The scale of things

[Hammer of Los]

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Thanks once again Allegro.

You may know you make me chuckle.

Man oh man.

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A Colorful Cloud Hints at a Very Violent Origin | Phil Plait
Bad Astronomy | Tuesday, 26FEB13

Halfway across the galaxy sits a most unusual object. Given the mundane name W49B, you might not think much of it, but once you see its portrait, you’ll change your mind.


^ The supernova remnant W49B, formed a thousand years ago in the titanic explosion of a massive star. Click to chandrasekharenate. Image credit: X-ray: NASA/CXC/MIT/L.Lopez et al.; Infrared: Palomar; Radio: NSF/NRAO/VLA

This image, a combination of pictures taken in X-rays, infrared, and radio waves, is, obviously, very pretty. But it tells an interesting tale, one I haven’t been seeing in the press release or write-ups so far.

W49B is a supernova remnant, the expanding gas blasted out from an exploding star. Ignoring how long it took the light to reach us, the remnant is only about a thousand years old, making it roughly the same age as the more famous Crab nebula. The structure of W49B, though, is very odd.

The star that exploded probably had a mass of 25 times that of the Sun, which is pretty hefty, putting it in the top tier of stars in the galaxy. Not many get that big. As it neared the end of its life, though, it shed a lot of its mass (though not all) through a super-dense wind of material, like a solar wind turned up to 11 (or 11 million). Over the next few hundred thousand years, it actually lost a majority of its mass this way.

Eventually, though, the end came. The core of the star ran out of fuel, which it was using to generate energy, which in turn was what was holding the star up. When the fuel ran out, it was like a stool with the legs kicked out form under it: The core collapsed, plunging down into itself at huge speeds. As it dropped down, the material started to rotate rapidly, like (to use a cliché) an ice skater bringing her arms in and increasing her spin.

At this point we’re not precisely sure what happens, but the thinking goes like this. The material in the very center of the collapsed core formed a black hole. But material just outside the hole probably formed a dense disk of material whirling around the black hole at nearly the speed of light. This whipped up huge amounts of heat and magnetism, and through methods not entirely understood formed a pair of beams, like lighthouse beams, blasting outward from the poles of the disk. These screamed out, boring right through the material still falling inward from the star.

Now I want to take a moment to let that sink in. Imagine you are just above the core of the star. Beneath you, in a millisecond, poof! The core is gone, collapsed down into a tiny point a million kilometers below you. Looking up, you see an octillion tons of superheated matter crashing down onto your head.

Got that apocalyptic picture clear? Yes? Now look down again: Those two beams of matter and energy come screaming out of the collapsed core at nearly the speed of light with enough power behind them to bore through that infalling matter like a megawatt laser through a warm patty of butter.

So we’re talking fairly serious events here.

And this is when what was left of the star exploded. All that remained after that was a black hole in the center, and material moving violently outward at high speed. That material, though, was not expanding in a sphere, but instead was moving preferentially along the direction of those beams, up and down, if you will.

Now, a thousand years later, we see the effects. Along the middle of the remnant you can see a blue streak. In the false color image, those are X-rays from iron, created in the blast itself. You can see how elongated that structure is, not spherical at all. That’s a dead giveaway this explosion was asymmetric, that is, not spherical.

This type of supernova explosion is called a Type Ic. Technically, that means it doesn’t appear to have any hydrogen or helium in it, which is rare. But it happens when a very massive star sheds its outer layers shortly before exploding; all the hydrogen and helium were blown away before the explosion. By the time the star explodes, that material has moved well out from the star.


^ The three-ring circus of Supernova
1987A. Click to embiggen. Image
credit: Dr. Christopher Burrows,
ESA/STScI and NASABut it’s still there. Eventually, the matter blasting out from the explosion slams into the previously-shed outer layers of the star. We see that in the above image as well. The yellow and pink material is where the expanding debris is colliding with the slower moving gas, hitting it so violently that powerful shock waves are formed.

I’m fascinated by the shape of that outer region of this object. You can see that it’s barrel-shaped, tilted lower left to upper right. But there also appear to be rings of material there, perpendicular to the barrel. I’ve seen that before: Supernova 1987A was a very well-studied exploding star; I got my PhD examining it with Hubble. It has a three-ring system around it like an hourglass. How those rings formed is still debated, but we know they were created from a powerful wind of gas from the star millennia before it exploded. When the star did explode, it lit them up like a flashbulb, making the gas glow.

Was W49B once a multiply-ringed structure similar to SN1987A? I suspect it’s possible, judging from the image. There are several rings of material visible in the Chandra image. And as it happens, the expanding debris from SN1987A is also highly elongated, suggesting a similar explosion as W49B. You can see that in this sequence of Hubble observation over a decade, showing the debris expanding inside the dense ring of gas (the middle of the three rings):


^ The debris from the supernova 1987A expands inside a ring of older material, seen in observations by Hubble taken over nearly a decade. Image credit: NASA/ESA, P. Challis, R. Kirshner (Harvard-Smithsonian Center for Astrophysics) and B. Sugerman (STScI)

There are differences, mostly that the debris from the SN1987A explosion is apparently expanding preferentially in the same plane as the ring, which is not at all what I would expect. But SN1987A was always a weirdo, and you have to be careful when comparing one supernova to another in this case.

Also, very intriguingly, there is no clear leftover object in the center of W49B, no obvious highly dense neutron star (which would be very obvious in X-rays, even after a millennium). We think therefore it formed a black hole, which fits with the scenario I described above. But the same thing is true for SN1987A! We’ve been searching for years, but no neutron star is evident. It’s possible a black hole formed there as well. It seems unlikely, because the effects of a black hole forming should have been seen when SN1987A went off, but in my opinion that’s not nearly as weird as forming a neutron star that we can’t seem to find. Either way, like I said, SN1987A was bizarre no matter how you slice it.

