Surf’s Up! Astronomers Ride Stellar Waves

Astronomers peer inside stars by interpreting the waves they create

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This week, first results from the Kepler mission are coming out in waves from the meeting of the American Astronomical Society (AAS) in Washington, DC. Carried along on those waves are papers on waves in stars. I’m referring to a branch of astronomy you’ll be hearing more about as Kepler and other missions begin to reveal the interior structures of stars- asteroseismology. So, what is asteroseismology?

Seismology is the study of earthquakes on Earth. But more importantly to our discussion, it is the study of seismic waves. Earthquakes produce different types of seismic waves that travel through different layers of rock, providing us with a way to image structures deep within the Earth. Essentially, large earthquakes provide us with a natural sonogram to look inside the Earth, far deeper then we can tunnel or drill. Since these waves propagate all the way from one side of the planet to the other we can look all the way to the center of the Earth. This is how we know the outer core of the Earth is liquid, and the relative dimensions and densities of the other parts of the Earth’s internal and surface structure.

Copyright Nick Strobel http://www.astronomynotes.com/

Asteroseismology, also known as stellar seismology, gives us the same kind of insight into the structure of stars. By studying the oscillations in pulsating stars, astronomers can peer into the very hearts of stars, one of the most difficult places to observe in the entire universe. The reason stellar interiors can be probed from oscillations is that different oscillation modes penetrate to different depths inside the star. Combining the rate, and amplitude of pulsation with other information, such as spectra, which reveals what the composition of the star is we obtain information on the internal structure of stars.

Stellar oscillation modes are divided into three categories, based on the force that drives them: acoustic, gravity, and surface-gravity wave modes. p-mode, or acoustic waves, have pressure as their force, hence the name “p-mode”. These waves can tell us things about the structure and density of regions below the surface of a star. g-mode, or gravity waves, are confined to the interior of the star. f-mode, or surface gravity waves are also gravity waves, but occur at or near the outer layers of stars, so they give us information about the surface conditions of stars.

Helioseismology is the study of the propagation of wave oscillations in the Sun. Since the Sun is the closest star to us, it is much easier to study its pulsations in greater detail. By interpreting solar oscillations we can even detect sunspots on the far side of the Sun before they rotate into view. Many of our models of stellar interiors are based on information gained through studying the Sun’s oscillations. But the Sun is only one star at one point in its evolution, so to really understand stars we need to observe many more stars of different size, mass, composition and age.

Kepler stares at a portion of the sky taking hi-precision photometric data

That is precisely what Kepler is doing right now. The satellite is staring at a 100 square degree section of the sky between Cygnus and Lyra continuously taking data on the brightness of over 150,000 stars for the next three to five years. While Kepler’s primary mission is to discover the existence and abundance of earth-like planets around stars, all this high precision photometry will be used for other science, especially studying variable stars of all types and performing asteroseismology on stars showing solar-like oscillations.

The much-anticipated release of the first science results from the Kepler mission January 4th, included numerous papers on asteroseismology and the potential for understanding stellar structure in unprecedented detail. Astronomers are riding the new wave of information on wave propagation in stars. Surf’s up!

Further reading:

The asteroseismic potential of Kepler: first results for solar-type stars
W. J. Chaplin, T. Appourchaux, Y. Elsworth, et al
http://arxiv.org/abs/1001.0506

Solar-like oscillations in low-luminosity red giants: first results from Kepler
T. R. Bedding, D. Huber, D. Stello, et al
http://arxiv.org/abs/1001.0229

Kepler Asteroseismology Program: Introduction and First Results
Ronald L. Gilliland, T. M. Brown, J. Christensen-Dalsgaard
http://arxiv.org/abs/1001.0139

Messier 100


Object Name: Messier 100
Alternative Designations: M100, NGC 4321
Object Type: Type Sc Spiral Galaxy
Constellation: Coma Berenices
Right Ascension: 12 : 22.9 (h:m)
Declination: +15 : 49 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.3 (mag)
Apparent Dimension: 7×6 (arc min)


