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Some stars have split personalities

USING THE NEW CAPABILITIES of the upgraded Karl G. Jansky Very Large Array (VLA) radio telescope system, scientists have discovered previously-unseen 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.

artist's impression shows a disc of dust and gas surrounding a star

This artist’s impression shows a disc of dust and gas surrounding a star that is still in the process of formation. Evidence suggests that such discs sometimes split, leading to the formation of two or more stars. Image courtesy ESO / L. Calçada.

“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 flat cloud, called a disc, of gas and dust whirling around one young stars splits, forming another new star in orbit with the first. Astronomers call it the disc fragmentation model.

Fits the model

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 discs would be expected. One of the systems also clearly had a disc 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.

Aerial view of VLA dishes in a Y-shape

Dishes of the Karl G. Jansky Very Large Array. NRAO image.

The new observations add to a growing body of evidence supporting the disc-fragmentation idea. In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disc of material. The two discs, they found, were aligned with each other in the same plane. Last year, Tobin and his colleagues found a large disc forming around a protostar in the initial phases of formation. This showed that discs are present early in the star formation process, a necessity for binary pairs to form through disc fragmentation.

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

Adapted from information issued by NRAO.

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NASA to keep watch on asteroid

2012 DA14 trajectory past Earth

Asteroid 2012 DA14 will pass close to the Earth on February 15 (February 16, Australian time) – so close in fact, that it will be nearer to us than the ring of communications and weather satellites that orbit our planet.

THE RECORD-SETTING CLOSE APPROACH of an asteroid on February 15 (early morning February 16, Australian time) is an exciting opportunity for scientists, and a research team will use US National Radio Astronomy Observatory (NRAO) and NASA telescopes to gain a key clue that will help them predict the future path of this nearby cosmic neighbour.

A 45-metre-wide asteroid called 2012 DA14, discovered just a year ago, will pass only 28,000 kilometres above the Earth’s surface. That’s closer than the geosynchronous communication and weather satellites. While the object definitely will not strike the Earth, this is a record close approach for an object of this size. Astronomers around the world are preparing to take advantage of the event to study the asteroid.

A team including NRAO astronomer Michael Busch will use a novel observing technique to determine which way the space rock is spinning as it speeds on its orbit through the solar system. The direction of its spin is an important factor in predicting how the object’s orbit will change over time.

“Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years,” Busch said.

Radar observations

Busch’s team will use the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) antennae at Pie Town and Los Alamos, New Mexico, along with a radar on NASA’s 70-metre-diameter antenna at Goldstone, California.

The Goldstone antenna will transmit a powerful beam of radio waves toward the asteroid, and NRAO’s New Mexico antennae will receive the waves reflected from the asteroid’s surface.

Because of the asteroid’s uneven surface and the different reflectivity of portions of the surface, the reflected radar signal will have a characteristic signature, or ‘speckles,’ as seen from Earth. By measuring which antenna in a widely-separated pair receives the speckle pattern first, the astronomers can learn which way the asteroid is spinning.

This way of using the telescopes is significantly different to their normal astronomical observing, and the research team has developed special techniques for processing the data.

Yarkovsky Effect graphic

How the Yarkovsky Effect slows an asteroid’s orbital motion; opposite rotation direction would speed up the orbital motion.

Asteroid’s ‘afternoon’ heat

How does this tell anything about the asteroid’s orbital changes? Just as the afternoon is the warmest part of the day on Earth, the space rock develops a warm region that radiates infrared light in its maximum amount during ‘afternoon’ on the asteroid. That outgoing infrared radiation provides a gentle but firm jet-like push to the asteroid.

The direction of the asteroid’s spin determines whether ‘afternoon’ is either forward or rearward of its direction of motion.

If the hot spot is forward of the direction of motion, the infrared push will slow the asteroid’s orbital speed, and if the hot spot is rearward of the direction of motion, it will speed up the orbital motion. This effect, over time, can make a significant change in the orbit. This is called the Yarkovsky Effect, after the engineer who first identified it.

“When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time,” Busch said.

