Friday, October 09, 2015

Waving goodbye

Credit: ESA/Hubble & NASA
Acknowledgement: Serge Meunier

This planetary nebula is called PK 329-02.2 and is located in the constellation of Norma in the southern sky. 

It is also sometimes referred to as Menzel 2, or Mz 2, named after the astronomer Donald Menzel who discovered the nebula in 1922.

When stars that are around the mass of the Sun reach their final stages of life, they shed their outer layers into space, which appear as glowing clouds of gas called planetary nebulae. The ejection of mass in stellar burnout is irregular and not symmetrical, so that planetary nebulae can have very complex shapes. In the case of Menzel 2 the nebula forms a winding blue cloud that perfectly aligns with two stars at its centre. In 1999 astronomers discovered that the star at the upper right is in fact the central star of the nebula, and the star to the lower left is probably a true physical companion of the central star.

For tens of thousands of years the stellar core will be cocooned in spectacular clouds of gas and then, over a period of a few thousand years, the gas will fade away into the depths of the Universe. The curving structure of Menzel 2 resembles a last goodbye before the star reaches its final stage of retirement as a white dwarf.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Serge Meunier.

Thursday, October 08, 2015

Banking X-Ray Data for the Future

Cambridge, MA - Archives, in their many forms, save information from today that people will want to access and study in the future. This is a critical function of all archives, but it is especially important when it comes to storing data from today’s modern telescopes.

NASA's Chandra X-ray Observatory has collected data for over sixteen years on thousands of different objects throughout the Universe. Once the data is processed, all of the data goes into an archive and is available to the public.

To celebrate American Archive Month, we are releasing a collection of new images from the Chandra archive.

By combining data from different observation dates, new perspectives of cosmic objects can be created. With archives like those from Chandra and other major observatories, such vistas will be available for future exploration.

The objects in this year's archive release are:

W44: Also known as G34.7-0.4, W44 is an expanding supernova remnant that is interacting with dense interstellar material that surrounds it. X-rays from Chandra (blue) show that hot gas fills the shell of the supernova remnant as it moves outward. Infrared observations from the Spitzer Space Telescope reveal the shell of the supernova remnant (green) as well as the molecular cloud (red) into which the supernova remnant is moving and the stars in the field of view.

SN 1987A: First seen in 1987, this supernova (dubbed SN 1987A) was the brightest supernova and nearest one to Earth in the last century. In a supernova explosion, a massive star runs out of fuel then collapses onto their core, flinging the outer layers of the star into space. By combining X-ray data from Chandra (blue) with optical data from the Hubble Space Telescope (appearing orange and red), astronomers can observe the evolution of the expanding shell of hot gas generated by the explosion and watch as a shock wave from the blast heats gas that once surrounded the doomed star. The two bright stars near SN 1987A are not associated with the supernova.

Kesteven 79: Like SN 1987A, this object, known as Kesteven 79, is the remnant of a supernova explosion, but one that went off thousands of years ago. When massive stars run out of fuel, their cores collapse, generating a shock wave that flings the outer layers of the star into space. An expanding shell of debris and the surviving dense central core are often heated to millions of degrees, and give off X-rays. In this image of Kesteven 79, X-rays detected by Chandra (red, green, and blue) have been combined with an optical image from the Digitized Sky Survey of the field of view that reveals the stars (appearing as white).

MS 0735.6+7421: The galaxy cluster MS 0735.6+7421 is home to one of the most powerful eruptions ever observed. X-rays detected by Chandra (blue) show the hot gas that comprises much of the mass of this enormous object. Within the Chandra data, holes, or cavities, can be seen. These cavities were created by an outburst from a supermassive black hole at the center of the cluster, which ejected the enormous jets detected in radio waves (pink) detected the Very Large Array. These data have been combined with optical data from Hubble of galaxies in the cluster and stars in the field of view (orange).

3C295: The vast cloud of 50-million-degree gas that pervades the galaxy cluster 3C295 is only visible with an X-ray telescope like Chandra. This composite image shows the superheated gas, detected by Chandra (pink), which has a mass equal to that of a thousand galaxies. Hubble's optical data (yellow) reveal some of the individual galaxies in the cluster. Galaxy clusters like 3C295 also contain large amounts of dark matter, which holds the hot gas and galaxies together. The total mass of the dark matter needed is typically five times as great as the gas and galaxies combined.

Guitar Nebula: The pulsar B2224+65 is moving through space very rapidly. Because of its high speed, the pulsar is creating a bow shock in its wake. This structure is known as the Guitar Nebula and the likeness of the musical instrument can be seen in the optical data (blue) of this composite image taken by Hubble and the Palomar Observatory. X-ray data from Chandra (pink) reveal a long jet that is coincident with the location of the pulsar at the tip of the "guitar," but is not aligned with its direction of motion. Astronomers will continue to study this system to determine the nature of this X-ray jet.

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:

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Wednesday, October 07, 2015

Mysterious Ripples Found Racing Through Planet-Forming Disk

AU Microscopii
Credit for Top Panel: NASA, ESA, G. Schneider (Steward Observatory), and the HST GO 12228 team
Credit for Bottom Panels: NASA, ESA, ESO, and A. Boccaletti (Paris Observatory)

Astronomers using NASA's Hubble Space Telescope and the European Southern Observatory's (ESO) Very Large Telescope in Chile have discovered never-before-seen moving features within the dusty disk surrounding the young, nearby star AU Microscopii (AU Mic). The fast-moving, wave-like structures are unlike anything ever observed in a circumstellar disk, said researchers of a new analysis. This new, unexplained phenomenon may provide valuable clues about how planets form inside these star-surrounding disks.

AU Mic is located 32 light-years away in the southern constellation Microscopium. It is an optimal star to observe because its circumstellar disk is tilted edge on to our view from Earth. This allows for certain details in the disk to be better seen.

Astronomers have been searching AU Mic's disk for any signs of clumpy or warped features that might offer evidence for planet formation. They discovered some very unusual, apparently outward-moving features near the star by using ESO's SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument, mounted on the Very Large Telescope.

"The images from SPHERE show a set of unexplained features in the disk, which have an arc-like, or wave-like structure, unlike anything that has ever been observed before," said Anthony Boccaletti of the Paris Observatory, the paper's lead author.

