Thursday, August 31, 2017

Archaeology of active galaxies across the electromagnetic spectrum

This image of B2 0924+30 was obtained with LOFAR at 150 MHz. In this object, the analysis of the radio spectrum99 extended to low frequencies reveals that the activity ceased around 50 Myr ago.  Image credit: A. Shulevski. 

a, The LOFAR image at 150 MHz shows the amorphous morphology of the remnant radio source. b, This morphology is also confirmed by observations at higher frequencies from the Westerbork Synthesis Radio Telescope (WSRT). c, The radio spectrum constructed from fluxes obtained at different frequencies with various radio telescopes (as indicated) and shown with their error bars (WENSS, Westerbork Northern Sky Survey; GB6, Green Bank 6-cm). The best fit of the data is shown in blue. The radio spectrum shows a very steep slope at high frequencies, which indicates that the central source has turned off. However, at low frequencies the spectrum (α ~ 0.74) is not much steeper than the original injection index. The overall shape of the spectrum is thought to be66 a source that has spent most of its life in a dying phase (t off = 60 Myr versus t on = 15 Myr). Figure adapted from ref. 100, ESO.

Evolution of the accretion rate (including turbulence, cooling, AGN heating and rotation) as a fraction of the cooling rate. This illustrates the changes in accretion rate (and therefore level of activity) on short timescales. Figure reproduced from ref. 20, Oxford University Press

a, Ground-based optical image of IC 2497 (top), Hanny’s Voorwerp (bottom in green), and a nearby companion galaxy (left). The ‘green’ emission of the Hanny’s Voorwerp is highly ionized gas. This image is a composite of blue, visual and near-infrared light images taken with the WIYN telescope. b, Schematic of the lifecycle of optical AGNs. Panel a credit: WIYN / William Keel / Anna Manning. Panel b reproduced from ref. 31, Oxford University Press.




The timescales over which galaxies form and evolve are outside the reach of human life. Thus, astronomers need to use indirect methods to derive the history of galaxies. 
 
Important events happen during the life of a galaxy and they can change the course of its evolution. In particular, when the central supermassive black hole (SMBH) is active, it can release huge amounts of energy which can affect the surrounding gas and can impact the evolution of the entire galaxy. This effect has been recognised as crucial for explaining why galaxies look the way they do.

But how often and for how long is a SMBH active?
 
"This is not an easy question to answer," says Raffaella Morganti from ASTRON. "Astronomers are working hard to address it by using observations in different wavebands and perform a kind of ‘archaeology’ to trace the signatures of past nuclear activity. Extremely interesting is the role that the low-frequency radio telescopes and, in particular, LOFAR have in this. They offer new possibilities for major steps forward in this field. At low radio frequencies, where low-energy electrons can radiate for longer times, the astronomers can explore the phases in which a radio source is dying and, in some cases, is re-borne: an ideal task for LOFAR."
 
The status of the field and the progress on this fascinating topic are described in a review article appearing this week in Nature Astronomy, “Archaeology of active galaxies across the electromagnetic spectrum (https://www.nature.com/articles/s41550-017-0223-0 )” by Raffaella Morganti (a download can also be found at http://rdcu.be/vlUw). Among many things, the review summarises some of the recent results obtained by LOFAR, including those from the ERC-RadioLife group.

 

Wednesday, August 30, 2017

First detection of CH+ molecules in distant starburst galaxies provides insight into star formation history of the Universe

Artist’s impression of gas fueling distant starburst galaxies 

ALMA view of the Cosmic Eyelash



Videos

Zooming in on the Cosmic Eyelash
Zooming in on the Cosmic Eyelash



First detection of CH+ molecules in distant starburst galaxies provides insight into star formation history of the Universe


ALMA has been used to detect turbulent reservoirs of cold gas surrounding distant starburst galaxies. By detecting CH+ for the first time in the distant Universe this research opens up a new window of exploration into a critical epoch of star formation. The presence of this molecule sheds new light on how galaxies manage to extend their period of rapid star formation. The results appear in the journal Nature.


A team led by Edith Falgarone (Ecole Normale Supérieure and Observatoire de Paris, France) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to detect signatures of the carbon hydride molecule CH+ [1] in distant starburst galaxies [2]. The group identified strong signals of CH+ in five out of the six galaxies studied, including the Cosmic Eyelash (eso1012) [3]. This research provides new information that helps astronomers understand the growth of galaxies and how a galaxy’s surroundings fuel star formation.

CH+ is a special molecule. It needs a lot of energy to form and is very reactive, which means its lifetime is very short and it can’t be transported far. CH+ therefore traces how energy flows in the galaxies and their surroundings,” said Martin Zwaan, an astronomer at ESO, who contributed to the paper.

