Discovering Dust-Obscured Active Galaxies as They Grow

Figure 1: Images of 3 DOG's. The left, middle, and right panels show optical image from HSC, near-infrared image from VIKING, and mid-infrared image from WISE, respectively. The image size is 20 square arcsecond (1 arcsecond is 1/3600 degree). It is clear that DOGs are faint in the optical, but are extremely bright in the infrared. (Credit: Ehime University/NAOJ/NASA/ESO) 

Figure 2: The number density of DOGs that were newly selected in this study, as a function of infrared luminosity. Data represented by the red star is the HSC result. The research team found that (i) their infrared luminosity exceeds 10 trillion suns, and (ii) their number density is about 300 per cubic gigaparsecs (1 gigaparsec is about 3×1025 meter). (Credit: Ehime University/NAOJ/NASA/ESO)

Abstract

A group of researchers from Ehime University, Princeton University, and the National Astronomical Observatory of Japan (NAOJ) among others has performed an extensive search for Dust Obscured Galaxies (DOGs) using data obtained from the Subaru Strategic Program with Hyper Suprime-Cam (HSC). HSC is a new wide-field camera mounted at the prime focus of the Subaru Telescope and is an ideal instrument for searching for this rare and important class of galaxy. The research group discovered 48 DOGs, and has measured how common they are. Since DOGs are thought to harbor a rapidly growing black hole in their centers, these results give us clues for understanding the evolution of galaxies and supermassive black holes.

 

Co-Evolution of Galaxies and Supermassive Black Holes

How did galaxies form and evolve during the 13.8-billion-year history of the universe? This question has been the subject of intense observational and theoretical investigation. Recent studies have revealed that almost all massive galaxies harbor a supermassive black hole whose mass reaches up to a hundred thousand or even a billion times the mass of the sun, and their masses are tightly correlated with those of their host galaxies. This correlation suggests that supermassive black holes and their host galaxies have evolved together, closely interacting as they grow.

Dust Obscured Galaxies

The group of researchers, lead by Dr. Yoshiki Toba (Ehime University), focused on the Dust Obscured Galaxies (DOGs) as a key population to tackle the mystery of the co-evolution of galaxies and black holes. DOGs are very faint in visible light, because of the large quantity of obscuring dust, but are bright in the infrared. The brightest infrared DOGs in particular are expected to harbor the most actively growing black hole. In addition, most DOGs are seen in the epoch when the star formation activity of galaxies reached its peak, 8-10 billion years ago. Thus both DOGs and their black holes are rapidly growing, at an early phase of their co-evolution. However, since DOGs are rare and are hidden behind significant amount of dust, previous visible light surveys have found very few such objects.

A Search for Dust Obscured Galaxies with HSC

Hyper Suprime-Cam (HSC) is a new instrument installed on the 8.2 meter Subaru Telescope in 2012. It is a wide-field camera with a field of view nine times the size of the full moon. An ambitious legacy survey with HSC started in March 2014 as a "Subaru strategic program (Note 1)"; total of 300 nights have been allocated for a five year period. The Subaru strategic program with HSC started to deliver large quantities of excellent imaging data.

The research team selected DOGs from early data from the HSC Subaru Strategic Program (SSP). DOGs are thousand times brighter in the infrared than the optical and the team selected their targets using the HSC and NASA's Wide-field Infrared Survey Explorer (WISE: Note 2). They also utilized the data from the VISTA Kilo-degree Infrared Galaxy survey (VIKING: Note 3). The all-sky survey data with WISE are crucial to discover spatially rare DOG while the VIKING data are useful to identify the DOGs more precisely.

Consequently, 48 DOGs were discovered. Each of these is 10 trillion times more luminous in the infrared than the sun. The number density of these luminous DOGs is about 300 per cubic gigaparsecs. It is theoretically predicted that these DOGs harbor an actively evolving supermassive black hole. This result provides researchers new insights into the mysteries of the co-evolution of galaxies and supermassive black holes from the unique observational prospects.

 

Summary and Future Prospects

In this research, the research team discovered 48 Dust Obscured Galaxies and revealed their statistical properties of infrared luminous DOGs in particular, for the first time.

The first author of the paper Dr. Yoshiki Toba said, "There are no instruments on large telescopes with the sensitivity and field of view of HSC, and hence HSC is unique in its ability to search for DOGs. The HSC survey will cover more than 100 times as much area of the sky as the area used for this study when it is complete, allowing the identification of thousands of DOGs in the near future. We are planning to investigate the detailed properties of DOGs and their central black holes using observations from many telescope."

Also, Professor Tohru Nagao, second author of the paper, said "The Subaru Strategic Program with HSC has just begun. In the near future, exciting results will be released not only from studies on galaxy evolution, but also from in fields such as solar systems, stars, nearby galaxies, and cosmology."

This research will be published on October 25, 2015 in the Publications of the Astronomical Society of Japan (PASJ) Subaru special issue (Toba et al. 2015, "Hyper-luminous Dust Obscured Galaxies discovered by the Hyper Suprime-Cam on Subaru and WISE", PASJ, Vol. 67, Issue. 5 ). Online version was posted on July 12, 2015. This work was supported from the Japan Society for the Promotion of Science (grant No. 25707010) and from the Yamada Science Foundation.

Notes:

1. In the Subaru Strategic Program, 300 nights have been allocated for five years in total. The superb resolution and sensitivity of these images enable us to find these rare and faint galaxies, to understand the growth and evolution of galaxies and black holes.
2. The Wide-field Infrared Survey Explorer (WISE) was launched by the National Aeronautics and Space Administration (NASA) in 2009. WISE performed an all-sky survey with high sensitivity in four bands (3.4, 4.6, 12, and 22 microns). WISE has observed over seven hundred million infrared sources so far.
3. The VISTA Kilo-degree Infrared Galaxy survey (VIKING) is performing a wide area near-infrared imaging survey with five broadband filters using the VISTA InfraRed Camera (VIRCAM) on the VISTA telescope operated by the European Southern Observatory (ESO).