But so is W49B. If it formed a black hole, it’s one of the youngest in the Milky Way, a whippersnapper at a thousand years young. But to me, that’s not the interesting story. What gets me is how the supernova exploded in the first place, with the spinning and the disk and the jets and the rings. That’s the real story here.

Plus one other thing, that is. When a black hole forms from an exploding star, and you get that spinning disk and high-energy pair of jets, you also get a tremendous flare of gamma rays, super-high-energy light. We call these events gamma-ray bursts, and they are the most energetic explosions in the Universe second only to the Big Bang itself. Was W490B such a burst? It turns out I’m not the only one to wonder about that. While we see GRBs all over the Universe, they tend to be very far away, which may mean they happened more when the Universe was young, billions of years ago. Yet there is some evidence they still occur today.

Perhaps that’s the biggest story here. As usual, with astronomy, when you observe a single object there is more than one tale to tell. But they’re all amazing, and all well worth hearing.

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Superfast Spinning Black Hole Tearing Up Space at Nearly the Speed of Light | Phil Plait
Bad Astronomy | Wednesday, 27FEB13


^ Artist’s illustration of matter falling into a black hole, with X-rays blasting out from the very center. Click to chandrasekharenate. Image credit: NASA/JPL-Caltech

Black holes are the Universe’s ultimate garbage disposals: Stuff falls in, and never gets back out. It can’t. To get out, you’d have to travel faster than the speed of light, which (as far as we know) is impossible.

Black holes grow by consuming matter, and in the centers of galaxies they can grow to huge size. In the gorgeous barred spiral galaxy NGC 1365 (shown below), there’s one lurking in the core that has about two million times as much mass as our Sun. Not only that, it is actively gobbling down matter, and that allows us to measure some interesting properties of this cosmic monster, including its spin. Astronomers observed NGC 1365’s black hole using the NuSTAR and XMM-Newton observatories, and were surprised to find out it’s spinning so fast that the outer edge is moving at very nearly the speed of light!

This takes some explaining. Hang on tightly, and for your own safety please keep your arms inside the blog post at all times.

Black holes are confusing, but the bottom line is that they are such highly-concentrated massive objects that their escape velocity is faster than light—I wrote a somewhat more lengthier explanation on the old blog here and here if you want more details. Once something falls in, it cannot get out, but some of the properties of that material remain: specifically mass, spin, and charge. That last bit is literally electrical charge, like how an electron has a negative charge. Physically it’s very interesting, but in practical terms it hardly comes up, so we can ignore it here.

Mass is the critical one, because the more mass a black hole has, the bigger it gets and the stronger its gravity is as well. But spin is important too. Look at, for example, a black hole forming via the collapse of a star’s core when the outer layers explode in a supernova. The core is spinning since the star rotates. As the core collapses, that spin rate increases, in much the same way a skater can increase his or her spin by bringing their arms in close to their body. This is called conservation of angular momentum; objects spinning tend to stay spinning due to momentum, just like any object in motion tends to stay in motion due to momentum. The total angular momentum depends on the object’s size and rate of spin. Increase one and the other must decrease; if you make something smaller it’ll spin faster.

So by the time the core of our doomed star collapses all the way down to a back hole, the spin can be ferociously large.

But there’s more. If there is material around the black hole falling in it can change the spin as well. If material fell straight into the black hole, the spin wouldn’t change much (if anything it would decrease, because the added mass makes the black hole bigger, so, like the skater throwing out his/her arms, the spin slows). But if that material comes in at a slight angle, it can actually add to the spin of the black hole, increasing its angular momentum. That gives a kick to the spin rate, bumping it up.


^ The massive spiral galaxy NGC 1365 has a huge black hole in its heart, spinning at nearly the speed of light. Click to galactinate. Image credit: ESO/P. Grosbøl

And that brings us back to NGC 1365, located about 60 million light years from Earth. Astronomers used NuSTAR to look at X-rays pouring out of material falling into the black hole there. As that material falls in it heats up to millions of degrees, blasting out X-rays that are easily bright enough to see from Earth with the right equipment. Careful observations allowed astronomers to see these X-rays coming from matter just before it reached The Point Of No Return, at a position called the Innermost Stable Circular Orbit, or ISCO. If it gets any closer, blooop! It falls in, and it’s gone.

As the material swirls around the black hole, it emits X-rays at a very specific energy—think of it as a color. But as it orbits that color gets smeared out due to the Doppler effect. The amount of smearing indicates how fast the material is moving, and that in turn can tell astronomers how fast the black hole is spinning. This can be complicated by the presence of dense clouds of material farther out from the black hole that absorb X-rays and mess up our observations. The new data from NuSTAR allowed astronomers to show that the smearing seen is definitely due to rotation and not obscuration, unambiguously revealing the black hole’s tremendous spin: just a hair below the speed of light!

Most black holes spin far slower than that, so something ramped this hole’s spin way up. One possibility, as I mentioned above, is material falling in over time. Another is that it ate one or more other black holes, which is creepy but possible. Galaxies collide, and when they do their central black holes can merge, growing larger. If the geometry is just right, this can create a single black hole with more spin. Due this a few times, and you can spin one up to fantastic speeds.

I’ll note that NGC 1365 is a massive galaxy, easily twice as large as the Milky Way (an we’re one of the biggest galaxies in the Universe). That’s exactly what you’d expect from a galaxy that’s spent a lifetime eating other ones. Cosmic cannibals grow fat when the hunting’s good.

