From NASA Chandra: “Galaxy Clusters Caught in a First Kiss”

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From NASA Chandra

June 25, 2019
Media contacts:
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu

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Composite

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X-ray

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Optical

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Radio

Credit: X-ray: NASA/CXC/RIKEN/L. Gu et al; Radio: NCRA/TIFR/GMRT; Optical: SDSS
Press Image, Caption, and Videos

Giant Metrewave Radio Telescope, an array of thirty telecopes, located near Pune in India

SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

For the first time, astronomers have found two giant clusters of galaxies that are just about to collide. This observation can be seen as a missing ‘piece of the puzzle’ in our understanding of the formation of structure in the Universe, since large-scale structures—such as galaxies and clusters of galaxies—are thought to grow by collisions and mergers. The result was published in Nature Astronomy on June 24th, 2019 and used data from NASA’s Chandra X-ray Observatory and other X-ray missions.

Clusters of galaxies are the largest known bound objects and consist of hundreds of galaxies that each contain hundreds of billions of stars. Ever since the Big Bang, these objects have been growing by colliding and merging with each other. Due to their large size, with diameters of a few million light years, these collisions can take about a billion years to complete. Eventually the two colliding clusters will have merged into one bigger cluster.

Because the merging process takes much longer than a human lifetime, we only see snapshots of the various stages of these collisions. The challenge is to find colliding clusters that are just at the stage of first touching each other.

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In theory, this stage has a relatively short duration and is therefore hard to find. It is like finding a raindrop that just touches the water surface in a photograph of a pond during a rain shower. Obviously, such a picture would show a lot of falling droplets and ripples on the water surface, but only few droplets in the process of merging with the pond. Similarly, astronomers found a lot of single clusters and merged clusters with outgoing ripples indicating a past collision, but until now no two clusters that are just about to touch each other.

An international team of astronomers now announced the discovery of two clusters on the verge of colliding. This enabled astronomers to test their computer simulations, which show that in the first moments a shock wave, analogous to the sonic boom produced by supersonic motion of an airplane, is created in between the clusters and travels out perpendicular to the merging axis. “These clusters show the first clear evidence for this type of merger shock,” says first author Liyi Gu from RIKEN national science institute in Japan and SRON Netherlands Institute for Space Research. “The shock created a hot belt region of 100-million-degree gas between the clusters, which is expected to extend up to, or even go beyond the boundary of the giant clusters. Therefore, the observed shock has a huge impact on the evolution of galaxy clusters and large scale structures.”

Astronomers are planning to collect more ‘snapshots’ to ultimately build up a continuous model describing the evolution of cluster mergers. SRON-researcher Hiroki Akamatsu: “More merger clusters like this one will be found by eROSITA, an X-ray all-sky survey mission that will be launched this year.

eRosita DLR MPG

Two other upcoming X-ray missions, XRISM and Athena, will help us understand the role of these colossal merger shocks in the structure formation history.”

JAXA XRSM spacecraft schematic

ESA Athena

Liyi Gu and his collaborators studied the colliding pair during an observation campaign, carried out with three X-ray satellites (ESA’s XMM-Newton satellite, NASA’s Chandra, and JAXA’s Suzaku satellite) and two radio telescopes (the Low-Frequency Array, a European project led by the Netherlands, and the Giant Metrewave Radio Telescope operated by National Centre for Radio Astrophysics of India).

ESA/XMM Newton

JAXA/Suzaku satellite

SKA LOFAR core (“superterp”) near Exloo, Netherlands

Other materials about the findings are available at:
http://chandra.si.edu

For more Chandra images, multimedia and related materials, visit:
http://www.nasa.gov/chandra

See the full article here .


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Please help promote STEM in your local schools.

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

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From European Space Agency: “What remains of the stars-Past and future generations of stars in NGC 300”

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From European Space Agency

25/02/2019
ESA/XMM-Newton (X-rays); MPG/ESO (optical); NASA/Spitzer (infrared). Acknowledgement: S. Carpano, Max-Planck Institute for Extraterrestrial Physics

ESA/XMM Newton


MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres

NASA/Spitzer Infrared Telescope

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This swirling palette of colours portrays the life cycle of stars in a spiral galaxy known as NGC 300.