Authors:

• Yoshiki Toba: Research Center for Space and Cosmic Evolution, Ehime University, Research Fellow
• Tohru Nagao: Research Center for Space and Cosmic Evolution, Ehime University, Professor
• Michael A. Strauss: Department of Astrophysical Sciences, Princeton University, Professor
• Kentaro Aoki: Subaru Telescope, National Astronomical Observatory of Japan, Subaru Support Astronomer
• Tomotsugu Goto: Institute of Astronomy and Department of Physics, National Tsing Hua University, Assistant professor
• Masatoshi Imanishi: Subaru Telescope, National Astronomical Observatory of Japan and SOKENDAI (Graduate University for Advanced Studies, Japan), Assistant professor
• Toshihiro Kawaguchi: Division of Physics, Sapporo Medical University, Lecturer
• Yuichi Terashima: Department of Physics, Ehime University, Professor
• Yoshihiro Ueda: Department of Astronomy, Graduate School of Science, Kyoto University, Associate Professor
• Satoshi Miyazaki: National Astronomical Observatory of Japan and SOKENDAI (Graduate University for Advanced Studies, Japan), Associate Professor and 24 other authors

Relevant Links:

• Dark Matter Map Begins to Reveal the Universe’s Early History (July 1, 2015 Subaru Telescope Press Release)
• Image of M31 Heralds the Dawn of HSC's Productivity (July 30, 2013 Subaru Telescope Press Release)
• Hyper Suprime-Cam Ushers in a New Era of Observational Astronomy (September 12, 2012 Subaru Telescope Press Release)
• Hyper Suprime Cam Project Website

Source: Subaru Telescope

Hubble Finds That the Nearest Quasar Is Powered by a Double Black Hole Artist's View of a Binary Black Hole

Artist's View of a Binary Black Hole

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

 Release Images

Optical-to-Ultraviolet Spectrum of Markarian 231

This simplified spectral plot shows the radiation emitted from the center of a nearby galaxy that hosts a quasar. Visible and infrared light coming from a disk surrounding a central black hole in the middle of the galaxy is measured. Surprisingly, ultraviolet light from the disk, as measured by the Hubble Space Telescope, shows a drop in radiation from the disk. This is evidence for a large gap in the center of the disk that is likely carved out by a second black hole orbiting the primary black hole. Credit: NASA, ESA, and P. Jeffries (STScI)

Astronomers using NASA's Hubble Space Telescope have found that Markarian 231 (Mrk 231), the nearest galaxy to Earth that hosts a quasar, is powered by two central black holes furiously whirling about each other.

The finding suggests that quasars — the brilliant cores of active galaxies — may commonly host two central supermassive black holes that fall into orbit about one another as a result of the merger between two galaxies. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars, which scientists then identify as quasars.

Scientists looked at Hubble archival observations of ultraviolet radiation emitted from the center of Mrk 231 to discover what they describe as "extreme and surprising properties."

If only one black hole were present in the center of the quasar, the whole accretion disk made of surrounding hot gas would glow in ultraviolet rays. Instead, the ultraviolet glow of the dusty disk abruptly drops off towards the center. This provides observational evidence that the disk has a big donut hole encircling the central black hole. The best explanation for the observational data, based on dynamical models, is that the center of the disk is carved out by the action of two black holes orbiting each other. The second, smaller black hole orbits in the inner edge of the accretion disk, and has its own mini-disk with an ultraviolet glow.

"We are extremely excited about this finding because it not only shows the existence of a close binary black hole in Mrk 231, but also paves a new way to systematically search binary black holes via the nature of their ultraviolet light emission," said Youjun Lu of the National Astronomical Observatories of China, Chinese Academy of Sciences.

"The structure of our universe, such as those giant galaxies and clusters of galaxies, grows by merging smaller systems into larger ones, and binary black holes are natural consequences of these mergers of galaxies," added co-investigator Xinyu Dai of the University of Oklahoma.

The central black hole is estimated to be 150 million times the mass of our sun, and the companion weighs in at 4 million solar masses. The dynamic duo completes an orbit around each other every 1.2 years.

The lower-mass black hole is the remnant of a smaller galaxy that merged with Mrk 231. Evidence of a recent merger comes from the host galaxy's asymmetry, and the long tidal tails of young blue stars.

The result of the merger has been to make Mrk 231 an energetic starburst galaxy with a star-formation rate 100 times greater than that of our Milky Way galaxy. The infalling gas fuels the black hole "engine," triggering outflows and gas turbulence that incites a firestorm of star birth.

The binary black holes are predicted to spiral together and collide within a few hundred thousand years.

Mrk 231 is located 581 million light-years away.

The results were published in the August 14, 2015, edition of The Astrophysical Journal.

Contact 

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Jana Smith
University of Oklahoma, Norman, Ok.
405-325-1701
jana.smith@ou.edu

Xinyu Dai
University of Oklahoma, Norman, Ok.
405-325-3961
xdai@ou.edu

Source: HubbleSite

A youthful cluster

NGC 1783

Credit: ESA/Hubble & NASA

Acknowledgement: Judy Schmidt (geckzilla.com)

Shown here in a new image taken with the Advanced Camera for Surveys (ACS) on board the NASA/ESA Hubble Space Telescope, is the globular cluster NGC 1783. This is one of the biggest globular clusters in the Large Magellanic Cloud, a satellite galaxy of our own galaxy, the Milky Way, in the southern hemisphere constellation of Dorado.

First observed by John Herschel in 1835, NGC 1783 is nearly 160 000 light-years from Earth, and has a mass around 170 000 times that of the Sun.

Globular clusters are dense collections of stars held together by their own gravity, which orbit around galaxies like satellites. The image clearly shows the symmetrical shape of NGC 1783 and the concentration of stars towards the centre, both typical features of globular clusters.

By measuring the colour and brightness of individual stars, astronomers can deduce an overall age for a cluster and a picture of its star formation history. NGC 1783 is thought to be under one and a half billion years old — which is very young for globular clusters, which are typically several billion years old. During that time, it is thought to have undergone at least two periods of star formation, separated by 50 to 100 million years.