How CH+ traces energy can be thought of by analogy to being on a boat in a tropical ocean on a dark, moonless night. When the conditions are right, fluorescent plankton can light up around the boat as it sails. The turbulence caused by the boat sliding through the water excites the plankton to emit light, which reveals the existence of the the turbulent regions in the underlying dark water. Since CH+ forms exclusively in small areas where turbulent motions of gas dissipates, its detection in essence traces energy on a galactic scale. 

The observed CH+ reveals dense shock waves, powered by hot, fast galactic winds originating inside the galaxies’ star forming regions. These winds flow through a galaxy, and push material out of it, but their turbulent motions are such that part of the material can be re-captured by the gravitational pull of the galaxy itself. This material gathers into huge turbulent reservoirs of cool, low-density gas, extending more than 30 000 light-years from the galaxy’s star forming region [4]

With CH+, we learn that energy is stored within vast galaxy-sized winds and ends up as turbulent motions in previously unseen reservoirs of cold gas surrounding the galaxy,” said Falgarone, who is lead author of the new paper. “Our results challenge the theory of galaxy evolution. By driving turbulence in the reservoirs, these galactic winds extend the starburst phase instead of quenching it.” 

The team determined that galactic winds alone could not replenish the newly revealed gaseous reservoirs and suggests that the mass is provided by galactic mergers or accretion from hidden streams of gas, as predicted by current theory. 

This discovery represents a major step forward in our understanding of how the inflow of material is regulated around the most intense starburst galaxies in the early Universe,” says ESO’s Director for Science, Rob Ivison, a co-author on the paper. “It shows what can be achieved when scientists from a variety of disciplines come together to exploit the capabilities of the world's most powerful telescope.” 



Notes

[1] CH+ is an ion of the CH molecule known as methylidynium to chemists. It is one of the first three molecules ever discovered in the interstellar medium. Since its discovery in the early 1940s, the presence of CH+ in interstellar space has been a mystery because it is extremely reactive and hence disappears more quickly than other molecules.

[2] These galaxies are known for a much higher rate of star formation compared to sedate Milky Way-like galaxies, making these structures ideal to study galaxy growth and the interplay between gas, dust, stars, and the black holes at the centres of galaxies.

[3] ALMA was used to obtain spectra of each galaxy. A spectrum is a record of light, typically of an astronomical object, split into its different colours (or wavelengths), in much the same way that rain droplets disperse light to form a rainbow. Since every element has a unique “fingerprint” in a spectrum, spectra can be used to determine the chemical composition of observed objects.

[4] These turbulent reservoirs of diffuse gas may be of the same nature as the giant glowing haloes seen around distant quasars.



More Information


This research was presented in a paper entitled “Large turbulent reservoirs of cold molecular gas around high redshift starburst galaxies” by E. Falgarone et al., to appear in Nature on 30 August 2017.

The team is composed of E. Falgarone (Ecole Normale Supérieure and Observatoire de Paris, France), M.A. Zwaan (ESO, Germany), B. Godard (Ecole Normale Supérieure and Observatoire de Paris, France), E. Bergin (University of Michigan, USA), R.J. Ivison (ESO, Germany; University of Edinburgh, UK), P. M. Andreani (ESO, Germany), F. Bournaud (CEA/AIM, France), R. S. Bussmann (Cornell University, USA), D. Elbaz (CEA/AIM, France), A. Omont (IAP, CNRS, Sorbonne Universités, France), I. Oteo (University of Edinburgh, UK; ESO, Germany) and F. Walter (Max-Planck-Institut für Astronomie, Germany).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Links



Contacts
Edith Falgarone
Ecole Normale Supérieure — Observatoire de Paris
Paris, France
Tel: +33 01 4432 3347
Email:
edith.falgarone@ens.fr

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/News

Monday, August 28, 2017

The Puzzle of Ultra-Diffuse Galaxies

The central region of the Perseus galaxy cluster. This mosaic image is composed of many "tiles", individual deep exposures which were taken with the WHT. Ultra-diffuse galaxies are hard to spot, which is illustrated in the enlarged region containing one of the newly discovered faint objects. Projected on the sky the entire image has about the diameter of the full moon. Credit: Carolin Wittmann (ZAH). Large format: JPG


Our solar system is located in a spiral galaxy composed of billions of stars, the Milky Way. With the naked eye, we can see some 3000 stars in a dark night. However, if Earth would reside within an ultra-diffuse galaxy, we would only spot a few dozen stars on the sky. Galaxies of this type were either not able to produce more stars in the first place, or they got stripped of their stars by tidal forces.

Intriguingly, though, larger telescopes and improved imaging techniques have recently led to the discovery of many ultra-diffuse galaxies in the harshest environments possible: galaxy clusters.