This is a pretty amazing finding by the NuSTAR astronomers. It shows that extremely detailed X-rays observations are possible; something that’s very difficult and painstaking to do. It also demonstrates that we can take a pretty close look at black holes and tease out details that were previously not possible to see. This in turn means we can test a lot of the hypotheses we have about these monsters and improve our understanding of them.

By themselves, black holes are invisible, dark, and nearly impossible to observe. But they’re sloppy eaters, and this betrays many of their secrets. Even from 600 million trillion kilometers away.

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Weeks ago, while researching sonifications, I found the following Sound files of eight Kepler stars listed by Kepler Input Catalog number. These three are the first of the eight sound files.

KIC 3866709 mp3, 203 KB
KIC 5775232 mp3, 71.0 KB
KIC 7671081 mp3, 203 KB

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If you’d like to listen to the four mp3’s mentioned in the following NYT article, they are embedded to the left of the text on the page of origin. Recent posts in this thread are preferred to redundancies in this 2011 writing. Highlights mine.

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Listening to the Stars
The New York Times, DENNIS OVERBYE | 30JAN11

The search for distant planets starts with the vibrations of their stars, and in those vibrations lies a kind of music.

< The heart-shaped vibrations for the star KIC12253350.

“We only know the planet as well as we know the star,” said Natalie Batalha, an astronomer from San Jose State University who works on NASA’s planet-searching satellite Kepler. To that end, Kepler listens to the internal vibrations of stars, gleaning crucial information on their size and structure.

By speeding up this data and transforming it into sound waves, Kepler’s astronomers have produced a sort of iTunes sampler of the cosmos, individual stars banging and whistling.

“Some of these are music only the Borg could love,” said Jon Jenkins, a Kepler data analyst from the SETI Institute in Mountain View, Calif., referring to the cybernetic foes from the “Star Trek” series. Dr. Jenkins made the recordings presented here.

Kepler monitors the light of 156,000 stars, checking for dips in intensity caused when their planets, if they have any, pass in front of them. It also records high-frequency variations in stars’ light caused by vibrations or “starquakes” in the stars themselves, from which astronomers practicing the science of asteroseismology can deduce the age and size of the star.

By knowing how big the star really is, and the dips in light from the planetary crossings, astronomers can measure the exact size of any planet.

In these audio clips, several weeks’ worth of Kepler measurements of a star have been compressed into a few seconds.

Kepler 10b is the first rocky planet to be discovered by Kepler. The first audio contains only the vibrations of Kepler 10b’s star. The next audio clip has the sound of the planet going by as a “wump wump wump.”

KIC1268220 is an eclipsing binary, in which a pair of stars pass in front of each other, producing a bass thumping of eclipses along with a “whistling forest” of stellar vibrations, in the words of Dr. Jenkins.

KIC12253350 is an unusual star. On a graph, its oscillations follow a heart-shaped envelope. The Kepler astrophysicists do not understand why, but they liked it so much that they put the heart-shaped oscillations on a T-shirt with a quotation about the cosmos by Carl Sagan: “For such small creatures such as we the vastness is bearable only through love.”

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Cosmic Rays and Exploding Stars
Universe Today, Nancy Atkinson | 28FEB13

Scientists have know about cosmic rays for a century. But these high-energy subatomic particles, which stream through space at nearly the speed of light and crash into the Earth’s upper atmosphere, have been mostly a mystery. The primary reason: researchers have been unable to tell where they come from, or how they’re born. But new research has shed new light on the origins of cosmic rays: supernovae. (Read our article about this discovery.)

Today, Thursday, Feb. 28,at 20:00-20:30 UTC (12:00-12:30 p.m. PST, 3:00 pm EST) Dr. Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) will answer questions from the web. He led the research team that was able to track gamma rays — the most energetic form of electromagnetic radiation, or light — back to the remnants of supernova explosions, using the Fermi Gamma Ray Telescope. The finding offers the first astrophysical evidence for how cosmic rays are produced, as well as where they are generated: in the shock waves that emanate from an exploded star.

Science writer Bruce Lieberman will moderate the webcast and ask your questions about the new data on cosmic rays. Questions can be submitted via Twitter (use the hashtag #KavliAstro) or email (info@kavlifoundation.org).

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Looking Down Mount Etna’s Throat | Phil Plait
Bad Astronomy | Saturday, 02MAR13

The tallest active volcano in Europe is at it again. Sicily’s Mount Etna, a 3300-meter (2 mile) high mountain, is always active. Well, almost always: It’s been fairly quiet for nearly a year, but on Feb. 19 decided it was time to remind folks that it’s a force with which to be reckoned. It started blowing out ash, lava, lahars (mud flows), and pyroclastic flows—avalanches of burning hot ash, rock, and gas.

On board the International Space Station, the ash plume was easily visible as the astronauts flew just to the north of it:


^ Mount Etna, photographed by astronaut Chris Hadfield. Click to haphaestenate. Image credit: NASA

You can see the ash plume flowing east (left) over the coast of Sicily. The plume looks white, which means there’s probably lots of steam there too. To give you a sense of scale, the volcano is about 15 or so kilometers (9 miles) from the coast.

That shot was taken by Chris Hadfield. His fellow astronaut Kevin Ford took the following picture, when the ISS was more directly over the volcano:


^ Mount Etna, this time by astronaut Kevin Ford. Click to embiggen. Image credit: NASA

Looks like the wind had died down a bit for this one. This series of recent eruptions have been pretty violent, with seven large paroxysms in just over a week. The first were from the New Southeast Crater (Etna has a half dozen major craters), and were followed by eruptions from the Bocca Nuova Crater. Not only that, but apparently there has been activity seen in the saddle between the two craters, so it looks like at least one new fissure has opened up.

