Binary-star formation theory: New studies give a strong boost to swirling disk

Binary star formation through disk fragmentation.

The disk fragments under its own gravity, with a second star forming within the disk (center), surrounded by its own disk. 

Credit: Bill Saxton, NRAO/AUI/NSF

Using the new capabilities of the upgraded Karl G. Jansky Very Large Array (VLA), scientists have discovered previously-unseen binary companions to a pair of very young protostars.

The discovery gives strong support for one of the competing explanations for how double-star systems form.

Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed.

John Tobin

"The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation," said John Tobin, of the National Radio Astronomy Observatory (NRAO).

"That's what we've done with the stars we observed, and we got valuable new clues from them," he added.

Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first.

Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk.

Binary star formation through disk fragmentation starts (left) with a young star surrounded by a rotating disk of gas and dust. 

The disk fragments under its own gravity, with a second star forming within the disk (center), surrounded by its own disk. 

At right, the two stars form an orbiting pair. 100 Astronomical Units (AU) is roughly the diameter of our Solar System. 

Credit: Bill Saxton, NRAO/AUI/NSF

When Tobin and an international team of astronomers studied gas-enshrouded young stars roughly 1,000 light-years from Earth, they found that two had previously-unseen companions in the plane where their disks would be expected, perpendicular to the direction of the outflows from the systems.

One of the systems also clearly had a disk surrounding both young stars.

"This fits the theoretical model of companions forming from fragmentation in the disk," Tobin said. "This configuration would not be required by alternative explanations," he added.

The new observations add to a growing body of evidence supporting the disk-fragmentation idea.

In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disk of material.

The two disks, they found, were aligned with each other in the same plane.

Last year, Tobin and his colleagues found a large circumstellar disk forming around a protostar in the initial phases of star formation.

This showed that disks are present early in the star formation process, a necessity for binary pairs to form through disk fragmentation.

Leslie Looney

"Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed," said Leslie Looney of NRAO and the University of Illinois.

"The increased sensitivity of the VLA, produced by a decade-long upgrade project completed in 2012, made the new discovery possible," Claire Chandler of NRAO said.

The new capability was particularly valuable at the VLA's highest frequency band, from 40-50 GHz, where dust in the disks surrounding young stars emits radio waves.

The astronomers observed the young stars during 2012 with the VLA and with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California.

Tobin, Chandler, and Looney were part of a research team of astronomers from the U.S., Mexico, and the Netherlands.

The scientists published their findings in the Astrophysical Journal.

More information: iopscience.iop.org/0004-637X/779/2/93/

Black holes found in globular star clusters, upsetting 40 years of theory

The black hole above was discovered in the M62 star cluster, which is 23,000 light years away from Earth. 

These star clusters contain some of the oldest stars in the galaxy.

A Texas Tech University astrophysicist was part of a team of researchers that discovered the first examples of black holes in globular star clusters in our own galaxy, upsetting 40 years of theories against their possible existence.

Tom Maccarone, an associate professor of physics, said the team detected the existence of the black holes by using an array of radio telescopes to pick up a certain type of radio frequency released by these black holes as they eat a star next to them.

The results were published in the Astrophysical Journal and featured in the National Radio Astronomy Observatory's ENews news bulletin.

Globular star clusters are large groupings of stars thought to contain some of the oldest stars in the universe.

In the same distance from our sun to the nearest neighbour, Proxima Centauri, its nearest neighbor, these globular star clusters could have a million to tens of millions of stars, Maccarone said.

Tom Maccarone

"The stars can collide with one another in that environment," Maccarone said. "The old theory believed that the interaction of stars was thought to kick out any black holes that formed. They would interact with each other and slingshot black holes out of the cluster until they were all gone."

He compared it to water vapor coming off a hot cup of coffee. As some water molecules get hot enough to turn to steam, they are let go from their environment to float off into the atmosphere even though the coffee may be below the boiling temperature of water.

The old theory stated that the stars would kick the black holes out in the same fashion – occasionally, some black holes would have enough energy to escape the cluster, and gradually, they all would leave.

While the theory may still be displaced, Maccarone said it might still be somewhat true. Black holes might still get kicked out of globular star clusters, but at a much slower rate than initially believed.

Radio image (left) and x-ray image (right). The yellow circle shows the black hole found in the M62 star cluster in our Galaxy. The red circle denotes a neutron star close by.

In 2007, Maccarone made the first discovery of a black hole in a globular star cluster in the neighboring NGC4472 galaxy. But rather than finding it by using radio waves, Maccarone found it by seeing an X-ray emission from the gas falling into the black hole and heating up to a few million degrees.

"Six years ago I had made the first discoveries in other galaxies," he said. "It's surprisingly easier to find them in other galaxies than in our own, even though they're a thousand times as far away as these in our own galaxy are."

This year, he and his team discovered two examples of globular star clusters in our own galaxy which host black holes by finding radio emission by using the Very Large Array of radio telescopes in New Mexico.

