imaginary line between Phecda and Dubhe, and extend that just one step further into space as we explore the M81 and M82.

Discovered in December 1774 by JE Bode at Berlin and photographed as early as March 1899, these two deep sky favourites will appear as a pair to binoculars and low power telescope fields. The M81 is truly spiral perfection with its symmetrical structure and bright nucleus. Spanning approximately 36,000 light years in diameter, it is one of the densest known galaxies with one third of its mass concentrated at the core. Because it contains vast numbers of red and yellow giants, larger telescopes at power will see a golden “glow” to the structure – the combined luminosity of twenty billion suns.

Its neighbor – the M82 – is often mistaken in the small telescope for edge-on in appearance, but shows no sign of true spiral structure movement. Its light is polarized, leading science to believe it contains a super-massive magnetic field. The M82 is also a powerful radio source with huge masses of dust irradiated by stars possessing unusual spectral qualities. A violent outburst may have occurred within the galaxy as recently as 1.5 million years ago releasing the energy equivalent of several million exploding suns. Shock waves emanating from the M81 resemble the synchrotron radiation first associated with planetary nebula M1 – but on an enormous scale. Can you image a supernova remnant the size of an entire galactic core region?!

Roughly every one hundred million years, M81 and M82 make a “pass” at one another, reaching out with immensely powerful gravitational arms to intertwine the two galaxies. It is theorized that during the last interaction, M82 raised rippling density waves which circulated throughout M81. The result? Possibly the most perfectly formed spiral galaxy in all of space, but M81’s influence left M82 a broken galaxy – filled with exploded stars and colliding gas – a galaxy so violent it emits X-rays. Reactions induced by colliding dust and gas caused the birth of numerous brilliant stars – stars capable of creating dense atoms and extreme motion that causes immense magnetic fields. The end may already be envisioned for the M81 and M82. Scientists speculate within a few billion years, the two galaxies will combine, becoming indistinguishable but for the welter of radiation that the union leaves behind. We known this same fate may await our own galaxy as we combine with our largest neighbor – the Andromeda Galaxy – but don’t let that stop you from viewing the M81’s intense core and smooth spiral form – or the M82’s notched spindle shape tonight…

That’s billions of years in the future.

Tuesday, April 5 – This evening we will study another pair of galaxies that can be seen in large binoculars and are outstanding for telescopic study. Identify the triangle of stars that mark the “hips” of Leo. The southwestern star is Theta and about three finger widths to its south is Iota. If skies are transparent enough to see Eta between them, then you will have no problem locating the M65 and M66 to Eta’s east/southeast.

Discovered by Mechain in March 1780, apparently Mr. Messier didn’t notice the bright pair when a comet passed between them in 1773. At around 35 million light years away, you will find the M66 to be slightly brighter than its 200,000 light year distant western neighbor – the M65. While both are Sb classed spirals, the two couldn’t appear more different. The M65 has a bright nucleus and a smooth spiral structure with a dark dustlane at its eastern edge. The M66 has a more stellar core region with thick, bright arms that show knots to larger scopes – as well as a wonderful extension from the southern edge. If you are viewing with a larger scope, you may notice to the north of this famous pair yet another galaxy! The NGC 3628 is a similar magnitude edge-on beauty with a great dissecting dark dustlane. This pencil-slim, low surface brightness galaxy is a bit of a challenge for smaller scopes, but larger ones will find its warped central disc well worth high power study.

Congratulations! You’ve just conquered the “Leo Trio”.

Wednesday, April 6 – Tonight let’s head for another trio of galaxies that are suited best for mid-to-large aperture telescopes. Begin by heading west about a fist’s width from Regulus and identify 52 Leonis. Our mark is one and a half degrees south.

