Tagged: NRAO ALMA Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 6:22 am on October 25, 2013 Permalink | Reply
    Tags: , , , , NRAO ALMA   

    From NRAO for ALMA: “ALMA Reveals Ghostly Shape of ‘Coldest Place in the Universe’” 

    NRAO Icon
    National Radio Astronomy Observatory

    NRAO Banner

    At a cosmologically crisp one degree Kelvin (minus 458 degrees Fahrenheit), the Boomerang Nebula is the coldest known object in the Universe – colder, in fact, than the faint afterglow of the Big Bang, which is the natural background temperature of space.

    b

    bb
    Another image. credit NASA/ESA

    Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope have taken a new look at this intriguing object to learn more about its frigid properties and to determine its true shape, which has an eerily ghost-like appearance.

    As originally observed with ground-based telescopes, this nebula appeared lopsided, which is how it got its name. Later observations with the Hubble Space Telescope revealed a bow-tie-like structure. The new ALMA data, however, reveal that the Hubble image tells only part of the story, and the twin lobes seen in that image may actually be a trick of the light as seen at visible wavelengths.

    “This ultra-cold object is extremely intriguing and we’re learning much more about its true nature with ALMA,” said Raghvendra Sahai, a researcher and principal scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and lead author of a paper published in the Astrophysical Journal. “What seemed like a double lobe, or ‘boomerang’ shape, from Earth-based optical telescopes, is actually a much broader structure that is expanding rapidly into space.”

    The Boomerang Nebula, located about 5,000 light-years away in the constellation Centaurus, is a relatively young example of an object known as a planetary nebula. Planetary nebulae, contrary to their name, are actually the end-of-life phases of stars like our Sun that have sloughed off their outer layers. What remains at their centers are white dwarf stars, which emit intense ultraviolet radiation that causes the gas in the nebulae to glow and emit light in brilliant colors.

    The Boomerang is a pre-planetary nebula, representing the stage in a star’s life immediately preceding the planetary nebula phase, when the central star is not yet hot enough to emit enough ultraviolet radiation to produce the characteristic glow. At this stage, the nebula is seen by starlight reflecting off its dust grains.

    The outflow of gas from this particular star is expanding rapidly and cooling itself in the process. This is similar in principle to the way refrigerators use expanding gas to produce cold temperatures. The researchers were able to take the temperature of the gas in the nebula by seeing how it absorbed the cosmic microwave background radiation, which has a very uniform temperature of 2.8 degrees Kelvin (minus 455 degrees Fahrenheit).

    “When astronomers looked at this object in 2003 with Hubble, they saw a very classic ‘hourglass’ shape,” commented Sahai. “Many planetary nebulae have this same double-lobe appearance, which is the result of streams of high-speed gas being jettisoned from the star. The jets then excavate holes in a surrounding cloud of gas that was ejected by the star even earlier in its lifetime as a red giant.”

    Observations with single-dish millimeter wavelength telescopes, however, did not detect the narrow waist seen by Hubble. Instead, they found a more uniform and nearly spherical outflow of material.

    ALMA’s unprecedented resolution allowed the researchers to reconcile this discrepancy. By observing the distribution of carbon monoxide molecules, which glow brightly at millimeter wavelengths, the astronomers were able to detect the double-lobe structure that is seen in the Hubble image, but only in the inner regions of the nebula. Further out, they actually observed a more elongated cloud of cold gas that is roughly round.

    The researchers also discovered a dense lane of millimeter-sized dust grains surrounding the star, which explains why this outer cloud has an hourglass shape in visible light. The dust grains have created a mask that shades a portion of the central star and allows its light to leak out only in narrow but opposite directions into the cloud, giving it an hourglass appearance.

    “This is important for the understanding of how stars die and become planetary nebulae,” said Sahai. “Using ALMA, we were quite literally and figuratively able to shed new light on the death throes of a Sun-like star.”

    The new research also indicated that the outer fringes of the nebula are beginning to warm, even though they are still slightly colder than the cosmic microwave background. This warming may be due to the photoelectric effect — an effect first proposed by Einstein in which light is absorbed by solid material, which then re-emits electrons.

    Additional authors on this paper include Wouter Vlemmings, Chalmers University of Technology, Onsala, Sweden; Patrick Huggins, New York University, New York; Lars-Ake Nyman, Joint ALMA Observatory, Santiago de Chile; and Yiannis Gonidakis, CSIRO, Australia Telescope National Facility.

    See the full article here.

    The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.

    NRAO ALMA
    NRAO ALMA

    NRAO GBT
    NRAO GBT

    NRAO VLA
    NRAO VLA

    The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
    *The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

    Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

     
  • richardmitnick 5:18 pm on August 20, 2013 Permalink | Reply
    Tags: , , , , , NRAO ALMA   

    From ALMA: “ALMA Takes Close Look at Drama of Starbirth” 

    ESO ALMA Array
    ALMA

    20 August 2013

    From ESO

    Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have obtained a vivid close-up view of material streaming away from a newborn star. By looking at the glow coming from carbon monoxide molecules in an object called Herbig-Haro 46/47 they have discovered that its jets are even more energetic than previously thought. The very detailed new images have also revealed a previously unknown jet pointing in a totally different direction.

    starbirth

    Young stars are violent objects that eject material at speeds as high as one million kilometres per hour. When this material crashes into the surrounding gas it glows, creating a Herbig-Haro object. A spectacular example is named Herbig-Haro 46/47 and is situated about 1400 light-years from Earth in the southern constellation of Vela (The Sails). This object was the target of a study using ALMA during the Early Science phase, whilst the telescope was still under construction and well before the array was completed.