Locating Messier 100: As part of the Virgo Cluster of Galaxies, M100 is best found by returning to our “galaxy hopping” ways we’ve learned. Begin with the bright M84/84 pairing located in the heavily populated inner core of the Virgo Cluster of galaxies about halfway between Epsilon Virginis and Beta Leonis. Once identified, stay at the eyepiece a move your telescope north until you locate M99 and continue at least 3 or 4 more eyepiece fields. This is what is known as “sweeping”. When you reach a star pattern you are certain that you can identify, shift the telescope one eyepiece field to the east and continue northward for several eyepiece fields. If you have not seen the fairly large round patch of M100, continue the process carefully one eyepiece field at a time. (Not all eyepieces have the same apparent field of view, but use your lowest magnification.) M100 is face-on in presentation, so it will be a round of nebulousity that requires dark, clear skies and can be spotted with binoculars.

What You Are Looking At: M100 is a spiral galaxy, very similar to our own Milky Way. The galaxy has two distinct arms of young, hot and massive stars which show photographically as bright blue stars. These stars have formed recently from interactions with neighboring galaxies, but in a slightly odd way. “The total H I distribution is mostly confined to the radius of the optical disk, but a large though faint extension is seen in the H I data at 45” resolution on the SW side of the disk. NGC 4321 is asymmetric in H I and may be called “lopsided.” We have derived a rotation curve which agrees fairly well with what was previously published but shows more detail due to the higher resolution of our new observations. The rotation curve does not decline within the radius of the disk, but important differences are seen between the behavior of the approaching and the receding sides.” says Johan H. Knapen (et al), “These differences are caused by deviations from circular motions in the outer disk that are probably due to a close passage of the companion galaxy NGC 4322, which may also be the cause of the observed asymmetry in the total H I distribution. Deviations from circular motion due to density wave streaming are seen in the inner disk. From skewing of the velocity contours in the central part of NGC 4321, the presence of a nonaxisymmetric potential is deduced. Near-infrared and H? images indicate that a bar is indeed present in this galaxy. The deviations from circular motions seen in the velocity field can be identified with gas streaming around the bar in elongated orbits, in broad agreement with theoretical predictions.”

As one of Lord Rosse’s original 14 “spiral nebula”, Messier 100 seems to employ a perfect spiral shape – one that seems to lack a central bar structure. “We analyse new integral-field spectroscopy of the inner region (central 2.5 kpc) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this region. Fourier analysis of the velocity residuals obtained by subtracting an axisymmetric rotation model from the H? velocity field indicates that the distortions are global features generated by an m= 2 perturbation of the gravitational potential which can be explained by the nuclear bar.” says A. Castillo-Morales (et al). “This bar has been previously observed in the near-infrared but not in the optical continuum dominated by star formation. We detect the optical counterpart of this bar in the 2D distribution of the old stellar population (inferred from the equivalent width map of the stellar absorption lines). We apply the Tremaine–Weinberg method to the stellar velocity field to calculate the pattern speed of the inner bar, obtaining a value of ?b= 160 ± 70 km s?1 kpc?1 . This value is considerably larger than the one obtained when a simple bar model is considered. However, the uncertainties in the pattern speed determination prevent us from giving support to alternative scenarios.”

To study M100 is to take a look back into its growth and history… a history that apparently isn’t “going quietly into that good night”. Astronomers are still able to observe the remains of a star which exploded in 1979 – still shining as brightly in X-rays now as when it was first observed. This in itself is unusual because most supernova events fade fairly quickly in a period of just a few months. Dr. Stefan Immler at NASA’s Goddard Space Flight Center in Greenbelt, Md., led this observation using the European Space Agency’s XMM-Newton observatory. The star explosion (supernova), called SN 1979C, shows no sign of letting up, he said. By observing with the XMM-Newton optical/UV image of the galaxy M100 and supernova SN 1979C obtained with the Optical Monitor in the B, U, and UVW1 filters we’ve taken one of our deepest looks ever. The position of SN 1979C is marked by a white circle. The streak across the image is from an artifact caused by a dead detector column. The scale bar is 2 arc min, corresponding to 32,600 light years.

