The scale of things

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The Dark, Dusty Graves of the GRAIL Spacecraft | Phil Plait
Bad Astronomy | Thursday, March 28, 2013, at 8:00 AM

The twin GRAIL probes were sent into orbit around the Moon in the last days of 2011, designed to use gravity itself to measure the Moon’s interior composition and structure. On Dec. 17, 2012 they were sent plummeting to the surface after completing their major objectives, slamming into the ground near the Moon’s north pole.

Another mission, the Lunar Reconnaissance Orbiter, was able to spot the impact sites where the two spacecraft met their doom, and you can see them in these before-and-after shots:


^ The impact sites of the twin GRAIL spacecraft. The area before the impact is above, and after the impacts below (I brightened those images a bit to make it easier to see). Image credit: NASA/GSFC/Arizona State University

On the left, stacked vertically, is where GRAIL A (nicknamed Ebb) hit, and on the right is GRAIL B (Flow). As you can see in the bottom images, there are dust plumes that fanned out over the surface that weren’t there before. Note the scale; each image is about 200 meters across, twice the length of a football field. That may sound big, but the Moon has a lot of crater-saturated real estate. It’s amazing they found these sites.

< A wider view of the impact site, showing where they hit: the base of a lunar massif. Image credit: NASA/GSFC/Arizona State University

They actually hit near the base of a massif, or long mountain, on the south-facing bank, just a couple of thousand meters apart—they were flying together in the same orbit, to help measure the change in gravity due to changes in density of the lunar material beneath them. The lower they flew, the better their measurements, so in the end their orbits were lowered to just a few kilometers above the Moon. The final impact was placed at the north pole to avoid any possible contamination of historical spots like the Apollo landings.

The two spacecraft each approached the surface at 1.6 kilometers per second (1 mile per second)—twice as fast as a rifle bullet—moving south to north. Note the excavated material fanned out to the north as you’d expect from a low-angle impact. The irregular distribution is unusual though. Each made craters about 5 meters (16 feet) across.

And there’s another surprise, too: the ejected material is dark. Usually, dust blown out by impacts is lighter in color than the surrounding material, eventually darkening over the eons as it gets zapped by cosmic radiation and whacked by micrometeorite impacts (like, for example, the rays around the relative young impact crater Tycho). It’s not clear why there’s darker material under the surface where the impacts were.

Even in death, GRAIL was trying to teach us something about the Moon.

Controlled impacts are common in planetary exploration when missions are at their ends. Engineers and scientists do try to squeeze out every last drop of information they can in situations like that, which I think is fine, and even noble. We should all do so well in our own last moments.

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Astronomy Picture of the Day | 2013 March 31


Video Credit: Gateway to Astronaut Photography, NASA
Compilation: David Peterson (YouTube)
Music: Freedom Fighters (Two Steps from Hell)

Explanation: Many wonders are visible when flying over the Earth at night. A compilation of such visual spectacles was captured recently from the International Space Station (ISS) and set to rousing music. Passing below are white clouds, orange city lights, lightning flashes in thunderstorms, and dark blue seas. On the horizon is the golden haze of Earth’s thin atmosphere, frequently decorated by dancing auroras as the video progresses. The green parts of auroras typically remain below the space station, but the station flies right through the red and purple auroral peaks. Solar panels of the ISS are seen around the frame edges. The ominous wave of approaching brightness at the end of each sequence is just the dawn of the sunlit half of Earth, a dawn that occurs every 90 minutes.

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Fires in the Sky | Phil Plait
Bad Astronomy | Monday, April 1, 2013, at 8:00 AM

I really wasn’t planning on posting any more photos of comet C/2011 L4 (Pan-STARRS), since I figured it was tapped out.

I was wrong.

But first, I want to show you an astonishing photo taken by photographer Shannon Bileski of Manitoba. She was out doing some shooting when she heard there might be northern lights popping up. She got in her car, drove to a good spot near Lake Winnipeg, and starting taking pictures.

Getting good shots of an aurora is hard enough, taking some degree of luck. But what she got was just freaking amazing:


^ A very lucky shot of a shooting star and the northern lights. Image credit: Shannon Bileski, used by permission.

By coincidence, a bright meteor streaked through the sky as she was taking the picture above on Mar. 29, 2013. I might even call it a fireball; it clearly got far brighter even than Jupiter, which you can see on the left (just off the V shape of the horns of the constellation Taurus). It was no Chelyabinsk meteor—thank goodness!—but it was still pretty intense.

In a shot like this you don’t get the 3D perspective that helps you figure out distance. Usually in a picture of the sky the objects you see are all at vastly different distances; clouds might be a few kilometers up, while the stars, of course, are trillions of kilometers distant. But as it happens meteors and aurorae both occur at roughly the same altitude: 100 kilometers.