Located some six million light-years away, NGC 300 is relatively nearby. It is one of the closest galaxies beyond the Local Group – the hub of galaxies to which our own Milky Way galaxy belongs. Due to its proximity, it is a favourite target for astronomers to study stellar processes in spiral galaxies.

The population of stars in their prime is shown in this image in green hues, based on optical observations performed with the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at La Silla, Chile.

ESO WFI LaSilla 2.2-m MPG/ESO telescope at La Silla, 600 km north of Santiago de Chile at an altitude of 2400 metres

Red colours indicate the glow of cosmic dust in the interstellar medium that pervades the galaxy: this information derives from infrared observations made with NASA’s Spitzer space telescope, and can be used to trace stellar nurseries and future stellar generations across NGC 300.

A complementary perspective on this galaxy’s composition comes from data collected in X-rays by ESA’s XMM-Newton space observatory, shown in blue. These represent the end points of the stellar life cycle, including massive stars on the verge of blasting out as supernovas, remnants of supernova explosions, neutron stars, and black holes. Many of these X-ray sources are located in NGC 300, while others – especially towards the edges of the image – are foreground objects in our own Galaxy, or background galaxies even farther away.

The sizeable blue blob immediately to the left of the galaxy’s centre is especially interesting, featuring two intriguing sources that are part of NGC 300 and shine brightly in X-rays.

One of them, known as NGC 300 X-1, is in fact a binary system, consisting of a Wolf-Rayet star – an ageing hot, massive and luminous type star that drives strong winds into its surroundings – and a black hole, the compact remains of what was once another massive, hot star. As matter from the star flows towards the black hole, it is heated up to temperatures of millions of degrees or more, causing it to shine in X-rays.

The other source, dubbed NGC 300 ULX1, was originally identified as a supernova explosion in 2010. However, later observations prompted astronomers to reconsider this interpretation, indicating that this source also conceals a binary system comprising a very massive star and a compact object – a neutron star or a black hole – feeding on material from its stellar companion.

Data obtained in 2016 with ESA’s XMM-Newton and NASA’s NuSTAR observatories revealed regular variations in the X-ray signal of NGC 300 ULX1, suggesting that the compact object in this binary system is a highly magnetized, rapidly spinning neutron star, or pulsar.

NASA/DTU/ASI NuSTAR X-ray telescope

The large blue blob in the upper left corner is a much more distant object: a cluster of galaxies more than one billion light years away, whose X-ray glow is caused by the hot diffuse gas interspersed between the galaxies.

Explore NGC 300 in ESASky

See the full article here .


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Please help promote STEM in your local schools.

Stem Education Coalition

The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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From European Space Agency: “XMM-Newton captures final cries of star shredded by black hole”

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From European Space Agency

9 January 2019

Dheeraj Pasham
MIT Kavli Institute for Astrophysics and Space Research
Cambridge, MA, USA
Tel: +1-617-253-4845
Email: dheeraj@space.mit.edu

Alessia Franchini
University of Milan, Italy
University of Nevada, Las Vegas, USA
Email: alessia.franchini@unlv.edu

Norbert Schartel
XMM-Newton Project Scientist
European Space Agency
Email: norbert.schartel@esa.int

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

Astronomers using ESA’s XMM-Newton space observatory have studied a black hole devouring a star and discovered an exceptionally bright and stable signal that allowed them to determine the black hole’s spin rate.

ESA/XMM Newton

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XMM-Newton view

Astronomers using ESA’s XMM-Newton space observatory have studied a black hole devouring a star and discovered an exceptionally bright and stable signal that allowed them to determine the black hole’s spin rate.

Black holes are thought to lurk at the centre of all massive galaxies throughout the Universe, and are inextricably tied to the properties of their host galaxies. As such, revealing more about these behemoths may hold the key to understanding how galaxies evolve over time.