Etna is potentially dangerous, but hasn’t hit a major population center in nearly a century (though it’s come close). Still, like any giant of its kind, it bears close watch. Size isn’t what’s critical—it’s the type of activity that makes a volcano dangerous, including the locations of the nearby populations—but bear in mind this volcano is more than twice the height of Vesuvius, and the entire cone is roughly 40 km (25 miles) across. It’s been chosen as a Decade Volcano, one that is worthy of study due to its violent nature and potential for mayhem.

I’d imagine pictures from above are helpful for just this sort of thing. As we put more and more eyes in space, ones that look down, we’ll be seeing more amazing and important observations of volcanoes. Perhaps it’s my own fascination with astronomical dangers—Sun storms and asteroids and black holes, oh my!—but I love these pictures of more terrestrial dangers, too.

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Rare Eclipsing Binary Stars Provide Refined Measurements in the Universe
Universe Today, Nancy Atkinson | 06MAR13


^ The Large Magellanic Cloud, a neighboring galaxy to the Milky Way. The positions of eight faint and rare cool eclipsing binary stars are marked with crosses. Credit: ESO/R. Gendler

Precise observations of a rare class of binary stars have now allowed a team of astronomers to improve the measurement of the distance to one of our neighboring galaxies, the Large Magellanic Cloud, and in the process, refine the Hubble Constant, an astronomical calculation that helps measure the expansion of the Universe. The astronomers say this is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate.

The team used telescopes at ESO’s La Silla Observatory in Chile, the Las Campanas Observatory also in Chile and two from the University of Hawaii at Manoa, and the Las Campanas Observatoryas well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.

The new distance to the LMC is 163,000 light-years. The LMC is not the closest galaxy to the Milky Way; Canis Major Dwarf Galaxy, discovered in 2003 is considered the actual nearest neighbor at 42,000 light-years from the Galactic Center, and the Sagittarius Dwarf Elliptical Galaxy is about 50,000 light-years from the core of the Milky Way.

Astronomers ascertain the scale of the universe by first measuring the distances to close-by objects and then using them as standard candles — objects of known brightness — to pin down distances farther and farther out in the universe.

Up to now, finding an accurate distance to the LMC has proved elusive. Stars in that galaxy are used to fix the distance scale for more remote galaxies, so it is crucially important.

“This is a true milestone in modern astronomy. Because we know the distance to our nearest neighbor galaxy so precisely, we can now determine the rate at which the universe is expanding — the Hubble constant — with much better accuracy. This will allow us to investigate the physical nature of the enigmatic dark energy, the cause of the accelerated expansion of the universe,” says Dr. Rolf-Peter Kudritzki, an astronomer at the University of Hawaii’s Institute for Astronomy.

“For extragalactic astronomers,” said Dr. Fabio Bresolin, also from UH, “the distance to the Large Magellanic Cloud represents a fundamental yardstick with which the whole universe can be measured. Obtaining an accurate value for it has been a major challenge for generations of scientists. Our team has overcome the difficulties using an exquisitely accurate method, and is already working to cut the small remaining uncertainty by half in the next few years.”

The team worked out the distance to the LMC by observing rare close pairs of stars known as eclipsing binaries. As these stars orbit each other, they pass in front of each other. When this happens, as seen from Earth, the total brightness drops, both when one star passes in front of the other and, by a different amount, when it passes behind.

Read another recent article about studies that used eclipsing binaries to study the Light-travel-time Effect

By tracking these changes in brightness very carefully, and also measuring the stars’ orbital speeds, it is possible to work out how big the stars are, what their masses are, and other information about their orbits. When this is combined with careful measurements of the total brightness and colors of the stars, remarkably accurate distances can be found.

“Now we have solved this problem by demonstrably having a result accurate to 2%,” states Wolfgang Gieren (Universidad de Concepción, Chile) and one of the leaders of the team.

Sources: University of Hawaii, ESO

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Black Holes, Fermi Bubbles and the Milky Way
Universe Today, Tammy Plotner | 06MAR13

Deep at the heart of our galaxy lurks a black hole. This isn’t exciting news, but neither is it a very exciting place. Or is it? While all might be quiet on the western front now, there may be evidence that our galactic center was once home to some pretty impressive activity – activity which may have included multiple collision events and mergers of black holes as it gorged on a satellite galaxies. Thanks to new insights from a pair of assistant professors, Kelly Holley-Bockelmann at Vanderbilt and Tamara Bogdanovic at Georgia Institute of Technology, we have more evidence which points to the Milky Way’s incredibly active past.

“Tamara and I had just attended an astronomy conference in Aspen, Colorado, where several of these new observations were announced,” said Holley-Bockelmann. “It was January 2010 and a snow storm had closed the airport. We decided to rent a car to drive to Denver. As we drove through the storm, we pieced together the clues from the conference and realized that a single catastrophic event – the collision between two black holes about 10 million years ago – could explain all the new evidence.”

Now, imagine a night sky illuminated by a huge nebula, one that covers half the celestial sphere. This isn’t a dream, it’s a reality. These massive lobes of high-energy radiation are known as Fermi bubbles and they cover a region some 30,000 light years on either side of the Milky Way’s core. While we can’t observe them directly in visible light, these particles are moving along at close to 186,000 miles per second and glowing in x-ray and gamma ray wavelengths.