“This 25-year-old candle in the night has allowed us to study aspects of a star explosion never before seen in such detail,” Immler said. “All the important information that usually fades away in a couple of months is still there.” Among the many unique finds, Immler said, is the history of the star’s stellar wind dating back 16,000 years before the explosion. Such a history is not even known about our Sun. Also, the scientists could measure the density of the material around the star, another first. The lingering mystery, though, is how this star could fade away in visible light yet remain so radiant in X-rays. The results appear in The Astrophysical Journal. How is this accomplished? Through a composite XMM-Newton X-ray image of the galaxy M100 in soft (0.3-1.5 keV, red), medium (1.5-4 keV, green) and hard (4-10 keV, blue) X-rays. The image shows large amounts of diffuse X-ray emission from hot gas in the galaxy (red), various point-like X-ray sources and supernova SN 1979C south-east of the nucleus of M100 (marked by a white line). “We can use the X-ray light from SN 1979C as a ‘time machine’ to study the life of a dead star long before it exploded,” Immler said.

History: Messier 100 was originally discovered by Pierre Mechain on March 15, 1781. It was later confirmed and cataloged by Charles Messier on April 13, 1781 who wrote in his notes: “Nebula without star, of the same light as the preceding [M99], situated in the ear of Virgo. Seen by M. Mechain on March 15, 1781. The three nebulae, nos. 98, 99 & 100, are very difficult to recognize, because of the faintness of their light: one can observe them only in good weather, and near their passage of the Meridian.”

It would be observed and cataloged by both Herschels, but it was Admiral Smyth who described it the best: “A round nebula, pearly white, off the upper part of the Virgin’s left wing, and certainly at a great distance from Virgo’s ear of corn, where the Connaissance des Temps places it [actually Messier’s position is quite close]: indeed, the true site will be hit upon just one-fifth the way from Beta Leonis towards Arcturus. This is a large but pale objects, of little character, though it brightens from its attenuated edgestowards the centre; and is therefore proved to be globular. It was discovered by M. Méchain in 1781, and is accompanied by four small stars, at a little distance around it; besides minute points of light in the field, seen by occasional gleams.

We are now in the broad grand stratum of nebulae, which lies in a direction almost perpendicular to the Galaxy [Milky Way], and passes from the south, through Virgo, Berenices Hair, Canes Venatici, and te Great Bear, to the Pole, and beyond. This glorious but mysterious zone of diffused spots, is an indisputable memorial to all future times, of the unwearied industry and indomitable scientific energy of Sir William Herschel. Yet has this unrivaled contributor to knowledge been disparagingly described, as a man indulging in “speculations of no great value to astronomy, rather than engage in computations by which the science can really be benefited.” Save the mark! This is said of a philosopher of zeal and application hitherto unequaled: one whose contributions to the Philosophical Transactions prove the bold but circumspect grandeur of his conceptions, his consummate mechanical resources, and the exactness of his elaborate calculations. Herschel’s labor, however, transcended those of the ages in which he was cast, although he gave such animation and bias to sidereal astronomy that his mantle was caught at.”

May you, too, “save the mark”!

Top M100 image credit, Palomar Observatory courtesy of Caltech, M100 Hubble Image, Issac Newton Telescope True-color image of M100, M100 XMM Newton Images and M100 image courtesy of N.A.Sharp/NOAO/AURA/NSF.

Epsilon Aurigae Eclipse Mystery Solved with Your Help

If you’ve been helping out with the Citizen Sky project to monitor Epsilon Aurigae, then congratulations – the first of the results are in! Donald W. Hoard, a research scientist at Caltech announced the findings at the American Astronomical Society meeting in Washington, D.C. this morning. We invited our readers to participate in monitoring the star in August of 2009, and combined with observations from Spitzer, a 200-year old mystery has potentially been solved.

Epsilon Aurigae is a bright star in the constellation Auriga. It began to dim in brightness last August, which it does every 27 years. The star dims for over 2 years, with a slight brightening in the middle of the eclipse, making it the longest known orbital period for a stellar eclipse. The Citizen Sky project invited professional and amateur astronomers alike to aid in the observation of the star during this eclipse.

What exactly passes in front of the star was a mystery, though it was thought that a large disk of material with two stars orbiting tightly in the center is the cause of the eclipse. The disk itself is pretty huge – on the order of 8 astronomical units. There is a slight brightening during the middle of the eclipse that led astronomers to believe there is a hole created by the two stars in the center.