At that height, the air is dense enough that the pressure from the incoming chunk of rock compresses it, heating it up so that it can glow. It’s also at the right density to interact with subatomic particles blasting in from the Sun. Those particles energize the atoms in the air, causing them to glow. The green color comes from oxygen, while red can come from both oxygen and nitrogen.

What this means is that the meteor and the aurora are pretty much coincident in space; it’s not just a perspective effect. That’s cool.

But wait! There’s more!

A week or so earlier, on Mar. 20, my friend Babak Tafreshi was out taking night sky shots and caught comet Pan-STARRS with a burst of auroral activity:


^ Babak Tafreshi caught the comet Pan-STARRS (just visible on the right over the mountain ridge) and an aurora. Click to dirtysnowballenate. Image cedit: Babak Tafreshi, used by permission.

You can see the comet over the mountain range; the aurora became quite strong just minutes later. He was lucky to get both in the same shot. A few minutes either way and he would have missed one or the other. Incidentally, Shannon’s friend Sheila got a cool shot of the comet seen in the aurora. Wow.

Babak also made this lovely time-lapse animation of the images he took showing the comet setting, and then the aurora coming to life:



I’ve seen comets, and I’ve seen meteors (and I’ve seen sunny days I thought would never end). But I’ve still not seen a good aurora. Babak was in Tromsø, Norway, where a lot of photographers get amazing shots. I won’t be able to get there any time soon, so maybe it’ll have to wait for the next solar activity maximum in 2024 or so. In the meantime, I really hope I get a chance to see this ethereal beauty someplace closer.

I do love posting incredible pictures and video like these, but there’s nothing like seeing it for yourself. Some day.

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How to Reconstruct the Life of a Star
Universe Today, Nancy Atkinson | April 1, 2013


^ This image of Cep OB 3b was created by combining the light from four separate observations taken through different filters on the 0.9 meter telescope at Kitt Peak. The brightest yellow star near the center of the image is a foreground star, lying between us and the young cluster. The other bright stars are the massive young stars of the cluster that are heating the gas and dust in the cloud and blowing out cavities. Image processing was done by Dr. Travis Rector. Credit: NOAO.

It takes time to understand the life of stars. A star like our Sun takes tens of millions of years to form, and so much like archeologists who reconstruct ancient cities from shards of debris strewn over time, astronomers must reconstruct the birth process of stars indirectly, by observing stars in different stages of the process and inferring the changes that take place.

One of the best places to study the lives of stars is in star clusters. These regions that are rich with young stars provide astronomers much information that is relevant to the study of stars in general, but within a cluster, stars can form during a wide range of time, as a new study of the star cluster named Cep OB3b has shown.

“By studying nearby massive young clusters like Cep OB3b, we can gain a greater understanding of the environments out of which planets form,” said Thomas Allen from the University of Toledo, who is one of the authors of the new paper.

Located in the northern constellation of Cepheus, CepOB3b is similar in some ways to the famous cluster found in the Orion Nebula. But unlike the Orion Nebula, there is relatively little dust and gas obscuring our view of Cep OB3b. Its massive, hot stars have blown out cavities in the gaseous cloud with their intense ultraviolet radiation which mercilessly destroys everything in its path. Cep OB3b may show us what the Orion Nebular Cluster will look like in the future.

Allen and an international team of astronomers have found that the total number of young stars in the cluster is as high as 3,000. Infrared observations of the stars from the NASA Spitzer satellite show about 1,000 stars that are surrounded by disks of gas and dust from which solar systems may form. As the stars age, the disks disappear as the dust and gas get converted into planets or are dispersed into space.

But these observations pointed to a new mystery. Although the stars in Cep OB3b are thought to be about three million years old, in some parts of the cluster most of the stars had lost their disks, suggesting that the stars in those parts were older. This suggests that the cluster is surrounded by older stars, potential relics of previous clusters that have since expanded and dispersed.

To search for evidence for these relic clusters, Allen used the Mosaic camera on the 0.9 meter telescope at Kitt Peak National Observatory to observe wide field images of CepOB3b. These images show hot gas and its interaction with the stars and permit the team to study a curious cavity in the gas for evidence of older, yet still juvenile, stars that have lost their disks of gas and dust.

With these data, the team is searching for the previous generations of star formation in the region surrounding Cep OB3b, and piecing together the history of star formation in this magnificent region. When finished, this may provide clues how previous generations may have influenced the current generation of stars and planets forming in Cep OB3b.

Source: NOAO

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Cassini Spies a Forbidden Planet’s Flying Saucer Moon | Phil Plait
Bad Astronomy | Monday, April 1, 2013, at 1:10 PM

The Cassini spacecraft orbiting Saturn has taken a picture of a flying-saucer-shaped object using a force field to manipulate one of the planet’s rings.

