Universe Today

October 28, 2004March 24, 2012 by Mark Mortimer

Book Review: Space Tourism – Do You Want to Go?

Given the chance, most people would be off vacationing in space at a moment’s notice. Spencer’s plan is to make the holiday a lot more enjoyable than a weekend spent bouncing about Mir’s functional but restrictive interior. He has visions of space yachts in races similar to the America’s Cup; sentinel robots with self aware artificial intelligence maintain the yacht and keep the passengers happy; lunar dune buggies provide for excursions outside the yacht, much like excursions for cruise ships; and simulation centres on Earth train and condition people to their out-of-this-world holiday. With all this at hand, space vacationing would be very popular.

And popularity is a key condition for Spencer. He expects more than 800 people per month will be vacationing, once the infrastructure is in space. For example, a significant portion of the text describes the design of his own yacht, the Destiny. This yacht allows for a small group of passengers to mingle or enjoy solitary relaxation. Rooms, suites and common areas are created by self inflating structures. Environments are conditioned by service robots running on batteries. Safety is ensured by the afore mentioned AI sentinel. Self inflating space ports provide ‘harbours’ for the Destiny and her sister ships. There are even descriptions of coastguard like vessels that ensure the safety of the space lanes. All this is to allow the very rich to enjoy the Earth’s luxuries (wine, dining and dancing) while in the nouvelle regions of space. With this emphasis on pleasure, there should be no challenge meeting the monthly quota.

Though Spencer’s image of space tourism is wonderful, his tie-ins to the practicalities is not. He expects space tourism to be well established by the year 2050, in spite of today’s obvious challenges of building and maintaining the International Space Station. Because of this, his book reads a little too much like science fiction. Almost every aspect of his infrastructure requires large leaps in current scientific and engineering knowledge. For example, his space vessel windows will have material that, on verbal command, changes to allow different sun/radiation intensities into the cabin. This would be more believable if there were an estimate of the effort to get to the required state. Another example is that his vessels include a squad of specialized robots. However, there are no trade off assessments made between the cost and effectiveness of robots to people. Perhaps most telling is his reliance on a low cost orbital access vehicle for which we’re all waiting. In consequence when regarding practicalities, the book is much more of a marketing flyer than it is a business plan.

I think that to get the most out of this book, you must set aside the practical and pessimistic side of your mind and let your free thinking self take over. A particularly rewarding is a first hand account of a lottery winner taking a space holiday in the future. This person starts with describing their training and conditioning through simulation centres on Earth. Next are meetings with fellow passengers at the launch area, safety drills, and the launch to an orbiting port. From there, the winner heads into the space yacht and spends a few luxurious days watching the Earth spin beneath them and the stars twinkle all about. Onboard and off board, activities keep everyone happy and entertained. Upon completion and debarkation, the lottery winner becomes an outspoken advocate for space tourism. In summary, this chapter is the most entertaining and the highlight of the text.

In conclusion, the supposition of the authors is that, today, there is a valid space tourism movement that can lead to a real industry in the near future. The people of this movement believe that by continually highlighting the potential benefits and applauding any steps made in this direction, they will have eventual success. Dennis Tito’s self-paid trip is the landmark they often cite. Also, one complete chapter is dedicated to the progress in space tourism from the mid-1960’s to now. Though this chapter appears to be the summary of the author’s day timer or diary, it still is an interesting and unique view into the progression of space tourism movement from a nascent bottom feeder to today being an oft seen marketing tool and front page head liner. Perhaps, the subtitle would have been more accurate as, ‘do you want to tour in space, then jump on the band wagon!’.

Space tourism, to some people, will be the final industry to succeed in the thrust to the stars. John Spencer and Karen Rugg in their book Space Tourism – Do You Want to Go? show how space tourism can lead the way. They present plans and ideas to build upon the existing space tourism movement so that a full fledged bit of fun can happen in space. Just think what your longest drive might be during a friendly golf game on the moon!

To get your own copy, visit Countdown Creations.

