Thursday, May 17, 2018

Hubble shows the local Universe in ultraviolet

The glowing spiral arms of NGC 6744

Dwarf galaxy UGCA 281

Messier 66 — member of the Leo Triplet
Pockets of star formation in DDO 68

PR Image heic1810e
Wave of star formation in Messier 96

Parts of Messier 106

Using the unparalleled sharpness and ultraviolet observational capabilities of the NASA/ESA Hubble Space Telescope, an international team of astronomers has created the most comprehensive high-resolution ultraviolet-light survey of star-forming galaxies in the local Universe. The catalogue contains about 8000 clusters and 39 million hot blue stars.

Ultraviolet light is a major tracer of the youngest and hottest stars. These stars are short-lived and intensely bright. Astronomers have now finished a survey called LEGUS (Legacy ExtraGalactic UV Survey) that captured the details of 50 local galaxies within 60 million light-years of Earth in both visible and ultraviolet light.

The LEGUS team carefully selected its targets from among 500 candidate galaxies compiled from ground-based surveys. They chose the galaxies based on their mass, star-formation rate, and their abundances of elements heavier than hydrogen and helium. Because of the proximity of the selected galaxies, Hubble was able to resolve them into their main components: stars and star clusters. With the LEGUS data, the team created a catalogue with about 8000 young clusters and it also created a star catalogue comprising about 39 million stars that are at least five times more massive than our Sun.

The data, gathered with Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys, provide detailed information on young, massive stars and star clusters, and how their environment affects their development. As such, the catalogue offers an extensive resource for understanding the complexities of star formation and galaxy evolution.

One of the key questions the survey may help astronomers answer is the connection between star formation and the major structures, such as spiral arms, that make up a galaxy. These structured distributions are particularly visible in the youngest stellar populations.

By resolving the fine details of the studied galaxies, while also studying the connection to larger galactic structures, the team aims to identify the physical mechanisms behind the observed distribution of stellar populations within galaxies.

Figuring out the final link between gas and star formation is key to fully understanding galaxy evolution. Astronomers are studying this link by looking at the effects of the environment on star clusters, and how their survival is linked to their surroundings.

LEGUS will not only allow astronomers to understand the local Universe. It will also help interpret views of distant galaxies, where the ultraviolet light from young stars is stretched to infrared wavelengths due to the expansion of space. The NASA/ESA/CSA James Webb Space Telescope and its ability to observe in the far infrared will complement the LEGUS views.

More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Image credit: NASA, ESA, LEGUS team



Linda Smith
European Space Agency
Baltimore, Maryland, USA
Tel: 001 4103384926

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500

Wednesday, May 16, 2018

ALMA and VLT Find Evidence for Stars Forming Just 250 Million Years After Big Bang

Hubble and ALMA image of MACS J1149.5+2223
Galaxy cluster MACS j1149.5+223
ALMA observation of distant galaxy MACS 1149-JD1


ESOcast 161 Light: Distant galaxy reveals very early star formation (4K UHD)
ESOcast 161 Light: Distant galaxy reveals very early star formation (4K UHD)

Zooming in on the distant galaxy MACS1149, and beyond
Zooming in on the distant galaxy MACS1149, and beyond

Computer simulation of star formation in MACS1149-JD1
Computer simulation of star formation in MACS1149-JD1

Zooming in on the distant galaxy MACS 1149-JD1
Zooming in on the distant galaxy MACS 1149-JD1

Astronomers have used observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and ESO’s Very Large Telescope (VLT) to determine that star formation in the very distant galaxy MACS1149-JD1 started at an unexpectedly early stage, only 250 million years after the Big Bang. This discovery also represents the most distant oxygen ever detected in the Universe and the most distant galaxy ever observed by ALMA or the VLT. The results will appear in the journal Nature on 17 May 2018.

An international team of astronomers used ALMA to observe a distant galaxy called MACS1149-JD1. They detected a very faint glow emitted by ionised oxygen in the galaxy. As this infrared light travelled across space, the expansion of the Universe stretched it to wavelengths more than ten times longer by the time it reached Earth and was detected by ALMA. The team inferred that the signal was emitted 13.3 billion years ago (or 500 million years after the Big Bang), making it the most distant oxygen ever detected by any telescope [1]. The presence of oxygen is a clear sign that there must have been even earlier generations of stars in this galaxy.

“I was thrilled to see the signal of the distant oxygen in the ALMA data,” says Takuya Hashimoto, the lead author of the new paper and a researcher at both Osaka Sangyo University and the National Astronomical Observatory of Japan. “This detection pushes back the frontiers of the observable Universe.”

In addition to the glow from oxygen picked up by ALMA, a weaker signal of hydrogen emission was also detected by ESO’s Very Large Telescope (VLT). The distance to the galaxy determined from this observation is consistent with the distance from the oxygen observation. This makes MACS1149-JD1 the most distant galaxy with a precise distance measurement and the most distant galaxy ever observed with ALMA or the VLT.

“This galaxy is seen at a time when the Universe was only 500 million years old and yet it already has a population of mature stars,” explains Nicolas Laporte, a researcher at University College London (UCL) in the UK and second author of the new paper. “We are therefore able to use this galaxy to probe into an earlier, completely uncharted period of cosmic history.”

For a period after the Big Bang there was no oxygen in the Universe; it was created by the fusion processes of the first stars and then released when these stars died. The detection of oxygen in MACS1149-JD1 indicates that these earlier generations of stars had been already formed and expelled oxygen by just 500 million years after the beginning of the Universe.

