Tuesday, March 03, 2015

Pockets of Calm Protect Molecules around a Supermassive Black Hole

The central part of the galaxy M77, also known as NGC 1068, observed by ALMA and the NASA/ESA Hubble Space Telescope. Yellow: cyanoacetylene (HC3N), Red: carbon monosulfide (CS), Blue: carbon monoxide (CO), which are observed with ALMA. While HC3N is abundant in the central part of the galaxy (CND), CO is mainly distributed in the starburst ring. CS is distributed both in the CND and the starburst ring. Credit: ALMA(ESO/NAOJ/NRAO), S. Takano et al., NASA/ESA Hubble Space Telescope and A. van der Hoeven


Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered regions where certain organic molecules somehow endure the intense radiation near the supermassive black hole at the center of galaxy NGC 1068, also known to amateur stargazers as M77.

Such complex carbon-based molecules are thought to be easily obliterated by the strong X-rays and ultraviolet (UV) photons that permeate the environment surrounding supermassive black holes. The new ALMA data indicate, however, that pockets of calm exist even in this tumultuous region, most likely due to dense areas of dust and gas that shield molecules from otherwise lethal radiation.

Molecules Reveal Clues to Galactic Environments

Interstellar gas contains a wide variety of molecules, which differ wildly depending on the environment. For example, high-temperature, active star forming regions produce different molecules than would be found in colder interstellar regions. This enables scientists to probe the temperature and density of certain regions by studying their chemical composition.

Astronomers have long been studying the molecular signatures around supermassive black holes: both nearby starburst regions and surrounding rings of dust and gas known as a circumnuclear disks (CND) that spiral-in to feed an active black hole. These regions are important for understanding the evolution of galaxies. However, weak radio emission from the molecules there often makes observations difficult. 

ALMA Observations Trace Molecules

To better understand the complex and energetic environs around a supermassive black hole, the research team -- led by Shuro Takano at the National Astronomical Observatory of Japan (NAOJ) and Taku Nakajima at Nagoya University -- observed the spiral galaxy M77, which is located about 47 million light-years from Earth in the direction of the constellation Cetus (the Whale).

This galaxy is known to have an actively feeding central black hole, which indicates it has a substantial circumnuclear disk. That disk, in turn, is surrounded by a 3,500 light-year wide starburst ring. To probe these areas, the research team added ALMA’s extreme sensitivity and high-fidelity imaging capabilities to earlier observations conducted by the 45-meter radio telescope at the Nobeyama Radio Observatory of the National Astronomical Observatory of Japan (NAOJ).

The new ALMA observations clearly reveal the distributions of nine types of molecules in the surrounding disk and starburst ring.

“In this observation, we used only 16 antennas, which are about one-fourth of the complete number of ALMA antennas, but it was really surprising that we could get so many molecular distribution maps in less than two hours. We have never obtained such a quantity of maps in one observation,” said Takano, the leader of the research team.

The results clearly show that the molecular distribution varies according to the type of molecule. While carbon monoxide (CO) is distributed mainly in the starburst ring, five types of molecules, including complex organic molecules such as cyanoacetylene (HC3N) and acetonitrile (CH3CN), are concentrated primarily in the CND. In addition, carbon monosulfide (CS) and methanol (CH3OH) are distributed both in the starburst ring and the CND.

Shielding Complex Organics around a Black Hole

As the supermassive black hole devours the surrounding material, this disk is heated to such extreme temperatures that it emits intense X-rays and UV photons. When complex organic molecules are exposed to these photons, their atomic bonds are broken and the molecules are destroyed. Astronomers assumed that such regions would therefore be devoid of such complex organics. The ALMA observations, however, proved the contrary: Complex organic molecules are abundant in the CND, though not so in the broader starburst region. 

"It was quite unexpected that complex molecules with a large number of atoms like acetonitrile and cyanoacetylene are concentrated around the black hole's disk," said Nakajima.

The research team speculates that organic molecules remain intact in the CND due to the large amount of gas there, which acts as a barrier for the X-rays and UV photons, while organic molecules cannot survive the exposure to the strong UV photons in the starburst region where the gas density is comparatively lower.

The researchers point out that these results are a significant first step in understanding the structure, temperature, and density of gas surrounding the active black hole in M77. “We expect that future observations with wider bandwidth and higher resolution will show us the whole picture of this region," said Takano.

“ALMA has launched an entirely new era in astrochemistry,” said Eric Herbst of the University of Virginia in Charlottesville and a member of the research team. “Detecting and tracing molecules throughout the cosmos enables us to learn so much more about otherwise hidden areas, like the regions surrounding the black hole in M77.”

These results were published by Takano et al. as “Distributions of molecules in the circumnuclear disk and surrounding starburst ring in the Seyfert galaxy NGC 1068 observed with ALMA” (in the astronomical journal Publications of the Astronomical Society of Japan (PASJ), issued in August 2014) and by Nakajima et al. “A Multi-Transition Study of Molecules toward NGC 1068 based on High-Resolution Imaging Observations with ALMA” (in PASJ issued in February 2015).

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Contacts:

Charles Blue, 
NRAO Public Information Officer
(434) 296-0314;
cblue@nrao.edu

Masaaki Hiramatsu, 
PhD, Public Outreach Officer at NAOJ
+81-422-34-3630;
hiramatsu.masaaki@nao.ac.jp
 

This research was conducted by: 

• Shuro TAKANO (NAOJ Nobeyama Radio Observatory/SOKENDAI)
• Taku NAKAJIMA (Solar-Terrestrial Environment Laboratory, Nagoya University)
• Kotaro KOHNO (Institute of Astronomy/Research Center for the Early Universe, The University of Tokyo)
• Nanase HARADA (Academia Sinica Institute of Astronomy and Astrophysics [At the time of writing: Max Planck Institute for Radio Astronomy])
• Eric HERBST (University of Virginia)
• Yoichi TAMURA (Institute of Astronomy, The University of Tokyo)
• Takuma IZUMI (Institute of Astronomy, The University of Tokyo)
• Akio TANIGUCHI (Institute of Astronomy, The University of Tokyo)
• Tomoka TOSAKI (Joetsu University of Education)

Eric Herbst gratefully acknowledges the support of the National Science Foundation for his astrochemistry program. He also acknowledges support from the NASA Exo-biology and Evolutionary Biology program through a subcontract from Rensselaer Polytechnic Institute.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.