This ebb and flow of star-forming activity is an indicator of how much gas is available for star formation at any one time. When the most massive stars created in the first burst of formation explode as supernovae they blow away the gas needed to form further stars, but the gas reservoir can later be replenished by less massive stars which last longer and shed their gas less violently. After this gas flows to the dense central regions of the star cluster, a second phase of star formation can take place and once again the short-lived massive stars blow away any leftover gas. This cycle can continue a few times, at which time the remaining gas reservoir is thought to be too small to form any new stars.

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

Source: ESA/Hubble - Space Telescope

Abell 1033: Chandra Data Suggest Giant Collision Triggered "Radio Phoenix"

 Abell 1033
Credit  X-ray: NASA/CXC/Univ of Hamburg/F. de Gasperin et al; 
Optical: SDSS; Radio: NRAO/VLA 

JPEG (574.7 kb) - Large JPEG (5.6 MB) - Tiff (16.5 MB) - More Images - View on the Sky (WWT)

A Tour of NGC 5813
 

Astronomers have found evidence for a faded electron cloud "coming back to life," much like the mythical phoenix, after two galaxy clusters collided. This "radio phoenix," so-called because the high-energy electrons radiate primarily at radio frequencies, is found in Abell 1033. The system is located about 1.6 billion light years from Earth.

By combining data from NASA's Chandra X-ray Observatory, the Westerbork Synthesis Radio Telescope in the Netherlands, NSF's Karl Jansky Very Large Array (VLA), and the Sloan Digital Sky Survey (SDSS), astronomers were able to recreate the scientific narrative behind this intriguing cosmic story of the radio phoenix.

Galaxy clusters are the largest structures in the Universe held together by gravity. They consist of hundreds or even thousands of individual galaxies, unseen dark matter, and huge reservoirs of hot gas that glow in X-ray light. Understanding how clusters grow is critical to tracking how the Universe itself evolves over time.

Astronomers think that the supermassive black hole close to the center of Abell 1033 erupted in the past. Streams of high-energy electrons filled a region hundreds of thousands of light years across and produced a cloud of bright radio emission. This cloud faded over a period of millions of years as the electrons lost energy and the cloud expanded.

The radio phoenix emerged when another cluster of galaxies slammed into the original cluster, sending shock waves through the system. These shock waves, similar to sonic booms produced by supersonic jets, passed through the dormant cloud of electrons. The shock waves compressed the cloud and re-energized the electrons, which caused the cloud to once again shine at radio frequencies.

A new portrait of this radio phoenix is captured in this multi wavelength image of Abell 1033. X-rays from Chandra are in pink and radio data from the VLA are colored green. The background image shows optical observations from the SDSS. A map of the density of galaxies, made from the analysis of optical data, is seen in blue. Mouse over the image above to see the location of the radio phoenix.

The Chandra data show hot gas in the clusters, which seems to have been disturbed during the same collision that caused the re-ignition of radio emission in the system. The peak of the X-ray emission is seen to the south (bottom) of the cluster, perhaps because the dense core of gas in the south is being stripped away by surrounding gas as it moves. The cluster in the north may not have entered the collision with a dense core, or perhaps its core was significantly disrupted during the merger. On the left side of the image, a so-called wide-angle tail radio galaxy shines in the radio. The lobes of plasma ejected by the supermassive black hole in its center are bent by the interaction with the cluster gas as the galaxy moves through it.

Astronomers think they are seeing the radio phoenix soon after it had reborn, since these sources fade very quickly when located close to the center of the cluster, as this one is in Abell 1033. Because of the intense density, pressure, and magnetic fields near the center of Abell 1033, a radio phoenix is only expected to last a few tens of millions of years.

A paper describing these results was published in a recent issue of the Monthly Notices of the Royal Astronomical Society and a preprint is available online. The authors are Francesco de Gasperin from the University of Hamburg, Germany; Georgiana Ogrean and Reinout van Weeren from the Harvard-Smithsonian Center for Astrophysics; William Dawson from the Lawrence Livermore National Lab in Livermore, California; Marcus Brüggen and Annalisa Bonafede from the University of Hamburg, Germany, and Aurora Simionescu from the Japan Aerospace Exploration Agency in Sagamihara, Japan.

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 Abell 1033:

Scale: Image is about 17 arcmin across (about 7.5 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 10h 31m 33.70s | Dec +35° 04' 33.96"
Constellation: Leo Minor
Observation Date: 19 and 21 Feb 2013
Observation Time: 17 hours 35 min.
Obs. ID: 15084, 15614
Instrument: ACIS
References: de Gasperin, F. et al, 2015, MNRAS (accepted); arXiv:1501.00043
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Radio (Green); Density Map (Blue)
Distance Estimate: About 1.62 billion light years (z=0.1259)

Source: NASA’s Chandra X-ray Observatory

The night sky around the Twin Jet Nebula (ground-based image)

PR Image heic1518a

The Twin Jet Nebula

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The night sky around the Twin Jet Nebula (ground-based image)

Videos

PR Video heic1518a

Hubblecast 86: The wings of the Twin Jet Nebula

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Zooming in on the Twin Jet Nebula

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Panning across the Twin Jet Nebula

The shimmering colours visible in this NASA/ESA Hubble Space Telescope image show off the remarkable complexity of the Twin Jet Nebula. The new image highlights the nebula’s shells and its knots of expanding gas in striking detail. Two iridescent lobes of material stretch outwards from a central star system. Within these lobes two huge jets of gas are streaming from the star system at speeds in excess of one million kilometres per hour.

The cosmic butterfly pictured in this NASA/ESA Hubble Space Telescope image goes by many names. It is called the Twin Jet Nebula as well as answering to the slightly less poetic name of PN M2-9.

The M in this name refers to Rudolph Minkowski, a German-American astronomer who discovered the nebula in 1947. The PN, meanwhile, refers to the fact that M2-9 is a planetary nebula. The glowing and expanding shells of gas clearly visible in this image represent the final stages of life for an old star of low to intermediate mass. The star has not only ejected its outer layers, but the exposed remnant core is now illuminating these layers — resulting in a spectacular light show like the one seen here. However, the Twin Jet Nebula is not just any planetary nebula, it is a bipolar nebula.