But when did this earlier star formation occur? To find out, the team reconstructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. They found that the observed brightness of the galaxy is well-explained by a model where the onset of star formation corresponds to only 250 million years after the Universe began [2].

The maturity of the stars seen in MACS1149-JD1 raises the question of when the very first galaxies emerged from total darkness, an epoch astronomers romantically term “cosmic dawn”. By establishing the age of MACS1149-JD1, the team has effectively demonstrated that galaxies existed earlier than those we can currently directly detect.

Richard Ellis, senior astronomer at UCL and co-author of the paper, concludes: “Determining when cosmic dawn occurred is akin to the Holy Grail of cosmology and galaxy formation. With these new observations of MACS1149-JD1 we are getting closer to directly witnessing the birth of starlight! Since we are all made of processed stellar material, this is really finding our own origins.”

More Information

These results are published in a paper entitled: “The onset of star formation 250 million years after the Big Bang”, by T. Hashimoto et al., to appear in the journal Nature on 17 May 2018.

The research team members are: Takuya Hashimoto (Osaka Sangyo University/National Astronomical Observatory of Japan, Japan), Nicolas Laporte (University College London, United Kingdom), Ken Mawatari (Osaka Sangyo University, Japan), Richard S. Ellis (University College London, United Kingdom), Akio. K. Inoue (Osaka Sangyo University, Japan), Erik Zackrisson (Uppsala University, Sweden), Guido Roberts-Borsani (University College London, United Kingdom), Wei Zheng (Johns Hopkins University, Baltimore, Maryland, United States), Yoichi Tamura (Nagoya University, Japan), Franz E. Bauer (Pontificia Universidad Católica de Chile, Santiago, Chile), Thomas Fletcher (University College London, United Kingdom), Yuichi Harikane (The University of Tokyo, Japan), Bunyo Hatsukade (The University of Tokyo, Japan), Natsuki H. Hayatsu (The University of Tokyo, Japan; ESO, Garching, Germany), Yuichi Matsuda (National Astronomical Observatory of Japan/SOKENDAI, Japan), Hiroshi Matsuo (National Astronomical Observatory of Japan/SOKENDAI, Japan, Sapporo, Japan), Takashi Okamoto (Hokkaido University, Sapporo, Japan), Masami Ouchi (The University of Tokyo, Japan), Roser Pelló (Université de Toulouse, France), Claes-Erik Rydberg (Universität Heidelberg, Germany), Ikkoh Shimizu (Osaka University, Japan), Yoshiaki Taniguchi (The Open University of Japan, Chiba, Japan), Hideki Umehata (The University of Tokyo, Japan) and Naoki Yoshida (The University of Tokyo, Japan).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, 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 and with Australia as a strategic partner. 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Nicolas Laporte
University College London
London, United Kingdom
Tel: +44 7452 807 591

Richard Ellis
University College London
London, United Kingdom
Tel: +44 7885 403 334

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Source: ESO/News

Tuesday, May 15, 2018

Revealing the complexity of the nebula in NGC 1275 with SITELLE

Hα filamentary structure around NGC 1275.
Credits: Marie-Lou Gendron-Marsolais, Julie Hlavacek-Larrondo, Laurent Drissen and Maxime Pivin-Lapointe.  
Hi-res image

Movie showing how the filamentary structure of NGC 1275 varies with wavelength. 
Credits: Marie-Lou Gendron-Marsolais, Julie Hlavacek-Larrondo, Laurent Drissen and Maxime Pivin-Lapointe.

Ph.D. student Marie-Lou Gendron-Marsolais and professor Julie Hlavacek-Larrondo, from the Centre for Research in Astrophysics of Québec (CRAQ) and Université de Montréal, have joined the developers of SITELLE, Laurent Drissen and Thomas Martin from Université Laval, an instrument recently installed at the Canada-France-Hawaii telescope (CFHT), to reveal for the first time the intricate dynamic around the galaxy NGC 1275. 

Located 250 million light-years from earth, NGC 1275 is not an ordinary galaxy. It sits in the middle of the Perseus galaxy cluster, a gigantic cluster harboring thousands of galaxies in the constellation of the same name. NGC 1275 rests at the center of a hot and diffuse intracluster gas with an average temperature of tens of millions of degrees. This complex gas constitutes a large part of the luminous mass of galaxy clusters: the hot gas tends to cool and fall toward the galaxy while the central supermassive black hole releases powerful jets of energetic particles. These particles blow gigantic bubbles in the hot gas, preventing it from cooling. Astronomers generally dectect these bubbles by using radio radio telescopes. However, a spectacular network of thin intricate filaments surrounding the galaxy NGC 1275 is visible at specific optical wavelengths. "These types of filaments are often visible around galaxies that lie in similar environments... but their origin is a real mystery", declares Marie-Lou Gendron-Marsolais, lead author on the paper.

Extending over 250 000 light-years, two to three times the size of our own galaxy, the link between this large network of filaments and its environment is still unclear. Two theories are in conflict: the filaments could be condensing from the hot intracluster gas and sinking toward the center of the galaxy or being lifted by the bubbles created by the central supermassive black hole jets and dragged outward of the galaxy.

In order to unravel the mystery of these filaments, the international team of researchers have used SITELLE, an instrument at the Canada-France-Hawaii Telescope that enables the imaging of the galaxy at several different wavelengths at the same time. "This way we obtain a spectrum for each pixel of the image" declares Julie Hlavacek-Larrondo, a coauthor on the paper. "But what is unique about SITELLE is its incredibly large field of view, covering NGC 1275 in its entirety for the first time since the discovery of the nebula, 60 years ago", she adds.

