Friday, September 19, 2014

An interacting colossus

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

This picture, taken by the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2), shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused by its interactions with the smaller galaxy that can be seen just above NGC 6872, called IC 4970. They both lie roughly 300 million light-years away from Earth.

From tip to tip, NGC 6872 measures over 500 000 light-years across, making it the second largest spiral galaxy discovered to date. In terms of size it is beaten only by NGC 262, a galaxy that measures a mind-boggling 1.3 million light-years in diameter! To put that into perspective, our own galaxy, the Milky Way, measures between 100 000 and 120 000 light-years across, making NGC 6872 about five times its size.

The upper left spiral arm of NGC 6872 is visibly distorted and is populated by star-forming regions, which appear blue on this image. This may have been be caused by IC 4970 recently passing through this arm — although here, recent means 130 million years ago! Astronomers have noted that NGC 6872 seems to be relatively sparse in terms of free hydrogen, which is the basis material for new stars, meaning that if it weren’t for its interactions with IC 4970, NGC 6872 might not have been able to produce new bursts of star formation.

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

Source: ESA/Hubble - Space Telescope

 

Thursday, September 18, 2014

Hubble Helps Find Smallest Known Galaxy with a Supermassive Black HoleDwarf Galaxy Near M60

Artist's Concept of Giant Black Hole in Center of Ultracompact Galaxy
Illustration Credit: NASA, ESA, and D. Coe and G. Bacon (STScI)
Release Images 

Dwarf Galaxy Near M60
Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.
Acknowledgment: J. Tonry (University of Hawaii), P. Cote (Dominion Astrophysical Observatory), and G. Fabbiano (Harvard-Smithsonian Center for Astrophysics).

Astronomers have found an unlikely object in an improbable place: a monster black hole lurking inside one of the tiniest galaxies known.

Though the black hole is five times the mass of the black hole at the center of our Milky Way, it is inside a galaxy that crams 140 million stars within a diameter of about 300 light-years, only 1/500th of our galaxy's diameter.

The dwarf galaxy containing the black hole, called M60-UCD1, is the densest galaxy ever seen. If you lived inside of it, the night sky would dazzle with at least 1 million stars visible to the naked eye (as opposed to 4,000 stars in our nighttime sky, as seen from Earth's surface).

The finding implies that there are many other very compact galaxies in the universe that contain supermassive black holes. The observation also suggests that dwarf galaxies may actually be the stripped remnants of larger galaxies that were torn apart during collisions with yet other galaxies — rather than small islands of stars born in isolation.

"We don't know of any other way you could make a black hole so big in an object this small," said University of Utah astronomer Anil Seth, lead author of an international study of the dwarf galaxy published in Thursday's issue of the journal Nature.

His team of astronomers used the Hubble Space Telescope and the Gemini North 8-meter optical and infrared telescope on Hawaii's Mauna Kea to observe M60-UCD1 and measure the black hole's mass. The sharp Hubble images provide information about the galaxy's diameter and stellar density. Spectroscopy with Gemini measures the stellar motions as affected by the black hole's pull. These data are used to calculate the mass of the unseen black hole.

Black holes are gravitationally collapsed, ultracompact objects that have a gravitational pull so strong that even light cannot escape. Supermassive black holes — those with the mass of at least 1 million stars like our Sun — are thought to be at the centers of many galaxies.

The black hole at the center of our Milky Way galaxy has the mass of 4 million suns, but as heavy as that is, it is less than 0.01 percent of the Milky Way's total mass. By comparison, the supermassive black hole at the center of M60-UCD1 is a stunning 15 percent of the small galaxy's total mass. "That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1," Seth said.

One explanation is that M60-UCD1 was once a large galaxy containing 10 billion stars, but then it passed very close to the center of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy got torn away and became part of M60.

The team believes that M60-UCD1 may eventually be pulled back to merge with the center of M60, which has its own monster black hole, weighing a whopping 4.5 billion solar masses (more than 1,000 times bigger than the black hole in our galaxy). When that happens, the black hole in M60-UCD1 will merge with the far more massive black hole in M60. The galaxies are 50 million light-years away.

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 conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

CONTACT 

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514

Lee Siegel
University of Utah, Salt Lake City, Utah
801-581-8993

Anil Seth
University of Utah, Salt Lake City, Utah
801-585-7793


Source: Hubble Site


Pulse of a Dead Star Powers Intense Gamma Rays

The blue dot in this image marks the spot of an energetic pulsar -- the magnetic, spinning core of star that blew up in a supernova explosion. Image credit: NASA/JPL-Caltech/SAO.  Full image and caption

Our Milky Way galaxy is littered with the still-sizzling remains of exploded stars. 

When the most massive stars explode as supernovas, they don't fade into the night, but sometimes glow ferociously with high-energy gamma rays. What powers these energetic stellar remains?

NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, is helping to untangle the mystery. The observatory's high-energy X-ray eyes were able to peer into a particular site of powerful gamma rays and confirm the source: A spinning, dead star called a pulsar. Pulsars are one of several types of stellar remnants that are left over when stars blow up in supernova explosions.

This is not the first time pulsars have been discovered to be the culprits behind intense gamma rays, but NuSTAR has helped in a case that was tougher to crack due to the distance of the object in question. NuSTAR joins NASA's Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia, each with its own unique strengths, to better understand the evolution of these not-so-peaceful dead stars.

"The energy from this corpse of a star is enough to power the gamma-ray luminosity we are seeing," said Eric Gotthelf of Columbia University, New York. Gotthelf explained that while pulsars are often behind these gamma rays in our galaxy, other sources can be as well, including the outer shells of the supernova remnants, X-ray binary stars and star-formation regions. Gotthelf is lead author of a new paper describing the findings in the Astrophysical Journal.