Ordinary planetary nebulae have one star at their centre, bipolar nebulae have two, in a binary star system.

Astronomers have found that the two stars in this pair each have around the same mass as the Sun, ranging from 0.6 to 1.0 solar masses for the smaller star, and from 1.0 to 1.4 solar masses for its larger companion. The larger star is approaching the end of its days and has already ejected its outer layers of gas into space, whereas its partner is further evolved, and is a small white dwarf.

The characteristic shape of the wings of the Twin Jet Nebula is most likely caused by the motion of the two central stars around each other. It is believed that a white dwarf orbits its partner star and thus the ejected gas from the dying star is pulled into two lobes rather than expanding as a uniform sphere. However, astronomers are still debating whether all bipolar nebulae are created by binary stars. Meanwhile the nebula’s wings are still growing and, by measuring their expansion, astronomers have calculated that the nebula was created only 1200 years ago.

Within the wings, starting from the star system and extending horizontally outwards like veins are two faint blue patches. Although these may seem subtle in comparison to the nebula’s rainbow colours, these are actually violent twin jets streaming out into space, at speeds in excess of one million kilometres per hour. This is a phenomenon that is another consequence of the binary system at the heart of the nebula. These jets slowly change their orientation, precessing across the lobes as they are pulled by the wayward gravity of the binary system.

The two stars at the heart of the nebula circle one another roughly every 100 years. This rotation not only creates the wings of the butterfly and the two jets, it also allows the white dwarf to strip gas from its larger companion, which then forms a large disc of material around the stars, extending out as far as 15 times the orbit of Pluto! Even though this disc is of incredible size, it is much too small to be seen on the image taken by Hubble.

An earlier image of the Twin Jet Nebula using data gathered by Hubble’s Wide Field Planetary Camera 2 was released in 1997. This newer version incorporates more recent observations from the telescope’s Space Telescope Imaging Spectrograph (STIS).

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition, submitted by contestant Judy Schmidt.

Notes

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

More Information

Image credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt

Links

• Images of Hubble
• PN M2-9 image from 1997
• Judy Schmidt’s image on Flickr

Contacts

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source:  ESA/HUBBLE - Space Telescope

IRIS and Hinode: A Stellar Research Team

This image taken on Oct. 19, 2013, shows a filament on the sun – a giant ribbon of relatively cool solar material threading through the sun's atmosphere, the corona. The individual threads that make up the filament are clearly discernible in this photo. This image was captured by the Solar Optical Telescope onboard JAXA/NASA’s Hinode solar observatory. Researchers studied this filament to learn more about material gets heated in the corona. Credits: JAXA/NASA/Hinode

A filament stretches across the lower half of the sun in this image captured by NASA’s Solar Dynamics Observatory on Feb. 10, 2015. Filaments are huge tubes of relatively cool solar material held high up in the corona by magnetic fields. Researchers simulated how the material moves in filament threads to explore how a particular type of motion could contribute to the extremely hot temperatures in the sun’s upper atmosphere, the corona.Credits: NASA/SDO

This is a simulation of a cross-section of a thread of solar material, called a filament, hovering in the sun's atmosphere. The yellow area is the thread itself, where the material is denser, and the black area is the surrounding, less dense material. The characteristic wave motion leads to complex turbulence around the edges of the yellow thread, which heats the surrounding black material. This model was created with the Aterui supercomputer at the Center for Computational Astrophysics at the National Astronomical Observatory of Japan.Credits: NAOJ/Patrick Antolin

Modern telescopes and satellites have helped us measure the blazing hot temperatures of the sun from afar. Mostly the temperatures follow a clear pattern: The sun produces energy by fusing hydrogen in its core, so the layers surrounding the core generally get cooler as you move outwards—with one exception. Two NASA missions have just made a significant step towards understanding why the corona—the outermost, wispy layer of the sun's atmosphere —is hundreds of times hotter than the lower photosphere, which is the sun’s visible surface.

In a pair of papers in The Astrophysical Journal, published on August 10, 2015, researchers—led by Joten Okamoto of Nagoya University in Japan and Patrick Antolin of the National Astronomical Observatory of Japan—observed a long-hypothesized mechanism for coronal heating, in which magnetic waves are converted into heat energy. Past papers have suggested that magnetic waves in the sun -- Alfvénic waves – have enough energy to heat up the corona. The question has been how that energy is converted to heat.

"For over 30 years scientists hypothesized a mechanism for how these waves heat the plasma," said Antolin. "An essential part of this process is called resonant absorption  -- and we have now directly observed resonant absorption for the first time."

Resonant absorption is a complicated wave process in which repeated waves add energy to the solar material, a charged gas known as plasma, the same way that a perfectly-timed repeated push on a swing can make it go higher. Resonant absorption has signatures that can be seen in material moving side to side and front to back.

To see the full range of motions, the team used observations from NASA’s Interface Region Imaging Spectrograph, or IRIS, and the Japan Aerospace Exploration Agency (JAXA)/NASA’s Hinode solar observatory to successfully identify signatures of the process. The researchers then correlated the signatures to material being heated to nearly corona-level temperatures. These observations told researchers that a certain type of plasma wave was being converted into a more turbulent type of motion, leading to lots of friction and electric currents, heating the solar material.

The researchers focused on a solar feature called a filament. Filaments are huge tubes of relatively cool plasma held high up in the corona by magnetic fields. Researchers developed a computer model of how the material inside filament tubes moves, then looked for signatures of these motions with sun-observing satellites.

“Through numerical simulations, we show that the observed characteristic motion matches well what is expected from resonant absorption,” said Antolin.

The signatures of these motions appear in three dimensions, making them difficult to observe without the teamwork of several missions. Hinode’s Solar Optical Telescope was used to make measurements of motions that appear, from our perspective, to be up-and-down or side-to-side, a perspective that scientists call plane-of-sky. The resonant absorption model relies on the fact that the plasma contained in a filament tube moves in a specific wave motion called an Alfvénic kink wave, caused by magnetic fields. Alfvénic kink waves in filaments can cause motions in the plane-of-sky, so evidence of these waves came from observations by Hinode’s extremely high-resolution optical telescope.