"We have been asking ourselves how these fragile objects are able to survive among such dense, massive accumulations of hundreds of large and small galaxies", explains Carolin Wittmann, PhD student at the Astronomisches Rechen-Institut (ARI) of the Zentrum für Astronomie der Universität Heidelberg (ZAH). Using very deep optical images obtained in 2012 with the Prime Focus Camera (PFIP) of the William Herschel Telescope (WHT), Ms Wittmann identified about 90 such galaxies in the core of the Perseus Cluster, 240 million light-years away. 

Astronomers wonder how these vulnerable galaxies are able to survive among such dense, massive accumulations of hundreds of large and small galaxies. Are they possibly protected by a high dark matter content? Or might they be just now in the process of tidal disruption?

"Surprisingly, most galaxies appear intact — only very few show signs of ongoing disruption," emphasizes Dr Thorsten Lisker, who initiated the project. If this means that the ultra-diffuse galaxies can withstand the strong tidal field of the Perseus Cluster, then they must contain a large amount of unseen mass—dark matter—whose gravitational attraction acts as a binding force.

A gallery of several ultra-diffuse galaxies discovered in the Perseus galaxy cluster. These objects are barely visible against the background. Diffuse bright spots are foreground stars in the Milky Way. Credit: Carolin Wittmann (ZAH). Large format: JPG

Tidal forces may, however, be the reason why galaxies with the largest sizes are not found in the Perseus cluster core, while being present in the outer regions of other galaxy clusters. Along with international partners, the researchers are now hoping to obtain data of similar quality on the outskirts of the Perseus Cluster, where the environmental influence would have been less strong, preserving more of the original structure of the galaxies.



More Information

C. Wittmann, T. Lisker, L. Ambachew Tilahun, E.K. Grebel, C. J. Conselice, S. Penny, J. Janz, J. S. Gallagher III, R. Kotulla, J. McCormac, 2017, "A population of faint low surface brightness galaxies in the Perseus cluster core", MNRAS, 470, 1512 [ ADS ]. 

"A Trace of Galaxies at the Heart of a Gigantic Galaxy Cluster", ZAH press release 115/2015, 21 August 2017. 


Contact:

Javier Méndez (Public Relations Officer)


Friday, August 25, 2017

A double discovery

Credit: ESA/Hubble & NASA


NGC 178 may be small, but it packs quite a punch. Measuring around 40 000 light-years across, its diameter is less than half that of the Milky Way, and it is accordingly classified as a dwarf galaxy. Despite its diminutive size, NGC 178 is busy forming new stars. On average, the galaxy forms stars totalling around half the mass of the Sun per year — enough to label it a starburst galaxy.

The galaxy’s discovery is an interesting, and somewhat confusing, story. It was originally discovered by American astronomer Ormond Stone in 1885 and dubbed NGC 178, but its position in the sky was recorded incorrectly — by accident the value for the galaxy’s right ascension (which can be thought of as the celestial equivalent of terrestrial longitude) was off by a considerable amount.

In the years that followed NGC 178 was spotted again, this time by French astronomer Stéphane Javelle. As no catalogued object occupied that position in the sky, Javelle believed he had discovered a new galaxy and entered it into the expanded Index Catalogue under the name IC 39. Later, American astronomer Herbert Howe also observed the object and corrected Stone’s initial mistake.

Many years later, astronomers finally noticed that NGC 178 and IC 39 were actually the same object!
This image of NGC 178 comprises data gathered by the Wide Field Planetary Camera 2 aboard the NASA/ESA Hubble Space Telescope.



Thursday, August 24, 2017

Best Ever Image of a Star’s Surface and Atmosphere

 PR Image eso1726a
VLTI reconstructed view of the surface of Antares 

PR Image eso1726b
Artist’s impression of the red supergiant star Antares

PR Image eso1726c
VLTI velocity map of the surface of Antares

PR Image eso1726d
The bright red star Antares in the constellation of Scorpius 



Videos
 
ESOcast 123 Light: Best Ever Image of a Star’s Surface and Atmosphere (4K UHD)

Zooming in on the red supergiant star Antares
Zooming in on the red supergiant star Antares

3D animation of Antares

Approaching Antares (artist's impression)



First map of motion of material on a star other than the Sun

Using ESO’s Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star — the red supergiant star Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares’s huge extended atmosphere. The results were published in the journal Nature.

To the unaided eye the famous, bright star Antares shines with a strong red tint in the heart of the constellation of Scorpius (The Scorpion). It is a huge and comparatively cool red supergiant star in the late stages of its life, on the way to becoming a supernova [1].

A team of astronomers, led by Keiichi Ohnaka, of the Universidad Católica del Norte in Chile, has now used ESO’s Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile to map Antares’s surface and to measure the motions of the surface material. This is the best image of the surface and atmosphere of any star other than the Sun.

