Posted on by Jason Major

The Secret Origin Story of Brown Dwarfs

Artist's impression of a Y-dwarf, the coldest known type of brown dwarf star. (NASA/JPL-Caltech)

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Sometimes called failed stars, brown dwarfs straddle the line between star and planet. Too massive to be “just” a planet, but lacking enough material to start fusion and become a full-fledged star, brown dwarfs are sort of the middle child of cosmic objects. Only first detected in the 1990s, their origins have been a mystery for astronomers. But a researchers from Canada and Austria now think they have an answer for the question: where do brown dwarfs come from?

If there’s enough mass in a cloud of cosmic material to start falling in upon itself, gradually spinning and collapsing under its own gravity to compress and form a star, why are there brown dwarfs? They’re not merely oversized planets — they aren’t in orbit around a star. They’re not stars that “cooled off” — those are white dwarfs (and are something else entirely.) The material that makes up a brown dwarf probably shouldn’t have even had enough mass and angular momentum to start the whole process off to begin with, yet they’re out there… and, as astronomers are finding out now that they know how to look for them, there’s quite a lot.

So how did they form?

According to research by Shantanu Basu of the University of Western Ontario and  Eduard I. Vorobyov from the University of Vienna in Austria and Russia’s Southern Federal University, brown dwarfs may have been flung out of other protostellar disks as they were forming, taking clumps of material with them to complete their development.

Basu and Vorobyov modeled the dynamics of protostellar disks, the clouds of gas and dust that form “real” stars. (Our own solar system formed from one such disk nearly five billion years ago.) What they found was that given enough angular momentum — that is, spin — the disk could easily eject larger clumps of material while still having enough left over to eventually form a star.

Model of how a clump of low-mass material gets ejected from a disk (S. Basu/E. Vorobyev)

The ejected clumps would then continue condensing into a massive object, but never quite enough to begin hydrogen fusion. Rather than stars, they become brown dwarfs — still radiating heat but nothing like a true star. (And they’re not really brown, by the way… they’re probably more of a dull red.)

In fact a single protostellar disk could eject more than one clump during its development, Basu and Vorobyov found, leading to the creation of multiple brown dwarfs.

If this scenario is indeed the way brown dwarfs form, it stands to reason that the Universe may be full of them. Since they are not very luminous and difficult to detect at long distances, the researchers suggest that brown dwarfs may be part of the answer to the dark matter mystery.

“There could be significant mass in the universe that is locked up in brown dwarfs and contribute at least part of the budget for the universe’s missing dark matter,” Basu said. “And the common idea that the first stars in the early universe were only of very high mass may also need revision.”

Based on this hypothesis, with the potential number of brown dwarfs that could be in our galaxy alone we may find that these “failed stars” are actually quite successful after all.

The team’s research paper was accepted on March 1 into The Astrophysical Journal.

Read more on the University of Western Ontario’s news release here.

Posted on by Jason Major

Where All The Hottest Stars Gather

The star cluster NGC 6604 (ESO)

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An ESO telescope captures a group of hot young stars that would outshine any Hollywood party!

At the upper left of this image is the star cluster NGC 6604, a grouping of hot young stars within a larger collection located in the sky near the much more famous Eagle Nebula (of “Pillars of Creation” fame.) The young stars, which burn bright and blue, are helping make a new generation of stars with their strong stellar winds, which condense nearby gas and dust into even more star-forming regions.

Eventually the new stars will replace the ones seen here, which, although big and bright, will quickly burn through their stellar fuel and fade. Such is the life cycle of massive stars — live fast and die young.

This image was acquired by the MPG/ESO 2.2-meter telescope at the European Southern Observatory’s La Silla Observatory in Chile. NGC 6604 is about 5,500 light-years from Earth, located in the constellation Serpens. Read more on the ESO news release here.