Installed at the top of Maunakea on the Big Island in 2015, SITELLE is the product of the expertise of a team led by the astrophysicist Laurent Drissen as well as the optical design specialist Simon Thibault, both professors at the Faculté des sciences et de génie of Université Laval, as well as the knowledge of CFHT and the high-performance technology business ABB.

With a spectra for each pixel, it is now possible to obtain the radial velocity of each filament, revealing their dynamics at an unprecedented level. "The motion of this network of filaments seems to be very complex. It does not seem to be from a uniform motion, rather it is extremely chaotic", declares Marie-Lou Gendron-Marsolais. The team is convinced that such observations will help illuminate the mysteries of these structures. Understanding the filaments' dynamics aids astronmers in the understanding the processes of heating and cooling of the gas feeding the central black hole. Unlocking this process constitutes a key element in the study of galaxy evolution and, at larger scale, of environment such as clusters of galaxies.

The results from the work led by Marie-Lou Gendron-Marsolais, Julie Hlavacek-Larrondo, Laurent Drissen, Thomas Martin and their international collaborators are published in a letter of the latest issue of the Monthly Notices of the Royal Astronomical Society.

Additional information:

Preprint (No login required)

Contact Information:

Media contacts

Mary Beth Laychak
Outreach manager
Canada-France-Hawaii Telescope

Robert Lamontagne
Public Outreach
Centre de recherche en astrophysique du Québec
Phone : (438) 495-3482

Science contacts:

Marie-Lou Gendron-Marsolais
Centre de recherche en astrophysique du Québec
Université de Montréal

Professor Julie Hlavacek-Larrondo
Centre de recherche en astrophysique du Québec
Université de Montréal

Professor Laurent Drissen
Centre recherche en astrophysique du Québec
Université Laval

Sunday, May 13, 2018

Dutch astronomers photograph possible toddler planet by chance

An international team of astronomers headed by Dutch researchers from Leiden University has coincidently found a small companion around the young double star CS Cha. The astronomers examined the dust disc of the binary, while they stumbled upon the companion. The researchers suspect that it is a planet in his toddler years that is still growing. The astronomers used the SPHERE instrument on the European Very Large Telescope in Chile. They will soon publish their findings in an article that is accepted by the journal Astronomy & Astrophysics.

The binary star CS Cha and his special companion are located some six hundred light years away from Earth in a star formation area in the southern constellation Chameleon. The double star is just two to three million years young. The researchers wanted to study the star to search for a dust disc and for planets in the making.

During their research on the binary star, the astronomers saw a small dot on the edge of their images. The researchers dived into the telescope archives and discovered the dot, but much fainter, also on 19 year old photographs taken with the Hubble Space Telescope and on 11 year old photographs of the Very Large Telescope. Thanks to the old photographs, the astronomers were able to show that the companion moves with the binary and that they belong together.

What the companion looks like and how it was formed is unclear. The researchers tried to fit various models on the observations, but they do not give a hundred percent certainty. The companion may be a small brown dwarf star, but it can also be a big super-Jupiter.

Lead author Christian Ginski (Leiden Observatory, Leiden University) explains: "The most exciting part is that the light of the companion is highly polarized. Such a preference in the direction of polarization usually occurs when light is scattered along the way. We suspect that the companion is surrounded by his own dust disc. The tricky part is that the disc blocks a large part of the light and that is why we can hardly determine the mass of the companion. So it could be a brown dwarf but also a super-Jupiter in his toddler years. The classical planet-forming-models can't help us."

In the future, the researchers want to examine the star and the companion in more detail. They want to use the international ALMA telescope on the Chajnantor plateau in the North Chilean Andes.


SPHERE is the abbreviation of Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. It is a powerful planet hunter that is attached to the European Very Large Telescope at Cerro Paranal in northern Chile. The instrument has partly been developed in the Netherlands. SPHERE can make direct images of exoplanets and dust discs around stars. The instrument bypasses the bright star and looks specifically at polarized light that is reflected by the atmosphere of an exoplanet or the dust disc around a star.

"First direct detection of a polarized companion outside of a resolved circumbinary disk around CS Cha*", C. Ginski (1, 2), M. Benisty (3, 4), R.G. van Holstein (1), A. Juhász (5), T.O.B. Schmidt (6), G. Chauvin (3, 4) , J. de Boer (1), M. Wilby (1), C.F. Manara (7), P. Delorme (4), F. Ménard (4), P. Pinilla (8), T. Birnstiel (9), M. Flock(10), C. Keller (1), M. Kenworthy (1), J. Milli (4, 11), J. Olofsson (12, 13), L. Pérez (14), F. Snik (1), en N. Vogt (12). 1. Universiteit Leiden; 2. Universiteit van Amsterdam; 3 en 14. Universidad de Chile (Chili); 4. Univ. Grenoble Alpes (Frankrijk); 5. University of Cambridge (Verenigd Koninkrijk); 6. Sorbonne Paris Cité (Frankrijk); 7 ESA/ESTEC, Noordwijk; 8. The University of Arizona (Verenigde Staten); 9. Ludwig-Maximilians-Universität München (Duitsland); 10. Max-Planck-Institut für Astronomie (Duitsland); 11. European Southern Observatory (Chili); 12 en 13. Universidad de Valparaíso (Chili), 2018, accepted for publication in Astronomy and Astrophysics. (free preprint)

Dutch news release

Source: Astronomie.NL

Saturday, May 12, 2018

NASA’s NICER Mission Finds an X-ray Pulsar in a Record-fast Orbit

The stars of IGR J17062–6143, illustrated here, circle each other every 38 minutes, the fastest-known orbit for a binary system containing an accreting millisecond X-ray pulsar. As they revolve, a superdense pulsar pulls gas from a lightweight white dwarf. The two stars are so close they would fit between Earth and the Moon. Credits: NASA’s Goddard Space Flight Center. Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

Scientists analyzing the first data from the Neutron star Interior Composition Explorer (NICER) mission have found two stars that revolve around each other every 38 minutes — about the time it takes to stream a TV drama. One of the stars in the system, called IGR J17062–6143 (J17062 for short), is a rapidly spinning, superdense star called a pulsar. The discovery bestows the stellar pair with the record for the shortest-known orbital period for a certain class of pulsar binary system.

