Formation of a planetary system around the star HD169142

Image at 7 mm wavelength of the dusty disk around the star HD 169142 obtained with the Very Large Array (VLA) at 7 mm wavelength. 

The positions of the protoplanet candidates are marked with plus signs (+) (Osorio et al. 2014, ApJ, 791, L36). 

The insert in the upper right corner shows, at the same scale, the bright infrared source in the inner disk cavity, as observed with the ESO's Very Large Telescope (VLT) at 3.8 micron wavelength 

(Reggiani et al. 2014, ApJ, 792, L23).

Planets are formed from disks of gas and dust that orbit around young stars. Once the "seed" of the planet, composed of a small aggregate of dust, is formed, it will continue to gather material and it will carve out a cavity or gap in the disk along its orbital path.

This transitional stage between the original disk and the planetary system, difficult to study and as yet little known, is precisely what has been observed in the star HD169142 and is discussed in two articles published in The Astrophysical Journal Letters.

"Although in recent years more than seventeen hundred extrasolar planets have been discovered, few of them have been directly imaged, and so far we have never been able to capture an unequivocal image of an still-forming planet", says Mayra Osorio, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) heading one of the articles.

"In HD 169142 we may be seeing indeed those seeds of gas and dust which will later become planets."

HD169142 is a young star with twice the mass of the Sun and whose disk extends up to two hundred and fifty astronomical units (an astronomical unit, or AU, is a unit equivalent to the distance between the Sun and the Earth: one hundred and fifty million kilometers).

The system is in an optimal orientation for the study of planet formation because the disk is seen face-on.

The first article explores the disk of HD169142 with the Very Large Array (VLA) radio telescope, which can detect centimeter-sized dust grains.

The results, combined with infrared data which trace the presence of microscopic dust, reveal two gaps in the disk, one in the inner region (between 0.7 and 20 AU) and another, farther out and less developed, between 30 and 70 AU.

"This structure already suggested that the disk was being modified by two planets or sub-stellar objects, but, additionally, the radio data reveal the existence of a clump of material within the external gap, located approximately at the distance of Neptune's orbit, which points to the existence of a forming planet", says Mayra Osorio (IAA-CSIC). One (or two) companions around HD169142

The second study focused on searching for infrared sources in the gaps of the disk, using ESO's Very Large Telescope (VLT).

They found a bright signal in the inner gap, which could correspond to a still-forming planet or to a young brown dwarf (a sort of failed star that never reached the threshold mass to trigger the nuclear reactions characteristic of stars).

Infrared data did not, however, corroborate the presence of an object in the outer gap as radio observations suggested.

This non detection could be due to technical limitations: the researchers have calculated that an object with a mass between one tenth and 18 times the Jupiter's mass surrounded by a cold envelope may well remain undetected at the observed wavelength.

"In future observations we will be able to verify whether the disk harbors one or two objects. In any case, HD 169142 remains as a promising object since it is one of the few known transitional disks and it is revealing to us the environment where planets are formed", says Mayra Osorio (IAA-CSIC).

More information: M. Osorio et al. "Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm". The Astrophysical Journal Letters, 791, L36. DOI: 10.1088/2041-8205/791/2/L36

M. Reggiani et al. "Discovery of a companion candidate in the HD169142 transition disk and the possibility of multiple planet formation". The Astrophysical Journal Letters, 792, L23, DOI: 10.1088/2041-8205/792/1/L23

A violent, complex scene of colliding galaxy clusters

Colliding galaxy clusters MACS J0717+3745, more than 5 billion light-years from Earth. Background is Hubble Space Telescope image; blue is X-ray image from Chandra, and red is VLA radio image. 

Credit: Van Weeren, et al.; Bill Saxton, NRAO /AUI /NSF; NASA.

Astronomers using the Karl G. Jansky Very Large Array (VLA) and the Chandra X-Ray Observatory have produced a spectacular image revealing new details of violent collisions involving at least four clusters of galaxies.