“If [Epsilon Aurigae] were an F star, with about 20 times the mass of the Sun…a single B star at the center of the disk doesn’t have enough mass to explain the orbital dynamics,” Hoard said. Other possibilities proposed were the presence of a black hole at the center of the disk, but there were no telltale X-rays coming from the system that would show a black hole was heating up matter in the disk.

Through observations by astronomers that participated in the project, as well as observations made by the Spitzer space telescope, a major revision of the properties of Epsilon Aurigae itself were in order.

“What we were most pleased to find an answer to… was that the results strongly tip towards a 2 solar-mass dying star. Sometime in the next few thousand years it will emerge as a planetary nebula,” Hoard said.

This means that instead of being a 20 solar-mass F-star supergiant, Epsilon Aurigae is in fact a 2 solar-mass F-star which is in the last stages of its life, and thus giant in size – about 300 Suns across. This, combined with a single B-star of about 5.9 solar masses at the center of the disk that orbits Epsilon Aurigae fit the observations very well, Hoard said.

Arne Henden of the American Association of Variable Star Observers (AAVSO), commenting on Hoard’s presentation at the press conference, said “Don says that we solved it, and I disagree. We need to determine the nature of the dusty disk that is involved – these are things that you see around young stellar objects, not older stellar objects.”

Hoard said that there was a curious property of the disk in that it was composed of larger grains of dust – more like grains of sand than microscopic dust motes.

“The observations that are being made by Citizen Sky project…will hopefully help answer this by providing answers about the composition of the disk and the temperature zones as the eclipse continues. We have these results in large part due to the effort of this huge group of citizen astronomers that are observing Epsilon Aurigae,” he said.

Epsilon Aurigae is still undergoing its eclipse, though the first phase ended right around the New Years Eve 2009. It will continue to be dim until early 2011, when it will begin to brighten again. There is still a lot to be answered about this system, and your help is needed, so keep (or start) observing and reporting! For more information on how to do so, visit Citizen Sky.

Source: AAS press conference on USTREAM, Citizen Sky press release

Arp’s Phantom Jet

Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.
Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.

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During the “Great Debate” of 1920 astronomers Herber Curtis and Harlow Shapley had a famous debate on the nature of “spiral nebulae”. Curtis argued they were “island universes” or what we would today call a galaxy. Shapley was of the opinion that they were spiral structures within our own galaxy. One of the evidences Shapley put forth was that another astronomer, Adriaan vanMaanen, had reported detecting rotation of these objects over a period of years leading to an overall rotation rate of ~105 years. If these spiral nebulae were truly as far (and thus, as large) as Curtis suggested this would mean they would be rotating well beyond the speed of light at their outer edges.

It was later determined vanMaanen’s rotation was a case of wishful thinking when Hubble eventually determined the true distance to the Andromeda galaxy. From then on, it was well established that galaxies are so large, their motions will not be observed in human lifetimes. Aside from local flare ups of supernovae and other such events, galaxies should be relatively static. Yet in just over 40 years, a distinct, large-scale feature in the galaxy NGC 3303 seems to have disappeared entirely.

In 1964, Halton Arp observed NGC 3303. This oddly shaped spiral galaxy he reported as having a jet protruding from the northwest side. It made it into his famous 1966 compilation of photographs entitled, “The Atlas of Peculiar Galaxies” as Arp object 192. A 2006 publication by Jeff Kanipe and Dennis Webb (The Arp Atlas of Peculiar Galaxies: A Chronicle and Observer’s Guide) listed this jet as a “challenge” for astronomers to capture.

In 2009, an advanced amateur named Rick Johnson attempted a long exposure of NGC 3303. When his image was finished, it was notably lacking the jet. The news of this eventually reached Kanipe and Webb and they suspected that the exposure was simply not long enough to have captured this object. To be sure, they consulted images of the galaxy from the Sloan Digital Sky Survey. The jet was missing from these images as well. A major feature on a galaxy had vanished in 45 years and no one had noticed until 2009.

The only plausible explanation was that the jet Arp detected didn’t really exist. It was possible it was a photographic defect in the glass plate on which the image was taken. Another possibility was that the imaged structure did exist, it just wasn’t what Arp suspected.