A black hole’s gravity is extreme, and can rip apart stars that stray too close. The debris from such torn-apart stars spirals inwards towards the hole, heats up, and emits intense X-rays.

Despite the number of black holes thought to exist in the cosmos, many are dormant – there is no in-falling material to emit detectable radiation – and thus difficult to study. However, every few hundred thousand years or so, a star is predicted to pass near enough to a given black hole that it is torn apart. This offers a brief window of opportunity to measure some fundamental properties of the hole itself, such as its mass and the rate at which it is spinning.

“It’s very difficult to constrain the spin of a black hole, as spin effects only emerge very close to the hole itself, where gravity is intensely strong and it’s difficult to see clearly,” says Dheeraj Pasham of the MIT Kavli Institute for Astrophysics and Space Research in Massachusetts, USA, and lead author of the new study [Science].

“However, models show that the mass from a shredded star settles into a kind of inner disc that throws off X-rays. We guessed that finding instances where this disc glows especially brightly would be a good way to constrain a black hole’s spin, but observations of such events weren’t sensitive enough to explore this region of strong gravity in detail – until now.”

Dheeraj and colleagues studied an event called ASASSN-14li.

ASASSN the all sky automated survey (ASAS) is a Polish project at Las Campanas Observatory in Chile, over 2,500 m -8,200 ft high

ASASSN-14li was discovered by the ground-based All-Sky Automated Survey for SuperNovae (ASASSN) on 22 November 2014. The black hole tied to the event is at least one million times as massive as the Sun.

“ASASSN-14li is nicknamed the ‘Rosetta Stone’ of these events,” adds Dheeraj. “All of its properties are characteristic of this type of event, and it has been studied by all currently operational major X-ray telescopes.”

Using observations of ASASSN-14li from ESA’s XMM-Newton and NASA’s Chandra and Swift X-ray observatories, the scientists hunted for a signal that was both stable and showed a characteristic wave pattern often triggered when a black hole receives a sudden influx of mass – such as when devouring a passing star.

NASA/Chandra X-ray Telescope

NASA Neil Gehrels Swift Observatory

They detected a surprisingly intense X-ray signal that oscillated over a period of 131 seconds for a long time: 450 days.

By combining this with information about the black hole’s mass and size, the astronomers found that the hole must be spinning rapidly – at more than 50% of the speed of light – and that the signal came from its innermost regions.

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Black hole host galaxy. Host galaxy of ASASSN-14li. X-ray: NASA/CXC/MIT/D. Pasham et al; Optical: HST/STScI/I. Arcavi
The host galaxy of ASASSN-14li, a black hole devouring a star, as observed by the NASA/ESA Hubble Space Telescope in optical wavelengths. The insert in the lower left shows the X-ray view obtained by NASA’s Chandra observatory.
Observations of ASASSN-14li have revealed an exceptionally bright and stable signal that oscillated over a period of 131 seconds for a long time: 450 days.
By combining this with information about the black hole’s mass and size, the astronomers found that the hole must be spinning rapidly – at more than 50% of the speed of light – and that the signal came from its innermost regions.

“It’s an exceptional finding: such a bright signal that is stable for so long has never been seen before in the vicinity of any black hole,” adds co-author Alessia Franchini of the University of Milan, Italy.

“What’s more, the signal is coming from right near the black hole’s event horizon – beyond this point we can’t observe a thing, as gravity is so strong that even light can’t escape.”

The study demonstrates a novel way to measure the spins of massive black holes: by observing their activity when they disrupt passing stars with their gravity. Such events may also help us to understand aspects of general relativity theory; while this has been explored extensively in ‘normal’ gravity, it is not yet fully understood in regions where gravity is exceptionally strong.

“XMM-Newton is incredibly sensitive to these signals, more so than any other X-ray telescope,” says ESA’s XMM-Newton Project Scientist Norbert Schartel. “The satellite provides the long, uninterrupted, detailed exposures that are crucial to detecting signals such as these.

