Magic Bubble – NGC 7635 by JP Metsavainio

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Away in the constellation of Cassiopeia some 7,100 light-years from Earth, a star 40 times more massive than our Sun is blowing a giant bubble of its own material into space. Inside its magic blue sphere, the gigantic star burns at blue flame intensity – rendering a 6 light year wide envelope of hot gas around it that’s expanding outward at a speed of 4 million miles per hour. Are you ready to open wide and step inside? Then welcome to a little dimensional magic….

As always, whenever we present a dimensional visualization it is done in two fashions. The first is called “Parallel Vision” and it is much like a magic eye puzzle. When you open the full size image and your eyes are the correct distance from the screen, the images will seem to merge and create a 3D effect. However, for some folks, this doesn’t work well – so Jukka has also created the “Cross Version”, where you simply cross your eyes and the images will merge, creating a central image which appears 3D. For some folks, this won’t work either… But I hope it does for you!

NGC 7635 Cross Vision by JP Metsavainio
NGC 7635 Cross Vision by JP Metsavainio

As the central star in NGC 7635 sheds its material, we can see it isn’t even and its appearance varies with the thickness of the surrounding gases. What appears to be cloud-like structures are very thick and illuminated by the star’s intense ultraviolet light. Believe it or not, it is here where the stellar “winds” blow the fastest and it won’t be long until these areas quickly erode. However, there is one feature that stands out more than any other – the “bubble-within-a-bubble”. What is it? It may be two distinct winds… Two distinct streamers of material colliding together.

“The bubble in NGC 7635 is the result of a fast stellar wind expanding into the interior of the larger H II region. However, the central star BD +60 2522 is appreciably offset (by about 1′) from the center of the bubble in the direction of the wall of the dense molecular cloud that defines this blister H II region.” says B.D. Moore (et al), “This offset is the result of evolution of the wind bubble into the density and pressure gradient established by the photoevaporative flow away from the cavity wall. The physical conditions around the bubble vary according to the medium into which the bubble is expanding. Away from the cavity wall the bubble is expanding into the low density interior of the H II region. Toward the wall, in the region of our images, the wind termination shock is very near the ionization front. The resulting physical structure, in which the photoevaporative flow away from the cloud wall is confined by the ram pressure of the wind.”

But, are we not seeing the proverbial forest because we’re too busy looking at the trees? “BD +60 is the ionizing star of NGC 7635, the so-called “Bubble Nebula”. NGC 7635 lies at the edge of a low-density clumpy molecular cloud and the nebula can be interpreted as a wind-blown bubble created by the interaction of the stellar wind of BD +60 with the ambient interstellar medium. While many investigations have focused on the nebula, little attention has been paid to the star itself.” says G. Rauw (et al), “Considerable progress in our understanding of the stellar winds of early-type stars has been achieved through extensive monitoring of their spectroscopic variability and the discovery that some of the cyclical variations could be related to a rotational modulation of the stellar wind. Since rotation is believed to shape the winds of Oef stars, these objects appear a priori as good candidates to search for a rotational wind modulation.”

Throughout their long term observing campaign, the group found strong profile variability on time scales of 2–3 days, variability on time scales of a few hours that might be related to non-radial pulsations, and even tentatively propose that the beating of several non-radial pulsation modes triggers transient large-scale density perturbations in a confined stellar wind that produce the 2–3 day time scale variability. “While this scenario could easily account for the lack of a single stable period (through the effect of the propagation velocity of the perturbation and the interplay of various clocks: pulsations, rotation…), it seems more difficult to explain the changing pattern of the TVS. For instance, if a density wave moves around the star, why would it not affect the absorption and the emission components in a similar manner?” says Rauw, “One possibility could be that the density perturbation affects the absorption column only as long as it remains close to the stellar surface whilst the impact on the emission lines would be larger when the perturbation has moved outwards, but this is admittedly still rather speculative.”

