Astronomy Cmarchesin: September 2016

Friday, September 30, 2016

The hidden dark side of NGC 24

Credit: ESA/Hubble & NASA

This shining disc of a spiral galaxy sits approximately 25 million light-years away from Earth in the constellation of Sculptor. Named NGC 24, the galaxy was discovered by British astronomer William Herschel in 1785, and measures some 40 000 light-years across.

This picture was taken using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys, known as ACS for short. It shows NGC 24 in detail, highlighting the blue bursts (young stars), dark lanes (cosmic dust), and red bubbles (hydrogen gas) of material peppered throughout the galaxy’s spiral arms. Numerous distant galaxies can also been seen hovering around NGC 24’s perimeter.

However, there may be more to this picture than first meets the eye. Astronomers suspect that spiral galaxies like NGC 24 and the Milky Way are surrounded by, and contained within, extended haloes of dark matter. Dark matter is a mysterious substance that cannot be seen; instead, it reveals itself via its gravitational interactions with surrounding material. Its existence was originally proposed to explain why the outer parts of galaxies, including our own, rotate unexpectedly fast, but it is thought to also play an essential role in a galaxy’s formation and evolution. Most of NGC 24’s mass — a whopping 80 % — is thought to be held within such a dark halo.

Source: ESA/Hubble - Space Telescope

Thursday, September 29, 2016

ALMA Catches Stellar Cocoon with Curious Chemistry

PR Image eso1634a

Artist's impression of the hot molecular core discovered in the Large Magellanic Cloud

PR Image eso1634b

ALMA results and the region seen in infrared light

The first of its kind to be found outside the Milky Way

A hot and dense mass of complex molecules, cocooning a newborn star, has been discovered by a Japanese team of astronomers using ALMA. This unique hot molecular core is the first of its kind to have been detected outside the Milky Way galaxy. It has a very different molecular composition from similar objects in our own galaxy — a tantalising hint that the chemistry taking place across the Universe could be much more diverse than expected.

A team of Japanese researchers have used the power of the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a massive star known as ST11 [1] in our neighbouring dwarf galaxy, the Large Magellanic Cloud (LMC). Emission from a number of molecular gases was detected. These indicated that the team had discovered a concentrated region of comparatively hot and dense molecular gas around the newly ignited star ST11. This was evidence that they had found something never before seen outside of the Milky Way — a hot molecular core [2].

Takashi Shimonishi, an astronomer at Tohoku University, Japan, and the paper's lead author enthused: "This is the first detection of an extragalactic hot molecular core, and it demonstrates the great capability of new generation telescopes to study astrochemical phenomena beyond the Milky Way."

The ALMA observations revealed that this newly discovered core in the LMC has a very different composition to similar objects found in the Milky Way. The most prominent chemical signatures in the LMC core include familiar molecules such as sulfur dioxide, nitric oxide, and formaldehyde — alongside the ubiquitous dust. But several organic compounds, including methanol (the simplest alcohol molecule), had remarkably low abundance in the newly detected hot molecular core. In contrast, cores in the Milky Way have been observed to contain a wide assortment of complex organic molecules, including methanol and ethanol.

Takashi Shimonishi explains: “The observations suggest that the molecular compositions of materials that form stars and planets are much more diverse than we expected.”

The LMC has a low abundance of elements other than hydrogen or helium [3]. The research team suggests that this very different galactic environment has affected the molecule-forming processes taking place surrounding the newborn star ST11. This could account for the observed differences in chemical compositions.

It is not yet clear if the large, complex molecules detected in the Milky Way exist in hot molecular cores in other galaxies. Complex organic molecules are of very special interest because some are connected to prebiotic molecules formed in space. This newly discovered object in one of our nearest galactic neighbours is an excellent target to help astronomers address this issue. It also raises another question: how could the chemical diversity of galaxies affect the development of extragalactic life?

Notes

[1] ST11’s full name is 2MASS J05264658-6848469. This catchily-named young massive star is defined as a Young Stellar Object. Although it currently appears to be a single star, it is possible that it will prove to be a tight cluster of stars, or possibly a multiple star system. It was the target of the science team’s observations and their results led them to realise that ST11 is enveloped by a hot molecular core

[2] Hot molecular cores must be: (relatively) small, with a diameter of less than 0.3 light-years; have a density over a thousand billion (10¹²) molecules per cubic metre (far lower than the Earth's atmosphere, but high for an interstellar environment); warm in temperature, at over –173 degrees Celsius. This makes them at least 80 degrees Celsius warmer than a standard molecular cloud, despite being of similar density. These hot cores form early on in the evolution of massive stars and they play a key role in the formation of complex chemicals in space.

[3] The nuclear fusion reactions that take place when a star has stopped fusing hydrogen to helium generate heavier elements. These heavier elements get blasted into space when massive dying stars explode as supernovae. Therefore, as our Universe has aged, the abundance of heavier elements has increased. Thanks to its low abundance of heavier elements, the LMC provides insight into the chemical processes that were taking place in the earlier Universe.