The VLTI is a unique facility that can combine the light from up to four telescopes, either the 8.2-metre Unit Telescopes, or the smaller Auxiliary Telescopes, to create a virtual telescope equivalent to a single mirror up to 200 metres across. This allows it to resolve fine details far beyond what can be seen with a single telescope alone.

How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century,” said Keiichi Ohnaka, who is also the lead author of the paper. “The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares — a crucial step towards clarifying this problem. The next challenge is to identify what’s driving the turbulent motions.”

Using the new results the team has created the first two-dimensional velocity map of the atmosphere of a star other than the Sun. They did this using the VLTI with three of the Auxiliary Telescopes and an instrument called AMBER to make separate images of the surface of Antares over a small range of infrared wavelengths. The team then used these data to calculate the difference between the speed of the atmospheric gas at different positions on the star and the average speed over the entire star [2]. This resulted in a map of the relative speed of the atmospheric gas across the entire disc of Antares — the first ever created for a star other than the Sun..

The astronomers found turbulent, low-density gas much further from the star than predicted, and concluded that the movement could not result from convection [3], that is, from large-scale movement of matter which transfers energy from the core to the outer atmosphere of many stars. They reason that a new, currently unknown, process may be needed to explain these movements in the extended atmospheres of red supergiants like Antares.

In the future, this observing technique can be applied to different types of stars to study their surfaces and atmospheres in unprecedented detail. This has been limited to just the Sun up to now,” concludes Ohnaka. “Our work brings stellar astrophysics to a new dimension and opens an entirely new window to observe stars.



Notes

[1] Antares is considered by astronomers to be a typical red supergiant. These huge dying stars are formed with between nine and 40 times the mass of the Sun. When a star becomes a red supergiant, its atmosphere extends outward so it becomes large and luminous, but low-density. Antares now has a mass about 12 times that of the Sun and a diameter about 700 times larger than the Sun’s. It is thought that it started life with a mass more like 15 times that of the Sun, and has shed three solar-masses of material during its life.

[2] The velocity of material towards or away from Earth can be measured by the Doppler Effect, which shifts spectral lines either towards the red or blue ends of the spectrum, depending on whether the material emitting or absorbing light is receding from or approaching the observer.

[3] Convection is the process whereby cold material moves downwards and hot material moves upwards in a circular pattern. The process occurs on Earth in the atmosphere and ocean currents, but it also moves gas around within stars.



More Information

This research was presented in a paper entitled “Vigorous atmospheric motion in the red supergiant star Antares”, by K. Ohnaka et al., published in the journal Nature.

The team is composed of K. Ohnaka (Universidad Católica del Norte, Antofagasta, Chile), G. Weigelt (Max- Planck-Institut für Radioastronomie, Bonn, Germany) and K. -H. Hofmann (Max- Planck-Institut für Radioastronomie, Bonn, Germany).

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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Links



Contacts

Keiichi Ohnaka
Instituto de Astronomía — Universidad Católica del Norte
Antofagasta, Chile
Tel: +56 55 235 5493
Email: k1.ohnaka@gmail.com

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/News

Wednesday, August 23, 2017

The Origin of Binary Stars

An image taken at submillimeter wavelengths of a star-forming core, showing that it contains two young stellar embryos. Astronomers have concluded from a systematic study of very young cores that most embryonic stars form in multiple systems, and later some of them separate. Credit:Sadavoy and Stahler


The origin of binary stars has long been one of the central problems of astronomy. One of the main questions is how stellar mass affects the tendency to be multiple. There have been numerous studies of young stars in molecular clouds to look for variations in binary frequency with stellar mass, but so many other effects can influence the result that the results have been inconclusive. These complicating factors include dynamical interactions between stars that can eject one member of a multiple system, or on the other hand might capture a passing star under the right circumstances.

Some studies, for example, found that younger stars are more likely to be found in binary pairs. One issue with much of the previous observational work, however, has been the small sample sizes.

CfA astronomer Sarah Sadavoy and her colleague used combined observations from a large radio wavelength survey of young stars in the Perseus cloud with submillimeter observations of the natal dense core material around these stars to identify twenty-four multiple systems. The scientists then used a submillimeter study to identify and characterize the dust cores in which the stars are buried.

They found that most of the embedded binaries are located near the centers of their dust cores, indicative of their still being young enough to have not drifted away. About half of the binaries are in elongated core structures, and they conclude that the initial cores were also elongated structures.

After modeling their findings, they argue that the most likely scenarios are the ones predicting that all stars, both single and binaries, form in widely separated binary pair systems, but that most of these break apart either due to ejection or to the core itself breaking apart. A few systems become more tightly bound. Although other studies have suggested this idea as well, this is the first study to do so based on observations of very young, still embedded stars. One of their most significant major conclusions is that each dusty core of material is likely to be the birthplace of two stars, not the single star usually modeled. This means that there are probably twice as many stars being formed per core than is generally believed.

