Astronomers Take Sharpest Photos Ever of the Night Sky

Equipped with the newly developed MagAO adaptive optics system, the Magellan Telescope revealed details about the Orion nebula. The background image, taken with the Hubble Space Telescope, shows the Trapezium cluster of young stars (pink) still in the process of forming. The middle inset photo reveals the binary nature of the Theta Ori C star pair. The bottom insert shows a different binary young star pair shaped by the stellar wind from Theta 1 Ori C. (Credit: Laird Close and Ya-Lin Wu; NASA, C.R. O'Dell and S.K. Wong)

Astronomers at the University of Arizona, the Arcetri Observatory near Florence, Italy and the Carnegie Observatory have developed a new type of camera that allows scientists to take sharper images of the night sky than ever before.

The team has been developing this technology for more than 20 years at observatories in Arizona, most recently at the Large Binocular Telescope, or LBT, and has now deployed the latest version of these cameras in the high desert of Chile at the Magellan 6.5-meter telescope.

"It was very exciting to see this new camera make the night sky look sharper than has ever before been possible," said UA astronomy professor Laird Close, the project's principal scientist. "We can, for the first time, make long-exposure images that resolve objects just 0.02 arcseconds across -- the equivalent of a dime viewed from more than a hundred miles away. At that resolution, you could see a baseball diamond on the moon."

The twofold improvement over past efforts rests on the fact that for the first time, a telescope with a large diameter primary mirror is being used for digital photography at its theoretical resolution limit in visible wavelengths -- light that the human eye can see.

"As we move towards shorter wavelengths, image sharpness improves," said Jared Males, a NASA Sagan Fellow at the UA's department of astronomy. "Until now, large telescopes could make the theoretically sharpest photos only in infrared -- or long wavelength -- light, but our new camera can take photos that are twice as sharp in the visible light spectrum."

These images are also at least twice as sharp as what the Hubble Space Telescope can make, because with its 21-foot diameter mirror, the Magellan telescope is much larger than Hubble with its 8-foot mirror. Until now, Hubble always produced the best visible light images, since even large ground-based telescope with complex adaptive optics imaging cameras could only make blurry images in visible light.

To overcome atmospheric turbulence, which plagues earth-based telescopes by causing the image to blur, Close's team developed a very powerful adaptive optics system that floats a thin (1/16th of an inch) curved glass mirror (2.8 feet across) on a magnetic field 30 feet above the telescope's primary mirror.

This so-called Adaptive Secondary Mirror (ASM) can change its shape at 585 points on its surface 1,000 times each second, counteracting the blurring effects of the atmosphere.

"As a result, we can see the visible sky more clearly than ever before," Close said. "It's almost like having a telescope with a 21-foot mirror in space."

The new adaptive optics system, called MagAO for "Magellan Adaptive Optics," has already made some important scientific discoveries, published today in three scientific papers in theAstrophysical Journal. As the system was being tested and received what astronomers call "first light," the team pointed it to a famous and well-studied massive star that gives the Great Orion Nebula (Object M42) most of its UV light. The Orion Nebula, located just below Orion's Belt visible as smudge of light even with regular binoculars.

Considered young at about 1 million years old, this star, called Theta 1 Ori C, has been previously known to be in fact a binary star pair made up of two stars called C1 and C2. However, the separation between the two is so small -- about the average distance between Earth and Uranus -- that astronomers had never been able to resolve the famous pair in a direct telescope photo.

Once MagAO and its visible science camera called VisAO were pointed towards Theta Ori 1 C, the results were immediate.

"I have been imaging Theta 1 Ori C for more than 20 years and never could directly see that it was in fact two stars," Close said. "But as soon as we turned on the MagAO system it was beautifully split into two stars."

In another result, MagAO has shed light on another mystery: How do how planets form from disks of dust and gas affected by the strong ionizing light called stellar wind coming from a massive star like Theta 1 Ori C, which has about 44 times the mass of the sun?

The team used MagAO and VisAO to look for red light from ionized hydrogen gas to trace out how the strong UV radiation and stellar wind from Theta 1 Ori C affects the disks around its neighboring stars.