At lower power you will see a triangle of galaxies. The largest and brightest is the M105 discovered by Mechain on March 24, 1781. This dense elliptical galaxy would appear to be evenly distributed, but the Hubble Space Telescope revealed a huge area within its core to be equal to about 50 million solar masses. Companion elliptical to the northeast – NGC 3384 will reveal a bright nucleus as well as an elongated form. The most faint of this group – NGC 3389 is receding spiral and for larger scopes will reveal a “patchiness” in structure.

Continue another degree south and enjoy another galactic pair. The widely spaced M96 and M95 are part of this galaxy grouping known as Leo I. The dusty spiral – M96 – will appear as a silver oval, whose nucleus is much sharper than its faint spiral arms that contained a supernova as recently as 1998. To M96’s west, you will discover one very beautiful barred spiral – M95. While both of these were discovered by Mechain only four days earlier than the M105, it wasn’t until recent years that they became the prime target of the Hubble Space Telescope. We enjoy the M95 for its unique ring-like arms and unmistakable barred core, but the HST was looking for cephid variables and determining the Hubble Constant. While we don’t need a space telescope to view this group of galaxies, we can now appreciate knowing that we can see 38 million light years away from our own backyard!

Thursday, April 7 – On this day in 1991, the Compton Gamma Ray Observatory (GRO) was deployed by space shuttle Atlantis. After serving for more than 9 years, the CRO plunged to a fiery death in the Pacific Ocean, but we can celebrate its accomplishments by viewing a source of gamma rays – the M87.

You may be able to detect the M87’s round glow with large binoculars slightly more than a fist’s width east of Epsilon Virginis with an 8th magnitude star, but telescope users will enjoy the most massive and luminous of all known galaxies. But there is much more here than meets the eye! Also known as Virgo A, the M87 is the fifth most intense radio source in the sky – 3C 274. It is also home to more than 4000 globular clusters (the Milky Way contains about 110) and a 4,000 light year long “jet” of high speed particles that could be associated with a black hole.

Friday, April 8 – Today’s highlight is a hybrid solar eclipse! Without the cursory lecture of safe solar observing techniques, observers in parts of Costa Rica, Panama, Venezuela and Columbia will enjoy the most exciting part of the show as the Sun moves from annular to total – and back to annular again around local sunset. For observers in Central America, the Caribbean and parts of South America, you will enjoy a spectacular partial eclipse that ranges anywhere from 80 to 90% coverage. Most of Mexico will get to see about half of the Sun in shadow, while the southern United States ranges from 20 to 40%. The northern-most limit cuts across central New Jersey, Pennsylvania, Ohio, Indiana, and southern Illinois and begins a southward arc ending in southern Arizona and California. For observers south of this line, it is still worth seeing a “bite” taken out of the Sun’s edge! For a list of times and many more details, please visit “Mr. Eclipse” – Fred Espenak – at this page.

Wishing you clear skies.

(Take advantage of tonight’s new moon to just roam around and enjoy the galaxy fields of Virgo. Never stress about identifying all you see, for the pleasure is just seeing them!)

Saturday, April 9 – This morning will present a unique opportunity for those who enjoy watching Jupiter’s moons. At 04:53 UT (12:43 a.m. ESDT), Io, Europa and Calisto will form a very close dance to Jupiter’s east. This formation will last for about an hour and will be well worth watching them move slowly apart.

Let’s use tonight’s dark sky to enjoy a “Jupiter-sized” planetary nebula – the M97. Often referred to as the “Owl”, you will find this sometimes difficult object about two and a half degrees south of Beta Ursae Majoris. Discovered on February 16, 1781 by the unsung hero Mechain, its visual brightness makes it a candidate for larger binoculars, but it takes a large aperture telescope to truly appreciate.

Graced by a 14th magnitude central star – one of the hottest known – this planetary nebula is highly unusual because we cannot clearly define its distance. The “Owl” is very complex, and its appearance has often been interpreted as a cylindrical torus viewed at an acute angle. What we see as “eyes” may be the less dense ends of the cylinder. The shell itself is encased by a fainter nebula or lower ionization. While we once believed this type of formation was the result of an ancient novae, the M97 re-defines our thinking. This quiet type of emission activity may just be the result of a star’s old age… Giving the ancient “Owl” a place of honour in the north.