Reference(s): 
"Embedded Binaries and Their Dense Cores," Sarah I. Sadavoy and Steven W. Stahler, MNRAS 469, 3881, 2017.


Tuesday, August 22, 2017

Hunting Molecules with the MWA

The centre of the Milky Way at radio wavelengths
This image shows the centre of the Milky Way as seen by the Galactic Centre Molecular Line Survey. Credit: Chenoa Tremblay (ICRAR-Curtin)



Astronomers have used an Australian radio telescope to observe molecular signatures from stars, gas and dust in our galaxy, which could lead to the detection of complex molecules that are precursors to life.

Using the Murchison Widefield Array (MWA), a radio telescope located in the Murchison region of Western Australia, the team successfully detected two molecules called the mercapto radical (SH) and nitric oxide (NO).

“The molecular transitions we saw are from slow variable stars—stars at the end of their lives that are becoming unstable,” said Chenoa Tremblay from the International Centre for Radio Astronomy Research (ICRAR) and Curtin University.

“We use molecules to probe the Milky Way, to better understand the chemical and physical environments of stars, gas and dust,” she said.

“One of the unique aspects of this survey is that until now, no one has ever reported detections of molecules within the 70-300MHz frequency range of the MWA and this is the widest field-of-view molecular survey of the Milky Way ever published.”

Since the 1980s, frequencies greater than 80GHz have been used for this type of work due to the freedom from radio frequency interference emitted by our mobile phones, televisions and orbiting satellites. But the extreme “radio quietness” of the Murchison Radio-astronomy Observatory, where the telescope is located, allows astronomers to study molecular signatures from stars and star-forming regions at lower frequencies.

“Before this study, the mercapto radical had only been seen twice before at infrared wavelengths, in a different part of the electromagnetic spectrum,” said Dr Maria Cunningham from the University of New South Wales.

“This shows that molecules are emitting photons detectable around 100MHz and we can detect these molecular signatures using the MWA—it’s very exciting for us,” she said.

Following on from the pilot study, a survey of the Orion region is now in progress, again using the MWA, in the frequency range of 99-270MHz. The Orion nebula is a chemical-rich environment and one of the closest star-forming regions to Earth. The aim is to detect more chemical tracers in stars, compare these regions to the observations from the Galactic Centre pilot region and to better understand the emission mechanisms of these molecules. “This new technique paves the way for deeper surveys that can probe the Milky Way and other galaxies in search of molecular precursors to life,” said Tremblay.

“We might even discover signatures from long chain amino acids in the cold gas environments we’re observing—which is where they are likely to be most stable.”



Publication Details:

‘A First Look for Molecules between 103 and 133MHz using the Murchison Wide eld Array’, published in the Monthly Notices of the Royal Astronomical Society on July 21, 2017.




More Information: 

The MWA

The Murchison Widefield Array (MWA) is a low frequency radio telescope located at the Murchison Radio-astronomy Observatory in Western Australia’s Mid West. The MWA observes radio waves with frequencies between 70 and 320 MHz and was the first of the three Square Kilometre Array (SKA) precursors to be completed.

The SKA

Co-located primarily in South Africa and Western Australia, the SKA will be a collection of hundreds of thousands of radio antennas with a combined collecting area equivalent to approximately one million square metres, or one square kilometre.

ICRAR The International Centre for Radio Astronomy Research, or ICRAR, is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

CAASTRO

CAASTRO is a collaboration of The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University. It is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.




Monday, August 21, 2017

Scientists Improve Brown Dwarf Weather Forecasts

This artist's concept shows a brown dwarf with bands of clouds, thought to resemble those seen at Neptune and the other outer planets. 
Credit: NASA/JPL-Caltech. › Full image and caption


Dim objects called brown dwarfs, less massive than the Sun but more massive than Jupiter, have powerful winds and clouds -- specifically, hot patchy clouds made of iron droplets and silicate dust. Scientists recently realized these giant clouds can move and thicken or thin surprisingly rapidly, in less than an Earth day, but did not understand why. 

Now, researchers have a new model for explaining how clouds move and change shape in brown dwarfs, using insights from NASA's Spitzer Space Telescope. Giant waves cause large-scale movement of particles in brown dwarfs' atmospheres, changing the thickness of the silicate clouds, researchers report in the journal Science. The study also suggests these clouds are organized in bands confined to different latitudes, traveling with different speeds in different bands. 

"This is the first time we have seen atmospheric bands and waves in brown dwarfs," said lead author Daniel Apai, associate professor of astronomy and planetary sciences at the University of Arizona in Tucson.

Just as in Earth's ocean, different types of waves can form in planetary atmospheres. For example, in Earth's atmosphere, very long waves mix cold air from the polar regions to mid-latitudes, which often lead clouds to form or dissipate. 