In recent years, the Max-Planck Institute for Astronomy's H.E.S.S. experiment has identified more than 80 incredibly powerful sites of gamma rays, called high-energy gamma-ray sources, in our Milky Way. Most of these have been associated with prior supernova explosions, but for many, the primary source of observed gamma rays remains unknown.

The gamma-ray source pinpointed in this new study, called HESS J1640-465, is one of the most luminous discovered so far. It was already known to be linked with a supernova remnant, but the source of its power was unclear. While data from Chandra and the European Space Agency's XMM-Newton telescopes hinted that the power source was a pulsar, intervening clouds of gas blocked the view, making it difficult to see.

NuSTAR complements Chandra and XMM-Newton in its capability to detect higher-energy range of X-rays that can, in fact, penetrate through this intervening gas. In addition, the NuSTAR telescope can measure rapid X-ray pulsations with fine precision. In this particular case, NuSTAR was able to capture high-energy X-rays coming at regular fast-paced pulses from HESS J1640-465. These data led to the discovery of PSR J1640-4631, a pulsar spinning five times per second -- and the ultimate power source of both the high-energy X-rays and gamma rays.

How does the pulsar produce the high-energy rays? The pulsar's strong magnetic fields generate powerful electric fields that accelerate charged particles near the surface to incredible speeds approaching that of light. The fast-moving particles then interact with the magnetic fields to produce the powerful beams of high-energy gamma rays and X-rays.

"The discovery of a pulsar engine powering HESS J1640-465 allows astronomers to test models for the underlying physics that result in the extraordinary energies generated by these rare gamma-rays sources," said Gotthelf.

"Perhaps other luminous gamma-ray sources harbor pulsars that we can't detect," said Victoria Kaspi of McGill University, Montreal, Canada, a co-author on the study. "With NuSTAR, we may be able to find more hidden pulsars."

The new data also allowed astronomers to measure the rate at which the pulsar slows, or spins down (about 30 microseconds per year), as well as how this spin-down rate varies over time. The answers will help researchers understand how these spinning magnets -- the cores of dead stars -- can be the source of such extreme radiation in our galaxy.

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA's Jet Propulsion Laboratory in Pasadena, California, for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation in Dulles, Virginia. Its instrument was built by a consortium including Caltech, JPL, the University of California, Berkeley, Columbia University, New York, NASA's Goddard Space Flight Center, Greenbelt, Maryland, the Danish Technical University in Denmark, Lawrence Livermore National Laboratory in Livermore, California, ATK Aerospace Systems in Goleta, California, and with support from the Italian Space Agency (ASI) Science Data Center.

NuSTAR's mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located in Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, California. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, California

whitney.clavin@jpl.nasa.gov



Wednesday, September 17, 2014

Violent Origins of Disc Galaxies Probed by ALMA

Distribution of molecular gas in 30 merging galaxies

 Videos

Merger between two galaxies (artist’s impression)
Merger between two galaxies (artist’s impression)


New observations explain why Milky Way-like galaxies are so common in the Universe 

For decades scientists have believed that galaxy mergers usually result in the formation of elliptical galaxies. Now, for the the first time, researchers using ALMA and a host of other radio telescopes have found direct evidence that merging galaxies can instead form disc galaxies, and that this outcome is in fact quite common. This surprising result could explain why there are so many spiral galaxies like the Milky Way in the Universe.

An international research group led by Junko Ueda, a Japan Society for the Promotion of Science postdoctoral fellow, has made surprising observations that most galaxy collisions in the nearby Universe — within 40–600 million light-years from Earth — result in so-called disc galaxies. Disc galaxies — including spiral galaxies like the Milky Way and lenticular galaxies — are defined by pancake-shaped regions of dust and gas, and are distinct from the category of elliptical galaxies.

It has, for some time, been widely accepted that merging disc galaxies would eventually form an elliptically shaped galaxy. During these violent interactions the galaxies do not only gain mass as they merge or cannibalise each-other, but they are also changing their shape throughout cosmic time, and therefore changing type along the way.

Computer simulations from the 1970s predicted that mergers between two comparable disc galaxies would result in an elliptical galaxy. The simulations predict that most galaxies today are elliptical, clashing with observations that over 70% of galaxies are in fact disc galaxies. However, more recent simulations have suggested that collisions could also form disc galaxies.

To identify the final shapes of galaxies after mergers observationally, the group studied the distribution of gas in 37 galaxies that are in their final stages of merging. The Atacama Large Millimeter/sub-millimeter Array (ALMA) and several other radio telescopes [1] were used to observe emission from carbon monoxide (CO), an indicator of molecular gas. 

The team’s research is the largest study of molecular gas in galaxies to date and provides unique insight into how the Milky Way might have formed. Their study revealed that almost all of the mergers show pancake-shaped areas of molecular gas, and hence are disc galaxies in the making. Ueda explains: “For the first time there is observational evidence for merging galaxies that could result in disc galaxies. This is a large and unexpected step towards understanding the mystery of the birth of disc galaxies.

Nonetheless, there is a lot more to discover. Ueda added: “We have to start focusing on the formation of stars in these gas discs. Furthermore, we need to look farther out in the more distant Universe. We know that the majority of galaxies in the more distant Universe also have discs. We however do not yet know whether galaxy mergers are also responsible for these, or whether they are formed by cold gas gradually falling into the galaxy. Maybe we have found a general mechanism that applies throughout the history of the Universe.”

