Friday, September 28, 2012

Peering to the Edge of a Black Hole

Streaming out from the center of the galaxy M87 like a cosmic searchlight is one of nature's most amazing phenomena, a black-hole-powered jet of sub-atomic particles traveling at nearly the speed of light. In this Hubble Space Telescope image, the blue of the jet contrasts with the yellow glow from the combined light of billions of unseen stars and the yellow, point-like globular clusters that make up this galaxy. Credit: NASA and the Hubble Heritage Team

This artist's conception shows the region immediately surrounding a supermassive black hole (the black spot near the center). The black hole is orbited by a thick disk of hot gas. The center of the disk glows white-hot, while the edge of the disk is shown in dark silhouette. Magnetic fields channel some material into a jet-like outflow - the greenish wisps that extend to upper right and lower left. A dotted line marks the innermost stable circular orbit, which is the closest distance that material can orbit before becoming unstable and plunging into the black hole.  Credit: Chris Fach (Perimeter Institute & University of Waterloo)

Cambridge, MA - Using a continent-spanning telescope, an international team of astronomers has peered to the edge of a black hole at the center of a distant galaxy. For the first time, they have measured the black hole's "point of no return" - the closest distance that matter can approach before being irretrievably pulled into the black hole. 

 A black hole is a region in space where the pull of gravity is so strong that nothing, not even light, can escape. Its boundary is known as the event horizon. 

 "Once objects fall through the event horizon, they're lost forever," says lead author Shep Doeleman, assistant director at the MIT Haystack Observatory and research associate at the Harvard-Smithsonian Center for Astrophysics (CfA). "It's an exit door from our universe. You walk through that door, you're not coming back." 

 The team examined the black hole at the center of a giant elliptical galaxy called Messier 87 (M87), which is located about 50 million light-years from Earth. That black hole is 6 billion times more massive than the Sun. It's surrounded by an accretion disk of gas swirling toward the black hole's maw. Although the black hole is invisible, the accretion disk is hot enough to glow. 

 "Even though this black hole is far away, it's so big that its apparent size on the sky is about the same as the black hole at the center of the Milky Way," says co-author Jonathan Weintroub of the CfA. "That makes it an ideal target for study." 

 According to Einstein's theory of general relativity, a black hole's mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it's only 5.5 times the size of the black hole's event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole. 

 The observations were made by linking together radio telescopes in Hawaii, Arizona and California to create a virtual telescope called the Event Horizon Telescope, or EHT. The EHT is capable of seeing details 2,000 times finer than the Hubble Space Telescope. 

 The team plans to expand its telescope array, adding radio dishes in Chile, Europe, Mexico, Greenland, and the South Pole, in order to obtain even more detailed pictures of black holes in the future. 

 The work is being published in Science Express. 

 This release is being issued jointly with MIT. 

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:

David A. Aguilar
 Director of Public Affairs
 Harvard-Smithsonian Center for Astrophysics

 Christine Pulliam
Public Affairs Specialist
 Harvard-Smithsonian Center for Astrophysics

Hubble portrays a dusty spiral galaxy

NGC 4183
Credit:  ESA/Hubble & NASA
Acknowledgement: Luca Limatola

The NASA/ESA Hubble Space Telescope has provided us with another outstanding image of a nearby galaxy. This week, we highlight the galaxy NGC 4183, seen here with a beautiful backdrop of distant galaxies and nearby stars. Located about 55 million light-years from the Sun and spanning about eighty thousand light-years, NGC 4183 is a little smaller than the Milky Way. This galaxy, which belongs to the Ursa Major Group, lies in the northern constellation of Canes Venatici (The Hunting Dogs).

NGC 4183 is a spiral galaxy with a faint core and an open spiral structure. Unfortunately, this galaxy is viewed edge-on from the Earth, and we cannot fully appreciate its spiral arms. But we can admire its galactic disc.

The discs of galaxies are mainly composed of gas, dust and stars. There is evidence of dust over the galactic plane, visible as dark intricate filaments that block the visible light from the core of the galaxy. In addition, recent studies suggest that this galaxy may have a bar structure. Galactic bars are thought to act as a mechanism that channels gas from the spiral arms to the centre, enhancing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy.

British astronomer William Herschel first observed NGC 4183 on 14 January 1778.

This picture was created from visible and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys. The field of view is approximately 3.4 arcminutes wide.

This image uses data identified by Luca Limatola in the Hubble's Hidden Treasures image processing competition.

Source:  ESA/Hubble - Space Telescope

Thursday, September 27, 2012

Astronomers see galaxy-altering quasars ignite

Artist's concept
Credit: ESO/M. Cornmesser

Analysing data from NASA's Spitzer and Hubble Space Telescopes an international team of astronomers around Tanya Urrutia from AIP has caught sight of luminous quasars igniting after galaxies collide. Quasars are bright, energetic regions around giant, active black holes in galactic centers.

The new observations shed light on a key early period of galactic evolution when quasars and their host galaxies begin to interact, but before the two have settled down after recent galactic smashups.

"For the first time in a large sample, we are catching galactic systems when feedback between the galaxy and the quasar is still in action," said Tanya Urrutia, a postdoctoral researcher at the Leibniz Institute for Astrophysics in Potsdam, Germany and lead author of a study appearing in the Astrophysical Journal. "Quasars profoundly influence galaxy evolution and they shape the properties of the massive galaxies we see today."

Although immensely powerful and visible across billions of light years, quasars are actually quite tiny, at least compared to an entire galaxy. Quasars span a few light years, and their inner areas casting out high-velocity winds compare roughly in size only to that of our solar system. It takes a beam of light about ten hours to cross that distance. A large galaxy, however, stretches across tens of thousands of light years, or an area many millions of times larger.

"An amazing aspect of this work is that something that is happening on a very small scale can affect the host galaxy so much," said Urrutia. "To put it in context, it is a bit like if somebody playing around with a stick at the beach could affect the behavior of all the oceans in the world."

The transition of young, star-making galaxies to the old, quiet, elliptical galaxies we see in the modern Universe is strongly linked to the activity of central supermassive black holes, astronomers have learned. When galaxies merge together into a bigger galaxy, central black holes spark up as quasars, send out powerful winds and beam energy across the cosmos. The new study probes how the quasars work in altering the host galaxies' star-making abilities.

Urrutia and her team looked at 13 particularly jazzed-up quasars at a distance of about six billion light-years or so, back when the universe was a little more than half its current age. The quasars' light was reddened by the presence of lots of dust. Cosmic dust absorbs visible light and then re-emits it in longer, redder wavelengths, including the infrared light that Spitzer sees.

The dustier, redder quasars turned up in galaxies with more disturbed shapes, as revealed in observations by Hubble. This evidence pointed to those luminous quasars having been ignited by a recent major merger between two sizeable galaxies.

The astronomers also gauged how voraciously the supermassive black holes at the hearts of the quasars were feeding. In further Spitzer observations, the researchers saw that the reddest quasars most actively slurping up matter occurred in the most disturbed galaxies. In essence, Spitzer and Hubble witnessed the galaxies and quasars in a stage of co-evolution, with the state of one connected to the state of the other.

Other findings of the new study bolster theories about where this shared evolution will lead. The galactic mergers, which ignited central quasars and shrouded them in dust, also kicked off waves of star formation. Stars form from pockets of cold gas and dust, and galaxy collisions are known to trigger bursts of star birth.

Notably, the fast-feeding black holes that sport prominent quasars in the study appear to be growing still in size. Astronomers have previously established a relationship between a central black hole's mass and the brightness of a host galaxy. However, in the young quasars studied, the black holes did not turn out to be as massive as would be expected. The black holes still have some catching up to do, it seems, with the rest of the processes spurred by the merger.

As the black holes grow, high-velocity winds from these monsters will scatter the cold gas needed to create new stars. In the process, the galaxies will start to transition from star-generating youth to an old age populated by dying stars. Urrutia and her team noted winds already rushing from some of the observed galaxies' central supermassive black holes.

In the overall chronology of galactic evolution, then, it looks like waves of new star birth happen before the central holes grow and their quasars flare. "According to our results, the onset of star formation preceded the ignition of the quasar," said Urrutia. "The evolution of quasars is intimately linked with the evolution of galaxies and the formation of their stars." 

Image Caption: 

Quasars, as pictured here in this artist's concept, are bright, energetic regions around giant, active black holes in galactic centers. Although immensely powerful and visible across billions of light years, quasars are actually quite tiny, at least compared to an entire galaxy. Quasars span a few light years, and their inner areas casting out high-velocity winds compare roughly in size only to that of our solar system. It takes a beam of light about ten hours to cross that distance.

The galaxies that play host to quasars, in contrast, typically span tens of thousands of light years. Surprisingly, the activity in the compact quasar cores is thought to dramatically influence the evolution the surrounding galaxies, and have a significant impact on the properties of massive galaxies seen today.

A research team using data from NASA's Spitzer and Hubble Space telescopes have for the first time found a large sample of galaxies during a key early period of galactic evolution when quasars and their host galaxies begin to interact, but before the two have settled down after recent galactic smashups.(Credit: ESO/M. Cornmesser)

Further information: 

Science contact: 

Dr Tanya Urrutia, 
+49 331-7499-664

Media contact: 

Dr Gabriele Schönherr / Kerstin Mork,
+49 331-7499-469

The key areas of research at the Leibniz Institute for Astrophysics (Astrophysics Institute Potsdam – AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the Institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

Wednesday, September 26, 2012

The Rich Colours of a Cosmic Seagull

Close-up view of the head of the Seagull Nebula

The Seagull Nebula on the borders of the constellations of Monoceros and Canis Major

Wide-field view of the entire Seagull Nebula (IC 2177)


Zooming in on the Seagull Nebula (IC 2177)

Panning across the head of the Seagull Nebula

This new image from ESO’s La Silla Observatory shows part of a stellar nursery nicknamed the Seagull Nebula. This cloud of gas, formally called Sharpless 2-292, seems to form the head of the seagull and glows brightly due to the energetic radiation from a very hot young star lurking at its heart. The detailed view was produced by the Wide Field Imager on the MPG/ESO 2.2-metre telescope.

Nebulae are among the most visually impressive objects in the night sky. They are interstellar clouds of dust, molecules, hydrogen, helium and other ionised gases where new stars are being born. Although they come in different shapes and colours many share a common characteristic: when observed for the first time, their odd and evocative shapes trigger astronomers’ imaginations and lead to curious names. This dramatic region of star formation, which has acquired the nickname of the Seagull Nebula, is no exception.

This new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile shows the head part of the Seagull Nebula [1]. It is just one part of the larger nebula known more formally as IC 2177, which spreads its wings with a span of over 100 light-years and resembles a seagull in flight. This cloud of gas and dust is located about 3700 light-years away from Earth. The entire bird shows up best in wide-field images.

The Seagull Nebula lies just on the border between the constellations of Monoceros (The Unicorn) and Canis Major (The Great Dog) and is close to Sirius, the brightest star in the night sky. The nebula lies more than four hundred times further away than the famous star.

The complex of gas and dust that forms the head of the seagull glows brightly in the sky due to the strong ultraviolet radiation coming mostly from one brilliant young star — HD 53367 [2] — that can be spotted in the centre of the image and could be taken to be the seagull’s eye.

The radiation from the young stars causes the surrounding hydrogen gas to glow with a rich red colour and become an HII region [3]. Light from the hot blue-white stars is also scattered off the tiny dust particles in the nebula to create a contrasting blue haze in some parts of the picture.

Although a small bright clump in the Seagull Nebula complex was observed for the first time by the German-British astronomer Sir William Herschel back in 1785, the part shown here had to await photographic discovery about a century later.

By chance this nebula lies close in the sky to the Thor’s Helmet Nebula (NGC 2359), which was the winner of ESO’s recent Choose what the VLT Observes contest (ann12060). This nebula, with its distinctive shape and unusual name, was picked as the first ever object selected by members of the public to be observed by ESO’s Very Large Telescope. These observations are going to be part of the celebrations on the day of ESO’s 50th anniversary, 5 October 2012. The observations will be streamed live from the VLT on Paranal. Stay tuned!


[1] This object has received many other names through the years  — it is known as Sh 2-292, RCW 2 and Gum 1. The name Sh 2-292 means that the object is the #292 in the second Sharpless catalogue of HII regions, published in 1959. The RCW number refers to the catalogue compiled by Rodgers, Campbell and Whiteoak and published in 1960. This object was also the first in an earlier list of southern nebulae compiled by Colin Gum, and published in 1955.

[2] HD 53367 is a young star with twenty times the mass of our Sun. It is classified as a Be star, which are a type of B star with prominent hydrogen emission lines in its spectrum. This star has a five solar mass companion in a highly elliptical orbit.

[3] HII regions are so named as they consist of ionised hydrogen (H) in which the electrons are no longer bound to protons. HI is the term used for un-ionised, or neutral, hydrogen. The red glow from HII regions occurs because the protons and electrons recombine and in the process emit energy at certain well-defined wavelengths or colours. One such prominent transition (called hydrogen alpha, or H-alpha) leads to the strong red colour.
More information

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.



 Richard Hook
 ESO, La Silla, Paranal, E-ELT & Survey Telescopes Public Information Officer
 Garching bei München, Germany
 Tel: +49 89 3200 6655
 Cell: +49 151 1537 3591

Tuesday, September 25, 2012

Hubble goes to the eXtreme to assemble the deepest ever view of the Universe

The Hubble eXtreme Deep Field

The Hubble eXtreme Deep Field (annotated)

Distances in the Hubble eXtreme Deep Field

Location and size of the Hubble eXtreme Deep Field (ground-based image)


eXtreme Deep Field zoom and flythrough

Size of the eXtreme Deep Field

Like photographers assembling a portfolio of their best shots, astronomers have assembled a new, improved portrait of our deepest-ever view of the Universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining ten years of NASA/ESA Hubble Space Telescope observations taken of a patch of sky within the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full Moon.

The Hubble Ultra Deep Field is an image of a small area of space in the constellation of Fornax (The Furnace), created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over one million seconds of observation, the resulting image revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the Universe ever taken at that time.

The new full-colour XDF image is even more sensitive than the original Hubble Ultra Deep Field image, thanks to the additional observations, and contains about 5500 galaxies, even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness that the unaided human eye can see [1].

Magnificent spiral galaxies similar in shape to the Milky Way and its neighbour the Andromeda galaxy appear in this image, as do large, fuzzy red galaxies in which the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years as the stars within them age.

Peppered across the field are tiny, faint, and yet more distant galaxies that are like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like the Milky Way — is laid out in this one remarkable image.

Hubble pointed at a tiny patch of southern sky in repeat visits made over the past decade with a total exposure time of two million seconds [2]. More than 2000 images of the same field were taken with Hubble’s two primary cameras: the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light. These were then combined to form the XDF.

“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before,” said Garth Illingworth of the University of California at Santa Cruz, principal investigator of the Hubble Ultra Deep Field 2009 (HUDF09) programme.

The Universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early Universe was a time of dramatic birth for galaxies containing brilliant blue stars far brighter than our Sun. The light from those past events is just arriving at Earth now, and so the XDF is a time tunnel into the distant past when the Universe was just a fraction of its current age. The youngest galaxy found in the XDF existed just 450 million years after the Universe’s birth in the Big Bang.

Before Hubble was launched in 1990, astronomers were able to see galaxies up to about seven billion light-years away, half way back to the Big Bang. Observations with telescopes on the ground were not able to establish how galaxies formed and evolved in the early Universe.

Hubble gave astronomers their first view of the actual forms of galaxies when they were young. This provided compelling, direct visual evidence that the Universe is truly changing as it ages. Like watching individual frames of a motion picture, the Hubble deep surveys reveal the emergence of structure in the infant Universe and the subsequent dynamic stages of galaxy evolution.

The planned NASA/ESA/CSA James Webb Space Telescope (Webb telescope) will be aimed at the XDF, and will study it with its infrared vision. The Webb telescope will find even fainter galaxies that existed when the Universe was just a few hundred million years old. Because of the expansion of the Universe, light from the distant past is stretched into longer, infrared wavelengths. The Webb telescope’s infrared vision is ideally suited to push the XDF even deeper, into a time when the first stars and galaxies formed and filled the early “dark ages” of the Universe with light.


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

The HUDF09 team members are G. Illingworth (University of California, Santa Cruz), R. Bouwens (Leiden University), M. Carollo (Swiss Federal Institute of Technology, Zurich (ETH)), M. Franx (Leiden University), I. Labbe (Leiden University), D. Magee and P. Oesch (University of California, Santa Cruz), M. Stiavelli (Space Telescope Science Institute), M. Trenti (University of Cambridge), P. van Dokkum (Yale University), and V. Gonzalez (University of California Observatories/Lick Observatory).

[1] The faintest objects detected in the XDF are 31st magnitude.

[2] The total exposure time is approximately two million seconds, or 23 days. Because Hubble can only observe for about 45 minutes of every 97-minute orbit, the observations that make up the XDF represent 50 days of telescope time.

Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team


 Garth Illingworth
 University of California
 Santa Cruz, California, USA
 Tel: +1-831-459-2843

 Richard Hook
 Garching, Germany
 Tel: +49-89-3200-6655

 Ray Villard
 Space Telescope Science Institute
 Baltimore, USA
 Tel: +1-410-338-4514

Monday, September 24, 2012

Using artificial intelligence to chart the universe

Supergalactic plot of the Cosmic Web Structure
A slice through the three dimensional Local Universe with side 370 Million light years is shown. The red circles represent observed galaxies from the 2MRS survey. The blue circles are random galaxies filled in the so-called zone of avoidance, where the stars of our Milky Way do not permit us to observe extragalactic sources. The light and dark colour code stands for the density field reconstruction using the KIGEN artificial intelligence code showing the cosmic web matching the distribution of galaxies. Image #1

Sky plot of the Comic Web Structure
The projected density field on the sky up to distances of  about 185 Million light years distance obtained by the KIGEN code from the 2MRS data is shown. Image #2

Astronomers in Germany have developed an artificial intelligence algorithm to help them chart and explain the structure and dynamics of the universe around us. The team, led by Francisco Kitaura of the Leibniz Institute for Astrophysics in Potsdam, report their results in the journal Monthly Notices of the Royal Astronomical Society.

Scientists routinely use large telescopes to scan the sky, mapping the coordinates and estimating the distances of hundreds of thousands of galaxies and so enabling scientists to map the large-scale structure of the Universe. But the distribution they see is intriguing and hard to explain, with galaxies forming a complex ‘cosmic web’ showing clusters, filaments connecting them, and large empty regions in between.

The driving force for such a rich structure is gravitation. Around 5 percent of the cosmos appears to be made of ‘normal’ matter that makes up the stars, planets, dust and gas we can see and around 23 percent is made up of invisible ‘dark’ matter. The largest component, some 72 percent of the cosmos, is made up of a mysterious ‘dark energy’ thought to be responsible for accelerating the expansion of the Universe. This Lambda Cold Dark Matter (LCDM) model for the universe was the starting point for the work of the Potsdam team.

Measurements of the residual heat from the Big Bang – the so-called Cosmic Microwave Background Radiation or CMBR – allow astronomers to determine the motion of the Local Group, the cluster of galaxies that includes the Milky Way, the galaxy we live in. Astronomers try to reconcile this motion with that predicted by the distribution of matter around us, but this is compromised by the difficulty of mapping the dark matter in the same region.

“Finding the dark matter distribution corresponding to a galaxy catalogue is like trying to make a geographical map of Europe from a satellite image during the night which only shows the light coming from dense populated areas”, says Dr Kitaura.

His new algorithm is based on artificial intelligence (AI). It starts with the fluctuations in the density of the universe seen in the CMBR, then models the way that matter collapses into today’s galaxies over the subsequent 13700 million years. The results of the AI algorithm are a close fit to the observed distribution and motion of galaxies.

Dr Kitaura comments, “Our precise calculations show that the direction of motion and 80 percent of the speed of the galaxies that make up the Local Group can be explained by the gravitational forces that arise from matter up to 370 million light years away. In comparison the Andromeda Galaxy, the largest member of the Local Group, is a mere 2.5 million light years distant so we are seeing how the distribution of matter at great distances affects galaxies much closer to home.

Our results are also in close agreement with the predictions of the LCDM model. To explain the rest of the 20 percent of the speed, we need to consider the influence of matter up to about 460 million light years away, but at the moment the data are less reliable at such a large distance.

Despite this caveat, our model is a big step forward. With the help of AI, we can now model the universe around us with unprecedented accuracy and study how the largest structures in the cosmos came into being.”

Since 2011 Francisco Kitaura has been working at the AIP. His publication is available online on and will soon be published in Monthly Notices of the Royal Astronomical Society (MNRAS).

Science contact:

Dr. Francisco-Shu Kitaura, +49 331-7499 447,

Research, Images, Movies:

Press contact:

Dr. Gabriele Schönherr / Kerstin Mork, +49 331-7499 469,

The key topics of the Leibniz Institute for Astrophysics are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.

NASA's Chandra Shows Milky Way is Surrounded by Halo of Hot Gas

Labeled Image of Galactic Halo
Credit: Illustration: NASA/CXC/M.Weiss; 
NASA/CXC/Ohio State/A Gupta et al 

WASHINGTON -- Astronomers have used NASA's Chandra X-ray Observatory to find evidence our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The estimated mass of the halo is comparable to the mass of all the stars in the galaxy. 

If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the "missing baryon" problem for the galaxy. 

Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos. Measurements of extremely distant gas halos and galaxies indicate the baryonic matter present when the universe was only a few billion years old represented about one-sixth the mass and density of the existing unobservable, or dark, matter. In the current epoch, about 10 billion years later, a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for. 

In a recent study, a team of five astronomers used data from Chandra, the European Space Agency's XMM-Newton space observatory and Japan's Suzaku satellite to set limits on the temperature, extent and mass of the hot gas halo. Chandra observed eight bright X-ray sources located far beyond the galaxy at distances of hundreds of millions of light-years. The data revealed X-rays from these distant sources are absorbed selectively by oxygen ions in the vicinity of the galaxy. The scientists determined the temperature of the absorbing halo is between 1 million and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun. 

Other studies have shown that the Milky Way and other galaxies are embedded in warm gas with temperatures between 100,000 and 1 million kelvins. Studies have indicated the presence of a hotter gas with a temperature greater than 1 million kelvins. This new research provides evidence the hot gas halo enveloping the Milky Way is much more massive than the warm gas halo. 

 "We know the gas is around the galaxy, and we know how hot it is," said Anjali Gupta, lead author of The Astrophysical Journal Letters paper describing the research. "The big question is, how large is the halo, and how massive is it?" 

To begin to answer this question, the authors supplemented Chandra data on the amount of absorption produced by the oxygen ions with XMM-Newton and Suzaku data on the X-rays emitted by the gas halo. They concluded that the mass of the gas is equivalent to the mass in more than 10 billion suns, perhaps as large as 60 billion suns. 

"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus. "It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large."

The estimated mass depends on factors such as the amount of oxygen relative to hydrogen, which is the dominant element in the gas. Nevertheless, the estimation represents an important step in solving the case of the missing baryons, a mystery that has puzzled astronomers for more than a decade.

Although there are uncertainties, the work by Gupta and colleagues provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy. The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection.

The paper describing these results was published in the Sept. 1 issue of The Astrophysical Journal. Other co-authors were Yair Krongold of Universidad Nacional Autonoma de Mexico in Mexico City; Fabrizio Nicastro of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; and Massimiliano Galeazzi of University of Miami in Coral Gables, Fla.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.

For Chandra images, multimedia and related materials, visit: 

For an additional interactive image, podcast, and video on the finding, visit: 

Media contacts:
J.D. Harrington
Headquarters, Washington

Peter Edmonds
Chandra X-ray Center,
Cambridge, Mass.

Fast Facts for Galactic Halo:
Credit Illustration: NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A Gupta et al
Release Date September 24, 2012
Category Normal Galaxies & Starburst Galaxies
Coordinates (J2000) 8 different targets were used
Observation Date 
38 pointings between 06 Dec 2000 and 07 April 2012
Observation Time 
764 hours 53 min. (31 days, 19 hours, 53 min)
Obs. ID 
2090-2094, 2335, 3168, 3567, 3669, 4148-4149, 4399, 4416, 4441-4442, 4901, 4910, 5151, 5318, 5331-5332, 6091, 6151, 6874, 8379, 8388, 9151, 9713, 9898-9899, 10575, 10662, 11387-11388, 11965-11966, 13097, 14266
Gupta, A et al, 2012, ApJ, 756:L8; arXiv:1205.5037

Friday, September 21, 2012

Discovery of an Ancient Celestial City Undergoing Rapid Growth: A Young Protocluster of Active Star-Forming Galaxies

Using the Multi-Object Infrared Camera and Spectrograph (MOIRCS) mounted on the Subaru Telescope, a team of astronomers led by Dr. Masao Hayashi (National Astronomical Observatory of Japan or NAOJ) and Dr. Tadayuki Kodama (Subaru Telescope, NAOJ) has discovered a protocluster of galaxies in the midst of a vigorous process of formation. It is the densest and most active protocluster ever identified at so great a distance, 11 billion light years away from Earth (Note 1). The star formation rate in the protocluster is intense, sometimes reaching a rate over 100 times greater than that of the Milky Way Galaxy. Although old, inactive elliptical galaxies dominate present-day galaxy clusters, the recently discovered protocluster is a site where progenitors of clusters of current elliptical galaxies were just forming and growing rapidly. It will serve as an ideal laboratory for investigating how a cluster develops and how a special, dense environment can influence the formation and evolution of galaxies. 

Research to Investigate the Formation of Protoclusters

The properties of galaxies strongly depend upon where they reside. Some galaxies occupy crowded, gravitationally bound regions called "galaxy clusters" and "galaxy groups" while others live in deserted areas called "general fields". In the present-day Universe, galaxy clusters generally contain old, elliptical galaxies that are not actively forming stars, and general fields usually encompass young disk galaxies that are actively forming stars. Why do these galaxies segregate into different habitats in the Universe? Investigation of the formation of distant protoclusters that are progenitors of local galaxy clusters may provide an answer. Clusters or "ancient cities" of galaxies are not everywhere. Discovering them in their "adolescence", when the surrounding environment influences their development, is likely to yield the best basis for studying how clusters of galaxies form. 

The current research team focused their search on star-forming galaxies associated with the protocluster USS1558-003 (Note 2), which is 11 billion light years way from Earth. This target is a very dense region of old, mature or "red-burning" galaxies (Note 3), and occurs in the epoch from 9 to 11 billion years ago when the adolescent galaxies were growing vigorously. The team used MOIRCS mounted on the Subaru Telescope for their research; they also fitted MOIRCS with a narrowband filter customized for this target to capture the H-alpha emission lines (Note 4) coming from the star-forming regions (Figure 1). In addition, they searched for extremely red galaxies that are inactive and passively evolving.

Figure 1: Two views of the protocluster. (Left) A near-infrared, false-color image of the region (clump 2) where galaxies in the protocluster most strongly cluster. The objects marked with open green circles are H-alpha emitting galaxies. North is up, and east is to the left. (Right) Blinking images of broadband (Ks) and narrowband (H-alpha) emitters. The encircled objects showing H-alpha emitting galaxies are much brighter in the narrowband than in the Ks-band. (Credit: NAOJ)

Results Showing an Ancient Celestial City Undergoing Rapid Growth

The wide-field observations revealed that three notable galaxy groups of various sizes (Figure 2) make up the protocluster. The number of galaxies concentrated in these clumps is very high, about 15 times greater than that of general fields in the Universe at the same cosmic time. No other region known so far in the ancient Universe of 11 billion years ago or more has so many strongly clustered galaxies. The intense star-forming activity in the entire observed region of the protocluster amounts to new star formation equivalent to 10,000 Suns per year. The activity is analogous to watching the swift construction of an ancient, developing city, when elliptical galaxies were very young and growing rapidly in a dense environment.

Figure 2: A wide-field map of an ancient celestial city, the USS1558-003 protocluster. The map shows the distances of the three clumps of galaxies from each other relative to the radio galaxy USS1558-003 located at (0,0). More specifically, the horizontal and vertical axes show relative distances in right ascensions and declinations in arcminute units with respect to the radio galaxy. North is up, and east is to the left. The black dots are all galaxies selected in this field. Magenta dots show old, passively evolving galaxies. Blue squares represent star-forming galaxies with H-alpha emission lines, while red ones show red-burning galaxies. Large gray circles show the three clumps of galaxies. (Credit: NAOJ)

Another important discovery about this protocluster is that almost all of the transitioning red-burning galaxies tend to be confined to the dense clumps. Their apparent preference for a location in the densest environment probably means that the protocluster is actually in its growth phase and having some environmental effects on the galaxies. The research team plans to examine the individual galaxies more closely in order to reveal what is actually happening as the cluster is forming.

Future Prospects from the MAHALO-Subaru Project

The results presented in this article are among the many exciting new findings that are just emerging from the "MAHALO-Subaru" project (Note 5), which focuses on identifying the fundamental physical processes that determine the properties of galaxies in dense environments. The project's research team, led by Dr. Kodama, is conducting systematic observations of a large sample of galaxy clusters and protoclusters at various distances, hence at various cosmic times. The results show that galaxy clusters observed at distances greater than 9 billion light years away generally have active star formation, even in their densest central regions, in contrast to present-day clusters in which old, inactive elliptical galaxies dominate. It appears that clusters grow from the inside out. They first grow rapidly in cores of protoclusters, and the sites of active growth of galaxies spread to the surrounding outskirts, like suburbs forming at the periphery of a city.

The research contributes to an understanding of how clusters and the galaxies within them form and grow with cosmic time. The research team sums it up: "We are now at the stage when we are using various new instruments to show in detail the internal structures of galaxies in formation so that we can identify the physical mechanisms that control and determine the properties of galaxies."


These results are published in the September 20, 2012 edition of the Astrophysical Journal (Hayashi et al., 2012, ApJ, 757, 15).
 The authors of the paper are:
Masao Hayashi, National Astronomical Observatory of Japan (NAOJ), Japan
Tadayuki Kodama, Subaru Telescope, NAOJ, Hawaii
Ken-ichi Tadaki, University of Tokyo, Japan
Yusei Koyama, Durham University, United Kingdom
Ichi Tanaka, Subaru Telescope, NAOJ, Hawaii


The authors thank Subaru Telescope for providing them with an opportunity to perform these exciting, important observations.

Support for this research was provided by The Japan Society for the Promotion of Science through Grant-in-Aid for Scientific Research 18684004 and 21340045.

  1. At a redshift of 2.53, this is about 2.6 billion years since the Big Bang.
  2. The protocluster is located toward the constellation Serpens in the equatorial region of the sky and is associated with the radio galaxy USS1558-003 at (16:01:17.3 -00:28:48:00)
  3. A red-burning galaxy is a galaxy population in transition between actively forming stars in bursts and losing its star-forming activities. See the Subaru Telescope press release entitled "Red-Burning Galaxies Hold the Key to Galaxy Evolution"
  4. H-alpha is a characteristic spectral line originating from star-forming regions within the galaxy. More specifically, it is a nebular emission line of neutral hydrogen's Balmer series at rest-frame 6563 angstrom. An emission line is a type of spectral line that indicates the radiation received from an object and provides information about its temperature and composition. Hydrogen is one of the most abundant elements in the early Universe, and it creates an H-alpha spectral line when ionized hydrogen recombines with an electron (a particle with a negative electrical charge).
  5. MAHALO-Subaru: MApping H-Alpha and Lines of Oxygen with Subaru. Mahalo means "thank you" in the Hawaiian language.

Glowing gas and dark dust in a side-on spiral

NGC 4634
ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope has produced a sharp image of NGC 4634, a spiral galaxy seen exactly side-on. Its disc is slightly warped by ongoing interactions with a nearby galaxy, and it is crisscrossed by clearly defined dust lanes and bright nebulae.

NGC 4634, which lies around 70 million light-years from Earth in the constellation of Coma Berenices, is one of a pair of interacting galaxies. Its neighbour, NGC 4633, lies just outside the upper right corner of the frame, and is visible in wide-field views of the galaxy. While it may be out of sight, it is not out of mind: its subtle effects on NGC 4634 are easy to see to a well-trained eye.

Gravitational interactions pull the neat spiral forms of galaxies out of shape as they get closer to each other, and the disruption to gas clouds triggers vigorous episodes of star formation. While this galaxy’s spiral pattern is not directly visible thanks to our side-on perspective, its disc is slightly warped, and there is clear evidence of star formation.

Along the full length of the galaxy, and scattered around parts of its halo, are bright pink nebulae. Similar to the Orion Nebula in the Milky Way, these are clouds of gas that are gradually coalescing into stars. The powerful radiation from the stars excites the gas and makes it light up, much like a fluorescent sign. The large number of these star formation regions is a telltale sign of gravitational interaction.

The dark filamentary structures that are scattered along the length of the galaxy are caused by cold interstellar dust blocking some of the starlight.

Hubble’s image is a combination of exposures in visible light produced by Hubble’s Advanced Camera for Surveys and the Wide Field and Planetary Camera 2.

Source:  ESA/Hubble - Space Telescope

Thursday, September 20, 2012

NASA's Solar Fleet Peers Into Coronal Cavities

Scientists want to understand what causes giant explosions in the sun's atmosphere, the corona, such as this one. The eruptions are called coronal mass ejections or CMEs and they can travel toward Earth to disrupt human technologies in space. To better understand the forces at work, a team of researchers used NASA data to study a precursor of CMEs called coronal cavities. Credit: NASA/Solar Dynamics Observatory (SDO) . View Larger

The sun's atmosphere dances. Giant columns of solar material – made of gas so hot that many of the electrons have been scorched off the atoms, turning it into a form of magnetized matter we call plasma – leap off the sun's surface, jumping and twisting. Sometimes these prominences of solar material, shoot off, escaping completely into space, other times they fall back down under their own weight. 

The prominences are sometimes also the inner structure of a larger formation, appearing from the side almost as the filament inside a large light bulb. The bright structure around and above that light bulb is called a streamer, and the inside "empty" area is called a coronal prominence cavity. 

 Such structures are but one of many that the roiling magnetic fields and million-degree plasma create in the sun's atmosphere, the corona, but they are an important one as they can be the starting point of what's called a coronal mass ejection, or CME. CMEs are billion-ton clouds of material from the sun’s atmosphere that erupt out into the solar system and can interfere with satellites and radio communications near Earth when they head our way.

 "We don't really know what gets these CMEs going," says Terry Kucera, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "So we want to understand their structure before they even erupt, because then we might have a better clue about why it's erupting and perhaps even get some advance warning on when they will erupt."

 Kucera and her colleagues have published a paper in the Sept. 20, 2012, issue of The Astrophysical Journal on the temperatures of the coronal cavities. This is the third in a series of papers -- the first discussed cavity geometry and the second its density -- collating and analyzing as much data as possible from a cavity that appeared over the upper left horizon of the sun on Aug. 9, 2007 (below). By understanding these three aspects of the cavities, that is the shape, density and temperature, scientists can better understand the space weather that can disrupt technologies near Earth. 

 The faint oval hovering above the upper left limb of the sun in this picture is known as a coronal cavity. NASA’s Solar and Terrestrial Relations Observatory (STEREO) captured this image on Aug. 9, 2007. A team of scientists extensively studied this particular cavity in order to understand more about the structure and magnetic fields in the sun's atmosphere. Credit: NASA/STEREO. View Larger

 The Aug. 9 cavity lay at a fortuitous angle that maximized observations of the cavity itself, as opposed to the prominence at its base or the surrounding plasma. Together the papers describe a cavity in the shape of a croissant, with a giant inner tube of looping magnetic fields -- think something like a slinky -- helping to define its shape. The cavity appears to be 30% less dense than the streamer surrounding it, and the temperatures vary greatly throughout the cavity, but on average range from 1.4 million to 1.7 million Celsius (2.5 to 3 million Fahrenheit), increasing with height.

 Trying to describe a cavity, a space that appears empty from our viewpoint, from 93 million miles away is naturally a tricky business. "Our first objective was to completely pin down the morphology," says Sarah Gibson, a solar scientist at the High Altitude Observatory at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. who was an author on all three cavity papers. "When you see such a crisp clean shape like this, it’s not an accident. That shape is telling you something about the physics of the magnetic fields creating it, and understanding those magnetic fields can also help us understand what’s at the heart of CMEs."

 To do this, the team collected as much data from as many instruments from as many perspectives as they could, including observations from NASA’s Solar Terrestrial Relations Observatory (STEREO), ESA and NASA’s Solar and Heliospheric Observatory (SOHO), the JAXA/NASA mission Hinode, and NCAR's Mauna Loa Solar Observatory.

 They collected this information for the cavity’s entire trip across the face of the sun along with the sun’s rotation. Figuring out, for example, why the cavity was visible on the left side of the sun but couldn’t be seen as well on the right held important clues about the structure’s orientation, suggesting a tunnel shape that could be viewed head on from one perspective, but was misaligned for proper viewing from the other. The cavity itself looked like a tunnel in a crescent shape, not unlike a hollow croissant. Magnetic fields loop through the croissant in giant circles to support the shape, the way a slinky might look if it were narrower on the ends and tall in the middle – the entire thing draped in a sheath of thick plasma. The paper describing this three-dimensional morphology appeared in The Astrophysical Journal on Dec. 1, 2010.

 Next up, for the second paper, was the cavity’s density. Figuring out density and temperature was a trickier prospect since one’s point of view of the sun is inherently limited. Because the sun’s corona is partially transparent, it is difficult to tease out differences of density and temperature along one’s line of sight; all the radiation from a given line hits an instrument at the same time in a jumble, information from one area superimposed upon every other.