Review by Mark Mortimer

October 28, 2004December 21, 2015 by Fraser Cain

Most Active Sun in 8,000 Years

The activity of the Sun over the last 11,400 years, i.e., back to the end of the last ice age on Earth, has now for the first time been reconstructed quantitatively by an international group of researchers led by Sami K. Solanki from the Max Planck Institute for Solar System Research (Katlenburg-Lindau, Germany). The scientists have analyzed the radioactive isotopes in trees that lived thousands of years ago. As the scientists from Germany, Finland, and Switzerland report in the current issue of the science journal “Nature” from October 28, one needs to go back over 8,000 years in order to find a time when the Sun was, on average, as active as in the last 60 years. Based on a statistical study of earlier periods of increased solar activity, the researchers predict that the current level of high solar activity will probably continue only for a few more decades.

The research team had already in 2003 found evidence that the Sun is more active now than in the previous 1000 years. A new data set has allowed them to extend the length of the studied period of time to 11,400 years, so that the whole length of time since the last ice age could be covered. This study showed that the current episode of high solar activity since about the year 1940 is unique within the last 8000 years. This means that the Sun has produced more sunspots, but also more flares and eruptions, which eject huge gas clouds into space, than in the past. The origin and energy source of all these phenomena is the Sun’s magnetic field.

Since the invention of the telescope in the early 17th century, astronomers have observed sunspots on a regular basis. These are regions on the solar surface where the energy supply from the solar interior is reduced owing to the strong magnetic fields that they harbour. As a consequence, sunspots are cooler by about 1,500 degrees and appear dark in comparison to their non-magnetic surroundings at an average temperature of 5,800 degrees. The number of sunspots visible on the solar surface varies with the 11-year activity cycle of the Sun, which is modulated by long-term variations. For example, there were almost no sunspots seen during the second half of the 17th century.

For many studies concerning the origin of the active sun and its potential effect on long-term variations of Earth’s climate, the interval of time since the year 1610, for which systematic records of sunspots exist, is much too short. For earlier times the level of solar activity must be derived from other data. Such information is stored on Earth in the form of “cosmogenic” isotopes. These are radioactive nuclei resulting from collisions of energetic cosmic ray particles with air molecules in the upper atmosphere. One of these isotopes is C-14, radioactive carbon with a half life of 5730 years, which is well known from the C-14 method to determine the age of wooden objects. The amount of C-14 produced depends strongly on the number of cosmic ray particles that reach the atmosphere. This number, in turn, varies with the level of solar activity: during times of high activity, the solar magnetic field provides an effective shield against these energetic particles, while the intensity of the cosmic rays increases when the activity is low. Therefore, higher solar activity leads to a lower production rate of C-14, and vice versa.

By mixing processes in the atmosphere, the C-14 produced by cosmic rays reaches the biosphere and part of it is incorporated in the biomass of trees. Some tree trunks can be recovered from below the ground thousands of years after their death and the content of C-14 stored in their tree rings can be measured. The year in which the C-14 had been incorporated is determined by comparing different trees with overlapping life spans. In this way, one can measure the production rate of C-14 backward in time over 11,400 years, right to the end of the last ice age. The research group have used these data to calculate the variation of the number of sunspots over these 11,400 years. The number of sunspots is a good measure also for the strength of the various other phenomena of solar activity.

The method of reconstructing solar activity in the past, which describes each link in the complex chain connecting the isotope abundances with the sunspot number with consistent quantitative physical models, has been tested and gauged by comparing the historical record of directly measured sunspot numbers with earlier shorter reconstructions on the basis of the cosmogenic isotope Be-10 in the polar ice shields. The models concern the production of the isotopes by cosmic rays, the modulation of the cosmic ray flux by the interplanetary magnetic field (the open solar magnetic flux), as well as the relation between the large-scale solar magnetic field and the sunspot number. In this way, for the first time a quantitatively reliable reconstruction of the sunspot number for the whole time since the end of the last ice age could be obtained.

Because the brightness of the Sun varies slightly with solar activity, the new reconstruction indicates also that the Sun shines somewhat brighter today than in the 8,000 years before. Whether this effect could have provided a significant contribution to the global warming of the Earth during the last century is an open question. The researchers around Sami K. Solanki stress the fact that solar activity has remained on a roughly constant (high) level since about 1980 – apart from the variations due to the 11-year cycle – while the global temperature has experienced a strong further increase during that time. On the other hand, the rather similar trends of solar activity and terrestrial temperature during the last centuries (with the notable exception of the last 20 years) indicates that the relation between the Sun and climate remains a challenge for further research.