According to Fulai Guo and William G. Mathews of the University of California at Santa Cruz: “The Fermi bubbles provide plausible evidence for a recent powerful AGN jet activity in our Galaxy, shedding new insights into the origin of the halo CR population and the channel through which massive black holes in disk galaxies release feedback energy during their growth.”

However, our galactic center is home to more than just some incredible bubbles – it’s the location of three of the most massive clusters of young stars within the Milky Way’s realm. Known as the Central, Arches and Quintuplet clusters, each grouping houses several hundred hot, young stars which dwarf the Sun. They will live short, bright, violent lives… burning out in a scant few million years. Because they live fast and die young, these cluster stars must have formed within recent years during a eruption of star formation near the galactic center – another clue to this cosmic puzzle.

“Because of their high mass, and apparent top-heavy IMF, the Galactic Center clusters contain some of the most massive stars in the Galaxy. This is important, as massive stars are key ingredients and probes of astrophysical phenomena on all size and distance scales, from individual star formation sites, such as Orion, to the early Universe during the age of reionization when the first stars were born. As ingredients, they control the dynamical and chemical evolution of their local environs and individual galaxies through their influence on the energetics and composition of the interstellar medium.” says Donald F. Figer. “They likely play an important role in the early evolution of the first galaxies, and there is evidence that they are the progenitors of the most energetic explosions in the Universe, seen as gamma ray bursts. As probes, they define the upper limits of the star formation process and their presence likely ends further formation of nearby lower mass stars. They are also prominent output products of galactic mergers, starburst galaxies, and active galactic nuclei.”

To deepen the mystery, take a closer look at our central black hole. It spans about 40 light seconds in diameter and weighs about four million solar masses. According to what we know, this should produce intensive gravitational tides – ones that should be sucking in the surroundings. So how is it that astronomers have uncovered groups of new, bright stars closer than 3 light years from the event horizon? Of course, they could be on their way to oblivion, but the data shows these stars seem to have formed there. That’s quite a feat considering it would require a molecular cloud 10,000 times more dense than the one located at our galactic center! Shouldn’t there also be old stars located there as well? The answer is yes, there should be… but there are far fewer than what we can observe and what current theoretical models predict.

Holley-Bockelmann wasn’t about to let the problem rest. When she returned home, she enlisted the aid of Vanderbilt graduate student Meagan Lang to help solve the riddle. Then they recruited Pau Amaro-Seoane from the Max Planck Institute for Gravitational Physics in Germany, Alberto Sesana from the Institut de Ciències de l’Espai in Spain, and Vanderbilt Research Assistant Professor Manodeep Sinha to help. With so many bright minds to help solve this riddle, they soon arrived at a plausible explanation – one which matches observations and allows for testable predictions.

According to their theory, a Milky Way satellite galaxy began migrating towards our core. As it merged with our galaxy, its mass was torn away, leaving only its black hole and a small collection of gravitationally bound stars. After several million years, this “leftover” eventually reached the galactic center and the black holes began to merge. As the smaller black hole was swirled around the larger, it plowed up huge furrows of gas and dust, pushing it into the larger black hole and created the Fermi bubbles. The dueling gravitational forces weren’t gentle… these intense tides were quite capable of compressing the molecular clouds surrounding the core into the density required to produce fresh, young stars. Perhaps the very young stars we now observe at the galactic center?

However, there’s more to the picture than meets the eye. This same plowing of the cosmic turf would have also pushed out existing older stars from the vicinity of the massive central black hole. It’s a scene which fits current models where a black hole merger flings stars out into the galaxy at hyper velocities… a scene which fits the observation of a lack of old stars at the boundaries of our supermassive black hole.

“The gravitational pull of the satellite galaxy’s black hole could have carved nearly 1,000 stars out of the galactic centre,” said Bogdanovic. “Those stars should still be racing through space, about 10,000 light years away from their original orbits.”

Can any of this be proved? The answer is yes. Thanks to large scale surveys like the Sloan Digital Sky Survey, we should be able to pinpoint stars moving at a higher velocity than stars which haven’t been subjected to a similar interaction. If astronomers like Holley-Bockelmann and Bogdanovic look at the hard evidence, they are likely to discover a credible number of high velocity stars which will validate their Milky Way merger model.

Or are they just blowing bubbles?

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^ Dark Lightning | ScienceCasts

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Reflection and Emission | Phil Plait
Bad Astronomy | 08MAR13

Near the top of the constellation Orion lies a star that you might easily pass over scanning the heavens. It’s just barely visible to the naked eye on a dark night, another white spark among thousands.

But this star, called HD 34989 (among other alphanumeric designations) is special. For one thing, it’s massive, probably 10 times the mass of our Sun. It’s also incredibly luminous, shining 15,000 times brighter than the Sun. Put that in the center of our solar system, and the global warming we’re experiencing now would seem like the deep freeze. Happily, it’s over a thousand light years away.

But in that location, it sits in the middle of a fairly large cloud of gas and dust, too. Because the star is so bright, it profoundly affects that nebula, as you can see for yourself in this exquisite photograph by Adam Block:


^ Photo of the nebula Sharpless 2-236. Click to ennebulenate. Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Adam took this picture with the 0.8 meter (32 inch) Schulman Telescope (RCOS) on Mt. Lemmon in Arizona. HD 34989 is pretty obvious; it’s the intensely bright star in the middle. The gas and dust are obvious, too…but what’s the deal with those colors? Why is some of the gas red, and some blue?

I’m glad you asked. Let us reflect on this question.