Posted on by Nancy Atkinson

Astronomers See Stars Changing Right Before Their Eyes in Orion Nebula

This new view of the Orion nebula highlights fledging stars hidden in the gas and clouds. Image credit: NASA/ESA/JPL-Caltech/IRAM

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A gorgeous new image from the tag team effort of the Herschel and Spitzer Space telescopes shows a rainbow of colors within the Orion nebula. The different colors reflect the different wavelengths of infrared light captured by the two space observatories, and by combining their observations, astronomers can get a more complete picture of star formation. And in fact, astronomers have spotted young stars in the Orion nebula changing right before their eyes, over a span of just a few weeks!

Astronomers with Herschel mapped this region of the sky once a week for six weeks in the late winter and spring of 2011. Notice the necklace of stars strung across the middle of the image? Over just that short amount of time, a discernible change in the stars took place as they appeared to be rapidly heating up and cooling down. The astronomers wondered if the stars were actually maturing from being star embryos, moving towards becoming full-fledged stars.

To monitor for activity in protostars, Herschel’s Photodetector Array Camera and Spectrometer stared in long infrared wavelengths of light, tracing cold dust particles, while Spitzer took a look at the warmer dust emitting shorter infrared wavelengths. In this data, astronomers noticed that several of the young stars varied in their brightness by more than 20 percent over just a few weeks.

As this twinkling comes from cool material emitting infrared light, the material must be far from the hot center of the young star, likely in the outer disk or surrounding gas envelope. At that distance, it should take years or centuries for material to spiral closer in to the growing starlet, rather than mere weeks.

The astronomers said a couple of scenarios could account for this short span. One possibility is that lumpy filaments of gas funnel from the outer to the central regions of the star, temporarily warming the object as the clumps hit its inner disk. Or, it could be that material occasionally piles up at the inner edge of the disk and casts a shadow on the outer disk.

“Herschel’s exquisite sensitivity opens up new possibilities for astronomers to study star formation, and we are very excited to have witnessed short-term variability in Orion protostars,” said Nicolas Billot, an astronomer at the Institut de Radioastronomie Millimétrique (IRAM) in Grenada, Spain who is preparing a paper on the findings along with his colleagues. “Follow-up observations with Herschel will help us identify the physical processes responsible for the variability.”

Source: NASA

Posted on by Nancy Atkinson

‘Dark Markings of the Sky’ are Hiding Star Formation

This image from the APEX telescope, of part of the Taurus Molecular Cloud, shows a sinuous filament of cosmic dust more than ten light-years long. Could life exist in molecular clouds like this one? Credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin.

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This stunning new image shows a sinuous filament of cosmic dust more than ten light-years long. The makeup of filamentary cloud structures like this used to be a mystery, and in the early 20th century, Edward Emerson Barnard compiled a photographic atlas of these features, calling them “dark markings of the sky,” as these regions appeared as dark lanes, with no stars visible. Barnard correctly argued that this appearance was due to “obscuring matter in space.” Today we call segments in this particular cloud Barnard 211 and Barnard 213, or the Taurus Molecular Cloud. And we now know that these are clouds of interstellar gas and dust grains. But also, within these clouds, newborn stars are hidden, and dense clouds of gas are on the verge of collapsing to form yet more stars.

The Taurus Molecular Cloud is one of the closest regions of star formation to us. It is located in the constellation of Taurus about 450 light-years from Earth. The cosmic dust grains are so cold that observations at wavelengths of around one millimeter, such as these made with the LABOCA camera on APEX (Atacama Pathfinder Experiment) telescope in Chile, are needed to detect their faint glow.

This image shows two parts of a long filament. The dust grains — tiny particles similar to very fine soot and sand — absorb visible light, blocking our view of the rich star field behind the clouds. The Taurus Molecular Cloud is particularly dark at visible wavelengths, as it lacks the massive stars that illuminate the nebulae in other star-formation regions such as Orion.

But active star formation is taking place. This is why observations at longer wavelengths, such as the millimeter range, are essential for understanding the early stages of star formation.