When Charles Messier attempted to look for comets, he kept a list of 109 objects that were not comets so he wouldn’t be confused by them. To tell true comets apart from the other fuzzy objects he observed, he observed them over a period of nights. If they moved with respect to background stars, they must be relatively nearby. If not, they were likely very distant. Was Arp’s jet the opposite; A nearby object that had simply moved out of the field of view since his original image?

Kanipe contacted the Minor Planet Center to determine if any of the known asteroids or minor planets had been in the vicinity when the image was taken. It turned out that a minor planet, TU240, discovered on 6 October 2002 by the Near Earth Asteroid Telescope on Haleakala, Maui, Hawaii, was very near to NGC 3303 when Arp imaged it confirming it was a strong candidate for Arp’s disappearing jet.

This isn’t the first time an object has been pre-discovered and its true nature simply missed when it was imaged. There is evidence that the planet Neptune was observed at least three different times (including by Galileo) before its nature was understood. But for this TU240,  this is expected to be the earliest prediscovery photograph. As a result, TU240 was given a new designation just after Thanksgiving 2009. It is now listed as 84447 Jeffkanipe.

(Read this story as told by Rick Johnson at the BAUT Forums.)

Probing the Explosive History of Eta Car

Eta Carinae as imaged by the Gemini South telescope in Chile with the Near Infrared Coronagraphic Imager (NICI) using adaptive optics to reduce blurring by turbulence in the Earth’s atmosphere. In this image the bipolar lobes of the Homunculus Nebula are visible with the never-before imaged “Little Homunculus Nebula” visible as a faint blue glow, mostly in the lower lobe. The Butterfly Nebula is visible (region circled) as the yellowish glow with dark filamentary structure close to, and mostly below/left, of the central star system (the central star system appears as a dark spot due to the coronagraphic blocking (occulting) disk used to eliminate the star’s bright glare).

Caption: Eta Carinae as imaged by the Gemini South telescope in Chile with the Near Infrared Coronagraphic Imager (NICI) using adaptive optics to reduce blurring by turbulence in the Earth’s atmosphere. In this image the bipolar lobes of the Homunculus Nebula are visible with the never-before imaged “Little Homunculus Nebula” visible as a faint blue glow, mostly in the lower lobe. The Butterfly Nebula is visible (region circled) as the yellowish glow with dark filamentary structure close to, and mostly below/left, of the central star system (the central star system appears as a dark spot due to the coronagraphic blocking (occulting) disk used to eliminate the star’s bright glare).

I can’t seem to stop writing about Luminous Blue Variable (LBV) stars this week. And new research discussed at the AAS conference this week continues the trend. As part of a series of short talks on exploding stars, John Martin of the University of Illinois, Springfield spoke on his work with the LBV Eta Carinae.

Eta Carinae is often cited as one of the most likely stars of which we know to erupt as a core collapse supernova. It has a mass of nearly 100 times that of the sun. Although it hasn’t exploded as a supernova yet, its history has seen some pronounced brightenings. In 1843, Eta Carinae underwent a massive eruption that lasted 20 years and shed an estimated 20 times the mass of the sun. During that time, it became the second brightest stellar object in the sky (note: Eta Car is most readily visible from the southern hemisphere). It also emitted as much energy as a typical supernova although spread out over the duration instead of the quick burst as in a real supernova. Martin called this great eruption an “impostor supernova.”

To probe the internal structure of the outburst Martin and his team used the Near Infrared Chronographic Imager (NICI) on the Gemini South telescope in Chile. The use of infrared allowed the team to peer through the dusty outer layers of the nebula which absorb visible light. The device also used a device to block the light from the central star allowing the team to look through the glare and more directly explore the surrounding structure.

“The Gemini images have allowed us to perform something akin to an autopsy by peeling away the obscuring, outer dusty skin and giving us a glimpse of what’s inside,” Martin said. “In the process we’re finding things we have never imaged before and didn’t expect. It’s like finding your murder victim has a third lung, an extra liver, or something more exotic hidden away under their skin!”