Combined with an earlier image from NASA's Hubble Space Telescope (HST), the new observations show a complex region more than 5 billion light-years from Earth where the collisions are triggering a host of phenomena that scientists still are working to understand.

The HST image forms the background of this composite, with the X-ray emission detected by Chandra in blue and radio emission seen by the VLA in red.

The X-rays indicate hot, tenuous gas that pervades the region containing the galaxy clusters.

The large, oddly-shaped red feature at the center probably is a region where shocks caused by the collisions are accelerating particles that then interact with magnetic fields and emit the radio waves.

"The complex shape of this region is unique; we've never spotted anything like this before," said Reinout van Weeren, an Einstein Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

"The shape probably is the result of the multiple ongoing collisions," he added.

The new radio and X-ray observations are much more sensitive than previous ones, the scientists said. The combination of these images will make this region one of the best-studied examples of cluster-cluster collisions yet known, and can yield new insights on the complex interactions during cluster mergers.

Together, the merging clusters are called MACS J0717+3745, which also is one of the HST Frontier Fields for which HST will produce the deepest observations ever.

The scientists presented their findings to the American Astronomical Society's meeting in Boston, Mass.

The straight, elongated radio-emitting object is a foreground galaxy whose central black hole is accelerating jets of particles in two directions. The red object at bottom-left is a radio galaxy that probably is falling into the cluster.

Elliptical galaxies: Chandra helps explain 'red and dead galaxies'

Credit: X-ray: NASA /Chandra CXC /Stanford Univ /N.Werner et al.

NASA's Chandra X-ray Observatory has shed new light on the mystery of why giant elliptical galaxies have few, if any, young stars.

This new evidence highlights the important role that supermassive black holes play in the evolution of their host galaxies.

Because star-forming activity in many giant elliptical galaxies has shut down to very low levels, these galaxies mostly house long-lived stars with low masses and red optical colours.

Astronomers have therefore called these galaxies "red and dead."

Previously it was thought that these red and dead galaxies do not contain large amounts of cold gas—the fuel for star formation, helping to explain the lack of young stars.

ESA's Herschel Space Observatory

However, astronomers have used ESA's Herschel Space Observatory to find surprisingly large amounts of cold gas in some giant elliptical galaxies.

In a sample of eight galaxies, six contain large reservoirs of cold gas.

This is the first time that astronomers have seen large quantities of cold gas in giant elliptical galaxies that are not located at the center of a massive galaxy cluster.

With lots of cold gas, astronomers would expect many stars to be forming in these galaxies, contrary to what is observed.

To try to understand this inconsistency, astronomers studied the galaxies at other wavelengths, including X-rays and radio waves.

The Chandra observations map the temperature and density of hot gas in these galaxies.

For the six galaxies containing abundant cold gas, including NGC 4636 and NGC 5044 shown here, the X-ray data provide evidence that the hot gas is cooling, providing a source for the cold gas observed with Herschel.

However, the cooling process stops before the cold gas condenses to form stars. What prevents the stars from forming?

A strong clue comes from the Chandra images. The hot gas in the center of the six galaxies containing cold gas appears to be much more disturbed than in the cold gas-free systems.

This is a sign that material has been ejected from regions close to the central black hole. These outbursts are possibly driven, in part, by clumpy, cold gas that has been pulled onto the black hole.

The outbursts dump most of their energy into the center of the galaxy, where the cold gas is located, preventing the cold gas from cooling sufficiently to form stars.

The other galaxies in the sample, NGC 1399 and NGC 4472, are also forming few if any stars, but they have a very different appearance. No cold gas was detected in these galaxies, and the hot gas in their central regions is much smoother.

Additionally, they have powerful jets of highly energetic particles, as shown in radio images from the National Science Foundation's Karl G. Jansky Very Large Array.

These jets are likely driven by hot gas falling towards the central supermassive black holes.

By pushing against the hot gas, the jets create enormous cavities that are observed in the Chandra images, and they may heat the hot, X-ray emitting gas, preventing it from cooling and forming cold gas and stars.