More complicated were the line-of-sight observations—line-of-sight means motions in the third dimension, toward and away from us. The resonant absorption process can convert the Alfvénic kink wave into another Alfvénic wave motion. To see this conversion process we need to simultaneously observe motions in the plane-of-the-sky and the line-of-sight direction. This is where IRIS comes in. IRIS takes a special type of data called spectra. For each image taken by IRIS’s ultraviolet telescope, it also creates a spectrum, which breaks down the light from the image into different wavelengths.

Analyzing separate wavelengths can provide scientists with additional details such as whether the material is moving toward or away from the viewer. Much like a siren moving toward you sounds different from one moving away, light waves can become stretched or compressed if their source is moving toward or away from an observer. This slight change in wavelength is known as the Doppler effect. Scientists combined their knowledge of the Doppler effect with the expected emissions from a stationary filament to deduce how the filaments were moving in the line-of-sight.

“It’s the combination of high-resolution observations in all three regimes—time, spatial, and spectral—that enabled us to see these previously unresolved phenomena,” said Adrian Daw, mission scientist for IRIS at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Using both the plane-of-sky observations from Hinode and line-of-sight observations from IRIS, researchers discovered the characteristic wave motions consistent with their model of this possible coronal heating mechanism. What's more, they also observed material heating up in conjunction with the wave motions, further confirming that this process is related to heating in the solar atmosphere.

“We would see the filament thread disappear from the filter that is sensitive to cool plasma and reappear in a filter for hotter plasma,” said Bart De Pontieu, science lead for IRIS at Lockheed Martin Solar and Astrophysics Lab in Palo Alto, California.

In addition, comparison of the two wave motions, showed a time delay, known as a phase difference. The researchers’ model predicted this phase difference, thus providing some of the strongest evidence that the team was correctly understanding their observations.

Though resonant absorption plays a key role in the complete process, it does not directly cause heating. The researchers’ simulation showed that the transformed wave motions lead to turbulence around the edges of the filament tubes, which heats the surrounding plasma.

It seems that resonant absorption is an excellent candidate for the role of an energy transport mechanism—though these observations were taken in the transition region rather than the corona, researchers believe that this mechanism could be common in the corona as well.

“Now the work starts to study if this mechanism also plays a role in heating plasma to coronal temperatures,” said De Pontieu.

With the launch of over a dozen missions in the past twenty years, our understanding of the sun and how it interacts with Earth and the solar system is better than at any time in human history. Heliophysics System Observatory missions are working together to unravel the coronal heating problem and the sun’s other remaining mysteries.

Led by the Japan Aerospace Exploration Agency, the Hinode mission is a collaboration between the space agencies of Japan, the United States, the United Kingdom and Europe. IRIS is a NASA Small Explorer; NASA Goddard manages the Explorer Program for NASA's Science Mission Directorate in Washington. Lockheed Martin designed the IRIS observatory and manages the mission for NASA.

Related Links 

• For more on IRIS   
• For more on Hinode

Sarah Frazier
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Source: NASA/Hinode

Gaia's first year of scientific observations

Stellar density map

Copyright: ESA/Gaia – CC BY-SA 3.0 IGO

Last Friday, 21 August, ESA’s billion-star surveyor, Gaia, completed its first year of science observations in its main survey mode. 

After launch on 19 December 2013 and a six-month long in-orbit commissioning period, the satellite started routine scientific operations on 25 July 2014. Located at the Lagrange point L2, 1.5 million km from Earth, Gaia surveys stars and many other astronomical objects as it spins, observing circular swathes of the sky. By repeatedly measuring the positions of the stars with extraordinary accuracy, Gaia can tease out their distances and motions through the Milky Way galaxy. 

For the first 28 days, Gaia operated in a special scanning mode that sampled great circles on the sky, but always including the ecliptic poles. This meant that the satellite observed the stars in those regions many times, providing an invaluable database for Gaia’s initial calibration.

At the end of that phase, on 21 August 2014, Gaia commenced its main survey operation, employing a scanning law designed to achieve the best possible coverage of the whole sky.

Since the start of its routine phase, the satellite recorded 272 billion positional or astrometric measurements 54.4 billion brightness or photometric data points, and 5.4 billion spectra.

The Gaia team have spent a busy year processing and analysing these data, en route towards the development of Gaia’s main scientific products, consisting of enormous public catalogues of the positions, distances, motions and other properties of more than a billion stars. Because of the immense volumes of data and their complex nature, this requires a huge effort from expert scientists and software developers distributed across Europe, combined in Gaia’s Data Processing and Analysis Consortium (DPAC).

“The past twelve months have been very intense, but we are getting to grips with the data, and are looking forward to the next four years of nominal operations,” says Timo Prusti, Gaia project scientist at ESA. “We are just a year away from Gaia's first scheduled data release, an intermediate catalogue planned for the summer of 2016. With the first year of data in our hands, we are now halfway to this milestone, and we’re able to present a few preliminary snapshots to show that the spacecraft is working well and that the data processing is on the right track.”

 The parallax method of measuring a star's distance
Copyright: ESA/Medialab

As one example of the ongoing validation, the Gaia team has been able to measure the parallax for an initial sample of two million stars.

Parallax is the apparent motion of a star against a distant background observed over the period of a year and resulting from the Earth's real motion around the Sun; this is also observed by Gaia as it orbits the Sun alongside Earth. But parallax is not the only movement seen by Gaia: the stars are also really moving through space, which is called proper motion.

Gaia has made an average of roughly 14 measurements of each star on the sky thus far, but this is generally not enough to disentangle the parallax and proper motions.

To overcome this, the scientists have combined Gaia data with positions extracted from the Tycho-2 catalogue, based on data taken between 1989 and 1993 by Gaia's predecessor, the Hipparcos satellite.

This restricts the sample to just two million out of the more than one billion that Gaia has observed so far, but yields some useful early insights into the quality of its data.

The nearer a star is to the Sun, the larger its parallax, and thus the parallax measured for a star can be used to determine its distance. In turn, the distance can be used to convert the apparent brightness of the star into its true brightness or ‘absolute luminosity’.

