Posted on by Mark Mortimer

Book Review: Centauri Dreams

First a bit of a background. We’ve a long way to go. Alpha Centauri is 4.3 light years away (about 13 zeros after the one when considering kilometres). Voyager 1, the fastest man made object, is speeding at 3.6 AU’s per year (about 8 zeros after the one in kilometres per year). Were a person to be on it, some 100,000 years would pass before entering Alpha Centauri’s solar system. This won’t happen as Voyager 1 travels another path, but this is the problem in a nutshell, it’s too far for today’s chemically driven rockets. With most people expecting a return on investment well within ten years then there would be little support in waiting thousands of generations for payback. Given this impracticality Gilster presents options and methods that might reduce the travel time to within one generation.

The first chapter sets the background of who’s doing what, where they are keeping themselves busy and, sometimes, when their activities first appear upon the scene. Scores of researchers’ names arise, especially physicists, mathematicians and astronomers, but a sprinkling of other esoteric specialists such as Internet designers, clearly demonstrates the broad response to this challenge. NASA’s programs and facilities predominate. CERN appears as does the Brookhaven National Laboratory. Early visionaries from the 1800’s and even earlier make a brief appearance. Applicable science fiction stories from the early 1900’s get noted, while the predominance of technically valid work dates from about 1960 on. This shows that on the whole, considerable thought and work has gone into advancing concepts for high speed interstellar travel.

Five chapters follow and represent the real meat of this book. These look at different methods of getting a useful payload to our neighbouring stars and they focus on well known and lesser known means of propulsion. Antimatter, sails, ramjets and fusion runways get their dues. Field-drives, providing force from the interaction of matter and fields get an honourable mention. Each chapter clearly and simply describes the methods of the chosen propulsion and the state (or technical level) of the research. Interviews with today’s investigators provide a superb insider’s view of activities. If you’re looking to identify locations for grad studies, there is a bonus as key investigating sites get identified alongside. Exciting sections detail the latest in experiments and technical investigations. The Planetary Society’s solar sail lifts off soon, antimatter is getting expansive new containers, lasers push model crafts up against Earth’s gravitational pull and a mini-magentospheric plasma propulsion prototype undergoes testing. Each of these might answer the riddle about how we propel ourselves at near light speed but as pointed out, the breakthrough technology may yet be around the corner.

One chapter seems a little bit like a lost child. This deals with communication and guidance. Of course these issues will need to be addressed, but it seems a bit early to be worrying about setting up extra-planetary webs or designing their communication protocol for that real long distance feeling. The guidance/navigation portion seems equally out of place. As the propulsion method so drastically constrains the mission, this discussion is preemptive. Still, as the title states, this book plans for interstellar exploration, hence communication and guidance are relevant and their consideration is warranted.

And yes, the title says it all. Alpha Centauri is a dreamers destination but dreams are only the beginning. Imagination gets us out of the constraints of everyday thinking and planning will see that effort gets well applied. As depicted within the book, many people share this dream. Some are incredibly lucky and can make it their life’s work. Others contribute directly in their part time or indirectly whether through related research, writing fiction or, as Gilster is undertaking, performing outreach activities. The link from imagination, to serious consideration and eventual trials constantly arises as either a sign of humanity’s adaptability or perhaps a sign of genetic coding. Nevertheless, time and again, imaginations are shown to conceive of the knowledge that thrusts plans out of the realm of fiction and into the laboratory where researchers make it reality.

Stars twinkle all about us at night. Perhaps maliciously inviting or teasing like a temptress, either way they remain today too far to fathom visiting today. Science fiction had imaginaries who gave detailed if somewhat fanciful means of propulsion between the stars. Paul Gilster in Centauri Dreams: Imagining and Planning Interstellar Exploration shows that real science is advancing technologies that could make this trip practical. The plans of the scientists and other technical may soon bear fruit and future generations of humans would have a much better and more exciting life amongst the stars.

Read more reviews online or order your own copy from Amazon.com.

Review by Mark Mortimer

Posted on by Fraser Cain

Would We Mistake Signals from ET?

Researchers from the University of Michigan think that the current programs to search for extraterrestrial intelligence (SETI) might not be able to distinguish signals from the noise of nearby stars. They showed how an efficient message sent through radio waves is nearly indistinguishable from the ordinary thermal radiation coming from stars. If extraterrestrial civilizations have been transmitting for a long time, they’ll probably have optimized their communications to save power, and so we won’t recognize it when we hear it.

If ET ever phones home, chances are Earthlings wouldn’t recognize the call as anything other than random noise or a star.

New research shows that highly efficient electromagnetic transmissions from our neighbors in space would resemble the thermal radiation emitted by stars.

University of Michigan physicist Mark Newman, along with biologist Michael Lachmann and computer scientist Cristopher Moore, have extended the pioneering 1940s research of Claude Shannon to electromagnetic transmissions in a paper published last month in the American Journal of Physics called, “The Physical Limits of Communication, or Why any sufficiently advanced technology is indistinguishable from noise.” Lachmann is at the Max Planck Institute in Leipzig, Germany; Moore is at the University of New Mexico in Albuquerque.