The images reveal a train of wave-like arches, resembling ripples in water. After spotting the features in the SPHERE data the team turned to earlier Hubble images of the disk, taken in 2010 and 2011. The wave-like nature of some of these features were not recognized in the initial Hubble observations. But once astronomers reprocessed the Hubble images they not only identified the features but realized that they had changed over time. The researchers report that these ripples are moving — and they are moving very fast.

"We ended up with enough information to track the movement of these strange features over a 3- to 4-year period," explained team member Christian Thalmann of the Swiss Federal Institute of Technology in Zurich, Switzerland. "By doing this, we found that the arches are racing away from the star at speeds of up to 10 kilometers per second (22,000 miles per hour)!" Co-investigator Carol Grady of Eureka Scientific in Oakland, California, added, "Because nothing like this has been observed or predicted in theory we can only hypothesize when it comes to what we are seeing and how it came about."

The ripples farther away from the star seem to be moving faster than those closer to it. At least three of the features are moving so fast that they are likely escaping from the gravitational attraction of the star. Such high speeds rule out the possibility that these features are caused by objects, like planets, gravitationally disturbing material in the disk. The team has also ruled out a series of phenomena as explanations, including the collision of two massive and rare asteroid-like objects releasing large quantities of dust and spiral waves triggered by instabilities in the system's gravity.

"One explanation for the strange structure links them to the star's flares. AU Mic is a star with high flaring activity. This is typical for such young, relatively cool, low-mass stars. AU Mic often lets off huge and sudden bursts of energy from on or near its surface,” said co-author and leader of the Hubble team Glenn Schneider of Steward Observatory in Tucson, Arizona. "One of these flares could perhaps have triggered something on one of the planets — if there are planets — like a violent stripping of material, which could now be propagating through the disk, propelled by the flare's force."

The team plans to continue to observe the AU Mic system to try to understand what is happening. But, for now, these curious features remain an unsolved mystery.

The results will be published Oct. 8 in the British science journal Nature.


Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Felicia Chou
NASA Headquarters, Washington, D.C.

Mathias Jäger
ESA/Hubble, Garching, Germany

Anthony Boccaletti
Paris Observatory, CNRS, Paris, France

Glenn Schneider
Steward Observatory, University of Arizona, Tucson, Arizona

Source: HubbleSite

The Deepest Ground-based Photometry in a Crowded Field

Left: (Ks, F606W-Ks) color–magnitude diagram of NGC 1851; the detail of the double SGB is shown in the inset. Right: same as the left panel with average photometric (random) uncertainties indicated. Overlaid is the fiducial line with the approximate locations of the main sequence turnoff and main sequence knee highlighted by red dots.

Ultraviolet image of the globular cluster NGC 1851 in the southern constellation Columba.
Credit: NASA/JPL-Caltech/SSC/Ricardo Schiavo (UVA)

Expecting to resolve stars deep into the crowded field of a globular cluster is a tall order for ground-based telescopes. However, Paolo Turri (University of Victoria, Canada) and colleagues have used the Gemini Multi-conjugate adaptive optics System (GeMS) with the Gemini South Adaptive Optics Imager (GSAOI) to do just that. Their data present the most accurate and deepest near-infrared photometry from the ground of a crowded field. It also illustrates the remarkable potential of MCAO-equipped Extremely Large Telescopes of the future.

Their Ks measurements of the Galactic globular cluster NGC 1851 are combined with HST photometry and the resulting color-magnitude diagram demonstrates that the ground-based data is of an unprecedented depth and precision for crowded field observations. The delivered image quality approaches Gemini’s diffraction limit, with an average measured full-width at half-maximum (FHWM) of 0.09 arcsecond. The work is published in The Astrophysical Journal Letters.

The Extremely Large Telescopes currently under construction have a collecting area that is an order of magnitude larger than the present largest optical telescopes. For seeing-limited observations the performance will scale as the collecting area, but with the successful use of adaptive optics (AO), for many applications it will scale as D4 (where D is the diameter of the primary mirror). Central to the success of the ELTs, therefore, is the successful use of multi-conjugate adaptive optics (MCAO) which applies a high degree of correction over a field of view larger than the few arcseconds that limits classical AO systems. In this Letter, we report on the analysis of crowded field images taken on the central region of the galactic globular cluster NGC 1851 in the Ks band using the Gemini Multi-conjugate Adaptive Optics System (GeMS) at the Gemini South Telescope, the only science-grade MCAO system in operation. We use this cluster as a benchmark to verify the ability to achieve precise near-infrared photometry by presenting the deepest Ks photometry in crowded fields ever obtained from the ground. We construct a color–magnitude diagram in combination with the F606W band from the Hubble Space Telescope/Advanced Camera for Surveys. As well as detecting the “knee” in the lower main sequence at Ks '20.5, we also detect the double subgiant branch of NGC 1851, which demonstrates the high photometric accuracy of GeMS in crowded fields. 

Tuesday, October 06, 2015

Searching for Orphan Stars Amid Starbirth Fireworks

The HH 24 jet complex emanates from a dense cloud core that hosts a small multiple protostellar system known as SSV63. The nebulous star to the south is the visible T Tauri star SSV59. Color image based on the following filters with composite image color assignments in parenthesis: g (blue), r (cyan), I (orange), hydrogen-alpha (red), sulfur II (blue)) images obtained with GMOS on Gemini North in 0.5 arcsecond seeing, and NIRI. Field of view is 4.2x5.1 arcminutes, orientation: north up, east left. Image produced by Travis Rector.  Credit: Gemini Observatory/AURA/B. Reipurth, C. Aspin, T. Rector.  Download JPG 945KB | TIFF 7.8MB 

A new Gemini Observatory image reveals the remarkable “fireworks” that accompany the birth of stars. The image captures in unprecedented clarity the fascinating structures of a gas jet complex emanating from a stellar nursery at supersonic speeds. The striking new image hints at the dynamic (and messy) process of star birth. Researchers believe they have also found a collection of runaway (orphan) stars that result from all this activity.

Gemini Observatory has released one of the most detailed images ever obtained of emerging gas jets streaming from a region of newborn stars. The region, known as the Herbig-Haro 24 (HH 24) Complex, contains no less than six jets streaming from a small cluster of young stars embedded in a molecular cloud in the direction of the constellation of Orion.