The data from NICER also show J17062’s stars are only about 186,000 miles (300,000 kilometers) apart, less than the distance between Earth and the Moon. Based on the pair’s breakneck orbital period and separation, scientists involved in a new study of the system think the second star is a hydrogen-poor white dwarf.

“It’s not possible for a hydrogen-rich star, like our Sun, to be the pulsar’s companion,” said Tod Strohmayer an astrophysicist at Goddard and lead author on the paper. “You can’t fit a star like that into an orbit so small.”

A previous 20-minute observation by the Rossi X-ray Timing Explorer (RXTE) in 2008 was only able to set a lower limit for J17062’s orbital period. NICER, which was installed aboard the International Space Station last June, has been able to observe the system for much longer periods of time. In August, the instrument focused on J17062 for more than seven hours over 5.3 days. Combining additional observations in October and November, the science team was able to confirm the record-setting orbital period for a binary system containing what astronomers call an accreting millisecond X-ray pulsar (AMXP).

When a massive star goes supernova, its core collapses into a black hole or a neutron star, which is small and superdense — around the size of a city but containing more mass than the Sun. Neutron stars are so hot the light they radiate passes red-hot, white-hot, UV-hot and enters the X-ray portion of the electromagnetic spectrum. A pulsar is a rapidly spinning neutron star.

The 2008 RXTE observation of J17062 found X-ray pulses recurring 163 times a second. These pulses mark the locations of hot spots around the pulsar’s magnetic poles, so they allow astronomers to determine how fast it’s spinning. J17062’s pulsar is rotating at about 9,800 revolutions per minute.

Hot spots form when a neutron star’s intense gravitational field pulls material away from a stellar companion — in J17062, from the white dwarf — where it collects into an accretion disk. Matter in the disk spirals down, eventually making its way onto the surface. Neutron stars have strong magnetic fields, so the material lands on the surface of the star unevenly, traveling along the magnetic field to the magnetic poles where it creates hot spots.

The constant barrage of in-falling gas causes accreting pulsars to spin more rapidly. As they spin, the hot spots come in and out of the view of X-ray instruments like NICER, which record the fluctuations. Some pulsars rotate over 700 times per second, comparable to the blades of a kitchen blender. X-ray fluctuations from pulsars are so predictable that NICER’s companion experiment, the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT), has already shown they can serve as beacons for autonomous navigation by future spacecraft.

Over time, material from the donor star builds up on the surface of the neutron star. Once the pressure of this layer builds up to the point where its atoms fuse, a runaway thermonuclear reaction occurs, releasing the energy equivalent of 100 15-megaton bombs exploding over every square centimeter, explained Strohmayer. X-rays from such outbursts can also be captured by NICER, although one has yet to be seen from J17062.

The researchers were able to determine that J17062’s stars revolve around each other in a circular orbit, which is common for AMXPs. The white dwarf donor star is a “lightweight,” only around 1.5 percent of our Sun’s mass. The pulsar is much heavier, around 1.4 solar masses, which means the stars orbit a point around 1,900 miles (3,000 km) from the pulsar. Strohmayer said it’s almost as if the donor star orbits a stationary pulsar, but NICER is sensitive enough to detect a slight fluctuation in the pulsar’s X-ray emission due to the tug from the donor star.

“The distance between us and the pulsar is not constant,” Strohmayer said. “It’s varying by this orbital motion. When the pulsar is closer, the X-ray emission takes a little less time to reach us than when it’s further away. This time delay is small, only about 8 milliseconds for J17062's orbit, but it’s well within the capabilities of a sensitive pulsar machine like NICER.”

The results of the study were published May 9 in The Astrophysical Journal Letters.

NICER’s mission is to provide high-precision measurements to further study the physics and behavior of neutron stars. Other first-round results from the instrument have provided details about one object’s thermonuclear bursts and explored what happens to the accretion disk during these events.

“Neutron stars turn out to be truly unique nuclear physics laboratories, from a terrestrial standpoint,” said Zaven Arzoumanian, a Goddard astrophysicist and lead scientist for NICER. “We can’t recreate the conditions on neutron stars anywhere within our solar system. One of NICER’s key objectives is to study subatomic physics that isn’t accessible anywhere else.”

NICER is an Astrophysics Mission of Opportunity within NASA's Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA's Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

By Jeanette Kazmierczak
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Editor: Rob Garner


Friday, May 11, 2018

Massive Cluster Galaxies Move in Unexpected Ways

Figure 1. MS0440+02 galaxy cluster. The central galaxy is a multi-component BCG formed by six bright elliptical spheroids, all at the same redshift. This is a color composite GMOS South image (g, r, i) of the clusters. The size of the image is 2.6 x 2.6 arcmin2 (N up, E left). Credit: R. Carrasco (Gemini Observatory/AURA) and Tomás Verdugo (UNAM).  Full resolution TIFF

Figure 2. The slope η of the velocity dispersion profile is plotted against the central velocity dispersion σ0 for galaxies in multiple different samples. The blue points represent brightest galaxies in groups (BGGs) of high (square) and low (circles) density, while the green, red, and yellow points represent brightest cluster galaxies (BCGs) in various samples of galaxy clusters. The grey points indicate generic “early-type galaxies” (ETGs). The slope η is negative if the velocity dispersion decreases with radius and positive if it rises. Thus, massive BCGs tend to have rising profiles, with the stellar velocities responding to the cluster potential at larger radii. [Reproduced from Loubser et al. 2018, MNRAS, in press.]  Full resolution JPEG

Astronomers using data from both of the Gemini Multi-Object Spectrographs (GMOS - North and South) measured the motions of stars within a sample of 32 massive elliptical cluster galaxies and found the stellar motions inconsistent with these galaxies’ solitary cousins. 