There are two ways for an object to be visible. One is if it reflects light from a nearby source (which is how we see the vast majority of objects around us), and the other is if it is intrinsically giving off, or emitting, light.

The star HD 34989 is emitting light, and that light is very blue. In fact, it gives off a lot of ultraviolet light. The gas cloud has a lot of hydrogen in it, which loves to absorb that UV light. When an atom of hydrogen gets zapped with UV, the electron gets blown off the atom. But then the remaining atom (really just a proton) has a positive charge, and attracts any electron around it. If one meets up with it, they combine once again to form a neutral atom. Due to complicated quantum mechanic effects, the electron jumps down a series of discrete energy levels, a bit like a ball rolling down a staircase. Every time it does that, it gives off a little bit of light.

As it happens, one of those energy level jumps is very popular among the excited hydrogen atoms. When an electron makes that drop, it emits a photon (a particle of light) in the red part of the spectrum. This emission is called hydrogen-alpha, or H-alpha for short (or even Hα if you want to get all fancy and Greek). It’s very common in warm gas clouds where some bright star is nearby.

So in this case the gas is energized by the star, and responds by emitting that glorious red color. There is a special Hα filter astronomers use to specifically observe that light, which Adam used in this picture to enhance the glowing hydrogen. In this case, the cloud is called an emission nebula.

So where does the blue come from then? That one’s easier. It’s just the blue light of the star reflected! In this case, the culprit isn’t gas, it’s dust—thick clumps of complex molecules created when stars are born, and when they die. It’s strewn throughout the galaxy, especially where you see big gas clouds.

That dust acts a bit like a mirror. When the light from the star hits it, that light gets scattered every which way, and some of it heads toward us. The star is blue, so it makes the dust look blue. That’s called a reflection nebula.

Many times where you see a blue reflection nebula you also see red emission gas as well. Not always, but that’s clearly the case here; in fact they have two different names: vdB38 for the reflection nebula and Sharpless 2-236 for the emission nebula. On Flickr I found a nice set of images showing how the reflected and emitted light can be combined to make a single image like Adam’s. You can see why astronomers use these filters; it helps distinguish what’s physically happening in the nebula.

Interestingly, not all the dust in that cloud is scattering the star’s light. See that sharp ridge of red at the bottom left of the nebula, right where we start to see blue light? That’s probably the edge of a large, dense cloud of dust called a molecular cloud (those are common in that part of space). The edge of it is being lit by the star, making it look brighter. This is very similar to what lights up the Orion Nebula and other famous (and gorgeous) objects.

It’s hard to believe all that is lit by a single star, but it is. Mind you, that whole glowing gas cloud is something like five light year across—50 trillion kilometers (30 trillion miles)! But HD 34989 is a monster. Only one star in a thousand is as massive, hot, and bright as it is. Which is something you should be thankful for; you don’t want to be too close to something like that…especially since, in a few million years or so, it’ll explode as a supernova. For something like that, it’s always best to be sitting at a safe distance. A thousand light years will do me just fine.

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Domenico Vicinanza is educating and entertaining scientists and the public. It sounds as if he’s got a plan, and he’s been workin’ it.


^ Domenico Vicinanza | Super Computing 2011 Conference, Seattle
Twitter Stream Rendered as a Live Music Performance

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REFER Higgs Boson-like Particle Sonification | The Voyager 1 Magnetic Field Sonification | Domenico Vicinanza profile | Domenico Vicinanza interview | Lost Sounds Orchestra | GÉANT Arts and Culture | GÉANT Project Home | DANTE Home
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^ Domenico Vicinanza | a brief talk, EMI Technical Conference
Vilnius, 2011. (GÉANT)

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Thanks, ShinShinKid, for a different perspective (from the Images only thread).

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All of the text is here, but I altered the format a bit.
Highlights mine.

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Howdy, Neighbor! New Twin Stars Are Third Closest to the Sun | Phil Plait
Bad Astronomy | Monday, 11MAR13


^ WISE image of WISE 1049-5319, a newly-discovered binary star that’s the third closest star system to the Sun. Inset is an image from the Gemini telescope, showing the true binary nature of the stars. Click to enwilsonate. Image credit: NASA/JPL/Gemini Observatory/AURA/NSF

Astronomers have discovered some new neighbors: A pair of dim brown dwarf stars that are a mere 6.5 light years from Earth! Called WISE 1049-5319, they are the third-closest star system to us, after the Alpha Centauri triple star about 4.3 light years away, and Barnard’s star about six light years distant.

You’d think we’d have a pretty good census of close stars, since they’d be easy to spot. But that’s not the case, because not all stars are bright. Brown dwarfs are extremely faint—the first was only discovered in 1994—because unlike our Sun or other normal stars, they are not actively using nuclear fusion in their cores to generate heat and light. It takes a certain amount of mass to be able to squeeze atomic nuclei hard enough to get them to fuse, and brown dwarfs are just under that limit. They are far more massive than planets but still short of being “true” stars. They range in mass from about 13 – 75 times that of Jupiter.

So one can be pretty close to us and still remain undetected. In this case, the stars were actually seen back in 1978, and twice again in more recent images. However, no one noticed them because they were so faint. Astronomer Kevin Luhman spotted them in images taken by the Wide-Field Infrared Survey Explorer, a NASA satellite that scanned the sky several times in infrared light, well outside what our eyes can see. Brown dwarfs don’t give off much visible light, but they’re warm, so they glow pretty well in the infrared.