“We’re only just beginning to understand the complex physics at play here. By finding instances where the mass from a shredded star glows especially brightly we can build a census of the black holes in the Universe, and probe how matter behaves in some of the most extreme areas and conditions in the cosmos.”

The black hole tied to the event is at least one million times as massive as the Sun.

“ASASSN-14li is nicknamed the ‘Rosetta Stone’ of these events,” adds Dheeraj. “All of its properties are characteristic of this type of event, and it has been studied by all currently operational major X-ray telescopes.”

See the full article here .


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Please help promote STEM in your local schools.

Stem Education Coalition

The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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From European Space Agency via Manu Garcia at IAC- “Tracing the Universe: X-ray survey supports standard cosmological model”


From Manu Garcia, a friend from IAC.

The universe around us.
Astronomy, everything you wanted to know about our local universe and never dared to ask.

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From European Space Agency

04 October 2018

Marguerite Pierre
CEA Saclay, France
Email: marguerite.pierre@cea.fr

Norbert Schartel
XMM-Newton Project Scientist
European Space Agency
Email: norbert.schartel@esa.int

Scanning the sky for X-ray sources, ESA’s XMM-Newton X-ray observatory has been busy with the XXL Survey, its largest observational programme to date. The second batch of data from the survey has just been released, including information on 365 galaxy clusters, which trace the large-scale structure of the Universe and its evolution through time, and on 26 000 active galactic nuclei (AGN).

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The 365 galaxy clusters of the XXL Survey – X-ray view. Credit: ESA/XMM-Newton/XXL Survey

ESA/XMM Newton

By examining two large regions of the sky at great sensitivity, this is the first X-ray survey to detect enough galaxy clusters and AGN in contiguous volumes of space to make it possible for scientists to map the distribution of these objects out to the distant Universe in unprecedented detail. The results are compatible with expectations from the currently-accepted cosmological model.

X-rays are produced in some of the most energetic processes in the Universe, but because they are blocked by Earth’s atmosphere, they can only be observed from space. When X-ray telescopes observe the extragalactic Universe, they basically see two sources: the hot gas pervading clusters of galaxies, and Active Galactic Nuclei (AGN) – bright, compact regions at the centres of some galaxies where a supermassive black hole is accreting the surrounding matter.

ESA’s XMM-Newton is one of the most powerful X-ray telescopes ever placed in orbit. Over the last eight years, it has spent 2000 hours measuring X-ray radiation as part of the XXL Survey, which searched for galaxy clusters and AGN by scanning two areas of seemingly-empty sky each measuring 25 square degrees (as a reference, the full moon measures about half a degree across).

The first set of XXL data was released in 2015; it included 100 of the brightest galaxy clusters and 1000 AGN. This month, a new data catalogue was published containing an astonishing 365 clusters and 26 000 AGN. The first results using this data are published in a special issue of Astronomy & Astrophysics.

The survey mapped X-ray clusters so distant that the light left them when the Universe was just half of its present age, and AGN that are even further away. Some of the observed sources are so far-flung that XMM-Newton received no more than 50 X-ray photons from them, making it challenging to tell whether they are clusters or AGN.

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Multi-wavelength view of galaxy cluster XLSSC006. Credit: ESA/XMM-Newton (X-rays); CFHT (optical); XXL Survey



CFHT Telescope, Maunakea, Hawaii, USA, at Maunakea, Hawaii, USA,4,207 m (13,802 ft) above sea level

“It was relatively easy to find galaxy clusters and AGN, because they are the only extragalactic objects visible in X-ray light,” explains Marguerite Pierre from CEA Saclay, France.

“But we had to use several other telescopes collecting light at many different wavelengths, as well as extensive computing facilities, to gather more information about each source, including pinning down their nature and distance.”

Matter in the Universe is not evenly distributed but forms a cosmic web of filaments shaped by gravity, with galaxy clusters found at their intersections. Galaxy clusters are the largest bound entities in the Universe – they trace the highest density peaks in its large-scale structure, making them a powerful tool for answering questions about cosmology.