"This is the highest concentration of jets known anywhere," says Principal Investigator Bo Reipurth of the University of Hawaii’s Institute for Astronomy (IfA), who adds, "We also think the very dynamic environment causes some of the lowest mass stars in the area to be expelled, and our Gemini data are supporting that idea."

Reipurth along with co-researcher, Colin Aspin, also at the IfA, are using the Gemini North data from the Gemini Multi-Object Spectrograph (GMOS), as well as the Gemini Near-Infrared Imager, to study the region which was discovered in 1963 by George Herbig and Len Kuhi. Located in the Orion B cloud, at a distance of about 400 parsecs, or about 1,300 light-years from our Solar System, this region is rich in young stars and has been extensively studied in all types of light, from radio waves to X-rays.

"The Gemini data are the best ever obtained from the ground of this remarkable jet complex and are showing us striking new detail," says Aspin. Reipurth and Aspin add that they are particularly interested in the fine structure and "excitation distribution" of these jets.

"One jet is highly disturbed, suggesting that the source may be a close binary whose orbit perturbs the jet body," says Reipurth.

The researchers report that the jet complex emanates from what is called a Class~I protostar, SSV63, which high-resolution infrared imaging reveals to have at least five components. More sources are found in this region, but only at longer, submillimeter wavelengths of light, suggesting that there are even younger, and more deeply embedded sources in the region. All of these embedded sources are located within the dense molecular cloud core.

A search for dim optical and infrared young stars has revealed several faint optical stars located well outside the star-forming core. In particular, a halo of five faint Hydrogen-alpha emission stars (which emit large amounts of red light) has been found with GMOS surrounding the HH 24 Complex well outside the dense cloud core. Gemini spectroscopy of the hydrogen alpha emission stars show that they are early or mid-M dwarfs (very low-mass stars), with at least one of which being a borderline brown dwarf.

The presence of these five very low-mass stars well outside the star-forming cloud core is puzzling, because in their present location the gas is far too tenuous for the stars to have formed there. Instead they are likely orphaned protostars ejected shortly after birth from the nearby star-forming core. Such ejections occur when many stars are formed closely together within the same cloud core. The crowded stars start moving around each other in a chaotic dance, ultimately leading to the ejection of the smallest ones.

A consequence of such ejections is that pairs of the remaining stars bind together gravitationally. The dense gas that surrounds the newly formed pairs brakes their motion, so they gradually spiral together to form tight binary systems with highly eccentric orbits. Each time the two components are closest in their orbits they disturb each other, leading to accretion of gas, and an outflow event that we see as supersonic jets. The many knots in the jets thus represent a series of such perturbations.

Monday, October 05, 2015

The Environments of Radio-Bright Active Galaxies

A Chandra X-ray Observatory image of the galaxy cluster Abell 2125, showing its complex of galaxies and very hot gas clouds in the process of merging. Some galaxies in clusters host active black-hole nuclei that are ejecting jets of particles and emitting at radio wavelengths. A new study finds evidence that the cluster environment plays an important role in determining the nature of accretion onto the black hole. Credit: NASA/CXC/UMass/Q.D.Wang et al.

The nucleus of an active galaxy contains a massive black hole that is vigorously accreting material. In the process, the nucleus typically ejects jets of rapidly moving charged particles that radiate brightly at many wavelengths, in particular radio wavelengths. Active galaxies display a range of dramatically different properties and one categorization uses the radio emission, finding one class that is bright in the radio and a second group that is comparatively faint. Astronomers suspect that the reason for the difference is a different rate of accretion onto the central black hole, but there are other activities that also seem to correlate with the radio emission including nearby star formation, for example, or the age of the galaxy. Astronomers are therefore trying to identify the ones that might be causal.

Feedback from the intergalactic medium onto a galaxy's nucleus has recently been identified as an important driver of galaxy evolution, and the question naturally arises about the role of such feedback in a galaxy’s radio activity and the accompanying effects. CfA astronomers Ralph Kraft and Dan Evans and their colleagues used the Chandra X-Ray Telescope in the first systematic X-ray study of the cluster environment of radio galaxies all dating from the same epoch. The X-ray emission is the key to understanding how the gas accretes onto the black hole.

The team observed fifty-five radio emitting sources spanning a factor of a thousand in radio luminosity, twenty-five of them classified as bright. They found that the bright radio sources show evidence of high accretion from a circumnuclear disk. The faint sources, on the other hand, have a more uncertain mechanism, perhaps the chaotic accretion of cool gas clouds; significantly, their radio emission strength is strongly correlated with the cluster richness and central density, while no such correlations were found for the bright sources. The scientists conclude that there are strong environmental differences between these two classes consistent with thinking that the cluster environment supports the fueling of emission. This evidence has prompted the team to study next the relationships between the gas in the intracluster medium and the other phenomena associated with the two classes.


"The Link between Accretion Mode and Environment in Radio-Loud Active Galaxies," J. Ineson, J. H. Croston, M. J. Hardcastle, R. P. Kraft, D. A. Evans, and M. Jarvis, MNRAS 453, 2682, 2015.

Friday, October 02, 2015

The Mountain

El Teide

This was filmed between 4th and 11th April 2011. I had the pleasure of visiting El Teide.

Spain´s highest mountain @(3718m) is one of the best places in the world to photograph the stars and is also the location of Teide Observatories, considered to be one of the world´s best observatories.

The goal was to capture the beautiful Milky Way galaxy along with one of the most amazing mountains I know El Teide. I have to say this was one of the most exhausting trips I have done. There was a lot of hiking at high altitudes and probably less than 10 hours of sleep in total for the whole week. Having been here 10-11 times before I had a long list of must-see locations I wanted to capture for this movie, but I am still not 100% used to carrying around so much gear required for time-lapse movies.

A large sandstorm hit the Sahara Desert on the 9th April ( and at approx 3am in the night the sandstorm hit me, making it nearly impossible to see the sky with my own eyes.