The distribution and motions of the clouds on brown dwarfs in this study are more similar to those seen on Jupiter, Saturn, Uranus and Neptune. Neptune has cloud structures that follow banded paths too, but its clouds are made of ice. Observations of Neptune from NASA's Kepler spacecraft, operating in its K2 mission, were important in this comparison between the planet and brown dwarfs.

"The atmospheric winds of brown dwarfs seem to be more like Jupiter's familiar regular pattern of belts and zones than the chaotic atmospheric boiling seen on the Sun and many other stars," said study co-author Mark Marley at NASA's Ames Research Center in California's Silicon Valley.

Brown dwarfs can be thought of as failed stars because they are too small to fuse chemical elements in their cores. They can also be thought of as "super planets" because they are more massive than Jupiter, yet have roughly the same diameter. Like gas giant planets, brown dwarfs are mostly made of hydrogen and helium, but they are often found apart from any planetary systems. In a 2014 study using Spitzer, scientists found that brown dwarfs commonly have atmospheric storms.

Due to their similarity to giant exoplanets, brown dwarfs are windows into planetary systems beyond our own. It is easier to study brown dwarfs than planets because they often do not have a bright host star that obscures them. 

"It is likely the banded structure and large atmospheric waves we found in brown dwarfs will also be common in giant exoplanets," Apai said. 

Using Spitzer, scientists monitored brightness changes in six brown dwarfs over more than a year, observing each of them rotate 32 times. As a brown dwarf rotates, its clouds move in and out of the hemisphere seen by the telescope, causing changes in the brightness of the brown dwarf. Scientists then analyzed these brightness variations to explore how silicate clouds are distributed in the brown dwarfs.

Researchers had been expecting these brown dwarfs to have elliptical storms resembling Jupiter's Great Red Spot, caused by high-pressure zones. The Great Red Spot has been present in Jupiter for hundreds of years and changes very slowly: Such "spots" could not explain the rapid changes in brightness that scientists saw while observing these brown dwarfs. The brightness levels of the brown dwarfs varied markedly just over the course of an Earth day. 

To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands. 

University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

"When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness," Karalidi said. "When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave."

The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior. 

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit:  http://spitzer.caltech.edu - https://www.nasa.gov/spitzer


News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425

elizabeth.landau@jpl.nasa.gov



Friday, August 18, 2017

A distorted duo Credit: ESA/Hubble & NASA


IC 1727, UGC 1249
Credit:  ESA/Hubble & NASA


Gravity governs the movements of the cosmos. It draws flocks of galaxies together to form small groups and more massive galaxy clusters, and brings duos so close that they begin to tug at one another. This latter scenario can have extreme consequences, with members of interacting pairs of galaxies often being dramatically distorted, torn apart, or driven to smash into one another, abandoning their former identities and merging to form a single accumulation of gas, dust, and stars.

The subject of this NASA/ESA Hubble Space Telescope image, IC 1727, is currently interacting with its near neighbour, NGC 672 (which is just out of frame). The pair’s interactions have triggered peculiar and intriguing phenomena within both objects — most noticeably in IC 1727. The galaxy’s structure is visibly twisted and asymmetric, and its bright nucleus has been dragged off-centre. 

In interacting galaxies such as these, astronomers often see signs of intense star formation (in episodic flurries known as starbursts) and spot newly-formed star clusters. They are thought to be caused by gravity churning, redistributing, and compacting the gas and dust. In fact, astronomers have analysed the star formation within IC 1727 and NGC 672 and discovered something interesting — observations show that simultaneous bursts of star formation occurred in both galaxies some 20 to 30 and 450 to 750 million years ago. The most likely explanation for this is that the galaxies are indeed an interacting pair, approaching each other every so often and swirling up gas and dust as they pass close by.



Thursday, August 17, 2017

The little star that survived a Supernova

The progenitor of LP40-365 could be a binary star system like the one shown in this animation. Here, an ultra-massive and compact dead star called a white dwarf (shown as a small white star) is accreting matter from its giant companion (the larger red star). The material escapes from the giant and forms an accretion disk around the white dwarf. Once enough material is accreted onto the white dwarf, a violent thermonuclear runaway tears it apart and destroys the entire system. The giant star and the surviving fragment of the white dwarf are flung into space at tremendous speeds. The surviving white dwarf shrapnel hurtles towards our region of the Galaxy, where its radiation is detected by ground based telescopes. Copyright Russell Kightley (http://scientific.pictures), used with permission.



