Wednesday, November 30, 2016

First Signs of Weird Quantum Property of Empty Space? VLT observations of neutron star may confirm 80-year-old prediction about the vacuum

The polarisation of light emitted by a neutron star
Wide field view of the sky around the very faint neutron star RX J1856.5-3754

VLT image of the area around the very faint neutron star RX J1856.5-3754


The polarisation of light emitted by a neutron star
The polarisation of light emitted by a neutron star

Zooming in on the very faint neutron star RX J1856.5-3754
Zooming in on the very faint neutron star RX J1856.5-3754

VLT observations of neutron star may confirm 80-year-old prediction about the vacuum

By studying the light emitted from an extraordinarily dense and strongly magnetised neutron star using ESO’s Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarisation of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.

A team led by Roberto Mignani from INAF Milan (Italy) and from the University of Zielona Gora (Poland), used ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile to observe the neutron star RX J1856.5-3754, about 400 light-years from Earth [1].

Despite being amongst the closest neutron stars, its extreme dimness meant the astronomers could only observe the star with visible light using the FORS2 instrument on the VLT, at the limits of current telescope technology.

Neutron stars are the very dense remnant cores of massive stars — at least 10 times more massive than our Sun — that have exploded as supernovae at the ends of their lives. They also have extreme magnetic fields, billions of times stronger than that of the Sun, that permeate their outer surface and surroundings.

These fields are so strong that they even affect the properties of the empty space around the star. Normally a vacuum is thought of as completely empty, and light can travel through it without being changed. But in quantum electrodynamics (QED), the quantum theory describing the interaction between photons and charged particles such as electrons, space is full of virtual particles that appear and vanish all the time. Very strong magnetic fields can modify this space so that it affects the polarisation of light passing through it.

Mignani explains: “According to QED, a highly magnetised vacuum behaves as a prism for the propagation of light, an effect known as vacuum birefringence.”

Among the many predictions of QED, however, vacuum birefringence so far lacked a direct experimental demonstration. Attempts to detect it in the laboratory have not yet succeeded in the 80 years since it was predicted in a paper by Werner Heisenberg (of uncertainty principle fame) and Hans Heinrich Euler.

"This effect can be detected only in the presence of enormously strong magnetic fields, such as those around neutron stars. This shows, once more, that neutron stars are invaluable laboratories in which to study the fundamental laws of nature." says Roberto Turolla (University of Padua, Italy).

After careful analysis of the VLT data, Mignani and his team detected linear polarisation — at a significant degree of around 16% — that they say is likely due to the boosting effect of vacuum birefringence occurring in the area of empty space surrounding RX J1856.5-3754 [2].

Vincenzo Testa (INAF, Rome, Italy) comments: "This is the faintest object for which polarisation has ever been measured. It required one of the largest and most efficient telescopes in the world, the VLT, and accurate data analysis techniques to enhance the signal from such a faint star."

"The high linear polarisation that we measured with the VLT can’t be easily explained by our models unless the vacuum birefringence effects predicted by QED are included," adds Mignani.

This VLT study is the very first observational support for predictions of these kinds of QED effects arising in extremely strong magnetic fields," remarks Silvia Zane  (UCL/MSSL, UK).
Mignani is excited about further improvements to this area of study that could come about with more advanced telescopes: “Polarisation measurements with the next generation of telescopes, such as ESO’s European Extremely Large Telescope, could play a crucial role in testing QED predictions of vacuum birefringence effects around many more neutron stars.”

This measurement, made for the first time now in visible light, also paves the way to similar measurements to be carried out at X-ray wavelengths," adds Kinwah Wu (UCL/MSSL, UK).

More Information

This research was presented in the paper entitled “Evidence for vacuum birefringence from the first optical polarimetry measurement of the isolated neutron star RX J1856.5−3754”, by R. Mignani et al., to appear in Monthly Notices of the Royal Astronomical Society.

The team is composed of R.P. Mignani (INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Milano, Italy; Janusz Gil Institute of Astronomy, University of Zielona Góra, Zielona Góra, Poland), V. Testa (INAF - Osservatorio Astronomico di Roma, Monteporzio, Italy), D. González Caniulef (Mullard Space Science Laboratory, University College London, UK), R. Taverna (Dipartimento di Fisica e Astronomia, Università di Padova, Padova, Italy), R. Turolla (Dipartimento di Fisica e Astronomia, Università di Padova, Padova, Italy; Mullard Space Science Laboratory, University College London, UK), S. Zane (Mullard Space Science Laboratory, University College London, UK) and K. Wu (Mullard Space Science Laboratory, University College London, UK).