More Information

This research was presented in a paper published in the Astrophysical Journal on August 9, 2016, entitled The Detection of a Hot Molecular Core in the Large Magellanic Cloud with ALMA.

The team is composed of Takashi Shimonishi (Frontier Research Institute for Interdisciplinary Sciences & Astronomical Institute, Tohoku University, Japan), Takashi Onaka (Department of Astronomy, The University of Tokyo, Japan), Akiko Kawamura (National Astronomical Observatory of Japan, Japan) and Yuri Aikawa (Center for Computational Sciences, The University of Tsukuba, Japan)

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

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

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Contact:

Takashi Shimonishi
Frontier Research Institute for Interdisciplinary Sciences
Tohoku University, Sendai, Miyagi, Japan
Email: shimonishi@astr.tohoku.ac.jp

Masaaki Hiramatsu
NAOJ Chile Observatory EPO officer
Tel: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Source: ESO

Wednesday, September 28, 2016

Precision Measurements of Exoplanet Velocities

An artist's conception of Kepler 62-e, a super-Earth exoplanet. Astronomers working to detect super-Earths around the most common kind of stars, M dwarfs, have successfully tested infrared techniques that overcome some of the limitations of optical measurements. Credit: NASA/Kepler mission

The search for exoplanets via the radial velocity technique has been underway for nearly thirty years, measuring the wobbles in a star's motion caused by the presence of orbiting bodies. The method has been very successful and has detected hundreds of exoplanets, but has been overtaken (at least in numbers of detections) by the transit method, which looks for dips in the star's light. The radial velocity method has some powerful advantages, however, most notably that it can spot planets that do not pass across the face of the star ("transit"). The majority of radial velocity targets (so far) have been stars similar roughly to our Sun, but this neglects the majority of stars, the less massive class M dwarfs, which make up 75% of the stars in the solar neighborhood. Surveys of some nearby M dwarfs have been able to reach astonishing velocity precisions - as tiny as a few meters per second (4.5 miles per hour) -- adequate to detect a super-Earth orbiting in the star’s habitable zone (where surface water remains liquid). In order to detect an Earth-mass planet around a solar-type star, however, precisions twenty times better are needed.

One of the technical challenges in measuring radial velocities for M-dwarfs is that they are relatively faint in the optical. Near infrared techniques can ameliorate this issue because the stars are brighter in the infrared, but naturally face some other problems. CfA astronomers John Johnson and Dave Latham were part of a team of scientists working to advance infrared techniques for radial velocity studies of M-dwarfs. Using the current infrared instruments on NASA’s Infrared Telescope Facility in Hawaii, the astronomers were able to achieve about three meters per second precision on some test M stars, demonstrating that the technique and the methods used to process and analyze the data are reliable. There are next generation infrared instruments are in the pipeline, and the new paper demonstrates that they should be able to spot super-Earths and mini-Neptunes in the habitable zones of M dwarfs.

Reference(s):

"Retrieval of Precise Radial Velocities from Near-infrared High-resolution Spectra of Low-mass Stars," Peter Gao, Plavchan P., Gagné J, Furlan E., Bottom M., Anglada-Escudé G., White R., Davison C. L., Beichman C., Brinkworth C., Johnson J., Ciardi D., Wallace K., Mennesson B., von Braun K., Vasisht G., Prato L., Kane S. R., Tanner A., Crawford T. J., Latham D., Rougeot R., Geneser C. S., and Catanzarite J., PASP 128, 104, 2016.

Source: Smithsonian Astrophysical Observatory (SAO)

Tuesday, September 27, 2016

NASA's Hubble Spots Possible Water Plumes Erupting on Jupiter's Moon Europa

This composite image shows suspected plumes of water vapor erupting at the 7 o'clock position off the limb of Jupiter's moon Europa. The plumes, photographed by NASA's Hubble's Space Telescope Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter. Hubble's ultraviolet sensitivity allowed for the features, rising over 100 miles above Europa's icy surface, to be discerned. The water is believed to come from a subsurface ocean on Europa. The Hubble data were taken on January 26, 2014. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. Credit: NASA, ESA, W. Sparks (STScI), and the USGS Astrogeology Science Center

Artist's View of Plumes on Europa

Credit: NASA, ESA, and G. Bacon (STScI)

Europa Transiting Geometry

This diagram shows how the plumes on Europa are seen in silhouette as the moon moves across the face of Jupiter. Europa makes a complete orbit of Jupiter in just 3.5 Earth days. Credit: NASA, ESA, and A. Feild (STScI). Release images

Astronomers using NASA's Hubble Space Telescope have imaged what may be water vapor plumes erupting off the surface of Jupiter's moon Europa. This finding bolsters other Hubble observations suggesting the icy moon erupts with high-altitude water vapor plumes.

The observation increases the possibility that missions to Europa may be able to sample Europa's ocean without having to drill through miles of ice.

"Europa's ocean is considered to be one of the most promising places that could potentially harbor life in the solar system," said Geoff Yoder, acting associate administrator for NASA's Science Mission Directorate in Washington, D.C.. "These plumes, if they do indeed exist, may provide another way to sample Europa's subsurface."