Just how common is it for a huge star to form a bubble around itself? “Massive stars evolve across the HR diagram, losing mass along the way and forming a variety of ring nebulae. During the main sequence stage, the fast stellar wind sweeps up the ambient interstellar medium to form an interstellar bubble. After a massive star evolves into a red giant or a luminous blue variable, it loses mass copiously to form a circumstellar nebula. As it evolves further into a WR star, the fast WR wind sweeps up the previous mass loss and forms a circumstellar bubble. Observations of ring nebulae around massive stars not only are fascinating, but also are useful in providing templates to diagnose the progenitors of supernovae from their circumstellar nebulae.” says You-Hua Chu of the University of Illinois Astronomy Department, “The fast stellar wind of a main sequence O star sweeps up the ambient interstellar medium (ISM) to form an interstellar bubble, which consists of a dense shell of interstellar material. Intuitively, we would expect around most O stars an interstellar bubble similar to the Bubble Nebula (NGC 7635) to be visible; however, hardly any O stars in HII regions have ring nebulae, suggesting that these interstellar bubbles are rare.”

Like a child chewing gum, the bubble will continue to expand. And what comes after the bubble? Why, the “bang” of course. And when it comes to a star going bang, than can only mean a supernova. “By pursuing the calculation through the various stages of massive star evolution, using a realistic mass loss history as input, we simulate the creation and evolution of a wind-blown bubble around the star up to the time of the supernova explosion.” says A. J. van Marle (et al), “The outflowing matter encounters an inner shock, where its velocity is reduced to nearly zero. The kinetic energy of the wind becomes thermal energy. This interaction creates a “hot bubble” of nearly stationary, hot gas. The thermal pressure of the hot bubble drives a shell into the surrounding interstellar medium. Here it is assumed, that the pressure driven shell will be restrained only by the ram pressure created by its own velocity and the density of the surrounding medium. This assumption is correct if we consider the surrounding medium to be cold. However, if we take photo-ionization into account the situation becomes rather more complicated. First of all, the photoionized gas will have a much higher pressure than the cold ISM. Therefore, the HII region will expand, driving a shell into the ISM. Second, the hot-bubble created by the stellar wind will now expand into a hot HII region, which means that the thermal pressure restraining the shell, will no longer be negligible compared to the ram pressure. A wind-blown bubble expanding into a compact HII region can be observed in NGC 7635.”

So how do we know when the final moments have come? “As the star ages, it becomes a red supergiant with a dense and slow wind. The number of ionizing photons drops. Therefore, the HII region disappears. Owing to the low density, recombination will take a long time, but radiative cooling will cause a decrease in thermal pressure. The hot wind-bubble, which keeps its high pressure, expands into the surrounding gas, creating a new shell. A third shell appears close to the star, as the drop in ram pressure from the RSG wind causes the wind bubble to expand inward, sweeping up the wind material.” say van Marle, “The presence of an expanding HII region changes the density structure of the nebula during the main sequence. Our main goal at this time is to simulate the circumstellar environment of stars between 25 M and 40 M at the time of the supernova explosion.”

Magic bubbles? Just stay out of the way when they pop!

Many thanks to JP Metsavainio of Northern Galactic for his magical personal image and allowing us this incredible look at distant beauty!

Journey Inside M104

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Almost every amateur astronomer is familiar with the Sombrero Galaxy (also known as M104 or NGC 4594) – an unbarred spiral galaxy in the constellation Virgo. We’ve seen it in both small and large telescopes, picked up its ghostly signature in binoculars and dreamed over its structure in photographs. Now, for the first time ever, Jukka Metsavainio is giving us the opportunity to visualize what it might be like to approach this amazing galaxy from space and see it in dimension. Step inside and let’s learn.

Like all our our “stereo” image produced for UT by Jukka Metsavainio, two versions are presented here. The one above is parallel vision – where you relax your eyes and when you are a certain distance from the monitor screen the two images will merge into one to produce a 3D version. The second – which appears below – is crossed vision. This is for those who have better success crossing their eyes to form a third, central image where the dimensional effect occurs. Jukka’s visualizations of what M104 would look like if we were able to see it in dimension comes from studying the object, photographing it, knowing the field star distances and the different wavelengths of light. Are you ready to “cross” the boundary? Then let’s rock…

Sombrero Cross by Jukka Metsavainio
Sombrero Cross by Jukka Metsavainio

Discovered by Pierre Mechain in 1781 and added by Charles Messier’s own hand to his personal notes on May 11, 1781, Messier Object 104 wasn’t officially added to the official catalog of Messier objects until 1921 by Camille Flammarion. Although Messier had already ended his studies, he hadn’t quite ended his fascination with the sky and when Pierre discovered this amazing galaxy, he confirmed his observation by adding his description of a “very faint nebula” to the records. On May 9, 1784 – almost three years later to the date – Sir William Herschel independently recovered the galaxy and whose notes state: “Extended [elongated]. Very bright toward the middle. 5 or 6′ long.”