Monday, March 02, 2015

An Old-looking Galaxy in a Young Universe

Location of the distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689 (annotated)

Infrared/visible-light view of the distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689

The distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689

Wide-field view of the sky around the rich galaxy cluster Abell 1689



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Video

A zoom into Abell 1689 and a very remote dusty galaxy
A zoom into Abell 1689 and a very remote dusty galaxy



ALMA and VLT probe surprisingly dusty and evolved galaxy

One of the most distant galaxies ever observed has provided astronomers with the first detection of dust in such a remote star-forming system and tantalising evidence for the rapid evolution of galaxies after the Big Bang. The new observations have used ALMA to pick up the faint glow from cold dust in the galaxy A1689-zD1 and used ESO’s Very Large Telescope to measure its distance.

A team of astronomers, led by Darach Watson from the University of Copenhagen, used the Very Large Telescope’s X-shooter instrument along with the Atacama Large Millimeter/submillimeter Array (ALMA) to observe one of the youngest and most remote galaxies ever found. They were surprised to discover a far more evolved system than expected. It had a fraction of dust similar to a very mature galaxy, such as the Milky Way. Such dust is vital to life, because it helps form planets, complex molecules and normal stars.

The target of their observations is called A1689-zD1 [1]. It is observable only by virtue of its brightness being amplified more than nine times by a gravitational lens in the form of the spectacular galaxy cluster, Abell 1689, which lies between the young galaxy and the Earth. Without the gravitational boost, the glow from this very faint galaxy would have been too weak to detect.

We are seeing A1689-zD1 when the Universe was only about 700 million years old — five percent of its present age [2]. It is a relatively modest system — much less massive and luminous than many other objects that have been studied before at this stage in the early Universe and hence a more typical example of a galaxy at that time.

A1689-zD1 is being observed as it was during the period of reionisation, when the earliest stars brought with them a cosmic dawn, illuminating for the first time an immense and transparent Universe and ending the extended stagnation of the Dark Ages. Expected to look like a newly formed system, the galaxy surprised the observers with its rich chemical complexity and abundance of interstellar dust.

After confirming the galaxy’s distance using the VLT,” said Darach Watson, “we realised it had previously been observed with ALMA. We didn’t expect to find much, but I can tell you we were all quite excited when we realised that not only had ALMA observed it, but that there was a clear detection. One of the main goals of the ALMA Observatory was to find galaxies in the early Universe from their cold gas and dust emissions — and here we had it!

This galaxy was a cosmic infant — but it proved to be precocious. At this age it would be expected to display a lack of heavier chemical elements — anything heavier than hydrogen and helium, defined in astronomy as metals. These are produced in the bellies of stars and scattered far and wide once the stars explode or otherwise perish. This process needs to be repeated for many stellar generations to produce a significant abundance of the heavier elements such as carbon, oxygen and nitrogen.

Surprisingly, the galaxy A1689-zD1 seemed to be emitting a lot of radiation in the far infrared [3], indicating that it had already produced many of its stars and significant quantities of metals, and revealed that it not only contained dust, but had a dust-to-gas ratio that was similar to that of  much more mature galaxies.

Although the exact origin of galactic dust remains obscure,” explains Darach Watson, “our findings indicate that its production occurs very rapidly, within only 500 million years of the beginning of star formation in the Universe — a very short cosmological time frame, given that most stars live for billions of years.”

The findings suggest A1689-zD1 to have been consistently forming stars at a moderate rate since 560 million years after the Big Bang, or else to have passed through its period of extreme starburst very rapidly before entering a declining state of star formation.

Prior to this result, there had been concerns among astronomers that such distant galaxies would not be detectable in this way, but A1689-zD1 was detected using only brief observations with ALMA.

Kirsten Knudsen (Chalmers University of Technology, Sweden), co-author of the paper, added, “This amazingly dusty galaxy seems to have been in a rush to make its first generations of stars. In the future, ALMA will be able to help us to find more galaxies like this, and learn just what makes them so keen to grow up.”


Notes

[1] This galaxy was noticed earlier in the Hubble images, and suspected to be very distant, but the distance could not be confirmed at that time.

[2] This corresponds to a redshift of 7.5.

[3] This radiation is stretched by the expansion of the Universe into the millimetre wavelength range by the time it gets to Earth and hence can be detected with ALMA.  


More Information

This research was presented in a paper entitled “A dusty, normal galaxy in the epoch of reionization” by D. Watson et al., to appear online in the journal Nature on 2 March 2015.

The team is composed of D. Watson (Niels Bohr Institute, University of Copenhagen, Denmark), L. Christensen (University of Copenhagen), K. K. Knudsen (Chalmers University of Technology, Sweden), J. Richard (CRAL, Observatoire de Lyon, Saint Genis Laval, France), A. Gallazzi (INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy) and M. J. Michalowski (SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK).

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


Links

Contacts

Darach Watson
Niels Bohr Institute
University of Copenhagen, Denmark
Tel: +45 2480 3825
Email: darach@dark-cosmology.dk

Kirsten K. Knudsen
Chalmers University of Technology
Onsala, Sweden
Tel: +46 31 772 5526
Cell: +46 709 750 956
Email: kirsten.knudsen@chalmers.se

Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Source: ESO


Measuring gas velocities in galaxy clusters with X-ray images

Fig 1: Schematic illustration of gas density distribution in a spherically symmetric cluster in perfect hydrostatic equilibrium (v=0, top) and in a slightly disturbed cluster (v ≠ 0, middle). Slow large-scale perturbations in a stratified cluster atmosphere can be interpreted as internal waves (as illustrated in the bottom panel), similar to waves in the ocean, where the velocity of water and the amplitude of waves are linked. In clusters, similar perturbations are caused by a variety of reasons, including minor mergers or the activity of the central supermassive black holes.