"Close to Theta 1 Ori C, there are two very young stars surrounded by disks of gas and dust," said Ya-Lin Wu, a graduate student and lead author on one of the publications. "Theta 1 Ori C pummels those disks with stellar wind and UV light. It looks like they are being bent backwards by a strong wind."

MagAO's photo revealed that the two stars and their protoplanetary disks are heavily distorted into teardrop shapes as the strong UV light and wind create shock fronts and drag gas downwind of the pair.

The distribution of gas and dust in young planetary systems is another unsolved problem in planet formation. The team used VisAO's simultaneous/spectral differential imager, or SDI, to estimate the mass of another intriguing object in the Orion Nebula: one of a few stars in Orion sporting a rare "silhouette disk." The SDI camera allowed the light from the star to be removed at a very high level -- offering, for the first time, a clear look at the inner regions of the silhouette.

"The disk lies in front of the bright Orion nebula, so we see the dark shadow cast as the dust in the disk absorbs background light from the nebula," said Kate Follette, a graduate student and lead author of one of the three papers published in theAstrophysical Journal. "Picture a moth flying across a bright movie screen: Its body will appear opaque, while the wings will be partially transparent. Our SDI instrument allows us to peer into the silhouette and trace how much dust is at each location in the disk based on how transparent or opaque it is."

"We were surprised to find that the amount of attenuated light from the nebula never reached an opaque point," she said. "It seems as though the outer parts of this disk have less dust than we would have expected."

"It is important to understand how dust is laid out in these objects because that dust and gas is what nature uses to build planets," Close explained. "Our new imaging capabilities revealed there is very little dust and gas in the outer part of the disk."

According to Close, the silhouette disk might have been close to the massive star Theta 1 Ori C at some point, which might have blown away its outer dust and gas.

"This tells us something about planet-forming disks in these dense, stellar nurseries," Close said. "There appears to be a limit to the formation of massive planets very far away from their parent stars. One possible explanation might be the presence of a massive star like Theta 1 Ori C stripping away the outer gas and dust."

Source : University of Arizona. 

By Science and Universe

A Magnetar at the Heart of Our Milky Way

This is an artist's impression of PSR J1745-2900, a pulsar with a very high magnetic field ("magnetar") in direct vicinity of the central source of our Galaxy, a supermassive black hole of approximately 4 million times the mass of our sun. Measurements of the pulsar imply that a strong magnetic field exists in the vicinity around the black hole. (Credit: MPIfR/Ralph Eatough.)

Astronomers have discovered a magnetar at the centre of our Milky Way. This pulsar has an extremely strong magnetic field and enables researchers to investigate the direct vicinity of the black hole at the heart of the galaxy. An international team of scientists headed by the Max Planck Institute for Radio Astronomy in Bonn have, for the first time, measured the strength of the magnetic field around this central source and were able to show that the latter is fed by magnetic fields. These control the inflow of mass into the black hole, also explaining the x-ray emissions of this gravity trap.

The discovery of a pulsar closely orbiting the candidate supermassive black hole at the centre of the Milky Way (called Sagittarius A*, or Sgr A* in short) has been one of the main aims of pulsar astronomers for the last 20 years. Pulsars, those extremely precise cosmic clocks, could be used to measure the properties of space and time around this object, and to see if Einstein's theory of General Relativity could hold up to the strictest tests.

Shortly after the announcement of a flaring X-ray source in the direction of the Galactic centre by NASA's Swift telescope, and the subsequent discovery of pulsations with a period of 3.76 seconds by NASA's NuSTAR telescope, a radio follow-up program was started at the Effelsberg radio observatory of the Max Planck Institute for Radio Astronomy (MPIfR).

"As soon as we heard about the discovery of regular pulsations with the NuSTAR telescope we pointed the Effelsberg 100-m dish in the direction of the Galactic centre," says Ralph Eatough from MPIfR's Fundamental Physics Research department, the lead author of the study. "On our first attempt the pulsar was not clearly visible, but some pulsars are stubborn and require a few observations to be detected. The second time we looked, the pulsar had become very active in the radio band and was very bright. I could hardly believe that we had finally detected a pulsar in the Galactic centre!" Because this pulsar is so special, the research team spent a lot of effort to prove that it was a real object in deep space and not due to human-made radio interference created on Earth.