The plumes are estimated to rise about 125 miles (200 kilometers) before, presumably, raining material back down onto Europa's surface. Europa has a huge global ocean containing twice as much water as Earth's oceans, but it is protected by a layer of extremely cold and hard ice of unknown thickness. The plumes provide a tantalizing opportunity to gather samples originating from under the surface without having to land or drill through the ice.

The team, led by William Sparks of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, observed these finger-like projections while viewing Europa's limb as the moon passed in front of Jupiter.

The original goal of the team's observing proposal was to determine whether Europa has a thin, extended atmosphere, or exosphere. Using the same observing method that detects atmospheres around planets orbiting other stars, the team also realized if there was water vapor venting from Europa's surface, this observation would be an excellent way to see it.

"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it," Sparks explained. "If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."

In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They saw what could be plumes erupting on three of these occasions.

This work provides supporting evidence for water plumes on Europa. In 2012, a team led by Lorenz Roth of Southwest Research Institute in San Antonio, Texas, detected evidence for water vapor erupting from the frigid south polar region of Europa and reaching more than 100 miles (160 kilometers) into space. Although both teams used Hubble's Space Telescope Imaging Spectrograph (STIS) instrument, each used a totally independent method to arrive at the same conclusion.

"When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it's pretty similar to what Roth and his team found," Sparks said. "The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work."

But as of yet, the two teams have not simultaneously detected the plumes using their independent techniques. Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically erupt for some time and then die down. For example, observations by Roth's team within a week of one of the detections by Sparks' team failed to detect any plumes.

If confirmed, Europa would be the second moon in the solar system known to have water vapor plumes. In 2005, NASA's Cassini orbiter detected jets of water vapor and dust spewing off the surface of Saturn's moon Enceladus.

Scientists may use the infrared vision of the James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity on Europa. NASA also is formulating a mission to Europa with a payload that could confirm the presence of plumes and study them from close range during multiple flybys.

"Hubble's unique capabilities enabled it to capture these plumes, once again demonstrating Hubble's ability to make observations it was never designed to make," said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington, D.C. "This observation opens up a world of possibilities, and we look forward to future missions — such as the James Webb Space Telescope — to follow-up on this exciting discovery."

The work by Sparks and his colleagues will be published in the Sept. 29 issue of The Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Contact:

Sean Potter / Laurie Cantillo
NASA Headquarters, Washington, D.C.
202-358-1536 / 202-358-1077
sean.potter@nasa.gov / laura.l.cantillo@nasa.gov

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

William Sparks
Space Telescope Science Institute, Baltimore, Maryland
410-338-4843
sparks@stsci.edu

Source: HubbleSite

Monday, September 26, 2016

Twin jets pinpoint the heart of an active galaxy

3-mm GMVA image of the galaxy NGC 1052 showing a compact region at the centre and two jets (bottom), and sketch of the system with an accretion disk and two regions of entangled magnetic fields forming two powerful jets (top). The compact region in the image pinpoints the location of the supermassive black hole at the heart of NGC 1052, and the enormous magnetic fields surrounding the event horizon trigger the two powerful jets observed with our radio telescopes. © Anne-Kathrin Baczko et al., Astronomy & Astrophysics

Magnetism dominates environment of the central black hole

An international team of astronomers has measured the magnetic field in the vicinity of a supermassive black hole. A bright and compact feature of only 2 light days in size was directly observed by a world-wide ensemble of millimeter-wave radio telescopes in the heart of the active galaxy NGC 1052. The observations yield a magnetic field value at the event horizon of the central black hole between 0.02 and 8.3 Tesla. The team, led by the PhD student Anne-Kathrin Baczko, believes that such a large magnetic field provides enough magnetic energy to power the strong relativistic jets in active galaxies. The results are published in the present issue of Astronomy & Astrophysics.

The technique used to investigate the inner details of NGC 1052 is known as very-long-baseline interferometry, and has the potential to locate compact jet cores at sizes close to the event horizon of the powering black hole. The black hole itself remains invisible. Usually, the black hole position can only be inferred indirectly by tracking the wavelength-dependent jet-core position, which converges to the jet base at zero wavelength. The unknown offset from the jet base and the black hole makes it difficult to measure fundamental physical properties in most galaxies. The striking symmetry observed in the reported observations between both jets in NGC1052 allows the astronomers to locate the true center of activitiy inside the central feature, which makes, with the exception of our Galactic Centre, the most precisely known location of a super massive black hole in the universe. Anne-Kathrin Baczko, who performed this work at the Universities of Erlangen-Nürnberg and Würzburg and at the Max-Planck-Institut für Radioastronomie, says: “NGC 1052 is a true key source, since it pinpoints directly and unambiguously the position of a supermassive black hole in the nearby universe.”

NGC 1052 is an elliptical galaxy in a distance of approximately 60 million light years in the direction of the constellation Cetus (the Whale).