Astronomers plot the absolute luminosities of stars against their temperatures – which are estimated from the stars' colours – to generate a ‘Hertzsprung-Russell diagram’, named for the two early 20th century scientists who recognised that such a diagram could be used as a tool to understand stellar evolution. 

Gaia's first Hertzsprung-Russell diagram

Copyright: ESA/Gaia/DPAC/IDT/FL/DPCE/AGIS

“Our first Hertzsprung-Russell diagram, with absolute luminosities based on Gaia’s first year and the Tycho-2 catalogue, and colour information from ground-based observations, gives us a taste of what the mission will deliver in the coming years,” says Lennart Lindegren, professor at the University of Lund and one of the original proposers of the Gaia mission.

As Gaia has been conducting its repeated scans of the sky to measure the motions of stars, it has also been able to detect whether any of them have changed their brightness, and in doing so, has started to discover some very interesting astronomical objects.

Gaia has detected hundreds of transient sources so far, with a supernova being the very first on 30 August 2014. These detections are routinely shared with the community at large as soon as they are spotted in the form of ‘Science Alerts’, enabling rapid follow-up observations to be made using ground-based telescopes in order to determine their nature.

One transient source was seen undergoing a sudden and dramatic outburst that increased its brightness by a factor of five. It turned out that Gaia had discovered a so-called ‘cataclysmic variable’, a system of two stars in which one, a hot white dwarf, is devouring mass from a normal stellar companion, leading to outbursts of light as the material is swallowed. The system also turned out to be an eclipsing binary, in which the relatively larger normal star passes directly in front of the smaller, but brighter white dwarf, periodically obscuring the latter from view as seen from Earth.

Unusually, both stars in this system seem to have plenty of helium and little hydrogen. Gaia’s discovery data and follow-up observations may help astronomers to understand how the two stars lost their hydrogen.

The Cat's Eye Nebula

Copyright: NASA/ESA/HEIC/The Hubble Heritage Team/STScI/AURA (background image); 

ESA/Gaia/DPAC/UB/IEEC (blue points)

Gaia has also discovered a multitude of stars whose brightness undergoes more regular changes over time. Many of these discoveries were made between July and August 2014, as Gaia performed many subsequent observations of a few patches of the sky close to the ecliptic poles. This closely sampled sequence of observations made it possible to find and study variable stars located in these regions.

Located close to the south ecliptic pole is the famous Large Magellanic Cloud (LMC), a dwarf galaxy and close companion of our own galaxy, the Milky Way. Gaia has delivered detailed light curves for dozens of RR Lyrae type variable stars in the LMC, and the fine details revealed in them testify to the very high quality of the data. 

Another curious object covered during the same mission phase is the Cat’s Eye Nebula, a planetary nebula also known as NGC 6543, which lies close to the north ecliptic pole.

Planetary nebulae are formed when the outer layers of an aging low-mass star are ejected and interact with the surrounding interstellar medium, leaving behind a compact white dwarf. Gaia made over 200 observations of the Cat’s Eye Nebula, and registered over 84 000 detections that accurately trace out the intricate gaseous filaments that such objects are famous for. As its observations continue, Gaia will be able to see the expansion of the nebular knots in this and other planetary nebulae.  

Gaia's asteroid detections

Copyright: ESA/Gaia/DPAC/CU4, L. Galluccio, F. Mignard, P. Tanga (Observatoire de la Côte d'Azur)

Closer to home, Gaia has detected a wealth of asteroids, the small rocky bodies that populate our solar system, mainly between the orbits of Mars and Jupiter. Because they are relatively nearby and orbiting the Sun, asteroids appear to move against the stars in astronomical images, appearing in one snapshot of a given field, but not in images of the same field taken at later times. 

Gaia scientists have developed special software to look for these ‘outliers’, matching them with the orbits of known asteroids in order to remove them from the data being used to study stars. But in turn, this information will be used to characterise known asteroids and to discover thousands of new ones. 

Finally, in addition to the astrometric and photometric measurements being made by Gaia, it has been collecting spectra for many stars. The basic use of these data is to determine the motions of the stars along the line-of-sight by measuring slight shifts in the positions of absorption lines in their spectra due to the Doppler shift. But in the spectra of some hot stars, Gaia has also seen absorption lines from gas in foreground interstellar material, which will allow the scientists to measure its distribution. 

 “These early proof-of-concept studies demonstrate the quality of the data collected with Gaia so far and the capabilities of the processing pipeline. The final data products are not quite ready yet, but we are working hard to provide the first of them to the community next year. Watch this space,” concludes Timo.

About Gaia

Gaia is an ESA mission to survey one billion stars in our galaxy and local galactic neighbourhood in order to build the most precise 3D map of the Milky Way and answer questions about its origin and evolution.

The mission’s primary scientific product will be a catalogue with the positions, motions, brightnesses, and colours of the surveyed stars. An intermediate version of the catalogue will be released in 2016. In the meantime, Gaia's observing strategy, with repeated scans of the entire sky, is allowing the discovery and measurement of many transient events across the sky, which are shared with the community at large in the form of Science Alerts.

The nature of the Gaia mission leads to the acquisition of an enormous quantity of complex, extremely precise data, and the data-processing challenge is a huge task in terms of expertise, effort and dedicated computing power. A large pan-European team of expert scientists and software developers, the Data Processing and Analysis Consortium (DPAC), located in and funded by many ESA member states, is responsible for the processing and validation of Gaia's data, with the final objective of producing the Gaia Catalogue. Scientific exploitation of the data will only take place once they are openly released to the community.

For further information, please contact:

Markus Bauer 



ESA Science and Robotic Exploration Communication Officer




Tel: +31 71 565 6799





Mob: +31 61 594 3 954





Email: markus.bauer@esa.int




Timo Prusti



Gaia Project Scientist


Email: timo.prusti@esa.int

Source: ESA/GAIA

Feathery filaments in Mon R2

Feathery filaments in Mon R2

Copyright: ESA/Herschel/PACS/SPIRE/HOBYS Key Programme consortium
Hi-res JPJ - Hi-res TIF

Fierce flashes of light ripple through delicate tendrils of gas in this new image, from ESA’s Herschel space observatory, which shows the dramatic heart of a large and dense cosmic cloud known as Mon R2. This cloud lies some 2700 light-years away and is studded with hot, newly-formed stars.