Yes, I know what today is! But I assure you, this picture is quite real:


^ Prometheus (the moon, not the movie) seen by the Cassini Saturn spaceprobe. Click to bringeroffirenate. Image credit: NASA/JPL-Caltech/Space Science Institute

The object is Saturn’s moon Prometheus, a chunk of ice about 136 kilometers (85 miles) long. It orbits Saturn near the planet’s narrow F ring, and that’s no coincidence. Prometheus and its sister moon Pandora flank the ring (Prometheus on the inside—toward Saturn—and Pandora on the outer side), and the force of their gravity helps constrain the tight path of the ring particles. For this reason they’re called shepherd moons.


^ Prometheus up close and personal, from a Jan. 27, 2010 encounter by Cassini. Image credit: NASA/JPL/Space Science Institute

This picture threw me for a moment. Prometheus is elongated and potato-shaped, while Pandora is somewhat squatter. In some pictures Pandora is the one that looks like a flying saucer, but the angle of the sunlight here gives Prometheus a decidedly alien spaceshipy look. It looks very much like an April Fools’ Day picture just posted by International Space Station Commander Chris Hadfield, too.

In fact, this looks so much like the United Planets Cruiser C57-D—on today of all days—I had to make sure this picture was real. As far as I can tell, it is. That’s good! After all, I wouldn’t want to create a Tempest in a teapot.

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Astronomers Watch as a Black Hole Eats a Rogue Planet
Universe Today, Nancy Atkinson | April 2, 2013

In Star Wars, the Millennium Falcon narrowly escaped being devoured by an exogorth (space slug) slumbering inside an asteroid crater. An unsuspecting rogue giant planet wasn’t as lucky. Astronomers using the Integral space observatory were able to watch as the planet was eaten by a black hole that had been inactive for decades. It woke up just in time to make a meal out of the unwary planet.

“The observation was completely unexpected, from a galaxy that has been quiet for at least 20–30 years,” says Marek Nikolajuk of the University of Bialystok, Poland, lead author of the paper in Astronomy & Astrophysics.

Nikolajuk and his team added that the event is a preview of a similar feeding event that is expected to take place with the black hole at the center of our own Milky Way Galaxy.


^ Screen capture from the ESA video.

The discovery in galaxy NGC 4845, 47 million light-years away, was made by Integral, with follow-up observations from ESA’s XMM-Newton, NASA’s Swift and Japan’s MAXI X-ray monitor on the International Space Station.

Astronomers were using Integral to study a different galaxy when they noticed a bright X-ray flare coming from another location in the same wide field-of-view. Using XMM-Newton, the origin was confirmed as NGC 4845, a galaxy never before detected at high energies.

Along with Swift and MAXI, the emission was traced from its maximum in January 2011, when the galaxy brightened by a factor of a thousand, and then as it subsided over the course of the year.

By analyzing the characteristics of the flare, the astronomers could determine that the emission came from a halo of material around the galaxy’s central black hole as it tore apart and fed on an object of 14–30 Jupiter masses, and so the astronomers say the object was either a super-Jupiter or a brown dwarf.

This object appears to have been ‘wandering,’ which would fit the description of recent studies that have suggested that free-floating planetary-mass objects of this kind may occur in large numbers in galaxies, ejected from their parent solar systems by gravitational interactions.

The black hole in the center of NGC 4845 is estimated to have a mass of around 300,000 times that of our own Sun. The astronomers said it also appears to enjoy playing with its food: the way the emission brightened and decayed shows there was a delay of 2–3 months between the object being disrupted and the heating of the debris in the vicinity of the black hole.

“This is the first time where we have seen the disruption of a substellar object by a black hole,” said co-author Roland Walter of the Observatory of Geneva, Switzerland. “We estimate that only its external layers were eaten by the black hole, amounting to about 10% of the object’s total mass, and that a denser core has been left orbiting the black hole.”

The flaring event in NGC 4845 might be similar to what is expected to happen with the supermassive black hole at the center of our own Milky Way Galaxy, perhaps even this year, when an approaching Earth-mass gas cloud is expected to meet its demise.

Along with the object seen being eaten by the black hole in NGC 4845, these events will tell astronomers more about what happens to the demise of different types of objects as they encounter black holes of varying sizes.

“Estimates are that events like these may be detectable every few years in galaxies around us, and if we spot them, Integral, along with other high-energy space observatories, will be able to watch them play out just as it did with NGC 4845,” said Christoph Winkler, ESA’s Integral project scientist.