The magnetic field by the supermassive black hole was determined measuring the compactness and the brightness of the central region of the elliptical galaxy NGC 1052. This feature is as compact as 57 microarcseconds in diameter, equivalent to the size of a DVD on the surface of the moon. This amazing resolution was obtained by the Global mm-VLBI Array, a network of radio telescopes in Europe, the USA, and East Asia, that is managed by the Max-Planck-Institut für Radioastronomie. “It yields unprecedented image sharpness, and is soon to be applied to get event-horizon scales in nearby objects”, says Eduardo Ros from the MPI für Radioastronomie and collaborator in the project.

The unique powerful twin jets at a close distance, similar to the well-known active galaxy M 87, puts NGC 1052 in the pole position for future observations of nearby powerful galaxies in the oncoming era opened by the addition of ALMA, the Atacama Large Millimetre array, to the world-wide networks in radio interferometry.

The observation may help solving the long-standing mystery of how the powerful relativistic jets are formed, that can be seen in many active galaxies. The result has important astrophysical implications, since we see that jets can be driven by the extraction of magnetic energy from a rapidly rotating supermassive black hole.

Three telescopes participating in the Global Millimetre VLBI Array (GMVA): MPIfR’s Effelsberg 100m (above), IRAM’s Pico Veleta 30m (lower left) and Plateau de Bure 15m telescopes (lower right). © IRAM (Pico Veleta & Plateau de Bure); Norbert Junkes (Effelsberg & compilation)

The Global Millimetre VLBI Array consists of telescopes operated by the MPIfR, IRAM, Onsala, Metsähovi, Yebes and the VLBA. The data were correlated at the correlator of the MPIfR in Bonn, Germany. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. MPIfR scientists involved in the project are Anne-Kathrin Baczko, the first author, Eduardo Ros, Thomas Krichbaum, Andrei Lobanov and J. Anton Zensus

Source: Max Planck Institute for Radio Astronomy

Contact:

Anne-Kathrin Baczko
Phone:+49 2228 525 366
Email: baczko@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Prof. Dr. Eduardo Ros
Phone:+49 228 525-125
Email: ros@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
Email: njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Original Paper:

A highly magnetized twin-jet base pinpoints a supermassive black hole?
A.-K. Baczko, R. Schulz, M. Kadler, E. Ros, M. Perucho, T. P. Krichbaum, M. Böck, M. Bremer, C. Grossberger, M. Lindqvist, A. P. Lobanov, K. Mannheim, I. Martí-Vidal, C. Müller, J. Wilms, and J. A. Zensus, 2016, Astronomy & Astrophysics, 593, A47.

Links

Radio Astronomy / VLBI
Research Department "Radio Astronomy. VLBI" at MPIfR Bonn

Univ. Würzburg
Lehrstuhl für Astronomie, Universität Würzburg

Dr. Karl-Remeis-Sternwarte
Astronomisches Institut der Univ. Erlangen-Nürnberg

GMVA
Global Millimetre VLBI Array (GMVA)

Radio Telescope
Effelsberg Effelsberg Radio Telescope

IRAM
Institute de Radioastronomie Millimetrique (IRAM)

Movie

NGC1052

Zoom into the compact central region of NGC1052 observed at 3 mm wavelength (86 GHz). The video starts at an observing wavelength of 1.3 cm (corresponding to a frequency of 22 GHz), and going over 7 mm (43 GHz) to a shortest wavelength of 3 mm.

Sunday, September 25, 2016

Hubble Views a Colorful Demise of a Sun-like Star

NGC 2440

Credits: NASA, ESA, and K. Noll (STScI),

Acknowledgment: The Hubble Heritage Team (STScI/AURA)

This image, taken by the NASA/ESA Hubble Space Telescope, shows the colorful "last hurrah" of a star like our sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the center. Our sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years.

Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers called them the name because through small telescopes they resembled the disks of the distant planets Uranus and Neptune.

The planetary nebula in this image is called NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of more than 360,000 degrees Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bowtie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.

The material expelled by the star glows with different colors depending on its composition, its density and how close it is to the hot central star. Blue samples helium; blue-green oxygen, and red nitrogen and hydrogen.

Editor: Karl Hille

Source: NASA/Solar System and Beyond

Saturday, September 24, 2016

Summer fireworks on Rosetta's comet

Comet outburst

Copyright: OSIRIS: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA;
NavCam: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Guide to comet activity

Copyright: OSIRIS: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA;
NavCam: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Summer outburst sources

Cliff collapse and comet activity

Brief but powerful outbursts seen from Comet 67P/Churyumov–Gerasimenko during its most active period last year have been traced back to their origins on the surface.

In the three months centred around the comet’s closest approach to the Sun, on 13 August 2015, Rosetta’s cameras captured 34 outbursts.

These violent events were over and above regular jets and flows of material seen streaming from the comet’s nucleus. The latter switch on and off with clockwork repeatability from one comet rotation to the next, synchronised with the rise and fall of the Sun’s illumination.