Sunday, April 10 – Tonight’s singular destination can be detected as a faint glow in binoculars, can be found with the smallest of telescopes, but provides a stunning view with aperture. Set your sights on bright Spica and head eleven degrees due west…

Once again discovered by Mechain, the M104 – “Sombrero” – is one of the finest examples of an edge-on galaxy in the night sky. The “Sombrero” has a huge, bulging bright core region, well-defined spiral arms and a bold, dark dustlane. The core region is highly conspicuous and contains a vastly populated globular cluster system. As the dominating member of the 104 group, this fantastic galaxy is the one of the very first discovered in redshift. At around 400 million light years away, it is receding at about 700 miles per second, but that won’t stop you from enjoying its wonderful transparent qualities and star spangled field!

Until next week? Keep looking up and enjoying the wonders of the Cosmos! Light speed… ~Tammy Plotner

Posted on by Fraser Cain

Portrait of Pandora in the Rings

Pandora is seen in this dramatic view, orbiting just beyond the outer edge of Saturn’s F ring. Several bright areas are visible within the F ring. In the main rings, the Keeler gap and the Encke gap, with a bright ringlet, are also visible. Pandora is 84 kilometers (52 miles) across.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 18, 2005, at a distance of approximately 1.2 million kilometers (746,000 miles) from Pandora and at a Sun-Pandora-spacecraft, or phase, angle of 108 degrees. The image scale is 7 kilometers (4 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For additional images visit the Cassini imaging team homepage http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

And the Winner is…

Thanks to everyone who threw your name into the hat to win the Apollo 13 DVD, and the winner is… drum roll… Richard Hobbs. I received a total of 472 entries, and a lot of great emails too, so thanks for getting involved. This was fun, and I think I’ll convince publishers to send me more copies of stuff in the future so I can give it away.

Of course, if you didn’t win, you can still purchase a copy from Amazon.com.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Earth Seen in Gamma Rays

A NASA-funded scientist has produced a new type of picture of the Earth from space, which complements the familiar image of our “blue marble”. This new picture is the first detailed image of our planet radiating gamma rays, a type of light that is millions to billions of times more energetic than visible light.

The image portrays how the Earth is constantly bombarded by particles from space. These particles, called cosmic rays, hit our atmosphere and produce the gamma-ray light high above the Earth. The atmosphere blocks harmful cosmic rays and other high-energy radiation from reaching us on the Earth’s surface.

“If our eyes could see high-energy gamma rays, this is what the Earth would look like from space,” said Dr. Dirk Petry of NASA Goddard Space Flight Center in Greenbelt, Md. “Other planets — most famously, Jupiter — have a gamma-ray glow, but they are too far away from us to image in any detail.”

Petry assembled this image from seven years of data from NASA’s Compton Gamma-Ray Observatory, which was active from 1991 to 2000. The Compton Observatory orbited the Earth at an average altitude of about 260 miles (420 km). From this distance, the Earth appears as a huge disk with an angular diameter of 140 degrees. The long exposure and close distance enabled Petry to produce a gamma-ray image of surprisingly high detail. “This is essentially a seven-year exposure,” Petry said.

The gamma rays produced in the Earth’s atmosphere were detected by Compton’s EGRET instrument, short for Energetic Gamma-Ray Experiment Telescope. In fact, 60 percent of the gamma rays detected by EGRET were from Earth and not deep space. Although it makes a pretty image, local gamma-ray production interferes with observations of distant gamma-ray sources, such as black holes, pulsars, and supernova remnants.

Petry created this gamma-ray Earth image to better understand the impact of “local” cosmic-ray and gamma-ray interactions on an upcoming NASA mission called GLAST, the Gamma-ray Large Area Space Telescope. GLAST is planned for launch in 2007. Its main instrument, the Large Area Telescope, is essentially EGRET’s successor.