Read more about this particular region at the ESO website.

Posted on by Nancy Atkinson

Starbursts May Actually Destroy Globular Clusters

The Galactic globular cluster M80 in the constellation Scorpius contains several hundred thousand stars. Credit: HST/NASA/ESA

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It seems logical to assume that long ago, the amount of globular clusters increased in our galaxy during star-making frenzies called ‘starbursts.’ But a new computer simulation shows just the opposite: 13 billion years ago, starbursts may have actually destroyed many of the globular clusters that they helped to create.

“It is ironic to see that starbursts may produce many young stellar clusters, but at the same time also destroy the majority of them,” said Dr. Diederik Kruijssen of the Max Planck Institute for Astrophysics. “This occurs not only in galaxy collisions, but should be expected in any starburst environment”

Astronomers have wondered why throughout the Universe, typical globular star clusters contain about the same number of stars. In contrast much younger stellar clusters can contain almost any number of stars, from fewer than 100 to many thousands.

The new computer simulation by Kruijssen and his team proposes that this difference could be explained by the conditions under which globular clusters formed early on in the evolution of their host galaxies.

In the early Universe, starbursts were common. Large galaxies were in clusters, and collisions occurred often. The computer simulation showed that during starbursts, gas, dust and stars were still being sloshed around from the galaxy collision, with the pull of gravity on the globular clusters constantly changing. This was enough to rip apart most of the globular clusters and only the biggest ones were strong enough to survive. The simulations showed most of the star clusters were destroyed shortly after their formation, when the galactic environment was still very hostile to the young clusters. But after the environment calmed down, the surviving globular clusters have survived – now living quietly – and we can still enjoy their beauty.

In their paper, the astronomers say that this explains why the number of stars contained within globular clusters is roughly the same across the entire Universe. “It therefore makes perfect sense that all globular clusters have approximately the same large number of stars,” said Kruijssen. “Their smaller brothers and sisters that didn’t contain as many stars were doomed to be destroyed.”

Kruijssen and his team said that while the very brightest and largest clusters were capable of surviving the galaxy collision due to their own gravitational attraction, numerous smaller clusters were effectively destroyed by the rapidly changing gravitational forces.

The fact that globular clusters are comparable everywhere then indicates that the environments in which they formed were very similar, regardless of the galaxy they currently reside in. Kruijssen and his team says globular clusters can therefore be used to shed more light on how the first generations of stars and galaxies were born.

“In the nearby Universe, there are several examples of galaxies that have recently undergone large bursts of star formation,” said Kruijssen. “It should therefore be possible to see the rapid destruction of small stellar clusters in action. If this is indeed found by new observations, it will confirm our theory for the origin of globular clusters.”

This new finding may also tie in with other recent findings from Spitzer and ESO that starburst activity may have only lasted around 100 million years and may have also been cut short when black holes formed at the center of galaxies.

Source: Max-Planck Institute for Astrophysics. Paper: Kruijssen et al, “Formation versus destruction: the evolution of the star cluster population in galaxy mergers”

Posted on by Paul Scott Anderson

New Study Shows How Trace Elements Affect Stars’ Habitable Zones

Comparison of the habitable zone around the Sun in our solar system and around the star Gliese 581. Credit: ESO

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Habitable zones are the regions around stars, including our own Sun, where conditions are the most favourable for the development of life on any rocky planets that happen to orbit within them. Generally, they are regions where temperatures allow for liquid water to exist on the surface of these planets and are ideal for “life as we know it.” Specific conditions, due to the kind of atmosphere, geological conditions, etc. must also be taken into consideration, on a case-by-case basis.

Now, by examining trace elements in the host stars, researchers have found clues as to how the habitable zones evolve, and how those elements also influence them. To determine what elements are in a star, scientists study the wavelengths of its light. These trace elements are heavier than the hydrogen and helium gases which the star is primarily composed of. Variations in the composition of these stars are now thought to affect the habitable zones around them.