Notes


[1] The data were obtained by ALMA; the Combined Array for Research in Millimeter-wave Astronomy: a millimeter array consisting of 23 parabola antennas in California; the Submillimeter Array a submillimeter array consisting of eight parabola antennas in Mauna Kea, Hawaii; the Plateau de Bure Interferometer; the NAOJ Nobeyama Radio Observatory 45m radio telescope; USA’s National Radio Astronomy Observatory 12m telescope; USA's Five College Radio Astronomy Observatory 14m telescope; IRAM’s 30m telescope; and the Swedish-ESO Submillimeter Telescope as a supplement.

More information


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


These observation results were published in The Astrophysical Journal Supplement (August 2014) as Ueda et al. "Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas Discs".


The team is composed of Junko Ueda (JSPS postdoctoral fellow/National Astronomical Observatory of Japan [NAOJ]), Daisuke Iono (NAOJ/The Graduate University for Advanced Studies [SOKENDAI]), Min S. Yun (The University of Massachusetts), Alison F. Crocker (The University of Toledo), Desika Narayanan (Haverford College), Shinya Komugi (Kogakuin University/ NAOJ), Daniel Espada (NAOJ/SOKENDAI/Joint ALMA Observatory), Bunyo Hatsukade (NAOJ), Hiroyuki Kaneko (University of Tsukuba), Yoichi Tamura (The University of Tokyo), David J. Wilner (Harvard-Smithsonian Center for Astrophysics), Ryohei Kawabe (NAOJ/ SOKENDAI/The University of Tokyo) and Hsi-An Pan (Hokkaido University/SOKENDAI/NAOJ)


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”.

Links


Contacts


Junko Ueda
JSPS postdoctoral fellow/NAOJ
Tel: +88 422 34 3117
Email:
junko.ueda@nao.ac.jp

Lars Lindberg Christensen
Head of ESO ePOD
Garching bei München, Germany
Tel: +49 89 3200 6761
Cell: +49 173 3872 621
Email:
lars@eso.org 

Masaaki Hiramatsu
NAOJ Chile Observatory EPO officer
Tel: +88 422 34 3630
Email:
hiramatsu.masaaki@nao.ac.jp

Source: ESO 

WASP-18: NASA's Chandra X-ray Observatory Finds Planet That Makes Star Act Deceptively Old

WASP-18
Credit: X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS; Illustration: NASA/CXC/M.Weiss

A new study using data from NASA's Chandra X-ray Observatory has shown that a planet is making the star that it orbits act much older than it actually is, as explained in our latest press release. The artist's illustration featured in the main part of this graphic depicts the star, WASP-18, and its planet, WASP-18b. 

WASP-18b is a "hot Jupiter," a giant exoplanet that orbits very close to its star, located about 330 light years from Earth. Specifically, the mass of WASP-18b is estimated to be about ten times that of Jupiter, yet it orbits its star about once every 23 hours. By comparison, it takes Jupiter about 12 years to complete one trip around the Sun from its great distance.

The new Chandra data of the WASP-18 system show that this huge planet is so close to its star that it may be causing a dampening of the star's magnetic field. As stars age, their X-ray and magnetic activity decreases. Astronomers determined that WASP-18 is only between 500 million and 2 billion years old, a relatively young age for a star. Given this age, astronomers expect that WASP-18 would be giving off copious amounts of X-rays.

Surprisingly, the long Chandra observations reveal no X-rays being emitted from WASP-18, as seen in the lower inset box. The same field-of-view in the upper inset box shows that in optical light WASP-18 is a bright source. Using established relations between the magnetic activity and X-ray emission of stars and their age, the researchers concluded that WASP-18 is about 100 times less active than it should be at its age.

The low amount of magnetic activity from WASP-18 is shown in the artist's illustration by the lack of sunspots and strong flares on the surface of the star. The weak X-ray emission from the star has relatively little effect on the outer atmosphere of the nearby planet, giving it a symmetrical appearance. By contrast, much stronger X-rays from the star CoRoT-2a are eroding the atmosphere of its nearby planet, producing a tail-like appearance.

Tidal forces from the gravitational pull of the massive planet - similar to those the Moon has on Earth's tides but on a much larger scale - may be responsible for disrupting the magnetic field of the star. The strength of the magnetic field in a star depends on the amount of convection, the process by which hot gas moves around the stellar interior. The planet's gravity may cause motions of gas inside the star that weaken the convection. Because WASP-18 has a narrower convection zone than most stars, it is more vulnerable to the impact of tidal forces that tug at it.

The effect of tidal forces from the planet may also explain an unusually high amount of lithium found in earlier, optical studies of WASP-18. Lithium is usually abundant in younger stars, but over time convection carries lithium to the hot inner regions of a star, where it is destroyed by nuclear reactions. If there is less convection, the lithium does not circulate into the interior of the star as much, allowing more of it to survive.

These results were published in the July 2014 issue of Astronomy and Astrophysics and are available online. The first author is Ignazio Pillitteri of the Istituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy. The co-authors are Scott Wolk of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; Salvatore Sciortino also from INAF-Osservatorio Astronomico di Palermo in Italy and Victoria Antoci from Aarhus University in Denmark.