An international team of astronomers led by Stephane Vennes at the Astronomical Institute in the Czech Republic have identified a white dwarf moving faster than the escape velocity of the Milky Way. This high velocity star is thought to be shrapnel thrown away millions of years ago from the site of an ancient, peculiar Type Ia supernova explosion. The team used telescopes located in Arizona, the Canary Islands and Maunakea’s GRACES, a high resolution spectrograph that combines the large aperture of the Gemini North telescope with Espadons, the high resolution spectropolarimeter at CFHT, via a 250m optical fiber link.

Type Ia supernovae play an important role important in our understanding of the Universe. They act as standard candles, astronomical objects for which astronomers have a decent estimate of their intrinsic brightness or luminosity. Astronomers can estimate the true total luminosity of a Type Ia supernovae and use that information to determine the distance. Despite astronomers’ understanding of the luminosity and distance relationship for Type Ia supernovae, very little is known about the explosions themselves. Astronomers build models aimed at a deeper understanding of the engine powering these explosions.

One of these models suggest that at the heart of a Type Ia supernova is a compact star known as a white dwarf. If the white dwarf has a close companion star, over time the gravity of the white dwarf may attract gas from the other star. This continuous feeding compresses the white dwarf to such a high density and temperature that the white dwarf is engulfed in a thermonuclear explosion. It is thought that nothing survives this kind of explosion. However, a new class of models called "subluminous type 1a supernova also known as a Type Iax” can leave a partially burnt remnant that is instantly ejected at high velocity.

"Such a cataclysmic binary star has never been caught feeding and getting just ready for the explosion," commented Stephane Vennes, leading author of the Science article. "All we ever witness is the aftermath of the explosion, that is the bright flash in the distant Universe that even outshines the galaxy hosting that event. But now, with the discovery of a surviving remnant of the white dwarf itself, we have direct clues to the nature of the most important actor involved in these events."

The team studied the white dwarf star LP40-365 for two-years with telescopes located in Arizona, the Canary Islands, and Hawaii. The new star was first identified with the National Science Foundation's (NSF) Mayall four-meter telescope at Kitt Peak National Observatory in Arizona. "We selected this object for observation with the spectrograph at the four-meter telescope because of its large apparent motion across the celestial sphere. Thousands of objects like this one are known, but the sky was partly cloudy on that night and we had to go for the brightest star available which turned out to be LP40-365," said team member Adela Kawka, underpinning the importance of serendipity in astronomy. "We alerted team members J.R. Thorstensen and E. Alper at Dartmouth College, and P. Nemeth at the Karl Remeis Observatory for urgent follow-up observations."

A final, crowning data set was obtained with the help of team member Viktor Khalack at the Université de Moncton using a unique instrument, GRACES on Maunakea. GRACES is a collaboration between the Canada-France-Hawaii Telescope and the NSF Gemini Observatory. When GRACES is in use, CFHT’s spectropolarimeter Espadons receives light fed by an optical fiber hooked to its neighbor on the summit, the eight-meter Gemini North telescope. “GRACES provides astronomers the best of both worlds, the light collecting power of the Gemini observatory combined with a state of the art instrument like Espadons. The combination packs a powerful punch and creates opportunities for discoveries like this one” says Nadine Manset, the GRACES instrument scientist at CFHT.

After collecting the data, the team used state of the art computer codes for analysis. The analysis proved the compact nature of the star and its exotic chemical composition. "The extreme peculiarity of the atmosphere required a lengthy and complex model atmosphere analysis which crunched several weeks of computing time. But the results proved very exciting. Such a peculiar atmosphere devoid of hydrogen and helium is rare indeed," commented team member Peter Nemeth. The analysis also revealed an extraordinary Galactic trajectory. "The extremely high velocity of this star puts it on a path out of the Milky Way with no return ever," said team member Lilia Ferrario.

Supernova models and simulations did entertain the possibility of observing surviving stellar remnants in the aftermath of a supernova explosion. The unique object LP40-365 is the first observational evidence for surviving bound remnants of failed supernovae and therefore it is an invaluable object to improve our understanding of these cosmological standard candles.

Many more of these objects are lurking in the Milky Way and awaiting discovery. The recent ESA/Gaia mission may well help us discover many more of these objects and help us understand how a little white dwarf star can survive supernova explosions. 



Additional information

Official press release
Paper



Contact Information:

Mary Beth Laychak
Outreach Program Manager
Canada-France-Hawaii Telescope
65-1238 Mamalahoa Hwy
Kamuela, HI 96743
808-885-3121
laychak@cfht.hawaii.edu

Science contact

Stephane Vennes
Astronomical Institute
The Czech Academy of Sciences
Fricova 298
251 65 Ondrejov
Czech Republic
+420 323620217
vennes@asu.cas.cz