By 1828, John Herschel was seeing things much differently: “There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (s of) it. Surely no illusion.” Then Emil Dreyer in 1877: “Remarkable, very bright, very large, extremely extended toward position angle 92 deg, very suddenly much brighter toward the middle where there is a nucleus.” And the results of Curtis from the same year “A remarkable, slightly curved, clear-cut dark lane runs along the entire length to the south of the nucleus; probably the finest known example of this phenomenon. There are very slight traces of spiral whorls.” But it was 1912 and Vesto M. Slipher at Lowell Observatory who was about to make the most amazing discovery of all…

During 1910, Slipher (and later Carl Wirtz) was the first to use a spectroscope to observe the radial velocities of galaxies. What Vesto noticed was that M104 appeared to be cruising away from Earth at 700 miles per second. Such an tremendous speed was an important clue that the Sombrero was really another galaxy, and that the universe was expanding in all directions – but they didn’t know that at the time. At home (within our Milky Way galaxy) noted redshifts almost always correspond to the line of sight velocities associated with the objects being observed. These observations of redshifts and blueshifts have allowed science to measure velocities by a method first designed in 1868 by British astronomer William Huggins. Redshift is also an important tool to measure the velocity of gas of interstellar clouds, the rotation of galaxies, and the actions of accretion around neutron stars and black holes.

What we know now is there’s a supermassive black hole at the center of the Sombrero… one of the most massive black holes measured in any nearby galaxies. According the the findings by a research group led by John Kormendy and using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun was present at the core. No wonder the eye is drawn there! The nucleus is also a strong source of synchrotron emission – produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields. Although we can’t see radio waves, the low ionization nuclear emission region (LINER) at M104’s heart may be the energy source that weakly ionizes the gas in the Sombrero Galaxy.

And what of the dark dust ring? It’s cold atomic hydrogen gas. According to infrared spectroscopic studies, it’s the primary site for star formation and not the amazing nucleus. “The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGNs in previous research.” Says George Bendo, “The weak nuclear 160 um emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low-ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity.”

Take the time to check out this beautiful galaxy yourself. You’ll find it eleven degrees west of Spica….

Weekend SkyWatcher’s Forecast – November 7-9, 2008

Greetings, fellow StarGeezers! It’s Friiiii day… And another great weekend forecast. Does having all this Moon around get you down? It shouldn’t. Where else could you find another world that you could so intimately study detail with even the most modest of telescopes or binoculars? Instead of cursing Luna’s presence, get out your optics and enjoy! While we’re at it, we’ll take a look at some very interesting stars – both in the sky and from planet Earth. It’s time to head out into the dark… Cuz’ here’s what’s up!

Friday, November 7, 2008 – Today in 1996, the Mars Global Surveyor left on its journey. Just 30 years beforehand on this same day, Lunar Orbiter 2 was launched. Tonight let’s launch our way toward the Moon as we begin our observing evening with a look at a far northern crater – J. Herschel.

Residing on the mid-northern edge of Mare Frigoris, this huge, shallow old crater spans 156 kilometers and bear the scars of the years. Look for the deeper and younger crater Horrebow on the southwestern wall – for it has obliterated another, older wall crater.

Ready to aim for a bullseye? Then follow the “Archer” and head right for the bright, reddish star Aldebaran. Set your eyes, scopes or binoculars there and let’s look into the “eye” of the Bull.

Known to the Arabs as Al Dabaran, or “the Follower,” Alpha Tauri got its name because it appears to follow the Pleiades across the sky. In Latin it was called Stella Dominatrix, yet the Olde English knew it as Oculus Tauri, or very literally the “eye of Taurus.” No matter which source of ancient astronomical lore we explore, there are references to Aldebaran.

As the 13th brightest star in the sky, it almost appears from Earth to be a member of the V-shaped Hyades star cluster, but this association is merely coincidental, since it is about twice as close to us as the cluster is. In reality, Aldebaran is on the small end as far as K5 stars go, and like many other orange giants, it could possibly be a variable. Aldebaran is also known to have five close companions, but they are faint and very difficult to observe with backyard equipment. At a distance of approximately 68 light-years, Alpha is “only” about 40 times larger than our own Sun and approximately 125 times brighter. To try to grasp such a size, think of it as being about the same size as Earth’s orbit! Because of its position along the ecliptic, Aldebaran is one of the very few stars of first magnitude that can be occulted by the Moon.