Additional observations were performed in parallel and subsequently with other radio telescopes around the world (Jodrell Bank, Very Large Array, Nançay). "We were too excited to sleep in between observations! We were calculating flux densities at 6am on Saturday morning and we could not believe that this magnetar had just turned on so bright." says Evan Keane from the Jodrell Bank Observatory. Other collaborations worked at different telescopes (Australia Telescope/ATCA, Parkes and Green Bank Telescope). A research paper on the ATCA results by Shannon & Johnston appears in this week's issue of the British journal MNRAS.

"The Effelsberg radio telescope was built such that it could observe the Galactic centre. And 40 years later it detects the first radio pulsar there," explains Heino Falcke, professor at Radboud Universiteit Nijmegen. "Sometimes we have to be patient. It was a laborious effort, but finally we succeeded."

The newly found pulsar, labelled PSR J1745-2900, belongs to a specific subgroup of pulsars, the so-called magnetars. Magnetars are pulsars with extremely high magnetic fields of the order of 100 million (108) Tesla, about 1000 times stronger than the magnetic fields of ordinary neutron stars, or 100,000 billion times Earth's magnetic field. The emission from these objects is also known to be highly polarized. Measurements of the rotation of the plane of polarization caused by an external magnetic field (the so-called Faraday effect) can be used to infer the strength of the magnetic field along the line-of-sight to the pulsar.

The magnetic field strength in the vicinity of the black hole at the centre of the Galaxy is an important property. The black hole is gradually swallowing its surroundings (mainly hot ionized gas) in a process of accretion. Magnetic fields caused by this in-falling gas can influence the structure and dynamics of the accretion flow, helping or even hindering the process. The new pulsar has allowed measurements of the strength of the magnetic field at the beginning of the accretion flow to the central black hole, indicating there is indeed a large-scale and strong magnetic field.

"In order to understand the properties of Sgr A*, we need to comprehend the accretion of gas into the black hole," says Michael Kramer, director at MPIfR and head of its Fundamental Physics research department. "However, up to now, the magnetization of the gas, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Our study changes that by using the discovered pulsar to probe the strength of the magnetic field at the start of this accretion flow of gas into the central object."

Source : Max-Planck-Gesellschaft.

By Science and Universe

Dwarf Galaxy Caught Ramming Into a Large Spiral

Observations with Chandra have revealed a giant

cloud of superheated gas in a galaxy 

about 60 

million light years from Earth. 

(Credit: X-ray: 

NASA/CXC/Huntingdon Inst. for 

X-ray 

Astronomy/G.Garmire, Optical: ESO/VLT)

Observations with NASA's Chandra X-ray Observatory have revealed a massive cloud of multimillion-degree gas in a galaxy about 60 million light years from Earth. The hot gas cloud is likely caused by a collision between a dwarf galaxy and a much larger galaxy called NGC 1232. If confirmed, this discovery would mark the first time such a collision has been detected only in X-rays, and could have implications for understanding how galaxies grow through similar collisions.

An image combining X-rays and optical light shows the scene of this collision. The impact between the dwarf galaxy and the spiral galaxy caused a shock wave − akin to a sonic boom on Earth -- that generated hot gas with a temperature of about 6 million degrees. Chandra X-ray data, in purple, show the hot gas has a comet-like appearance, caused by the motion of the dwarf galaxy. Optical data from the European Southern Observatory's Very Large Telescope reveal the spiral galaxy in blue and white. X-ray point sources have been removed from this image to emphasize the diffuse emission.

Near the head of the comet-shaped X-ray emission (mouse over the image for the location) is a region containing several very optically bright stars and enhanced X-ray emission. Star formation may have been triggered by the shock wave, producing bright, massive stars. In that case X-ray emission would be generated by massive star winds and by the remains of supernova explosions as massive stars evolve.