The galaxies chosen are known as brightest cluster galaxies (BCGs) because they are the brightest members of large galaxy clusters. The international team of astronomers obtained Gemini spectra to find the relative velocities of stars within each galaxy and then determine the central stellar velocity dispersions and radial dispersion profiles for each galaxy. “This is similar to what we see in our own Solar System with the different velocities of the planets around the Sun,” said John Blakeslee, Gemini Observatory's Head of Science. “We use the planets’ velocities to determine our Solar System’s mass distribution and it is also how we know the Sun’s mass accurately.”

The researchers discovered a surprising variety in the shapes of the velocity dispersion profiles for the BCGs, with a large fraction showing rising dispersion profiles (Figure 2). A rising velocity dispersion profile means that the stars within these galaxies are moving faster as you look further from the galaxy’s core in response to an increasing gravitational force. In comparison, rising velocity dispersion profiles are much rarer in other massive ellipticals that are not BCGs, including many brightest galaxies in groups (BGGs).

“You would naively think that massive elliptical galaxies are a homogeneous, well-behaved class of objects, but the most massive beasts, those in the centers of groups and clusters, continue to surprise us,” said Ilani Loubser, an astronomer at North-West University in South Africa and the lead author of the study, which has been accepted for publication in Monthly Notices of the Royal Astronomical Society. She also noted, “The quality, and the wealth of information we can measure from the GMOS spectra (even in poor weather), is remarkable!”

BCGs tend to reside near the centers of their respective clusters, and are therefore generally embedded within extended distributions of both light and dark matter. The sample of BCGs in this study included some of the most massive known galaxies in the Universe out to a distance of about 3.2 billion light years (z ~ 0.3).

The study also found that the slopes of the velocity dispersion profiles correlate with the galaxy luminosity, in the sense that the increase in the speed of the stars is greater in brighter BCGs, as well as BGGs. Whether the full diversity in the observed velocity dispersion profiles is consistent with standard models for the growth of massive galaxies is not yet clear. More detailed comparisons with velocity dispersion profiles in cosmological simulations are needed.

Gemini Observatory

Thursday, May 10, 2018

Sagittarius A* Swarm: Black Hole Bounty Captured in the Milky Way Center

 Sagittarius A* Swarm
NASA/CXC/Columbia Univ./C. Hailey et al.

Astronomers have discovered evidence for thousands of black holes located near the center of our Milky Way galaxy using data from NASA's Chandra X-ray Observatory.

This black hole bounty consists of stellar-mass black holes, which typically weigh between five to 30 times the mass of the Sun. These newly identified black holes were found within three light years — a relatively short distance on cosmic scales — of the supermassive black hole at our Galaxy's center known as Sagittarius A* (Sgr A*).

Theoretical studies of the dynamics of stars in galaxies have indicated that a large population of stellar mass black holes — as many as 20,000 — could drift inward over the eons and collect around Sgr A*. This recent analysis using Chandra data is the first observational evidence for such a black hole bounty.

A black hole by itself is invisible. However, a black hole — or neutron star — locked in close orbit with a star will pull gas from its companion (astronomers call these systems "X-ray binaries"). This material falls into a disk and heats up to millions of degrees and produces X-rays before disappearing into the black hole. Some of these X-ray binaries appear as point-like sources in the Chandra image.

A team of researchers, led by Chuck Hailey of Columbia University in New York, used Chandra data to search for X-ray binaries containing black holes that are located near Sgr A*. They studied the X-ray spectra — that is the amount of X-rays seen at different energies — of sources within about 12 light years of Sgr A*.

The team then selected sources with X-ray spectra similar to those of known X-ray binaries, which have relatively large amounts of low energy X-rays. Using this method they detected fourteen X-ray binaries within about three light years of Sgr A*. Two X-ray sources likely to contain neutron stars based on the detection of characteristic outbursts in previous studies were then eliminated from the analysis.

The dozen remaining X-ray binaries are identified in the labeled version of the image using red colored circles. Other sources with relatively large amounts of high energy X-rays are labeled in white, and are mostly binaries containing white dwarf stars.

Hailey and his collaborators concluded that a majority of these dozen X-ray binaries are likely to contain black holes. The amount of variability they have shown over timescales of years is different from that expected for X-ray binaries containing neutron stars.

Only the brightest X-ray binaries containing black holes are likely to be detectable at the distance of Sgr A*. Therefore, the detections in this study imply that a much larger population of fainter, undetected X-ray binaries — at least 300 and up to a thousand — containing stellar-mass black holes should be present around Sgr A*.

This population of black holes with companion stars near Sgr A* could provide insight into the formation of X-ray binaries from close encounters between stars and black holes. This discovery could also inform future gravitational wave research. Knowing the number of black holes in the center of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them.