Fast Facts for WASP-18:

Scale: Inset image is about 5.3 arcmin across (about 0.5 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 01h 37m 25.00s | Dec -45º 40' 40.30"
Constellation: Phoenix
Observation Date: 26 Feb 2013
Observation Time: 23 hours 43 min.
Obs. ID: 14566
Instrument: ACIS
References: Pillitteri, I et al, 2014, A&A, 567, 128; arXiv:1406.2620
Color Code: Inset: X-ray (Pink), Optical (Red, Green, Blue)
Distance Estimate: About 326 light years



Tuesday, September 16, 2014

Cold Gas in the Pipe Nebula

 
One portion of the vast dark cloud of interstellar dust called the Pipe Nebula (shown here is the object Barnard 59). The Pipe Nebula is known for being massive, and so a likely candidate for young stars, yet it is cold and dark with few signs of star formation. Astronomers have observed fifty-two dense cores in the Pipe in six key interstellar molecules using millimeter telescopes, and find clump temperatures as low as thirteen kelvin. Credit: ESO

The Pipe Nebula is a prominent dark molecular cloud located about 430 light-years from us. It contains about ten thousand solar-masses of material, making it one of the closest giant molecular complexes to us, and with dimensions of about 10 by 46 light-years, one of the largest. These properties should make it an excellent place to study star formation up close, except for one problem: there is very little star formation underway there. Instead, the Pipe Nebula has become one of the prime cases for testing ideas about star formation, since apparently an abundance of material is not enough by itself to produce new stars.

The Pipe Nebula is not uniform in density; it contains a large population of dense, low-mass cores, about 134 distinct objects. In other molecular clouds these cores evolve into young stars, but in the Pipe they remain quiescent. Astronomers have been using radio astronomy techniques to study the density and temperatures of particular molecular species in these cold cores, for example species of carbon monoxide and ammonia, whose relative line strengths can quantify these parameters.

CfA astronomers Jan Frobrich, Karin Oberg, and Charlie Lada, together with four colleagues, have now completed a study of fifty-two of the Pipe’s cores in the light from six additional molecules that are particularly useful in characterizing star formation activity, and also complemented that data with infrared images from Herschel that show the cold dust distribution. They report that the dense cores in the Pipe are very cold indeed, between 13 and 19 kelvin,with the coldest ones containing the most obscuring dust. The astronomers find that one molecule in particular, N2H+, is the only species to exclusively trace the very densest and coldest cores, making this molecule a key diagnostic for future studies to figure out why these dense cores do not form stars.

Reference(s): 


"Some Like It Cold: Molecular Emission and Effective Dust Temperatures of Dense Cores in the Pipe Nebula," Jan Forbrich, Karin Öberg, Charles J. Lada, Marco Lombardi, Alvaro Hacar, João Alves, and Jill M. Rathborne, A&A, 568, A27, 2014.


Gemini Frontier Field: First Data Now Available

Figure 1. Part of MACS J0416-2403 seen by GSAOI. The average angular resolution is about 80 milliarcseconds, the full field-of-view of the data released is nearly twice as large as shown here. 

Figure 2. Comparison of the Ks-band (2.2 micron) image taken with GSAOI (left) and the H-band (1.6 micron) image as observed with HST/WFC3. While not as deep as HST data, the new GeMS/GSAOI dataset offers twice the resolution on the distant universe

The first data from the Gemini Frontier Fields are now available for astronomers. This dataset features wide-field adaptive optics images of a strong lensing galaxy cluster obtained with the GeMS adaptive optics system and GSAOI on the Gemini South telescope. 

Massive clusters of galaxies provide astronomers with a unique view of the very distant Universe behind them as well as revealing their galaxies themselves. The deep gravitational potential of clusters distorts and amplifies the background galaxies - an effect known as strong gravitational lensing. In this way, galaxies that are otherwise unobservable with existing telescopes, are acquirable. This circumstance allows astronomers to study these distant galaxies in great detail, shedding light on how the very young universe looked, and pushing the frontiers of our knowledge. 

In the course of the Frontier Fields campaign, the Hubble Space Telescope (HST) observed six galaxy clusters, selected for their strong lensing effects. Deep optical and near-infrared images are already included in the HST dataset, augmented by additional X-ray and far-infrared observations with the Chandra and Spitzer space telescopes, respectively. However, one limitation of the HST data is its sensitivity cut-off at wavelengths longer than 1.7 microns. 

A Director's Discretionary Time program at Gemini has helped to fill the gap at 2.2 microns (Ks-band), utilizing Gemini's advanced multi-conjugated adaptive optics system, GeMS with the Gemini South Adaptive Optics Imager (GSAOI). Staff astronomer Rodrigo Carrasco led the observations, and the first of three targets visible from Gemini South in Chile is MACS J0416.1-2403, which is available now. Observations of the galaxy cluster Abell 2744 have started recently, and Abell 370 is slated for observation at Gemini South over the next year. 

GeMS/GSAOI delivers near diffraction-limited images in the near infrared (0.9-2.5 microns), over a field nearly as large as HST's Wide Field Camera 3 (WFC3). Using five artificial laser guide stars, and up to three natural guide stars, GeMS/GSAOI can correct for atmospheric turbulence at an unprecedented level, making it the most powerful wide-field adaptive optics system currently available to astronomers. This system is also the only multi-conjugated adaptive optics system currently operational at an 8-meter-class telescope. "We have achieved an angular resolution of 70-100 milliarcseconds with these data, which is a factor of two better than HST/WFC3, even though we did not go as deep as HST. These are truly spectacular data!" says Mischa Schirmer, a staff astronomer at Gemini who led the data processing effort. 

The fully calibrated and co-added images of MACS J0416.1-2403 are now available to the scientific community in order to maximize scientific return. 

The associated paper is available from http://arxiv.org/abs/1409.1820.

Contacts:



Monday, September 15, 2014

Three eyes on the sky track laws of Nature 10 billion years agoTriple telescope research


Astronomers have focused the three most powerful optical telescopes in the world on a single point in the sky to test one of Nature’s fundamental laws. 

An international team, led by researchers from Swinburne University of Technology, observed a quasar – the extremely bright surroundings of a supermassive black hole – using the Very Large Telescope in Chile and the W M Keck Observatory and Subaru Telescope, both in Hawaii.