Fig 2: X-ray image of the Coma cluster as seen with Chandra observatory.
The substructure seen in the image implies that the X-ray emitting gas is not at rest. 


X-ray observations provide us with detailed information on the density and temperature of the hot gas inside galaxy clusters. The other major gas characteristic that still needs to be measured is the gas velocity. While current generation X-ray observatories lack the required energy resolution to measure velocities directly, future observatories such as ASTRO-H and ATHENA will address this limitation.

An international team including MPA scientists has shown that the power spectrum of the velocity field can inferred indirectly from existing X-ray images of relaxed clusters. Numerical simulations confirm this simple theoretical idea, opening a way of probing gas velocities using already existing X-ray data. 

Galaxy clusters are the largest gravitationally bound structures in the present Universe. Hot gas (with temperatures of 10 to 100 million Kelvin) fills their gravitational potential wells and shines in the X-ray band, making the clusters an easy target for orbital X-ray observatories. Both the density and the temperature of the gas in clusters is routinely measured using X-ray data, while it is notoriously difficult to directly measure the turbulent motion of the gas via the Doppler shift of X-ray lines. Since the information on the turbulent gas velocities would have profound implications for the mass determination of clusters and for determining the plasma microphysics, new approaches have been developed to indirectly measure the gas velocities using existing X-ray data. One of these approaches is based on the analysis of small-scale fluctuations in X-ray images as described below. 

In relaxed clusters the gas approaches the state of hydrostatic equilibrium, when all thermodynamic properties are aligned along surfaces with equal gravitational potential, making X-ray images smooth and round (see Fig.1). These stratified and stable atmospheres of cluster gas bear much similarity to the Earth's atmosphere or to water in the oceans where cold and dense material tends to be below hotter and lighter material due to the combined action of gravity and buoyancy. Slow subsonic perturbations of such atmospheres can be represented as a combination of internal (gravity) waves, very much like waves in the ocean (bottom panel of Fig.1). In oceans there is a simple relation: the larger the amplitude of the waves, the higher the velocity of water. Is the same true for gas in galaxy clusters? Both theoretical analysis and numerical simulations have shown that this is indeed the case.

The main idea is that gas is disturbed on large scales and that this results in a cascade of waves. In clusters these waves are creating perturbations in the gas density that are visible in X-ray images as small-scale fluctuations of the surface brightness relative to a smooth global model. Our analysis shows that there is a simple linear relation between the gas velocities and density perturbations. Moreover, this relation holds for a broad range of scales: on large scales, where buoyancy effects dominate (internal waves), as well as on small scales where the isotropic turbulent cascade usually develops. At these small scales, the entropy of the gas acts as a passive scalar advected by the velocity field and makes the gas displacement visible in X-rays. 

Based on these arguments one can expect that in relaxed clusters (i.e. clusters which are only slightly disturbed) the power spectrum of the velocity field can simply be recovered from the power spectrum of density fluctuations. The latter can be straightforwardly estimated from X-ray images. 

Numerical simulations (cosmological simulations of cluster formation and pure hydrodynamic simulations with turbulence) confirm this conclusion and open an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters. 

Once the gas velocities can be measured directly with future X-ray observatories, it will be possible to push this analysis further and search for differences between the density and velocity power spectra. Strong departures of the two power spectra from the universal behavior described above can then be used to constrain physical effects such as conductivity or viscosity in the gas.

Eugene Churazov (MPA), Massimo Gaspari (MPA), Irina Zhuravleva (Stanford), Alex Schekochihin (Oxford), Rashid Sunyaev (MPA)


References:
 
Zhuravleva I., Churazov E., Schekochihin A. A., Lau E. T., Nagai D., Gaspari  M., Allen S. W., Nelson K., Parrish I. J., The Relation between Gas Density and Velocity Power Spectra in Galaxy Clusters: Qualitative Treatment and Cosmological Simulations, 2014, ApJL, 788, 13
 
Gaspari M., Churazov E., Nagai D., Lau E. T., Zhuravleva, I., The relation between gas density and velocity power spectra in galaxy clusters: high-resolution hydrodynamic simulations and the role of conduction,2014, A&A, 569A, 67
 
Gaspari M., Churazov E., Constraining turbulence and conduction in the hot ICM through density perturbations, 2013, A&A, 559A, 78
 
Churazov E.; Vikhlinin A.; Zhuravleva I.; Schekochihin A.; Parrish I.; Sunyaev R.; Forman W.; Böhringer H.; Randall S., X-ray surface brightness and gas density fluctuations in the Coma cluster, 2012, MNRAS, 421,1123


Sunday, March 01, 2015

Astronomers find newborn stars at the edge of the Galaxy

Negative WISE W1 image of the newly found cluster Camargo 438 and 439. The cluster is about 16,000 light years away, so the image is about 24 light years across. The black dots in the image are individual stars. Credit: D. Camargo/NASA/WISE


Brazilian astronomers have made a remarkable discovery: a cluster of stars forming on the very edge of the Galaxy. The team, led by Denilso Camargo of the Federal University of Rio Grande do Sul in Porto Alegre, Brazil, publish their results in the journal Monthly Notices of the Royal Astronomical Society.

The Milky Way, the Galaxy we live in, has a barred spiral shape, with arms of stars, gas and dust winding out from a central bar. Viewed from the side, the Galaxy would appear relatively flat, with most of the material in a disc and the central regions.

Stars form inside massive and dense clumps of gas in so-called giant molecular clouds (GMCs) that are mainly located in the inner part of the galactic disc. With many clumps in a single GMC, most (if not all) stars are born together in clusters.