An even larger population of stellar-mass black holes without companion stars should be present near Sgr A*. According to theoretical follow-up work by Aleksey Generozov of Columbia and his colleagues, more than about 10,000 black holes and as many as 40,000 black holes should exist in the center of the Galaxy.

While the authors strongly favor the black hole explanation, they cannot rule out the possibility that up to about half of the observed dozen sources are from a population of millisecond pulsars, i.e., very rapidly rotating neutron stars with strong magnetic fields.

A paper describing these results appeared in the April 5th issue of the journal Nature. 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 Sagittarius A* Swarm:

Scale: Image is about 6 arcmin (45 light years) across
Category: Black Holes, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 17h 45m 40s | Dec -29° 00´ 28.00"
Constellation: Sagittarius
Observation Date: February 2002-April 2013
Observation Time: 389 hours 33 min (16 days 5 hours 33 min)
Obs. ID: 2943, 2951, 2952, 2953, 2954, 3392, 3393, 3663, 3665, 3549, 4683, 4684, 5950, 5951, 5952, 5953, 5954, 6363, 6113, 6639, 6640, 6641, 6642, 6643, 6644, 6645, 6646, 7554, 7555, 7556, 7557, 7558, 7559, 9169, 9170, 9171, 9172, 9173, 9174, 10556, 11843, 13016, 13017, 14941, 14942
Instrument: ACIS
References: Hailey, C et al, 2018, Nature, 556, 70
Color Code: X-ray Blue
Distance Estimate: About 26,000 light years

Wednesday, May 09, 2018

Exiled Asteroid Discovered in Outer Reaches of Solar System

Artist’s impression of exiled asteroid 2004 EW95
Orbital exile


ESOcast 160 Light: Lost in Space (4K UHD)
ESOcast 160 Light: Lost in Space (4K UHD)

Lost in space (artist's impression)
Lost in space (artist's impression)

Asteroid fly-by
Asteroid fly-by

Orbit in exile
Orbit in exile 

ESO telescopes find first confirmed carbon-rich asteroid in Kuiper Belt

An international team of astronomers has used ESO telescopes to investigate a relic of the primordial Solar System. The team found that the unusual Kuiper Belt Object 2004 EW95 is a carbon-rich asteroid, the first of its kind to be confirmed in the cold outer reaches of the Solar System. This curious object likely formed in the asteroid belt between Mars and Jupiter and has been flung billions of kilometres from its origin to its current home in the Kuiper Belt.

The early days of our Solar System were a tempestuous time. Theoretical models of this period predict that after the gas giants formed they rampaged through the Solar System, ejecting small rocky bodies from the inner Solar System to far-flung orbits at great distances from the Sun [1]. In particular, these models suggest that the Kuiper Belt — a cold region beyond the orbit of Neptune — should contain a small fraction of rocky bodies from the inner Solar System, such as carbon-rich asteroids, referred to as carbonaceous asteroids [2].

Now, a recent paper has presented evidence for the first reliably-observed carbonaceous asteroid in the Kuiper Belt, providing strong support for these theoretical models of our Solar System’s troubled youth. After painstaking measurements from multiple instruments at ESO’s Very Large Telescope (VLT), a small team of astronomers led by Tom Seccull of Queen’s University Belfast in the UK was able to measure the composition of the anomalous Kuiper Belt Object 2004 EW95, and thus determine that it is a carbonaceous asteroid. This suggests that it originally formed in the inner Solar System and must have since migrated outwards [3].

The peculiar nature of 2004 EW95 first came to light during routine observations with the NASA/ESA Hubble Space Telescope by Wesley Fraser, an astronomer from Queen’s University Belfast who was also a member of the team behind this discovery. The asteroid’s reflectance spectrum — the specific pattern of wavelengths of light reflected from an object — was different to that of similar small Kuiper Belt Objects (KBOs), which typically have uninteresting, featureless spectra that reveal little information about their composition.

The reflectance spectrum of 2004 EW95 was clearly distinct from the other observed outer Solar System objects,” explains lead author Seccull. “It looked enough of a weirdo for us to take a closer look.

The team observed 2004 EW95 with the X-Shooter and FORS2 instruments on the VLT. The sensitivity of these spectrographs allowed the team to obtain more detailed measurements of the pattern of light reflected from the asteroid and thus infer its composition.

However, even with the impressive light-collecting power of the VLT, 2004 EW95 was still difficult to observe. Though the object is 300 kilometres across, it is currently a colossal four billion kilometres from Earth, making gathering data from its dark, carbon-rich surface a demanding scientific challenge.

It’s like observing a giant mountain of coal against the pitch-black canvas of the night sky,” says co-author Thomas Puzia from the Pontificia Universidad Católica de Chile.

Not only is 2004 EW95 moving, it’s also very faint,” adds Seccull. “We had to use a pretty advanced data processing technique to get as much out of the data as possible.

Two features of the object’s spectra were particularly eye-catching and corresponded to the presence of ferric oxides and phyllosilicates. The presence of these materials had never before been confirmed in a KBO, and they strongly suggest that 2004 EW95 formed in the inner Solar System.

Seccull concludes: “Given 2004 EW95’s  present-day abode in the icy outer reaches of the Solar System, this implies that it has been flung out into its present orbit by a migratory planet in the early days of the Solar System.”

While there have been previous reports of other ‘atypical’ Kuiper Belt Object spectra, none were confirmed to this level of quality,” comments Olivier Hainaut, an ESO astronomer who was not part of the team. “The discovery of a carbonaceous asteroid in the Kuiper Belt is a key verification of one of the fundamental predictions of dynamical models of the early Solar System.