The quasar light passed through three different galaxies, some 10, 9 and 8 billion years ago, on its way to Earth. These galaxies absorbed a characteristic pattern of colours out of the quasar light, revealing the strength of electromagnetism – one of Nature’s four fundamental forces – in the early and distant Universe.

“We need to compare the barcode patterns from three telescopes to be sure they’re right.”

Previous studies, using a large number of quasars, had found hints that electromagnetism might be different in the distant reaches of the Universe – slightly weaker or slightly stronger than on Earth.

“If that’s true, we’d need a completely new understanding of fundamental physics,” Mr Evans said.
“So it’s crucial to triple check whether and how the telescopes are distorting the barcodes.”

By comparing the barcodes, the researchers found small differences between the telescopes.

“The beauty of our method is that we can also use the barcodes themselves to correct each telescope accurately,” said Swinburne Associate Professor Michael Murphy, who co-authored the work.

“Once corrected, all three telescopes gave the same answer: electromagnetism hasn’t changed, within a few parts per million, over 10 billion years. I think this is the most reliable measurement of its kind so far”.

The team is now making similarly careful measurements in many other galaxies.

“With our new techniques and new quasar observations recently complete, we can make the most accurate check to see whether electromagnetism’s strength really is changing or not,” Associate Professor Murphy said.

The study forms part of Tyler Evans’ PhD work and uses Swinburne’s collaborative agreement with Caltech (USA) to access the Keck Observatory in Hawaii. The results are accepted for publication in the Monthly Notices of the Royal Astronomical Society and are available online.



Contact

Lea Kivivali
lkivivali@swin.edu.au
Department: Corporate & Government Affairs Unit

Phone: +61392145428


Gaia discovers its first supernova

Artist's impression of Type Ia supernova
Copyright: ESA/ATG medialab/C. Carreau
 
Discovery of supernova Gaia14aaa
Copyright: ESA/Gaia/DPAC/Z. Kostrzewa-Rutkowska (Warsaw University Astronomical Observatory) & G. Rixon (Institute of Astronomy, Cambridge)
 
Copyright: M. Fraser/S. Hodgkin/L. Wyrzykowski/H. Campbell/N. Blagorodnova/Z. Kostrzewa-Rutkowska/Liverpool Telescope/SDSS 

While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away. 

This powerful event, now named Gaia14aaa, took place in a distant galaxy some 500 million light-years away, and was revealed via a sudden rise in the galaxy’s brightness between two Gaia observations separated by one month. 

Gaia, which began its scientific work on 25 July, repeatedly scans the entire sky, so that each of the roughly one billion stars in the final catalogue will be examined an average of 70 times over the next five years. 

“This kind of repeated survey comes in handy for studying the changeable nature of the sky,” comments Simon Hodgkin from the Institute of Astronomy in Cambridge, UK. 

Many astronomical sources are variable: some exhibit a regular pattern, with a periodically rising and declining brightness, while others may undergo sudden and dramatic changes. 

“As Gaia goes back to each patch of the sky over and over, we have a chance to spot thousands of ‘guest stars’ on the celestial tapestry,” notes Dr Hodgkin. “These transient sources can be signposts to some of the most powerful phenomena in the Universe, like this supernova.” 

Dr Hodgkin is part of Gaia’s Science Alert Team, which includes astronomers from the Universities of Cambridge, UK, and Warsaw, Poland, who are combing through the scans in search of unexpected changes.  

It did not take long until they found the first ‘anomaly’ in the form of a sudden spike in the light coming from a distant galaxy, detected on 30 August. The same galaxy appeared much dimmer when Gaia first looked at it just a month before. 

“We immediately thought it might be a supernova, but needed more clues to back up our claim,” explains Łukasz Wyrzykowski from the Warsaw University Astronomical Observatory, Poland. 

Other powerful cosmic events may resemble a supernova in a distant galaxy, such as outbursts caused by the mass-devouring supermassive black hole at the galaxy centre. 

However, in Gaia14aaa, the position of the bright spot of light was slightly offset from the galaxy’s core, suggesting that it was unlikely to be related to a central black hole. 

So, the astronomers looked for more information in the light of this new source. Besides recording the position and brightness of stars and galaxies, Gaia also splits their light to create a spectrum. In fact, Gaia uses two prisms spanning red and blue wavelength regions to produce a low-resolution spectrum that allows astronomers to seek signatures of the various chemical elements present in the source of that light.
Copyright: ESA/Gaia/DPAC/N. Blagorodnova, 
M. Fraser, H. Campbell, A. Hall (Institute of Astronomy, Cambridge)

“In the spectrum of this source, we could already see the presence of iron and other elements that are known to be found in supernovas,” says Nadejda Blagorodnova, a PhD student at the Institute of Astronomy in Cambridge. 

In addition, the blue part of the spectrum appears significantly brighter than the red part, as expected in a supernova. And not just any supernova: the astronomers already suspected it might be a ‘Type Ia’ supernova – the explosion of a white dwarf locked in a binary system with a companion star. 

While other types of supernovas are the explosive demises of massive stars, several times more massive than the Sun, Type Ia supernovas are the end product of their less massive counterparts. 

Low-mass stars, with masses similar to the Sun’s, end their lives gently, puffing up their outer layers and leaving behind a compact white dwarf. Their high density means that white dwarfs can exert an intense gravitational pull on a nearby companion star, accreting mass from it until the white dwarf reaches a critical mass that then sparks a violent explosion. 

To confirm the nature of this supernova, the astronomers complemented the Gaia data with more observations from the ground, using the Isaac Newton Telescope (INT) and the robotic Liverpool Telescope on La Palma, in the Canary Islands, Spain. 

A high-resolution spectrum, obtained on 3 September with the INT, confirmed not only that the explosion corresponds to a Type Ia supernova, but also provided an estimate of its distance. This proved that the supernova happened in the galaxy where it was observed. 

