Stellar Parenting: Making New Stars By ‘Adopting’ Stray Cosmic Gases

Among the most striking objects in the universe are glittering, dense swarms of stars known as globular clusters. Astronomers had long thought globular clusters formed their millions of stars in bulk at around the same time, with each cluster’s stars having very similar ages, much like twin brothers and sisters. Yet recent discoveries of young stars in old globular clusters have scrambled this tidy picture.

stray cosmic gases

Instead of having all their stellar progeny at once, globular clusters can somehow bear second or even third sets of thousands of sibling stars. Now a new study led by researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, and including astronomers at Northwestern University, the Adler Planetarium and the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), might explain these puzzling, successive stellar generations.

Using observations by the Hubble Space Telescope, the research team has for the first time found young populations of stars within globular clusters that have apparently developed courtesy of star-forming gas flowing in from outside of the clusters themselves. This method stands in contrast to the conventional idea of the clusters’ initial stars shedding gas as they age in order to spark future rounds of star birth.

The study will be published in the Jan. 28 issue of the journal Nature.

“This study offers new insight on the problem of multiple stellar populations in star clusters,” said study lead author Chengyuan Li, an astronomer at KIAA and NAOC who also is affiliated with the Chinese Academy of Sciences’ Purple Mountain Observatory. “Our study suggests the gaseous fuel for these new stellar populations has an origin that is external to the cluster, rather than internal.

In a manner of speaking, globular clusters appear capable of “adopting” baby stars — or at least the material with which to form new stars — rather than creating more “biological” children as parents in a human family might choose to do.

“Our explanation that secondary stellar populations originate from gas accreted from the clusters’ environments is the strongest alternative idea put forward to date,” said Richard de Grijs, also an astronomer at KIAA and Chengyuan’s Ph.D. advisor. “Globular clusters have turned out to be much more complex than we once thought.”

Globular clusters are spherical, densely packed groups of stars orbiting the outskirts of galaxies. Our home galaxy, the Milky Way, hosts several hundred. Most of these local, massive clusters are quite old, however, so the KIAA-led research team turned their attention to young and intermediate-aged clusters found in two nearby dwarf galaxies, collectively called the Magellanic Clouds.

Specifically, the researchers used Hubble observations of the globular clusters NGC 1783 and NGC 1696 in the Large Magellanic Cloud, along with NGC 411 in the Small Magellanic Cloud. Scientists routinely infer the ages of stars by looking at their colors and brightnesses. Within NGC 1783, for example, Li, de Grijs and colleagues identified an initial population of stars aged 1.4 billion years, along with two newer populations that formed 890 million and 450 million years ago.

What is the most straightforward explanation for these unexpectedly differing stellar ages? Some globular clusters might retain enough gas and dust to crank out multiple generations of stars, but this seems unlikely, said study co-author Aaron M. Geller of Northwestern University and the Adler Planetarium in Chicago.

“Once the most massive stars form, they are like ticking time bombs, with only about 10 million years until they explode in powerful supernovae and clear out any remaining gas and dust,” Geller said.”Afterwards, the lower-mass stars, which live longer and die in less violent ways, may allow the cluster to build up gas and dust once again.

“The KIAA-led research team proposes that globular clusters can sweep up stray gas and dust they encounter while moving about their respective host galaxies. The theory of newborn stars arising in clusters as they “adopt” interstellar gases actually dates back to a 1952 paper. More than a half-century later, this once speculative idea suddenly has key evidence to support it.

In the study, the KIAA researchers analyzed Hubble observations of these star clusters, and then Geller and his Northwestern colleague Claude-André Faucher-Giguère carried out calculations that show this theoretical explanation is possible in the globular clusters this team studied.

“We have now finally shown that this idea of clusters forming new stars with accreted gas might actually work,” de Grijs said, “and not just for the three clusters we observed for this study, but possibly for a whole slew of them.”

Future studies will aim to extend the findings to other Magellanic Cloud as well as Milky Way globular clusters.

Strong Magnetic Fields Discovered in Majority of Stars

An international group of astronomers led by the University of Sydney has discovered strong magnetic fields are common in stars, not rare as previously thought, which will dramatically impact our understanding of how stars evolve.

Structure of Stars (artist’s impression)

Using data from NASA’s Kepler mission, the team found that stars only slightly more massive than the Sun have internal magnetic fields up to 10 million times that of the Earth, with important implications for evolution and the ultimate fate of stars.