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



Roberto Mignani
INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica Milano
Milan, Italy
Tel: +39 02 23699 347
Cell: +39 328 9685465

Vincenzo Testa
INAF - Osservatorio Astronomico di Roma
Monteporzio Catone, Italy
Tel: +39 06 9428 6482

Roberto Turolla
University of Padova
Padova, Italy
Tel: +39-049-8277139

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

Monday, November 28, 2016

Violent Collision of Massive Supernova with Surrounding Gas Powers Superluminous Supernovae

Artist's conception of a shock-interacting supernova. Successive eruptions of a massive star produce ejecta with different velocities: the blue ring corresponds to slowly moving layers which are punched by fast ejecta (red-to-yellow) which shoots out. Interaction of those gas masses is via radiating shock waves which produce enormous amounts of light. This explains the phenomenon of Superluminous Supernovae with minimum requirements to the energy budget of explosions. (Credit: Kavli IPMU). Large Size jpg / Medium size jpg

Absolute u-band light curves for a fast-fading SLSN-I SN 2010gx and for a slowly fading one PTF09cnd are shown together with two calculated light curves for models N0 and B0 (from the paper by Sorokina et al.), which demonstrates that the interacting scenario can explain both narrow and broad light curves. The light curve of the typical (with “normal” luminosity) SN Ic, SN 1994I, is plotted for comparison. (Credit: Kavli IPMU). Large Size jpg / Medium size jpg

In a unique study, an international team of researchers including members from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) simulated the violent collisions between supernovae and its surrounding gas— which is ejected before a supernova explosion, thereby giving off an extreme brightness.

Many supernovae have been discovered in the last decade with peak luminosity one-to-two orders of magnitude higher than for normal supernovae of known types. These stellar explosions are called Superluminous Supernovae (SLSNe).

Some of them have hydrogen in their spectra, while some others demonstrate a lack of hydrogen. The latter are called Type I, or hydrogen-poor, SLSNe-I. SLSNe-I challenge the theory of stellar evolution, since even normal supernovae are not yet completely understood from first principles.

Led by Sternberg Astronomical Institute researcher Elena Sorokina, who was a guest investigator at Kavli IPMU, and Kavli IPMU Principal Investigator Ken’ichi Nomoto, Scientific Associate Sergei Blinnikov, as well as Project Researcher Alexey Tolstov, the team developed a model that can explain a wide range of observed light curves of SLSNe-I in a scenario which requires much less energy than other proposed models.

The models demonstrating the events with the minimum energy budget involve multiple ejections of mass in presupernova stars. Mass loss and buildup of envelopes around massive stars are generic features of stellar evolution. Normally, those envelopes are rather diluted, and they do not change significantly the light produced in the majority of supernovae.

In some cases, large amount of mass are expelled just a few years before the final explosion. Then, the “clouds” around supernovae may be quite dense. The shockwaves produced in collisions of supernova ejecta and those dense shells may provide the required power of light to make the supernova much brighter than a “naked” supernova without pre-ejected surrounding material.

This class of the models is referred to as “interacting” supernovae. The authors show that the interacting scenario is able to explain both fast and slowly fading SLSNe-I, so the large range of these intriguingly bright objects can in reality be almost ordinary supernovae placed into extraordinary surroundings.

Another extraordinarity is the chemical composition expected for the circumstellar “clouds.” Normally, stellar wind consists of mostly hydrogen, because all thermonuclear reactions happen in the center of a star, while outer layers are hydrogenous.

In the case of SLSNe-I, the situation must be different. The progenitor star must lose its hydrogen and a large part of helium well before the explosion, so that a few months to a few years before the explosion, it ejects mostly carbon and oxygen, and then explode inside that dense CO cloud. Only this composition can explain the spectral and photometric features of observed hydrogen-poor SLSNe in the interacting scenario.

It is a challenge for the stellar evolution theory to explain the origin of such hydrogen- and helium-poor progenitors and the very intensive mass loss of CO material just before the final explosion of the star. These results have been published in a paper accepted by The Astrophysical Journal.

Details of the paper were published in September’s The Astrophysical Journal.

Paper Details:

The Astrophysical Journal

Type I Super-luminous Supernovae as Explosions inside Non-Hydrogen Circumstellar Envelopes


E.I. Sorokina (1), S.I. Blinnikov (2), K. Nomoto (3), R. Quimby (4), and A. Tolstov (5)
  1. Elena Sorokina, Sternberg Astronomical Institute, Moscow State University, GSP-1, Leninskie Gory, 119991 Moscow, Russia
  2. S. I. Blinnikov, Institute for Theoretical and Experimental Physics, 117218 Moscow, Russia
  3. Ken’ichi Nomoto, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
  4. Robert Quimby, Cahill Center for Astrophysics, California Institute of Technology, 1200 E. California Blvd., MC 249-17 Pasedena, CA 91125
  5. Alexey Tolstov, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
DOI: 10.3847/0004-637X/829/1/17 (Published September 15, 2016)

Paper abstract

(The Astrophysical Journal): Link 1510.00834, October 2015.

Research contact:

Ken’ichi Nomoto
Principal Investigator and Project Professor
Kavli Institute for the Physics and Mathematics of the Universe
TEL: +81-04-7136-6567

Alexey Tolstov
Project Researcher
Kavli Institute for the Physics and Mathematics of the Universe

Useful links: The Astrophysical Journal

All images, including those of some of the authors, can be downloaded from here.

Friday, November 25, 2016

Hubble spies NGC 3274

Credit: ESA/Hubble & NASA, D. Calzetti

This image of the spiral galaxy NGC 3274 comes courtesy of the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3). Hubble’s WFC3 vision spreads from the ultraviolet light through to the near infrared , allowing astronomers to study a wide range of targets, from nearby star formation through to galaxies in the most remote regions of the cosmos.