Saturday, November 8, 2008 – Even if you only use binoculars tonight, you can’t miss the beautiful C-shape of Sinus Iridum as it comes into view on the lunar surface. As we have learned, the mountains ringing it are called the Juras, and the crater punctuating them is named Bianchini. Do you remember what the bright tips of the opening into the “Bay of Rainbows” are called? That’s right: Promontorium LaPlace to the northeast and Promontorium Heraclides to the southwest. Now take a good look at Heraclides… Just south of here is where Luna 17 landed, leaving the Lunokhod rover to explore!

Born on this day in 1656, the great Edmund Halley made his mark on history as he became best known for determining the orbital period of the comet which bears his name. English scientist Halley had multiple talents however, and in 1718 discovered that what were then referred to as “fixed stars,” actually displayed (proper) motion! If it were not for Halley, Sir Isaac Newton may never have published his now famous work on the laws of gravity and motion.

Now turn your eyes or binoculars just west of bright Aldebaran and have a look at the Hyades Star Cluster. As noted yesterday, Aldebaran appears to be part of this large, V-shaped group, but is not an actual member. The Hyades cluster is one of the nearest galactic clusters, and it is roughly 130 light-years away at its center. This moving group of stars is drifting slowly away toward Orion, and in another 50 million years will require a telescope to view!

Sunday, November 9, 2008 – Today is the birth date of Carl Sagan. Born in 1934, Sagan was an American planetologist, exobiologist, popularizer of science and astronomy, and novelist. During his lifetime, Sagan published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. His influential work and enthusiasm inspired us all. As Dr. Sagan once said, “Personally, I would be delighted if there were a life after death, especially if it permitted me to continue to learn about this world and others, if it gave me a chance to discover how history turns out.”

May his dreams live on..

If Carl were with us tonight, he would encourage amateurs at every level of astronomical ability! So let us honor his memory by beginning with an optical pairing of stars known as Zeta and Chi Ceti, a little more than a fistwidth northeast of bright Beta. Now have a look with binoculars or small scopes because you’ll find that each has its own optical companion!

Now drop south-southwest less than a fistwidth to have a look at something so unusual that you can’t help but be charmed – the UV Ceti System (RA 01 39 01 Dec -17 57 01).

What exactly is it? Also known as L 726-8, you are looking at two of the smallest and faintest stars known. This dwarf red binary system is the sixth nearest star to our solar system and resides right around nine light-years away. While you are going to need at least an intermediate-size scope to pick up these near 13th magnitude points of light, don’t stop observing right after you locate it. The fainter member of the two is what is known as a “Luyten’s Flare Star” (hence the “L” in its name). Although it doesn’t have a predictable timetable, this seemingly uninteresting star can jump two magnitudes in less than 60 seconds and drop back to “normal” within minutes – the cycle repeating possibly two or three times every 24 hours. A most incredible incident was recorded in 1952 when UV jumped from magnitude 12.3 to 6.8 in just 20 seconds!

No matter what you choose to look at tonight, as Dr. Sagan would say: “We are all star stuff.”

Have a great week and I’ll see you… Under the stars!

This week’s awesome photos are: Crater J. Herschel – Credit: Wes Higgins, Aldebaran – Credit: Palomar Observatory, courtesy of Caltech, Sinus Iridum – Credit: Wes Higgins, Edmund Halley (widely used public image), The Hyades Star Cluster – Credit: NASA, Carl Sagan (widely used public image), and Chi and the UV Ceti System – Credit: Palomar Observatory, courtesy of Caltech. Our many thanks to you!

Unique Telescope Facility Opens In Swiss Biosphere

In the easternmost part of Switzerland near the Italian border, lies a pristine area of land ranging from 1,400 to 3,173 meters above sea level. It encompasses 172,400 hectares of forests, alpine grasslands and bare rocks or screes that are strictly protected and not inhabited. Each year, around 50 researchers from Switzerland and abroad carry out scientific studies in the area. A research committee is responsible for the coordination of the various projects, such as hydrology, meteorology, biodiversity, ecology. Now, another specialty is arriving in this area in form of a private endeavor – astronomy.