The structure and evolution of the Universe is described by a set of cosmological parameters, which include the density of its various components and the rate that it is expanding. Currently, we know the value of many of these parameters fairly well, but large samples of cosmic tracers at a variety of distances are required to more accurately describe the underlying structure of the Universe. The ultimate goal of the XXL Survey is to provide an extensive, well-characterised catalogue of clusters that can be used to constrain the cosmological parameters.

ESA’s Planck satellite determined values for cosmological parameters by studying the cosmic microwave background [CMB], which is information from the very early Universe.

CMB per ESA/Planck


ESA/Planck 2009 to 2013

After estimating these parameters using the latest data from the XXL Survey – which is based on information from the more recent Universe – scientists compared their findings against the Planck values.

“Although we didn’t find as many galaxy clusters as predicted by the Planck cosmological model, we obtained a distribution of clusters and AGN that is compatible with the currently favoured cosmological model, which resorts to Einstein’s cosmological constant as an explanation for the accelerated expansion of the Universe, rather than invoking even more exotic possibilities,” explains Marguerite Pierre.

“We can already improve on the Planck estimate for the cosmological constant, even though our analysis has only been carried out on half of the XXL cluster sample; we will spend the next couple of years analysing the rest of the data with the aim of refining the cosmological constraints.”

It is more difficult to estimate values for the cosmological parameters using AGN, as their properties are affected by many external influences. Scientists have instead been using the AGN data from the XXL Survey to understand more about how black holes form and evolve.

Thanks to XXL, this is the first time that scientists have been able to measure the three-dimensional clustering effect of distant X-ray clusters and AGN on very large scales. They can now finally see where the AGN are located within the large-scale structure of the Universe indicated by the galaxy clusters.

The results confirm that XMM-Newton is a powerful survey machine. They also pave the way for the final cosmological analysis of this survey, which will provide independent constraints on the cosmological parameters to unravel more mysteries of the Universe.

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The 365 galaxy clusters of the XXL Survey – Optical view. Credit: CFHT Legacy Survey/CTIO/XXL Survey

The cosmic web will be probed further by ESA’s future Euclid satellite, which will observe light emitted up to 10 billion years ago.

ESA/Euclid spacecraft

Euclid will see a huge number of sources, as it will detect optical and infrared light; with its large surveyed area and rich multi-wavelength coverage, the XXL data will serve as a reference for these observations.

Observations by XMM-Newton have also raised new questions about the physics of galaxy clusters, which will be investigated in greater detail by ESA’s next X-ray mission, Athena.

ESA/Athena spacecraft depiction

Due to launch in 2031, Athena will be far more sensitive than its predecessor. While XMM-Newton can observe clusters at a variety of distances from us, probing different epochs in the Universe’s history, Athena will observe clusters so distant that their light left them as they were forming, telling us even more about the way these gigantic structures take shape and evolve.

n the meantime, scientists in the XXL collaboration plan to process the remaining observations and review data using improved processing techniques. The final XXL data release containing even more X-ray sources, as well as the complete cosmological analysis, is foreseen for 2021.

“It is very exciting that data from this space telescope is contributing to our understanding of the evolution of the Universe,” concludes Norbert Schartel, XMM-Newton Project Scientist at ESA. “This was made possible thanks to the collaboration between a huge number of institutions across many different countries.”

Notes for Editors

The results are presented in a series of 20 papers by the XXL Survey collaboration, published in a special issue of Astronomy & Astrophysics [link is above].

The European Space Agency’s X-ray Multi-Mirror Mission, XMM-Newton, was launched in December 1999. The largest scientific satellite to have been built in Europe, it is also one of the most sensitive X-ray observatories ever flown. More than 170 wafer-thin, cylindrical mirrors direct incoming radiation into three high-throughput X-ray telescopes. XMM-Newton’s orbit takes it almost a third of the way to the Moon, allowing for long, uninterrupted views of celestial objects.