The team’s paper: Tidal disruption of a super-Jupiter in NGC 4845

Source: ESA

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A Distorted Galaxy And Its Cloaked Clouds of Gas | Phil Plait
Bad Astronomy | Tuesday, April 2, 2013, at 8:00 AM

I find all galaxies to be beautiful, from huge, symmetric elliptical puffballs to glorious, grand design spirals.

But man, J082354.96 is seriously messed up. It’s still beautiful, though:


^ Hubble image of J082354.96, a distorted galaxy 650 million light years away. Click to galactinate. Image credit: ESA/Hubble & NASA, M. Hayes

Wow. It's quite the train wreck, and can definitely be labeled as “peculiar”. That’s an actual galaxy type, along with elliptical, disk (or spiral, like our Milky Way), and irregular. That last is for galaxies with no overall shape; peculiars have a definite shape, just a weird one.

J08 is about 650 million light years away, and clearly has something going on to give it this weird, drawn out, and oddly pleasing curvy hooked shape. To any astronomer’s eye, it’s obviously undergone an interaction: a cosmic collision with or nearby pass of another galaxy. That will commonly elongate a galaxy like this, and even cause those curls at the ends. As two galaxies collide (and sometimes merge), the huge collective gravities of each stretch the other out like taffy, and an off-center collision can cause vast arcs of gas and stars to be drawn out.

Interestingly, it’s not clear to me where the other galaxy is that did this. It’s possible they merged completely, forming J08 as we see it now, disturbed and weird but probably beginning to settle down after the eons-long encounter. If they didn’t merge, though, it’s difficult to say what happened to the other galaxy just from examining this image alone. There are a couple of galaxies near J08 in the full picture, but without knowing their distance they could be located much closer or farther from Earth than J08 itself, completely unrelated to it.

This galaxy was observed by Hubble to find out what it looks like in ultraviolet light, as part of a study the structure of these galaxies. UV is strongly emitted by hot, massive, blue stars, which don’t live very long. As it happens, J08 is a starburst galaxy, cranking stars out at a high rate. A lot of those stars are the massive and hot kind, and they light up the gas and dust around them—these are strung out along the galaxy, which you can see as those blue regions in the Hubble picture. This is actually pretty typical after a big galaxy collision; gas clouds collide, collapse, and form stars at a furious rate.

However, there’s more going on here. The UV light seen in the Hubble image above is pretty much emitted by stars and warm gas. But if you look farther into the ultraviolet, a new feature comes up, a very special color of UV strongly emitted by hydrogen gas. When you hit a hydrogen atom with enough energy, its sole electron will jump from one energy level to the next, like a person hopping up a step on a staircase. In this case, the electron jumps up from the bottom energy level to the next one up. After a time, it’ll plop back down and emit a UV photon at 121.6 nanometers wavelength (way outside what the human eye can see)[/b]. This light is so special it has its own name: Lyman Alpha, or Lyα.

The astronomers studying J08 used the orbiting GALEX observatory to take a look at the Lyα being emitted in the galaxy. They processed the data to remove a lot of unwanted light interfering with the Lyα, and what they found is interesting:


^ Comparison of the ultraviolet including Lyman alpha emission (top) and optical light (bottom) from the galaxy. A bright star visible in the lower image was masked out by the researchers in the top image to prevent interference. Credit: ESA/Hubble & NASA, M. Hayes; GALEX

In the upper image (a combination of several observations from Hubble and GALEX), red shows light from warm gas clouds, green from the massive stars, and the Lyα (normally invisible to the human eye) is colored blue. As you can see, quite a bit of Lyα appears to be coming from the outskirts of the galaxy. It’s coming from the interior as well, but that’s overwhelmed by the other light and hard to see here. The point is that the Lyα emission is also coming from parts of the galaxy well beyond where we see visible light being emitted. J08 is an extreme example (the galaxy itself is stretched out) but they found similar results in about a dozen other galaxies they looked at as well.

It turns out that many galaxies are surrounded by a thin halo of hydrogen gas, but it’s very hard to detect because it’s spread out. It doesn’t emit optical light we can see, and it’s too cold to emit UV light on its own. But those massive hot stars are sending out light at all colors of UV, including Lyα, and the gas on the outskirts absorbs and re-emits it, betraying its presence. That’s why we see Lyα coming from the outer parts of the galaxy. The actual mechanism occurring is more complicated than this—isn't it always?—but that's the basics of it. J08 and the others were chosen because they’re relatively nearby, and their structures could be picked out by Hubble. Once we understand how and where Lyα is emitted by them, we can use that to better understand more distant galaxies where we can’t see the structure directly.

This is important to know because Lyα is used to determine how many hot, massive stars are born in these kinds of galaxies. It also reveals the structures of these galaxies, including the location of gas that is otherwise invisible. It’s also used in other ways, like finding the distances to galaxies and vast gas clouds, and even what conditions were like in the early Universe. All that from a simple quirk in the simplest atom of them all.