Adapted from information issued by the National Radio Astronomy Observatory. Yarkovsky Effect graphic by Alexandra Bolling, NRAO / AUI / NSF. Orbit graphic by P. Chodas, NASA / JPL.

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The Manatee Nebula

W50 supernova remnant

The W50 supernova remnant – now known as the Manatee Nebula – seen at radio wavelengths (green) against the background of stars and dust (seen at infrared wavelengths).

  • Supernova remnant cloud imaged by VLA radio telescope system
  • The cloud closely resembles the endangered Florida manatee
  • Manatees are gentle giants, until black holes, which are far from gentle

A NEW VIEW of a 20,000-year-old supernova remnant and shows how this giant cloud resembles a beloved endangered species, the Florida Manatee.

Known as W50, the supernova remnants is one of the largest ever viewed by the US National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA), which has recently been upgraded. Nearly 700 light-years across, seen from Earth W50 covers two degrees on the sky – that’s as wide as four full Moons.

The enormous W50 cloud formed when a giant star, 18,000 light-years away, exploded as a supernova around twenty thousand years ago, sending its outer gases flying outward in an expanding bubble.

The remaining, gravitationally-crushed relic of that giant star, most likely a black hole, feeds on gas from a very close, companion star. The cannibalised gas collects in a swirling cloud around the black hole.

The black hole’s powerful magnetic field snags charged particles out of the cloud and channels them outward in powerful jets travelling at nearly the speed of light.

The system shines brightly in both radio waves and X-rays and is known collectively as the SS 433 microquasar.

Over time, the microquasar’s jets have forced their way through the expanding gases of the W50 bubble, eventually punching bulges outward on either side. The jets also wobble, like an unstable spinning top, and blaze vivid corkscrew patterns across the inflating bulges.

Florida manatee

A Florida manatee rests underwater in Three Sisters Springs in Crystal River, Florida.

New namesake

When the W50 image reached the NRAO director’s office, Heidi Winter, the director’s executive assistant, saw the likeness to a manatee, the endangered marine mammals known as ‘sea cows’ that congregate in warm waters in the south-eastern United States.

Florida manatees are gentle giants that average around three metres long, weigh over 500kg, and spend up to eight hours a day grazing on sea plants. They occupy the remainder of their day resting, often on their backs with their flippers crossed over their large bellies, in a pose closely resembling W50.

Dangerous encounters with boat propellers injure many of these curious herbivores, giving them deep, curved scars similar in appearance to the arcs made by the powerful jets on the large W50 remnant.

Thanks to Ms Winter’s suggestion, the National Radio Astronomy Observatory has adopted a new nickname for W50: The Manatee Nebula.

Adapted from information issued by NRAO. W50 image courtesy NRAO / AUI / NSF, K. Golap, M. Goss; NASA’s Wide Field Survey Explorer (WISE). Manatee image courtesy Tracy Colson.

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Galactic super-volcano in action

HST image of M87

This Hubble Space Telescope image shows the central core and accompanying outflowing "jet" of the giant elliptical galaxy M87. In the centre of the galaxy there lurks a supermassive black hole.

A galactic “super-volcano” in the massive galaxy known as M87 is erupting and blasting gas outwards, as witnessed by NASA’s Chandra X-ray Observatory and the US National Science Foundation’s (NSF) Very Large Array (VLA) of radio telescopes.

The cosmic volcano is being driven by a giant black hole in the galaxy’s centre and preventing hundreds of millions of new stars from forming.

At a distance of about 50 million light-years, M87 is relatively close to Earth and lies at the centre of the Virgo cluster, which contains thousands of galaxies.

M87’s location, coupled with long observations over Chandra’s lifetime, has made it an excellent subject for investigations of how a massive black hole impacts its environment.

Core of the galaxy M87

This is the core of the galaxy M87, seen at X-ray and radio wavelengths. A huge black hole, hiding in the middle, is ejecting energetic particles that push gas outwards. That gas would ordinarily form millions of new stars, so the black hole's activity is acting like a brake on star formation.

“Our results show in great detail that supermassive black holes have a surprisingly good control over the evolution of the galaxies in which they live,” said Norbert Werner of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University and the SLAC National Accelerator Laboratory, who led one of two papers describing the study.