[1] Current dynamical models of the evolution of the early Solar System, such as the grand tack hypothesis and the Nice model, predict that the giant planets migrated first inward and then outward, disrupting and scattering objects from the inner Solar System. As a consequence, a small percentage of rocky asteroids are expected to have been ejected into orbits in the Oort Cloud and Kuiper belt.

[2] Carbonaceous asteroids are those containing the element carbon or its various compounds. Carbonaceous — or C-type — asteroids can be identified by their dark surfaces, caused by the presence of carbon molecules.

[3] Other inner Solar System objects have previously been detected in the outer reaches of the Solar System, but this is the first carbonaceous asteroid to be found far from home in the Kuiper Belt.

More Information

This research was presented in a paper entitled “2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt” by T. Seccull et al., which appeared in The Astrophysical Journal Letters.

The team was composed of Tom Seccull (Astrophysics Research Centre, Queen’s University Belfast, UK), Wesley C. Fraser (Astrophysics Research Centre, Queen’s University Belfast, UK) , Thomas H. Puzia (Institute of Astrophysics, Pontificia Universidad Católica de Chile, Chile), Michael E. Brown (Division of Geological and Planetary Sciences, California Institute of Technology, USA) and Frederik Schönebeck (Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Germany).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, 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 and with Australia as a strategic partner. 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Tom Seccull
Postgraduate Research Student — Queen's University, Belfast
Belfast, United Kingdom
Tel: +44 2890 973091

Wesley C. Fraser
Lecturer — Queen’s University, Belfast
Belfast, United Kingdom
Tel: +44 28 9097 1084

Thomas H. Puzia
Professor — Institute of Astrophysics, Pontificia Universidad Catolica
Santiago, Chile
Tel: +56-2 2354 1645

Calum Turner
ESO Assistant Public Information Officer
Garching bei München Tel: +49 89 3200 6670

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Source: ESO/News

Thursday, May 03, 2018

NGC 6231: Stellar Family Portrait in X-rays

NGC 6231
Credit X-ray: NASA/CXC/Univ. of Valparaiso/M. Kuhn et al; IR: NASA/JPL/WISE

In some ways, star clusters are like giant families with thousands of stellar siblings. These stars come from the same origins — a common cloud of gas and dust — and are bound to one another by gravity. Astronomers think that our Sun was born in a star cluster about 4.6 billion years ago that quickly dispersed.

By studying young star clusters, astronomers hope to learn more about how stars — including our Sun — are born. NGC 6231, located about 5,200 light years from Earth, is an ideal testbed for studying a stellar cluster at a critical stage of its evolution: not long after star formation has stopped.
The discovery of NGC 6231 is attributed to Giovanni Battista Hodierna, an Italian mathematician and priest who published observations of the cluster in 1654. Sky watchers today can find the star cluster to the southwest of the tail of the constellation Scorpius.

NASA's Chandra X-ray Observatory has been used to identify the young Sun-like stars in NGC 6231, which have, until recently, been hiding in plain sight. Young star clusters like NGC 6231 are found in the band of the Milky Way on the sky. As a result, interloping stars lying in front of or behind NGC 6231 greatly outnumber the stars in the cluster. These stars will generally be much older than those in NGC 6231, so members of the cluster can be identified by selecting signs of stellar youth.

Young stars stand out to Chandra because they have strong magnetic activity that heats their outer atmosphere to tens of millions of degrees Celsius and causes them to emit X-rays. Infrared measurements assist in verifying that an X-ray source is a young star and in inferring the star's properties.

This Chandra X-ray image of NGC 6231 shows a close-up of the inner region of the cluster. Chandra can detect a range of X-ray light, which has been split into three bands to create this image. Red, green, and blue represents the lower, medium, and high-energy X-rays. The brightest X-ray emission is white.

The Chandra data, combined with infrared data from the Visible and Infrared Survey Telescope for Astronomy (VISTA) Variables in the Vía Lactéa survey has provided the best census of young stars in NGC 6231 available. An infrared image from NASA’s Wide-field Infrared Survey explorer is shown on the left.

There are an estimated 5,700 to 7,500 young stars in NGC 6231 in the Chandra field of view, about twice the number of stars in the well-known Orion star cluster. The stars in NGC 6231 are slightly older (3.2 million years on average) than those in Orion (2.5 million years old). However, NGC 6231 is much larger in volume and therefore the number density of its stars, that is, their proximity to one another, is much lower, by a factor of about 30. These differences enable scientists to study the diversity of properties for star clusters during the first few million years of their life.

Chandra studies of this and other young star clusters, have allowed astronomers to build up a sample from which cluster evolution can be studied. These clusters come from dozens of star-forming regions, but NGC 6231 adds a crucial piece to this puzzle because it shows how a cluster looks after the end of star formation. A comparison of the ages, sizes and masses of clusters in this sample implies that NGC 6231 has expanded from a more compact initial state, but it has not expanded sufficiently fast for its stars to break free from the cluster’s gravitational pull. Astronomers are not sure what will happen next: will it remain held together by gravity? Or will its constituents one day disperse as our Sun’s ancestral cluster once did?

Nearby star-forming regions frequently contain multiple star clusters, most of which are individually less massive than NGC 6231. The simple structure of NGC 6231, along with its relatively high mass, suggests that NGC 6231 was built up by mergers of several star clusters early its lifetime, a process known as "hierarchical cluster assembly".