Denilso’s team looked at data from NASA’s orbiting Wide-Field Infrared Survey Explorer (WISE) observatory. They not only found GMCs thousands of light years above and below the galactic disc, but that one of them unexpectedly contained two clusters of stars. This is the first time astronomers have found stars being born in such a remote location.

The new clusters, named Camargo 438 and 439, are within the molecular cloud HRK 81.4-77.8. This cloud is thought to be about 2 million years old and is around 16000 light years beneath the galactic disk, an enormous distance away from the usual regions of star formation, in the direction of the constellation of Cetus.

Denilso believes there are two possible explanations. In the first case, the 'chimney model', violent events such as supernova explosions eject dust and gas out of the galactic disk. The material then falls back, in the process merging to form GMCs.

The other idea is that the interaction between our Galaxy and its satellites, the Magellanic Clouds, may have disturbed gas that falls into the Galaxy, again leading to the creation of GMCs and stars.
Denilso commented: "Our work shows that the space around the Galaxy is a lot less empty that we thought. The new clusters of stars are truly exotic. In a few million years, any inhabitants of planets around the stars will have a grand view of the outside of the Milky Way, something no human being will probably ever experience.

"Now we want to understand how the ingredients for making stars made it to such a distant spot. We need more data and some serious work on computer models to try to answer this question."

The chimney model would need several hundred massive stars to have exploded as supernovae over several generations, creating a 'superwind' that threw HRK 81.4-77.8 into its present position. Over millions of years, the bubbles created by the explosions may then themselves compress material, forming more stars and fuelling the ejection of material in a 'galactic fountain', where the dust and gas eventually rains back on to the disk.

Media contact
Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035

rm@ras.org.uk

Science contact
Denilso Camargo
Federal University of Rio Grande do Sul
Porto Alegre
Brazil
Tel: +55 51 3308-6513

denilso.camargo@ufrgs.br

Images and captions

Further information
The research was carried out by Dr Denilso Camargo, Dr Eduardo Bica, Dr Charles Bonatto and Gustavo Bonatto (MSc Gustavo SALERNO), of the Federal University of Rio Grande do Sul and Colégio Militar de Porto Alegre - Exército Brasileiro.

It appears in the paper D. Camargo et al., "Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4-77.8", Monthly Notices of the Royal Astronomical Society, vol. 448, pp. 1930-1936, 2015, published by Oxford University Press.

Notes for editors
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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Saturday, February 28, 2015

The galaxies NGC 2623 in the final stages of their titanic merger. The violent encounter has produced widespread star formation. A systematic new study of galaxy simulations examines where in merging systems the star formation activity tends to take place. Hubble Legacy Archive, ESA, NASA, APOD; Processing - Martin Pugh


Collisions between galaxies, and even less dramatic gravitational encounters between them, are recognized as triggering star formation. Observations of luminous galaxies, powered by starbursts, are consistent with this conclusion. Numerical simulations also support this picture, with gravity funneling copious amounts of gas into the central regions of galaxies, fueling powerful bursts of star formation there. But starbursts are not ubiquitous in interacting galaxies. Triggering therefore depends on many factors, including the specific merger geometry (how they come together), the properties of the progenitor galaxies (how much gas is available for new stars), and time-scale (maybe the starburst has yet to happen, or has finished?)

CfA astronomer Lars Hernquist and six colleagues computed seventy-five simulated galaxy collisions under a wide range of conditions in order to investigate the question of where the induced star formation is located. Observational tests of this property are difficult to make because many of the most interesting cases are far enough away that individual regions can’t easily be distinguished for study. For the same reason, it is often hard to tell in which of the two merging galaxies (or both?) the starburst take place.

The results of these simulations were clear: the interactions enhanced the star formation activity in the centers of galaxies, and in particular in roughly the central ten thousand light-years. (By way of comparison, our Sun is about twenty-five thousand light-years away from the Milky Way’s center.) The scientists discovered several other important effects about the star formation as well: it was actually suppressed in the outer regions of the galaxies (depending on the merger geometry); at later merger stages it often formed a ring around the central zone, and its strength was critically dependent on whether the rotations of the galaxies were in the same direction (star formation enhanced) or opposite (star formation suppressed). The new generation of telescopes under construction should have the capability of improving the observations, and this theoretical work will help guide the new research.


 Reference(s)

"Mapping Galaxy Encounters in Numerical Simulations: The Spatial Extent of Induced Star Formation," Jorge Moreno, Paul Torrey, Sara L. Ellison, David R. Patton, Asa F. L. Bluck, Gunjan Bansal, and Lars Hernquist, MNRAS 448, 1107, 2015.




Found: Ancient, super-bright quasar with massive black hole

This is an artist's rendering of a very distant, very ancient quasar
Courtesy of the European Southern Observatory (M. Kornmesser)


Washington, D.C.— Quasars--supermassive black holes found at the center of distant massive galaxies--are the most-luminous beacons in the sky. These central supermassive black holes actively accrete the surrounding materials and release a huge amount of their gravitational energy. An international team of astronomers, including Carnegie’s Yuri Beletsky, has discovered the brightest quasar ever found in the early universe, which is powered by the most massive black hole observed for an object from that time. Their work is published February 26 by Nature.

The quasar was found at a redshift of z=6.30. This is a measurement of how much the wavelength of light emitted from it that reaches us on Earth is stretched by the expansion of the universe. As such, it can be used to calculate the quasar’s age and distance from our planet. A higher redshift means larger distance and hence looking further back in time.

At a distance of 12.8 billion light years from Earth, this quasar was formed only 900 million years after the Big Bang. Named SDSS J0100+2802, studying this quasar will help scientists understand how quasars evolved in the earliest days of the universe. There are only 40 known quasars have a redshift of higher than 6, a point that marks the beginning of the early universe.

“This quasar is very unique. Just like the brightest lighthouse in the distant universe, its glowing light will help us to probe more about the early universe,” said team-leader Xue-Bing Wu of Peking University and the Kavli Institute of Astronomy and Astrophysics.

