Monday, August 21, 2017

Scientists Improve Brown Dwarf Weather Forecasts

This artist's concept shows a brown dwarf with bands of clouds, thought to resemble those seen at Neptune and the other outer planets. 
Credit: NASA/JPL-Caltech. › Full image and caption


Dim objects called brown dwarfs, less massive than the Sun but more massive than Jupiter, have powerful winds and clouds -- specifically, hot patchy clouds made of iron droplets and silicate dust. Scientists recently realized these giant clouds can move and thicken or thin surprisingly rapidly, in less than an Earth day, but did not understand why. 

Now, researchers have a new model for explaining how clouds move and change shape in brown dwarfs, using insights from NASA's Spitzer Space Telescope. Giant waves cause large-scale movement of particles in brown dwarfs' atmospheres, changing the thickness of the silicate clouds, researchers report in the journal Science. The study also suggests these clouds are organized in bands confined to different latitudes, traveling with different speeds in different bands. 

"This is the first time we have seen atmospheric bands and waves in brown dwarfs," said lead author Daniel Apai, associate professor of astronomy and planetary sciences at the University of Arizona in Tucson.

Just as in Earth's ocean, different types of waves can form in planetary atmospheres. For example, in Earth's atmosphere, very long waves mix cold air from the polar regions to mid-latitudes, which often lead clouds to form or dissipate. 

The distribution and motions of the clouds on brown dwarfs in this study are more similar to those seen on Jupiter, Saturn, Uranus and Neptune. Neptune has cloud structures that follow banded paths too, but its clouds are made of ice. Observations of Neptune from NASA's Kepler spacecraft, operating in its K2 mission, were important in this comparison between the planet and brown dwarfs.

"The atmospheric winds of brown dwarfs seem to be more like Jupiter's familiar regular pattern of belts and zones than the chaotic atmospheric boiling seen on the Sun and many other stars," said study co-author Mark Marley at NASA's Ames Research Center in California's Silicon Valley.

Brown dwarfs can be thought of as failed stars because they are too small to fuse chemical elements in their cores. They can also be thought of as "super planets" because they are more massive than Jupiter, yet have roughly the same diameter. Like gas giant planets, brown dwarfs are mostly made of hydrogen and helium, but they are often found apart from any planetary systems. In a 2014 study using Spitzer, scientists found that brown dwarfs commonly have atmospheric storms.

Due to their similarity to giant exoplanets, brown dwarfs are windows into planetary systems beyond our own. It is easier to study brown dwarfs than planets because they often do not have a bright host star that obscures them. 

"It is likely the banded structure and large atmospheric waves we found in brown dwarfs will also be common in giant exoplanets," Apai said. 

Using Spitzer, scientists monitored brightness changes in six brown dwarfs over more than a year, observing each of them rotate 32 times. As a brown dwarf rotates, its clouds move in and out of the hemisphere seen by the telescope, causing changes in the brightness of the brown dwarf. Scientists then analyzed these brightness variations to explore how silicate clouds are distributed in the brown dwarfs.

Researchers had been expecting these brown dwarfs to have elliptical storms resembling Jupiter's Great Red Spot, caused by high-pressure zones. The Great Red Spot has been present in Jupiter for hundreds of years and changes very slowly: Such "spots" could not explain the rapid changes in brightness that scientists saw while observing these brown dwarfs. The brightness levels of the brown dwarfs varied markedly just over the course of an Earth day. 

To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands. 

University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

"When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness," Karalidi said. "When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave."

The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior. 

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit:  http://spitzer.caltech.edu - https://www.nasa.gov/spitzer


News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425

elizabeth.landau@jpl.nasa.gov



Friday, August 18, 2017

A distorted duo Credit: ESA/Hubble & NASA


IC 1727, UGC 1249
Credit:  ESA/Hubble & NASA


Gravity governs the movements of the cosmos. It draws flocks of galaxies together to form small groups and more massive galaxy clusters, and brings duos so close that they begin to tug at one another. This latter scenario can have extreme consequences, with members of interacting pairs of galaxies often being dramatically distorted, torn apart, or driven to smash into one another, abandoning their former identities and merging to form a single accumulation of gas, dust, and stars.