XXL is an international project based around an XMM Very Large Programme surveying two 25 square degree extragalactic fields at a depth of about 5 × 10-15 erg cm-2 s-1 in the 0.5-2 keV band for point-like sources. Multi-band information and spectroscopic follow-up of the X-ray sources are obtained through a number of survey programmes.

Besides XMM-Newton, the study is based on data from the following telescopes and astronomical facilities: the European Southern Observatory (ESO) in Chile; the Canada-France-Hawaii Telescope in Hawaii, USA [above]; the William Herschel Telescope on La Palma, Canary Islands, Spain; the Anglo-Australian Telescope at the Siding Spring Observatory, Australia; the Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile; the Giant Metrewave Radio Telescope near Pune, India; the Australia Telescope Compact Array at the Paul Wild Observatory, Australia; and NASA’s Spitzer Space Telescope.

ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).
elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo


ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)


AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)


NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Giant Metrewave Radio Telescope, an array of thirty telecopes, located near Pune in India

CSIRO Australia Compact Array, six radio telescopes at the Paul Wild Observatory, is an array of six 22-m antennas located about twenty five kilometres (16 mi) west of the town of Narrabri in Australia.

NASA/Spitzer Infrared Telescope

The study also relies on extensive calculations performed at the computing centres of IN2P3/CNRS, France, of the University of Geneva, Switzerland, of the Laboratoire d’Astrophysique de Marseille, France, and of the INAF-IASF in Milan, Italy.

See the full article here .


five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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From ESA: “Where is the Universe’s missing matter?”

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European Space Agency

18 April 2018

Jiangtao Li
University of Michigan, USA
Email: jiangtal@umich.edu
Tel: 734-383-2089

Joel Bregman
University of Michigan, USA
Email: jbregman@umich.edu
Tel: 734-764-2667

Norbert Schartel
XMM-Newton Project Scientist
European Space Agency
Email: norbert.schartel@esa.int

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Searching galactic haloes for ‘missing’ matter. No image credit.

ESA/XMM Newton

Astronomers using ESA’s XMM-Newton space observatory have probed the gas-filled haloes around galaxies in a quest to find ‘missing’ matter thought to reside there, but have come up empty-handed – so where is it?

All the matter in the Universe exists in the form of ‘normal’ matter or the notoriously elusive and invisible dark matter, with the latter around six times more prolific.

Curiously, scientists studying nearby galaxies in recent years have found them to contain three times less normal matter than expected, with our own Milky Way Galaxy containing less than half the expected amount.

Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

“This has long been a mystery, and scientists have spent a lot of effort searching for this missing matter,” says Jiangtao Li of the University of Michigan, USA, and lead author of a new paper http://iopscience.iop.org/article/10.3847/2041-8213/aab2af/meta .

“Why is it not in galaxies — or is it there, but we are just not seeing it? If it’s not there, where is it? It is important we solve this puzzle, as it is one of the most uncertain parts of our models of both the early Universe and of how galaxies form.”

Rather than lying within the main bulk of the galaxy, the part can be observed optically, researchers thought it may instead lie within a region of hot gas that stretches further out into space to form a galaxy’s halo. These hot, spherical haloes have been detected before, but the region is so faint that it is difficult to observe in detail – its X-ray emission can become lost and indistinguishable from background radiation. Often, scientists observe a small distance into this region and extrapolate their findings but this can result in unclear and varying results.

Jiangtao and colleagues wanted to measure the hot gas out to larger distances using ESA’s XMM-Newton X-ray space observatory. They looked at six similar spiral galaxies and combined the data to create one galaxy with their average properties.

“By doing this, the galaxy’s signal becomes stronger and the X-ray background becomes better behaved,” adds co-author Joel Bregman, also of the University of Michigan.

“We were then able to see the X-ray emission to about three times further out than if observing a single galaxy, which made our extrapolation more accurate and reliable.”

Massive and isolated spiral galaxies offer the best chance to search for missing matter. They are massive enough to heat gas to temperatures of millions of degrees so that they emit X-rays, and have largely avoided being contaminated by other material through star formation or interactions with other galaxies.