I find it fascinating that the Universe is so accommodating to our inquisitive nature. It leaves clues everywhere about itself, and all you need to learn about it is a bit of math and physics, technology, and above all curiosity. With those features in combination, the entire cosmos can be revealed.

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First-Ever High Resolution Radio Images of Supernova 1987A
Universe Today, Nancy Atkinson | April 3, 2013


^ An overlay of radio emission (contours) and a Hubble space telescope image of Supernova 1987A. Credit: ICRAR (radio contours) and Hubble (image.)

On February 23, 1987, the brightest extragalactic supernova in history was seen from Earth. Now 26 years later, astronomers have taken the highest resolution radio images ever of the expanding supernova remnant at extremely precise millimeter wavelengths. Using the Australia Telescope Compact Array radio telescope in New South Wales, Australia, Supernova 1987A has been now observed in unprecedented detail. The new data provide some unique imagery that takes a look at the different regions of the supernova remnant.

“Not only have we been able to analyze the morphology of Supernova 1987A through our high resolution imaging, we have compared it to X-ray and optical data in order to model its likely history,” said Bryan Gaensler, Director of CAASTRO (Centre for All-sky Astrophysics) at the University of Sydney.


^ Radio image at 7 mm. Credit: ICRAR Radio image of the remnant of SN 1987A produced from observations performed with the Australia Telescope Compact Array (ATCA).

SN 1987A has been on one of the most-studied astronomical objects, as its “close” proximity in the Large Magellanic Cloud allows it to be a focus for researchers around the world. Astronomers say it has provided a wealth of information about one of the Universe’s most extreme events.

“Imaging distant astronomical objects like this at wavelengths less than 1 centimetre demands the most stable atmospheric conditions,” said lead author, Giovanna Zanardo of ICRAR, the International Center for Radio Astronomy Research. “For this telescope these are usually only possible during cooler winter conditions but even then, the humidity and low elevation of the site makes things very challenging.”

Unlike optical telescopes, a radio telescope can operate in the daytime and can peer through gas and dust allowing astronomers to see the inner workings of objects like supernova remnants, radio galaxies and black holes.

“Supernova remnants are like natural particle accelerators, the radio emission we observe comes from electrons spiraling along the magnetic field lines and emitting photons every time they turn. The higher the resolution of the images the more we can learn about the structure of this object,” said Professor Lister Staveley-Smith, Deputy Director of ICRAR and CAASTRO.


^ An RGB overlay of the supernova remnant. Credit: ICRAR. A Red/Green/Blue overlay of optical, X-Ray and radio observations made by 3 different telescopes. In red are the 7-mm (44GHz) observations made with the Australian Compact Array in New South Wales, in green are the optical observations made by the Hubble Space Telescope, and in blue is an X-ray view of the remnant, observed by Nasa’s space based Chandra X-ray Observatory.

Scientists study the evolution of supernovae into supernova remnants to gain an insight into the dynamics of these massive explosions and the interaction of the blast wave with the surrounding medium.

The team suspects a compact source or pulsar wind nebula to be sitting in the centre of the radio emission, implying that the supernova explosion did not make the star collapse into a black hole. They will now attempt to observe further into the core and see what’s there.

Their paper was published in the Astrophysical Journal.

Source: ICRAR

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NASA’s Great Observatories Provide a Sparkly New View of the Small Magellanic Cloud
Universe Today, Nancy Atkinson | April 3, 2013


^ A part of the Small Magellanic Cloud galaxy is dazzling in this new view from NASA’s Great Observatories. The Small Magellanic Cloud, or SMC, is a small galaxy about 200,000 light-years way that orbits our own Milky Way spiral galaxy. Credit: NASA.

This is just pretty! NASA’s Great Observatories — the Hubble Space Telescope, the Chandra X-Ray Observatory and the Spitzer Infrared Telescope — have combined forces to create this new image of the Small Magellanic Cloud. The SMC is one of the Milky Way’s closest galactic neighbors. Even though it is a small, or so-called dwarf galaxy, the SMC is so bright that it is visible to the unaided eye from the Southern Hemisphere and near the equator.

What did it take to create this image? Let’s take a look at the images from each of the observatories:


^ The Small Magellenic Cloud in infrared, from the Spitzer Infrared Telescope. Credit: NASA.


^ The Small Magellenic Cloud in infrared, from the Spitzer Infrared Telescope. Credit: NASA.


^ The Small Magellenic Cloud as seen in optical wavelengths from the Hubble Space Telescope. Credit: NASA.