“This is the first supernova in what we expect to be a long series of discoveries with Gaia,” says Timo Prusti, ESA’s Gaia Project Scientist. 

Supernovas are rare events: only a couple of these explosions happen every century in a typical galaxy. But they are not so rare over the whole sky, if we take into account the hundreds of billions of galaxies that populate the Universe. 

Astronomers in the Science Alert Team are currently getting acquainted with the data, testing and optimising their detection software. In a few months, they expect Gaia to discover about three new supernovas every day. 

In addition to supernovas, Gaia will discover thousands of transient sources of other kinds – stellar explosions on smaller scale than supernovas, flares from young stars coming to life, outbursts caused by black holes that disrupt and devour a nearby star, and possibly some entirely new phenomena never seen before. 

“The sky is ablaze with peculiar sources of light, and we are looking forward to probing plenty of those with Gaia in the coming years,” concludes Dr Prusti. 

More information
 
For details about Gaia's Science Alerts see the Notes for Editors.

For further information, please contact:
 
Markus Bauer 



ESA Science and Robotic Exploration Communication Officer




Tel: +31 71 565 6799





Mob: +31 61 594 3 954





Email:
markus.bauer@esa.int




Timo Prusti



Gaia Project Scientist


Email:
timo.prusti@esa.int

Simon Hodgkin
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 766657
Email:
sth@ast.cam.ac.uk

Lukasz Wyrzykowski
Warsaw University Astronomical Observatory
Warsaw, Poland
Tel: +48 608 648817
Email:
lw@astrouw.edu.pl

Nadejda Blagorodnova
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 337548
Email:
nblago@ast.cam.ac.uk

Source: ESA


Friday, September 12, 2014

Mysterious quasar sequence explained

This graph shows the distribution of about 20,000 luminous Sloan Digital Sky Survey quasars in the two-dimensional space of broad line width versus FeII strength, color-coded by the strength of the narrow [OIII] line emission. The strong horizontal trend is the main sequence of quasars driven by the efficiency of the black hole accretion, while the vertical spread of broad line width is largely due to our viewing angle to the inner region of the quasar. A larger version is available here.

Pasadena, CA—Quasars are supermassive black holes that live at the center of distant massive galaxies. They shine as the most luminous beacons in the sky across the entire electromagnetic spectrum by rapidly accreting matter into their gravitationally inescapable centers. New work from Carnegie’s Hubble Fellow Yue Shen and Luis Ho of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University solves a quasar mystery that astronomers have been puzzling over for 20 years. Their work, published in the September 11 issue of Nature, shows that most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

Quasars display a broad range of outward appearances when viewed by astronomers, reflecting the diversity in the conditions of the regions close to their centers. But despite this variety, quasars have a surprising amount of regularity in their quantifiable physical properties, which follow well-defined trends (referred to as the “main sequence” of quasars) discovered more than 20 years ago. Shen and Ho solved a two-decade puzzle in quasar research: What unifies these properties into this main sequence?

Using the largest and most-homogeneous sample to date of over 20,000 quasars from the Sloan Digital Sky Survey, combined with several novel statistical tests, Shen and Ho were able to demonstrate that one particular property related to the accretion of the hole, called the Eddington ratio, is the driving force behind the so-called main sequence. The Eddington ratio describes the efficiency of matter fueling the black hole, the competition between the gravitational force pulling matter inward and the luminosity driving radiation outward. This push and pull between gravity and luminosity has long been suspected to be the primary driver behind the so-called main sequence, and their work at long last confirms this hypothesis.

Of additional importance, they found that the orientation of an astronomer’s line-of-sight when looking down into the black hole’s inner region plays a significant role in the observation of the fast-moving gas innermost to the hole, which produces the broad emission lines in quasar spectra. This changes scientists’ understanding of the geometry of the line-emitting region closest to the black hole, a place called the broad-line region: the gas is distributed in a flattened, pancake-like configuration. Going forward, this will help astronomers improve their measurements of black hole masses for quasars. 

“Our findings have profound implications for quasar research. This simple unification scheme presents a pathway to better understand how supermassive black holes accrete matter and interplay with their environments,” Shen said. 

“And better black hole mass measurements will benefit a variety of applications in understanding the cosmic growth of supermassive black holes and their place in galaxy formation,” Ho added.


**********************

Support for this research was provided by NASA’s Hubble Fellowship, awarded by the Space Telescope Science Institute, operated by the Association of Universites for Research in Astronomy Inc. for NASA, the Kavli Foundation, Peking University, and the Chinese Academy of Science through a grant from the Strategic Priority Research Program.



A spattering of blue

Credit: ESA/Hubble, NASA, D. Calzetti (UMass) and the LEGUS Team

Far beyond the stars in the constellation of Leo (The Lion) is irregular galaxy IC 559.

IC 559 is not your everyday galaxy. With its irregular shape and bright blue spattering of stars, it is a fascinating galactic anomaly. It may look like sparse cloud, but it is in fact full of gas and dust which is spawning new stars.

Discovered in 1893, IC 559 lacks the symmetrical spiral appearance of some of its galactic peers and not does not conform to a regular shape. It is actually classified as a “type Sm” galaxy — an irregular galaxy with some evidence for a spiral structure.

Irregular galaxies make up about a quarter of all known galaxies and do not fall into any of the regular classes of the Hubble sequence. Most of these uniquely shaped galaxies were not always so — IC 559 may have once been a conventional spiral galaxy that was then distorted and twisted by the gravity of a nearby cosmic companion.

This image, captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3, combines a wide range of wavelengths spanning the ultraviolet, optical, and infrared parts of the spectrum.