Still missing

The team’s results showed that the halo surrounding galaxies like the ones observed cannot contain all of the missing matter after all. Despite extrapolating out to almost 30 times the radius of the Milky Way, nearly three-quarters of the expected material was still missing.

Milky Way Dark Matter Halo Credit ESO L. Calçada

There are two main alternative theories as to where it could be: either it is stored in another gas phase that is poorly observed – perhaps either a hotter and more tenuous phase or a cooler and denser one – or within a patch of space that is not covered by our current observations or emits X-rays too faintly to be detected.

Either way, since the galaxies do not contain enough missing matter they may have ejected it out into space, perhaps driven by injections of energy from exploding stars or by supermassive black holes.

“This work is important to help create more realistic galaxy models, and in turn help us better understand how our own Galaxy formed and evolved,” says Norbert Schartel, ESA XMM-Newton project scientist. “This kind of finding is simply not possible without the incredible sensitivity of XMM-Newton.”

“In the future, scientists can add even more galaxies to our study samples and use XMM-Newton in collaboration with other high-energy observatories, such as ESA’s upcoming Advanced Telescope for High-ENergy Astrophysics, Athena, to probe the extended, low-density parts of a galaxy’s outer edges, as we continue to unravel the mystery of the Universe’s missing matter.”

See the full article here .

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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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From ESA: “Stellar winds behaving unexpectedly”

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European Space Agency

2 February 2018

Yaël Nazé
Université de Liège
Belgium
Tel: +32 4 366 97 20
Email: naze@astro.ulg.ac.be

Norbert Schartel
XMM-Newton Project Scientist
European Space Agency
Email: Norbert.Schartel@esa.int

Markus Bauer
Head of the Joint Communication Office
European Space Agency
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int

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Stellar wind evolution. The binary star system HD 5980 as observed by ESA’s XMM-Newton between 2000 and 2016.

ESA’s XMM-Newton has spotted surprising changes in the powerful streams of gas from two massive stars, suggesting that colliding stellar winds don’t behave as expected.

ESA/XMM Newton

Massive stars – several times larger than our Sun – lead turbulent lives, burning their nuclear fuel rapidly and pouring large amounts of material into their surroundings throughout their short but sparkling lives.

These fierce stellar winds can carry the equivalent of Earth’s mass in a month and travel at millions of kilometres per hour, so when two such winds collide they unleash enormous amounts of energy.

The cosmic clash heats the gas to millions of degrees, making it shine brightly in X-rays.

Normally, colliding winds change little because neither do the stars nor their orbits. However, some massive stars behave dramatically.

This is the case with HD 5980, a pairing of two huge stars each 60 times the mass of our Sun and only about 100 million kilometres apart – closer than we are to our star.

2
Position of HD 5980
Released 16/02/2007
Copyright NASA, ESA, A. Nota (STScI/ESA)
A Hubble Space Telescope view of the cluster NGC 346 – the arrow indicates the position of HD 5980.

One had a major outburst in 1994, reminiscent of the eruption that turned Eta Carinae into the second brightest star in the sky for about 18 years in the 19th century.

3
Star Eta Carinae
Released 16/02/2007
Copyright J. Morse (Univ. of Colorado)/NASA
The star Eta Carinae was seen to erupt in the 19th century. During the eruption, the star lost 10 to 20 solar masses of material, which now forms a nebula around it. Astronomers observed a similar outburst from HD 5980 in 1993-94. This Hubble Space Telescope’s image thus shows how HD 5980 might look like in a century.

While it is now too late to study Eta Carinae’s historic eruption, astronomers have been observing HD 5980 with X-ray telescopes to study the hot gas.

In 2007, Yaël Nazé of the University of Liège, Belgium, and her colleagues discovered the collision of winds from these stars using observations made by ESA’s XMM-Newton and NASA’s Chandra X-ray telescopes between 2000 and 2005.

Then they looked at it again with XMM-Newton in 2016.