AAV Lue-Stailas is a new center for amateur astrophotography in the eastern Alps of Switzerland. Built on a sunny terrace at 1935 m (6300 ft) and facing south into the beautiful valley of Muestair, the center’s prime geographical location benefits from excellent sky conditions with about 250 clear nights a year. Thanks to its rigorous protection policy, Val Muestair was able to keep much of its original rural and natural habitat. This will soon be honored by the regions participation in a new high-alpine UNESCO Biosphere Reserve in the European Alps, the Val Muestair/Swiss National Park Reserve. AAV Lue-Stailas will collaborate with this unique “Biosfera”-Project in order to bring its pristine skies to the public. The center will open in March of 2009, the International Year of Astronomy.

AAV Lue-Stailas is the brainchild of Václav and Jitka Ourednik who hold both a PhD in neuroscience and have been studying the regenerative capacity of the central nervous system for over 20 years. While pursuing competitive research and publishing in foremost scientific journals, they present their scientific results at international symposia and organize professional meetings and seminars. But what’s happening in Switzerland has been born of the unique love of both the micro and macro cosmos. Says Jitka, “The views through a microscope can be remarkably similar to vistas in the universe imaged through a telescope such as the Hubble Space Telescope (HST) or simulated with computers according to current cosmological theories.”

Microscope VS. TelescopeInner Space or Outer Space?

–caption: Filamentous clusters of galaxies as pictured by the HST (left) or in a computer simulation (right). Neuronal cell culture as seen in a fluorescent microscope.

In order to promote public awareness for the need to protect the natural habitat and dark skies, Václav and Jitka have decided to make their life-long hobby a profession and create a center for amateur astrophotography in Europe. Their search for the best possible location for hosting a unique telescope facility lasted several years. Finally, being both fond of the Swiss Alps, they chose a sunny terrace at an altitude of 2000 m in the county of Lue in eastern Switzerland for the creation of the Alpine Astrovillage Lue-Stailas. Says Vaclav, “Recent statistics show that the global interest in astronomy increases every year dramatically. Moreover, people are not only interested in astronomy and astrophotography but they also realize how important their contribution is in the preservation of our global natural habitat, which also includes the protection of dark night skies by a strict control of light pollution.”

At Alpine Astro Village, each living quarters/studio will have its own automated dome, telescope and imaging equipment, which can be, if needed, operated from the studios. Another treat of the center are its two robotic telescopes in Australia for remote imaging of the southern skies.. Yet, although the main purpose of the site is astrophotography, and there will also be telescopes set up for visual exploration for public activities like star parties and AAV club activities, there’s just a little more to this sphere than the astronomy angle:

“One of the unique aspects of AAV Lue-Stailas is that we strive to maintain and profit from the contrast of embedding our center of modern life style and high-tech equipment within the historical heritage of the region . This allows the visitors to fully enjoy and capture the beauty of the local night sky while having the opportunity to enjoy all the treasures of the valley and its vicinity during the day” say the Ouredniks, “The region provides limitless opportunities for daytime nature walks, biking tours, or demanding hiking expeditions. In winter, downhill skiing is less than one car-hour away (famous resorts such as Davos, Pontresina, St-Moritz…)and cross-country ski tracks are right at our center’s door step. We also strongly suggest visiting of the neighboring villages in the valley and beyond. You will find beautiful, traditional, and historic architecture, led by the Monastery of Saint John in Muestair, a United Nations Educational, Scientific and Cultural Organization World Heritage Center dating from the 8th century and famous for its frescos from the times of Charlemagne. A visit to Val Muestair and AAV Lue-Stailas will stay forever in your memory.”

And so will meeting the lovely, giving Vaclav and Jitka Ourednik.

Here’s an article about another project like this: remember Biosphere 2?

SkyWatcher Alert: Pleiades Occultation on April 8

Moon and M44 by John CudworthSure. For those of us who hang around the night sky, we know the Pleiades and the Moon frequently venture near each other during the course of a year, but it’s much less common for the Moon to be in a crescent phase when they visit. Because the light of the nearby Moon often overpowers the cool, blue star cluster M45, SkyWatchers rarely have the opportunity to see the Moon sedately cover its stars. Not this time… Continue reading “SkyWatcher Alert: Pleiades Occultation on April 8”