By contrast, outbursts are much brighter than the usual jets – sudden, brief, high-speed releases of dust. They are typically seen only in a single image, indicating that they have a lifetime shorter than interval between images – typically 5–30 minutes.

A typical outburst is thought to release 60–260 tonnes of material in those few minutes.

On average, the outbursts around the closest approach to the Sun occurred once every 30 hours – about 2.4 comet rotations. Based on the appearance of the dust flow, they can be divided into three categories.

One type is associated with a long, narrow jet extending far from the nucleus, while the second involves a broad, wide base that expands more laterally. The third category is a complex hybrid of the other two.

“As any given outburst is short-lived and only captured in one image, we can’t tell whether it was imaged shortly after the outburst started, or later in the process,” notes Jean-Baptiste Vincent, lead author of the paper published today in Monthly Notices of the Astronomical Society .

“As a result, we can’t tell if these three types of plume ‘shapes’ correspond to different mechanisms, or just different stages of a single process.

"But if just one process is involved, then the logical evolutionary sequence is that an initially long narrow jet with dust is ejected at high speed, most likely from a confined space.

"Then, as the local surface around the exit point is modified, a larger fraction of fresh material is exposed, broadening the plume ‘base’.

"Finally, when the source region has been altered so much as not to be able to support the narrow jet anymore, only a broad plume survives.”

The other key question is how these outbursts are triggered.

The team found that just over half of the events occurred in regions corresponding to early morning, as the Sun began warming up the surface after many hours in darkness.

The rapid change in local temperature is thought to trigger thermal stresses in the surface that might lead to a sudden fracturing and exposure of volatile material. This material rapidly heats up and vaporises explosively.

The other events occurred after local noon – after illumination of a few hours.

These outbursts are attributed to a different cause, where the cumulative heat makes its down to pockets of ‘volatiles’ buried beneath the surface, again causing sudden heating and an explosion.

“The fact that we have clear morning and noon outbursts points to at least two different ways of triggering an outburst,” says Jean-Baptiste.

But it is also possible that yet another cause is involved in some outbursts.

“We found that most of the outbursts seem to originate from regional boundaries on the comet, places where there are changes in texture or topography in the local terrain, such as steep cliffs, pits or alcoves,” adds Jean-Baptiste.

Indeed, the fact that boulders or other debris are also seen around the regions identified as the sources of the outbursts confirms that these areas are particularly susceptible to erosion.

While slowly eroding cliff faces are thought to be responsible for some of the regular, long-lived jet features, a weakened cliff edge may also suddenly collapse at any time, night or day. This collapse would reveal substantial amounts of fresh material and could lead to an outburst even when the region is not exposed to sunlight.

At least one of the events studied took place in local darkness and may be linked to cliff collapse.

“Studying the comet over a long period of time has given us the chance to look into the difference between ‘normal’ activity and short-lived outbursts, and how these outbursts may be triggered,” says Matt Taylor, ESA’s Rosetta project scientist.

“Studying how these phenomena vary as the comet progresses along its orbit around the Sun give us new insight into how comets evolve during their lifetimes.”

Notes for Editors

“ Summer fireworks on Comet 67P ,” by J.-B. Vincent et al is accepted for publication in Monthly Notices of the Royal Astronomical Society.

This article also uses information from “ Are fractured cliffs the source of cometary dust jets? Insights from OSIRIS/Rosetta at 67P ,” by J.-B. Vincent et al, published in Astronomy & Astrophysics 2015

Of the 34 outbursts, 26 were detected with the OSIRIS narrow-angle camera, three with the OSIRIS wide-angle camera, and five with the Navigation Camera.

For further information, please contact:

Jean-Baptiste Vincent
Max Planck Institute for Solar System Research, Gottingen, Germany
Email: vincent@mps.mpg.de

Matt Taylor 
ESA Rosetta project scientist 
Email: matt.taylor@esa.int

Markus Bauer        
ESA Science and Robotic Exploration Communication Officer         
Tel: +31 71 565 6799         
Mob: +31 61 594 3 954         
Email: markus.bauer@esa.int

Source: ESA/Rosetta

Friday, September 23, 2016

ALMA Explores the Hubble Ultra Deep Field

ALMA surveyed the Hubble Ultra Deep Field, uncovering new details of the star-forming history of the universe. This close-up image reveals one such galaxy (orange), rich in carbon monoxide, showing it is primed for star formation. The blue features are galaxies imaged by Hubble. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble

ALMA surveyed the Hubble Ultra Deep Field, uncovering new details of the star-forming history of the universe. This animated GIF reveals one such galaxy (orange), rich in carbon monoxide, showing it is primed for star formation. The blue features are galaxies imaged by Hubble. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble

A trove of galaxies, rich in dust and cold gas (indicating star-forming potential) was imaged by ALMA (orange) in the Hubble Ultra Deep Field. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble

Animated GIF showing a trove of galaxies, rich in dust and cold gas (indicating star-forming potential) that was imaged by ALMA (orange) in the Hubble Ultra Deep Field. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble

Looking back through cosmic time in the Hubble Ultra Deep Field, ALMA traced the presence of carbon monoxide gas. This enabled astronomers to create a 3-D image of the star-forming potential of the cosmos. Credit: R. Decarli (MPIA); ALMA (ESO/NAOJ/NRAO)

Videos

Animation revealing ALMA's exploration of the Hubble Ultra Deep Field. The new ALMA observations, which are significantly deeper and sharper than previous surveys at millimeter wavelengths, reveal a population of galaxies that is not clearly evident in any other deep surveys of the sky and trace the previously unknown abundance of star-forming gas at different points in time. The ALMA data (orange) is supperimposed on the Hubble data. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble. Music: Mark Mercury

Interview with astronomer Fabian Walter explaining recent ALMA observations of the Hubble Ultra Deep Field. Credit: B. Saxton & J. Hellerman (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble

Uncovers Insights into 'Golden Age' of Galaxy Formation

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has explored the same distant corner of the universe first revealed in the iconic image of the Hubble Ultra Deep Field (HUDF).

The new ALMA observations, which are significantly deeper and sharper than previous surveys at millimeter wavelengths, trace the previously unknown abundance of star-forming gas at different points in time, providing new insights into the "Golden Age" of galaxy formation approximately 10 billion years ago.

The researchers presented their findings today at the Half a Decade of ALMA conference in Palm Springs, California. The results also are accepted for publication in a series of seven scientific papers appearing in the Astrophysical Journal.

Just like the pioneering deep-field observations with the NASA/ESA Hubble Space Telescope, scientists using ALMA surveyed a seemingly unremarkable section of the cosmos in a so-called "blind search." This type of observation probes a specific region of space to see what can be discovered serendipitously rather than homing in on a predetermined target, like an individual galaxy or star-forming nebula.

"We conducted the first fully blind, three-dimensional search for cool gas in the early universe," said Chris Carilli, an astronomer with the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, and member of the research team. "Through this, we discovered a population of galaxies that is not clearly evident in any other deep surveys of the sky."

Unlike Hubble, which studies visible and infrared light from bright cosmic objects like stars and galaxies, ALMA studies the faint millimeter-wavelength light emitted by cold gas and dust, the raw material of star formation. ALMA's ability to see a completely different portion of the electromagnetic spectrum allows astronomers to study a different class of astronomical objects, such as massive star-forming clouds and protoplanetary disks, as well as objects that are too faint to observe in visible light.

The new ALMA observations were specifically tailored to detect galaxies that are rich in carbon monoxide (CO), a tracer molecule that identifies regions rich in molecular gas and primed for star formation. Even though these molecular gas reservoirs give rise to star formation in galaxies, they are invisible to Hubble. ALMA can therefore reveal the "missing half" of the galaxy formation and evolution process.

"These newly detected carbon-monoxide rich galaxies represent a substantial contribution to the star-formation history of the universe," said Roberto Decarli, an astronomer with the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and member of the research team. "With ALMA we have opened a pathway for studying the early formation and assembly of galaxies in the Hubble Ultra Deep Field."

The new ALMA observations of the HUDF include two distinct, yet complementary types of data: continuum observations, which reveal dust emission and star formation, and a spectral line survey, which looks at the cold molecular gas fueling star formation. The line survey is particularly valuable because it includes information about the degree to which light from distant objects has been redshifted by the expansion of the universe. Greater redshift means that an object is further away and seen farther back in time.

With the most recent observations, astronomers were able to create a three-dimensional map of star-forming gas as it evolves over cosmic time, from the present to about two billion years after the Big Bang.

"The new ALMA results imply a rapidly rising gas content in galaxies with increasing look-back time," said Manuel Aravena, an astronomer with the Diego Portales University in Santiago, Chile, and member of the research team. "This increasing gas content is likely the root cause for the remarkable increase in star formation rates during the peak epoch of galaxy formation, some 10 billion years ago."

Astronomers specifically selected the area of study in the HUDF, a region of space in the constellation Fornax, so ground-based telescopes in the Southern Hemisphere, like ALMA, could probe the region as well, expanding our knowledge of the very distant universe.

The current ALMA observations, which required approximately 40 hours of observing time, cover an area of the sky that is one arcminute on each side, about one sixth of the total HUDF. An approved future 150-hour observing campaign dubbed ASPECS – the ALMA Spectroscopic Survey in the Hubble UDF -- will cover a much larger area and further illuminate the star-forming potential history of the universe.

"By supplementing our understanding of this missing star-forming material, the forthcoming large spectroscopic survey will complete our view of the well-known galaxies in the iconic Hubble Ultra Deep Field," said Fabian Walter, also with the MPIA and member of the research team.