The various colors represent wavelengths of light across a broad spectrum. X-rays from NASA’s Chandra X-ray Observatory are shown in purple; visible-light from NASA’s Hubble Space Telescope is colored red, green and blue; and infrared observations from NASA’s Spitzer Space Telescope are also represented in red.

The three telescopes highlight different aspects of this lively stellar community. Winds and radiation from massive stars located in the central, disco-ball-like cluster of stars, called NGC 602a, have swept away surrounding material, clearing an opening in the star-forming cloud.

Find out more at this page from Chandra, and this one from JPL.

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Wrapping Around The Mystery Of Spiral Galaxy Arms
Universe Today, Tammy Plotner | April 3, 2013


^ Credit: Thiago Ize & Chris Johnson (Scientific Computing and Imaging Institute)

How disk galaxies form their spiral arms have been puzzling astrophysicists for almost as long as they have been observing them. With time, they have come to two conclusions… either this structure is caused by differences in gravity sculpting the gas, dust and stars into this familiar shape, or its just a random occurrence which comes and goes with time.

Now researchers are beginning to wrap their conclusions around findings based on new supercomputer simulations – simulations which involve the motion of up to 100 million “stellar particles” that mimic gravitational and astrophysical forces which shape them into natural spiral structure. The research team from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics are excited about these conclusions and report the simulations may hold the essential clues of how spiral arms are formed.

“We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” says UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist.

“The spiral arms are self-perpetuating, persistent, and surprisingly long lived,” adds Vogelsberger.

When it comes to spiral structure, it’s probably the most widely occurring of universal shapes. Our own Milky Way galaxy is considered to be a spiral galaxy and around 70% of the galaxies near to us are also spiral structured. When we think in a broader sense, just how many things take on this common formation? Whisking up dust with a broom causes particles to swirl into a spiral shape… draining water invokes a swirling pattern… weather formations go spiral. It’s a universal happening and it happens for a reason. Apparently that reason is gravity and something to perturb it. In the case of a galaxy, it’s a giant molecular cloud – the star-forming regions. Introduced into the simulation, the clouds, says D’Onghia, a UW-Madison professor of astronomy, act as “perturbers” and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely.

“We find they are forming spiral arms,” explains D’Onghia. “Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.”



So, what of companion galaxies? Can spiral structure be caused by proximity? The new research also takes that into account and models for “stand alone” galaxies as well. However, that’s not all the study included. According to Vogelsberger and Hernquist, the new computer-generated simulations are focusing on clarifying observational data. They are taking a closer look at the high-density molecular clouds and the “gravitationally induced holes in space” which act as “the mechanisms that drive the formation of the characteristic arms of spiral galaxies.”

Until then, we know spiral structure isn’t just a chance happening and – to wrap things up – it’s probably the most common form of galaxy in our Universe.

Original Story Source: Harvard-Smithsonian Center for Astrophysics.

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Building the Alpha Magnetic Spectrometer: 16 Years in 3 Minutes
Universe Today, Nancy Atkinson | April 3, 2013

The Alpha Magnetic Spectrometer on board the International Space Station released its first results today (read about them here) after having been in space since 2011. But this particle physics experiment was years in the making. In just 3 minutes, you can watch 16 years of building, preparing, launching and activating this detector.

Below, watch another video from NASA that provides an overview of the AMS:




^ Endeavour approaches the International Space Station. Visible is the Alpha Magnetic Spectrometer in the payload bay. Credit: NASA

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Tantalizing Hints of WIMPy Dark Matter | Phil Plait
Bad Astronomy | Wednesday, April 3, 2013, at 12:30 PM


^ The Alpha Magnetic Spectrometer on board the space station. Image credit: NASA/CERN

[UPDATE (Apr. 3, 2013): Over at the Starts With A Bang blog, Ethan Siegel is substantively more suspicious of the results I write about below, saying that the press release (upon which I based a large part of this post) is incorrect, even misleading. He includes results from some other experiments which are interesting and which run counter to the AMS-2 results, including some from Fermi about which I was unaware. I'll be very interested to hear more expert opinions about this as time goes on.]

New results from an important scientific experiment aboard the International Space Station have strengthened the case for dark matter. Interestingly, too, the results point toward what dark matter might actually be—and that’s one of the biggest goals in physics right now.

The experiment is called the Alpha Magnetic Spectrometer-2, and what it does is measure cosmic rays. This is a generic term given to subatomic particles that zip around the cosmos. They come from the Sun, they come from exploding stars, they come from black holes…and they may come from dark matter (more on that in just a sec). Cosmic rays can be electrons, protons, helium nuclei, even antimatter—real particles that are like matter but have an opposite charge. So an antielectron (called a positron) is exactly like an electron but has a positive charge. An antiproton (sadly, not called a negatron, though it really should be) is just like a proton but has a negative charge, and so on.