The study was led by Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University. Young and his team presented their findings on January 11, 2012 at the annual meeting of the American Astronomical Society in Austin, Texas. He and his colleagues have examined more than a hundred dwarf stars so far.

An abundance of these elements can affect how opaque a star’s plasma is. Calcium, sodium, magnesium, aluminum and silicon have been found to also have small but significant effects on a star’s evolution – higher levels tended to result in cooler, redder stars. As Young explains, “The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity. A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star.”

The lifetime of a star’s habitable zone can also be influenced by another element – oxygen. Young continues: “The habitable lifetime of an orbit the size of Earth’s around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars. For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the Sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets.”

As well as the habitable zone, the composition of a star can determine the eventual composition of any planets that form. The carbon-oxygen and magnesium-silicon ratios of stars can affect whether a planet will have magnesium or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). A star’s composition can also play a role in whether a rocky planet might have carbon-based rock instead of silicon-based rock like our planet. Even the interior of planets could be affected, as radiocative elements would determine whether a planet has a molten core or a solid one. Plate tectonics, thought to be important for the evolution of life on Earth, depend on a molten interior.

Young and his team are now looking at 600 stars, ones that are already being targeted in exoplanet searches. They plan to produce a list of the 100 best stars which could have potentially habitable planets.

Posted on by Nancy Atkinson

Hitchcock Haunts a Nebula

The star-forming region NGC 3324. The intense radiation from several of NGC 3324's massive, blue-white stars has carved out a cavity in the surrounding gas and dust. The ultraviolet radiation from these young hot stars also cause the gas cloud to glow in rich colors. Credit: ESO

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First impression after seeing this new image of NGC 3324? It’s Alfred Hitchcock, bulbous nose and all (see image below for comparison). The right edge of the wall of gas and dust in this star-forming region really bears a strong resemblance to the famous profile of the British film director and producer, notorious for his thriller movies from the 1940’s through the 1970’s.

NGC 3324 is located in the southern constellation of Carina, roughly 7500 light-years from Earth. It is on the northern outskirts of the chaotic environment of the Carina Nebula. All the gas and dust here fueled a burst of star birth several millions of years ago and led to the creation of several hefty and very hot stars that are prominent in the new picture.

Alfred Hitchcock. Via iwatchstuff.com

A nickname for the NGC 3324 region is the ‘Gabriela Mistral Nebula,’ after the Nobel Prize-winning Chilean poet but I think I’ll start a petition to call it the Hitchcock Nebula. Hitchcock liked to make cameo appearances in his own movies, and perhaps he is making a pareidoliaic guest appearance here.

The new image of NGC 3324 was taken with the Wide Field Imager on the the European Southern Observatory’s 2.2-metre telescope at the La Silla Observatory in Chile. Read more about it on the ESO website.

Posted on by Tammy Plotner

Young Magnetic Star Possesses Precise Carbon Dioxide Ring

Artist's conception image of a young star surrounded by a disk (made up of rings) (Credits: NASA/JPL-Caltech)

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Catching a ring – or accretion disk – around a star isn’t unusual. However, catching a sharply defined carbon-dioxide ring around a young, magnetic star that’s precisely 1 AU away with a width 0.32 AU or less might raise a few eyebrows. This isn’t just any disk, either… It’s been likened as a “rope-like structure” and there’s even more to the mystery. It’s encircling a Herbig Ae star.

Discovered with the European Southern Observatory’s Very Large Telescope, the edges of this accretion disk are uniquely crisp. Located in the constellation of Centaurus at about 700 light years distant, V1052 (HD 101412) is a parent star with an infrared excess. “HD 101412 is most unusual in having resolved, magnetically split spectral lines which reveal a surface field modulus that varies between 2.5 to 3.5 kG.” says C.R. Cowley (et al). Previous studies “have surveyed molecular emission in a variety of young stellar objects. They found the emission to be much more subdued in Herbig Ae/Be stars than their cooler congeners, the T Tauri stars. This was true for HD 101412 as well, which was among the 25 Herbig Ae/Be stars they discussed. One exception, however, was the molecule CO2, which had a very large flux in HD 101412; indeed, only one T Tauri star had a higher CO2 flux.”

It’s not unusual for carbon dioxide to be found near young stars, but it is a bit more normal for it to be distributed throughout the disk region. “It’s exciting because this is the most constrained ring we’ve ever seen, and it requires an explanation,” explains Cowley, who is professor emeritus at the University of Michigan and leader of the international research effort. “At present time, we just don’t understand what makes it a rope rather than a dish.”

Because V1052 itself is different could be the reason. It is hypothesized the magnetic fields may be holding the rings in the disk structure at a certain distance. The idea has also been forwarded that there may be “shepherding planets”, much like Saturn’s ring structure, which may be the cause. “What makes this star so special is its very strong magnetic field and the fact that it rotates extremely slow compared to other stars of the same type,” said Swetlana Hubrig, of the Leibniz Institute for Astrophysics Potsdam (AIP), Germany.

One thing that is certain is how clean and well-defined the disk lines are centered around the Earth/Sun distance. This accords well with computer modeling where “A wider disk will not fit the observations.” These observations – and the exotic parent star – have been under intense scrutiny since 2008 and the findings have been recently published on-line in Astronomy and Astrophysics. It’s work that helps deepen the understanding of the interaction between central stars, their magnetic fields, and planet-forming disks. It also allows for fact finding when it comes to diverse systems and better knowledge of how solar systems form… even unusual ones.

“Why do turbulent motions not tear the ring apart?” Cowley wondered. “How permanent is the structure? What forces might act to preserve it for times comparable to the stellar formation time itself?”

When it comes to Herbig Ae stars, they are not only rare, but present a rare opportunity for study. In this case, it gives the team something to be quite excited about.

“This star is a gift of nature,” Hubrig said

Original Story Source: Leibniz Institute for Astrophysic News Release. For Further Reading: The narrow, inner CO ring around the magnetic Herbig Ae star, HD 101412.

Posted on by Paul Scott Anderson

Citizen Scientist Project Finds Thousands of ‘Star Bubbles’

A prominent star bubble. Credit: NASA / The Milky Way Project / Zooniverse

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Remember when you were a kid and blowing bubbles was such great fun? Well, stars kind of do that too. The “bubbles” are partial or complete rings of dust and gas that occur around young stars in active star-forming regions, known as stellar nurseries. So far, over 5,000 bubbles have been found, but there are many more out there awaiting discovery. Now there is a project that you can take part in yourself, to help find more of these intriguing objects.

The Milky Way Project, part of Zooniverse, has been cataloguing these cosmic bubbles thanks to assistance from the public, or “citizen scientists” – anyone can help by examining images from the Spitzer Space Telescope, specifically the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and the Multiband Imaging Photometer for Spitzer Galactic Plane Survey (MIPSGAL).

They have been seen before, but now the task is to find as many as possible in the newer, high-resolution images from Spitzer. A previous catalogue of star bubbles in 2007 listed 269 of them. Four other researchers had found about 600 of them in 2006. Now they are being found by the thousands. As of now, the new catalogue lists 5,106 bubbles, after looking at almost half a million images so far. As it turns out, humans are more skilled at identifying them in the images than a computer algorithm would be. People are better at pattern recognition and then making a judgment based on the data as to what actually is a bubble and what isn’t.

The bubbles form around hot, young massive stars where it is thought that the intense light being emitted causes a shock wave, blowing out a space, or bubble, in the surrounding gas and dust.