More Information

The following papers are accepted for publication in the Astrophysical Journal [http://apj.aas.org].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Search for [CII] line and dust emission in 6< z < 8 galaxies," M. Aravena et al. [Preprint: https://arxiv.org/pdf/1607.06772v2.pdf].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: implications for spectral line intensity mapping at millimeter wavelengths and CMB spectral distortions," C.L. Carilli et al. [Preprint: http://arxiv.org/pdf/1607.06773v3.pdf].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular gas reservoirs in high-redshift galaxies," R. Decarli et al. [Preprint: https://arxiv.org/pdf/1607.06771v2.pdf].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: CO luminosity functions and the evolution of the cosmic density of molecular gas," R. Decarli et al. [Preprint: https://arxiv.org/pdf/1607.06770v2.pdf].

"ALMA spectroscopic survey in the Hubble Ultra Deep Field: Continuum number counts, resolved 1.2-mm extragalactic background, and properties of the faintest dusty star forming galaxies," M. Aravena et al. [Preprint:https://arxiv.org/pdf/1607.06769v2.pdf].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Survey description," F. Walter et al. [Preprint: https://arxiv.org/abs/1607.06768].

"ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and Stellar Mass," R. Bouwens et al. [Preprint: https://arxiv.org/pdf/1606.05280v4.pdf].

Source: National Radio Astronomy Observatory (NRAO)

Thursday, September 22, 2016

Hubble Finds Planet Orbiting Pair of Stars

OGLE-2007-BLG-349

Credit: NASA, ESA, and G. Bacon (STScI)

Release Images

Astronomers using NASA's Hubble Space Telescope, and a trick of nature, have confirmed the existence of a planet orbiting two stars in the system OGLE-2007-BLG-349, located 8,000 light-years away towards the center of our galaxy.

The planet orbits roughly 300 million miles from the stellar duo, about the distance from the asteroid belt to our sun. It completes an orbit around both stars roughly every seven years. The two red dwarf stars are a mere 7 million miles apart, or 14 times the diameter of the moon's orbit around Earth.

The Hubble observations represent the first time such a three-body system has been confirmed using the gravitational microlensing technique. Gravitational microlensing occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.

The three objects were discovered in 2007 by an international collaboration of five different groups: Microlensing Observations in Astrophysics (MOA), the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing Lensing Anomalies Network (PLANET), and the Robonet Collaboration. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify.

"The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star," explained David Bennett of the NASA Goddard Space Flight Center in Greenbelt, Maryland, the paper's first author.

The sharpness of the Hubble images allowed the research team to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun. "So, the model with two stars and one planet is the only one consistent with the Hubble data," Bennett said.

Bennett's team conducted the follow-up observations with Hubble's Wide Field Planetary Camera 2. "We were helped in the analysis by the almost perfect alignment of the foreground binary stars with the background star, which greatly magnified the light and allowed us to see the signal of the two stars," Bennett explained.

Kepler has discovered 10 other planets orbiting tight binary stars, but these are all much closer to their stars than the one studied by Hubble.

Now that the team has shown that microlensing can successfully detect planets orbiting double-star systems, Hubble could provide an essential role in this new realm in the continued search for exoplanets.

The team's results have been accepted for publication in The Astronomical Journal.

Contact:

Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

David Bennett
NASA Goddard Space Flight Center in Greenbelt, Maryland
301-286-5473 (office) / 574-315-6621 (cell)
david.p.bennett@nasa.gov

Source : HubbleSite

Wednesday, September 21, 2016

ALMA Uncovers Secrets of Giant Space Blob

PR Image eso1632a

Computer simulation of a Lyman-alpha Blob

PR Image eso1632b

Infographic explaining how a Lyman-alpha Blob functions

PR Image eso1632c

Giant space blob glows from within

PR Image eso1632d

Closing in on a giant space blob

PR Image eso1632e

Wide-field view of the sky around a giant space blob

Videos

PR Video eso1632a

Zooming in on a giant space blob

An international team using ALMA, along with ESO’s Very Large Telescope and other telescopes, has discovered the true nature of a rare object in the distant Universe called a Lyman-alpha Blob. Up to now astronomers did not understand what made these huge clouds of gas shine so brightly, but ALMA has now seen two galaxies at the heart of one of these objects and they are undergoing a frenzy of star formation that is lighting up their surroundings. These large galaxies are in turn at the centre of a swarm of smaller ones in what appears to be an early phase in the formation of a massive cluster of galaxies. The two ALMA sources are expected to evolve into a single giant elliptical galaxy.

Lyman-alpha Blobs (LABs) are gigantic clouds of hydrogen gas that can span hundreds of thousands of light-years and are found at very large cosmic distances. The name reflects the characteristic wavelength of ultraviolet light that they emit, known as Lyman-alpha radiation [1]. Since their discovery, the processes that give rise to LABs have been an astronomical puzzle. But new observations with ALMA may now have now cleared up the mystery.

One of the largest Lyman-alpha Blobs known, and the most thoroughly studied, is SSA22-Lyman-alpha blob 1, or LAB-1. Embedded in the core of a huge cluster of galaxies in the early stages of formation, it was the very first such object to be discovered — in 2000 — and is located so far away that its light has taken about 11.5 billion years to reach us.