Source: ESA/Hubble - Space Telescope

Thursday, September 11, 2014

Puppis A: An X-ray Tapestry

Puppis A
Credit: X-ray: NASA/CXC/IAFE/G.Dubner et al & ESA/XMM-Newton

The destructive results of a powerful supernova explosion reveal themselves in a delicate tapestry of X-ray light, as seen in this image from NASA's Chandra X-Ray Observatory and the European Space Agency's XMM-Newton.

The image shows the remains of a supernova that would have been witnessed on Earth about 3,700 years ago. The remnant is called Puppis A, and is around 7,000 light years away and about 10 light years across. This image provides the most complete and detailed X-ray view of Puppis A ever obtained, made by combining a mosaic of different Chandra and XMM-Newton observations. Low-energy X-rays are shown in red, medium-energy X-rays are in green and high energy X-rays are colored blue.

These observations act as a probe of the gas surrounding Puppis A, known as the interstellar medium. The complex appearance of the remnant shows that Puppis A is expanding into an interstellar medium that probably has a knotty structure.

Supernova explosions forge the heavy elements that can provide the raw material from which future generations of stars and planets will form. Studying how supernova remnants expand into the galaxy and interact with other material provides critical clues into our own origins.

A paper describing these results was published in the July 2013 issue of Astronomy and Astrophysics and is available online. The first author is Gloria Dubner from the Instituto de Astronomía y Física del Espacio in Buenos Aires in Argentina.



Fast Facts for Puppis A:


Release Date: September 10, 2014
Scale: Image is about 1.5 degrees across (About 180 light years)
Category: Supernovas & Supernova Remnants
Coordinates (J2000): RA 08h 23m 08.16s | Dec -42º 41' 41.40"
Constellation: Puppis
Observation Date: 9 pointings between January 2000 and November 2010
Observation Time: 44 hours 45 min (1 day 20 hours 45 min).
Obs. ID: 750, 1949-1951, 5564, 6371, 12548, 13183
Instrument: ACIS
References: Dubner, G. et al, 2013, A&A, 555; arXiv:1305.1275; Arendt, R. et al, 2010, ApJ 725:585  
Color Code: X-ray (Red, Green, Blue)
Distance Estimate: About 7,000 light years




First Evidence for Water Ice Clouds Found outside Solar System


Washington, D.C.—A team of scientists led by Carnegie's Jacqueline Faherty has discovered the first evidence of water ice clouds on an object outside of our own Solar System. Water ice clouds exist on our own gas giant planets--Jupiter, Saturn, Uranus, and Neptune--but have not been seen outside of the planets orbiting our Sun until now. Their findings are published today by The Astrophysical Journal Letters and are available here.

At the Las Campanas Observatory in Chile, Faherty, along with a team including Carnegie's Andrew Monson, used the FourStar near infrared camera to detect the coldest brown dwarf ever characterized. Their findings are the result of 151 images taken over three nights and combined. The object, named WISE J085510.83-071442.5, or W0855, was first seen by NASA's Wide-Field Infrared Explorer mission and published earlier this year. But it was not known if it could be detected by Earth-based facilities.
"This was a battle at the telescope to get the detection," said Faherty. 

Chris Tinney, an Astronomer at the Australian Centre for Astrobiology, UNSW Australia and co-author on the result stated: "This is a great result. This object is so faint and it’s exciting to be the first people to detect it with a telescope on the ground."

Brown dwarfs aren't quite very small stars, but they aren't quite giant planets either. They are too small to sustain the hydrogen fusion process that fuels stars. Their temperatures can range from nearly as hot as a star to as cool as a planet, and their masses also range between star-like and giant planet-like. They are of particular interest to scientists because they offer clues to star-formation processes. They also overlap with the temperatures of planets, but are much easier to study since they are commonly found in isolation. 

W0855 is the fourth-closest system to our own Sun, practically a next-door neighbor in astronomical distances. A comparison of the team's near-infrared images of W0855 with models for predicting the atmospheric content of brown dwarfs showed evidence of frozen clouds of sulfide and water. 

"Ice clouds are predicted to be very important in the atmospheres of planets beyond our Solar System, but they've never been observed outside of it before now," Faherty said. 

The paper's other co-author is Andrew Skemer of the University of Arizona. 

*  *  *  *  *

This work was supported by the Australian Research Council. It made use of data from the NASA WISE mission, which was a joint project of the University of California Los Angeles and the Jet Propulsion Laboratory and Caltech, funded by NASA. It also made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory and Caltech, under contract with NASA.


Wednesday, September 10, 2014

This Star Cluster Is Not What It Seems

PR Image eso1428a  
The globular star cluster Messier 54

The globular star cluster Messier 54 in the constellation of Sagittarius

Wide-field view of the sky around the globular star cluster Messier 54

 

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Videos

Zooming in on the globular star cluster Messier 54
Zooming in on the globular star cluster Messier 54

Close-up view of the globular star cluster Messier 54
Close-up view of the globular star cluster Messier 54


This new image from the VLT Survey Telescope at ESO’s Paranal Observatory in northern Chile shows a vast collection of stars, the globular cluster Messier 54. This cluster looks very similar to many others but it has a secret. Messier 54 doesn’t belong to the Milky Way, but is part of a small satellite galaxy, the Sagittarius Dwarf Galaxy. This unusual parentage has now allowed astronomers to use the Very Large Telescope (VLT) to test whether there are also unexpectedly low levels of the element lithium in stars outside the Milky Way. 

The Milky Way galaxy is orbited by more than 150 globular star clusters, which are balls of hundreds of thousands of old stars dating back to the formation of the galaxy. One of these, along with several others in the constellation of Sagittarius (The Archer), was found in the late eighteenth century by the French comet hunter Charles Messier and given the designation Messier 54.