"As the black hole eats a star, these jets of material are coming out," he said.

"Most of the material falls into the black hole, but some is thrown outwards in a jet. To see that jet of material, we look for a radio emission. We found a few radio emissions coming from this globular star cluster that we couldn't explain any other way."

Maccarone said seeing black holes in globular clusters may provide a way for them to get close enough to one another to merge into bigger black holes.

"These mergers may produce the 'ripples in spacetime' we call gravitational waves," he said. "Trying to detect gravitational waves is one of the biggest problems in physics right now, because it would be the strongest test of whether Einstein's theory of relativity is correct."

More information: iopscience.iop.org/0004-637X/

Harvard Astronomer Pays Tribute to Van Gogh with Hubble Mosaic

One night, Harvard astronomer Alex Parker was camped out at the telescope for a spot of star-gazing, and found himself facing a long, dry period of waiting for the clouds to clear.

To pass the time, he started playing around with various images from the Hubble Space Telescope, and ended up assembling them into a colorful mosaic.

The resulting image? A recreation of Vincent van Gogh's most famous painting, "Starry Night".

Alex Parker, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics’ Institute for Theory and Computation, has created several astronomical videos on his own time and posted them on the Internet. 

His latest video depicts the 2,299 planet candidates Kepler has found since it began searching for planets around stars in 2009. 

According to sources "Parker used photo-mosaicing software to assemble the digital collage."

He had been thinking about using Hubble images to make a mosaic for awhile, since the telescope's 22nd anniversary was approaching; he just needed the right circumstances to find the time -- a cloudy night.

"Observing can be all over the map," Parker reported about his artistic endeavour. "You will be shut out by clouds on some nights, have to evacuate the mountain because of high winds and ice on other nights, and other times there isn't a moment to pause because you're taking data at such a high rate all night."

Turing's Morphogen Theory: Supporting Evidence Discovered

A team of UK researchers claims to have put forth the first ever experimental evidence in support of a long-standing theory about how biological patterns such as a leopard’s spots or a tiger’s stripes are formed.

The study was the work of experts from King’s College London, and according to a February 19 press release from the school, “The findings provide evidence to support a theory first suggested in the 1950s by famous code-breaker and mathematician Alan Turing,” who championed the idea that “regular repeating patterns in biological systems are generated by a pair of morphogens that work together as an ‘activator’ and ‘inhibitor’.”

Their work “not only demonstrates a mechanism which is likely to be widely relevant in vertebrate development, but also provides confidence that chemicals called morphogens, which control these patterns, can be used in regenerative medicine to differentiate stem cells into tissue,” the college added.

To test their theory, the King’s College London researchers analyzed the development of regularly-spaced ridges that can be found in the mouths of mice.

Alan Turing

By conducting experiments using embryos of the rodents, they were able to discover the pair of morphogens that work together to help determine where each of the ridges will be formed.

Each chemical influenced the other, the university said, alternately activating or inhibiting production in order to control the creation of the ridge pattern on the roof of a mouse’s mouth.

The morphogens involved in the process were identified by the scientists as Fibroblast Growth Factor (FGF) and Sonic Hedgehog (Shh), and by studying them, they learned that when each chemical’s activity is increased or decreased, it affected the pattern of the ridges in the mouth in the same way that Turing’s equations had predicted they would.

“For the first time the actual morphogens involved in this process have been identified and the team were able to see exactly the effects predicted by Turing’s 60-year-old speculative theory,” the college press release stated.

“Regularly spaced structures, from vertebrae and hair follicles to the stripes on a tiger or zebrafish, are a fundamental motif in biology.

There are several theories about how patterns in nature are formed, but until now there was only circumstantial evidence for Turing’s mechanism.

Dr Jeremy Green

Our study provides the first experimental identification of an activator-inhibitor system at work in the generation of stripes – in this case, in the ridges of the mouth palate,” Dr. Jeremy Green from the Department of Craniofacial Development at King’s Dental Institute added in a statement.

While Green admitted that the discovery was “not of great medical significance,” he said that they are “extremely valuable” in validating Turing’s theories from the 1950s.

He also says that their discovery has made them confident that these morphogen chemicals could be used in the future to create regenerative medicine to heal or recreate structures and/or patterns when turning stem cells into other types of tissues.

The research was funded by the Medical Research Council and is published online in the journal Nature Genetics.

Scottish Engineers prove space communications theory

When American space pioneer, Dr Robert L Forward, proposed in 1984 a way of greatly improving satellite telecommunications using a new family of orbits, some claimed it was impossible.

But now engineers at the University of Strathclyde's Advanced Space Concepts Laboratory have proved that Forward was right.

The late Dr Forward - a renowned physicist who worked in the United States and from his second home in Scotland - believed it was possible to use 'displaced orbits' to deploy more satellites to the north or south of the Earth's equator, helping to meet the growing demand for communications.