Two papers describing recent studies of NGC 6231, both led by Michael Kuhn while at the Universidad de Valparaíso in Chile, have been published and are available online at and

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 6231:

Scale: Infrared image is ~5 degrees across (about 452 light years); Right: Xray image is ~16 arcmin across (about 24 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 16h 54m 08.51s | Dec -41° 49' 36.0"
Constellation: Scorpius
Observation Date: July 2005
Observation Time: 33 hours 30 minutes
Obs. ID: 5372, 6291
Instrument: ACIS
References: Kuhn, M. et al. 2017, AJ, 154, 87; arXiv:1706.00017 Kuhn, M. et al. 2017, AJ, 154, 214; arXiv:1710.01731
Color Code: Left: Infrared (red, yellow, green, cyan, blue); Right: X-ray (red, green, blue).
Distance Estimate: About 1.59 kpc (5,190 light years)

Wednesday, May 02, 2018

Hubble detects helium in the atmosphere of an exoplanet for the first time

Artist’s impression of WASP-107b


Artist’s impression of WASP-107b
Artist’s impression of WASP-107b

Creation of absorption lines
Creation of absorption lines

Light interacting with atmosphere
Light interacting with atmosphere

Astronomers using the NASA/ESA Hubble Space Telescope have detected helium in the atmosphere of the exoplanet WASP-107b. This is the first time this element has been detected in the atmosphere of a planet outside the Solar System. The discovery demonstrates the ability to use infrared spectra to study exoplanet extended atmospheres.

The international team of astronomers, led by Jessica Spake, a PhD student at the University of Exeter in the UK, used Hubble’s Wide Field Camera 3 to discover helium in the atmosphere of the exoplanet WASP-107b This is the first detection of its kind.

Spake explains the importance of the discovery: “Helium is the second-most common element in the Universe after hydrogen. It is also one of the main constituents of the planets Jupiter and Saturn in our Solar System. However, up until now helium had not been detected on exoplanets - despite searches for it.”

The team made the detection by analysing the infrared spectrum of the atmosphere of WASP-107b [1]. Previous detections of extended exoplanet atmospheres have been made by studying the spectrum at ultraviolet and optical wavelengths; this detection therefore demonstrates that exoplanet atmospheres can also be studied at longer wavelengths.

“The strong signal from helium we measured demonstrates a new technique to study upper layers of exoplanet atmospheres in a wider range of planets,” says Spake “Current methods, which use ultraviolet light, are limited to the closest exoplanets. We know there is helium in the Earth’s upper atmosphere and this new technique may help us to detect atmospheres around Earth-sized exoplanets – which is very difficult with current technology.”

WASP-107b is one of the lowest density planets known: While the planet is about the same size as Jupiter, it has only 12% of Jupiter’s mass. The exoplanet is about 200 light-years from Earth and takes less than six days to orbit its host star.

The amount of helium detected in the atmosphere of WASP-107b is so large that its upper atmosphere must extend tens of thousands of kilometres out into space. This also makes it the first time that an extended atmosphere has been discovered at infrared wavelengths.

Since its atmosphere is so extended, the planet is losing a significant amount of its atmospheric gases into space — between ~0.1-4% of its atmosphere’s total mass every billion years [2].

As far back as the year 2000, it was predicted that helium would be one of the most readily-detectable gases on giant exoplanets, but until now, searches were unsuccessful.

David Sing, co-author of the study also from the University of Exeter, concludes: “Our new method, along with future telescopes such as the NASA/ESA/CSA James Webb Space Telescope, will allow us to analyse atmospheres of exoplanets in far greater detail than ever before.”


[1] The measurement of an exoplanet’s atmosphere is performed when the planet passes in front of its host star. A tiny portion of the star’s light passes through the exoplanet’s atmosphere, leaving detectable fingerprints in the spectrum of the star. The larger the amount of an element present in the atmosphere, the easier the detection becomes.

[2] Stellar radiation has a significant effect on the rate at which a planet’s atmosphere escapes. The star WASP-107 is highly active, supporting the atmospheric loss. As the atmosphere absorbs radiation it heats up, so the gas rapidly expands and escapes more quickly into space.

More Information 

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

The study was published in the paper “Helium in the eroding atmosphere of an exoplanet”, published in Nature.

The international team of astronomers in this study consists of J. J. Spake (University of Exeter, UK), D. K. Sing (University of Exeter, UK; Johns Hopkins University, USA), T. M. Evans (University of Exeter, UK), A. Oklopčić (Harvard-Smithsonian Center for Astrophysics, USA), V. Bourrier (Observatoire de l’Université de Genève, Switzerland), L. Kreidberg (Harvard Society of Fellows, USA; Harvard-Smithsonian Center for Astrophysics, USA), B. V. Rackham (University of Arizona, USA), J. Irwin (Harvard-Smithsonian Center for Astrophysics, USA), D. Ehrenreich (Observatoire de l’Université de Genève, Switzerland), A. Wyttenbach (Observatoire de l’Université de Genève, Switzerland), H. R. Wakeford (Space Telescope Science Institute, USA), Y. Zhou (University of Arizona, USA), K. L. Chubb (University College London, UK), N. Nikolov (University of Exeter, UK), J. Goyal (University of Exeter, UK), G. W. Henry (Tennessee State University, USA), M. H. Williamson (Tennessee State University, USA), S. Blumenthal (Space Telescope Science Institute, USA), D. Anderson (Keele University, UK), C. Hellier (Keele University, UK), D. Charbonneau (Harvard-Smithsonian Center for Astrophysics, USA), S. Udry (Observatoire de l’Université de Genève, Switzerland), and N. Madhusudhan (University of Cambridge, UK)

Image credit: NASA, ESA



Jessica Spake
University of Exeter
Exeter, UK

David Sing
University of Exeter
Exeter, UK
Tel: +44 1392725652

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500

Source: ESA/Hubble/News