    The new images reveal fine detail in two jets, one coming towards Earth and one moving away. The receding jet was almost invisible in earlier pictures made in visible light, due to obscuration by the dust clouds surrounding the new-born star. ALMA has not only provided much sharper images than earlier facilities but also allowed astronomers to measure how fast the glowing material is moving through space.

    These new observations of Herbig-Haro 46/47 revealed that some of the ejected material had velocities much higher than had been measured before. This means the outflowing gas carries much more energy and momentum than previously thought.

    The team leader and first author of the new study, Héctor Arce (Yale University, USA) explains that ‘ALMA’s exquisite sensitivity allows the detection of previously unseen features in this source, like this very fast outflow. It also seems to be a textbook example of a simple model where the molecular outflow is generated by a wide-angle wind from the young star.’

    The observations were obtained in just five hours of ALMA observation time – even though ALMA was still under construction at the time – similar quality observations with other telescopes would have taken ten times longer.

    ‘The detail in the Herbig-Haro 46/47 images is stunning. Perhaps more stunning is the fact that, for these types of observations, we really are still in the early days. In the future ALMA will provide even better images than this in a fraction of the time,’ adds Stuartt Corder (Joint ALMA Observatory, Chile), a co-author on the new paper.

    Diego Mardones (Universidad de Chile), another co-author, emphasises that ‘this system is similar to most isolated low mass stars during their formation and birth. But it is also unusual because the outflow impacts the cloud directly on one side of the young star and escapes out of the cloud on the other. This makes it an excellent system for studying the impact of the stellar winds on the parent cloud from which the young star is formed.'”

    See the full ESO article, with notes and associated photos and videos here.

    From NRAO

    “While observing a newborn star, astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope discovered twin jets of matter blasting out into space at record-breaking speed. These surprisingly forceful molecular “winds” could help refine our understanding of how stars impact their cloudy nurseries and shape their emerging stellar systems.

    During their formative years, stars both take in and blast away tremendous amounts of matter. When this ejected material collides with the surrounding gas it glows, forming what is known as a Herbig-Haro (HH) object. This give-and-take can greatly impact the way a stellar system evolves and also reshape the surrounding nebula of dust and gas from which either single or whole families of stars form.

    By studying one such stellar neighborhood, dubbed HH 46/47, the international team of astronomers uncovered high-velocity streams of carbon monoxide (CO) molecules flowing away from a star buried deep within its cloudy stellar nursery.

    ALMA’s superb sensitivity and the orientation of the star enabled the researchers to detect two jets of CO, when only one had ever been seen before. The data also revealed that this material was rushing along at 40 kilometers per second, which is 3 to 4 times faster than seen in previous CO observations.

    ‘The ALMA data reveal molecular gas close to the protostar at velocities much higher that ever observed from such an object,’ said Héctor Arce from Yale University, the principal investigator on this study. ‘This means that this rapidly fleeing gas carries much more energy and momentum than previously thought, which could significantly impact the evolution of this emerging stellar system.’

    The star, which is located 1,400 light-years away in the constellation Vela, is relatively young — on the order of a few hundred thousand years. The astronomers speculate that it is not significantly different from what our infant Sun would have looked like, though a little less massive.

    In their youth, stars bulk-up by drawing in material from a surrounding disk of dust and gas. A portion of this material, however, gets diverted and caught-up in the star’s magnetic fields causing it to be spewed out as jets from the stars’ north and south poles.

    Since there is a direct relationship between the jets and a star’s accretion disk, there is a great deal to be learned about stellar formation by simply studying the jets.

    ALMA discovered the high-velocity outflowing gas hidden within very wide-angle winds. The data also revealed that the surrounding cloud material was being pushed and accelerated by the winds. Since this is a normal, not very special protostar, the astronomers believe that the same features can be found elsewhere. If so, Arce speculates, astronomers would have to change their view on how much impact these outflows have. ‘If it has lots of energy, it can clear surrounding gas, leaving just the star and its surrounding disk of planet-forming dust and gas,’ said Arce.

    These new observations also suggest that there have been episodes of outflow followed by quieter, less active periods. This would mean that there has also been episodic accretion of material onto the star.

    Diego Mardones, a co-author on the study with the University of Chile, emphasizes that ‘this system is similar to most isolated low mass stars during their formation and birth. But it is also unusual because the outflow impacts the cloud directly on one side of the young star and escapes out of the cloud on the other. This makes it an excellent system for studying the impact of the stellar winds on the parent cloud from which the young star formed.’

    ‘The detail in the Herbig-Haro 46/47 images is stunning. Perhaps more stunning is the fact that, for these types of observations, we really are still in the early days. In the future, ALMA will provide even better images than this in a fraction of the time,’ adds Stuartt Corder with the National Radio Astronomy Observatory (NRAO), a co-author on the new paper.

    The results are published in the Astrophysical Journal.”

    See the full NRAO article here.

    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small

    ESO 50

    NAOJ


    ScienceSprings is powered by MAINGEAR computers

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
Follow

Get every new post delivered to your Inbox.

Join 377 other followers

%d bloggers like this: