Monday, March 27, 2017

First evidence of rocky planet formation in Tatooine system

A disc of rocky debris from a disrupted planetesimal surrounds white dwarf plus brown dwarf binary star. The white dwarf is the burned-out core of a star that was probably similar to the Sun, the brown dwarf is only ~60 times heavier than Jupiter, and the two stars go around each other in only a bit over two hours. Credit: Mark Garlick, UCL, University of Warwick and University of Sheffield.  Full resolution JPEG

Using the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, a team led by Jay Farihi (University College London) found, for the first time, a dust and debris disk surrounding a binary star with a white dwarf as a substellar companion. To date, almost all of the known planetary systems which include a white dwarf are single stars. Using GMOS spectra Farihi et al. identified critical metal features in the spectrum as well as the higher Balmer lines. From the Gemini data the team estimated a surface temperature of 21,800 Kelvin (about 3.5 times hotter than the Sun) and a mass of ~0.4 solar masses for the white dwarf star and a mass of ~0.063 solar masses for the companion. 

The research is published in the February 27th online issue of Nature Astronomy.

The following text is provided verbatim from the University College London press release

Evidence of planetary debris surrounding a double sun, ‘Tatooine-like’ system has been found for the first time by a UCL-led team of researchers.

Published today in Nature Astronomy and funded by the Science and Technology Facilities Council and the European Research Council, the study finds the remains of shattered asteroids orbiting a double sun consisting of a white dwarf and a brown dwarf roughly 1000 light-years away in a system called SDSS 1557.

The discovery is remarkable because the debris appears to be rocky and suggests that terrestrial planets like Tatooine – Luke Skywalker’s home world in Star Wars – might exist in the system. To date, all exoplanets discovered in orbit around double stars are gas giants, similar to Jupiter, and are thought to form in the icy regions of their systems.

In contrast to the carbon-rich icy material found in other double star systems, the planetary material identified in the SDSS 1557 system has a high metal content, including silicon and magnesium. These elements were identified as the debris flowed from its orbit onto the surface of the star, polluting it temporarily with at least 1017 g (or 1.1 trillion US tons) of matter, equating it to an asteroid at least 4 km in size.

Lead author, Dr Jay Farihi (UCL Physics & Astronomy), said: “Building rocky planets around two suns is a challenge because the gravity of both stars can push and pull tremendously, preventing bits of rock and dust from sticking together and growing into full-fledged planets. With the discovery of asteroid debris in the SDSS 1557 system, we see clear signatures of rocky planet assembly via large asteroids that formed, helping us understand how rocky exoplanets are made in double star systems."

In the Solar System, the asteroid belt contains the leftover building blocks for the terrestrial planets Mercury, Venus, Earth, and Mars, so planetary scientists study the asteroids to gain a better understanding of how rocky, and potentially habitable planets are formed. The same approach was used by the team to study the SDSS 1557 system as any planets within it cannot yet be detected directly but the debris is spread in a large belt around the double stars, which is a much larger target for analysis.

The discovery came as a complete surprise, as the team assumed the dusty white dwarf was a single star but co-author Dr Steven Parsons (University of Valparaíso and University of Sheffield), an expert in double star (or binary) systems noticed the tell-tale signs. "We know of thousands of binaries similar to SDSS 1557 but this is the first time we've seen asteroid debris and pollution. The brown dwarf was effectively hidden by the dust until we looked with the right instrument", added Parsons, "but when we observed SDSS 1557 in detail we recognised the brown dwarf's subtle gravitational pull on the white dwarf."

The team studied the binary system and the chemical composition of the debris by measuring the absorption of different wavelengths of light or ‘spectra’, using the Gemini Observatory South telescope and the European Southern Observatory Very Large Telescope, both located in Chile. 

Co-author Professor Boris Gänsicke (University of Warwick) analysed these data and found they all told a consistent and compelling story. "Any metals we see in the white dwarf will disappear within a few weeks, and sink down into the interior, unless the debris is continuously flowing onto the star. We'll be looking at SDSS 1557 next with Hubble, to conclusively show the dust is made of rock rather than ice."

Notes to Editors
For more information or to speak to the researchers involved, please contact Dr Rebecca Caygill, UCL press office. T: +44 (0)20 3108 3846 / +44 (0)7733 307 596, E:

J. Farihi, S. G. Parsons, B. T. Gansicke, ‘A circumbinary debris disk in a polluted white dwarf system’ will be published by Nature Astronomy at 1600 London time / 1100 US Eastern Time on 27 February 2017 and is under a strict embargo until then. DOI: 10.1038/s41550-016-0032.

About UCL (University College London)
UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world's top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 38,000 students from 150 countries and over 12,000 staff. Our annual income is more than £1 billion. | Follow us on Twitter @uclnews | Watch our YouTube channel
About the University of Warwick
The University of Warwick is consistently ranked in the top 10 universities in the UK and top 100 in the world. It is one of the UK's leading universities, with an acknowledged reputation for excellence in research, teaching and innovation, alongside pioneering links with business and industry.

About the University of Sheffield
With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities.

A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2016 and was voted number one university in the UK for Student Satisfaction by Times Higher Education in 2014. In the last decade it has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life.

Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.

About the Science and Technology Facilities Council (STFC)
The Science and Technology Facilities Council is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio including supporting UK work in space and ground-based astronomy technologies and research.

Sunday, March 26, 2017

With Astronomy Rewind, Citizen Scientists Will Bring Zombie Astrophotos Back to Life

At left is a photograph of the Orion Nebula from page 396 of the June 1905 Astrophysical Journal -- without coordinate labels to fix its celestial position and orientation. was able to recognize the star pattern, after which the image was rotated more than 180° to put north up and placed in context on the sky in WorldWide Telescope. Credits: American Astronomical Society, NASA/SAO Astrophysics Data System & WorldWide Telescope. Low Resolution (jpg)

"There's no telling what discoveries await," says Alyssa Goodman (Harvard-Smithsonian Center for Astrophysics, CfA), one of the project's founders. "Turning historical scientific literature into searchable, retrievable data is like turning the key to a treasure chest."

Astronomy Rewind is the latest citizen-science program on the Zooniverse platform, which debuted at Oxford University a decade ago with Galaxy Zoo and now hosts more than 50 active "people-powered" projects across a variety of scientific disciplines. After going through a short exercise to learn what they're looking for, users will view scanned pages from the journals of the American Astronomical Society (AAS) dating from the 19th century to the mid-1990s, when the Society began publishing electronically. Volunteers' first task will be to determine what types of images the pages contain: photos of celestial objects with (or without) sky coordinates? maps of planetary surfaces with (or without) grids of latitude and longitude? graphs or other types of diagrams?

The images of most interest are ones whose scale, orientation, and sky position can be nailed down by some combination of labels on or around the images plus details provided in the text or captions. Pictures that lack such information but clearly show recognizable stars, galaxies, or other celestial objects will be sent to, an automated online service that compares astrophotos to star catalogs to determine what areas of sky they show.

Modern electronic astronomical images often include information about where they fit on the sky, along with which telescope and camera were used and many other details. But such "metadata" are useful to researchers only if the original image files are published along with the journal articles in which they’re analyzed and interpreted. This isn’t always the case -- though it's becoming more common with encouragement by the AAS -- so some electronic journal pages will eventually be run through Astronomy Rewind and too.

Thanks to these human-assisted and automated efforts, many thousands of "new old" images will ultimately end up in NASA's and others' data repositories alongside pictures from the Hubble Space Telescope. They will also be incorporated into the Astronomy Image Explorer, a service of the AAS and its journal-publishing partner, the UK Institute of Physics (IOP) Publishing, and viewable in WorldWide Telescope, a powerful data-visualization tool and digital sky atlas originally developed by Microsoft Research and now managed by the AAS.

The scans of pages from the AAS journals -- the Astronomical Journal (AJ), Astrophysical Journal (ApJ), ApJ Letters, and the ApJ Supplement Series -- are being provided by the Astrophysics Data System (ADS), a NASA-funded bibliographic service and archive at the Smithsonian Astrophysical Observatory (SAO), part of the CfA.

Astronomy Rewind is built on a foundation laid by the ADS All-Sky Survey, an earlier effort to extract scientifically valuable images from old astronomy papers using computers. "It turns out that machines aren’t very good at recognizing celestial images on digitized pages that contain a mixture of text and graphics," says Alberto Accomazzi (SAO/ADS). "And they really get confused with multiple images of the sky on the same page. Humans do much better."

Accomazzi's CfA colleague Goodman, who runs a collaboration called Seamless Astronomy to develop, refine, and share tools that accelerate the pace of astronomical research, helped bring ADS and Zooniverse together. According to Zooniverse co-investigator Laura Trouille (Adler Planetarium), 1.6 million volunteers have made about 4 billion image classifications or other contributions using the platform over the last 10 years. "This isn't just busywork," says Trouille. "Zooniverse projects have led to many surprising discoveries and to more than 100 peer-reviewed scientific publications."

If Astronomy Rewind attracts volunteers in numbers comparable to other astronomy projects on Zooniverse, Trouille estimates that at least 1,000 journal pages will be processed daily. Each page will be examined by five different citizen scientists; the more of them agree on what a given page shows, the higher the confidence that they're right. It shouldn't take more than a few months to get through the initial batch of pages from the AAS journals and move most of them on to the next stage, where the celestial scenes they contain will be annotated with essential information, extracted into digital images, mapped onto the sky, and made available to anyone who wants access to them.

"You simply couldn't do a project like this in any reasonable amount of time without 'crowdsourcing,'" says Julie Steffen, AAS Director of Publishing. "Astronomy Rewind will breathe new life into old journal articles and put long-lost images of the night sky back into circulation, and that's exciting. But what's more exciting is what happens when a volunteer on Zooniverse looks at one of our journal pages and goes, 'Hmm, that’s odd!' That'll be the first step toward learning something new about the universe."

This video provides a quick demonstration of the value of placing "antique" astronomy images back on the sky in WorldWide Telescope through the project called Astronomy Rewind.

Astronomy Rewind and its partners and precursors have received funding from NASA's Astrophysics Data Analysis Program, Microsoft Research,, Centre de Données astronomiques de Strasbourg (CDS), IOP Publishing, and the American Astronomical Society (AAS).

The American Astronomical Society (AAS), established in 1899, is the major organization of professional astronomers in North America. The membership (approx. 8,000) also includes physicists, mathematicians, geologists, engineers, and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy. The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the universe, which it achieves through publishing, meeting organization, education and outreach, and training and professional development.

IOP Publishing provides publications through which leading-edge scientific research is distributed worldwide. Beyond IOP’s core journals program of more than 70 publications, high-value scientific information is made easily accessible through an ever-evolving portfolio of community websites, magazines, open-access conference proceedings, and a multitude of electronic services. The company is focused on making the most of new technologies and continually improving electronic interfaces to make it easier for researchers to find exactly what they need, when they need it, in the format that suits them best. IOP Publishing is part of the Institute of Physics (IOP), a leading scientific society with more than 50,000 international members. The Institute aims to advance physics for the benefit of all by working to advance physics research, application, and education; and engaging with policymakers and the public to develop awareness and understanding of physics. Any financial surplus earned by IOP Publishing goes to support science through the activities of the Institute.

Zooniverse is the world's largest and most popular platform for people-powered research. This research is made possible by volunteers -- hundreds of thousands of people around the world who come together to assist professional researchers. Its goal is to enable research that would not otherwise be possible or practical. Zooniverse research results in new discoveries, datasets useful to the wider research community, and many refereed publications.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

Rick Fienberg / Julie Steffen
AAS Press Officer / AAS Director of Publishing
+1 202-328-2010 x116 / +1 202-328-2010 x125 /

Rob Bernstein
Publisher, IOP Publishing
+1 202-747-1807

Megan Watzke / Peter Edmonds
Harvard-Smithsonian Center for Astrophysics
+1 617-496-7998 / +1 617-571-7279 /

Alyssa Goodman
Professor of Astronomy, Harvard University
Harvard-Smithsonian Center for Science

Laura Trouille
Director of Citizen Science, Adler Planetarium
Co-Investigator, Zooniverse
+1 312-322-0820

Saturday, March 25, 2017

Andromeda's Bright X-Ray Mystery Solved by NuSTAR

NASA's Nuclear Spectroscope Telescope Array, or NuSTAR, has identified a candidate pulsar in Andromeda -- the nearest large galaxy to the Milky Way. This likely pulsar is brighter at high energies than the Andromeda galaxy's entire black hole population. Image credit: NASA/JPL-Caltech/GSFC/JHU .  › Full image and caption

The Milky Way's close neighbor, Andromeda, features a dominant source of high-energy X-ray emission, but its identity was mysterious until now. As reported in a new study, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission has pinpointed an object responsible for this high-energy radiation. 

The object, called Swift J0042.6+4112, is a possible pulsar, the dense remnant of a dead star that is highly magnetized and spinning, researchers say. This interpretation is based on its emission in high-energy X-rays, which NuSTAR is uniquely capable of measuring. The object's spectrum is very similar to known pulsars in the Milky Way.

It is likely in a binary system, in which material from a stellar companion gets pulled onto the pulsar, spewing high-energy radiation as the material heats up. 

"We didn't know what it was until we looked at it with NuSTAR," said Mihoko Yukita, lead author of a study about the object, based at Johns Hopkins University in Baltimore. The study is published in The Astrophysical Journal.

This candidate pulsar is shown as a blue dot in a NuSTAR X-ray image of Andromeda (also called M31), where the color blue is chosen to represent the highest-energy X-rays. It appears brighter in high-energy X-rays than anything else in the galaxy. 

The study brings together many different observations of the object from various spacecraft. In 2013, NASA's Swift satellite reported it as a high-energy source, but its classification was unknown, as there are many objects emitting low energy X-rays in the region. The lower-energy X-ray emission from the object turns out to be a source first identified in the 1970s by NASA's Einstein Observatory. 
Other spacecraft, such as NASA's Chandra X-ray Observatory and ESA's XMM-Newton had also detected it. However, it wasn't until the new study by NuSTAR, aided by supporting Swift satellite data, that researchers realized it was the same object as this likely pulsar that dominates the high energy X-ray light of Andromeda.

Traditionally, astronomers have thought that actively feeding black holes, which are more massive than pulsars, usually dominate the high-energy X-ray light in galaxies. As gas spirals closer and closer to the black hole in a structure called an accretion disk, this material gets heated to extremely high temperatures and gives off high-energy radiation. This pulsar, which has a lower mass than any of Andromeda's black holes, is brighter at high energies than the galaxy's entire black hole population.

Even the supermassive black hole in the center of Andromeda does not have significant high-energy X-ray emission associated with it. It is unexpected that a single pulsar would instead be dominating the galaxy in high-energy X-ray light.

"NuSTAR has made us realize the general importance of pulsar systems as X-ray-emitting components of galaxies, and the possibility that the high energy X-ray light of Andromeda is dominated by a single pulsar system only adds to this emerging picture," said Ann Hornschemeier, co-author of the study and based at NASA's Goddard Space Flight Center, Greenbelt, Maryland.
Andromeda is a spiral galaxy slightly larger than the Milky Way. It resides 2.5 million light-years from our own galaxy, which is considered very close, given the broader scale of the universe. Stargazers can see Andromeda without a telescope on dark, clear nights. 

"Since we can't get outside our galaxy and study it in an unbiased way, Andromeda is the closest thing we have to looking in a mirror," Hornschemeier said.

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR's mission operations center is at UC Berkeley, and the official data archive is at NASA's High Energy Astrophysics Science Archive Research Center. ASI provides the mission's ground station and a mirror archive. JPL is managed by Caltech for NASA.

For more information on NuSTAR, visit: -

News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.

Source: JPL-Caltech

Friday, March 24, 2017

Hubble detects supermassive black hole kicked out of galactic core

Galaxy with an ejected supermassive black hole

Gravitational waves eject black hole from galaxy

Astronomers suspect gravitational waves

An international team of astronomers using the NASA/ESA Hubble Space Telescope have uncovered a supermassive black hole that has been propelled out of the centre of the distant galaxy 3C186. The black hole was most likely ejected by the power of gravitational waves. This is the first time that astronomers found a supermassive black hole at such a large distance from its host galaxy centre.

Though several other suspected runaway black holes have been seen elsewhere, none has so far been confirmed. Now astronomers using the NASA/ESA Hubble Space Telescope have detected a supermassive black hole, with a mass of one billion times the Sun’s, being kicked out of its parent galaxy. “We estimate that it took the equivalent energy of 100 million supernovae exploding simultaneously to jettison the black hole,” describes Stefano Bianchi, co-author of the study, from the Roma Tre University, Italy.

The images taken by Hubble provided the first clue that the galaxy, named 3C186, was unusual. The images of the galaxy, located 8 billion light-years away, revealed a bright quasar, the energetic signature of an active black hole, located far from the galactic core. “Black holes reside in the centres of galaxies, so it’s unusual to see a quasar not in the centre,” recalls team leader Marco Chiaberge, ESA-AURA researcher at the Space Telescope Science Institute, USA.

The team calculated that the black hole has already travelled about 35 000 light-years from the centre, which is more than the distance between the Sun and the centre of the Milky Way. And it continues its flight at a speed of 7.5 million kilometres per hour [1]. At this speed the black hole could travel from Earth to the Moon in three minutes.

Although other scenarios to explain the observations cannot be excluded, the most plausible source of the propulsive energy is that this supermassive black hole was given a kick by gravitational waves [2] unleashed by the merger of two massive black holes at the centre of its host galaxy. This theory is supported by arc-shaped tidal tails identified by the scientists, produced by a gravitational tug between two colliding galaxies.

According to the theory presented by the scientists, 1-2 billion years ago two galaxies — each with central, massive black holes — merged. The black holes whirled around each other at the centre of the newly-formed elliptical galaxy, creating gravitational waves that were flung out like water from a lawn sprinkler [3]. As the two black holes did not have the same mass and rotation rate, they emitted gravitational waves more strongly along one direction. When the two black holes finally merged, the anisotropic emission of gravitational waves generated a kick that shot the resulting black hole out of the galactic centre.

“If our theory is correct, the observations provide strong evidence that supermassive black holes can actually merge,” explains Stefano Bianchi on the importance of the discovery. “There is already evidence of black hole collisions for stellar-mass black holes, but the process regulating supermassive black holes is more complex and not yet completely understood.”

The researchers are lucky to have caught this unique event because not every black hole merger produces imbalanced gravitational waves that propel a black hole out of the galaxy. The team now wants to secure further observation time with Hubble, in combination with the Atacama Large Millimeter/submillimeter Array (ALMA) and other facilities, to more accurately measure the speed of the black hole and its surrounding gas disc, which may yield further insights into the nature of this rare object.


[1] As the black hole cannot be observed directly, the mass and the speed of the supermassive black holes were determined via spectroscopic analysis of its surrounding gas.

[2] First predicted by Albert Einstein, gravitational waves are ripples in space that are created by accelerating massive objects. The ripples are similar to the concentric circles produced when a rock is thrown into a pond. In 2016, the Laser Interferometer Gravitational-wave Observatory (LIGO) helped astronomers prove that gravitational waves exist by detecting them emanating from the union of two stellar-mass black holes, which are several times more massive than the Sun.

[3] The black holes get closer over time as they radiate away gravitational energy.

More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results of the study were presented in the paper The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?, to appear in the journal Astronomy & Astrophysics.

The international team of astronomers in this study consists of Marco Chiaberge (STScI, USA; Johns Hopkins University, USA), Justin C. Ely (STScI, USA), Eileen Meyer (University of Maryland Baltimore County, USA), Markos Georganopoulos (University of Maryland Baltimore County, USA; NASA Goddard Space Flight Center, USA), Andrea Marinucci (Università degli Studi Roma Tre, Italy), Stefano Bianchi (Università degli Studi Roma Tre, Italy), Grant R. Tremblay (Yale University, USA), Brian Hilbert (STScI, USA), John Paul Kotyla (STScI, USA), Alessandro Capetti (INAF - Osservatorio Astrofisico di Torino, Italy), Stefi Baum (University of Manitoba, Canada), F. Duccio Macchetto (STScI, USA), George Miley (University of Leiden, Netherlands), Christopher O’Dea (University of Manitoba, Canada), Eric S. Perlman (Florida Institute of Technology, USA), William B. Sparks (STScI, USA) and  Colin Norman (STScI, USA; Johns Hopkins University, USA)

Image credit: NASA, ESA, M. Chiaberge (STScI/ESA)



Marco Chiaberge
Space Telescope Science Institute
Baltimore, USA
Tel: +1 410 338 4980

Stefano Bianchi
Roma Tre University
Rome, Italy
Tel: +39 657337241

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 17662397500

Defying cosmic convention

Credit: ESA/Hubble & NASA

Some galaxies are harder to classify than others. Here, Hubble’s trusty Wide Field Camera 3 (WFC3) has captured a striking view of two interacting galaxies located some 60 million light-years away in the constellation of  Leo (The Lion). The more diffuse and patchy blue glow covering the right side of the frame is known as NGC 3447 — sometimes NGC 3447B for clarity, as the name NGC 3447 can apply to the overall duo. The smaller clump to the upper left is known as NGC 3447A.

The trouble with space is that it is, to state the obvious, really, really big. Astronomers have for hundreds of years been discovering and naming galaxies, stars, cosmic clouds and more. Unifying and regulating the conventions and classifications for everything ever observed is very difficult, especially when you get an ambiguous object like NGC 3447, which stubbornly defies easy categorisation.

Overall, we know NGC 3447 comprises a couple of interacting galaxies, but we’re unsure what each looked like before they began to tear one another apart. The two sit so close that they are strongly influenced and distorted by the gravitational forces between them, causing the galaxies to twist themselves into the unusual and unique shapes seen here. NGC 3447A appears to display the remnants of a central bar structure and some disrupted spiral arms, both properties characteristic of certain spiral galaxies. Some identify NGC 3447B as a former spiral galaxy, while others categorise it as being an irregular galaxy.

Thursday, March 23, 2017

Saturn's Rings Viewed in the Mid-infrared Show Bright Cassini Division

Figure 1: A three-color composite of the mid-infrared images of Saturn on January 23, 2008 captured with COMICS on the Subaru Telescope. The Cassini Division and the C ring appear bright. Color differences reflect the temperatures; the warmer part is blue, the cooler part is red. (Credit: NAOJ)

A team of researchers has succeeded in measuring the brightnesses and temperatures of Saturn's rings using the mid-infrared images taken by the Subaru Telescope in 2008. The images are the highest resolution ground-based views ever made. They reveal that, at that time, the Cassini Division and the C ring were brighter than the other rings in the mid-infrared light and that the brightness contrast appeared to be the inverse of that seen in the visible light (Figure 1). The data give important insights into the nature of Saturn's rings.

Subaru Views Saturn

The Subaru Telescope also has observed Saturn several times over the years. Dr. Hideaki Fujiwara, Subaru Public Information Officer/Scientist, analyzed data taken in January 2008 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the telescope to produce a beautiful image of Saturn for public information purposes. During the analysis, he noticed that the appearance of Saturn's rings in the mid-infrared part of the spectrum was totally different from what is seen in the visible light

Saturn's main rings consist of the C, B, and A rings, each with different populations of particles. The Cassini Division separates the B and A rings. The 2008 image shows that the Cassini Division and the C ring are brighter in the mid-infrared wavelengths than the B and A rings appear to be (Figure 1). This brightness contrast is the inverse of how they appear in the visible light, where the B and A rings are always brighter than the Cassini Division and the C ring (Figure 2).

Figure 2: Comparison of the images of Saturn's rings in the 2008 view in the mid-infrared (left) and the visible light (right). The visible light image was taken on March 16, 2008 with the 105-cm Murikabushi telescope at Ishigakijima Astronomical Observatory. The radial brightness contrast of Saturn's rings is the inverse between the two wavelength ranges. (Credit: NAOJ)

"Thermal emission" from ring particles is observed in the mid-infrared, where warmer particles are brighter. The team measured the temperatures of the rings from the images, which revealed that the Cassini Division and the C ring are warmer than the B and A rings. The team concluded that this was because the particles in the Cassini Division and C ring are more easily heated by solar light due to their sparser populations and darker surfaces.

On the other hand, in the visible light, observers see sunlight being reflected by the ring particles. Therefore, the B and A rings, with their dense populations of particles, always seem bright in the visible wavelengths, while the Cassini Division and the C ring appear faint. The difference in the emission process explains the inverse brightnesses of Saturn's rings between the mid-infrared and the visible-light views.

Changing Angles Change the Brightnesses

It turns out that the Cassini Division and the C ring are not always brighter than the B and A rings, even in the mid-infrared. The team investigated images of Saturn's rings taken in April 2005 with COMICS, and found that the Cassini Division and the C ring were fainter than the B and A rings at that time, which is the same contrast to what was seen in the visible light (Figure 3).

Figure 3: Comparison of the mid-infrared images of Saturn's rings on April 30, 2005 (top) and January 23, 2008 (bottom). Although both of the images were taken in the mid-infrared, the radial contrast of Saturn's rings is the inverse of each other. (Credit: NAOJ)

The team concluded that the "inversion" of the brightness of Saturn's rings between 2005 and 2008 was caused by the seasonal change in the ring opening angle to the Sun and Earth. Since the rotation axis of Saturn inclines compared to its orbital plane around the Sun, the ring opening angle to the Sun changes over a 15-year cycle. This makes a seasonal variation in the solar heating of the ring particles. The change in the opening angle viewed from the Earth affects the apparent filling factor of the particles in the rings. These two variations – the temperature and the observed filling factor of the particles – led to the change in the mid-infrared appearance of Saturn's rings.

The data taken with the Subaru Telescope revealed that the Cassini Division and the C ring are sometimes bright in the mid-infrared though they are always faint in visible light. "I am so happy that the public information activities of the Subaru Telescope, of which I am in charge, led to this scientific finding," said Dr. Fujiwara. "We are going to observe Saturn again in May 2017 and hope to investigate the nature of Saturn's rings further by taking advantages of observations with space missions and ground-based telescopes."

This research is published in Astronomy & Astrophysics, Volume 599, A29 and posted on-line on February 23, 2017 (Fujiwara et al., 2017, "Seasonal variation of the radial brightness contrast of Saturn's rings viewed in mid-infrared by Subaru/COMICS"). This work is supported JSPS KAKENHI Grant Numbers JP23103002 and JP26800110.

The research team:

  • Hideaki Fujiwara: Subaru Telescope, National Astronomical Observatory of Japan, USA
  • Ryuji Morishima: University of California, Los Angeles/Jet Propulsion Laboratory, California Institute of Technology, USA
  • Takuya Fujiyoshi: Subaru Telescope, National Astronomical Observatory of Japan, USA
  • Takuya Yamashita: National Astronomical Observatory of Japan, Japan

Wednesday, March 22, 2017

NASA's Swift Mission Maps a Star's 'Death Spiral' into a Black Hole

This artist’s rendering shows the tidal disruption event named ASASSN-14li, where a star wandering too close to a 3-million-solar-mass black hole was torn apart. The debris gathered into an accretion disk around the black hole. New data from NASA's Swift satellite show that the initial formation of the disk was shaped by interactions among incoming and outgoing streams of tidal debris. Credit: NASA's Goddard Space Flight Center. Hi-res image

Some 290 million years ago, a star much like the sun wandered too close to the central black hole of its galaxy. Intense tides tore the star apart, which produced an eruption of optical, ultraviolet and X-ray light that first reached Earth in 2014. Now, a team of scientists using observations from NASA's Swift satellite have mapped out how and where these different wavelengths were produced in the event, named ASASSN-14li, as the shattered star's debris circled the black hole.

"We discovered brightness changes in X-rays that occurred about a month after similar changes were observed in visible and UV light," said Dheeraj Pasham, an astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, and the lead researcher of the study. "We think this means the optical and UV emission arose far from the black hole, where elliptical streams of orbiting matter crashed into each other."

This animation illustrates how debris from a tidally disrupted star collides with itself, creating shock waves that emit ultraviolet and optical light far from the black hole. According to Swift observations of ASASSN-14li, these clumps took about a month to fall back to the black hole, where they produced changes in the X-ray emission that correlated with the earlier UV and optical changes. Credits: NASA's Goddard Space Flight Center. This video is public domain and can be downloaded from the Scientific Visualization Studio.

Astronomers think ASASSN-14li was produced when a sun-like star wandered too close to a 3-million-solar-mass black hole similar to the one at the center of our own galaxy. For comparison, the event horizon of a black hole like this is about 13 times bigger than the sun, and the accretion disk formed by the disrupted star could extend to more than twice Earth's distance from the sun.

When a star passes too close to a black hole with 10,000 or more times the sun's mass, tidal forces outstrip the star's own gravity, converting the star into a stream of debris. Astronomers call this a tidal disruption event. Matter falling toward a black hole collects into a spinning accretion disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe. Tidal disruption flares carry important information about how this debris initially settles into an accretion disk.

Astronomers know the X-ray emission in these flares arises very close to the black hole. But the location of optical and UV light was unclear, even puzzling. In some of the best-studied events, this emission seems to be located much farther than where the black hole's tides could shatter the star. Additionally, the gas emitting the light seemed to remain at steady temperatures for much longer than expected.

ASASSN-14li was discovered Nov. 22, 2014, in images obtained by the All Sky Automated Survey for SuperNovae (ASASSN), which includes robotic telescopes in Hawaii and Chile. Follow-up observations with Swift's X-ray and Ultraviolet/Optical telescopes began eight days later and continued every few days for the next nine months. The researchers supplemented later Swift observations with optical data from the Las Cumbres Observatory headquartered in Goleta, California.   

In a paper describing the results published March 15 in The Astrophysical Journal Letters, Pasham, Cenko and their colleagues show how interactions among the infalling debris could create the observed optical and UV emission.

Tidal debris initially falls toward the black hole but overshoots, arcing back out along elliptical orbits and eventually colliding with the incoming stream.

"Returning clumps of debris strike the incoming stream, which results in shock waves that emit visible and ultraviolet light," said Goddard's Bradley Cenko, the acting Swift principal investigator and a member of the science team. "As these clumps fall down to the black hole, they also modulate the X-ray emission there."

Future observations of other tidal disruption events will be needed to further clarify the origin of optical and ultraviolet light.

Goddard manages the Swift mission in collaboration with Pennsylvania State University in University Park, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.


By Francis Reddy
NASA's Goddard Space Flight Center in Greenbelt, Md.
Editor: Karl Hille

Tuesday, March 21, 2017

Protostar Blazes Bright, Reshaping Its Stellar Nursery

Inside the Cats's Paw Nebula, as seen in an infrared image from NASA's Spitzer Space Telescope (left), ALMA discovered that an infant star is undergoing an intense growth spurt, shining nearly 100 brighter than before and reshaping its stellar nursery (right). Credit: ALMA (ESO/NAOJ/NRAO), T. Hunter; C. Brogan, B. Saxton (NRAO/AUI/NSF); GLIMPSE, NASA/JPL-Caltech

ALMA image of the glowing dust inside NGC 6334I, a protocluster containing an infant star that is undergoing an intense growth spurt, likely triggered by an avalanche of gas falling onto its surface. Credit: ALMA (ESO/NAOJ/NRAO); C. Brogan, B. Saxton (NRAO/AUI/NSF)

Comparing observations by two different millimeter-wavelength telescopes, ALMA and the SMA, astronomers noted a massive outburst in a star-forming cloud. Because the ALMA images are more sensitive and show finer detail, it was possible to use them to simulate what the SMA could have seen in 2015 and 2016. By subtracting the earlier SMA images from the simulated images, astronomers could see that a significant change had taken place in MM1 while the other three millimeter sources (MM2, MM3, and MM4) are unchanged. Credit: ALMA (ESO/NAOJ/NRAO); SMA, Harvard/Smithsonian CfA

A massive protostar, deeply nestled in its dust-filled stellar nursery, recently roared to life, shining nearly 100 times brighter than before. This outburst, apparently triggered by an avalanche of star-forming gas crashing onto the surface of the star, supports the theory that young stars can undergo intense growth spurts that reshape their surroundings.

Astronomers made this discovery by comparing new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile with earlier observations from the Submillimeter Array (SMA) in Hawaii.

"We were amazingly fortunate to detect this spectacular transformation of a young, massive star,” said Todd Hunter, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Va., and lead author on a paper published in the Astrophysical Journal Letters. "By studying a dense star-forming cloud with both ALMA and the SMA, we could see that something dramatic had taken place, completely changing a stellar nursery over a surprisingly short period of time."

In 2008, before the era of ALMA, Hunter and his colleagues used the SMA to observe a small but active portion of the Cat's Paw Nebula (also known as NGC 6334), a star-forming complex located about 5,500 light-years from Earth in the direction of the southern constellation Scorpius. This nebula is similar in many respects to its more northern cousin, the Orion Nebula, which is also brimming with young stars, star clusters, and dense cores of gas that are on the verge of becoming stars. The Cat's Paw Nebula, however, is forming stars at a faster rate.

The initial SMA observations of this portion of the nebula, dubbed NGC 6334I, revealed what appeared to be a typical protocluster: a dense cloud of dust and gas harboring several still-growing stars.

Young stars form in these tightly packed regions when pockets of gas become so dense that they begin to collapse under their own gravity. Over time, disks of dust and gas form around these nascent stars and funnel material onto their surfaces helping them grow.

This process, however, may not be entirely slow and steady. Astronomers now believe that young stars can also experience spectacular growth spurts, periods when they rapidly acquire mass by gorging on star-forming gas.

The new ALMA observations of this region, taken in 2015 and 2016, reveal that dramatic changes occurred toward a portion of the protocluster called NGC 6334I-MM1 after the original SMA observations. This region is now about four times brighter at millimeter wavelengths, meaning that the central protostar is nearly 100 times more luminous than before.

The astronomers speculate that leading up to this outburst, an uncommonly large clump of material was drawn into the star's accretion disk, creating a logjam of dust and gas. Once enough material accumulated, the logjam burst, releasing an avalanche of gas onto the growing star.

This extreme accretion event greatly increased the star’s luminosity, heating its surrounding dust. It’s this hot, glowing dust that the astronomers observed with ALMA. Though similar events have been observed in infrared light, this is the first time that such an event has been identified at millimeter wavelengths.

To ensure that the observed changes were not the result of differences in the telescopes or simply a data-processing error, Hunter and his colleagues used the ALMA data as a model to accurately simulate what the SMA -- with its more modest capabilities -- would have seen if it conducted similar observations in 2015 and 2016. By digitally subtracting the actual 2008 SMA images from the simulated images, the astronomers confirmed that there was indeed a significant and consistent change to one member of the protocluster.

"Once we made sure we were comparing the two sets of observations on an even playing field, we knew that we were witnessing a very special time in the growth of a star," said Crystal Brogan, also with the NRAO and co-author on the paper.

Further confirmation of this event came from complementary data taken by the Hartebeesthoek Radio Astronomy Observatory in South Africa. This single-dish observatory was monitoring the radio signals from masers in the same region. Masers are the naturally occurring cosmic radio equivalent of lasers. They are powered by a variety of energetic processes, including outbursts from rapidly growing stars.

The data from the Hartebeesthoek observatory reveal an abrupt and dramatic spike in maser emission from this region in early 2015, only a few months before the first ALMA observation. Such a spike is precisely what astronomers would expect to see if there were a protostar undergoing a major growth spurt.

"These observations add evidence to the theory that star formation is punctuated by a sequence of dynamic events that build up a star, rather than a smooth continuous growth," concluded Hunter. "It also tells us that it is important to monitor young stars at radio and millimeter wavelengths, because these wavelengths allow us to peer into the youngest, most deeply embedded star-forming regions. Catching such events at the earliest stage may reveal new phenomena of the star-formation process."

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

# # #

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.

This research is presented in a paper titled "An extraordinary outburst in the massive protostellar system NGC6334I-MM1: Quadrupling of the millimeter continuum," by T.R. Hunter et al., published in the Astrophysical Journal Letters [].


Charles Blue

Monday, March 20, 2017

Hubble Discovery of Runaway Star Yields Clues to Breakup of Multiple-Star System

Wayward Newborn Stars Fleeing from Their Birthplace
Credits: NASA, ESA, K. Luhman (Penn State University), and M. Robberto (STScI)

As British royal families fought the War of the Roses in the 1400s for control of England's throne, a grouping of stars was waging its own contentious skirmish — a star wars far away in the Orion Nebula.

The stars were battling each other in a gravitational tussle, which ended with the system breaking apart and at least three stars being ejected in different directions. The speedy, wayward stars went unnoticed for hundreds of years until, over the past few decades, two of them were spotted in infrared and radio observations, which could penetrate the thick dust in the Orion Nebula.

The observations showed that the two stars were traveling at high speeds in opposite directions from each other. The stars' origin, however, was a mystery. Astronomers traced both stars back 540 years to the same location and suggested they were part of a now-defunct multiple-star system. But the duo's combined energy, which is propelling them outward, didn't add up. The researchers reasoned there must be at least one other culprit that robbed energy from the stellar toss-up.

Now NASA's Hubble Space Telescope has helped astronomers find the final piece of the puzzle by nabbing a third runaway star. The astronomers followed the path of the newly found star back to the same location where the two previously known stars were located 540 years ago. The trio reside in a small region of young stars called the Kleinmann-Low Nebula, near the center of the vast Orion Nebula complex, located 1,300 light-years away.

"The new Hubble observations provide very strong evidence that the three stars were ejected from a multiple-star system," said lead researcher Kevin Luhman of Penn State University in University Park, Pennsylvania. "Astronomers had previously found a few other examples of fast-moving stars that trace back to multiple-star systems, and therefore were likely ejected. But these three stars are the youngest examples of such ejected stars. They're probably only a few hundred thousand years old. In fact, based on infrared images, the stars are still young enough to have disks of material leftover from their formation."
xtremely fast on their way out of the Kleinmann-Low Nebula, up to almost 30 times the speed of most of the nebula's stellar inhabitants. Based on computer simulations, astronomers predicted that these gravitational tugs-of-war should occur in young clusters, where newborn stars are crowded together. "But we haven't observed many examples, especially in very young clusters," Luhman said. "The Orion Nebula could be surrounded by additional fledging stars that were ejected from it in the past and are now streaming away into space."

The team's results will appear in the March 20, 2017 issue of The Astrophysical Journal Letters.

Luhman stumbled across the third speedy star, called "source x," while he was hunting for free-floating planets in the Orion Nebula as a member of an international team led by Massimo Robberto of the Space Telescope Science Institute in Baltimore, Maryland. The team used the near-infrared vision of Hubble's Wide Field Camera 3 to conduct the survey. During the analysis, Luhman was comparing the new infrared images taken in 2015 with infrared observations taken in 1998 by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). He noticed that source x had changed its position considerably, relative to nearby stars over the 17 years between Hubble images, indicating the star was moving fast, about 130,000 miles per hour.

The astronomer then looked at the star's previous locations, projecting its path back in time. He realized that in the 1470s source x had been near the same initial location in the Kleinmann-Low Nebula as two other runaway stars, Becklin-Neugebauer (BN) and "source I."

BN was discovered in infrared images in 1967, but its rapid motion wasn't detected until 1995, when radio observations measured the star's speed at 60,000 miles per hour. Source I is traveling roughly 22,000 miles per hour. The star had only been detected in radio observations; because it is so heavily enshrouded in dust, its visible and infrared light is largely blocked.

The three stars were most likely kicked out of their home when they engaged in a game of gravitational billiards, Luhman said. What often happens when a multiple system falls apart is that two of the member stars move close enough to each other that they merge or form a very tight binary. 
In either case, the event releases enough gravitational energy to propel all of the stars in the system outward. The energetic episode also produces a massive outflow of material, which is seen in the NICMOS images as fingers of matter streaming away from the location of the embedded source I star.

Future telescopes, such as the James Webb Space Telescope, will be able to observe a large swath of the Orion Nebula. By comparing images of the nebula taken by the Webb telescope with those made by Hubble years earlier, astronomers hope to identify more runaway stars from other multiple-star systems that broke apart.

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

Related Links:


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514 /

Kevin Luhman
Penn State University, University Park, Pennsylvania

Source: HubbleSite


Sunday, March 19, 2017

ALMA's ability to see a "Cosmic Hole" confirmed

The image shows the measurement of the SZ effect in the galaxy cluster RX J1347.5-1145 taken with ALMA (blue). The background image was taken by the Hubble Space Telescope. A "hole" caused by the SZ effect is seen in the ALMA observations.  Credit: ALMA (ESO/NAOJ/NRAO), Kitayama et al., NASA/ESA Hubble Space Telescope

Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) successfully imaged a radio "hole" around a galaxy cluster 4.8 billion light-years away from us. This is the highest resolution image ever taken of such a hole caused by the Sunyaev-Zel'dovich effect (SZ effect). The image proves ALMA's high capability to investigate the distribution and temperature of gas around galaxy clusters through the SZ effect.

A research team led by Tetsu Kitayama, a professor at Toho University, Japan, used ALMA to investigate the hot gas in a galaxy cluster. The hot gas is a key component to understand the nature and evolution of galaxy clusters. Even though the hot gas does not emit radio waves detectable with ALMA, the gas scatters the radio waves of the Cosmic Microwave Background and makes a "hole" around the galaxy cluster. This is the Sunyaev-Zel'dovich effect [1].