For more than two hundred years after its discovery Messier 54 was thought to be similar to the other Milky Way globulars. But in 1994 it was discovered that it was actually associated with a separate galaxy — the Sagittarius Dwarf Galaxy. It was found to be at a distance of around 90 000 light-years — more than three times as far from Earth as the galactic centre.

Astronomers have now observed Messier 54 using the VLT as a test case to try to solve one of the mysteries of modern astronomy — the lithium problem.

Most of the light chemical element lithium now present in the Universe was produced during the Big Bang, along with hydrogen and helium, but in much smaller quantities. Astronomers can calculate quite accurately how much lithium they expect to find in the early Universe, and from this work out how much they should see in old stars. But the numbers don’t match — there is about three times less lithium in stars than expected. This mystery remains, despite several decades of work [1].

Up to now it has only been possible to measure lithium in stars in the Milky Way. But now a team of astronomers led by Alessio Mucciarelli (University of Bologna, Italy) has used the VLT to measure how much lithium there is in a selection of stars in Messier 54. They find that the levels are close to those in the Milky Way. So, whatever it is that got rid of the lithium seems not to be specific to the Milky Way.

This new image of the cluster was created from data taken with the VLT Survey Telescope (VST) at the Paranal Observatory. As well as showing the cluster itself it reveals the extraordinarily dense forest of much closer Milky Way stars that lie in the foreground.

Notes


[1] There are several possible proposed solutions to the riddle. The first is that the calculations of the amounts of lithium produced in the Big Bang are wrong — but very recent tests suggest that this is not the case. The second is that the lithium was somehow destroyed in the earliest stars, before the formation of the Milky Way. The third is that some process in the stars has gradually destroyed lithium during their lives.

More information


This research was presented in a paper, “The cosmological Lithium problem outside the Galaxy: the Sagittarius globular cluster M54”, by A. Mucciarelli et al., to appear in Monthly Notices of the Royal Astronomical Society (Oxford University Press).


The team is composed of: A. Mucciarelli (University of Bologna, Italy), M. Salaris (Liverpool John Moores University, Liverpool, UK), P. Bonifacio (Observatoire de Paris, France), L. Monaco (ESO, Santiago, Chile) and S. Villanova (Universidad de Concepcion, Concepcion, Chile).


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”.

Links

Contacts


Alessio Mucciarelli
University of Bologna
Bologna, Italy
Tel: +39 051 20 95705
Email:
alessio.mucciarelli2@unibo.it

Lars Lindberg Christensen
Head of ESO ePOD
Garching bei München, Germany
Tel: +49 89 3200 6761
Cell: +49 173 3872 621
Email:
lars@eso.org

Source: ESO

Interactive dark matter could explain Milky Way’s missing satellite galaxies

The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University. Click  here for a full resolution image

Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University. Click  here for a larger image 

Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.

This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.

Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.

Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.

Scientists think clumps of dark matter – or haloes – that emerged from the early Universe, trapped the intergalactic gas needed to form stars and galaxies. Scattering the dark matter particles wipes out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.

Lead author Dr Celine Boehm, in the Institute for Particle Physics Phenomenology at Durham University, said: "We don’t know how strong these interactions should be, so this is where our simulations come in."

"By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the Universe."

"This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics."

There are several theories about why there are not more galaxies orbiting the Milky Way, which include the idea that heat from the Universe’s first stars sterilised the gas needed to form stars. The researchers say their current findings offer an alternative theory and could provide a novel technique to probe interactions between other particles and cold dark matter.

Co-author Professor Carlton Baugh said: "Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter."
 
"The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe."

"However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought."

The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.

The work was funded by the Science and Technology Facilities Council and the European Union.

Media contacts

Durham University Media Relations Team
Tel: +44 (0)191 334 6075

media.relations@durham.ac.uk

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

rm@ras.org.uk

The science contacts are available for interview via down-the-line broadcast quality TV facilities from the Durham City campus, via broadcast provider Globelynx.

To access the fixed camera and circuit directly, broadcasters can log into Globelynx. The IFB number is +44 (0)191 384 2019. If you have not booked a Globelynx feed before please call +44 (0)20 7963 7060 for assistance.

A broadcast quality ISDN radio line is also available at Durham University and bookings can be arranged via the Media Relations Team on the contact details above. The ISDN number is +44 (0)191 386 2749.
A landline number is available in the Media Suite which houses the television and radio facilities: +44 (0)191 334 6472.

Science contacts

All the contacts are available for interview on Monday 8 and Tuesday 9 September.
Professor Carlton Baugh
Institute for Computational Cosmology
Durham University
Tel: +44 (0)191 33 43542

c.m.baugh@durham.ac.uk

Ryan Wilkinson
Institute for Computational Cosmology
Durham University
Tel: +44 (0)191 33 45753

ryan.wilkinson@durham.ac.uk

Jascha Schewtschenko
Institute for Computational Cosmology
Durham University
Tel: +44 (0)191 33 43710

j.a.schewtschenko@durham.ac.uk

Images and captions

Images are available for download from the RAS website and from the Durham media relations team.

The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University.

Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University

Further information

This research has been published in Boehm C. el al., 2014, "Using the Milky Way satellites to study interactions between cold dark matter and radiation", Monthly Notices of the Royal Astronomical Society, vol. 445, p. L31-L35, published by Oxford University Press. A preprint version is available on the arXiv.

Useful Web Links

Notes for editors

The DiRAC Data Centric system at Durham University is operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility. The DiRAC system is funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/H008519/1, STFC DiRAC Operations grant ST/K003267/1, and Durham University. DiRAC is part of the National E-Infrastructure.


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