With a luminosity of 420 trillion that of our own Sun’s, this new quasar is seven times brighter than the most distant quasar known (which is 13 billion years away). It harbors a black hole with mass of 12 billion solar masses, proving it to be the most luminous quasar with the most massive black hole among all the known high redshift quasars.

The team developed a method of detecting quasars at redshifts of 5 and higher. These detections were verified by the 6.5-meter Multiple Mirror Telescope (MMT) and 8.4m Large Binocular Telescope (LBT) in Arizona; the 6.5m Magellan Telescope at Carnegie’s Las Campanas Observatory in Chile; and the 8.2m Gemini North Telescope in Hawaii.

“This quasar is a unique laboratory to study the way that a quasar’s black hole and host galaxy co-evolve,” Beletsky said. “Our findings indicate that in the early Universe, quasar black holes probably grew faster than their host galaxies, although more research is needed to confirm this idea.”
Other co-authors on the paper are: FeigeWang, Jinyi Yang, and Qian Yang, also of Peking University and the Kavli Institute; Xiaohui Fan of University of Arizona and the Kavli Institute; Weimin Yi of the Chinese Academy of Sciences; Wenwen Zuo of Peking University and the Chinese Academy of Sciences; Fuyan Bian of Australian National University; Linhua Jiang and RanWang of the Kavli Institute; and Ian D. McGreer and David Thompson of University of Arizona.

This work was funded by the NSFC, the Strategic Priority Research Program ”The Emergence of Cosmological Structures” of the Chinese Academy of Sciences, the National Key Basic Research Program of China, and the U.S. NSF.


Friday, February 27, 2015

ESOcast 72: Looking Deeply into the Universe in 3D


MUSE goes beyond Hubble in the Hubble Deep Field South

MUSE stares at the Hubble Deep Field South

The Hubble Deep Field South in the constellation of Tucana

Hubble Deep Field South — Multiple Windows on the Universe



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Videos

ESOcast 72 – Looking Deeply into the Universe in 3D
ESOcast 72 – Looking Deeply into the Universe in 3D

MUSE view of the Hubble Deep Field South
MUSE view of the Hubble Deep Field South

MUSE view of the Hubble Deep Field South
MUSE view of the Hubble Deep Field South

MUSE view of the Hubble Deep Field South
MUSE view of the Hubble Deep Field South

A video view of MUSE data of the Hubble Deep Field South
A video view of MUSE data of the Hubble Deep Field South


The MUSE instrument on ESO’s Very Large Telescope has given astronomers the best ever three-dimensional view of the deep Universe. After staring at the Hubble Deep Field South region for only 27 hours, the new observations reveal the distances, motions and other properties of far more galaxies than ever before in this tiny piece of the sky. They also go beyond Hubble and reveal previously invisible objects.

By taking very long exposure pictures of regions of the sky, astronomers have created many deep fields that have revealed much about the early Universe. The most famous of these was the original Hubble Deep Field, taken by the NASA/ESA Hubble Space Telescope over several days in late 1995. This spectacular and iconic picture rapidly transformed our understanding of the content of the Universe when it was young. It was followed two years later by a similar view in the southern sky — the Hubble Deep Field South.

But these images did not hold all the answers — to find out more about the galaxies in the deep field images, astronomers had to carefully look at each one with other instruments, a difficult and time-consuming job. But now, for the first time, the new MUSE instrument can do both jobs at once — and far more quickly.

One of the first observations using MUSE after it was commissioned on the VLT in 2014 was a long hard look at the Hubble Deep Field South (HDF-S). The results exceeded expectations.

After just a few hours of observations at the telescope, we had a quick look at the data and found many galaxies — it was very encouraging. And when we got back to Europe we started exploring the data in more detail. It was like fishing in deep water and each new catch generated a lot of excitement and discussion of the species we were finding,”  explained Roland Bacon (Centre de Recherche Astrophysique de Lyon, France, CNRS) principal investigator of the MUSE instrument and leader of the commissioning team.

For every part of the MUSE view of HDF-S there is not just a pixel in an image, but also a spectrum revealing the intensity of the light’s different component colours at that point — about 90 000 spectra in total [1]. These can reveal the distance, composition and internal motions of hundreds of distant galaxies — as well as catching a small number of very faint stars in the Milky Way.

Even though the total exposure time was much shorter than for the Hubble images, the HDF-S MUSE data revealed more than twenty very faint objects in this small patch of the sky that Hubble did not record at all [2].

The greatest excitement came when we found very distant galaxies that were not even visible in the deepest Hubble image. After so many years of hard work on the instrument, it was a powerful experience for me to see our dreams becoming reality,” adds Roland Bacon.

By looking carefully at all the spectra in the MUSE observations of the HDF-S, the team measured the distances to 189 galaxies. They ranged from some that were relatively close, right out to some that were seen when the Universe was less than one billion years old. This is more than ten times the number of measurements of distance than had existed before for this area of sky.

For the closer galaxies, MUSE can do far more and look at the different properties of different parts of the same galaxy. This reveals how the galaxy is rotating and how other properties vary from place to place. This is a powerful way of understanding how galaxies evolve through cosmic time.

Now that we have demonstrated MUSE’s unique capabilities for exploring the deep Universe, we are going to look at other deep fields, such as the Hubble Ultra Deep field. We will be able to study thousands of galaxies and to discover new extremely faint and distant galaxies. These small infant galaxies, seen as they were more than 10 billion years in the past, gradually grew up to become galaxies like the Milky Way that we see today,” concludes Roland Bacon.

 

Notes

 

[1] Each spectrum covers a range of wavelengths from the blue part of the spectrum into the near-infrared (475‒930 nanometres).

[2] MUSE is particularly sensitive to objects that emit most of their energy at a few particular wavelengths as these show up as bright spots in the data. Galaxies in the early Universe typically have such spectra, as they contain hydrogen gas glowing under the ultraviolet radiation from hot young stars.

 

More information

 

This research was presented in a paper entitled “The MUSE 3D view of the Hubble Deep Field South” by R. Bacon et al., to appear in the journal Astronomy & Astrophysics on 26 February 2015.