Shannon showed that a message transmitted with optimal efficiency is indistinguishable from random noise to a receiver unfamiliar with the language in the message. For example, an e-mail message whose first few letters are AAAAA contains little information because the reader can easily guess what probably comes next?another A. The message is totally non-random. On the other hand, a message beginning with a sequence of letters like RPLUOFQX contains a lot of information because you cannot easily guess the next letter.

Paradoxically, however, the same message could just be a random jumble of letters containing no information at all; if you don’t know the code used for the message you can’t tell the difference between an information-rich message and a random jumble of letters.

Newman and his collaborators have shown that a similar result holds true for radio waves.

When electromagnetic waves are used as the transmission medium, the most information efficient format for a message is indistinguishable from ordinary thermal radiation?the same kind of radio waves that are emitted by hot bodies like stars. In other words, an efficiently coded radio message coming from outer space would look no different from a normal star in the sky.

So, suppose an alien in space decided to pick up signs of Earth life. It would have a pretty easy time of it, since our radio and television signals are zigzagging all over the place and are inefficiently coded and easily distinguishable from stars.

But say a human tries to tune into extraterrestrial life.

“People do this, and when they do, they are looking for non-random stuff,” Newman said. “But what if (the aliens) have gotten it down? With a few hundred years practice at doing this, you’d have discovered the most efficient way to encode your radio messages. So to us, their communication would look just like another star, a hot object.”

After all, Newman said, in the universe’s 12 billion-year history, it’s likely that extraterrestrials?if they exist?have communicated with each other longer than our paltry 80-year history of radio broadcasting. “In which case, they’ve probably gotten very good at this by now.”

Said Newman: “Our message is that, even for the people who do believe this, they’re probably wasting their time. If they did pick up a signal from little green men, it would probably look like a star to them and they would just pass over it and move on to the next thing.”

Original Source: UMich News Release

Posted on by Fraser Cain

Dusty Universe is a Mystery

Image credit: NASA/JPL/UA
Astronomers who think they know how the very early universe came to have so much interstellar dust need to think again, according to new results from the Spitzer Space Telescope.

In the last few years, observers have discovered huge quantities of interstellar dust near the most distant quasars in the very young universe, only 700 million years after the cosmos was born in the Big Bang.

“And that becomes a big question,” said Oliver Krause of the University of Arizona Steward Observatory in Tucson and the Max Planck Institute for Astronomy in Heidelberg. “How could all of this dust have formed so quickly?”

Astronomers know two processes that form the dust, Krause said. One, old sun-like stars near death generate dust. Two, infrared space missions have revealed the dust is produced in supernovae explosions.

“The first process takes several billion years,” Krause noted. “Supernovae explosions, by contrast, produce dust in much less time, only about 10 million years.”

So when astronomers reported detecting submillimeter emission from massive amounts of cold interstellar dust in the supernova remnant Cassiopeia A last year, some considered the mystery solved. Type II supernovae like ‘Cas A’ likely produced the interstellar dust in the very early universe, they concluded. (Type II supernovae come from massive stars that blow apart in huge explosions after their cores collapse.)

Krause and colleagues from UA’s Steward Observatory and the Max Planck institute in Heidelberg have now discovered that the detected submillimeter emission comes not from the Cas A remnant itself but from the molecular cloud complex known to exist along the line of sight between Earth and Cas A. They report the work in the Dec. 2 issue of Nature.

Cas A is the youngest known supernova remnant in our Milky Way. It is about 11,000 light years away, behind the Perseus spiral arm clouds that are roughly 9,800 light years away. Krause suspects that the Perseus clouds explain why late 17th century astronomers didn’t report observing the brilliant Cas A outburst around A.D. 1680. Cas A is so close to Earth that the supernova should have been the brightest stellar object in the sky, but dust in the Perseus clouds eclipsed the view.

The Arizona and German team mapped Cas A at 160-micron wavelengths using the ultra-heat-sensitive Multiband Imaging Photometer (MIPS) aboard the Spitzer Space Telescope. These long wavelengths are the most sensitive to cold interstellar dust emission. They then compared the results with maps of interstellar gas previously made with radio telescopes. They found that the dust in these interstellar clouds account for virtually all the emission at 160 microns from the direction of Cas A.

Minus the emission from this dust, there is no evidence for large amounts of cold dust in Cas A, the team concludes.

“Astronomers will have to go on searching for the source of the dust in the early universe,” UA Steward Observatory astronomer and Regents’ Professor George Rieke said. Rieke is principal investigator for the Spitzer Space Telescope’s MIPS instrument and a co-author of the Nature paper.

“Solving this riddle will show astronomers where and how the first stars formed, or perhaps indicate there is some non-stellar process that can produce large amounts of dust,” Rieke said. “Either way, (finding the source of the dust) will reveal what went on at the formative stage for stars and galaxies, an epoch that is nearly unobserved in any other way.”