“This is tremendously exciting, and totally unexpected,” said lead researcher, astrophysicist Associate Professor Dennis Stello from the University of Sydney.

“Because only 5 percent of stars were previously thought to host strong magnetic fields, current models of how stars evolve lack magnetic fields as a fundamental ingredient,” Associate Professor Stello said. “Such fields have simply been regarded insignificant for our general understanding of stellar evolution. “Our result clearly shows this assumption needs to be revisited.”

The research is based on previous work led by the Californian Institute of Technology (Caltech) and including Associate Professor Stello, which found that measurements of stellar oscillations, or sound waves, inside stars could be used to infer the presence of strong magnetic fields. The findings are published today in the journal Nature.

This latest research used that result to look at a large number of evolved versions of our Sun observed by Kepler. More than 700 of these so-called red giants were found to show the signature of strong magnetic fields, with some of the oscillations suppressed by the force of the fields.

“Because our sample is so big we have been able to dig deeper into the analysis and can conclude that strong magnetic fields are very common among stars that have masses of about 1.5-2.0 times that of the Sun,” Associate Professor Stello explained.

“In the past we could only measure what happens on the surfaces of stars, with the results interpreted as showing magnetic fields were rare.”

Using a new technique called asteroseismology, which can ‘pierce through the surface’ of a star, astronomers can now see the presence of a very strong magnetic field near the stellar core, which hosts the central engine of the star’s nuclear burning. This is significant because magnetic fields can alter the physical processes that take place in the core, including internal rotation rates, which affects how stars grow old.

Most stars like the Sun oscillate continuously because of sound waves bouncing back-and-forth inside them. “Their interior is essentially ringing like a bell.” Associate Professor Stello said. “And like a bell, or a musical instrument, the sound they produce can reveal their physical properties.”

The team measured tiny brightness variations of stars caused by the ringing sound and found certain oscillation frequencies were missing in 60 percent of the stars because they were suppressed by strong magnetic fields in the stellar cores.

The results will enable scientists to test more directly theories of how magnetic fields form and evolve – a process known as magnetic dynamos – inside stars. This could potentially lead to a better general understanding of magnetic dynamos, including the dynamo controlling the Sun’s 22-year magnetic cycle, which is known to affect communication systems and cloud cover on Earth.

“Now it is time for the theoreticians to investigate why these magnetic fields are so common,” Associate Professor Stello concluded.

Unexpected Discovery of Charged Particles Driving Galactic Jets

One of the most significant and unexpected discoveries of the Chandra X-ray Observatory was that bright X-rays are also emitted by these jets. The X-rays are also produced by the acceleration of charged particles, but there are other possible mechanisms as well.

galactic jets4

Fast-moving particles can scatter background light, boosting it into the X-ray band. Alternatively, shocks can generate X-ray emission (or at least a significant portion of it), either as the jets interact with stellar winds and interstellar medium or, within the jet, as a consequence of jet variability, instability, turbulence, or other phenomena.

Super-massive black holes at the centers of galaxies can spawn tremendous bipolar jets when matter in the vicinity forms a hot, accreting disk around the black hole. The rapidly moving charged particles in the jets radiate when they are deflected by magnetic fields; these jets were discovered at radio wavelengths several decades ago.

In the most dramatic cases, the energetic particles move at speeds close to the speed of light and extend over hundreds of thousands of light-years, well beyond the visible boundaries of the galaxy. The physical processes that drive these jets and cause them to radiate are among the most important outstanding problems of modern astrophysics.

CfA astronomer Aneta Siemiginowska and her colleagues have studied the bright radio jet galaxy Pictoris A, located almost five hundred million light-years away, using very deep Chandra measurements – the observations used an accumulated total of over four days of time, spread over a fourteen year period. These data enabled the first detailed analysis of the spectral character of the emission all along the jets. The emission turns out to be remarkably uniform everywhere, something that is extremely unlikely if scattering were responsible, but which is a natural consequence of the magnetic field process.

The scientists therefore reject the scattering model in favor of the latter. However, the jets do have within them many small clumps, internal structures, and lobes. Shocks and/or scattering are possible explanations for the emission in some of these structures.