Interestingly enough my camera was set for a 5 hour sequence of the milky way during this time and I was sure my whole scene was ruined. To my surprise, my camera had managed to capture the sandstorm which was backlit by Grand Canary Island making it look like golden clouds. The Milky Way was shining through the clouds, making the stars sparkle in an interesting way. So if you ever wondered how the Milky Way would look through a Sahara sandstorm, look at 00:32.

Available in Digital Cinema 4k.

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Music by my friend: Ludovico Einaudi - "Nuvole bianche" with permission.

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Source: Vimeo/Terjes

Credit: ESA/Hubble & NASA and S. Smartt (Queen's University Belfast)
Acknowledgement: Robert Gendler

Ribbons of dust festoon the galaxy NGC 613 in this new image from the NASA/ESA Hubble Space Telescope. NGC 613 is classified as a barred spiral galaxy for the bar-shaped band of stars and dust crossing its intensely glowing centre.

About two thirds of spiral galaxies show a characteristic bar shape like NGC 613 — our own galaxy appears to have one of these bars through its midline as well.

NGC 613 lies 65 million light-years away in the constellation of Sculptor (The Sculptor). It was first noted by the English astronomer William Herschel in 1798 and later by John Louis Emil Dreyer, a Danish–Irish astronomer, who recorded the object in his 1888 New General Catalogue of Nebulae and Clusters of Stars — hence the letters "NGC".

NGC 613's core looks bright and uniformly white in this image as a result of the combined light shining from the high concentration of stars packed into the core, but lurking at the centre of this brilliance lies a dark secret. As with nearly all spiral galaxies, a monstrous black hole resides at the heart of NGC 613. Its mass is estimated at about ten times that of the Milky Way's supermassive black hole and it is consuming stars, gas and dust. As this matter descends into the black hole's maw it radiates away energy and spews out radio waves. However, when looking at the the galaxy in the optical and infrared wavelengths used to take this image, there is no trace of the dark heart.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Robert Gendler.

Thursday, October 01, 2015

Solving the hydrostatic mass bias problem in cosmology with galaxy clusters

Fig 2: This plot shows the hydrostatic mass bias for galaxy clusters, i.e. the difference between the true mass and the estimated mass (with different models). Open symbols give the estimated mass without correction, the filled symbols the results when applying the new method. The three areas of the figure show simulated clusters in different dynamical stages, namely, the top 20% (rather relaxed), 50% (less disturbed) and 100% (all) clusters according how dynamically relaxed they are. The new method works well for all types of clusters and irrespective of the detailed procedures used in estimating the masses (indicated by different colors).  © MPA

Different methods are used to determine the mass of a galaxy cluster depending on both the dynamical relaxation state of the cluster (relaxed/ disturbed, evident from its X-ray image) and the spatial resolution of the observed image (well-resolved or not). With our solution to the hydrostatic mass bias problem, we can improve the accuracy of mass estimation for clusters belonging to all these categories. We will also be able to take advantage of the spatial information in the observations for the well-resolved, dynamically disturbed clusters. © MPA

Booming observations of galaxy clusters provide great opportunities for exploring the nature of Dark Energy. At the same time, they post great challenges to scientists. The "hydrostatic mass bias" problem, which leads to a systematic error in estimating the mass of galaxy clusters, is one big limitation when doing precision cosmology with galaxy clusters. Now researchers at MPA have developed a method to correct for it. 

Dark Energy is the most dominant energy component in the present-day universe, but its physical nature remains unknown. Dark Energy leaves unique signatures in the universe: it accelerates the expansion of the universe and slows down the growth of structure. As the largest gravitationally-bound structures in the universe, galaxy clusters are a sensitive tracer to these signatures. Thus, researchers can constrain the properties of Dark Energy by counting the numbers of clusters as a function of their masses at various cosmic times.

An accurate measurement of the masses of galaxy clusters is crucial for the success of this method. Although galaxy clusters get their name from observations of galaxies in optical light, the most precise way to estimate their masses - the so-called "hydrostatic mass estimation method" - comes from observations at X-ray wavelengths. X-ray images of galaxy clusters reveal the diffuse hot gas in galaxy clusters that accounts for 90% of their ordinary matter (see mock X-ray images in Fig. 1). In spite of its high temperature - which means high thermal velocities - this hot gas is trapped deep inside the galaxy cluster. This is because of the enormous gravitational attraction from the dark matter component, which makes up about 85% of the total mass of a cluster. (Ordinary matter accounts for only about 15% of the mass.)

The hydrostatic mass estimation method assumes that the hot gas is in hydrostatic equilibrium, i.e. its thermal pressure balances the gravitational pull. However, the hot gas in a galaxy cluster is never fully thermalized because it is continuously fed by mass accretion. The residue motions of the infalling gas leads to a non-thermal pressure support, together with possible contributions from magnetic fields and cosmic rays. This breaks the assumption of hydrostatic equilibrium and causes a bias of typically 5-30% to the mass estimation.

This hydrostatic mass bias problem calls for a better description of the underlying physics in galaxy clusters. Researchers at MPA have therefore developed a new analytical model for the non-thermal pressure, which captures the growth and dissipation of the random motions in the hot gas. Adding this contribution to the hydrostatic balance, they were able to correct for the mass estimations when testing with state-of-the-art cosmological hydrodynamics simulations (see Fig. 2), where the random motions are the dominating contribution to the hydrostatic mass bias. Remarkably, this correction method works for samples of galaxy clusters with various dynamical states (horizontal axis of Fig. 2).

Aided by this correction, the application of the precise hydrostatic mass estimation method can be extended to dynamically disturbed galaxy clusters as long as spatially well-resolved observations are available. With advances in the observation of the Sunyaev-Zeldovich (SZ) effect which directly probes the thermal pressure of the hot gas, spatially well-resolved data will be much easier to obtain, as researchers will no longer rely on the time-consuming X-ray temperature measurements. Already in the last few years, the Planck satellite, the South Pole Telescope and the Atacama Cosmology Telescope have detected more than a thousand galaxy clusters, most of them dynamically disturbed, via their SZ signal. Some of the data already have good spatial resolution.