< The Bullet Cluster, what many astronomers consider to be the smoking gun of evidence for dark matter. Click to enzwickynate. Image credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

So all these particles are whizzing around in space, and AMS-2 measures them. It can tell what kind of particle hits it, and how much energy it has, too. The energy of the particle is related to what made it, and what it’s done since that time. Some particles are made in low energy events, some in high energy events, and all of them have had to travel across space, dealing with the galaxy’s magnetic field as well. By the time it gets to Earth, the energy, direction, and type of particle all have their piece of the tale to tell.

Now, we know that dark matter exists. We’ve had evidence of it for a century now, both in the movement of galaxies as they orbit each other, and the way galaxies like ours rotate. Both indicate there is way more mass in galaxies than we can see—hence the term dark matter. Since that time, lots of other independent lines of evidence point toward dark matter’s existence as well, including the newly-announced results from Planck (I’ll note there are alternative ideas to dark matter, but even the best don’t do very well to explain what we see). The maddening thing is we don’t know what it is. We know what it isn’t: rogue planets, cold gas clouds, dead stars, black holes, and such. Any of those would give away their identities in other ways. We’ve been able to eliminate all the normal types of candidates.

All that’s left is some form of exotic subatomic particle. The best candidate is called a WIMP, for weakly interacting massive particle. A WIMP is a weird form of matter that doesn’t interact well with normal matter (which is why it’s hard to detect) but still has some mass. Over cosmic distances, the amount of this stuff adds up to give us the effects we see from dark matter.

One property of WIMPs is that if they come in contact with each other, they explode into energy and simpler subatomic particles (this process is called self-annihilation). It’s similar to what happens if an electron and positron come in contact. Bang! They turn into energy, à la E=mc2. In the case of WIMPs, through some complicated subatomic processes, one of the results is the creation of electrons and positrons.

AMS-2 is designed to look for all this. In its first 18 months of operation, it detected 25 billion cosmic ray events, about seven million of which where electrons and positrons. After sifting through all that, what it found was intriguing: an excess of positrons over what is expected from background radiation (the amount we expect to see from other, more normal sources). This has been seen before in previous experiments, but not to the accuracy AMS-2 has seen.


^ The excess fraction of positrons seen versus the energy of the particles. The data fit well with—but don't yet confirm—the idea that dark matter is WIMPy. Image credit: CERN

Not only that, but it could measure that positron excess compared to the energy of each particle. That’s important because different models predict different amounts of positrons depending on the energy of the positron itself. What AMS-2 found is that at low energies the excess is about 10 percent. At slightly higher energies it drops to 5 percent or so, then rises again at higher energies still:

This is very close to what’s predicted for dark matter WIMPs. That’s exciting! But it’s not conclusive. It could still be due to some other source, like pulsars—rapidly rotating super-dense balls of neutrons created when massive stars explode. These create particles furiously, and the signal is very much like that of WIMPs.

The good news is AMS-2 is not finished yet. These new results are milestone markers, not the final product. Over the next few years more and more data will be collected, and each positron seen adds to the total, making the data cleaner. Eventually, it’s hoped, the detections will be so accurate we’ll be able to say for sure whether these extra positrons are from dark matter or not.

In the meantime, other searches continue. The Large Hadron Collider in Geneva can also look for dark matter, and preparations have begun to improve its ability to do so. Other experiments are working toward this goal as well.

So I’m excited but cautious about this announcement. It shows pretty clearly the positron excess is real, and shows quite well that AMS-2 is up to the task of looking for dark matter. I’m glad to hear it; AMS-2 has something of an, um, interesting history (see the bottom of this article for more, as well as an article I wrote when AMS-2 was approved for flight) so at least now we can be glad it can do the job it was built to do.

And it shows once again that we stand at an amazing point in history, where we can for the first time take the measure of the Universe and truly understand its mechanisms. The overwhelming majority of the Universe is invisible to our eyes, so we have to build machines as proxies to look for us. But those are just extensions of ourselves, so really it’s through our own imagination and curiosity that we query the Universe, and it’s through science that we get the answers.

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Highlights mine.

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Space Station Detector Finds Extra Antimatter in Space, Maybe Dark Matter
Universe Today, Nancy Atkinson | April 3, 2013


^ From its vantage point about 400 km above Earth on the International Space Station, the Alpha Magnetic Spectrometer collects data from primordial cosmic rays from space. Credit: NASA

The first results from the largest and most complex scientific instrument on board the International Space Station has provided tantalizing hints of nature’s best-kept particle secrets, but a definitive signal for dark matter remains elusive. While the AMS has spotted millions of particles of antimatter – with an anomalous spike in positrons — the researchers can’t yet rule out other explanations, such as nearby pulsars.