This particular image combines observations gathered in five different filters, bringing together ultraviolet, visible, and infrared light to show off NGC 3274 in all its glory. As with all of the data Hubble sends back to Earth, it takes advantage of the telescope’s location in space above our planet’s distorting atmosphere. WFC3 returns clear, crisp, and detailed images time after time.

NGC 3274 is a relatively faint galaxy located over 20 million light-years away in the constellation of Leo (The Lion). The galaxy was discovered by Wilhelm Herschel in 1783. The galaxy PGC 213714 is also visible on the upper right of the frame, located much further away from Earth.

Thursday, November 24, 2016

Third Data Release for DECam Legacy Survey

DECaLS DR3 data (top) reach significantly deeper than SDSS images (bottom). In addition to foreground stars, nearby galaxy UGC4640 and many distant galaxies are visible within this 7.5’x5’ field-of-view.

The DECam Legacy Survey (DECaLS) has announced its third data release. An NOAO Survey Program led by co-PIs David Schlegel (LBNL) and Arjun Dey (NOAO), DECaLS uses the Dark Energy Camera (DECam) on the CTIO Blanco 4m telescope to image nearly square degrees of the extragalactic sky in three bands (g, r and z). Earlier data releases were made in June 2015 (DR1) and February 2016 (DR2). The current status of the survey is shown here

The third data release (DR3), which covers [4300, 4600, 8100] square degrees in [g, r, z] bands respectively, includes catalogs and images obtained between August 2014 and March 2016. DR3 also incorporates public data within the DECaLS footprint from other NOAO observing programs and photometry from NASA’s Wide-Field Infrared Surveyor’s maps of the sky. 

The final DECaLS sky coverage will extend in declination from approximately -18 to +30 degrees, and cover Galactic latitudes |b| > 18 degrees. The survey also overlaps the SDSS/BOSS extragalactic footprint. DECaLS will allow astronomers to probe the structure of the Milky Way, the nature of dark energy, and many other topics in astrophysics. All data are immediately non-proprietary and the project schedules two data releases per year.

The DR3 release includes raw data, individual calibrated DECam exposures, image coadds in 0.25x0.25 square degree “bricks”, source catalogs containing approximately 478 million unique sources, and an interactive sky viewer interface. An Image Gallery of Large Galaxies constructed by Dr. John Moustakas is also available. For further information regarding DR3, please see the survey website

DECaLS is one of three surveys that will jointly image 14,000 square degrees—nearly one-third of the sky—to provide targets for the Dark Energy Spectroscopic Instrument cosmology project. The other two projects are the Mayall z-band Legacy Survey (MzLS), which began in February 2016, and the Beijing-Arizona Sky Survey (BASS), currently underway at the Bok Telescope on Kitt Peak. MzLS and BASS will provide g- ,r-, and z- band imaging at declinations north of +34 degrees.

DECaLS DR3 data products are available through the NOAO Science Archive and ftp server. In addition, the NOAO Data Lab has developed a database to query all DR3 catalogs, which is available by contacting the Data Lab directly (

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Source: NOAO/Currents

Wednesday, November 23, 2016

Cyg X-3's Little Friend: A Stellar Circle of Life

Cygnus X-3
Credit: X-ray: NASA/CXC/SAO/M.McCollough et al, Radio: ASIAA/SAO/SMA  

A snapshot of the life cycle of stars has been captured where a stellar nursery is reflecting X-rays from a source powered by an object at the endpoint of its evolution. This discovery, described in our latest press release, provides a new way to study how stars form.

This composite image shows X-rays from NASA's Chandra X-ray Observatory (white) and radio data from the Smithsonian's Submillimeter Array (red and blue). The X-ray data reveal a bright X-ray source to the right known as Cygnus X-3, a system containing either a black hole or neutron star (a.k.a. a compact source) left behind after the death of a massive star. Within that bright source, the compact object is pulling material away from a massive companion star. Astronomers call such systems "X-ray binaries."

In 2003, astronomers presented results using Chandra's high-resolution vision in X-rays to identify a mysterious source of X-ray emission located very close to Cygnus X-3 on the sky (smaller white object to the upper left). The separation of these two sources is equivalent to the width of a penny about 800 feet away. A decade later, astronomers reported the new source is a cloud of gas and dust. 

In astronomical terms, this cloud is rather small - about 0.7 light years in diameter or under the distance between the Sun and Pluto's orbit.

Astronomers realized that this nearby cloud was acting as a mirror, reflecting some of the X-rays generated by Cygnus X-3 towards Earth. They nicknamed this object the "Little Friend" due to its close proximity to Cygnus X-3 on the sky and because it also demonstrated the same 4.8-hour variability in X-rays seen in the X-ray binary.

To determine the nature of the Little Friend, more information was needed. The researchers used the Submillimeter Array (SMA), a series of eight radio dishes atop Mauna Kea in Hawaii, to discover the presence of molecules of carbon monoxide. This is an important clue that helped confirm previous suggestions that the Little Friend is a Bok globule, small, dense, very cold clouds where stars can form. The SMA data also reveal the presence of a jet or outflow within the Little Friend, an indication that a star has started to form inside. The blue portion shows a jet moving towards us and the red portion shows a jet moving away from us.

These results were published in The Astrophysical Journal Letters, and the paper is also available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Fast Facts for Cyg X-3's Little Friend:

Scale: Image is 1.4 arcmin across (about 8.15 light years)
Category: Normal Stars & Star Clusters, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 20h 32m 25.50s | Dec +40° 57' 27.70"
Constellation: Cygnus
Observation Date: 26 Jan 2006
Observation Time: 13 hours 46 min
Obs. ID: 6601
Instrument: ACIS
References: McCollough, M. et al, 2016, ApJL, 830, L36; arXiv:1610.01923
Color Code: X-ray (Purple); Radio (Blue, Red)
Distance Estimate: About 20,000 light years

Tuesday, November 22, 2016

Record-breaking Faint Satellite Galaxy of the Milky Way Discovered

An international team led by researchers from Tohoku University has found an extremely faint dwarf satellite galaxy of the Milky Way. The team's discovery is part of the ongoing Subaru Strategic Survey using Hyper Suprime-Cam. The satellite, named Virgo I, lies in the direction of the constellation Virgo. At the absolute magnitude of -0.8 in the optical waveband (Note), it may well be the faintest satellite galaxy yet found. Its discovery suggests the presence of a large number of yet-undetected dwarf satellites in the halo of the Milky Way and provides important insights into galaxy formation through hierarchical assembly of dark matter.

Figure 1: The position of Virgo I in the constellation of Virgo (left). The right panel shows a density map of Virgo I's member stars in a 0.1 deg x 0.1 deg area, based on the stars located inside the green zone in the color-magnitude diagram of Virgo I shown in Figure 4. The color range from blue -> white -> yellow -> red indicates increasing density. (Credit: Tohoku University/National Astronomical Observation of Japan)

Movie: An animation showing locations of Milky Way Galaxy's satellite galaxies, featuring the newly discovered Virgo I. An image captured from the animation is shown here. The computer graphics was created using Mitaka, a four-dimensional digital universe viewer. In the image from the Subaru Telescope, Green circles denote the member candidate stars that might belong to Virgo I. (Credit: NAOJ)

Currently, some 50 satellite galaxies to the Milky Way have been identified. About 40 of them are faint and diffuse and belong to the category of so-called "dwarf spheroidal galaxies" (Figure 2). Many recently discovered dwarf galaxies, especially those seen in systematic photometric surveys such as the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES) are very faint with absolute luminosity in the optical waveband below -8 magnitude. These are so-called "ultra-faint dwarf galaxies". However, previous searches made use of telescopes with a diameter of 2.5 to 4 meters, so only satellites relatively close to the Sun or those with higher magnitudes were identified. Those that are more distant or faint ones in the halo of the Milky Way are yet to be detected (Figure 3).

Figure 2: Satellite galaxies associated with the Milky Way Galaxy. Squares are Large and Small Magellanic Clouds and circles are dwarf spheroidal galaxies.

Figure 3: False-color dwarf galaxy images taken with Subaru Telescope. Left: Leo II (V-band absolute magnitude MV = -11.9 mag). Middle: Boötes I (MV = -6.3 mag), where both images are taken with Suprime Cam. Right: HSC image of Virgo I (MV = -0.8 mag). Ultra-faint dwarf galaxies (Boötes I and Virgo I) are hard to detect from these images.

The combination of the large aperture of 8.2-meter Subaru Telescope and the large field-of-view Hyper Suprime-Cam (HSC) instrument is very powerful in this study. It enables an efficient search for very faint dwarf satellites over large areas of the sky. The first step in searching out a new dwarf galaxy is to identify an over density of stars in the sky, using photometric data. Next is to assess that the over dense appearance is not due to line-of-sight or accidental juxtapositions of unrelated dense fields, but is really a stellar system. The standard method for doing this is to look for a characteristic distribution of stars in the color-magnitude diagram (comparable to the Hertzsprung-Russell diagram (middle and left panels of Figure 4)). Stars in a general field shows no particular patterns in this diagram (right panel of Figure 4).

Figure 4: Stars in the color-magnitude diagram. Old stellar populations show a characteristic distribution along the curve seen in the diagram. From left to right: Boötes I, Segue I, Virgo I, and a general field outside Virgo I. The spatial distribution of the stars, which are located inside the green band for Virgo I, is shown in the right panel of Figure 1. Note that stars in a general field outside Virgo I (right panel) show no characteristic feature.

Finding Virgo I

Daisuke Homma, a graduate student at Tohoku University, found Virgo I under the guidance of his advisor, Masashi Chiba, and their international collaborators. "We have carefully examined the early data of the Subaru Strategic Survey with HSC and found an apparent over density of stars in Virgo with very high statistical significance, showing a characteristic pattern of an ancient stellar system in the color-magnitude diagram," he said. "Surprisingly, this is one of the faintest satellites, with absolute magnitude of -0.8 in the optical waveband. This is indeed a galaxy, because it is spatially extended with a radius of 124 light years – systematically larger than a globular cluster with comparable luminosity."

The faintest dwarf satellites identified so far was Segue I, discovered by SDSS (-1.5 mag) and Cetus II in DES (0.0 mag). Cetus II is yet to be confirmed, as it is too compact as a galaxy. Virgo I may ultimately turn out to be the faintest one ever discovered. It lies at a distance of 280,000 light years from the Sun, and such a remote galaxy with faint brightness has not been identified in previous surveys. It is beyond the reach of SDSS, which has previously surveyed the same area in the direction of the constellation Virgo (Figure 5).

Figure 5: The relation between the distance from the Sun and absolute magnitude in optical waveband for Milky Way satellites discovered so far. Virgo I is extremely faint and distant from the Sun and is beyond the reach of SDSS. Except for Virgo I, DES mostly discovers those outside SDSS's limit.

According to Chiba, the leader of this search project, the discovery has profound implications. "This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way," he said. "How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it."

Using HSC to Trace Galaxy Formation 

Formation of galaxies like the Milky Way is thought to proceed through the hierarchical assembly of dark matter, forming dark halos, and through the subsequent infall of gas and star formation affected by gravity. Standard models of galaxy formation in the context of the so-called cold dark matter (CDM) theory predict the presence of hundreds of small dark halos orbiting in a Milky Way-sized dark halo and a comparable number of luminous satellite companions. However, only tens of satellites have ever been identified. This falls well short of a theoretical predicted number, which is part of the so-called "missing satellite problem". Astronomers may need to consider other types of dark matter than CDM or to invoke baryonic physics suppressing galaxy formation to explain the shortfall in the number of satellites. Another possibility is that they have seen only a fraction of all the satellites associated with the Milky Way due to various observational biases. The issue remains unsolved.

One of the motivations for the Subaru Strategic Survey using HSC is to do increase observations in the search for Milky Way satellites. The early data from this survey is what led to the discovery of Virgo I. This program will continue to explore much wider areas of the sky and is expected to find more satellites like Virgo I. These tiny companions to be discovered in the near future may tell us much more about history of the Milky Way's formation.

The team's finding is published in the Astrophysical Journal in its November 14, 2016 on-line version and November 20, 2016 in the printed version, Volume 832, Number 1. The title of the paper is "A New Milky Way Satellite Discovered in the Subaru/Hyper Suprime-Cam Survey" by D. Homma et al., which is also available in preprint from arXiv:1609.04346v2. This work is supported by a JSPS Grant-in-Aid for Scientific Research (B) (JP 25287062) and a MEXT Grant-in-Aid for Scientific Research on Innovative Areas (JP15H05889, JP16H01086).

Research Team: 

Daisuke Homma (Tohoku University, Japan), Masashi Chiba (Tohoku University, Japan), Sakurako Okamoto (Shanghai Astronomical Observatory, China), Yutaka Komiyama (National Astronomical Observatory of Japan (NAOJ), Japan), Masayuki Tanaka (NAOJ, Japan), Mikito Tanaka (Tohoku University, Japan), Miho N. Ishigaki (Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Japan), Masayuki Akiyama (Tohoku University, Japan), Nobuo Arimoto (Subaru Telescope, NAOJ, USA), Jose A, Garmilla (Princeton University, USA), Robert H. Lupton (Princeton University, USA), Michael A. Strauss (Princeton University, USA), Hisanori Furusawa (NAOJ, Japan), Satoshi Miyazaki (NAOJ, Japan), Hitoshi Murayama (Kavli IPMU, WPI, University of Tokyo, Japan), Atsushi J. Nishizawa (Nagoya University, Japan), Masahiro Takada (Kavli IPMU, WPI, University of Tokyo, Japan), Tomonori Usuda (NAOJ, Japan), Shiang-Yu Wang (Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan)


For Comparison, the abolute magnitude in visible waveband for M31 (Andromeda Galaxy), Large Magellanic Cloud, and Small Magellanic Cloud are -21.77, -18.35 and -17.02, respectively, according to NASA/IPAC Extragalactic Database ( 

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Monday, November 21, 2016

Flash of invisible light help astronomers map the cosmic web

The radio pulse FRB 150807 The colour shows the frequency of the waves, which is like the colour of light. The brightness varies with frequency due to a process termed “scintillation”, which is caused by the twinkling of the burst in the cosmic web. This scintillation is the fingerprint of turbulence in the cosmic web and tells us that web is very placid. Credit: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO.

The location of the FRB 150807 The yellow circle shows the typical location of an FRB. There are thousands of stars and galaxies in this direction. Because the burst was very bright we were able to locate it to a small region near the edge of that circle, shown as the pink banana-shaped region in the inset. In this region there are only 6 detected galaxies. The position of the most likely host galaxy, VHS7, is highlighted on the plot. Credit: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO

A brief but brilliant burst of radiation that travelled at least a billion light years through Space to reach an Australian radio telescope last year has given scientists new insight into the fabric of the Universe.

ICRAR-Curtin University’s Dr Ryan Shannon, who co-led research into the sighting along with the California Institute of Technology’s Dr Vikram Ravi, said the flash, known as a Fast Radio Burst (FRB), was one of the brightest seen since FRBs were first detected in 2001. The flash was captured by CSIRO’s Parkes radio telescope in New South Wales.

Dr Shannon, from the Curtin node of ICRAR (the International Centre for Radio Astronomy Research) and CSIRO, said all FRBs contained crucial information but this FRB, the 18th detected so far, was unique in the amount of information it contained about the cosmic web – the swirling gases and magnetic fields between galaxies.

“FRBs are extremely short but intense pulses of radio waves, each only lasting about a millisecond. Some are discovered by accident and no two bursts look the same,” Dr Shannon said.

“This particular FRB is the first detected to date to contain detailed information about the cosmic web – regarded as the fabric of the Universe – but it is also unique because its travel path can be reconstructed to a precise line of sight and back to an area of space about a billion light years away that contains only a small number of possible home galaxies.”

Dr Shannon explained that the vast spaces between objects in the Universe contain nearly invisible gas and a plasma of ionised particles that used to be almost impossible to map, until this pulse was detected.

“This FRB, like others detected, is thought to originate from outside of Earth’s own Milky Way galaxy, which means their signal has travelled over many hundreds of millions of light years, through a medium that – while invisible to our eyes – can be turbulent and affected by magnetic fields,” Dr Shannon said.

“It is amazing how these very few milliseconds of data can tell how weak the magnetic field is along the travelled path and how the medium is as turbulent as predicted.”

This particular flash reached CSIRO’s Parkes radio telescope mid-last year and was subsequently analysed by a mostly Australian team.

A paper describing the FRB and the team’s findings was published today in the journal Science.

The Parkes telescope has been a prolific discoverer of FRBs, having detected the vast majority of the known population including the very first, the Lorimer burst, in 2001.

FRBs remain one of the most mysterious processes in the Universe and likely one of the most energetic ones. To catch more FRBs, astronomers use new technology, such as Parkes’ multibeam receiver, the Murchison Widefield Array (MWA) in Western Australia, and the upgraded Molonglo Observatory Synthesis Telescope near Canberra.

This particular FRB was found and analysed by a system developed by the supercomputing group led by Professor Matthew Bailes at Swinburne University of Technology.

Professor Bailes, who was a co-author on the Science paper, also heads The Dynamic Universe research theme in the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), which has seven Australian nodes including ICRAR-Curtin University.

“Ultimately, FRBs that can be traced to their cosmic host galaxies offer a unique way to probe intergalactic space that allow us to count the bulk of the electrons that inhabit our Universe,” Professor Bailes said.

“To decode and further understand the information contained in this FRB is an exceptional opportunity to explore the physical forces and the extreme environment out in Space.”

Original Publication

“The magnetic field and turbulence of the cosmic web measured using a brilliant fast radio burst” published November 17th 2016 in Science.

PDF copy available at Science.

More Information

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, the latter two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO 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.

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.


Dr Ryan Shannon (ICRAR-Curtin University, CSIRO)
Ph: +61 2 9372 4326
M: 61 403 692 028

Professor Matthew Bailes (CAASTRO, Swinburne University of Techology)
Ph: +61 3 9214 8782
M: +61 414 324 677

Kirsten Gottschalk (Media Contact, ICRAR)
Ph: +61 8 6488 7771
M: +61 438 361 876

Tamara Hunter (Media Contact, Curtin University)
Ph: +61 8 9266 3353
M: +61 401 103 683

Dr Wiebke Ebeling (Education and Outreach, CAASTRO)
Ph: +61 8 9266 9174
M: +61 423 933 444

Friday, November 18, 2016

A subtle swarm

Credit:  ESA/Hubble & NASA
Acknowledgements: Judy Schmidt (Geckzilla)

This Hubble image shows NGC 4789A, a dwarf irregular galaxy in the constellation of Coma Berenices. It certainly lives up to its name — the stars that call this galaxy home are smeared out across the sky in an apparently disorderly and irregular jumble, giving NGC 4789A a far more subtle and abstract appearance than its glitzy spiral and elliptical cousins.

These stars may look as if they have been randomly sprinkled on the sky, but they are all held together by gravity. The colours in this image have been deliberately exaggerated to emphasise the mix of blue and red stars. The blue stars are bright, hot and massive stars that have formed relatively recently, whereas the red stars are much older. The presence of both tells us that stars have been forming in this galaxy throughout its history.

At a distance of just over 14 million light-years away NGC 4789A is relatively close to us, allowing us to see many of the individual stars within its bounds. This image also reveals numerous other galaxies, far more distant, that appear as fuzzy shapes spread across the image.

Thursday, November 17, 2016

Kepler Mission Manager Update: K2 Marching On With Campaign 11

The comparison of two full frame images from the Kepler spacecraft show two black squares (Modules 3 and 7) and 19 red squares on the left. On the right, there are three black squares (Modules 3, 4 and 7) and 18 red squares. A red square indicates that data is being collected by the photometer and a black square indicates no data is being collected and that the module is no longer functional. Eighteen of the 21 science detector modules remain fully operational. Credits: NASA Ames/W. Stenzel

Kepler’s K2 mission is now in the midst of its eleventh campaign, observing a patch of sky in the direction of the constellation Sagittarius. During this campaign, it will observe 14,250 new targets, including the Galactic Center and Saturn's moons Titan and Enceladus.

Campaign 11 began on Sept. 24, but was interrupted for three days (Oct. 18-20) to make a small pointing correction to accommodate the imbalance that was created by broadcasting data from a different antenna on the other side of the spacecraft. Although the spacecraft is as big and heavy as an SUV, it actually turns slightly when we change the broadcasting antenna. This is like having your car begin to turn from the force of the blinking of your turn signal. Yes, the spacecraft is that delicately balanced! Data collection for Campaign 11 will continue until Dec. 7.

Since my last update, our investigation into the cause of the spacecraft's photometer—the onboard camera—being powered off in July during Campaign 10, confirms that that science detector Module 4 failed. The likely cause was a random part failure that resulted in a high electric current in the circuitry, which blew the protection fuse, disabling the detector but preventing the problem from propagating to other detectors. As part of the fault protection response, the photometer was powered off.

Eighteen of the 21 science detector modules remain fully operational. Two science modules had failed previously: Module 7 in January 2014 and Module 3 in January 2010. These are not unexpected events as the spacecraft ages in the harsh environment of space.

In September, the spacecraft had a unique opportunity to provide a 'wide-angle' view of comet 67P/Churyumov–Gerasimenko, making observations of its core and tail. These observations complement the close-in study of the comet provided by the European Space Agency's Rosetta spacecraft during the final month of its mission. These and the remainder of Campaign 10 data have been downlinked to the ground and are being processed for release at the public archive later this month.
We've also made changes with the Kepler and K2 project scientist personnel. On Aug. 15, Natalie Batalha was appointed as the project scientist for the Kepler mission. Since 1999, Natalie has served in numerous leadership roles throughout the mission including deputy principal investigator and science team lead. In addition to her responsibilities with the Kepler mission, Natalie is a co-lead of NASA's Nexus for Exoplanet System Science Coalition, and serves on the James Webb Space Telescope Advisory Committee. She also serves as a member of the NASA Advisory Council's Astrophysics Subcommittee, and, in 2013, participated on the task force to define NASA's 30-year Astrophysics Roadmap- Enduring Quests, Daring Visions: NASA Astrophysics in the Next Three Decades.

On Sept. 6, Jessie Dotson assumed the role of project scientist for the K2 mission. Dr. Dotson was formerly the deputy science office director for Kepler and, in 2011, established the Kepler Guest Observer Office. Most recently, she served as astrophysics branch chief in the Space Science and Astrobiology Division at NASA Ames. In 2014, Jessie helped formulate the Asteroid Threat Assessment Project (ATAP) at NASA Ames to quantify the risk to Earth of an asteroid impact. She currently leads the ATAP asteroid characterization team. In 2016, Jessie was awarded a NASA Outstanding Leadership Medal for her work as the astrophysics branch chief at Ames.

Together, Natalie and Jessie replace Steve Howell who served as Kepler project scientist since 2010 and K2 project scientist since mission conception in 2013. In that role, Steve oversaw Kepler science operations through the end of its prime mission, the recovery from the reaction wheel failure that nearly ended the mission, and the development and implementation of the K2 mission that gave Kepler a new lease on life. We commend Steve for his work as the Kepler/K2 project scientist, with notable leadership in catalyzing the science community to support Kepler's extended mission called K2.

In August, the team gathered for the annual year-in-review of spacecraft operations with Ball Aerospace, the designer, manufacturer and flight controller of Kepler. A topic of high interest is the on-board fuel reserve, which is expected to last into the spring of 2018.

At last count, Kepler has identified more than 5,100 planet candidates. Of these, more than 2,500 have been verified as bona fide planets. NASA’s next planet-hunting mission, the Transiting Exoplanet Survey Satellite (TESS), is scheduled to launch no later than June 2018. TESS will build upon Kepler’s success and search for exoplanets around the stars closest to the own solar system.


Charlie Sobeck​
Kepler and K2 mission manager
NASA's Ames Research Center 

Editor: Michele Johnson
Source: NASA/Kepler and K2 

Wednesday, November 16, 2016

A Hydrogen Rich, Passive Galaxy

A deep optical image of the gas-rich galaxy GASS 3505 which in at radio wavelengths shows a ring of neutral hydrogen gas, probably a result of accretion (there is a faint streamer seen to the left in this image). Astronomers conclude that the star formation in this object is very weak, less than about 0.1 solar-masses per year. Credit: Gereb et al. 2016

Cold gas in the form of neutral hydrogen atoms provides the reservoir for star formation in galaxies from the distant to the nearby Universe. Understanding how it accretes onto galaxies is of crucial importance because fresh supplies of gas fuel the ongoing star-forming. In the most popular version, accretion onto the galaxy occurs along cosmic filaments, and at least in more massive galaxies is heated by shocks in the process; in smaller galaxies the infalling material stays relatively cool. Since galaxies in the early universe are smaller, it is thought that this cold process of growth is more typical for them as well.

Astronomers studying accretion need to look at nearby galaxies both because they are brighter and because they have distinguishable spatial features such as tails, bridges, ringlike structures, warped discs, or lopsidedness that could result from accumulating gas. The GALEX Arecibo SDSS Survey (GASS) is a multi-wavelength, deep survey designed specifically to search for galaxies rich in atomic hydrogen. CfA astronomer Sean Moran and five colleagues searched GASS to select one object, GASS 3505, that has nearly ten billion solar-masses of atomic hydrogen and a round, relatively unstructured appearance in the optical. The team followed up with deep radio maps of the hydrogen emission using the Jansky Very Large Array.