Packed into the bright centre of this region are several hot ‘bubbles’ of ionised hydrogen, associated with newborn stars situated nearby. Here, gas heated to a temperature of 10 000 °C quickly expands outwards, inflating and enlarging over time. Herschel has explored the bubbles in Mon R2, finding them to have grown over the course of 100 000 to 350 000 years.

This process forms bubble-like cavities that lie within the larger Mon R2 cloud. These are known as HII regions and Mon R2 hosts four of them, clustered together in the central blue-white haze of bright light — one at the very centre, two stretching out like butterfly wings to the top left and bottom right, and another sitting just above the centre.

Each is associated with a different hot and luminous B-type star. These stars can be many times the mass of the Sun and usually appear with a blue hue due to their high temperature.

Astronomers have found that the hot bubbles in Mon R2 are enveloped by vast clouds of cold, dense gas, sitting within the filaments that stretch across the frame. In stark contrast to the gas in the hot bubbles, these clouds can be at temperatures as low as –260 °C, just above absolute zero.

This particular cluster of HII regions has been studied as part of the Herschel imaging survey of OB young stellar objects, or HOBYS, programme. This image combines multiple Herschel observations obtained with the PACS and SPIRE cameras and has been processed to highlight the cloud’s clumpy complex of filaments, visible here in great and dramatic detail.

Source: ESA

Interstellar Seeds Could Create Oases of Life

In this theoretical artist's conception of the Milky Way galaxy, translucent green "bubbles" mark areas where life has spread beyond its home system to create cosmic oases, a process called panspermia. New research suggests that we could detect the pattern of panspermia, if it occurs. Credit: NASA/JPL/R. Hurt. High Resolution (jpg) -Low Resolution (jpg)

We only have one example of a planet with life: Earth. But within the next generation, it should become possible to detect signs of life on planets orbiting distant stars. If we find alien life, new questions will arise. For example, did that life arise spontaneously? Or could it have spread from elsewhere? If life crossed the vast gulf of interstellar space long ago, how would we tell?

New research by Harvard astrophysicists shows that if life can travel between the stars (a process called panspermia), it would spread in a characteristic pattern that we could potentially identify.

"In our theory clusters of life form, grow, and overlap like bubbles in a pot of boiling water," says lead author Henry Lin of the Harvard-Smithsonian Center for Astrophysics (CfA).

There are two basic ways for life to spread beyond its host star. The first would be via natural processes such as gravitational slingshotting of asteroids or comets. The second would be for intelligent life to deliberately travel outward. The paper does not deal with how panspermia occurs. It simply asks: if it does occur, could we detect it? In principle, the answer is yes.

The model assumes that seeds from one living planet spread outward in all directions. If a seed reaches a habitable planet orbiting a neighboring star, it can take root. Over time, the result of this process would be a series of life-bearing oases dotting the galactic landscape.

"Life could spread from host star to host star in a pattern similar to the outbreak of an epidemic. In a sense, the Milky Way galaxy would become infected with pockets of life," explains CfA co-author Avi Loeb.

If we detect signs of life in the atmospheres of alien worlds, the next step will be to look for a pattern. For example, in an ideal case where the Earth is on the edge of a "bubble" of life, all the nearby life-hosting worlds we find will be in one half of the sky, while the other half will be barren.

Lin and Loeb caution that a pattern will only be discernible if life spreads somewhat rapidly. Since stars in the Milky Way drift relative to each other, stars that are neighbors now won't be neighbors in a few million years. In other words, stellar drift would smear out the bubbles.

This research has been accepted for publication in The Astrophysical Journal Letters.

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
617-495-7463
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

Colorful Calendar Celebrates 12th Anniversary of NASA's Spitzer

NASA's Spitzer Space Telescope is celebrating 12 years in space with a new digital calendar. The calendar's 12 images are shown here. Image credit: NASA/JPL-Caltech.  › Larger image 

Spitzer Scores of baby stars shrouded by dust are revealed in this infrared image of the star-forming region NGC 2174, as seen by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech.  › Full image and caption

Celebrate the 12th anniversary of NASA's Spitzer Space Telescope with a new digital calendar showcasing some of the mission's most notable discoveries and popular cosmic eye candy.

The digital calendar is online at: http://www.jpl.nasa.gov/images/spitzer/20150820/Spitzer12thAnniversaryCalendar.pdf

The calendar follows the life of the mission, with each month highlighting top infrared images and discoveries from successive years -- everything from a dying star resembling the eye of a monster to a star-studded, swirling galaxy. The final month includes a brand new image of the glittery star-making factory known as the Monkey Head nebula.

"You can't fully represent Spitzer's scientific bounty in only 12 images," said Michael Werner of NASA's Jet Propulsion Laboratory in Pasadena, California, the mission's project scientist and a Spitzer team member since 1977. "But these gems demonstrate Spitzer's unique perspectives on both the nearest, and the most distant, objects in the universe."

Spitzer, which launched into space on August 25, 2003, from Cape Canaveral, Florida, is still going strong. It continues to use its ultra-sensitive infrared vision to probe asteroids, comets, exoplanets (planets outside our solar system) and some of the farthest known galaxies. Recently, Spitzer helped discover the closest known rocky exoplanet to us, named HD219134b, at 21 light-years away.

In fact, Spitzer's exoplanet studies continue to surprise the astronomy community. The telescope wasn't originally designed to study exoplanets, but as luck -- and some creative engineering -- would have it, Spitzer has turned out to be a critical tool in the field, probing the climates and compositions of these exotic worlds. This pioneering work began in 2005, when Spitzer became the first telescope to detect light from an exoplanet.

Other top discoveries from the mission so far include:

-- Recipe for "comet soup." Spitzer observed the aftermath of the collision between NASA's Deep Impact spacecraft and comet Tempel 1, finding that cometary material in our own solar system resembles that around nearby stars.

-- The largest known ring around Saturn, a wispy, fine structure with 300 times the diameter of Saturn.