The team observed the galaxy cluster RX J1347.5-1145 located 4.8 billion light-years away. This galaxy cluster is well known among astronomers for its strong SZ effect and has been observed many times with radio telescopes. For example, the Nobeyama 45-m Radio Telescope, operated by the National Astronomical Observatory of Japan, has revealed an uneven distribution of the hot gas in this galaxy cluster, which was not seen in X-ray observations. To better understand the unevenness, astronomers need higher resolution observations. But relatively smooth and widely-distributed objects, such as the hot gas in galaxy clusters, are difficult to image with high-resolution radio interferometers.

To overcome this difficulty, ALMA utilized the Atacama Compact Array, also known as the Morita Array, the major Japanese contribution to the project. The Morita Array's smaller diameter antennas and the close-packed antenna configuration provide a wider field of view. By using the data from the Morita Array, astronomers can precisely measure the radio waves from objects subtending a large angle on the sky.
With ALMA, the team obtained an SZ effect image of RX J1347.5-1145, with twice the resolution and ten times better sensitivity than previous observations. This is the first image of the SZ effect with ALMA. The ALMA SZ image is consistent with the previous observations and better illustrates the pressure distribution of hot gas. This image proves that ALMA is highly capable of observing the SZ effect and clearly shows that a gigantic collision is ongoing in this galaxy cluster.

"It was nearly 50 years ago that the SZ effect was proposed for the first time," explains Kitayama. "The effect is pretty weak and it has been very difficult to image the effect with high resolution. Thanks to ALMA, this time we made a long-awaited breakthrough to pave a new path to probe the cosmic evolution."


[1] "Cosmic Microwave Background (CMB)" radio waves come from every direction. When CMB radio waves pass through the hot gas in a galaxy cluster, the radio waves interact with high-energy electrons in the hot gas and gain energy. As a result, the CMB radio waves shift to higher energy. Observing from the Earth, the CMB in the original energy range has less intensity near the galaxy cluster. This is called the "Sunyaev-Zel'dovich effect," first proposed by Rashid Sunyaev and Yakov Zel'dovich in 1970.

These observation results were published as Kitayama et al. "The Sunyaev-Zel'dovich effect at 5″: RX J1347.5-1145 imaged by ALMA" in the Publications of the Astronomical Society of Japan in October 2016.

The research team members are:

Tetsu Kitayama (Toho University), Shutaro Ueda (Japan Aerospace Exploration Agency), Shigehisa Takakuwa (Kagoshima University / Academia Sinica Institute of Astronomy and Astrophysics), Takahiro Tsutsumi (U. S. National Radio Astronomy Observatory), Eiichiro Komatsu (Max-Planck Institute for Astrophysics / Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo), Takuya Akahori (Kagoshima University), Daisuke Iono (National Astronomical Observatory of Japan / SOKENDAI), Takuma Izumi (The University of Tokyo), Ryohei Kawabe (National Astronomical Observatory of Japan / SOKENDAI / The University of Tokyo), Kotaro Kohno (The University of Tokyo), Hiroshi Matsuo (National Astronomical Observatory of Japan / SOKENDAI), Naomi Ota (Nara Women's University), Yasushi Suto (The University of Tokyo), Motokazu Takizawa (Yamagata University), and Kohji Yoshikawa (University of Tsukuba)

Saturday, March 18, 2017

ALMA peers into the hearts of stellar nurseries

NGC 6822
Credit: ESO, ALMA (ESO/NAOJ/NRAO)/A. Schruba, VLA (NRAO)/Y. Bagetakos/Little THINGS

With their spectacular glowing arms, grand spiral galaxies seem to get all the attention — but NGC 6822, a barred irregular dwarf galaxy, proves that regular spirals do not have a monopoly on galactic beauty. Also called Barnard’s galaxy, NGC 6822 is located in the constellation of Sagittarius just 1.6 million light-years away and is brimming with rich star formation regions.

This new image is a composite of older observations made with the Wide Field Imager attached to the 2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory and new data collected by the Atacama Large Millimeter/submillimeter Array (ALMA). The areas observed with ALMA are highlighted in the image and can be seen here in detail.

The observations by ALMA reveal the structure of star-forming gas clouds in unprecedented resolution. Observations in our own galaxy have shown that stars form in the dense cores of giant clouds of molecular hydrogen gas, the only places where gas can become cold enough to collapse under its own gravity. These conditions also foster the formation of other molecules, such as carbon monoxide, which are an indispensable tool in helping astronomers to detect galactic molecular hydrogen gas.

Until recently, astronomers have only been able to resolve star formation regions within the Milky Way — but now ALMA’s sharp sight provides a window into star formation in other galaxies. The analysis of the data revealed that, unlike in our own galaxy, the observed molecules are concentrated into small, dense cores of gas. This explains why it has been so hard to observe extragalactic star formation regions so far, especially in low mass, low metallicity galaxies. ALMA also found that the cores in NGC 6822 behave remarkably similarly to stellar nurseries in the Milky Way, indicating that the physics of star formation in these low-mass galaxies resemble that which we see in our own galaxy.

Source: ESO/Images

Friday, March 17, 2017

Seeing things sideways

Credit: ESA/Hubble & NASA

This image from Hubble’s Wide Field Camera 3 (WFC3) shows NGC 1448, a spiral galaxy located about 50 million light-years from Earth in the little-known constellation of Horologium (The Pendulum Clock). We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What’s going on?

Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure — a great example from Hubble is the telescope’s view of Messier 51, otherwise known as the Whirlpool Galaxy. However, the NGC 1448 frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from NGC 1448’s dense core, can just about be seen.

Although spiral galaxies might appear static with their picturesque shapes frozen in space, this is very far from the truth. The stars in these dramatic spiral configurations are constantly moving and spinning around the galaxy’s core, with those on the inside whirling around faster than those sitting further out. This makes the formation and continued existence of a spiral galaxy’s arms something of a cosmic puzzle, because the arms wrapped around the spinning core should become wound tighter and tighter as time goes on — but this is not what we see. This is known as the winding problem.