 Using a variety of techniques to tease density out from temperature, the team was able to determine that the cavity was 30% less than that of the surrounding streamer. This means that there is, in fact, quite a bit of material in the cavity. It simply appears dim to our eyes when compared with the denser, brighter areas nearby. The paper on the cavity’s density appeared in The Astrophysical Journal on May 20, 2011.

 "With the morphology and the density determined, we had found two of the main characteristics of the cavity, so next we focused on temperature," says Kucera. "And it turned out to be a much more complicated problem. We wanted to know if it was hotter or cooler than the surrounding material – the answer is that it is both."

 Ultimately, what Kucera and her colleagues found was that the temperature of the cavity was not – on average – hotter or cooler than the surrounding plasma.

 However, it was much more varied, with hotter and cooler areas that Kucera thinks link the much colder 10,000 degrees Celsius (17,000 F) prominence at the bottom to the million to two million degrees Celsius (1.8 million to 3.6 million degrees Fahrenheit) corona at the top. Other observations of cavities show that cavity features are constantly in motion creating a complicated flow pattern that the team would like to study further.

 While these three science papers focused on just the one cavity from 2007, the scientists have already begun comparing this test case to other cavities and find that the characteristics are fairly consistent. More recent cavities can also be studied using the high-resolution images from NASA’s Solar Dynamics Observatory (SDO), which launched in 2010.

 "Our point with all of these research projects into what might seem like side streets, is ultimately to figure out the physics of magnetic fields in the corona," says Gibson. "Sometimes these cavities can be stable for days and weeks, but then suddenly erupt into a CME. We want to understand how that happens. We’re accessing so much data, so it’s an exciting time – with all these observations, our understanding is coming together to form a consistent story."

Related Links - NASA's Solar Fleet

Karen C. Fox

Wednesday, September 19, 2012

NASA Telescopes Spy Ultra-Distant Galaxy Amidst Cosmic 'Dark Ages'

Galaxy Cluster MACS J1149+2223
Credit: NASA, ESA, W. Zheng (JHU),
M. Postman (
STScI), and the CLASH Team

News Release Images

With the combined power of NASA's Spitzer and Hubble space telescopes, as well as a cosmic magnification effect, astronomers have spotted what could be the most distant galaxy ever seen. Light from the young galaxy captured by the orbiting observatories first shone when our 13.7-billion-year-old universe was just 500 million years old.

The far-off galaxy existed within an important era when the universe began to transit from the so-called cosmic dark ages. During this period, the universe went from a dark, starless expanse to a recognizable cosmos full of galaxies. The discovery of the faint, small galaxy opens a window onto the deepest, most remote epochs of cosmic history.

"This galaxy is the most distant object we have ever observed with high confidence," said Wei Zheng, a principal research scientist in the department of physics and astronomy at Johns Hopkins University in Baltimore and lead author of a new paper appearing in Nature. "Future work involving this galaxy, as well as others like it that we hope to find, will allow us to study the universe's earliest objects and how the dark ages ended."

Light from the primordial galaxy traveled approximately 13.2 billion light-years before reaching NASA's telescopes. In other words, the starlight snagged by Hubble and Spitzer left the galaxy when the universe was just 3.6 percent of its present age. Technically speaking, the galaxy has a redshift, or "z," of 9.6. The term redshift refers to how much an object's light has shifted into longer wavelengths as a result of the expansion of the universe. Astronomers use redshift to describe cosmic distances.

Unlike previous detections of galaxy candidates in this age range, which were only glimpsed in a single color, or waveband, this newfound galaxy has been seen in five different wavebands. As part of the Cluster Lensing And Supernova Survey with Hubble Program, the Hubble Space Telescope registered the newly described, far-flung galaxy in four visible and infrared wavelength bands. Spitzer measured it in a fifth, longer-wavelength infrared band, placing the discovery on firmer ground.

Objects at these extreme distances are mostly beyond the detection sensitivity of today's largest telescopes. To catch sight of these early, distant galaxies, astronomers rely on gravitational lensing. In this phenomenon, predicted by Albert Einstein a century ago, the gravity of foreground objects warps and magnifies the light from background objects. A massive galaxy cluster situated between our galaxy and the newfound galaxy magnified the newfound galaxy's light, brightening the remote object some 15 times and bringing it into view.

Based on the Hubble and Spitzer observations, astronomers think the distant galaxy was less than 200 million years old when it was viewed. It also is small and compact, containing only about one percent of the Milky Way's mass. According to leading cosmological theories, the first galaxies indeed should have started out tiny. They then progressively merged, eventually accumulating into the sizable galaxies of the more modern universe.

These first galaxies likely played the dominant role in the epoch of reionization, the event that signaled the demise of the universe's dark ages. This epoch began about 400,000 years after the big bang when neutral hydrogen gas formed from cooling particles. The first luminous stars and their host galaxies emerged a few hundred million years later. The energy released by these earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the universe to ionize, or lose an electron, a state that the gas has remained in since that time.

"In essence, during the epoch of reionization, the lights came on in the universe," said paper co-author Leonidas Moustakas, a research scientist at NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both Hubble and Spitzer, NASA's James Webb Telescope, which is scheduled for launch in 2018. The newly described distant galaxy likely will be a prime target.

For more information about Spitzer, visit . For more information about Hubble, visit: .

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


J.D. Harrington
Headquarters, Washington

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.