Although these new results represent some dramatic improvements in our understanding of Pic A, high-resolution radio measurements of a large sample of similar jets are now needed to refine and extend the models. Large-scale X-ray jets, for example, have been also detected in very distant quasars. The results from Pic A, together with future Chandra observations, will help astronomers determine the extent to which these distant jets also rely on the same processes, or if they invoke other ones.

One Trillion Kilometers Apart: A Lonely Planet And Its Distant Star

A team of astronomers in the UK, USA and Australia have found a planet, until now thought to be a free floating or lonely planet, in a huge orbit around its star. Incredibly the object, designated as 2MASS J2126, is about 1 trillion (1 million million) kilometres from the star, or about 7000 times the distance from the Earth to the Sun. The researchers report the discovery in a paper in Monthly Notices of the Royal Astronomical Society.

star

In the last five years a number of free floating planets have been found. These are gas giant worlds like Jupiter that lack the mass for the nuclear reactions that make stars shine, so cool and fade over time. Measuring the temperatures of these objects is relatively straightforward, but it depends on both mass and age. This means astronomers need to find out how old they are, before they can find out if they are lightweight enough to be planets or if they are heavier ‘failed stars’ known as brown dwarfs.

US-based researchers found 2MASS J2126 in an infrared sky survey, flagging it as a possible young and hence low mass object. In 2014 Canadian researchers identified 2MASS J2126 as a possible member of a 45 million year old group of stars and brown dwarfs known as the Tucana Horologium Association. This made it young and low enough in mass to be classified as a free-floating planet.

In the same region of the sky, TYC 9486-927-1 is a star that had been identified as being young, but not as a member of any known group of young stars. Until now no one had suggested that TYC 9486-927-1 and 2MASS J2126 were in some way linked.

Lead author Dr Niall Deacon of the University of Hertfordshire has spent the last few years searching for young stars with companions in wide orbits. As part of the work, his team looked through lists of known young stars, brown dwarfs and free-floating planets to see if any of them could be related. They found that TYC 9486-927-1 and 2MASS J2126 are moving through space together and are both about 104 light years from the Sun, implying that they are associated.

“This is the widest planet system found so far and both the members of it have been known for eight years,” said Dr Deacon, “but nobody had made the link between the objects before. The planet is not quite as lonely as we first thought, but it’s certainly in a very long distance relationship.”

When they looked in more detail, the team were not able to confirm that TYC 9486-927-1 and 2MASS J2126 are members of any known group of young stars.

“Membership in a group of young stars is great for establishing an age,” said study co-author Josh Schlieder of the NASA Ames Research Center, “but when we can’t use that we need to resort to other methods.”

The team then looked at the spectrum – the dispersed light – of the star to measure the strength of a feature caused by the element lithium. This is destroyed early on in a star’s life so the more lithium it has, the younger it is. TYC 9486-927-1 has stronger signatures of lithium than a group of 45 million year old stars (the Tucana Horologium Association) but weaker signatures than a group of 10 million year old stars, implying an age between the two.

Based on this age the team was able to estimate the mass of 2MASS J2126, finding it to be between 11.6 to 15 times the mass of Jupiter. This placed it on the boundary between planets and brown dwarfs. It means that 2MASS J2126 has a similar mass, age and temperature to one of the first planets directly imaged around another star, beta Pictoris b.

“Compared to beta Pictoris b, 2MASS J2126 is more than 700 times further away from its host star,” said Dr Simon Murphy of the Australian National University, also a study co-author, “but how such a wide planetary system forms and survives remains an open question.”

2MASS J2126 is around 7000 Earth-Sun distances or 1 trillion kilometres away from its parent star, giving it the widest orbit of any planet found around another star. At such an enormous distance it takes roughly 900,000 years to complete one orbit, meaning it has completed less than fifty orbits over its lifetime. There is little prospect of any life on an exotic world like this, but any inhabitants would see their ‘Sun’ as no more than a bright star, and might not even imagine they were connected to it at all.

In Galaxy Clustering, Mass May Not Be The Only Thing That Matters

An international team of researchers, including Carnegie Mellon University’s Rachel Mandelbaum, has shown that the relationship between galaxy clusters and their surrounding dark matter halo is more complex than previously thought. The researchers’ findings, published in Physical Review Letters today (Jan. 25), are the first to use observational data to show that, in addition to mass, a galaxy cluster’s formation history plays a role in how it interacts with its environment.

galaxy cluster

There is a connection between galaxy clusters and their dark matter halos that holds a great deal of information about the universe’s content of dark matter and accelerating expansion due to dark energy. Galaxy clusters are groupings of hundreds to thousands of galaxies bound together by gravity, and are the most massive structures found in the universe. These clusters are embedded in a halo of invisible dark matter. Traditionally, cosmologists have predicted and interpreted clustering by calculating just the masses of the clusters and their halos. However, theoretical studies and cosmological simulations suggested that mass is not the only element at play — something called assembly bias, which takes into account when and how a galaxy cluster formed, also could impact clustering.