A team of astronomers, led by Jim Geach, from the Centre for Astrophysics Research of the University of Hertfordshire, UK, has now used the Atacama Large Millimeter/Submillimeter Array’s (ALMA) unparallelled ability to observe light from cool dust clouds in distant galaxies to peer deeply into LAB-1. This allowed them to pinpoint and resolve several sources of submillimetre emission [2].

They then combined the ALMA images with observations from the Multi Unit Spectroscopic Explorer (MUSE) instrument mounted on ESO’s Very Large Telescope (VLT), which map the Lyman-alpha light. This showed that the ALMA sources are located in the very heart of the Lyman-alpha Blob, where they are forming stars at a rate over 100 times that of the Milky Way.

Deep imaging with the NASA/ESA Hubble Space Telescope and spectroscopy at the W. M. Keck Observatory [3] showed in addition that the ALMA sources are surrounded by numerous faint companion galaxies that could be bombarding the central ALMA sources with material, helping to drive their high star formation rates.

The team then turned to a sophisticated simulation of galaxy formation to demonstrate that the giant glowing cloud of Lyman-alpha emission can be explained if ultraviolet light produced by star formation in the ALMA sources scatters off the surrounding hydrogen gas. This would give rise to the Lyman-alpha Blob we see.

Jim Geach, lead author of the new study, explains: “Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets. A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”

Understanding how galaxies form and evolve is a massive challenge. Astronomers think Lyman-alpha Blobs are important because they seem to be the places where the most massive galaxies in the Universe form. In particular, the extended Lyman-alpha glow provides information on what is happening in the primordial gas clouds surrounding young galaxies, a region that is very difficult to study, but critical to understand.

Jim Geach concludes, “What’s exciting about these blobs is that we are getting a rare glimpse of what’s happening around these young, growing galaxies. For a long time the origin of the extended Lyman-alpha light has been controversial. But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery: Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster. We are seeing a snapshot of the assembly of that galaxy 11.5 billion years ago.”

Notes

[1] The negatively charged electrons that orbit the positively charged nucleus in an atom have quantised energy levels. That is, they can only exist in specific energy states, and they can only transition between them by gaining or losing precise amounts of energy. Lyman-alpha radiation is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. The precise amount of energy lost is released as light with a particular wavelength, in the ultraviolet part of the spectrum, which astronomers can detect with space telescopes or on Earth in the case of redshifted objects. For LAB-1, at redshift of z~3, the Lyman-alpha light is seen as visible light.

[2] Resolution is the ability to see that objects are separated. At low resolution, several bright sources at a distance would seem like a single glowing spot, and only at closer quarters would each source be distinguishable. ALMA’s high resolution has resolved what previously appeared to be a single blob into two separate sources.

[3] The instruments used were the Space Telescope Imaging Spectograph (STIS) on the NASA/ESA Hubble Space Telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) mounted on the Keck 1 telescope on Hawaii.

More Information

This research was presented in a paper entitled “ALMA observations of Lyman-α Blob 1: Halo sub-structure illuminated from within” by J. Geach et al., to appear in the Astrophysical Journal.

The team is composed of J. E. Geach (Centre for Astrophysics Research, University of Hertfordshire, Hatfield, UK), D. Narayanan (Department of Physics and Astronomy, Haverford College, Haverford PA, USA; Department of Astronomy, University of Florida, Gainesville FL, USA), Y. Matsuda (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan; The Graduate University for Advanced Studies, Mitaka, Tokyo, Japan), M. Hayes (Stockholm University, Department of Astronomy and Oskar Klein Centre for Cosmoparticle Physics, Stockholm, Sweden), Ll. Mas-Ribas (Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway), M. Dijkstra (Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway), C. C. Steidel (California Institute of Technology, Pasadena CA, USA ), S. C. Chapman (Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada ), R. Feldmann (Department of Astronomy, University of California, Berkeley CA, USA ), A. Avison (UK ALMA Regional Centre Node; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, UK), O. Agertz (Department of Physics, University of Surrey, Guildford, UK), Y. Ao (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan), M. Birkinshaw (H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK), M. N. Bremer (H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK), D. L. Clements (Astrophysics Group, Imperial College London, Blackett Laboratory, London, UK), H. Dannerbauer (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain; Universidad de La Laguna, Astrofísica, La Laguna, Tenerife, Spain), D. Farrah (Department of Physics, Virginia Tech, Blacksburg VA, USA), C. M. Harrison (Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, UK), M. Kubo (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan), M. J. Michałowski (Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK), D. Scott (Department of Physics & Astronomy, University of British Columbia, Vancouver, Canada), M. Spaans (Kapteyn Astronomical Institute, University of Groningen, Groningen, Netherlands) , J. Simpson (Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK), A. M. Swinbank (Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, UK ), Y. Taniguchi (The Open University of Japan, Chiba, Japan), E. van Kampen (ESO, Garching, Germany), P. Van Der Werf (Leiden Observatory, Leiden University, Leiden, The Netherlands), A. Verma (Oxford Astrophysics, Department of Physics, University of Oxford, Oxford, UK) and T. Yamada (Astronomical Institute, Tohoku University, Miyagi, Japan).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).