Still, much more galaxy clusters will be detected without immediate spatially-resolved data. However the newly developed method is also useful for them. For example, the eROSITA survey will measure the X-ray emission of more than 50,000 galaxy clusters and their progenitors. Most of them will not be spatially well-resolved. Masses for these objects will be obtained by scaling relations between the mass and spatially-averaged observables, such as the mean X-ray luminosity, temperature, or their combination. Correcting the hydrostatic mass bias will lead to a more accurate calibration of the scaling relations, and thus allow researchers to better exploit the huge number of galaxy clusters to explore the nature of Dark Energy.


Shi, Xun  
Phone: 2253

Managing director
Phone: 2208

Phoenix Cluster: A Fresh Perspective on an Extraordinary Cluster of Galaxies

SPT-CLJ2344-4243 - Phoenix Cluster
Credit:  X-ray: NASA/CXC/MIT/M.McDonald et al; 
Optical: NASA/STScI; Radio: TIFR/GMRT


Galaxy clusters are often described by superlatives. After all, they are huge conglomerations of galaxies, hot gas, and dark matter and represent the largest structures in the Universe held together by gravity.

Galaxy clusters tend to be poor at producing new stars in their centers. They generally have one giant galaxy in their middle that forms stars at a rate significantly slower than most galaxies - including our Milky Way. The central galaxy contains a supermassive black holeroughly a thousand times more massive than the one at the center of our galaxy. Without heating by outbursts from this black hole, the copious amounts of hot gas found in the central galaxy should cool, allowing stars to form at a high clip. It is thought that the central black hole acts as a thermostat, preventing rapid cooling of surrounding hot gas and impeding star formation.

New data provide more details on how the galaxy cluster SPT-CLJ2344-4243, nicknamed the Phoenix Cluster for the constellation in which it is found, challenges this trend. The cluster has shattered multiple records in the past: In 2012, scientists announced that the Phoenix cluster featured the highest rate of cooling hot gas and star formation ever seen in the center of a galaxy cluster, and is the most powerful producer of X-rays of all known clusters. The rate at which hot gas is cooling in the center of the cluster is also the largest ever observed.

New observations of this galaxy cluster at X-ray, ultraviolet, and optical wavelengths by NASA's Chandra X-ray Observatory, the Hubble Space Telescope, and the Clay-Magellan telescope located in Chile, are helping astronomers better understand this remarkable object. Clay-Magellan's optical data reveal narrow filaments from the center of the cluster where stars are forming. These massive cosmic threads of gas and dust, most of which had never been detected before, extend for 160,000 to 330,000 lights years. This is longer than the entire breadth of the Milky Way galaxy, making them the most extensive filaments ever seen in a galaxy cluster.

These filaments surround large cavities - regions with greatly reduced X-ray emission - in the hot gas. The X-ray cavities can be seen in this composite image that shows the Chandra X-ray data in blue and optical data from the Hubble Space Telescope (red, green, and blue). For the location of these "inner cavities", mouse over the image. Astronomers think that the X-ray cavities were carved out of the surrounding gas by powerful jets of high-energy particles emanating from near a supermassive black hole in the central galaxy of the cluster. As matter swirls toward a black hole, an enormous amount of gravitational energy is released. 

Combined radio and X-ray observations of supermassive black holes in other galaxy clusters have shown that a significant fraction of this energy is released as jets of outbursts that can last millions of years. The observed size of the X-ray cavities indicates that the outburst that produced the cavities in SPT- CLJ2344-4243 was one of the most energetic such events ever recorded.

 Radio & Optical Image of Phoenix Cluster
Credit  X-ray: NASA/CXC/MIT/M.McDonald et al; 
Optical: NASA/STScI; Radio: TIFR/GMRT

However, the central black hole in the Phoenix cluster is suffering from somewhat of an identity crisis, sharing properties with both "quasars", very bright objects powered by material falling onto a supermassive black hole, and "radio galaxies" containing jets of energetic particles that glow in radio waves, and are also powered by giant black holes. Half of the energy output from this black hole comes via jets mechanically pushing on the surrounding gas (radio-mode), and the other half from optical, UV and X-radiation originating in an accretion disk (quasar-mode). Astronomers suggest that the black hole may be in the process of flipping between these two states.

X-ray cavities located farther away from the center of the cluster, labeled as "outer cavities", provide evidence for strong outbursts from the central black hole about a hundred million years ago (neglecting the light travel time to the cluster). This implies that the black hole may have been in a radio mode, with outbursts, about a hundred million years ago, then changed into a quasar mode, and then changed back into a radio mode.

It is thought that rapid cooling may have occurred in between these outbursts, triggering star formation in clumps and filaments throughout the central galaxy at a rate of about 610 solar masses per year. By comparison, only a couple new stars form every year in our Milky Way galaxy. The extreme properties of the Phoenix cluster system are providing new insights into various astrophysical problems, including the formation of stars, the growth of galaxies and black holes, and the co-evolution of black holes and their environment.

A paper describing these results, led by Michael McDonald (Massachusetts Institute of Technology), has been accepted for publication in The Astrophysical Journal and is 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 Phoenix Cluster:

Scale: Image is about 1.2 arcmin across (about 1.5 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 23h 44m 42.00s | Dec -42 42 52.60
Constellation: Phoenix
Observation Date: 3 pointings between Sep 2011 and Aug 2014
Observation Time: 36 hours 23 min (1 days 12 hours 23 min).
Obs. ID: 13401, 16135, 16545
Instrument: ACIS
Also Known As: SPT-CLJ2344-4243
References: arXiv:1508.05941
Color Code: X-ray (Blue); Optical (Red, Green, Blue)
Distance Estimate: About 5.7 billion light years; z=0.596

Wednesday, September 30, 2015

Discovery of the Companions of Millisecond Pulsars

An optical image of the globular cluster, 47 Tucanae. Astronomers have identified the orbiting companions to five millisecond pulsars in this cluster and found them all to be white dwarf stars.Credit: South African Astronomical Observatory

When a star with a mass of roughly ten solar masses finishes its life, it does so in a spectacular explosion known as a supernova, leaving behind as remnant "ash" a neutron star. Neutron stars have masses of one-to-several Suns, but they are tiny in size, only tens of kilometers. Neutron stars spin rapidly, and when they have associated rotating magnetic fields to constrain charged particles, these particles emit electromagnetic radiation in a lighthouse-like beam that can sweep past the Earth with great regularity every few seconds or less. Such neutron stars are known as pulsars. Pulsars are dramatic and powerful probes of supernovae, their progenitor stars, and the properties of nuclear matter under the extreme conditions that exist in these stars.