“Simulations have shown us that assembly bias should be part of our picture,” said Mandelbaum, a member of Carnegie Mellon’s McWilliams Center for Cosmology. “Confirming this observationally is an important piece of understanding galaxy and galaxy cluster formation and evolution.”

In the current study, the research team, led by Hironao Miyatake, Surhud More and Masahiro Takada of the Kavli Institute for the Physics and Mathematics of the Universe, analyzed observational data from the Sloan Digital Sky Survey’s DR8 galaxy catalog. Using this data, they demonstrated that when and where galaxies group together within a cluster impacts the cluster’s relationship with its dark matter environment.

The researchers divided close to 9,000 galaxy clusters into two groups based on the spatial distribution of the galaxies in each cluster. One group consisted of clusters with galaxies aggregated at the center and the other consisted of clusters in which the galaxies were more diffuse. They then used a technique called gravitational lensing to show that, while the two groups of clusters had the same mass, they interacted with their environment much differently. The group of clusters with diffuse galaxies were much more clumpy than the group of clusters that had their galaxies close to the center.

“Measuring the way galaxy clusters clump together on large scales is a linchpin of modern cosmology. We can go forward knowing that mass might not be the only factor in clustering,” Mandelbaum said.

Rare Dinosaur From Appalachia Identified

An international team of researchers has identified and named a new species of dinosaur that is the most complete, primitive duck-billed dinosaur to ever be discovered in the eastern United States.

dinosaur

This new discovery also shows that duck-billed dinosaurs originated in the eastern United States, what was then broadly referred to as Appalachia, before dispersing to other parts of the world. The research team outlined its findings in the Journal of Vertebrate Paleontology.

“This is a really important animal in telling us how they came to be and how they spread all over the world,” said Florida State University Professor of Biological Science Gregory Erickson, one of the researchers on the team.

They named the new dinosaur Eotrachodon orientalis, which means “dawn rough tooth from the east.” The name pays homage to “Trachodon,” which was the first duck-billed dinosaur named in 1856.

This duck-billed dinosaur — also known as a Hadrosaurid — was probably 20 to 30 feet long as an adult, mostly walked on its hind legs though it could come down on all four to graze on plants with its grinding teeth, and had a scaly exterior. But what set it apart is that it had a large crest on its nose.

“This thing had a big ugly nose,” Erickson said.

That large crest on the nose, plus indentations found in the skull and its unique teeth alerted Erickson and his colleagues from McWane Science Center in Birmingham, Ala., and the University of Bristol in the United Kingdom that the skeleton they had was something special.

The skeletal remains of this 83-million-year-old dinosaur were originally found by a team of amateur fossil enthusiasts alongside a creek in Montgomery County, Alabama in marine sediment. Dinosaurs from the South are extremely rare. A set with a complete skull is an even more extraordinary find. The dinosaur likely was washed out to sea by river or stream sediments after it died. When the group realized they had potentially discovered something of scientific importance, they contacted McWane Science Center in Birmingham, which dispatched a team to the site to carefully remove the remains from the surrounding rock.

After the bones were prepared and cleaned at McWane Science Center and the University of West Alabama, they were studied by a team of paleontologists including Erickson, former FSU doctoral student Albert Prieto-Marquez who is now at the University of Bristol, and Jun Ebersole, director of collections at McWane Science Center. Among the recovered remains of this new dinosaur are a complete skull, dozens of backbones, a partial hip bone and a few bones from the limbs.

It is one of the most complete dinosaur skeletons ever to be found in the eastern United States. Its teeth, which show this dinosaur’s remarkable ability to grind up plants in a manner like cows or horses, were present in early hadrosaurids, allowing them to consume a wide variety of plants as the group radiated around the world.

During the late Cretaceous Period, roughly 85 million years ago, North America was divided in half by a 1,000 mile ocean that connected the Gulf of Mexico to the Arctic Ocean. This body of water created two North American landmasses, Laramidia to the west and Appalachia to the east.