Authors of the Nature article, “No cold dust within the supernova remnant Cassiopeia A,” are Oliver Krause, Stephan M. Birkmann, George H. Rieke, Dietrich Lemke, Ulrich Klaas, Dean C. Hines and Karl D. Gordon.

Birkmann, Lemke and Klaas are with the Max Planck Institute for Astronomy in Heidelberg. Krause, Rieke, and Gordon are with the University of Arizona Steward Observatory. Hines is with the Space Science Institute in Boulder, Colo.

Original Source: UA News Release

Posted on by Fraser Cain

Sun Could Have Traded With Another Star

A hit TV program like “Antiques Roadshow” lures viewers with its universal appeal. Who wouldn’t want to find secret riches in their attic or basement? But rare paintings and heirloom jewelry aren’t the only valuable items waiting to be discovered. Cosmic treasures also lay hidden in the vast realm of outer space. Among the most highly prized of those treasures are planets that formed around other stars.

Astronomers have just gained an important clue to guide their hunt for extrasolar worlds. And that clue points to the unlikeliest of places – our own backyard.

“It’s possible that some of the objects in our solar system actually formed around another star,” says astronomer Scott Kenyon (Smithsonian Astrophysical Observatory).

How did these adopted worlds join our solar family? They arrived through an interstellar trade that took place more than 4 billion years ago when a wayward star brushed past our solar system. According to calculations made by Kenyon and astronomer Benjamin Bromley (University of Utah) and published in the Dec. 2, 2004, Nature, the Sun’s gravity plucked asteroid-sized objects from the visiting star. At the same time, the star pulled material from the outer reaches of our solar system into its grasp.

“There may not have been an equal exchange, but there was certainly an exchange,” says Bromley.

A Close Brush
Kenyon and Bromley reached this surprising conclusion while working to explain the mystery object Sedna, a world almost as large as Pluto but located much farther from the Sun. Sedna’s discovery in 2003 puzzled astronomers because of its unusual orbit – a 10,000-year-long oval whose closest approach to the Sun, 70 astronomical units, is well beyond the orbit of Neptune. (One astronomical unit, abbreviated A.U., is the average distance between the Earth and the Sun, or about 93 million miles.)

Understanding Sedna is a challenge because its orbit is far away from the gravitational influence of other planets in our solar system. However, the gravity of a passing star can pull objects beyond the orbit of Neptune, in the Kuiper Belt, into orbits like Sedna’s. Kenyon and Bromley have performed detailed computer simulations to show how this stellar fly-by likely took place.

The fly-by must have met two key requirements. First, the star must have stayed far enough away that it did not disrupt Neptune’s nearly circular orbit. Second, the encounter must have happened late enough in our solar system’s history that Sedna-like objects had time to form within the Kuiper Belt.

Kenyon and Bromley suggest that the near-collision occurred when our Sun was at least 30 million years old, and probably no more than 200 million years old. A fly-by distance of 150-200 A.U. would be close enough to disrupt the outer Kuiper Belt without affecting the inner planets.

According to the simulations, the passing star’s gravity would sweep clear the outer solar system beyond about 50 A.U., even as our Sun’s gravity pulled some of the alien planetoids into its grasp. The model explains both the orbit of Sedna and the observed sharp outer edge of our Kuiper Belt, where few objects reside beyond 50 A.U.

“A close fly-by from another star solves two mysteries at once. It explains both the orbit of Sedna and the outer edge of the Kuiper Belt,” says Bromley.

A Crowded Birthplace
But where did such a star come from, and where did it go? Since the fly-by happened more than 4 billion years ago, any suspects have long since escaped the Sun’s neighborhood. There is no practical way to find the culprit today.

The visitor’s origin may seem equally mystifying because the Sun currently lives in a sparse region of the Milky Way. Our closest neighbor is a distant 4 light-years away, and stellar close encounters are correspondingly rare. However, a near-collision would be much more likely for a young Sun if it were born in a dense star cluster, as recent evidence suggests.

“We believe that 90 percent of all stars form in clusters with a few hundred to a few thousand members,” says astronomer Charles Lada (Harvard-Smithsonian Center for Astrophysics). “The denser the cluster, the more likely the chance for an encounter between member stars.”

“This work is an important piece of evidence that the Sun formed in near proximity to other stars,” he adds.

Searching for Adopted Worlds
Kenyon and Bromley’s simulations indicate that thousands or possibly millions of alien Kuiper Belt Objects were stripped from the passing star. However, none have yet been positively identified. Sedna is probably homegrown, not captured. Among the known Kuiper Belt Objects, an icy rock dubbed 2000 CR105 is the best candidate for capture given its unusually elliptical and highly inclined orbit. But only the detection of objects with orbits inclined more than 40 degrees from the plane of the solar system will clinch the case for the presence of extrasolar planets in our backyard.