Eli Bressert, of the European Southern Observatory and Milky Way Project team member, stated that our galaxy “is basically like champagne, there are so many bubbles.” He adds, “We thought we were going to be able to answer a lot of questions, but it’s going to be bringing us way more questions than answers right now. This is really starting something new in astronomy that we haven’t been able to do.”

There are currently about 35,000 volunteers in the project; if you would like to take part, you can go to The Milky Way Project for more information.

Posted on by Jon Voisey

“Proplyd-like” Objects Discovered in Cygnus OB2

Hubble image of a Proplyd-like object in Cygnus OB2. Credit: Z. Levay and L. Frattare, STScI
Hubble image of a Proplyd-like object in Cygnus OB2. Credit: Z. Levay and L. Frattare, STScI

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The well known Orion Nebula is perhaps the most well known star forming regions in the sky. The four massive stars known as the trapezium illuminate the massive cloud of gas and dust busily forming into new stars providing astronomers a stunning vista to explore stellar formation and young systems. In the region are numerous “protoplanetary disks” or proplyds for short which are regions of dense gas around a newly formed star. Such disks are common around young stars and have recently been discovered in an even more massive, but less well known star forming region within our own galaxy: Cygnus OB2.

Ten times more massive than its more famous counterpart in Orion, Cygnus OB2 is a star forming region that is a portion of a larger collection of gas known as Cygnus X. The OB2 region is notable because, like the Orion nebula, it contains several exceptionally massive stars including OB2-12 which is one of the most massive and luminous stars within our own galaxy. In total the region has more than 65 O class stars, the most massive category in astronomers classification system. Yet for as bright as these stars are, Cygnus OB2 is not a popular target for amateur astronomers due to its position behind a dark obscuring cloud which blocks the majority of visible light.

But like many objects obscured in this manner, infrared and radio telescopes have been used to pierce the veil and study the region. The new study, led by Nicholas Wright at the Harvard-Smithsonian Center for Astrophysics, combines infrared and visual observations from the Hubble Space telescope. The observations revealed 10 objects similar in appearance to the Orion proplyds. The objects had long tails being blown away from the central mass due to the strong stellar winds from the central cluster similar to how proplyds in Orion point away from the trapezium. On the closer end, the objects were brightly ionized.

Yet despite the similarities, the objects may not be true proplyds. Instead, they may be regions known as “evaporating gaseous globules” or EGGs for short. The key difference between the two is whether or not a star has formed. EGGs are overdense regions within a larger nebula. Their size and density makes them resistant to the ionization and stripping that blows away the rest of the nebula. Because the interior regions are shielded from these dispersive forces, the center may collapse to form a star which is the requirement for a proplyd. So which are these?

In general, the newly discovered objects are far larger than those typically found in Orion. While Orion proplyds are nearly symmetric across an axis directed towards the central cluster, the OB2 objects have twisted tails with complex shapes. The objects are 18-113 thousand AU (1 AU = the distance between the Earth and Sun = 93 million miles = 150 million km) across making them significantly larger than the Orion proplyds and even larger than the largest known proplyds in NGC 6303.

Yet as different as they are, the current theoretical understanding of how proplyds work doesn’t put them beyond the plausible range. In particular, the size for a true proplyd is limited by how much stripping it feels from the central stars. Since these objects are further away from OB2-12 and the other massive stars than the Orion proplyds are from the trapezium, they should feel less dispersive forces and should be able to grow as large as is seen. Attempting to pierce the thick dust the objects contain and discover if central stars were present, the team examined the objects in the infrared and radio. Of the ten objects, seven had strong candidates central stellar sources.

Still, the stark differences make conclusively identifying the objects as either EGGs or proplyds difficult. Instead, the authors suggest that these objects may be the first discovery of an inbetween stage: old, highly evolved EGGs which have nearly formed stars making them more akin to young proplyds. If further evidence supports this, this finding would help fill in the scant observational details surrounding stellar formation. This would allow astronomers to more thoroughly test theories which are also tied to the understanding of how planetary systems form.