Original Source: Max Planck Society News Release

October 28, 2004March 24, 2012 by Fraser Cain

Survivor Found From Tycho’s Supernova

An international team of astronomers is announcing today that they have identified the probable surviving companion star to a titanic supernova explosion witnessed in the year 1572 by the great Danish astronomer Tycho Brahe and other astronomers of that era.

This discovery provides the first direct evidence supporting the long-held belief that Type Ia supernovae come from binary star systems containing a normal star and a burned-out white dwarf star. The normal star spills material onto the dwarf, which eventually triggers an explosion.

The results of this research, led by Pilar Ruiz-Lapuente of the University of Barcelona, Spain, are being published in the Oct. 28 British science journal Nature. “There was no previous evidence pointing to any specific kind of companion star out of the many that had been proposed. Here we have identified a clear path: the feeding star is similar to our Sun, slightly more aged,” Ruiz-Lapuente says. “The high speed of the star called our attention to it,” she added.

Type Ia supernovae are used to measure the history of the expansion rate of the universe and so are fundamental to helping astronomers understand the behavior of dark energy, an unknown force that is accelerating the expansion of the universe. Finding evidence to confirm the theory as to how Type Ia supernovae explode is critical to assuring astronomers that the objects can be better understood as reliable calibrators of the expansion of space.

The identification of the surviving member of the stellar duo reads like a crime scene investigation tale. Even though today’s astronomers arrived at the scene of the disaster 432 years later, using astronomical forensics they have nabbed one of the perpetrators rushing away from the location of the explosion (which is now enveloped in a vast bubble of hot gas called Tycho’s Supernova Remnant). For the past seven years the runaway star and its surroundings were studied with a variety of telescopes. The Hubble Space Telescope played a key role by precisely measuring the star’s motion against the sky background. The star is breaking the speed limit for that particular region of the Milky Way Galaxy by moving three times faster than the surrounding stars. Like a stone thrown by a sling, the star went hurtling off into space, retaining the velocity of its orbital motion when the system was disrupted by the white dwarf’s explosion.

This alone is only circumstantial evidence that the star is the perpetrator because there are alternative explanations to its suspicious behavior. It could be falling in at a high velocity from the galactic halo that surrounds the Milky Way’s disk. But spectra obtained with the 4.2-meter William Herschel Telescope in La Palma and the 10-meter W.M. Keck telescopes in Hawaii show that the suspect has the high heavy-element content typical of stars that dwell in the Milky Way’s disk, not the halo.

The star found by the Ruiz-Lapuente team is an aging version of our Sun. The star has begun to expand in diameter as it progresses toward a red-giant phase (the end stage of a Sun-like star’s lifetime). The star turns out to fit the profile of the perpetrator in one of the proposed supernova conjectures. In Type Ia supernova binary systems, the more massive star in the pair will age faster and eventually becomes a white dwarf star. When the slower-evolving companion star subsequently ages to the point where it begins to balloon in size, it spills hydrogen onto the dwarf. The hydrogen accumulates until the white dwarf reaches a critical and precise mass threshold, called the Chandrasekhar limit, where it explodes as a titanic nuclear bomb. The energy output of this explosion is so well known that it can be used as a standard candle for measuring vast astronomical distances. (An astronomical “standard candle” is any type of luminous object whose intrinsic power is so accurately determined that it can be used to make distance measurements based on the rate the light dims over astronomical distances).

“Among the various systems containing white dwarfs that receive material from a solar-mass companion, some are believed to be viable progenitors of Type Ia supernovae, on theoretical grounds. A system called U Scorpii has a white dwarf and a star similar to the one found here. These results would confirm that such binaries will end up in an explosion like the one observed by Tycho Brahe, but that would occur several hundreds of thousands of years from now,” says Ruiz-Lapuente.

An alternative theory of Type Ia supernovae is that two white dwarfs orbit each other, gradually losing energy through the emission of gravitational radiation (gravity waves). As they lose energy, they spiral in toward each other and eventually merge, resulting in a white dwarf whose mass reaches the Chandrasekhar limit, and explodes. “Tycho’s supernova does not appear to have been produced by this mechanism, since a probable surviving companion has been found,” says Alex Filippenko of the University of California at Berkeley, a co-author on this research. He says that, nevertheless, it is still possible there are two different evolutionary paths to Type Ia supernovae.