< Animation of the stars’ motion using observations going back to 1978. Click to embiggen. Image credit: NASA/STScI/JPL/IPAC/University of Massachusetts

WISE picked them up several times as it surveyed the sky. Luhman noticed the stars not because they were bright, but because they moved. All the stars you can see in the sky are moving, orbiting the center of the Milky Way galaxy, but they are so far away that motion is undetectable without telescopes. Even then, you usually have to wait years to detect it. But the closer a star is, the larger that motion seems; it’s like driving in a car and seeing nearby trees fly by while distant mountains appear nearly motionless.

Luhman noticed the stars’ motion in the WISE data and went back into the archives of other telescopes to find earlier observations. Over the past 30 years or so, the movement of the stars is obvious.

What’s not obvious is that there are two stars, not one. They orbit each other so closely they look like a single star. It was only when Luhman observed them with the huge Gemini telescope that it became apparent they were actually a binary star. He used Gemini to obtain spectra of the stars—breaking their light up into hundreds of individual wavelengths, like a rainbow with hundreds of colors—in order to determine their temperature, mass, and chemical composition. The spectra revealed these were, in fact, brown dwarfs far smaller than the Sun.

This is pretty exciting news for several reasons. For one, it’s always nice (and fun) to discover something surprising, especially when it’s so close. The distance itself is also interesting; if these two stars have planets they’ll be a lot easier to detect than usual because they are so close to us. Plus, the faintness of the stars will make any potential planets easier to see.

< Artist drawing of the two stars of WISE 1049-5319, with the Sun in the background. Image credit: Janella Williams, Penn State University

Also, for years I’ve wondered aloud if there are any stars closer than Alpha Centauri to us. Recent surveys of the sky have made that seem unlikely, but now I wonder. Those same surveys missed WISE 1049-5319. Could there be an even fainter star or stars closer to us? I’ll admit it’s unlikely, but not impossible.

And Alpha Centauri has a planet, discovered only in late 2012. We’ve seen planets around brown dwarfs before. They’re very unlikely to be Earth-like (brown dwarfs don’t give off enough heat to keep a planet warm enough for liquid water unless the planet orbits very close in), but what we’ve been finding, over and again, is that the Universe is capable of surprising us. It’s a big place, and amazingly we’re still finding new things in our own cosmic back yard. I’ll add that Barnard’s star, a faint red dwarf, was discovered in 1916. WISE 1049-5319 is the closest star system found in nearly a century, and it was sitting right there the whole time.

So, howdy neighbor! I hope you don’t mind if we lean over the fence and get to know you better. It’s not often we get new folks around here, and we’re a curious bunch.

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This is probably one of the most charming science-oriented videos with music I’ve seen. The maker, an astrophotographer, Christoph Malin, interspersed excerpts from ISS astronaut Dr. Don Pettit’s talk with four sections of time-lapsed videos with vocals and instrumentals that at moments almost command listening rather than balancing the images with what might be thought as an ethereal accompaniment of music. An opinion can be swayed by one’s musical taste, obviously. On the other hand, I’ve never produced a video, much less constructed a painstaking time-lapse. So what do I know. I just listen.

On this vimeo page, the music credits are: “Old Red Shoe” and instrumental “Sleepy Hollow Cemetry” by Phil Torres; “Stars” by Eero Joenrinne / Lucas; “Reaching” (outro) by Jesse Hozeny.

Links in original.

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The View from Above Our World | Phil Plait
Bad Astronomy | Monday, 11MAR13


^ The stars wheel above and the cities streak below in this frame from the time-lapse video, “The ISS Image Frontier”. Image credit: NASA/Christoph Malin

I have posted quite a few time-lapse videos over the past couple of years; some of them straight astronomy, others of landscapes, and some made from still images taken by astronauts aboard the International Space Station. Of those last, ISS astronaut Don Pettit has taken many of the pictures used to create them. He has lived on the station twice, totaling very nearly a year on board the orbiting platform.

During that time he essentially perfected the art of the photography of the Earth, taking thousands upon thousands of separate, stunning images. I’ve met Don at a meeting, and his enthusiasm for photographing our home world from space is refreshing, heartfelt, and quite infectious.

Astrophotographer Christoph Malin was quite properly infected. Malin took thousands of individual photos by Pettit and animated them, adding clips of Pettit giving a talk about his stay aboard the ISS and his photography there. He also set it to music, creating what is simply one the best time-lapse videos I have ever seen. Seriously, set aside 16 minutes of your busy day, sit back, and soak this in: “The ISS Image Frontier”. You’ll want to make this full-screen.


^ Making the Invisible Visible

When I first watched this, I was transfixed. I had seen some of the clips before, but usually in shorter videos. This longer format gave me more time to drink those in, and also could surprise me here and there with clips I hadn’t seen.

…but then, about halfway through, something amazing happened.

Many astronauts, even from back in the Apollo days, talk about an incredible feeling they get after a few days in space. As they gaze on the Earth from above, they lose their feeling of borders and nationality. The Saudi astronaut Sultan bin Salman Al-Saud, who flew on the Space Shuttle in 1985, commented on this, saying, “The first day or so we all pointed to our countries. The third or fourth day we were pointing to our continents. By the fifth day, we were aware of only one Earth.”

As I watched the video, I caught a brief glimpse of that feeling. As I watched the Earth glide by underneath, just watching it go past, I suddenly realized I had no idea what part of the planet I was seeing. Africa, America, Europe, Asia; I didn’t know, and more importantly, it didn’t matter. It was just Earth. But what struck me is I did recognize the stars, the familiar natural patterns of the northern summer constellations. For a moment, just a moment, I had the surpassingly extraordinary feeling that only the Universe mattered, not our names and labels and boundaries for it. I had never truly felt that before.