Some pulsars called millisecond pulsars spin much more quickly, and astronomers have concluded that in order to rotate so rapidly these objects must be regularly accreting material from a nearly companion star which in a binary orbit with it; the new material helps to spin-up the neutron star, which normally would gradually slow down. There are more than 200 known millisecond pulsars. An understanding of these pulsars has been hampered, however, by the fact that only about a dozen of them have had their companion stars directly detected and studied.

CfA astronomers Maureen van den Berg, Josh Grindlay, and Peter Edmonds and their colleagues used ultraviolet images from Hubble to identify the companion stars to two millisecond pulsars located in the globular cluster 47 Tucanae. They were also able to confirm a previous but tentative identification, and to confirm two more. They report that each is of these companions is a white dwarf star – an evolved star that can no longer sustain nuclear burning and which has shrunk to a fraction of its original radius. Each of these pulsars spins more than 120 times per second, and the companions orbit quite closely with periods ranging from only 0.43 days to 1.2 days, close enough to easily satisfy the requirements needed for this kind of cosmic cannibalism as the pulsars gradually feed on material from the white dwarfs. The new work significantly increases the number of identified and characterized millisecond pulsar companions.


"Discovery of Near-Ultraviolet Counterparts to Millisecond Pulsars in the Globular Cluster 47 Tucanae," L. E. Rivera-Sandoval, M. van den Berg, C. O. Heinke, H. N. Cohn, P. M. Lugger, P. Freire, J. Anderson, A. M. Serenelli, L. G. Althaus, A. M. Cool, J. E. Grindlay, P. D. Edmonds, R. Wijnands and N. Ivanova, MNRAS 453, 2707, 2015.

Tuesday, September 29, 2015

If our eyes could see gravitational waves

If our eyes could see gravitational waves
Copyright: NASA/C. Henze

Picture the scene: two gigantic black holes, each one a good fraction of the size of our Solar System spiralling around each other. Closer and closer they draw until they touch and merge into a single, even more gigantic gravitational prison.

But what would you actually see? For such a cataclysmic event, it might all take place with remarkable stealth because black holes by their very nature emit no light at all. Rather than light, it would be a different story if our eyes could see gravitational waves.

This is what the merger of two black holes would look like. It is a computer simulation of the gravitational waves that would ripple away from the titanic collision, a bit like the ripples on a pond when a pebble drops into the water.

In the case of gravitational waves, the disturbances are not in water but in the spacetime continuum. This is the mathematical ‘fabric' of space and time that Albert Einstein used to explain gravity.

Gravitational radiation has been indirectly observed but never seen directly. Its detection would open a whole new way of studying the Universe. As a result, astronomers are working on both ground-based and space-based detectors. And it is a real challenge.

Gravitational radiation is incredibly difficult to measure. The ripples cause atoms to ‘bob’ about to just 1 part in 1000 000 000 000 000 000 000. Building a detector to notice this is like measuring the distance from Earth to the Sun to the accuracy of the size of a hydrogen atom.

Following decades of technology development and experiments, detectors on the ground are nearing the required sensitivity. The first detections are expected in the next few years. But these detectors can see only half of the picture. The mass of the colliding black holes determines the frequency of the gravitational radiation.

The merger of small black holes, each about a few times the mass of the Sun, will create high-frequency gravitational waves that could be seen from the ground. But the giant black holes that sit at the heart of galaxies with masses of a million times that of the Sun will generate gravitational waves of much lower frequency. These cannot be detected with ground-based systems because seismic interference and other noise will overwhelm the signals. Hence, spaceborne observatories are needed.

ESA has selected the gravitational Universe as the focus for the third large mission in the Cosmic Vision plan, with a launch date of around 2034. 

Unlocking the gravitational Universe will require a highly ambitious mission. In preparation, ESA will launch LISA-Pathfinder this November to test some of the essential technologies needed to build confidence in future spaceborne gravitational wave observatories.

This image is from a simulation of two black holes merging and the resulting emission of gravitational radiation, published by NASA in 2012.

 Source: ESA

Monday, September 28, 2015

Pairs of Supermassive Black Holes in Galaxies May Be Rarer Than Previously Thought

At left is the galaxy J0702+5002, which the researchers concluded is not an X-shaped galaxy whose form is caused by a merger. At right is the galaxy J1043+3131, which is a "true" candidate for a merged system. Credit: Roberts, et al., NRAO/AUI/NSF

Credit: Roberts, et al.; Bill Saxton, NRAO/AUI/NSF

There may be fewer pairs of supermassive black holes orbiting each other at the cores of giant galaxies than previously thought, according to a new study by astronomers who analyzed data from the National Science Foundation's Karl G. Jansky Very Large Array (VLA) radio telescope.

Massive galaxies harbor black holes with millions of times more mass than our Sun at their centers. When two such galaxies collide, their supermassive black holes join in a close orbital dance that ultimately results in the pair combining. That process, scientists expect, is the strongest source of the long-sought, elusive gravitational waves, still yet to be directly detected.

"Gravitational waves represent the next great frontier in astrophysics, and their detection will lead to new insights on the Universe," said David Roberts of Brandeis University, lead author of the research. "It's important to have as much information as possible about the sources of these waves," he added.

Astronomers worldwide have begun programs to monitor fast-rotating pulsars throughout our Milky Way Galaxy in an attempt to detect gravitational waves. These programs seek to measure shifts in the signals from the pulsars caused by gravitational waves distorting the fabric of space-time. Pulsars are spinning, superdense neutron stars that emit lighthouse-like beams of light and radio waves that allow precise measurement of their rotation rates.

Roberts and his colleagues studied a sample of galaxies called "X-shaped radio galaxies," whose peculiar structure indicated the possibility that the radio-emitting jets of superfast particles ejected by disks of material swirling around the central black holes of these galaxies have changed directions. The change, astronomers had suggested, was caused by an earlier merger with another galaxy, causing the spin axis of the black hole as well as the jet axis to shift direction.