The centers of NGC 1399 and NGC 4472 look smoother in X-rays than the other galaxies, likely because their more powerful jets produce cavities further away from the center, where the X-ray emission is fainter, leaving their bright cores undisturbed.

More information: A paper describing these results was published on 24 February 2014 in Monthly Notices of the Royal Astronomical Society: mnras.oxfordjournals.org/content/439/3/2291 , Preprint: arxiv.org/abs/1310.5450

Hubble Image: Starbursting in the galaxy M82

Credit: Josh Marvil (NM Tech/NRAO), Bill Saxton (NRAO/AUI/NSF), NASA

Messier 82 (M82), the galaxy in which the nearest supernova in decades recently exploded, also is the closest galaxy that is undergoing a rapid burst of star formation, known as a starburst.

About 12 million light-years away, it is seen nearly edge-on, as shown in the larger, visible-light image from the Hubble Space Telescope.

The inset is a new radio image, made with the Karl G. Jansky Very Large Array (VLA), that reveals fresh information about the central 5,200 light-years of the galaxy.

The radio emission seen here is produced by ionized gas and by fast-moving electrons interacting with the interstellar magnetic field.

The bright dots are a mix of star-forming regions and supernova remnants, the debris from stellar explosions; analysis of the VLA data tells scientists which of these are which.

Scientists also are studying the faint, wispy features, many of which were previously unseen, to investigate their relationship with this galaxy's starburst-driven superwind.

Supernova 2014J is located outside the inset, to the right. VLA observations to date show that, like all other supernovae of its particular type, SN 2014J has not yet been found to be emitting radio waves.

Jansky Very Large Array (VLA): Solving a 30-year-old problem in massive star formation

This false-colour Very Large Array image of the ionized gas in the star forming region Sgr B2 Main was used to detect small but significant changes in brightness of several of the sources. 

The spots and filaments in this image are regions of ionized gas around massive stars. 

The changes in brightness detected support a model that could solve a 30-year-old question in high mass star formation. 

Credit: NRAO /Agnes Scott College

An international group of astrophysicists has found evidence strongly supporting a solution to a long-standing puzzle about the birth of some of the most massive stars in the universe.

Young massive stars, which have more than 10 times the mass of the Sun, shine brightly in the ultraviolet, heating the gas around them, and it has long been a mystery why the hot gas doesn't explode outwards.

Now, observations made by a team of researchers using the Jansky Very Large Array (VLA), a radio astronomy observatory in New Mexico, have confirmed predications that as the gas cloud collapses, it forms dense filamentary structures that absorb the star's ultraviolet radiation when it passes through them. As a result, the surrounding heated nebula flickers like a candle.

The findings were published recently in The Astrophysical Journal Letters.

"Massive stars dominate the lives of their host galaxies through their ionizing radiation and supernova explosions," said Mordecai-Mark Mac Low, a curator in the American Museum of Natural History's Department of Astrophysics and an author on the paper.

"All the elements heavier than iron were formed in the supernova explosions occurring at the ends of their lives, so without them, life on Earth would be very different."

Observations of the massive star forming region Sgr B2 were made with the Karl G. Jansky Very Large Array (VLA) in 1989 and 2012. 

The VLA has been operational since 1980 and received a major upgrade that was completed in 2011. 

Credit: NRAO/AUI

Stars form when huge clouds of gas collapse. Once the density and temperature are high enough, hydrogen fuses into helium, and the star starts shining.

The most massive stars, though, begin to shine while the clouds are still collapsing.

Their ultraviolet light ionizes the surrounding gas, forming a nebula with a temperature of 10,000 degrees Celsius. Simple models suggest that at this stage, the gas around massive stars will quickly expand.

But observations from the VLA radio observatory show something different: a large number of regions of ionized hydrogen (so-called HII regions) that are very small.

"In the old theoretical model, a high-mass star forms and the HII region lights up and begins to expand."

Chris De Pree

"Everything was neat and tidy," said lead author Chris De Pree, a professor of astronomy and director of the Bradley Observatory at Agnes Scott College.