During his presentation Martin also used an analogy of geology in which looking to deeper layers can give a chronological history since the inner layers would not have been expanding as long. Their infrared expedition revealed several structures never before seen in Eta Carinae. The region around the central star system contained wispy clouds which the team nicknamed the “Butterfly Nebula” (not to be confused with NGC 6302, which also has that moniker). They also discovered a smaller set of lobes which they dubbed the “Little Homunculus Nebula”. This structure was traced by mapping forbidden emission lines of Fe II.

New Studies on the Vela Star Forming Region

A false-color infrared image of the star forming complex in Vela. Two new studies have measured for the first time the dust emission at very long infrared wavelengths, and found a set of young stars that are accreting material and flaring. Credit: NASA and the Spitzer Space Telescope
A false-color infrared image of the star forming complex in Vela. Two new studies have measured for the first time the dust emission at very long infrared wavelengths, and found a set of young stars that are accreting material and flaring. Credit: NASA and the Spitzer Space Telescope

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This week at the AAS meeting scientists revealed two new studies on a star forming region in Vela. The first used the Balloon-borned Large Aperture Submillimeter Telescope (BLAST, a proptotype detector for the one on the new Herschel Space Telescope) to classify the young stars and begin mapping the warm dust in the region. The second searched the nebula for flaring young stars. Both studies are to appear in an upcoming publication of the Astrophysical Journal.

Although star formation has been well modeled and understood theoretically, observational astronomy is often made more difficult due to the fact that it occurs shrouded in dusty nebulae. Visible light absorbed by the nebula and reemitted as lower energy infrared light. Most of the wavelengths in this region cannot permeate Earth’s atmosphere.

In order to study regions like this, astronomers are forced to use balloon based and space observatories. Astronomers Massimo Marengo, Giovanni Fazio, and Howard Smith, together with an international team of scientists used BLAST to study just such a star forming region in Vela. The first of their studies searched the nebula for newly formed stars. To do this, they searched for behaviors shown to be indicative of star formation, “such as proto-stellar jets and molecular outflows.” Additionally, to truly classify as a proto-star, the object was required to show up at more than one wavelength. In searching for these candidates, they confirmed 13 cores originally reported by a previous team, but discounted one because it did not have the proper spectral characteristics (although they may still later collapse to form stars).

By analyzing the mass of the forming regions, the team was also able to show that the Core Mass Function (CMF, a function that describes the frequencies of proto-star cores of various masses) is very similar to the Initial Mass Function (IMF, which is the same thing but for already formed stars). Although this is unsurprising, it is a necessary observation to confirm our understanding of how stars form and to show that stars do indeed come from such nebulae.

Another unsurprising confirmation of stellar formation models is that forming cores in the nebula are notably warmer when they’ve reached the density sufficient to create fusion in the core and have an embedded protostar. These results, “can thus provide guidelines
for understanding the physical conditions where the transition between pre- and proto-stellar cores takes place.”

The second of their studies analyzed known young stars to search for large flares thought to be caused by material being accreted onto the young star. The region was imaged once and then a second time six months later. Over this period, 47 of some 170,000 observed stars had increases in brightness consistent with what was expected for flaring. Closer inspection of these stars 19 had the further characteristics (mass, age, environment) expected of such flares. Eight showed evidence of being extremely young (on the order of a hundred thousand years or less) and were still enshrouded in gravitationally bound disks of dust.

Although this cannot confirm the prediction of such youthful flares being due to infalling material (as opposed to magnetic fields or interactions with a companion) it does show that BLAST and its successor, Herschel, will be a powerful tool for further study.

Could A Faraway Supernova Threaten Earth?

Supernovae, just like any other explosions, are really cool. But, just like any other explosion, it’s preferable to have them happen at a good distance. The star T Pyxidis, which lies over 3,000 light-years away from the Earth in the constellation Pyxis, was previously thought to be far enough away that if anything happened in the way of a supernova, we’d be pretty safe.

According to Edward Sion, Professor of Astronomy and Physics at Villanova University, T Pyxidis may be in fact a “ticking time bomb,” and potential threat to the Earth if it were to go supernova, which it may do sometime in the future, though very, very far in the future on our timescale: by Scion’s calculations, at least 10 million years.