“These observations show the existence of new physical phenomena,” said AMS principal investigator Samuel Ting,” and whether from a particle physics or astrophysical origin requires more data. Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin.”


^ The positron fraction measured by AMS. Credit: CERN.

The AMS was brought to the ISS in 2011 during the final flight of space shuttle Endeavour, the penultimate shuttle flight. The $2 billion experiment examines ten thousand cosmic-ray hits every minute, searching for clues into the fundamental nature of matter.

During the first 18 months of operation, the AMS collected of 25 billion events. It found an anomalous excess of positrons in the cosmic ray flux — 6.8 million are electrons or their antimatter counterpart, positrons.

The AMS found the ratio of positrons to electrons goes up at energies between 10 and 350 gigaelectronvolts, but Ting and his team said the rise is not sharp enough to conclusively attribute it to dark matter collisions. But they also found that the signal looks the same across all space, which would be expected if the signal was due to dark matter – the mysterious stuff that is thought to hold galaxies together and give the Universe its structure.

Additionally, the energies of these positrons suggest they might have been created when particles of dark matter collided and destroyed each other.


^ A screenshot from Ting’s presentation at CERN on April 3, 2013. ‘It took us 18 years to complete this result,’ Ting said.

The AMS results are consistent with the findings of previous telescopes, like the Fermi and PAMELA gamma-ray instruments, which also saw a similar rise, but Ting said the AMS results are more precise.

The results released today do not include the last 3 months of data, which have not yet been processed.

“As the most precise measurement of the cosmic ray positron flux to date, these results show clearly the power and capabilities of the AMS detector,” Ting said.

Cosmic rays are charged high-energy particles that permeate space. An excess of antimatter within the cosmic ray flux was first observed around two decades ago. The origin of the excess, however, remains unexplained. One possibility, predicted by a theory known as supersymmetry, is that positrons could be produced when two particles of dark matter collide and annihilate. Ting said that over the coming years, AMS will further refine the measurement’s precision, and clarify the behavior of the positron fraction at energies above 250 GeV.

Although having the AMS in space and away from Earth’s atmosphere – allowing the instruments to receive a constant barrage of high-energy particles — during the press briefing, Ting explained the difficulties of operating the AMS in space. “You can’t send a student to go out and fix it,” he quipped, but also added that the ISS’s solar arrays and the departure and arrival of the various spacecraft can have an effect on thermal fluctuations the sensitive equipment might detect. “You need to monitor and correct the data constantly or you are not getting accurate results,” he said.

Despite recording over 30 billion cosmic rays since AMS-2 was installed on the International Space Station in 2011, the Ting said the findings released today are based on only 10% of the readings the instrument will deliver over its lifetime.

Asked how much time he needs to explore the anomalous readings, Ting just said, “Slowly.” However, Ting will reportedly provide an update in July at the International Cosmic Ray Conference.

More info: CERN press release, the team’s paper: First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV

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Astrophotos: We Have Liftoff from the Sun!
Universe Today, Nancy Atkinson | April 3, 2013


^ A large prominence from the Sun, on April 1, 2013. Credit and copyright: Paul Andrew.

Here are three images showing large prominences recently lifting off from the Sun’s surface. Solar prominences are sheets or arcs of luminous gas emanating from the Sun’s surface. They can loop hundreds of thousands of kilometers into space. In the image below by noted Australian amatuer Monty Leventhal, he estimates the prominence he captured stretches 233,000 km! Against the Sun, prominences appear dark, but against the sky they appear brighter. Prominences are held above the Sun’s surface by strong magnetic fields and can sometimes last for long periods of time.

See more and varied views below:


^ A negative image of the Sun and large prominences on March 31, 2013. Credit and copyright: César Cantú.


^ This digital filtergram shows an active prominence on the SE limb of the Sun, stretching across for approximately 233,000 km on March 27, 2013. Credit and copyright: Monty Leventhal.

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M64: The Black Eye Galaxy
Image Credit & Copyright: Martin Pugh

Explanation: This beautiful, bright, spiral galaxy is Messier 64, often called the Black Eye Galaxy or the Sleeping Beauty Galaxy for its heavy-lidded appearance in telescopic views. M64 is about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. In fact, the Red Eye Galaxy might also be an appropriate moniker in this colorful composition of narrow and wideband images. The enormous dust clouds obscuring the near-side of M64’s central region are laced with the telltale reddish glow of hydrogen associated with star forming regions. But they are not this galaxy’s only peculiar feature. Observations show that M64 is actually composed of two concentric, counter-rotating systems of stars, one in the inner 3,000 light-years and another extending to about 40,000 light-years and rotating in the opposite direction. The dusty eye and bizarre rotation is likely the result of a billion year old merger of two different galaxies.