"But the group of theorists I am working with were running numerical models that showed accretion was continuing during star formation, and that material was continuing to fall in toward the star after the HII region had formed."

More information: arxiv.org/abs/1312.7768

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/

ESO VLA Explores Dragon's Head Nebula in Large Magellanic Cloud - Video

A lesser known region of the Large Magellanic Cloud, NGC 2035 (right), has been photographed using the European Southern Observatory Very Large Telescope (VLT) in Chile. 

The effects of new star birth and stellar death are on display.

Credit: ESO

Chandra confirm evidence of jet in Milky Way's black hole

Composite image of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. 

Credit: X-ray: NASA /CXC /UCLA /Z. Li et al; Radio: NRAO /VLA

Astronomers have long sought strong evidence that Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is producing a jet of high-energy particles. 

Finally they have found it, in new results from NASA's Chandra X-ray Observatory and the National Science Foundation's Very Large Array (VLA) radio telescope.

Previous studies, using a variety of telescopes, suggested there was a jet, but these reports—including the orientation of the suspected jets—often contradicted each other and were not considered definitive.

"For decades astronomers have looked for a jet associated with the Milky Way's black hole. Our new observations make the strongest case yet for such a jet," said Zhiyuan Li of Nanjing University in China, lead author of a study appearing in an upcoming edition of the Astrophysical Journal and available online now.

Jets of high-energy particles are found throughout the universe, on large and small scales. They are produced by young stars and by black holes a thousand times larger than the Milky Way's black hole.

They play important roles in transporting energy away from the central object and, on a galactic scale, in regulating the rate of formation of new stars.

"We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole's spin axis.

This gives us important clues about the growth history of the black hole," said Mark Morris of the University of California at Los Angeles, a co-author of the study.

The study shows the spin axis of Sgr A* is pointing in one direction, parallel to the rotation axis of the Milky Way, which indicates to astronomers that gas and dust have migrated steadily into Sgr A* over the past 10 billion years.

If the Milky Way had collided with large galaxies in the recent past and their central black holes had merged with Sgr A*, the jet could point in any direction.

The jet appears to be running into gas near Sgr A*, producing X-rays detected by Chandra and radio emission observed by the VLA.

The two key pieces of evidence for the jet are a straight line of X-ray emitting gas that points toward Sgr A* and a shock front—similar to a sonic boom—seen in radio data, where the jet appears to be striking the gas.

Additionally, the energy signature, or spectrum, in X-rays of Sgr A* resembles that of jets coming from supermassive black holes in other galaxies.

Scientists think jets are produced when some material falling toward the black hole is redirected outward. Since Sgr A* is presently known to be consuming very little material, it is not surprising that the jet appears weak.

A jet in the opposite direction is not seen, possibly because of gas or dust blocking the line of sight from Earth or a lack of material to fuel the jet.

The region around Sgr A* is faint, which means the black hole has been quiet in the past few hundred years.

However, a separate Chandra study announced last month shows that it was at least a million times brighter before then.

"We know this giant black hole has been much more active at consuming material in the past. When it stirs again, the jet may brighten dramatically," said co-author Frederick K. Baganoff of the Massachusetts Institute of Technology in Cambridge, Mass.

More information: "Evidence for a Parsec-scale Jet from the Galactic Center Black Hole: Interaction with Local Gas," Zhiyuan Li, Mark R. Morris, and Frederick K. Baganoff. xxx.lanl.gov/abs/1310.0146

NASA Chandra: Black Hole-Powered Jets Collides with nearby Galaxy

Image Credit: NASA

This composite image of a galaxy illustrates how the intense gravity of a supermassive black hole can be tapped to generate immense power. 

The image contains X-ray data from NASA's Chandra X-ray Observatory (blue), optical light obtained with the Hubble Space Telescope (gold) and radio waves from the NSF’s Very Large Array (pink).

This multi-wavelength view shows 4C+29.30, a galaxy located some 850 million light years from Earth. 