In 1972 and 1973 the NASA satellite SAS-II captured the first resolved image of the Earth in gamma rays, but the detectors had less exposure time (a few months) and worse energy resolution.

Petry, a member of the GLAST team at NASA Goddard, is an assistant research professor at the Joint Center for Astrophysics of the University of Maryland, Baltimore Country. A scientific paper describing his work is available at:

http://xxx.lanl.gov/abs/astro-ph/0410487

Original Source: NASA News Release

Posted on by Fraser Cain

Hubble’s View of a Giant Elliptical Galaxy

Like dust bunnies that lurk in corners and under beds, surprisingly complex loops and blobs of cosmic dust lie hidden in the giant elliptical galaxy NGC 1316. This image made from data obtained with the NASA Hubble Space Telescope reveals the dust lanes and star clusters of this giant galaxy that give evidence that it was formed from a past merger of two gas-rich galaxies.

The combination of Hubble’s superb spatial resolution and the sensitivity of the Advanced Camera for Surveys (ACS), installed onboard Hubble in 2002 and used for these images, enabled uniquely accurate measurements of a class of red star clusters in NGC 1316. Astronomers conclude that these star clusters constitute clear evidence of the occurrence of a major collision of two spiral galaxies that merged together a few billion years ago to shape NGC 1316 as it appears today.

NGC 1316 is on the outskirts of a nearby cluster of galaxies in the southern constellation of Fornax, at a distance of about 75 million light-years. It is one of the brightest ellipticals in the Fornax galaxy cluster. NGC 1316, also known as Fornax A, is one of the strongest and largest radio sources in the sky, with radio lobes extending over several degrees of sky (well off the Hubble image).

NGC 1316’s violent history is evident in various ways. Wide-field imagery from Cerro Tololo Interamerican Observatory in Chile shows a bewildering variety of ripples, loops and plumes immersed in the galaxy’s outer envelope. Amongst these so-called “tidal” features, the narrow ones are believed to be the stellar remains of other spiral galaxies that merged with NGC 1316 some time during the last few billion years. The inner regions of the galaxy shown in the Hubble image reveal a complicated system of dust lanes and patches. These are thought to be the remains of the interstellar medium associated with one or more of the spiral galaxies swallowed by NGC 1316.

The U.S. team of scientists, led by Dr. Paul Goudfrooij of the Space Telescope Science Institute in Baltimore, Maryland, used the ACS onboard Hubble to study star clusters in several nearby giant elliptical galaxies. Their study of NGC 1316 focused on globular clusters, which are compact stellar systems with hundreds of thousands to millions of stars formed at the same time.

The unprecedented sensitivity of the Hubble ACS data permitted the team to detect faint globular clusters previously impossible to reach. By counting the number of globular clusters detected as a function of their brightness they could, for the first time, see evidence of the gradual disruption of star clusters created during a past merger of gas-rich galaxies. They found that the relative number of low-mass clusters is significantly lower in the inner regions than in the outer regions, by an amount consistent with theoretical predictions.

These Hubble ACS images were taken in March 2003. The color composite is a combination of data taken in F435W (blue), F555W (yellow-green), and F814W (infrared) filters. The team’s results have improved our understanding of how elliptical galaxies and their star clusters may have formed during galaxy mergers and then evolve to resemble ‘normal’ elliptical galaxies after several billions of years.

Original Source: Hubble News Release

Posted on by Fraser Cain

Ultraviolet View of Mimas

Image credit: NASA/JPL/SSI
Saturn’s moon Mimas shines in reflected ultraviolet light from the Sun in this Cassini image. Ultraviolet images of Saturn’s moons often reveal the walls of their myriad craters in greater contrast than do images taken in visible light. This view, which shows the large impact crater Herschel, is no exception. Mimas is 397 kilometers (247 miles) across.