Sion presented his findings at the American Astronomical Society Meeting in Washington, D.C. earlier today. T Pyxidis, which lies in the constellation Pyxis, is what is called a recurring nova. The star, which is a white dwarf, accretes gas from a companion star. As the amount of matter increases in the white dwarf, it occasionally builds up to the point where there is a runaway thermonuclear reaction in the star, and it ejects large quantities of material.

T Pyxidis has had five different outbursts over the course of observations of the star. It was the American Association of Variable Star Observers’ variable star of the month in April, 2002.  The first was in 1890, followed by another outburst in 1902 (these two were discovered much later on photographic plates in the Harvard plate collection). The next three were in 1920, 1944 and 1967. Its average for outbursts is about 19 years, but there hasn’t been one since the 1966 brightening.

The distance estimate to T Pyxidis, revised to 3,260 light-years from the previously estimated distance of 6,000 light-years has prompted a reconsideration of the details about the white dwarf. Hubble images that have been taken of the star would then have to be re-examined so as to revise the amount of mass the star is expected to be ejecting.

If the recurring novae are ejecting enough material, then the white dwarf would stay small enough to continue to go through the phase of recurring novae. However, if the shells of gas repeatedly ejected by the star do not carry enough mass away, it would eventually build up to pass the Chandrasekhar limit – 1.4 times the mass of the Sun – and become a Type Ia supernova, one of the most destructive events in our Universe.

Sion concluded the presentation with the statement (shown here on his last powerpoint slide) that “A Type Ia supernova exploding within 1000 parsecs of Earth will greatly affect our planet”

A supernova within 100 light-years of the Earth would likely be a catastrophic event for our planet, but something as far out as T Pyxidis may or may not damage the Earth. One of the journalists in attendance pointed out this possibility during the questions session and Sion said that the main danger lies in the amount of X-rays and gamma rays that stream from such an event, which could destroy the protective ozone layer of the Earth and leave the planet vulnerable to the ultraviolet light streaming from the Sun.

There remains some doubt as to whether T Pyxidis will go supernova at all. There is a good treatment of this subject in “The Nova Shell and Evolution of the Recurrent Nova T Pyxidis” by Bradley E. Schaefer et al. on Arxiv.

If you’re worried about the dangers of exploding stars, you should check out this video by Phil Plait, the Bad Astronomer. He’ll calm you down.

Source: AAS Press Conference on USTREAM, Space.com

Amazing Images

Moon from Earth

Here are some amazing images of space:

This is an amazing image of the Moon taken from the International Space Station orbiting Earth. What a view!


M83. Image credit: Hubble

This is a photograph of the spiral galaxy M83, one of the closest best examples we can see of a spiral galaxy. This image was captured by the Hubble Space Telescope.


Hurricane Ike

Here’s an image of Hurricane Ike captured by astronauts on board the International Space Station.


Apollo 11

Here’s a photo of NASA’s Apollo 11 lunar lander rising from the surface of the Moon to dock with the Command and Service module.


Halley's Comet

Here’s a picture of Halley’s comet taken by the Giotto spacecraft. You can see the nucleus of the comet tumbling in space and the tail trailing behind.

If you’d like to get more outer space pictures for yourself, check out NASA’s Astronomy Picture of the Day, as well as NASA’s Image of the Day.

Many of the best pictures of space come from the Hubble Space Telescope. You can see the latest images from the Hubble Site, and then an archive of old images at the Hubble Heritage site. There are also great pictures from the Chandra X-Ray Observatory and NASA’s Spitzer Space Telescope.

If you’d like pictures of the planets, check out NASA’s Planetary Photojournal, and here are links to missions at the planets in the Solar System. MESSENGER, Venus Express, the Lunar Reconnaissance Orbiter, Mars Reconnaissance Orbiter, Cassini, and New Horizons.

We’ve written many articles about amazing images for Universe Today. Here’s an article about some images from STS-129, and here are some images of the shuttle and Hubble transiting across the Sun.

We’ve recorded many episodes of Astronomy Cast about space. Try this one, Episode 99: The Milky Way.