On November 11, 1572, Tycho Brahe noticed a star in the constellation Cassiopeia that was as bright as the planet Jupiter (which was in the night sky in Pisces). No such star had ever been observed at this location before. It soon equaled Venus in brightness (which was at -4.5 magnitude in the predawn sky). For about two weeks the star could be seen in daylight. At the end of November it began to fade and change color, from bright white to yellow and orange to faint reddish light, finally fading away from visibility in March 1574, having been visible to the naked eye for about 16 months. Tycho’s meticulous record of the brightening and dimming of the supernova now allows astronomers to identify its “light signature” as that of a Type Ia supernova.

Tycho Brahe’s supernova was very important in that it helped 16th-century astronomers abandon the idea of the immutability of the heavens. At the present time, Type Ia supernovae remain key players in the newest cosmological discoveries. To learn more about them and their explosion mechanism, and to make them even more useful as cosmological probes, a current Hubble Space Telescope project led by Filippenko is studying a sample of supernovae in other galaxies at the very time they explode.

Original Source: Hubble News Release

October 27, 2004March 24, 2012 by Fraser Cain

False Colour Image of Titan

This image shows Titan in ultraviolet and infrared wavelengths. It was taken by Cassini’s imaging science subsystem on Oct. 26, 2004, and is constructed from four images acquired through different color filters. Red and green colors represent infrared wavelengths and show areas where atmospheric methane absorbs light. These colors reveal a brighter (redder) northern hemisphere. Blue represents ultraviolet wavelengths and shows the high atmosphere and detached hazes.

Titan has a gigantic atmosphere, extending hundreds of kilometers above the surface. The sharp variations in brightness on Titan’s surface (and clouds near the south pole) are apparent at infrared wavelengths. The image scale of this picture is 6.4 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 Cassini-Huygens 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 the latest news about the Cassini-Huygens mission, visit http://www.nasa.gov/cassini. For more information about the mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

October 27, 2004June 19, 2013 by Fraser Cain

Lunar Eclipse Tonight!

Okay, here’s your last reminder. There’s going to be a total lunar eclipse tonight, visible from the Americas, Europe and Africa. This is going to be the last eclipse visible until 2007, so I suggest that you set some time aside to enjoy this natural wonder. You don’t need any special equipment, just head outside, and watch the Moon as it darkens and then turns a beautiful red colour. Here’s an article about the eclipse that was posted a few weeks ago, and a full list of astrocameras that will be broadcasting the eclipse onto the Internet.

I hope you all get clear skies! Let me know how it goes for you.

Fraser Cain
Publisher
Universe Today

October 27, 2004 by Fraser Cain

Cosmic Corkscrew

Making an extra effort to image a faint, gigantic corkscrew traced by fast protons and electrons shot out from a mysterious microquasar paid off for a pair of astrophysicists who gained new insights into the beast’s inner workings and also resolved a longstanding dispute over the object’s distance.

The astrophysicists used the National Science Foundation’s Very Large Array (VLA) radio telescope to capture the faintest details yet seen in the plasma jets emerging from the microquasar SS 433, an object once dubbed the “enigma of the century.” As a result, they have changed scientists’ understanding of the jets and settled the controversy over its distance “beyond all reasonable doubt,” they said.

SS 433 is a neutron star or black hole orbited by a “normal” companion star. The powerful gravity of the neutron star or black hole draws material from the stellar wind of its companion into an accretion disk of material tightly circling the dense central object prior to being pulled onto it. This disk propels jets of fast protons and electrons outward from its poles at about a quarter of the speed of light. The disk in SS 433 wobbles like a child’s top, causing its jets to trace a corkscrew in the sky every 162 days.

The new VLA study indicates that the speed of the ejected particles varies over time, contrary to the traditional model for SS 433.

“We found that the actual speed varies between 24 percent to 28 percent of light speed, as opposed to staying constant,” said Katherine Blundell, of the University of Oxford in the United Kingdom. “Amazingly, the jets going in both directions change their speeds simultaneously, producing identical speeds in both directions at any given time,” Blundell added. Blundell worked with Michael Bowler, also of Oxford. The scientists’ findings have been accepted by the Astrophysical Journal Letters.