Working from an earlier list of 100 such objects, they collected archival data from the VLA to make new, more detailed images of 52 of them. Their analysis of the new images led them to conclude that only 11 are "genuine" candidates for galaxies that have merged, causing their radio jets to change direction. The jet changes in the other galaxies, they concluded, came from other causes.

Extrapolating from this result, the astronomers estimated that fewer than 1.3 percent of galaxies with extended radio emission have experienced mergers. This rate is five times lower than previous estimates.

"This could significantly lower the level of very-long-wave gravitational waves coming from X-shaped radio galaxies, compared to earlier estimates," Roberts said. "It will be very important to relate gravitational waves to objects we see through electromagnetic radiation, such as radio waves, in order to advance our understanding of fundamental physics," he added.

Gravitational waves, ripples in space-time, were predicted in 1916 by Albert Einstein as part of his theory of general relativity. The first evidence for such waves came from observations of a pulsar orbiting another star, a system discovered in 1974 by Joseph Taylor and Russell Hulse. Observations of this pair over several years showed that their orbits are decaying at exactly the rate predicted by Einstein's equations that indicate gravitational waves carrying energy away from the system.

Taylor and Hulse received the 1993 Nobel Prize in physics for this work, which confirmed a predicted effect of gravitational waves. However, no direct detection of such waves has yet been made.

Roberts worked with Jake Cohen and Jing Lu, Brandeis undergraduates who retrieved the data from the VLA archive and produced the images of the galaxies; and Lakshmi Saripalli and Ravi Subrahmanyan of the Raman research Institute in Bangalore, India. The researchers reported their results and analysis in a pair of papers in the Astrophysical Journal Letters and the Astrophysical Journal Supplements.

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


Dave Finley, Public Information Officer
(575) 835-7302

Sunday, September 27, 2015

"Fossils" of galaxies reveal the formation and evolution of massive galaxies

"Fossils" of galaxies reveal the formation and evolution of massive galaxies

An international team led by researchers at Swiss Federal Institute of Technology in Zürich observed massive dead galaxies in the universe 4 billion years after the Big Bang with the Subaru Telescope's Multi-Object InfraRed Camera and Spectrograph (MOIRCS). They discovered that the stellar content of these galaxies is strikingly similar to that of massive elliptical galaxies seen locally. Furthermore, they identified progenitors of these dead galaxies when they were forming stars at an earlier cosmic epoch, unveiling the formation and evolution of massive galaxies across 11 billion years of cosmic time.

In the local universe, massive galaxies hosting more than about 100 billion stars are predominantly dead elliptical galaxies, that is, without any signs of star-formation activity. Many questions remain on when, how and for how long star formation occurred in such galaxies before the cessation of star formation, as well as what happened since to form the dead elliptical galaxies seen today.

In order to address these issues, the research team made use of fossil records imprinted by stars in the spectra of distant dead galaxies which give important clues to their age, metal content, and element abundances. Local massive dead galaxies are about 10 billion years old and rich in heavy elements. Also, α-elements (Note 1), which measure the duration of star formation, are more abundant than iron, indicating that these galaxies formed a large amount of stars in a very short period. The team investigated the stellar content of galaxies in the distant universe 4 billion years after the Big Bang, in order to study galaxy evolution much closer to their formation epoch.

The team took the advantage of the MOIRCS's capability to observe multiple objects simultaneously, efficiently observing a sample of 24 faint galaxies. They created a composite spectrum that would have taken 200 hours of Subaru Telescope's time for a single spectrum of comparable quality (Figure 1).

Figure 1: Composite spectrum of 24 massive dead galaxies in the universe 4 billion years after the Big Bang. The spectra is equivalent to 200 hours of Subaru Telescope's observing time. Rectangles on the spectrum indicate spectral features, which are used to calculate the ages, the amount of heavy elements and the α-element abundance in the stellar populations of these galaxies. (Credit: ETH Zürich/NAOJ)  

Analysis of the composite spectrum shows that the age of the galaxies is already 1 billion years old when observed 4 billion years after the Big Bang. They host 1.7 times more heavy elements relative to the amount of hydrogen and their α-elements are twice enhanced relative to iron than the solar values. It is the first time that the α-element abundance in stars is measured in such distant dead galaxies, and it tells us that the duration of star formation in these galaxies was shorter than 1 billion years. These results reveal that these massive dead galaxies have evolved to today without further star formation (Figure 2).

Figure 2: Cosmic evolution of the age (Left), the abundance of heavy elements (Middle) and the abundance of α-elements relative to iron (Right) of massive dead elliptical galaxies. Gray data points show the results from previous works by other studies. The colored strip in the left panel is a prediction of their evolution if such massive elliptical galaxies formed 10 to 11 billion years ago (redshift of about 2.3) and evolved without forming new stars to the present universe (redshift of zero). The prediction agrees with the observed trend very well. The middle and left panels clearly show that chemical composition of massive elliptical galaxies does not evolve over cosmic time. (Credit: ETH Zürich/NAOJ)  

What do massive dead galaxies look like when they are forming stars? To answer this, the team investigated the progenitors of their sample based on their spectral analysis. The progenitors must be star-forming galaxies in the universe 1 billion years before the observed epoch for the dead galaxies. Indeed, they do find similarly massive star-forming galaxies at the right epoch and with the right star formation rate expected from the spectra. If these active galaxies continue to create stars at the same rate, they will immediately become more massive than seen in the present universe. Therefore, these galaxies will cease star formation soon and simply age.

This study establishes a consistent picture of the history of massive galaxies over 11 billion years of cosmic time. Dr. Masato Onodera who leads the team says, "We would like to explore galaxy evolution in more detail by carrying out an object-by-object study and by extending the method to an even earlier epoch."

This research was published on 1st August 2015 in The Astrophysical Journal (Onodera et al. 2015 "The Ages, Metallicities, and Element Abundance Ratios of Massive Quenched Galaxies at z~1.6"). This work was supported by the Japan Society for the Promotion of Science (Grant ID: 23224005) and the Program for Leading Graduate Schools. The preprint of the paper is available at this link.