The mass of the entire gas cloud is uncertain because it cannot be determined from the two-dimensional image whether the hot gas is concentrated in a thin pancake or distributed over a large, spherical region. If the gas is a pancake, the mass is equivalent to forty thousand Suns. If it is spread out uniformly, the mass could be much larger, about three million times as massive as the Sun. This range agrees with values for dwarf galaxies in the Local Group containing the Milky Way.

The hot gas should continue to glow in X-rays for tens to hundreds of millions of years, depending on the geometry of the collision. The collision itself should last for about 50 million years. Therefore, searching for large regions of hot gas in galaxies might be a way to estimate the frequency of collisions with dwarf galaxies and to understand how important such events are to galaxy growth.

An alternative explanation of the X-ray emission is that the hot gas cloud could have been produced by supernovas and hot winds from large numbers of massive stars, all located on one side of the galaxy. The lack of evidence of expected radio, infrared, or optical features argues against this possibility.

Article Source : Chandra X-ray Observatory.

by Science and Universe

Hubble finds source of Magellanic Stream

Astronomers explore origin of gas ribbon wrapped around our galaxy

Astronomers using the NASA/ESA Hubble Space Telescope have solved the 40-year-old mystery of the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way. New Hubble observations reveal that most of this stream was stripped from the Small Magellanic Cloud some two billion years ago, with a smaller portion originating more recently from its larger neighbour.

The Magellanic Clouds, two dwarf galaxies orbiting our galaxy, are at the head of a huge gaseous filament known as the Magellanic Stream. Since the Stream's discovery in the early 1970s, astronomers have wondered whether this gas comes from one or both of the satellite galaxies. Now, new Hubble observations show that most of the gas was stripped from the Small Magellanic Cloud about two billion years ago — but surprisingly, a second region of the stream was formed more recently from the Large Magellanic Cloud.

A team of astronomers determined the source of the gas filament by using Hubble's Cosmic Origins Spectrograph (COS), along with observations from ESO's Very Large Telescope, to measure the abundances  of heavy elements, such as oxygen and sulphur, at six locations along the Magellanic Stream. COS detected these elements from the way they absorb the ultraviolet light released by faraway quasars as it passes through the foreground Stream. Quasars are the brilliant cores of active galaxies.

The team found low abundances of oxygen and sulphur along most of the stream, matching the levels in the Small Magellanic Cloud about two billion years ago, when the gaseous ribbon was thought to have been formed.

Overview of the Large Magellanic Cloud
(ground-based image)

In a surprising twist, the team discovered a much higher level of sulphur in a region closer to the Magellanic Clouds. "We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," says Andrew Fox, a staff member supported by ESA at the Space Telescope Science Institute, USA, and lead author of one of two new papers reporting these results. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."

This discovery was unexpected; computer models of the Stream predicted that the gas came entirely out of the Small Magellanic Cloud, which has a weaker gravitational pull than its more massive cousin.

"As Earth's atmosphere absorbs ultraviolet light, it's hard to measure the amounts of these elements accurately, as you need to look in the ultraviolet part of the spectrum to see them," says Philipp Richter of the University of Potsdam, Germany, and lead author on the second of the two papers. "So you have to go to space. Only Hubble is capable of taking measurements like these."

All of the Milky Way's nearby satellite galaxies have lost most of their gas content — except the Magellanic Clouds. As they are more massive than these other satellites they can cling on to this gas, using it to form new stars. However, these Clouds are approaching the Milky Way and its halo of hot gas. As they drift closer to us, the pressure of this hot halo pushes their gas out into space. This process, together with the gravitational tug-of-war between the two Magellanic Clouds, is thought to have formed the Magellanic Stream .

"Exploring the origin of such a large stream of gas so close to the Milky Way is important," adds Fox. "We now know which of our famous neighbours, the Magellanic Clouds, created this gas ribbon, which may eventually fall onto our own galaxy and spark new star formation. It's an important step forward in figuring out how galaxies obtain gas and form new stars."

Source : Space Telescope Science Institute (STScI).
By Science and universe ( Nandan)