Kenyon and Bromley’s next goal is to estimate the sky density of captured objects so that they can make a survey to find such adopted worlds.

“In principle, large telescopes like the MMT Telescope [a joint Smithsonian/University of Arizona observatory] can find them if they’re numerous enough,” says Kenyon.

The calculations reported here were made using about 3,000 cpu-days of computer time at the supercomputing center at the Jet Propulsion Laboratory, Pasadena, Calif.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Knots in Saturn’s Rings

An intriguing knotted ringlet within the Encke Gap is the main attraction in this Cassini image. The Encke Gap is a small division near the outer edge of Saturn’s rings that is about 300 kilometers (190 miles) wide. The tiny moon Pan (20 kilometers, or 12 miles across) orbits within the gap and maintains it. Many waves produced by orbiting moons are visible.

The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 29, 2004, at a distance of about 807,000 kilometers (501,000 miles) from Saturn. The image scale is 4.5 kilometers (2.8 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 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 News Release

Posted on by Fraser Cain

Interview with Michiel Min

Michiel Min is a research student at the Astronomical Institute, University of Amsterdam, who carried out much of the data analysis behind the current ESO release, see: Ingredients are There to Make Rocky Planets. Michiel was able to talk with Universe Today in between his studies.

Universe Today: Do your findings help to explain the origin of our own solar system in better detail?

Michiel Min: The timescale of planet formation is still under debate. Our findings provide evidence that the small dust grains are already growing after a billion years. Our observations do provide a unique view of the building blocks of planets. It is clear from our findings that the building blocks of Earth-like planets, close to the star, are crystals (crystalline silicates), while the building blocks of the planets further out, are amorphous silicates. Also we see that the growth of dust grains seems to go easier closer to the star.

Have your observations provided an answer as to how these planetary systems around giant stars may have formed?

The main reason that only giant planets in close orbits have been found has to do with the way of detecting these systems. Taking into account the gravitational pull of the planet on the star does this. Most likely, these planetary systems formed in a similar way as our own solar system. However, in these systems, most likely, the planet has moved inwards due to friction in the disk. If a planet forms very close to the star, it is more likely that it will be a rockier, earth-like planet since its atmosphere will greatly evaporate. Detecting smaller, earth-like planets directly is very hard. At the moment, planet-finders like Darwin are being build to search, in a very clever way, for the signal of Earth-like planets. Our findings give us a look in the birthplace of these planets.

So, how close would a giant planet need to be to its parent star for its atmosphere not to evaporate away?

This depends all on the mass of the planet itself and the temperature of the star. Most likely, giant planets only form at distances beyond ~5 AU [750 million kilometres] around a solar type star. But this is only a very rough number. If one considers for example Pluto, which is a rocky planet that formed quite far away, it is clear that there is not a simple answer to this.

Michiel, could you please say a little about yourself, and how you became interested in astronomy?

Yes, I am a PhD student at the University of Amsterdam. I will finish my PhD in April 2005. I have always been interested in science and how nature works. I studied physics in Amsterdam, at the Free University. After this, I got interested in astronomy because it is one of the few fields in physics where you meet all the extremes of nature. I think this provides a unique challenge for the mind. The study of planetary systems is one of the most down-to-earth subjects in astronomy. It is directly related to our own Earth. I think the question ‘what created this planet?’ is fascinating. Also, the question how planetary systems form, can provide us with an answer to how unique our own solar system is, and how easy one forms a planet like the Earth around other stars.

Looking toward the future, how long do you think it will be before astronomers have the technical ability to detect earth-like planets?

There are currently two project running to make instruments for detecting planets: DARWIN (ESA) and Terrestrial Planet Finder (NASA). Both missions are planned for launch in the year 2014. Both these missions should be able to detect Earth-like planets.

I think we are in a very exciting time in that respect. Our findings imply that all the materials to form Earth-like planets are available in the regions where liquid water can exist. Also, the process of dust growth has started its way to forming larger bodies. In my opinion, this implies that it is very likely that the planet finders of ESA and NASA will detect planets around solar type stars. Our understanding of Venus, the Earth and Mars, puts nice constraints on the conditions we can expect on these planets, and if these conditions support the possibility of life. Therefore I hope, and think, the question if our solar system is unique or not, will be answered in the coming 10-15 years.

This research project was a collaboration with the Astronomical Institute of the University of Amsterdam, The Netherlands (NOVA PR) and the Max-Planck-Institute f?r Astronomie (Heidelberg, Germany (MPG PR). The Amsterdam team consists of Roy van Boekel, Michiel Min, Rens Waters, Carsten Dominik and Alex de Koter.

By Science Correspondent Richard Pearson.