The new VLA image shows two full turns of the jets’ corkscrew on both sides of the core. Analyzing the image showed that if material came from the core at a constant speed, the jet paths would not accurately match the details of the image.

“By simulating ejections at varying speeds, we were able to produce an exact match to the observed structure,” Blundell explained. The scientists first did their match to one of the jets. “We then were stunned to see that the varying speeds that matched the structure of one jet also exactly reproduced the other jet’s path,” Blundell said. Matching the speeds in the two jets reproduced the observed structure even allowing for the fact that, because one jet is moving more nearly away from us than the other, it takes light longer to reach us from it, she added.

The astrophysicists speculate that the changes in ejection speed may be caused by changes in the rate at which material is transferred from the companion star onto the accretion disk.

The detailed new VLA image also allowed the astrophysicists to determine that SS 433 is nearly 18,000 light-years distant from Earth. Earlier estimates had the object, in the constellation Aquila, as near as 10,000 light-years. An accurate distance, the scientists said, now allows them to better determine the age of the shell of debris blown out by the supernova explosion that created the dense, compact object in the microquasar. Knowing the distance accurately also allows them to measure the actual brightness of the microquasar’s components, and this, they said, improves their understanding of the physical processes at work in the system.

The breakthrough image was made using 10 hours of observing time with the VLA in a configuration that maximizes the VLA’s ability to see fine detail. It represents the longest “time exposure” of SS 433 at radio wavelengths, and thus shows the faintest details. It also represents the best such image that can be done with current technology. Because the jets in SS 433 are moving, their image would be “smeared” in a longer observation. In order to see even fainter details in the jets, the astrophysicists must await the greater sensitivity of the Expanded VLA, set to become available in a few years.

SS 433 was the first example of what now are termed microquasars, binary systems with either a neutron star or black hole orbited by another star, and emitting jets of material at high speeds. The strange stellar system received a wealth of media coverage in the late 1970s and early 1980s. A 1981 Sky & Telescope article was entitled, “SS 433 — Enigma of the Century.”

Because microquasars in our own Milky Way Galaxy are thought to produce their high-speed jets of material through processes similar to those that produce jets from the cores of galaxies, the nearby microquasars serve as a convenient “laboratory” for studying the physics of jets. The microquasars are closer and show changes more quickly than their larger cousins.

Katherine Blundell is a University Research Fellow funded by the UK’s Royal Society.

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

October 27, 2004March 24, 2012 by Fraser Cain

NASA’s New Supercomputer is World’s Fastest

NASA unveils its newest supercomputer today during a ribbon-cutting ceremony at the agency’s Ames Research Center, Moffett Field, Calif. The “Columbia” is one of the world’s most powerful supercomputing systems. Columbia was named to honor the crew of the Space Shuttle Columbia lost Feb. 1, 2003.

“This amazing new supercomputer system dramatically increases NASA’s capabilities and revolutionizes our capacity for conducting scientific research and engineering design,” said NASA Ames Research Center Director G. Scott Hubbard. “It will be one of the fastest, largest and most productive supercomputers in the world, providing an estimated 10-fold increase in NASA’s supercomputing capacity. It is already having a major impact on NASA’s science, aeronautics and exploration programs, in addition to playing a critical role in preparing the Space Shuttle for return to safe flight next year,” Hubbard said.

Comprised of an integrated cluster of 20 interconnected SGI? Altix? 512-processor systems, for a total of 10,240 Intel? Itanium? 2 processors, Columbia was built and installed at the NASA Advanced Supercomputing facility at Ames in less than 120 days.

“The Columbia system is a tremendous development for NASA and the nation. Simulation of the evolution of the Earth and planetary ecosystems with high fidelity has been beyond the reach of Earth scientists for decades,” NASA’s Deputy Associate Administrator, Science Mission Directorate Ghassem Asrar said. “With Columbia, scientists are already seeing dramatic improvements in the fidelity of simulations in such areas as hurricane track prediction, global ocean circulation, prediction of large scale structures in the universe, and the physics of supernova detonations,” he said.