The astronomers found that the cold gas is distributed in a ring around the galaxy about one hundred and sixty thousand light-years in diameter, within which extremely inefficient star formation is happening (about ten times less than the Milky Way’s value). The ring, it turns out, is connected to a complex stream of material that is a signature for infall and accretion; the stream is a reminder of how important faint morphological features are in understanding a galaxy’s evolution. The scientists, among other analysis, perform computer simulations of a merger that helps to explain the activity of GASS 3505, with slight discrepancies identifying the possible presence of some additional activity still to be confirmed and identified. Future surveys with a new generation of radio telescopes will be able to study these gas rich systems at cosmological distances.


“GASS 3505: The Prototype of HI-Excess, Passive Galaxies,” Geréb, K., Catinella, B. Cortese, L., Bekki, K., Moran, S. M., and Schiminovich, D., MNRAS 462, 382, 2016.

Tuesday, November 15, 2016

Are All Stars Created Equal?

Artist's impression of an accretion burst in a high-mass young stellar object like S255 NIRS 3. 
Image Credit: Deutsches SOFIA Institut (DSI).  Full resolution JPEG

Astronomers using critical observations from the Gemini Observatory have found the strongest evidence yet that the formation of more massive stars follow a path similar to their lower-mass brethren - but on steroids! 

The new findings, that include data from Gemini, SOFIA, Calar Alto, and the European Southern Observatory, show that the episodic explosive outbursts within what are called accretion disks, known to occur during the formation of average mass stars like our Sun, also happen in the formation of very massive stars. 

"These outbursts, which are several orders of magnitude larger than their lower mass siblings, can release about as much energy as our Sun delivers in over 100,000 years," said Dr. Alessio Caratti o Garatti of the Dublin Institute for Advanced Studies (Ireland). "Surprisingly, fireworks are observed not just at the end of the lives of massive stars, as supernovae, but also at their birth!" 

The international team of astronomers (led by Caratti o Garatti) published their work in the November 14th issue of the journal Nature Physics, presenting the first clear case that massive stars can form from clumpy disks of material – in much the same way as less massive stars. Previously it was thought that the accretion disks seen around lower mass stars would not survive around stars of higher mass due to their strong radiation pressure. Therefore, some other process would be necessary to account for the existence of more massive stars – which can exceed 50-100 times the mass of our Sun. 

"How accretion disks can survive around these massive stars is still a mystery, but the Gemini spectroscopic observations show the same fingerprints we see in lower mass stars," said Caratti o Garatti. "Probably the accretion bursts reduce the radiation pressure of the central source and allow the star to form, but we still have a lot of explaining to do in order to account for these observations." 

According to team member Dr. Bringfried Stecklum of the Thüringer Landessternwarte Tautenburg (Germany), "Studying the formation of high-mass stars is challenging because they are relatively rare and deeply embedded in their natal cloud, thus not visible in optical, or visible, light. This is why we need infrared instruments like the Near-infrared Integral Field Spectrograph at Gemini North on Maunakea in Hawai‘i." The outburst events are also very rapid, probably lasting only a few years or less - which, for a star, is the blink of an eye, adding to their rarity. 

"The birth of truly massive stars has been a mystery that astronomers have been studying for decades. Only now, with large, infrared-optimized telescopes like Gemini, are we able to probe the details of this short-lived and, now it seems, rather explosive process," notes Chris Davis, Program Director at the National Science Foundation which supports the operation of the Gemini Observatory and the development of its instruments. "These NIFS observations represent yet another coup for the Gemini Observatory." 

The developing star observed in this study, S255IR NIRS 3, is relatively distant, some 6,000 light years away, with a mass estimated at about 20 times the mass of our Sun. The Gemini observations reveal that the source of the explosive outburst is a huge clump of gas, probably about twice the mass of Jupiter, accelerated to supersonic speeds and ingested by the forming star. The team estimates that the outburst began about 16 months ago and according to Caratti o Garatti it appears that the outburst is still active, but much weaker. 

"While low-mass stars, and possible planetary systems, can form basically next door to our Sun, the formation of high-mass stars is a complex and relatively rapid process that tends to happen rather far away in our galaxy, thousands, or even tens of thousands of light years away," said Caratti o Garatti. He adds that the formation of these massive stars happens on timescales of 100,000 years, whereas it takes hundreds of times longer for lower mass stars like our Sun to form. "When we study the formation of higher mass stars it's like watching a timelapse move when compared to less massive stars, although the process for massive stars is fast and furious, it still takes tens of thousands of years!" 

"While this research presents the strongest case yet for similar formation processes for low and high mass stars, there is still lots to understand," concludes Stecklum. "Especially whether planets can form in the same way around stars at both ends of the mass spectrum." 

Science Contacts:

  • Alessio Caratti o Garatti
    Dublin Institute for Advanced Studies
    Office: +353 1 4406656 ext.342
    Cell: +353 87 1091628

  • Bringfried Stecklum
    Thüringer Landessternwarte Tautenburg
    Office: +49 36427 863
    Cell: +49 179 38088401

Media Contact:

  • Peter Michaud
    Gemini Observatory
    Hilo, Hawai‘i
    Cell: (808) 936-6643

Monday, November 14, 2016

NASA Space Telescopes Pinpoint Elusive Brown Dwarf