Wednesday, August 16, 2017

Supermassive Black Holes Feed on Cosmic Jellyfish

Example of a jellyfish galaxy

Example of a jellyfish galaxy

Visualisation of MUSE view of Jellyfish Galaxy

Example of a jellyfish galaxy



Videos 

ESOcast 122 Light: Supermassive Black Holes Feed on Cosmic Jellyfish (4K UHD)
ESOcast 122 Light: Supermassive Black Holes Feed on Cosmic Jellyfish (4K UHD)

Visualisation of galaxy undergoing ram pressure stripping
Visualisation of galaxy undergoing ram pressure stripping

Artist's impression of ram pressure stripping
Artist's impression of ram pressure stripping

Visualisation of a galaxy undergoing ram pressure stripping
Visualisation of a galaxy undergoing ram pressure stripping



ESO’s MUSE instrument on the VLT discovers new way to fuel black holes


Observations of “Jellyfish galaxies” with ESO’s Very Large Telescope have revealed a previously unknown way to fuel supermassive black holes. It seems the mechanism that produces the tentacles of gas and newborn stars that give these galaxies their nickname also makes it possible for the gas to reach the central regions of the galaxies, feeding the black hole that lurks in each of them and causing it to shine brilliantly. The results appeared today in the journal Nature.

An Italian-led team of astronomers used the MUSE (Multi-Unit Spectroscopic Explorer) instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study how gas can be stripped from galaxies. They focused on extreme examples of jellyfish galaxies in nearby galaxy clusters, named after the remarkable long “tentacles” of material that extend for tens of thousands of light-years beyond their galactic discs [1][2].

The tentacles of jellyfish galaxies are produced in galaxy clusters by a process called ram pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.

Six out of the seven jellyfish galaxies in the study were found to host a supermassive black hole at the centre, feeding on the surrounding gas [3]. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.

This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” said team leader Bianca Poggianti from the INAF-Astronomical Observatory of Padova in Italy. “It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy centre.” [4]

A long-standing question is why only a small fraction of supermassive black holes at the centres of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly? These results reveal a previously unknown mechanism by which the black holes can be fed.

Yara Jaffé, an ESO fellow who contributed to the paper explains the significance: “These MUSE observations suggest a novel mechanism for gas to be funnelled towards the black hole’s neighbourhood. This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.

The current observations are part of a much more extensive study of many more jellyfish galaxies that is currently in progress.

This survey, when completed, will reveal how many, and which, gas-rich galaxies entering clusters go through a period of increased activity at their cores,” concludes Poggianti. “A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe. Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.



Notes

[1] To date, just over 400 candidate jellyfish galaxies have been found.


[2] The results were produced as part of the observational programme known as GASP (GAs Stripping Phenomena in galaxies with MUSE), which is an ESO Large Programme aimed at studying where, how and why gas can be removed from galaxies. GASP is obtaining deep, detailed MUSE data for 114 galaxies in various environments, specifically targeting jellyfish galaxies. Observations are currently in progress.

[3] It is well established that almost every, if not every, galaxy hosts a supermassive black hole at its centre, between a few million and a few billion times as massive as our Sun. When a black hole pulls in matter from its surroundings, it emits electromagnetic energy, giving rise to some of the most energetic of astrophysical phenomena: active galactic nuclei (AGN).

[4] The team also investigated the alternative explanation that the central AGN activity contributes to stripping gas from the galaxies, but considered it less likely. Inside the galaxy cluster, the jellyfish galaxies are located in a zone where the hot, dense gas of the intergalactic medium is particularly likely to create the galaxy’s long tentacles, reducing the possibility that they are created by AGN activity. There is therefore stronger evidence that ram pressure triggers the AGN and not vice versa.



More Information


This research was presented in a paper entitled “Ram Pressure Feeding Supermassive Black Holes” by B. Poggianti et al., to appear in the journal Nature on 17 August 2017.

The team is composed of B. Poggianti (INAF-Astronomical Observatory of Padova, Italy), Y. Jaffé (ESO, Chile), A. Moretti (INAF-Astronomical Observatory of Padova, Italy), M. Gullieuszik (INAF-Astronomical Observatory of Padova, Italy), M. Radovich (INAF-Astronomical Observatory of Padova, Italy), S. Tonnesen (Carnegie Observatory, USA), J. Fritz (Instituto de Radioastronomía y Astrofísica, Mexico), D. Bettoni (INAF-Astronomical Observatory of Padova, Italy), B. Vulcani (University of Melbourne, Australia; INAF-Astronomical Observatory of Padova, Italy), G. Fasano (INAF-Astronomical Observatory of Padova, Italy), C. Bellhouse (University of Birmingham, UK; ESO, Chile), G. Hau (ESO, Chile) and A. Omizzolo (Vatican Observatory, Vatican City State).

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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Links



Contacts

Bianca Poggianti
INAF-Astronomical Observatory of Padova
Padova, Italy
Tel: +39 340 7448663
Email: bianca.poggianti@oapd.inaf.it

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Source: ESO/News