He proposed that the orbit of a geostationary satellite could be pushed above - or below - the usual geostationary ring around the Earth, which follows the line of the equator, by using a large solar sail propelled by the pressure of sunlight. However, critics later claimed that such 'displaced orbits' were impossible due to the unusual dynamics of the problem.

Now graduate student Shahid Baig and Professor Colin McInnes, Director of the Advanced Space Concepts Laboratory, have shown that Forward was in fact correct, in a new paper published in the Journal of Guidance, Control and Dynamics.

Professor McInnes said:"Satellites generally follow Keplerian Orbits, named after Johannes Kepler - the scientist who helped us understand orbital motion 400 years ago. Once it's launched, an unpowered satellite will 'glide' along a natural Keplerian orbit.

"However, we have devised families of closed, non-Keplerian orbits, which do not obey the usual laws of orbital motion. Families of these orbits circle the Earth every 24 hours, but are displaced north or south of the Earth's equator. The pressure from sunlight reflecting off a solar sail can push the satellite above or below geostationary orbit, while also displacing the centre of the orbit behind the Earth slightly, away from the Sun."

Although the displacement distance above or below the equator is small - of the order of 10 to 50 km - work on hybrid solar sails, which use both light pressure and thrust from a conventional electric propulsion system, is underway and aims to improve the displacement distance.

Professor McInnes added: "Other work is investigating 'polar stationary orbits', termed 'pole-sitters' by Forward, which use continuous low thrust to allow a spacecraft to remain on the Earth's polar axis, high above the Arctic or Antarctic. These orbits could be used to provide new vantage points to view the Earth's polar regions for climate monitoring."

Podcast: Richard Bradley on Risk based behaviour and Decision making theory

Zoeken philosophybites UPC

Podcast by Richard Bradley on Risk based behaviour and Decision making theory - This discussion, hosted by Philosopy Bites, draws somewhat from the tragic figure of UK polymath Frank Ramsey

Chaos Theory Moves on: What about Entanglement?

At the level of atoms, our definition of chaos has run into a problem.

Chaos is usually defined by a system’s movement: Set a pendulum swinging, track exactly where it goes, and its motion will reveal whether it is chaotic. Atoms, however, are governed by the uncertainty principle, which means that their location cannot be known precisely. What’s more, the laws of quantum mechanics say that hypersensitivity to initial conditions, which is considered the primary characteristic of a chaotic system, is physically impossible for atoms—at least in the way it’s understood at the classical level.

This presents a serious quandary because quantum mechanics is considered the most basic set of universal laws. Chaos must have some connection with the quantum level, but how it manifests itself, or how to quantify it, has thus far eluded physicists. Work published recently in Nature helps shed light on this problem as researchers working with cooled atoms searched for what they call signatures of chaos.

If such hypersensitivity to initial conditions cannot happen in a quantum system, other red flags of classical chaos might still be detectable. This could indicate that chaos in some form could exist at the level of atoms, or, at the very least, would imply a connection between quantum events and classical chaos. “Though you will never be able to find hypersensitivity to initial conditions in the quantum system, you are able to tell if the outward signs produced by classical chaotic systems are the same in quantum systems,” says Poul Jessen of Arizona State University, the lead researcher on the Nature paper.

In order to see these signatures, physicists have taken the conditions that cause chaotic behavior in human-scale systems and applied them on the atomic level. Jessen and his collaborators recently succeeded in making a quantum “kicked top” out of cesium atoms for the first time.

Kicked tops are an excellent example of chaotic systems when it comes to classic physics. You start an object twirling—say, a gyroscope—and then give it a series of kicks and twists as it spins. The initial condition that decides whether a gyroscope moves stably or chaotically is the direction of its axis when it starts spinning.

In order to visualize the gyroscope’s behaviour, the different values of its angular momentum are plotted on the surface of a globe. Some initial orientations of its axis cause the momentum to swerve in a “chaotic sea,” covering most of the surface of the globe. But other orientations cause the spin to settle into stable, regular motion in one of three main “islands” in the sea.

In their experiment, researchers substituted atoms for gyroscopes and looked at how angular momenta affected the atoms’ quantum states. What they found was intriguing: Some spins of the quantum top locked the atoms into a stable set of islands, while other values let the atoms’ quantum states wander erratically.

The number and location of the islands, when plotted, corresponded eerily to the classical model. So while the atoms’ behavior could not technically be called chaotic because they cannot show hypersensitivity, they mimicked the evolution of the classical, chaotic system almost exactly. Other measurements indicated that the system might have some sensitivity to disturbances, another interesting link to chaotic behaviour.

These observations alone provided good evidence that something related to chaos was happening. But the most fascinating result was that one of the strangest properties of atoms, entanglement, shot up in areas corresponding to the chaotic sea. When two quantum-scale objects, like atoms or nuclei, are entangled, performing an action on one instantaneously affects the other even if vast distances separate the entangled objects. Einstein famously called entanglement “spooky action at a distance,” and it forms the basis of modern attempts to built quantum computers.

Could entanglement be a signature of chaos?

Read the full article in Seed magazine ..............