The subject of this NASA/ESA Hubble Space Telescope image, IC 1727, is currently interacting with its near neighbour, NGC 672 (which is just out of frame). The pair’s interactions have triggered peculiar and intriguing phenomena within both objects — most noticeably in IC 1727. The galaxy’s structure is visibly twisted and asymmetric, and its bright nucleus has been dragged off-centre. 

In interacting galaxies such as these, astronomers often see signs of intense star formation (in episodic flurries known as starbursts) and spot newly-formed star clusters. They are thought to be caused by gravity churning, redistributing, and compacting the gas and dust. In fact, astronomers have analysed the star formation within IC 1727 and NGC 672 and discovered something interesting — observations show that simultaneous bursts of star formation occurred in both galaxies some 20 to 30 and 450 to 750 million years ago. The most likely explanation for this is that the galaxies are indeed an interacting pair, approaching each other every so often and swirling up gas and dust as they pass close by.



Thursday, August 17, 2017

The little star that survived a Supernova

The progenitor of LP40-365 could be a binary star system like the one shown in this animation. Here, an ultra-massive and compact dead star called a white dwarf (shown as a small white star) is accreting matter from its giant companion (the larger red star). The material escapes from the giant and forms an accretion disk around the white dwarf. Once enough material is accreted onto the white dwarf, a violent thermonuclear runaway tears it apart and destroys the entire system. The giant star and the surviving fragment of the white dwarf are flung into space at tremendous speeds. The surviving white dwarf shrapnel hurtles towards our region of the Galaxy, where its radiation is detected by ground based telescopes. Copyright Russell Kightley (http://scientific.pictures), used with permission.



An international team of astronomers led by Stephane Vennes at the Astronomical Institute in the Czech Republic have identified a white dwarf moving faster than the escape velocity of the Milky Way. This high velocity star is thought to be shrapnel thrown away millions of years ago from the site of an ancient, peculiar Type Ia supernova explosion. The team used telescopes located in Arizona, the Canary Islands and Maunakea’s GRACES, a high resolution spectrograph that combines the large aperture of the Gemini North telescope with Espadons, the high resolution spectropolarimeter at CFHT, via a 250m optical fiber link.

Type Ia supernovae play an important role important in our understanding of the Universe. They act as standard candles, astronomical objects for which astronomers have a decent estimate of their intrinsic brightness or luminosity. Astronomers can estimate the true total luminosity of a Type Ia supernovae and use that information to determine the distance. Despite astronomers’ understanding of the luminosity and distance relationship for Type Ia supernovae, very little is known about the explosions themselves. Astronomers build models aimed at a deeper understanding of the engine powering these explosions.

One of these models suggest that at the heart of a Type Ia supernova is a compact star known as a white dwarf. If the white dwarf has a close companion star, over time the gravity of the white dwarf may attract gas from the other star. This continuous feeding compresses the white dwarf to such a high density and temperature that the white dwarf is engulfed in a thermonuclear explosion. It is thought that nothing survives this kind of explosion. However, a new class of models called "subluminous type 1a supernova also known as a Type Iax” can leave a partially burnt remnant that is instantly ejected at high velocity.

"Such a cataclysmic binary star has never been caught feeding and getting just ready for the explosion," commented Stephane Vennes, leading author of the Science article. "All we ever witness is the aftermath of the explosion, that is the bright flash in the distant Universe that even outshines the galaxy hosting that event. But now, with the discovery of a surviving remnant of the white dwarf itself, we have direct clues to the nature of the most important actor involved in these events."

The team studied the white dwarf star LP40-365 for two-years with telescopes located in Arizona, the Canary Islands, and Hawaii. The new star was first identified with the National Science Foundation's (NSF) Mayall four-meter telescope at Kitt Peak National Observatory in Arizona. "We selected this object for observation with the spectrograph at the four-meter telescope because of its large apparent motion across the celestial sphere. Thousands of objects like this one are known, but the sky was partly cloudy on that night and we had to go for the brightest star available which turned out to be LP40-365," said team member Adela Kawka, underpinning the importance of serendipity in astronomy. "We alerted team members J.R. Thorstensen and E. Alper at Dartmouth College, and P. Nemeth at the Karl Remeis Observatory for urgent follow-up observations."