The radio emission comes from two jets of particles that are speeding at millions of miles per hour away from a supermassive black hole at the center of the galaxy. 

The estimated mass of the black hole is about 100 million times the mass of our Sun. The ends of the jets show larger areas of radio emission located outside the galaxy.

The X-ray data show a different aspect of this galaxy, tracing the location of hot gas. The bright X-rays in the center of the image mark a pool of million-degree gas around the black hole. 

Some of this material may eventually be consumed by the black hole, and the magnetized, whirlpool of gas near the black hole could in turn, trigger more output to the radio jet.

Most of the low-energy X-rays from the vicinity of the black hole are absorbed by dust and gas, probably in the shape of a giant doughnut around the black hole. 

This doughnut, or torus blocks all the optical light produced near the black hole, so astronomers refer to this type of source as a hidden or buried black hole. 

The optical light seen in the image is from the stars in the galaxy.

ALMA and VLA Image: Star Formation Close to Milky Way's Supermassive Black Hole

A combined ALMA and ESO's  Very Large Array (VLA) image of the galactic center. 

The supermassive black hole is marked by its traditional symbol Sgr A*. 

The red and blue areas, taken with ALMA, map the presence of silicon monoxide, an indicator of star formation. 

The blue areas have the highest velocities, blasting out at 150-200 kilometers per second. 

The green region, imaged with the VLA, traces hot gas around the black hole and corresponds to an area 3.5 by 4.5 light-years. 

Credit: Yusef-Zadeh et al., ALMA (ESO, NAOJ, NRAO), NRAO/AUI/NSF.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered signs of star formation perilously close to the supermassive black hole at the center of the Milky Way Galaxy.

If confirmed, this would be the first time that star formation was observed so close to the galactic center.

The center of our galaxy, 27,000 light-years away in the direction of the constellation Sagittarius, is home to a monstrous black hole with a mass of four million suns.

Extending outward from this gravitational behemoth for many light-years is a turbulent region of space that is thought to be wracked by such extreme tidal forces that any star-forming clouds of dust and gas would be stretched thin and shredded long before infant stars could emerge.

Yet against these extreme odds, ALMA spotted telltale jets of material bursting out of what appear to be dense cocoons of gas and dust.

These jets, if they were observed in more placid surroundings, would indicate the formation of a young star. The results were accepted for publication in the Astrophysical Journal Letters.

Farhad Yusef-Zadeh

"People think it is very hard to form stars near a supermassive black hole," said Farhad Yusef-Zadeh of Northwestern University.

"This is because the gravity of the black hole produces extreme tidal forces that would stretch and elongate molecular clouds, preventing them from ever accumulating enough mass to trigger star formation. But what we seem to have found are patches of dust and gas that have become so dense that they are able to overcome their inhospitable surroundings."

Yusef-Zadeh and his colleagues speculate that these molecular clouds have become so massive and dense, possibly by colliding together, that they cross the all-important threshold that allows internal gravity to take over, starting a chain of events that inexorably leads to the birth of a new star.

As this process evolves, material in these clouds clumps together and collapses into an ever denser mass that begins to rotate faster and faster.

This rapid rotation, possibly coupled with the star's magnetic field, accelerates some of the material and shoots it out into space along the nascent star's axis of rotation.

The astronomers were able to detect these characteristic jets of material by tracing the presence of the molecule silicon monoxide (SiO), which is relatively abundant in molecular clouds.

When excited during star formation, SiO emits a very specific set of wavelengths of light in the microwave, or millimeter range. This is precisely the window of light that ALMA was designed to study.

Silicon Monoxide (SiO)

"SiO is an excellent tracer of molecular outflows," said Yusef-Zadeh.

"What we see in these images from ALMA are outflows that appear very much like what we see in star-forming regions elsewhere in galaxy. So the environments may be very different, but once you get the right conditions, collapse takes place and you're able to create what we would observe to be run-of-the-mill massive or intermediate mass stars."