Columbia provides an integrated computing, visualization and data storage environment to help NASA meet its mission goals and the Vision for Space Exploration. The new system builds upon the highly successful collaboration between NASA, Silicon Graphics, Inc. (SGI) and Intel Corporation that developed the world’s first 512-processor Linux server. The server, the SGI? Altix? located at Ames was named “Kalpana,” after Columbia astronaut and Ames’ alumna Kalpana Chawla.

“With SGI and Intel, we set out to revitalize NASA’s computing capabilities, and the Columbia system has done so in a spectacular way,” said Walt Brooks, chief of NASA’s Advanced Supercomputing Division. “Not only were scientists doing real Earth and space analysis during the system build, but within days of the full installation, we achieved a Linpack benchmark rating of 42.7 teraflops on 16 nodes with an 88 percent efficiency rating, exceeding the current best reported number by a significant margin,” he said.

“With the completion of the Columbia system, NASA, SGI and Intel have created a powerful national resource, one that will serve scientists who strive to unlock the mysteries of this planet and the universe in which it dwells,” said SGI CEO Bob Bishop. “NASA should be commended for the remarkable boldness that made the new Columbia computer happen. Our long-standing partnership with the agency has triggered a new age in scientific discovery, and based on NASA’s initial success, it seems likely that we’ll be discussing new scientific breakthroughs in the very near future,” he said.
“The launching of the Columbia system shows what’s possible when government and technology leaders work together toward a goal of truly national importance,” said Paul Otellini, president and COO of Intel Corporation. “While this Itanium 2 processor-based system will be one of the highest performing computers ever created in the world, the real value is how this system will accelerate scientific design and research faster than before for years to come.”
The almost instant productivity of the Columbia supercomputer architecture and technology has made the system available to a broad spectrum of NASA-sponsored scientists. Feedback from scientists is extremely positive. Columbia already is enabling scientists to conduct research and analyze complex data much faster in a variety of scientific disciplines. The research and analysis ranges from providing more accurate hurricane predictions, to climate change, galaxy formation, black holes and supernovas.

Thanks to the powerful Columbia supercomputer, NASA scientists have developed an improved global circulation model. Initial results from this new model accurately predict when a hurricane is expected to hit land five days in advance, three days sooner than current methods, thereby helping reduce the potential impact on life and property.

Original Source: NASA News Release

October 27, 2004March 19, 2013 by Fraser Cain

Cassini Snaps Titan Close Up

The Cassini spacecraft beamed back information and pictures tonight after successfully skimming the hazy atmosphere of Saturn?s moon Titan. NASA’s Deep Space Network tracking station in Madrid, Spain, acquired a signal at about 6:25 p.m. Pacific Daylight Time (9:25 p.m. Eastern Daylight Time). As anticipated, the spacecraft came within 1,200 kilometers (750 miles) of Titan’s surface.

At the time, Cassini was about 1.3 billion kilometers (826 million miles) from Earth. Numerous images, perhaps as many as 500, were taken by the visible light camera and were being transmitted back to Earth. It takes 1 hour and 14 minutes for the images to travel from the spacecraft to Earth. The downlink of data will continue through the night into the early morning hours. Cassini project engineers will continue to keep a close watch on a rainstorm in Spain, which may interrupt the flow of data from the spacecraft.

The flyby was by far the closest any spacecraft has ever come to Titan, the largest moon of Saturn, perpetually drenched in a thick blanket of smog. Titan is a prime target of the Cassini-Huygens mission because it is the only moon in our solar system with an atmosphere. It is a cosmic time capsule that offers a look back in time to see what Earth might have been like before the appearance of life.

The Huygens probe, built and operated by the European Space Agency, is attached to Cassini; its release is planned on Christmas Eve. It will descend through Titan’s opaque atmosphere on Jan. 14, 2005, to collect data and touch down on the surface.

The latest information and images from Cassini are available at http://www.nasa.gov/cassini. Additional information on the mission and raw images are at http://saturn.jpl.nasa.gov.

Original Source: NASA/JPL/SSI News Release

October 26, 2004June 3, 2013 by Fraser Cain

Dark Matter Halo Puzzles Astronomers

Dark matter continues to confound astronomers, as NASA’s Chandra X-ray Observatory demonstrated with the detection of an extensive envelope of dark matter around an isolated elliptical galaxy. This discovery conflicts with optical data that suggest a dearth of dark matter around similar galaxies, and raises questions about how galaxies acquire and keep such dark matter halos.