The area of what was considered Appalachia is a bit wider than what we call Appalachia today. It began roughly in Georgia and Alabama and stretched all the way north into Canada.

“For roughly 100 million years, the dinosaurs were not able to cross this barrier,” Ebersole said. “The discovery of Eotrachodon suggests that duck-billed dinosaurs originated in Appalachia and dispersed to other parts of the world at some point after the seaway lowered, opening a land corridor to western North America.”

Added Erickson: “They just needed to get off the island. From there, they became the cows of the Cretaceous.”

Erickson brought some bone samples and teeth back to his lab at Florida State for further analysis. He found it difficult to pinpoint the exact age of the dinosaur because no growth lines appeared in the bone samples. However, the highly vascularized bones show that it was growing very rapidly at the time of death, akin to a teenager, and stood to get much larger — perhaps 20-30 feet in length, which is typical of duck-billed dinosaurs found elsewhere.

The remains of Eotrachodon are housed at McWane Science Center in Birmingham and are currently on display in Ebersole’s laboratory for the general public to view.

New Method Proposed To Probe The Beginning Of The Universe

How did the Universe begin? And what came before the Big Bang? Cosmologists have asked these questions ever since discovering that our Universe is expanding. The answers aren’t easy to determine. The beginning of the cosmos is cloaked and hidden from the view of our most powerful telescopes. Yet observations we make today can give clues to the universe’s origin. New research suggests a novel way of probing the beginning of space and time to determine which of the competing theories is correct.

universe

The most widely accepted theoretical scenario for the beginning of the Universe is inflation, which predicts that the universe expanded at an exponential rate in the first fleeting fraction of a second. However a number of alternative scenarios have been suggested, some predicting a Big Crunch preceding the Big Bang. The trick is to find measurements that can distinguish between these scenarios.

One promising source of information about the universe’s beginning is the cosmic microwave background (CMB) — the remnant glow of the Big Bang that pervades all of space. This glow appears smooth and uniform at first, but upon closer inspection varies by small amounts. Those variations come from quantum fluctuations present at the birth of the universe that have been stretched as the universe expanded.

The conventional approach to distinguish different scenarios searches for possible traces of gravitational waves, generated during the primordial universe, in the CMB. “Here we are proposing a new approach that could allow us to directly reveal the evolutionary history of the primordial universe from astrophysical signals. This history is unique to each scenario,” says coauthor Xingang Chen of the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Texas at Dallas.

While previous experimental and theoretical studies give clues to spatial variations in the primordial universe, they lack the key element of time. Without a ticking clock to measure the passage of time, the evolutionary history of the primordial universe can’t be determined unambiguously.

“Imagine you took the frames of a movie and stacked them all randomly on top of each other. If those frames aren’t labeled with a time, you can’t put them in order. Did the primordial universe crunch or bang? If you don’t know whether the movie is running forward or in reverse, you can’t tell the difference,” explains Chen.

This new research suggests that such “clocks” exist, and can be used to measure the passage of time at the universe’s birth. These clocks take the form of heavy particles, which are an expected product of the “theory of everything” that will unite quantum mechanics and general relativity. They are named the “primordial standard clocks.”

Subatomic heavy particles will behave like a pendulum, oscillating back and forth in a universal and standard way. They can even do so quantum-mechanically without being pushed initially. Those oscillations or quantum wiggles would act as clock ticks, and add time labels to the stack of movie frames in our analogy.

“Ticks of these primordial standard clocks would create corresponding wiggles in measurements of the cosmic microwave background, whose pattern is unique for each scenario,” says coauthor Yi Wang of The Hong Kong University of Science and Technology. However, current data isn’t accurate enough to spot such small variations.

Ongoing experiments should greatly improve the situation. Projects like CfA’s BICEP3 and Keck Array, and many other related experiments worldwide, will gather exquisitely precise CMB data at the same time as they are searching for gravitational waves. If the wiggles from the primordial standard clocks are strong enough, experiments should find them in the next decade. Supporting evidence could come from other lines of investigation, like maps of the large-scale structure of the universe including galaxies and cosmic hydrogen.

And since the primordial standard clocks would be a component of the “theory of everything,” finding them would also provide evidence for physics beyond the Standard Model at an energy scale inaccessible to colliders on the ground.