Posted on by Fraser Cain

Youngest Galaxy Found

Scientists using NASA’s Hubble Space Telescope have measured the age of what may be the youngest galaxy ever seen in the universe. By cosmological standards it is a mere toddler seemingly out of place among the grown-up galaxies around it. Called I Zwicky 18, it may be as young as 500 million years old (so recent an epoch that complex life had already begun to appear on Earth). Our Milky Way galaxy by contrast is over 20 times older, or about 12 billion years old, the typical age of galaxies across the universe. This “late-life” galaxy offers a rare glimpse into what the first diminutive galaxies in the early universe look like.

The galaxy is a member of a catalog of 30,000 nearby galaxies that Swiss astronomer Fred Zwicky assembled in the 1930’s by photographing the entire northern sky. Though astronomers have long suspected that this galaxy was a youngster, due to its primordial chemical makeup, Hubble’s exquisite sensitivity allowed astronomers to do a reliable census of the total stellar population in the galaxy. This allowed them to reliably identify the oldest stars inhabiting the galaxy, thereby setting an upper limit on the galaxy’s age.

The baby galaxy managed to remain in an embryonic state as a cold gas cloud of primeval hydrogen and helium for most of the duration of the universe’s evolution. As innumerable galaxies blossomed all over space this late-bloomer did not begin active star formation until some 13 billion years after the Big Bang, and went through a sudden first starburst only some 500 million years ago.

Located only 45 million light-years away ? much closer than other young galaxies in the nearly 14 billion light-year span of the universe ? I Zwicky 18 might represent the only opportunity for astronomers to study in detail the building blocks from which galaxies are formed. It remains a puzzle why the gas in the dwarf galaxy, in contrast to that in other galaxies, took so long ? nearly the age of the universe ? to collapse under the influence of gravity to form its first stars.

“I Zwicky 18 is a bona fide young galaxy,” said Trinh Thuan, professor of astronomy at the University of Virginia, who co-authored the study with Yuri Izotov from the Kiev Observatory. “This is extraordinary because one would expect young galaxies to be forming only around the first billion years or so after the Big Bang, not some 13 billion years later. And young galaxies were expected to be very distant, at the edge of the observable universe, but not in the local universe,” Izotov said.

The finding, reported in the December 1 issue of the Astrophysical Journal, provides a new insight into how galaxies first formed. The galaxy I Zwicky 18 offers a glimpse of what the early Milky Way may have looked like 13 billion years ago. Another set of Hubble observations by a different team give a slightly older age of 1 billion years to the galaxy, still keeping it a comparative newborn. Goran Ostlin of Stockholm Observatory, and Mustapha Mouhcine of the University of Nottingham, used Hubble’s Near Infrared Camera and Multi-Object Spectrometer to find a population of cool red stars, which are slightly older than the stars seen by the Advanced Camera for Surveys Camera. The results are to be published in Astronomy & Astrophysics.

To prove that I Zwicky 18 is a new galaxy, Thuan and Izotov needed to show that it was devoid of stars from the first several billion years after the Big Bang, the period when a large fraction of stars in the universe were formed. Though astronomers had suspected that the galaxy was exceptionally young, they had to wait for Hubble to provide the needed sensitivity to detect whether or not older stars, faint red giants, existed within the dwarf galaxy. Hubble’s Advanced Camera for Surveys needed a very long exposure, requiring 25 telescope orbits to look for the faintest stars in the galaxy. The presence of old stars in the galaxy would have indicated that the galaxy itself was old, like all other known galaxies in the universe.

Large galaxies such as the Milky Way are thought to grow hierarchically, with smaller galaxies merging into bigger galaxies, like tributaries merging into large rivers. I Zwicky 18 is prototypical of this early population of small dwarf galaxies. “These building block dwarf galaxies are too faint and too small to be studied without the most sensitive instruments even in the local universe, let alone in the far reaches of the cosmos,” Thuan said.

Further evidence for the youth of I Zwicky 18 is the fact that its interstellar gas is “nearly pristine,” Thuan said, and composed mostly of hydrogen and helium, the primary two light elements created in the Big Bang, during the first three minutes of the universe’s existence. The dwarf galaxy includes only a sprinkling of the other heavier elements such as carbon, nitrogen, or oxygen that are created later as stars develop. The near absence of such heavy elements suggests that much of the primordial gas in the dwarf galaxy has not managed to form stars that subsequently manufacture heavy elements.

Original Source: Hubble News Release

Posted on by Fraser Cain

Supernova in a Distant Galaxy NGC 6118

Images of beautiful galaxies, and in particular of spiral brethren of our own Milky Way, leaves no-one unmoved. It is difficult indeed to resist the charm of these impressive grand structures. Astronomers at Paranal Observatory used the versatile VIMOS instrument on the Very Large Telescope to photograph two magnificent examples of such “island universes”, both of which are seen in a southern constellation with an animal name. But more significantly, both galaxies harboured a particular type of supernova, the explosion of a massive star during a late and fatal evolutionary stage.

This image is of the impressive spiral galaxy NGC 6118 [1], located near the celestial equator, in the constellation Serpens (The Snake). It is a comparatively faint object of 13th magnitude with a rather low surface brightness, making it pretty hard to see in small telescopes. This shyness has prompted amateur astronomers to nickname NGC 6118 the “Blinking Galaxy” as it would appear to flick into existence when viewed through their telescopes in a certain orientation, and then suddenly disappear again as the eye position shifted.