That moment was ephemeral, but the memory remains. The astronauts, who experience this for days, weeks, even months, must have that lingering sensation in their brain for a long, long time. I wonder if the lasting legacy of space travel won’t be the technology we gain, or the scientific knowledge acquired, but the feeling of community, of belonging to that planet, experienced at a visceral level.

How much woe would be averted if everyone could feel that, if even for only a moment?

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ALMA Eyes Most Distant Star-forming Galaxy
Universe Today, Tammy Plotner | 13MAR13


^ This schematic image represents how light from a distant galaxy is distorted by the gravitational effects of a nearer foreground galaxy, which acts like a lens and makes the distant source appear distorted, but brighter, forming characteristic rings of light, known as Einstein rings. An analysis of the distortion has revealed that some of the distant star-forming galaxies are as bright as 40 trillion Suns, and have been magnified by the gravitational lens by up to 22 times. Credit: ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

Let’s turn down the lights and set the stage… We’re moving off through space, looking not only at distant galaxies, but the incredibly distant past. Once upon a time astronomers assumed that star formation began in massive, bright galaxies as a concentrated surge. Now, new observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) are showing us that these deluges of stellar creation may have begun much earlier than they thought.

According to the latest research published in today’s edition of the journal, Nature, and in the Astrophysical Journal, researchers have revealed fascinating discoveries taken with the new international ALMA observatory – which celebrates its inauguration today. Among its many achievements, ALMA has given us a look even deeper into space – showing us ancient galaxies which may be billions of light years distant. The observations of these starburst galaxies show us that stars were created in a frenzy out of huge deposits of cosmic gas and dust.



“The more distant the galaxy, the further back in time one is looking, so by measuring their distances we can piece together a timeline of how vigorously the Universe was making new stars at different stages of its 13.7 billion year history,” said Joaquin Vieira (California Institute of Technology, USA), who led the team and is lead author of the paper in the journal Nature.

Just how did these observations come about? Before ALMA, an international team of researchers employed the US National Science Foundation’s 10-metre South Pole Telescope (SPT ) to locate these distant denizens and then homed in on them to take a closer look at the “stellar baby boom” during the Universe’s beginning epoch. What they found surprised them. Apparently star forming galaxies are even more distant than previously suspected… their onslaught of stellar creation beginning some 12 billion years ago. This time frame places the Universe at just under 2 billion years old and the star formation explosion occurring some billion years sooner than astronomers assumed. The ALMA observations included two galaxies – the “most distant of their kind ever seen” – that contained an additional revelation. Not only did their distance break astronomical records, but water molecules have been detected within them.

However, two galaxies aren’t the only score for ALMA. The research team took on 26 galaxies at wavelengths of around three millimetres. The extreme sensitivity of this cutting edge technology utilizes the measurement of light wavelengths – wavelengths produced by the galaxy’s gas molecules and stretched by the expansion of the Universe. By carefully measuring the “stretch”, astronomers are able to gauge the amount of time the light has taken to reach us and refine its point in time.

“ALMA’s sensitivity and wide wavelength range mean we could make our measurements in just a few minutes per galaxy – about one hundred times faster than before,” said Axel Weiss (Max-Planck-Institut für Radioastronomie in Bonn, Germany), who led the work to measure the distances to the galaxies. “Previously, a measurement like this would have been a laborious process of combining data from both visible-light and radio telescopes.”

For the most part, ALMA’s observations would be sufficient to determine the distance, but the team also included ALMA’s data with the Atacama Pathfinder Experiment (APEX) and ESO’s Very Large Telescope for a select few galaxies. At the present time, astronomers are only employing a small segment of ALMA’s capabilities – just 16 of the 66 massive antennae – and focusing on brighter galaxies. When ALMA is fully functional, it will be able to zero in on even fainter targets. However, the researchers weren’t about to miss any opportunities and utilized gravitational lensing to aid in their findings.


^ This montage combines data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The ALMA images, represented in red, show the distant, background galaxies, being distorted by the gravitational lens effect produced by the galaxies in the foreground, depicted in the Hubble data in blue. The background galaxies appear warped into rings of light known as Einstein rings, which encircle the foreground galaxies. Credit:ALMA (ESO/NRAO/NAOJ), J. Vieira et al.

“These beautiful pictures from ALMA show the background galaxies warped into multiple arcs of light known as Einstein rings, which encircle the foreground galaxies,” said Yashar Hezaveh (McGill University, Montreal, Canada), who led the study of the gravitational lensing. “We are using the massive amounts of dark matter surrounding galaxies half-way across the Universe as cosmic telescopes to make even more distant galaxies appear bigger and brighter.”

Just how bright is bright? According to the news release, the analysis of the distortion has shown that a portion of these far-flung, star-forming galaxies could be as bright as 40 trillion Suns… then magnified up to 22 times more through the aid of gravitational lensing.

“Only a few gravitationally lensed galaxies have been found before at these submillimetre wavelengths, but now SPT and ALMA have uncovered dozens of them.” said Carlos De Breuck (ESO), a member of the team. “This kind of science was previously done mostly at visible-light wavelengths with the Hubble Space Telescope, but our results show that ALMA is a very powerful new player in the field.”

“This is an great example of astronomers from around the world collaborating to make an amazing discovery with a state-of-the-art facility,” said team member Daniel Marrone (University of Arizona, USA). “This is just the beginning for ALMA and for the study of these starburst galaxies. Our next step is to study these objects in greater detail and figure out exactly how and why they are forming stars at such prodigious rates.”

Bring the house lights back up, please. As ALMA peers ever further into the past, maybe one day we’ll catch our own selves… looking back.