Intergalactic Connection is Older, Longer than Thought

Our galaxy has a streamer, though it’s not like the ones you had on your bike as a kid: this streamer is a flow of largely hydrogen gas that originates in the Large and Small Magellanic Clouds, two of our closest galactic neighbors. New observations of the stream have helped to revise its age and extent, and show it to be longer and much older than previous estimates.

The Magellanic Stream, which was discovered over 30 years ago, flows from the two galaxies closest to the Milky Way, the Large and Small Magellanic Clouds. These clouds, which are actually two irregular dwarf galaxies, are 150,000 to 200,000 light-years away, and are visible in the southern hemisphere.

The stream connects up with the Milky Way about 70,000 light years from the Solar System, in the constellation of the Southern Cross.

Using the Green Bank Telescope (GBT), a team of astronomers took over 100 hours of observations of the streamer. These observations were combined with those from other radio telescopes, including the Aricebo telescope in Puerto Rico, to further constrain both its extent and age.

Their observations were presented at the American Astronomical Society’s meeting in Washington D.C., and a paper has been submitted to the Astrophysical Journal. The team included David Nidever and Steven Majewski of the Department of Astronomy at the University of Virginia, Butler Burton of the Leiden Observatory and the National Radio Astronomy Observatory and Lou Nigra of the University of Wisconsin.

Previous observations of the stream showed it to have gaps between the Magellanic Clouds and where it enters the Milky Way, but these revised observations show it to be one continuous stream between the three galaxies. The stream is also at least forty percent longer that previously estimated.

The Magellanic Stream was also determined by the astronomers to be much older than had been estimated before: up from 1.75 billion years old to 2.5 billion years old. Just how does this long-lived intergalactic trail of hydrogen crumbs start off in the Magellanic Clouds?

“The new age of the stream puts its beginning at about the time when the two Magellanic Clouds may have passed close to each other, triggering massive bursts of star formation. The strong stellar winds and supernova explosions from that burst of star formation could have blown out the gas and started it flowing toward the Milky Way,” said David Nidever in a NRAO press release.

By getting a better picture of how the gas flows from the Magellanic Clouds into the Milky Way, astronomers have been able to determine with better accuracy just how far away the two galaxies are, as well as their  interactions with the tidal forces of the Milky Way.

This team has collaborated before on the exploration of the Magellanic Stream and its origins. You can read about their previous findings on Arxiv right here, which were also published in the Astrophysical Journal.

Source: NRAO press release

ALMA Telescope Links Third Antenna

Well, they’re 1/22 of the way there: the Atacama Large Millimeter/submillimeter Array (ALMA), planned to be one of the largest ground-based observatories in the world, successfully linked 3 of its 66 antennas together. This is the next step in working out all of the bugs associated with linking together the whole array, which should happen sometime in 2012.

ALMA is a “microwave” telescope array that will be the largest such ground-based observatory in the world once it is completely online. Telescopes like ALMA are called interferometers because they use the principle of very-long baseline interferometry – by linking separate telescopes together, a larger telescope of the effective resolution of the distance between the separate elements is achieved.

We reported on the first image taken by two of the antennas back in November. Information from a pair of the antennas was gathered to test the electronic functioning of the system, but errors from the system itself and those that creep in because of the atmosphere were weeded out by this latest test that included a third antenna. This test is called a “closure phase”, essentially the self-calibration of the antennas in terms of reconciling the information they are taking in with the signals present from noise.

Fred Lo, director of the National Radio Astronomy Observatory (NRAO) – which is the contributing organization of North America to the ALMA array – said of the test in a press release,”This successful test shows that we are well on the way to providing the clear, sharp ALMA images that will open a whole new window for observing the Universe. We look forward to imaging stars and planets as well as galaxies in their formation processes.”

ALMA can gather information in the electromagnetic spectrum at a wavelength that is less than 1 millimeter. Because the planned array is so large, it will eventually be able to resolve unprecedented images of some of the first galaxies to form after the Big Bang, and will also be able to capture the formation of planets around stars, as well as information on the late stages in the life of stars.

ALMA is located in the Atacama desert in Chile at about 5,000 meters (16,500 feet) above sea level. This high and dry location allows the telescope to receive more of the light in the submillimeter; water vapor in the atmosphere of the Earth absorbs light in this part of the spectrum.

Source: NRAO press release