Member of the research team (as of the publication of Onodera et al. 2015):

  • Masato Onodera, C. Marcella Carollo, Sandro Tacchella (ETH Zürich, Swizerland)
  • Alvio Renzini (INAF-Padova, Italy)
  • Michele Cappellari (Oxford University, UK)
  • Chiara Mancini (Padova University, Italy)
  • Nobuo Arimoto, Yoshihiko Yamada (Subaru Telescope, Japan)
  • Emanuele Daddi (CEA/Saclay, France)
  • Raphaël Gobat (KIAS, South Korea)
  • Veronica Strazzullo (Ludwig Maximilians University, Germany)


  1. α-elements are elements which have an atomic number that is a multiple of 4, i.e., of the helium nucleus. In this article, it refers to elements produced by Type II supernovae such as oxygen, neon, magnesium, silicon, sulfur, calcium, and titanium. 

Too big for its boots: black hole is 30 times expected size

An image of the galaxy SAGE0536AGN, from the Vista Magellanic Clouds survey. 
The galaxy is the elliptical object in the centre of the frame.

A still frame from a movie, illustrating an active galactic nucleus, with jets of material flowing from out from a central black hole. Credit: NASA / Dana Berry / SkyWorks Digital (See for the full movie). Click  here for a full size image

The central supermassive black hole of a recently discovered galaxy is far larger than should be possible, according to current theories of galactic evolution. New work, carried out by astronomers at Keele University and the University of Central Lancashire, shows that the black hole is much more massive than it should be, compared to the mass of the galaxy around it. The scientists publish their results in a paper in Monthly Notices of the Royal Astronomical Society.

The galaxy, SAGE0536AGN, was initially discovered with NASA's Spitzer space telescope in infrared light. Thought to be at least 9 billion years old, it contains an active galactic nucleus (AGN), an incredibly bright object resulting from the accretion of gas by a central supermassive black hole. The gas is accelerated to high velocities due to the black hole's immense gravitational field, causing this gas to emit light.

The team has now also confirmed the presence of the black hole by measuring the speed of the gas moving around it. Using the Southern African Large Telescope, the scientists observed that an emission line of hydrogen in the galaxy spectrum (where light is dispersed into its different colours – a similar effect is seen using a prism) is broadened through the Doppler Effect, where the wavelength (colour) of light from objects is blue- or red-shifted depending on whether they are moving towards or away from us. The degree of broadening implies that the gas is moving around at high speed, a result of the strong gravitational field of the black hole.

These data have been used to calculate the black hole's mass: the more massive the black hole, the broader the emission line. The black hole in SAGE0536AGN was found to be 350 million times the mass of the Sun.

But the mass of the galaxy itself, obtained through measurements of the movement of its stars, has been calculated to be 25 billion solar masses. This is seventy times larger than that of the black hole, but the black hole is still thirty times larger than expected for this size of galaxy.

"Galaxies have a vast mass, and so do the black holes in their cores. This one though is really too big for its boots – it simply shouldn’t be possible for it to be so large", said Dr Jacco van Loon, an astrophysicist at Keele University and the lead author on the new paper.

In ordinary galaxies the black hole would grow at the same rate as the galaxy, but in SAGE0536AGN the black hole has grown much faster, or the galaxy stopped growing prematurely. Because this galaxy was found by accident, there may be more such objects waiting to be discovered. Time will tell whether SAGE0536AGN really is an oddball, or simply the first in a new class of galaxies.

Media contact

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x113
Mob: +44 (0)7802 877 699

Science contact

Dr Jacco van Loon
Keele University
Tel: +44(0)1782 73 3331

Further information

The new work appears in "An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole", Jacco Th. van Loon and Anne E. Sansom, Monthly Notices of the Royal Astronomical Society, vol. 453 (3), pp. 2341-2348, Oxford University Press.

Notes for editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3900 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter

Saturday, September 26, 2015

Radio Telescopes Could Spot Stars Hidden in the Galactic Center

In this infrared image from NASA's Spitzer Space Telescope, stellar winds flowing out from the fast-moving star Zeta Ophiuchi are creating a bow shock seen as glowing gossamer threads, which, for this star, are only seen in infrared light. A similar process in the galactic center could allow us to find stars we can't see any other way, according to new research.  High Resolution (jpg) - Low Resolution (jpg)

Cambridge, MA - The center of our Milky Way galaxy is a mysterious place. Not only is it thousands of light-years away, it's also cloaked in so much dust that most stars within are rendered invisible. Harvard researchers are proposing a new way to clear the fog and spot stars hiding there. They suggest looking for radio waves coming from supersonic stars.

"There's a lot we don’t know about the galactic center, and a lot we want to learn," says lead author Idan Ginsburg of the Harvard-Smithsonian Center for Astrophysics (CfA). "Using this technique, we think we can find stars that no one has seen before."

The long path from the center of our galaxy to Earth is so choked with dust that out of every trillion photons of visible light coming our way, only one photon will reach our telescopes. Radio waves, from a different part of the electromagnetic spectrum, have lower energies and longer wavelengths. They can pass through the dust unimpeded.

On their own, stars aren’t bright enough in the radio for us to detect them at such distances. However, if a star is traveling through gas faster than the speed of sound, the situation changes. Material blowing off of the star as a stellar wind can plow into the interstellar gases and create a shock wave. And through a process called synchrotron radiation, electrons accelerated by that shock wave produce radio emission that we could potentially detect.

"In a sense, we're looking for the cosmic equivalent of a sonic boom from an airplane," explains Ginsburg.

To create a shock wave, the star would have to be moving at a speed of thousands of miles per second. This is possible in the galactic center since the stars there are influenced by the strong gravity of a supermassive black hole. When an orbiting star reaches its closest approach to the black hole, it can easily acquire the required speed.

The researchers suggest looking for this effect from one already known star called S2. This star, which is hot and bright enough to be seen in the infrared despite all the dust, will make its closest approach to the Galactic center in late 2017 or early 2018. When it does, radio astronomers can target it to look for radio emission from its shock wave.

"S2 will be our litmus test. If it's seen in the radio, then potentially we can use this method to find smaller and fainter stars – stars that can’t be seen any other way," says co-author Avi Loeb of the CfA.

This work is reported in a paper authored by Idan Ginsburg, Xiawei Wang, Avi Loeb, and Ofer Cohen (CfA). It has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

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:

Christine Pulliam
Media Relations Manager
Harvard-Smithsonian Center for Astrophysics