For more than a decade, astronomers have puzzled over the origin of stars seen whipping around the black hole that lurks at the center of our galaxy.

These massive, young stars (less than 10 million years old) are rocketing through an area of space where it was thought they had no business being.

Astronomers believe that they either formed elsewhere under more placid conditions and migrated inward or they somehow overcame their turbulent childhoods to emerge as relatively normal and well-adjusted stellar objects.

"Though this question of stars near the galactic center is still open ended, ALMA will definitely have the power and sensitivity to shed more light on the mystery," said Al Wootten, the North America ALMA Project Scientist with the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia.

"These latest studies do suggest that the conditions necessary for star formation could extend much closer to the galactic center than we previously believed."

NSF VLA Image: Microquasar Makes a Giant Manatee Nebula

W50 supernova remnant in radio (green) against the infrared background of stars and dust (red). Credits: NRAO/AUI/NSF, K. Golap, M. Goss; NASA's Wide Field Survey Explorer (WISE).

A new view of a 20,000-year old supernova remnant demonstrates the upgraded imaging power of the National Science Foundation's (NSF) Karl G. Jansky Very Large Array (VLA) and provides more clues to the history of this giant cloud that resembles a beloved endangered species, the Florida Manatee.

W50 is one of the largest supernova remnants ever viewed by the VLA. At nearly 700 light years across, it covers two degrees on the sky - that's the span of four full Moons!

Aquila, 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 cannibalized gas collects in a disk around the black hole.

The disk and black hole's network of powerful magnetic field lines acts like an enormous railroad system to snag charged particles out of the disk and channel them outward in powerful jets traveling at nearly the speed of light.

This system of a black hole and its feeder star shines brightly in both radio waves and X-rays and is known collectively as the SS433 microquasar.

Over time, the micro quasar'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.

Karl G. Jansky Very Large Array (VLA): Black-Hole Discovery Changes Picture of Messier 22

An unexpected discovery by astronomers using the National Science Foundation's Karl G. Jansky Very Large Array (VLA) is forcing scientists to rethink their understanding of the environment in globular star clusters, tight-knit collections containing hundreds of thousands of stars.

The astronomers used the VLA to study a globular cluster called Messier 22 (M22), a group of stars more than 10,000 light-years from Earth.

They hoped to find evidence for a rare type of black hole in the cluster's center.

They wanted to find what scientists call an intermediate-mass black hole, more massive than those a few or more times the Sun's mass, but smaller than the supermassive black holes found at the cores of galaxies.

"We didn't find what we were looking for, but instead found something very surprising -- two smaller black holes," said Laura Chomiuk, of Michigan State University and the National Radio Astronomy Observatory.

"That's surprising because most theorists said there should be at most one black hole in the cluster," she added.

Laura Chomiuk

Black holes, concentrations of mass so dense that not even light can escape them, are left over after very massive stars have exploded as supernovae.

In a globular cluster, many of these stellar-mass black holes probably were produced early in the cluster's 12-billion-year history as massive stars rapidly passed through their life cycles.

Simulations have indicated that these black holes would fall toward the center of the cluster, then begin a violent gravitational dance with each other, in which all of them or perhaps all but a single one would be thrown completely out of the cluster.

"There is supposed to be only one survivor possible," said Jay Strader, of Michigan State University and the Harvard-Smithsonian Center for Astrophysics.

Jay Strader

"Finding two black holes, instead of one, in this globular cluster definitely changes the picture," he said.

The astronomers suggest some possible explanations. First, the black holes themselves may gradually work to puff up the central parts of the cluster, reducing the density and thus the rate at which black holes eject each other through their gravitational dance.

Alternatively, the cluster may not be as far along in the process of contracting as previously thought, again reducing the density of the core.

"Future VLA observations will help us learn about the ultimate fate of black holes in globular clusters," Chomiuk said.

The two black holes discovered with the VLA were the first stellar-mass black holes to be found in any globular cluster in our own Milky Way Galaxy, and also are the first found by radio, instead of X-ray, observations.