There is of course no such problem for the VLT’s enormous light-collecting power and ability to produce sharp images, and this magnificent galaxy is here seen in unequalled detail. The colour photo is based on a series of exposures behind different optical filters, obtained with the VIMOS multi-mode instrument on the 8.2-m VLT Melipal telescope during several nights around August 21, 2004.

About 80 million light-years away, NGC 6118 is a grand-design spiral seen at an angle, with a very small central bar and several rather tightly wound spiral arms (it is classified as of type “SA(s)cd” [2]) in which large numbers of bright bluish knots are visible. Most of them are active star-forming regions and in some, very luminous and young stars can be perceived.

Of particular interest is the comparatively bright stellar-like object situated directly North of the galaxy’s centre, near the periphery (see PR Photo 33b/04): it is Supernova 2004dk that was first reported on August 1, 2004. Observations a few days later showed this to be a supernova of Type Ib or Ic [3], caught a few days before maximum light. This particular kind of supernova is believed to result from the demise of a massive star that has somehow lost its entire hydrogen envelope, probably as a result of mass transfer in a binary system, before exploding.

Also visible on the image is the trail left by a satellite, which passed by during one of the exposures taken in the B filter, hence its blue colour. This is an illustration that even in such a remote place as the Paranal Observatory in the Atacama desert, astronomers are not completely sheltered from light pollution.

The second galaxy imaged by the VLT is another spiral, the beautiful multi-armed NGC 7424 that is seen almost directly face-on. Located at a distance of roughly 40 million light-years in the constellation Grus (the Crane), this galaxy was discovered by Sir John Herschel while observing at the Cape of Good Hope.

This other example of a “grand design” galaxy is classified as “SAB(rs)cd” [2], meaning that it is intermediate between normal spirals (SA) and strongly barred galaxies (SB) and that it has rather open arms with a small central region. It also shows many ionised regions as well as clusters of young and massive stars. Ten young massive star clusters can be identified whose size span the range from 1 to 200 light-years. The galaxy itself is roughly 100,000 light-years across, that is, quite similar in size to our own Milky Way galaxy.

Because of its low surface brightness, this galaxy also demands dark skies and a clear night to be observed in this impressive detail. When viewed in a small telescope, it appears as a large elliptical haze with no trace of the many beautiful filamentary arms with a multitude of branches revealed in this striking VLT image. Note also the very bright and prominent bar in the middle.

On the evening of 10 December 2001, Australian amateur astronomer Reverend Robert Evans, observing from his backyard in the Blue Mountains west of Sydney, discovered with his 30cm telescope his 39th supernova, Supernova 2001ig in the outskirts of NGC 7424. Of magnitude 14.5 (that is, 3000 times fainter than the faintest star that can be seen with the unaided eye), this supernova brightened quickly by a factor 8 to magnitude 12.3. A few months later, it had faded to an insignificant object below 17th magnitude. By comparison, the entire galaxy is of magnitude 11: at the time of its maximum, the supernova was thus only three times fainter than the whole galaxy. It must have been a splendid firework indeed!

By digging into the vast Science Archive of the ESO Very Large Telescope, it was possible to find an image of NGC 7424 taken on June 16, 2002 by Massimo Turatto (Observatorio di Padova-INAF, Italy) with the FORS 2 instrument on Yepun (UT4). Although, the supernova was already much fainter than at its maximum 6 months earlier, it is still very well visible on this image (see PR Photo 33d/04).

Spectra taken with ESO’s 3.6-m telescope at La Silla over the months following the explosion showed the object to evolve to a Type Ib/c supernova. By October 2002, the transition to a Type Ib/c supernova was complete. It is now believed that this supernova arose from the explosion of a very massive star, a so-called Wolf-Rayet star, which together with a massive hot companion belonged to a very close binary system in which the two stars orbited each other once every 100 days or so. Future detailed observations may reveal the presence of the companion star that survived this explosion but which is now doomed to explode as another supernova in due time.

[1] NGC stands for “New General Catalogue”. Published in 1888 by J.L.E. Dreyer, this New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel contains 7840 objects of which 3200 are galaxies.

[2] Spiral galaxies take their name from the spectacular spiral arms that wind around in a very thin disc. Following the celebrated classification by American astronomer Edwin Hubble, spiral galaxies are classified into two families, so-called normal spirals (SA) and barred spirals (SB), and are further divided into types Sa, Sb and Sc depending on the opening of the spiral arms and the relative brightness of the central area. In barred spiral galaxies, the nucleus is crossed by a bar of stars at the ends of which the spiral arms begin. The (rs) in the classification testifies to the presence of an internal ring (r) surrounding the nucleus of the galaxy as well as to the fact that the spiral arms begin directly at the nucleus (s).