“We expected HD 5980 to fade gently over the years as the erupting star settled back to normal – but to our surprise it did just the opposite,” says Yaël.

They found the pair was two and a half times brighter than a decade earlier, and its X-ray emission was even more energetic.

“We had never seen anything like that in a wind–wind collision.”


ESA’s XMM-Newton has spotted surprising changes in the powerful streams of gas from two massive stars in the binary star system HD 5980. One of the two stars had a major outburst reminiscent of the 19th-century eruption of Eta Carinae, and astronomers expected that its X-ray emission would fade gently over the years. Instead, they found the pair was two and a half times brighter than a decade earlier, and its X-ray emission was even more energetic, suggesting that colliding stellar winds don’t behave as expected.

With less material ejected but more light emitted, it was difficult to explain what was happening.

Finally, they found a theoretical study that offers a fitting scenario.

“When stellar winds collide, the shocked material releases plenty of X-rays. However, if the hot matter radiates too much light, it rapidly cools, the shock becomes unstable and the X-ray emission dims.

“This somewhat counterintuitive process is what we thought happened at the time of our first observations, more than 10 years ago. But by 2016, the shock had relaxed and the instabilities had diminished, allowing the X-ray emission to rise eventually.”

These are the first observations that substantiate this previously hypothetical scenario. Yaël’s colleagues are now testing the new result in greater detail through computer simulations.

“Unique discoveries like this demonstrate how XMM-Newton keeps providing astronomers with fresh material to improve our understanding of the most energetic processes in the Universe,” says Norbert Schartel, XMM-Newton project scientist at ESA.

Science paper:
A changing wind collision, The Astrophysical Journal.

See the full article here .

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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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From Chandra: “X-rays Reveal Temperament of Possible Planet-hosting Stars”

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NASA Chandra Telescope

NASA Chandra

September 6, 2017

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Credit X-ray: NASA/CXC/Queens Univ. of Belfast/R.Booth, et al.; Illustration: NASA/CXC/M.Weiss

X-rays may provide valuable information about whether a star system will be hospitable to life on planets.

Stellar X-rays mirror magnetic activity, which can produce energetic radiation and eruptions that could impact surrounding planets.

Researchers used Chandra and XMM-Newton to study 24 stars like the Sun that were at least one billion years old.

ESA/XMM Newton X-ray telescope

The latest study indicates older Sun-like stars settle down relatively quickly, boosting prospects for life to develop on planets around them.

A new study using data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton suggests X-rays emitted by a planet’s host star may provide critical clues to just how hospitable a star system could be. A team of researchers looked at 24 stars similar to the Sun, each at least one billion years old, and how their X-ray brightness changed over time.

Since stellar X-rays mirror magnetic activity, X-ray observations can tell astronomers about the high-energy environment around the star. In the new study the X-ray data from Chandra and XMM-Newton revealed that stars like the Sun and their less massive cousins calm down surprisingly quickly after a turbulent youth.

To understand how quickly stellar magnetic activity level changes over time, astronomers need accurate ages for many different stars. This is a difficult task, but new precise age estimates have recently become available from studies of the way that a star pulsates using NASA’s Kepler and ESA’s CoRoT missions. These new age estimates were used for most of the 24 stars studied here.

Astronomers have observed that most stars are very magnetically active when they are young, since the stars are rapidly rotating. As the rotating star loses energy over time, the star spins more slowly and the magnetic activity level, along with the associated X-ray emission, drops.

Although it is not certain why older stars settle down relatively quickly, astronomers have ideas they are exploring. One possibility is that the decrease in rate of spin of the older stars occurs more quickly than it does for the younger stars. Another possibility is that the X-ray brightness declines more quickly with time for older, more slowly rotating stars than it does for younger stars.

A paper describing these results has been accepted for publication in the Monthly Notices of the Royal Astronomical Society, and is available online. The other co-authors are Victor Silva Aguirre from Aarhus University in Denmark and Scott Wolk from CfA.

A Quick Look at GJ 176

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

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