The team is composed of R. Bacon (Observatoire de Lyon, CNRS, Université Lyon, Saint Genis Laval, France [Lyon]), J. Brinchmann (Leiden Observatory, Leiden University, Leiden, The Netherlands [Leiden]), J. Richard (Lyon), T. Contini (Institut de Recherche en Astrophysique et Planétologie, CNRS, Toulouse, France; Université de Toulouse, France [IRAP]), A. Drake (Lyon), M. Franx (Leiden), S. Tacchella (ETH Zurich, Institute of Astronomy, Zurich, Switzerland [ETH]), J. Vernet (ESO, Garching, Germany), L. Wisotzki (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany [AIP]), J. Blaizot (Lyon), N. Bouché (IRAP), R. Bouwens (Leiden), S. Cantalupo (ETH), C.M. Carollo (ETH), D. Carton (Leiden), J. Caruana (AIP), B. Clément (Lyon), S. Dreizler (Institut für Astrophysik, Universität Göttingen, Göttingen, Germany [AIG]), B. Epinat (IRAP; Aix Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille, Marseille, France), B. Guiderdoni (Lyon), C. Herenz (AIP), T.-O. Husser (AIG), S. Kamann (AIG), J. Kerutt (AIP), W. Kollatschny (AIG), D. Krajnovic (AIP), S. Lilly (ETH), T. Martinsson (Leiden), L. Michel-Dansac (Lyon), V. Patricio (Lyon), J. Schaye (Leiden), M. Shirazi (ETH), K. Soto (ETH), G. Soucail (IRAP), M. Steinmetz (AIP), T. Urrutia (AIP), P. Weilbacher (AIP) and T. de Zeeuw (ESO, Garching, Germany; Leiden).

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

 

Links

 

Contacts


Roland Bacon
CRAL - Centre de recherche astrophysique de Lyon
Saint-Genis-Laval, France
Tel: +33 478 86 85 59
Cell: +33 608 09 14 27
Email:
roland.bacon@univ-lyon1.fr

Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org

Source: ESO


A galactic cloak for an exploding star

Credit: ESA/Hubble & NASA
Acknowledgement: Gilles Chapdelaine


The galaxy pictured here is NGC 4424, located in the constellation of  Virgo. It is not visible with the naked eye but has been captured here with the NASA/ESA Hubble Space Telescope.

Although it may not be obvious from this image, NGC 4424 is in fact a spiral galaxy. In this image it is seen more or less edge on, but from above you would be able to see the arms of the galaxy wrapping around its centre to give the characteristic spiral form .

In 2012 astronomers observed a supernova in NGC 4424 — a violent explosion marking the end of a star’s life. During a supernova explosion, a single star can often outshine an entire galaxy. However, the supernova in NGC 4424, dubbed SN 2012cg, cannot be seen here as the image was taken ten years prior to the explosion. Along the central region of the galaxy, clouds of dust block the light from distant stars and create dark patches.

To the left of NGC 4424 there are two bright objects in the frame. The brightest is another, smaller galaxy known as LEDA 213994 and the object closer to NGC 4424 is an anonymous star in our Milky Way.

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



Source: ESA/Hubble - Space Telescope

Thursday, February 26, 2015

Supermassive Black Hole Lurks at Dawn of the Universe

The spectrum obtained using the Gemini Near-Infrared Spectrograph (GNIRS) combined with observations from the Magellan Telescope appears in red; gaps are regions of low sky transparency. The optical spectrum (from the Large Binocular Telescope; black) and noise (magenta) are also plotted. The inset shows the three components of the fit to a portion of the near-infrared emission. The ionized magnesium (Mg II; blue) is used to estimate the extremely large black hole mass mass, of 12 billion times the mass of the Sun. Figure credit: Nature.
 

Infrared observations with the Gemini North telescope have confirmed a 12 billion solar mass black hole in an exceptionally bright quasar in the very early universe. The finding, led by a Chinese team, used Gemini, as well as telescopes from around the world, to discover and characterize an extremely massive black hole from a period when the universe was very young (about 900 million years after the Big Bang). This observation requires extremely rapid growth of the black hole. While black holes of comparable mass have been observed after they have had billions of years to gradually gain mass over cosmic history this quasar challenges astronomers to figure out how such a huge object could exist so early in the history of the universe. 
 
The research is published in the February 26th issue of Nature, led by Xue-Bing Wu at Peking University in Beijing. 

Abstract: So far, roughly 40 quasars with redshifts greater than z=6 have been discovered. Each quasar contains a black hole with a mass of about one billion solar masses. The existence of such black holes when the Universe was less than one billion years old presents substantial challenges to theories of the formation and growth of black holes and the coevolution of black holes and galaxies. Here we report the discovery of an ultraluminous quasar, SDSSJ010013.021280225.8, at redshift z=6.30. It has an optical and near-infrared luminosity a few times greater than those of previously known z>6 quasars. On the basis of the deep absorption trough on the blue side of the Lyman-a emission line in the spectrum, we estimate the proper size of the ionized proximity zone associated with the quasar to be about 26 million light years, larger than found with other z>6.1 quasars with lower luminosities. We estimate (on the basis of a near-infrared spectrum) that the black hole has a mass of ~1.2 x 1010 solar masses, which is consistent with the 1.3 x 1010 solar masses derived by assuming an Eddington-limited accretion rate. 



 

NGC 2276: NASA's Chandra Finds Intriguing Member of Black Hole Family Tree

NGC 2276
Credit  X-ray: NASA/CXC/SAO/M.Mezcua et al & NASA/CXC/INAF/A.Wolter et al; 
Optical: NASA/STScI and DSS; Inset: Radio: EVN/VLBI

JPEG (247.8 kb) - Large JPEG (2.2 MB) - Tiff (37.1 MB) - More Images


Tour of NGC 2207



A newly discovered object in the galaxy NGC 2276 may prove to be an important black hole that helps fill in the evolutionary story of these exotic objects, as described in our latest press release. The main image in this graphic contains a composite image of NGC 2766 that includes X-rays from NASA's Chandra X-ray Observatory (pink) combined with optical data from the Hubble Space Telescope and the Digitized Sky Survey (red, green and blue). The inset is a zoom into the interesting source that lies in one of the galaxy's spiral arms. This object, called NGC 2276-3c, is seen in radio waves (red) in observations from the European Very Long Baseline Interferometry Network, or EVN.

Astronomers have combined the X-ray and radio data to determine that NGC 2766-3c is likely an intermediate-mass black hole (IMBH). As the name suggests, IMBHs are black holes that are larger than stellar-mass black holes that contain about five to thirty times the mass of the Sun, but smaller than supermassive black holes that are millions or even billions of solar masses. The researchers estimated the mass of NGC 2766-3c using a well-known relationship between how bright the source is in radio and X-rays, and the mass of the black hole. The X-ray and radio brightness were based on observations with Chandra and the EVN. They found that NGC 2276-3c contains about 50,000 times the mass of the Sun.

IMBHs are interesting to astronomers because they may be the seeds that eventually evolve into supermassive black holes. They also may be strongly influencing their environment. This latest result on NGC 2276-3c suggests that it may be suppressing the formation of new stars around it. The EVN radio data reveal an inner jet that extends about 6 light years from NGC 2276-3c. Additional observations by the NSF's Karl Jansky Very Large Array (VLA) show large-scale radio emission extending out to over 2,000 light years away from the source.

A region along the jet extending to about 1,000 light years away from NGC 2766-3c is devoid of young stars. This might provide evidence that the jet has cleared out a cavity in the gas, preventing new stars from forming there. The VLA data also reveal a large population of stars at the edge of the radio emission from the jet. This enhanced star formation could take place either when the material swept out by the jet collides with dust and gas in between the stars in NGC 2276, or when triggered by the merger of NGC 2276 with a dwarf galaxy.

In a separate study, Chandra observations of this galaxy have also been used to examine its rich population of ultraluminous X-ray sources (ULXs). Sixteen X-ray sources are found in the deep Chandra dataset seen in this composite image, and eight of these are ULXs including NGC 2276-3c. Chandra observations show that one apparent ULX observed by ESA's XMM-Newton is actually five separate ULXs, including NGC 2276-3c. This ULX study shows that about five to fifteen solar masses worth of stars are forming each year in NGC 2276. This high rate of star formation may have been triggered by a collision with a dwarf galaxy, supporting the merger idea for the IMBH's origin.

The study on NGC 2276-3c was conducted by Mar Mezcua (previously in the Instituto de Astrofisica de Canarias and now at the Harvard-Smithsonian Center for Astrophysics), Tim Roberts (University of Durham, UK), Andrei Lobanov ( Max Planck Institute for Radio Astronomy, Germany), and Andrew Sutton (University of Durham) and will appear in the Monthly Notices of the Royal Astronomical Society (MNRAS). A separate paper on the ULX population in NGC 2276 will also appear in MNRAS and the authors on that study are Anna Wolter (National Institute for Astrophysics (INAF) in Milan, Italy), Paolo Esposito (INAF), Michela Mapelli (INAF, Padova), Fabio Pizzolato (University of Milan, Italy), and Emanuele Ripamonti (University of Padova, Italy).

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 NGC 2276:

Scale: Image is 4.5 arcmin across (about 140,000 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 07h 27m 14.48s | Dec +85° 45' 16.20"
Constellation: Cepheus
Observation Date: 23 Jun 2004 and 24 May 2013
Observation Time: 19 hours 30 min.
Obs. ID: 4968, 15648
Instrument: ACIS
References: Mezcua, M et al, 2015, MNRAS (accepted); arXiv:1501.04897; Wolter, A. et al, 2015, MNRAS (accepted); arXiv:1501.01994
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Inset: Radio (Red)
Distance Estimate: About 100 million light years


Wednesday, February 25, 2015

Quadruplets in a Stellar Womb

An image at radio wavelengths of a young stellar quadruplet. Astronomers have discovered four distinct gas condensations in a clumpy, filamentary gas cloud (white) surrounded by dust (blue). The locations of the condensations in this image are marked with black and red dots. The four condensations are destined to form a bound multiple star system, and one of them (the red dot) has already turned on as a protostar. Credit: Nature; Pineda


More than half of all stars are in multiple systems: binary stars, or even triplets or quadruplets, that orbit one another. No one is quite sure how or why they form, but the effects can be significant, for example influencing the character of their planets. Our Sun is uncommon in having no companion star, perhaps suggesting that its configuration of planets is equally uncommon.

There are two principal ideas about how multiple stars form: fragmentation in the early stages of birth, or the gravitational capture of a nearby star later on. Computer simulations of star formation find that both are reasonable possibilities, and so astronomers have been trying to make observations to refine the models and the conclusions. Writing in this week’s journal Nature, Alyssa Goodman and her collaborators report finding a nearby stellar nursery where quadruplets are being born. The region is in the star forming molecular cloud in the direction of the constellation of Perseus, about 825 light-years away. Scientists have known for decades about a protostar in this area, a dense core of material that is developing into a small star about one-tenth of a solar-mass in size.

Using radio wavelength observations of dense molecular gas, ammonia in particular, the team discovered that around this protostar are several filamentary gas structures in which they detected three other condensations. The other three embryos are two to three times more massive than the main protostar, and models suggest they will become stars soon - in roughly forty thousand years. The longest dimension of the complex is only about ten thousand astronomical units (one AU is the average distance of the Earth from the Sun), and so these objects are close enough together for gravity to be the major influence in their development; velocity measurements confirm that the objects are physically associated.

It is possible – even likely - that during the stars’ development their orbital motions will prompt the ejection of one or two members from the system, but for now it appears that at least one binary pair will survive for longer times. Other stellar systems need to be examined in order to see how widespread these young multiplets really are, but the new results support models in which multiple stars form very early in the stellar womb.