[3] Supernovae are classified into different types, depending on the appearance of their spectrum. Type II supernovae show the presence of hydrogen lines in their spectra while Type I lack this signature. Type I have been subdivided into Type Ia, Ib and Ic. Type I supernovae are all believed to arise in binary stellar systems.

Original Source: ESO News Release

Posted on by Fraser Cain

Reminder: Year in Space 2005 Desk Calendar

With the holidays rapidly approaching, I just wanted to give you another reminder about the 2005 “Year in Space” desk calendar as a potential gift for all the space enthusiasts in your life. This 144-page calendar has a weekly space image, daily Moon phases, space trivia, and sky events. It only costs $10.95 (discounted from $14.95), and includes free shipping in the US. Just mention Universe Today on the order form.

Click here to learn more about the calendar.

Happy holiday shopping.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

What’s Up This Week – Nov 29 – Dec 5, 2004

Image credit: NOAO/AURA/NSF
Monday, November 29 – With a short time until the Moon rises tonight, why not journey with me once again to Cassiopeia? We will start our studies with the western-most of the bright stars – Beta. Also known as “Caph”, Beta Cassiopeiae is approximately 45 light years away and known to be a rapid variable. Viewers with larger telescopes are challenged to find the 14th magnitude optical companion to Caph at about 23″ in separation. Tonight, using our previous study star Alpha and Beta, we are going to learn to locate a Messier object with ease!

By drawing an imaginary line between Alpha and Beta, we extend that line the same distance and angle beyond Beta and find the M52. Found on September 7, 1774 by Charles Messier, this magnitude 7 galactic cluster is easily seen in both binoculars and small telescopes. Comprised of roughly 200 members, this open cluster is roughly about 3,000 light years in distance and spans approximately 10-15 light years. Containing several different magnitudes, larger telescopes will easily perceive blue components as well as orange and yellow. The M52 (NGC7654) is a young, very compressed cluster whose approximate age is about the same as the Plieades. For those with large telescopes wanting a challenge? Try spotting a faint patch of nebulosity just 36′ to the southwest. This is the NGC7635, more commonly known as the “Bubble Nebula”. Best of luck!

Tuesday, November 30 – Tonight the Moon will be at apogee, or its greatest greatest distance from Earth. For those of you staying up late it will form a nearly straight line with Castor and Pollux with Saturn below and to the right. For those preferring to take your astronomy at an earlier hour? We’ll be delighted that the Moon will be out of the way for several hours as we adventure further into Cassiopeia! Returning the Cassiopeia’s central-most star – Gamma, tonight we will move towards the southeast and identify Delta. Also known as Ruchbah, this long-term and very slight variable star is about 45 light years away, but we are going to use it as our marker as we head just one degree northeast and discover the M103. As the last object in the original Messier catalog, the M103 (NGC581) was actually credited to Mechain in 1781. Easily spotted in binoculars and small scopes this rich open cluster is around magnitude 7, making it a prime study object. At about 8000 light years away and spanning approximately 15 light years, the M103 offers up superb views in a variety of magnitudes and colors, with a notable red in the south and a pleasing yellow and blue double to the northwest.

Telescopes and larger binoculars viewers are encouraged to move about a degree and half east of M103 to view a small and challenging chain of open clusters, the NGC654, NGC663 and NGC659! Surprisingly larger than the M103, NGC663 is a lovely fan-shaped concentration of stars with about 15 or so members that resolve easily to smaller aperture. For the telescope, head north for NGC654, (difficult, but not impossible to a 114mm scope) who has a bright star on its’ southern border. South of NGC663 is the NGC659 which is definitely a challenge for small scopes, but its presence will be revealed just northeast of two conspicuous stars in the field of view.

Wednesday, December 1 – What better way to start a new month than to get up early to see four planets and the Moon?! Just before dawn, the waning gibbous Moon will appear in the sky just above Saturn with the Gemini “Twins”, Castor and Pollux, to the west. Below and to the east of bright Luna is the mighty Jupiter, and you will find Venus and Mars slow dancing together near the horizon. What a fine show!

While Cassiopeia is still fresh in our minds, let’s return again tonight for some additional studies. Starting with Delta, let’s hop to the northeast corner of our “flattened W” and identify 520 light year distant Epsilon. For larger telescopes only, it will be a challenge to find 12″ diameter, magnitude 13.5 planetary nebula I.1747 in the same field with magnitude 3.3 Epsilon!

Using both Delta and Epsilon as our “guide stars” let’s draw an imaginary line between the pair extending from southwest to northeast and continue the same distance until you stop at visible Iota. Now go to the eyepiece! As a quadruple system, Iota will require a telescope and a night of steady seeing to split its three visible components. Approximately 160 light years away, this challenging system will show little or no color to smaller telescopes other than white, but to large aperture, the primary may appear slightly yellow and the companion stars a faint blue. At high magnification, the 8.2 magnitude “C” star will easily break away from the 4.5 primary 7.2″ to the east/southeast, but look closely at that primary.. hugging in very close (2.3″) to the west/southwest and looking like a “bump” on its side is the B star!