-- First exoplanet weather map of temperature variations over the surface of a gas exoplanet. Results suggested the presence of fierce winds.

-- Asteroid and planetary smashups. Spitzer has found evidence for several rocky collisions in other solar systems, including one thought to involve two large asteroids.

-- The hidden lairs of newborn stars. Spitzer's infrared images have provided unprecedented views into the hidden cradles where young stars grow up, revolutionizing our understanding of stellar birth.

-- Buckyballs in space. Buckyballs are soccer-ball-shaped carbon molecules that have important technological applications on Earth.

-- One of the most remote planets known, lying about 13,000 light-years away, deep within our galaxy. Spitzer continues to help in the search for exoplanets using a state-of-the-art method called microlensing.

-- Massive clusters of galaxies. Spitzer has identified many more distant galaxy clusters than were previously known.

-- "Big baby" galaxies. Spitzer and Hubble has found remote galaxies that were much more massive and mature than expected.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit:  http://www.nasa.gov/spitzer - http://spitzer.caltech.edu

Media Contact

Elizabeth Landau / Whitney Clavin
818-354-6425 / 818-354-4673
Jet Propulsion Laboratory, Pasadena, California
elizabeth.landau@jpl.nasa.gov / whitney.clavin@jpl.nasa.gov 

Source: JPL-Caltech

A cosmic couple

Hen 2-427

Credit:ESA/Hubble & NASA
Acknowledgement: Judy Schmidt (geckzilla.com)

Here we see the spectacular cosmic pairing of the star Hen 2-427 — more commonly known as WR 124 — and the nebula M1-67 which surrounds it. Both objects, captured here by the NASA/ESA Hubble Space Telescope are found in the constellation of Sagittarius and lie 15 000 light-years away.

The star Hen 2-427 shines brightly at the very centre of this explosive image and around the hot clumps of gas are ejected into space at over 150 000 kilometres per hour.

Hen 2-427 is a Wolf–Rayet star, named after the astronomers Charles Wolf and Georges Rayet. Wolf–Rayet are super-hot stars characterised by a fierce ejection of mass.

The nebula M1-67 is estimated to be no more than 10 000 years old — just a baby in astronomical terms — but what a beautiful and magnificent sight it makes.

A version of this image was released in 1998, but has now been re-reduced with the latest software.

Source: ESA/Hubble - Space Telescope

The tumultuous heart of our Galaxy

X-ray view of the Galactic Centre
Copyright: ESA/XMM-Newton/G. Ponti et al. 2015 
Hi-res JPG - Hi-res TIF

The Galactic Centre through the emission of heavy elements
Copyright: ESA/XMM-Newton/G. Ponti et al. 2015

Hi-res JPG - Hi-res TIF

This new image of powerful remnants of dead stars and their mighty action on the surrounding gas from ESA's XMM-Newton X-ray observatory reveals some of the most intense processes taking place at the centre of our galaxy, the Milky Way.

The bright, point-like sources that stand out across the image trace binary stellar systems in which one of the stars has reached the end of its life, evolving into a compact and dense object – a neutron star or black hole. 

Because of their high densities, these compact remnants devour mass from their companion star, heating the material up and causing it to shine brightly in X-rays.

The central region of our galaxy also contains young stars and stellar clusters, and some of these are visible as white or red sources sprinkled throughout the image, which spans about one thousand light-years.

Most of the action is occurring at the centre, where diffuse clouds of gas are being carved by powerful winds blown by young stars, as well as by supernovas, the explosive demise of massive stars.

The supermassive black hole sitting at the centre of the Galaxy is also responsible for some of this action. Known as Sagittarius A*, this black hole has a mass a few million times that of our Sun, and it is located within the bright, fuzzy source to the right of the image centre.

While black holes themselves do not emit light, their immense gravitational pull draws in the surrounding matter that, in the process, emits light at many wavelengths, most notably X-rays. In addition, two lobes of hot gas can be seen extending above and below the black hole.

Astronomers believe that these lobes are caused either directly by the black hole, which swallows part of the material that flows onto it but spews out most of it, or by the cumulative effect of the numerous stellar winds and supernova explosions that occur in such a dense environment.

This image, showing us an unprecedented view of the Milky Way's energetic core, was put together in a new study by compiling all observations of this region that were performed with XMM-Newton, adding up to about one and a half months of monitoring in total. 

he large, elliptical structure to the lower right of Sagittarius A* is a super-bubble of hot gas, likely puffed up by the remnants of several supernovas at its centre. While this structure was already known to astronomers, this study confirms for the first time that it consists of a single, gigantic bubble rather than the superposition of several, individual supernova remnants along the line of sight.

Another huge pocket of hot gas, designated the 'Arc Bubble' due to its crescent-like shape, can be seen close to the image centre, to the lower left of the supermassive black hole. It is being inflated by the forceful winds of stars in a nearby stellar cluster, as well as by supernovae; the remnant of one of these explosions, a candidate pulsar wind nebula, was detected at the core of the bubble.

The rich data set compiled in this study contains observations that span the full range of X-ray energies covered by XMM-Newton; these include some energies corresponding to the light emitted by heavy elements such as silicon, sulphur and argon, which are produced primarily in supernova explosions. By combining these additional information present in the data, the astronomers obtained another, complementary view of the Galactic Centre, which reveals beautifully the lobes and bubbles described earlier on.

In addition, this alternative view also displays the emission, albeit very faint, from warm plasma in the upper and lower parts of the image. This warm plasma might be the collective macroscopic effect of outflows generated by star formation throughout this entire central zone.

Another of the possible explanations for such emission links it to the turbulent past of the now not-so-active supermassive black hole. Astronomers believe that, earlier on in the history of our galaxy, Sagittarius A* was accreting and ejecting mass at a much higher rate, like the black holes found at the centre of many galaxies, and these diffuse clouds of warm plasma could be a legacy of its ancient activity.  

Related scientific papers:

The XMM-Newton view of the central degrees of the Milky Way, by G. Ponti et al. 

The Galactic Centre XMM-Newton monitoring project is supported by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society.

Source: ESA