“And it doesn’t stop there. The black hole’s reach extends ever farther into the entire cluster, similar to how one small volcano can affect practically an entire hemisphere on Earth.”

The space around M87 is filled with hot gas glowing in X-ray light, which has been detected by Chandra. As this gas cools, it should fall in toward the M87’s centre where it could continue to cool even faster and form new stars.

However, radio observations with the Very Large Array suggest that in M87 jets of very energetic particles produced by the black hole interrupt this process. These jets lift up the relatively cool gas near the centre of the galaxy and produce shock waves in the galaxy’s “atmosphere” because of their supersonic speed.

In M87, the plumes of cooler gas being lifted upwards contain as much mass as all of the gas contained within 12,000 light-years of the centre of the galaxy cluster.

This shows the black hole-powered volcano is very efficient at blasting the galaxy free of the gas that would otherwise cool down and form stars.

The eruption in M87 that lifted up the cooler gas must have occurred about 150 million years earlier, but a smaller eruption only about 11 million years earlier produced the shock wave.

Adapted from information issued by Chandra X-ray Centre.

Images courtesy Tod R. Lauer, Sandra M. Faber / NASA / X-ray (NASA / CXC / KIPAC / N. Werner, E. Million et al); radio (NRAO / AUI / NSF / F. Owen)

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New star-forming regions found

The Orion Nebula

The Orion Nebula, an example of an H II gas cloud, where hydrogen gas is ionised and glows.

  • Previously-unknown star forming regions found
  • Scattered through the Milky Way
  • Hold chemical clues to stellar evolution

Astronomers studying the Milky Way have discovered a large number of previously-unknown regions where massive stars are being formed. Their discovery provides important new information about the structure of our home Galaxy and promises to yield new clues about the chemical composition of the Galaxy.

“We can clearly relate the locations of these star-forming sites to the overall structure of the Galaxy,” said Thomas Bania, of Boston University.

“Further studies will allow us to better understand the process of star formation and to compare the chemical composition of such sites at widely different distances from the Galaxy’s centre.”

Bania worked with Loren Anderson of the Astrophysical Laboratory of Marseille in France, Dana Balser of the US National Radio Astronomy Observatory (NRAO), and Robert Rood of the University of Virginia.

Gas clouds hidden from view

Artist's impression of the Milky Way looking from above

Our current understanding of the major components of our galaxy, the Milky Way (artist's impression shown here). Astronomers have found dozens more star-forming regions known as H II clouds.

The star-forming regions the astronomers sought, called H II regions, are sites where hydrogen atoms are ionised, or stripped of their electrons, by the intense radiation of the massive, young stars. To find these regions hidden from visible-light detection by the Milky Way’s gas and dust, the researchers used infrared and radio telescopes.

“We found our targets by using the results of infrared surveys done with NASA’s Spitzer Space Telescope and of surveys done with the US National Science Foundation’s (NSF) Very Large Array (VLA) radio telescope,” Anderson said. “Objects that appear bright in both the Spitzer and VLA images we studied are good candidates for H II regions.”

The astronomers then used the NSF’s giant Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, an extremely sensitive radio telescope. With the GBT, they were able to detect specific radio frequencies emitted by electrons as they recombined with protons to form hydrogen.

This evidence of recombination confirmed that the regions contained ionised hydrogen and thus are H II regions.

Our Galaxy’s chemical mix

Further analysis enabled the astronomers to determine the locations of the H II regions.  They found concentrations of the regions at the end of the Galaxy’s central elongated region and in its spiral arms. Their analysis also showed that 25 of the regions are farther from the Galaxy’s centre than the Sun.

“Finding the ones beyond the [Sun’s location] is important, because studying them will provide important information about the chemical evolution of the Galaxy,” Bania said. “There is evidence that the abundance of heavy elements changes with increasing distance from the Galactic centre.”

“We now have many more objects to study and improve our understanding of this effect.”

Adapted from information issued by NRAO / NASA / JPL-Caltech / R. Hurt (SSC-Caltech) / HHT (AURA / STScI / NASA).