Reference (s):

"The Formation of a Quadruple Star System with Wide Separation," Jaime E. Pineda, Stella S. R. Offner, Richard J. Parker, Hector G. Arce, Alyssa A. Goodman, Paola Caselli, Gary A. Fuller, Tyler L. Bourke & Stuartt A. Corder, Nature, 518, 213, 2015




Artist's impression of black-hole wind in a galaxy and XMM-Newton and NuSTAR spectrum of the quasar PDS 456

XMM-Newton and NuSTAR
Copyright: NASA/JPL-Caltech; Insert: ESA 


This illustration shows the powerful wind driven by the supermassive black hole at the centre of a galaxy. The schematic figure in the insert depicts the innermost regions of the galaxy where a black hole accretes the surrounding matter (light grey) at a very high pace via a disc (darker grey). At the same time, part of that matter is cast away through powerful winds.

A study based on joint observations with ESA's XMM-Newton and NASA's NuSTAR X-ray telescopes of the quasar PDS 456, which hosts a very active black hole, has shown that the winds driven by a black hole can be wide and almost spherical. This discovery supports the picture of black holes having a significant impact on star formation of their host galaxy.

The artwork of the galaxy is based on an image of the Pinwheel galaxy (Messier 101) taken by the NASA/ESA Hubble Space Telescope.


Copyright: NASA/JPL-Caltech/Keele Univ.
Source: ESA/XMM-Newton 

This plot of data from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's (ESA's) XMM-Newton determines for the first time the shape of ultra-fast winds from supermassive black holes, or quasars. The winds blow in every direction, in a nearly spherical fashion, coming from both sides of a galaxy (only one side is shown in the artist's impression here). 

The plot shows the brightness of X-ray light from an extremely luminous quasar called PDS 456, with the highest-energy rays on the right. XMM-Newton sees lower-energy X-rays, and NuSTAR, higher. XMM Newton had previously observed PDS 456 in 2001. At that time, it had measured the X-rays up to an energy level of 11 kiloelectron volts. From those data, researchers detected a dip in the X-ray light, called an absorption feature (see dip in plot). The dip is caused by iron atoms – which are carried by the winds along with other matter – absorbing the X-ray light of a particular energy. What's more, the absorption feature is 'blue-shifted," meaning that the winds are speeding toward us.

These data told researchers that at least some of the winds were blowing toward us – but they didn't reveal whether those winds were confined to a narrow beam along our line of sight, or were blowing in all directions. That's because XMM-Newton had only detected absorption features, which by definition occur in front of a light source, in this case, the quasar. To probe what was happening at the other sides of the quasar, the astronomers needed to find an emission feature, which would indicate that the iron was scattering X-ray light at a particular energy in all directions, not only toward the observer.

NuSTAR and XMM-Newton teamed up to observe PDS 456 simultaneously in 2013 and 2014, and the results of that campaign are shown in this plot. NuSTAR data are represented as orange circles and XMM-Newton as blue squares. The NuSTAR data reveal the baseline of the "continuum" quasar light (see gray line) – or what the quasar would look like without any winds. What stands out is the bump to the left of the dips. That is an iron emission signature, the telltale sign that the black-hole winds blow to the sides and in all directions.


Source: ESA/XMM-Newton

Tuesday, February 24, 2015

Dark Matter Guides Growth of Supermassive Black Holes

This illustration shows two spiral galaxies - each with supermassive black holes at their center - as they are about to collide and form an elliptical galaxy. New research shows that galaxies' dark matter halos influence these mergers and the resulting growth of supermassive black holes. Credit: NASA/CXC/M.Weiss.High Resolution (jpg) - Low Resolution (jpg)


Cambridge, MA -Every massive galaxy has a black hole at its center, and the heftier the galaxy, the bigger its black hole. But why are the two related? After all, the black hole is millions of times smaller and less massive than its home galaxy.

A new study of football-shaped collections of stars called elliptical galaxies provides new insights into the connection between a galaxy and its black hole. It finds that the invisible hand of dark matter somehow influences black hole growth.

"There seems to be a mysterious link between the amount of dark matter a galaxy holds and the size of its central black hole, even though the two operate on vastly different scales," says lead author Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics (CfA).

This new research was designed to address a controversy in the field. Previous observations had found a relationship between the mass of the central black hole and the total mass of stars in elliptical galaxies. However, more recent studies have suggested a tight correlation between the masses of the black hole and the galaxy's dark matter halo. It wasn't clear which relationship dominated.

In our universe, dark matter outweighs normal matter - the everyday stuff we see all around us - by a factor of 6 to 1. We know dark matter exists only from its gravitational effects. It holds together galaxies and galaxy clusters. Every galaxy is surrounded by a halo of dark matter that weighs as much as a trillion suns and extends for hundreds of thousands of light-years.

To investigate the link between dark matter halos and supermassive black holes, Bogdan and his colleague Andy Goulding (Princeton University) studied more than 3,000 elliptical galaxies. They used star motions as a tracer to weigh the galaxies' central black holes. X-ray measurements of hot gas surrounding the galaxies helped weigh the dark matter halo, because the more dark matter a galaxy has, the more hot gas it can hold onto.

They found a distinct relationship between the mass of the dark matter halo and the black hole mass - a relationship stronger than that between a black hole and the galaxy's stars alone.

This connection is likely to be related to how elliptical galaxies grow. An elliptical galaxy is formed when smaller galaxies merge, their stars and dark matter mingling and mixing together. Because the dark matter outweighs everything else, it molds the newly formed elliptical galaxy and guides the growth of the central black hole.

"In effect, the act of merging creates a gravitational blueprint that the galaxy, the stars and the black hole will follow in order to build themselves," explains Bogdan.

The paper describing this work has been accepted for publication in the Astrophysical Journal. This result relied on data from the Sloan Digital Sky Survey and the ROSAT X-ray satellite's all-sky survey.

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
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

cpulliam@cfa.harvard.edu