The observed galaxy, known as NGC 4555, is unusual in that it is a fairly large, elliptical galaxy that is not part of a group or cluster of galaxies. In a paper to be published in the November 1, 2004 issue of the Monthly Notices of the Royal Astronomical Society, Ewan O’Sullivan of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA and Trevor Ponman of the University of Birmingham, United Kingdom, use the Chandra data to show that the galaxy is embedded in a cloud of 10-million-degree-Celsius gas.

This hot gas cloud has a diameter of about 400,000 light years, about twice that of the visible galaxy. An enormous envelope, or halo, of dark matter is needed to confine the hot cloud to the galaxy. The total mass of the dark matter halo is about ten times the combined mass of the stars in the galaxy, and 300 times the mass of the hot gas cloud.

A growing body of evidence indicates that dark matter – which interacts with itself and “normal” matter only through gravity – is the dominant form of matter in the universe. According to the popular “cold dark matter” theory, dark matter consists of mysterious particles left over from the dense early universe that were moving slowly when galaxies and galaxy clusters began to form.

“The observed properties of NGC 4555 confirm that elliptical galaxies can posses dark matter halos of their own, regardless of their environment,” said O’Sullivan. “This raises an important question: what determines whether elliptical galaxies have dark matter halos?”

Most large elliptical galaxies are found in groups and clusters of galaxies, and are likely the product of the merger of two spiral galaxies. In such an environment, the dark matter halos can be stripped away by gravitational tidal force and added to other galaxies or the group as a whole. Therefore, it is difficult to determine how much dark matter the original galaxies had, and how much they have lost to the group as a whole through interactions with their environment.

The importance of the issue of the intrinsic amount of dark matter associated with an elliptical galaxy has recently increased owing to a report by an international team of astronomers led by Aaron Romanowsky of the University of Nottingham, United Kingdom. This team found little, if any evidence of dark matter in three relatively nearby elliptical galaxies. Two of these were in loose galaxy groups, and one was isolated. Their result, based on optical data from the 4.2 meter William Herschel Telescope on the Spanish island of La Palma, is in clear conflict with the X-ray data on NGC 4555. The optical technique used to search for dark matter in the nearby elliptical galaxies could not be applied to NGC 4555 because it is more than 3 times as far away from Earth.

Either the galaxies observed by Romanowsky and colleagues have lost their dark matter halos through earlier interactions with other galaxies, or their dark matter halos are much more extended, or they formed without dark matter halos. The first option is possible for the galaxies in groups, but very unlikely for the isolated galaxy. The second and third options are still open, but would require a modification – perhaps a major modification – of the cold dark matter theory of galaxy formation.

“This is clearly a question which deserves further consideration,” said O’Sullivan. “It seems likely that much more theoretical and observational work on elliptical galaxies will be required before this issue can be resolved.”

Chandra observed NGC 4555 with its Advanced CCD Imaging Spectrometer (ACIS) in February 2003. NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu
and
http://chandra.nasa.gov

Original Source: Chandra News Release

October 26, 2004March 24, 2012 by Fraser Cain

Cassini Closes in on Titan

This image taken on Oct. 24, 2004, reveals Titan’s bright “continent-sized” terrain known as Xanadu. It was acquired with the narrow angle camera on Cassini’s imaging science subsystem through a spectral filter centered at 938 nanometers, a wavelength region at which Titan’s surface can be most easily detected. The surface is seen at a higher contrast than in previously released imaging science subsystem images due to a lower phase angle (Sun-Titan-Cassini angle), which minimizes scattering by the haze.

The image shows details about 10 times smaller than those seen from Earth. Surface materials with different brightness properties (or albedos) rather than topographic shading are highlighted. The image has been calibrated and slightly enhanced for contrast. It will be further processed to reduce atmospheric blurring and to optimize mapping of surface features. The origin and geography of Xanadu remain mysteries at this range. Bright features near the south pole (bottom) are clouds. On Oct. 26, Cassini will acquire images of features in the central-left portion of this image from a position about 100 times closer.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release