Dropping back to the lowest of powers, place Iota to the southwest edge of the eyepiece, it’s time to study two incredibly interesting stars that should appear in the same field of view to northeast. When both of these stars are at their maximum, they are easily the brightest of stars in the field. Their names are SU (southernmost) and RZ (northernmost) Cassiopeiae and both are unique! SU is a pulsing Cepheid variable located about 1000 light years away and will show a distinctive red coloration. RZ is a rapidly eclipsing binary that can change from magnitude 6.4 to magnitude 7.8 in less than two hours. Wow!

Thursday, December 2 – Once again utilizing early darkness, let’s go back to Cassiopeia. Remembering Alpha’s position as the westernmost star, go there with your finder scope or binoculars and locate bright Sigma and Rho (who both have a dimmer companion) and will appear to the southwest. It is between these two stars that you will find the NGC7789.

Absolutely one of the finest of rich galactic opens bordering on a loose globular, the NGC7789 has a population of about 1000 stars and spans a mind-boggling 40 light years. At well over a billion years old, the stars in this 5000 light year distant galactic cluster have already evolved into red-giants or super-giants. Discovered by Caroline Herschel in the 18th century, this huge cloud of stars has an average magnitude of 10, making it a great large binocular object, superb small telescope target, and a total fantasy of resolution for larger instruments.

Friday, December 3 – Tonight we will haunt Cassiopeia one last time – for the seasoned observer. Our first challenge of the evening will be to return to Gamma where we will locate two patches of nebulosity in the same field of view. The IC59 and IC63 are challenging because of the bright influence of the star, but by moving the star to the edge of the field of view you may be able to locate these two splendid small nebulae. If you do not have success with this pair, why not move on to Alpha? About one and a half degrees due east you will find a small collection of finder scope stars that mark the area of NGC281. This distinctive cloud of stars and ghostly nebula make this NGC object a fine challenge!

The last we will study will be two small elliptical galaxies that are achievable in mid-sized scopes. Locate Omicron Cassiopeiae about 7 degrees north of the M31 and discover a same field of view galactic pair that is associated with the Andromeda group, NGC185 and NGC147.

The constellation of Cassiopeia contains many, many more fine star clusters, nebulae and even more galaxies. For the casual observer, simply tracing over the rich star fields with binoculars is a true pleasure, for there are many bright asterisms best enjoyed at low power. Scopists will return to “rock with the Queen” year after year for its many challenging treasures. Enjoy it tonight!

Saturday, December 4 – It’s a comet hunter’s night… Are you ready? Then let’s be glad we have several hours until the Moon rises tonight so we have an opportunity to locate and view these fine comets!

If you were able to spot NGC654 and NGC659, earlier in the week, then you’ve got what it takes to find C/2004 Q1 (Tucker)! Holding an estimated magnitude 10.5, it is possible to see this comet with large binoculars and small telescopes. You will find Comet Tucker cruising through Andromeda just a bit southwest of M31.

Before Southern Hemisphere viewers begin to feel left out, why don’t we try chasing a comet tonight viewable to both of us? Comet 78P/Gehrels has an estimated magnitude of 10.7, putting it within range of most large binoculars and small telescopes. You will find it at the corner southern corner of the Aries/Taurus border, but it will be moving through Aries on this date and nearer to the border of Cetus and not too far from Lambda.

Next up is a comet suitable for mid-size to large aperture telescopes. Comet 29P/Schwassmann-Wachman will be at an estimated magnitude 12 but is beginning to fade. At this time you may be able to see about 55″ of coma! The hunting directions for 29/P show that it’s located on the Pegasus/Pices border and roughly halfway between 80 Pegasus and 26 Pices.

Northern viewers? Break out the big muscle for C/2001 Q4 (NEAT). At an estimated magnitude 12, it can be found in Draco buzzing along just south of Psi and a bit north of Omega. While you’re there, head on south to Iota and see if you can locate C/2003 T4 (LINEAR). At a rough magnitude of 12.5, T4 will sport a slight coma of 1.7″ and is moving west just slightly south of Iota.

How about one more? Then let’s go for 32P/Comas Sola. With an estimated magnitude of 12 with a slight coma of 1.1′, 39P has now moved into Aries and can be found just slightly northwest of Mu Cetii. Talk about some great challenges… I’ll race you there!

Sunday, December 5 – Although no one likes to get up early in the morning, you might find the trip quite worth it to see Mars and Venus together in the pre-dawn skies. The fat and gibbous Venus will make a splendid contrast with tiny, dusty red Mars as they stand together in the skies at just slightly more than one degree apart.

(We’re a little “uncertain”, but we do believe Werner Heisenberg was born on this day in 1901.)

Until next week? Keep looking up and enjoying the wonders of the Cosmos! Wishing you clear skies and light speed… ~Tammy Plotner