The image was taken with the Cassini spacecraft narrow-angle camera using a filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The image was acquired on Feb. 18, 2005, at a distance of approximately 938,000 kilometers (583,000 miles) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 99 degrees. The image scale is 6 kilometers (4 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. For additional images visit the Cassini imaging team homepage http://ciclops.org.

Original Source: NASA/JPL News Release

Posted on by Mark Mortimer

Book Review: Big Dish

The focal points in this book are the three largest communication antennas built by NASA, the backbone of the deep space network. Built roughly 120 degrees apart around the globe; Goldstone in California, Canberra in Australia, and Madrid in Spain, they spanned 64 metres in diameter originally though were later upgraded to 70 metres. Perhaps barely acknowledged by most space enthusiasts, they perform the critical service of linking us to our robot progeny in our reach off of Earth. Probes get sent commands to fire thrusters and in return send bits and bytes of video images of planets and moons. Robots get instructions to travel foreign terrains and provide visual treats of foreign lands. And perhaps most exciting, people on the moon interacted in (near) real time with Earth based operators. And lunar travel is the point in time when this book’s story begins.

Mudgway lays the groundwork to his story by outlining some of the significant political and space related issues. In the heydays of the 1960’s, a ready fiscal budget for space helped ensure the winning of the race and the build out of infrastructure like the antennae. Though the technology was still in its infancy a quick ramp up had to occur to meet the expectations of the space progam. On top of this groundwork he then builds a description of the existing state of technology and the requirements for the location and operation of the new antennae. What then follows in the book is an easy reading, chronologically arranged narrative of how the chosen people made it happen.

The narrative itself reads more like a fire side chat than like a specific technical treatise. The historical background and political circumstances embellish the reasoning for site selection. People’s names crop up, predominantly Bill Merrick the design and construction manager. Some of their more colourful actions and sayings enliven the text and remind the reader that people, not structures, were the central concern. Company names and their involvement get a slice of attention as well. So, as much as this book’s subject concerns the history of the antenna stations of the deep space network, the inclusion of people and extraneous events keeps the reading light and easy.

Nevertheless, the antenna stations are the main focus and there is a lot to learn within the book. Site selection had to meet limits on radio interference, ground stability and proximity of a workforce, even if Bogong moths were the initial main residents. Component fabrication and site build out gets a thorough description, from the laying of the continuous concrete ring 100 feet in diameter, 11 feet wide and 3 feet deep to using the quadripod support to install the feed system. In a pleasant manner, Mudgway effectively includes a sense of urgency by continually noting the need for the antenna to either support the manned space program or to be ready for a space probe doing a “once only” fly by of a distant planet.

Construction of the antenna encompasses a major portion of the book, though Mudgway also includes goodly portions on the operations and maintenance. We read how, just like a private residence, the antennae’s demands continually expanded to quickly exceed 100% availability. Then upgrades and procedure modifications allowed for better (faster and greater) abilities whose benefits were again quickly consumed by voracious researchers. Routine issues must have arisen, though none are included. Two major problems arose and are noted. One involves azimuthal motion. Oil allows a pad to travel across a steel runner. But if the runner gets uneven, contact occurs, and the antenna couldn’t turn until after signficiant repair work. In elevation, gears and bearings allowed the 4,000 ton dish to rotate in elevation, that is, until the bearings cracked. Again, things got very stressful and Mudgway does a wonderful job of describing the event, the people and the fix.

In a conversational, light tone, using generalist language, Mudgway gives an easy reading history of the antenna stations and the people involved. A reader can pick up some on the design and construction of the antenna and the people involved, however, don’t expect to learn much on the intricacies of microwave design or operation. Also, though chronological, the flow is uneven, at times like an old river that wanders and meanders without a clear focus, even though a destination does get reached.

The deep space network is the phone network that allows people to communicate with their mechanical offspring throughout our solar system. Douglas Mudgway in his book Big Dish, Building America’s Deep Space Connection to the Planets, gives a very smooth historical narrative of the people and events around the design, construction and upgrade of the three largest of the antennae.

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Review by Mark Mortimer