A final, crowning data set was obtained with the help of team member Viktor Khalack at the Université de Moncton using a unique instrument, GRACES on Maunakea. GRACES is a collaboration between the Canada-France-Hawaii Telescope and the NSF Gemini Observatory. When GRACES is in use, CFHT’s spectropolarimeter Espadons receives light fed by an optical fiber hooked to its neighbor on the summit, the eight-meter Gemini North telescope. “GRACES provides astronomers the best of both worlds, the light collecting power of the Gemini observatory combined with a state of the art instrument like Espadons. The combination packs a powerful punch and creates opportunities for discoveries like this one” says Nadine Manset, the GRACES instrument scientist at CFHT.

After collecting the data, the team used state of the art computer codes for analysis. The analysis proved the compact nature of the star and its exotic chemical composition. "The extreme peculiarity of the atmosphere required a lengthy and complex model atmosphere analysis which crunched several weeks of computing time. But the results proved very exciting. Such a peculiar atmosphere devoid of hydrogen and helium is rare indeed," commented team member Peter Nemeth. The analysis also revealed an extraordinary Galactic trajectory. "The extremely high velocity of this star puts it on a path out of the Milky Way with no return ever," said team member Lilia Ferrario.

Supernova models and simulations did entertain the possibility of observing surviving stellar remnants in the aftermath of a supernova explosion. The unique object LP40-365 is the first observational evidence for surviving bound remnants of failed supernovae and therefore it is an invaluable object to improve our understanding of these cosmological standard candles.

Many more of these objects are lurking in the Milky Way and awaiting discovery. The recent ESA/Gaia mission may well help us discover many more of these objects and help us understand how a little white dwarf star can survive supernova explosions. 



Additional information

Official press release
Paper



Contact Information:

Mary Beth Laychak
Outreach Program Manager
Canada-France-Hawaii Telescope
65-1238 Mamalahoa Hwy
Kamuela, HI 96743
808-885-3121
laychak@cfht.hawaii.edu

Science contact

Stephane Vennes
Astronomical Institute
The Czech Academy of Sciences
Fricova 298
251 65 Ondrejov
Czech Republic
+420 323620217
vennes@asu.cas.cz


Wednesday, August 16, 2017

Supermassive Black Holes Feed on Cosmic Jellyfish

Example of a jellyfish galaxy

Example of a jellyfish galaxy

Visualisation of MUSE view of Jellyfish Galaxy

Example of a jellyfish galaxy



Videos 

ESOcast 122 Light: Supermassive Black Holes Feed on Cosmic Jellyfish (4K UHD)
ESOcast 122 Light: Supermassive Black Holes Feed on Cosmic Jellyfish (4K UHD)

Visualisation of galaxy undergoing ram pressure stripping
Visualisation of galaxy undergoing ram pressure stripping

Artist's impression of ram pressure stripping
Artist's impression of ram pressure stripping

Visualisation of a galaxy undergoing ram pressure stripping
Visualisation of a galaxy undergoing ram pressure stripping



ESO’s MUSE instrument on the VLT discovers new way to fuel black holes


Observations of “Jellyfish galaxies” with ESO’s Very Large Telescope have revealed a previously unknown way to fuel supermassive black holes. It seems the mechanism that produces the tentacles of gas and newborn stars that give these galaxies their nickname also makes it possible for the gas to reach the central regions of the galaxies, feeding the black hole that lurks in each of them and causing it to shine brilliantly. The results appeared today in the journal Nature.

An Italian-led team of astronomers used the MUSE (Multi-Unit Spectroscopic Explorer) instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study how gas can be stripped from galaxies. They focused on extreme examples of jellyfish galaxies in nearby galaxy clusters, named after the remarkable long “tentacles” of material that extend for tens of thousands of light-years beyond their galactic discs [1][2].

The tentacles of jellyfish galaxies are produced in galaxy clusters by a process called ram pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.

Six out of the seven jellyfish galaxies in the study were found to host a supermassive black hole at the centre, feeding on the surrounding gas [3]. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.

This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” said team leader Bianca Poggianti from the INAF-Astronomical Observatory of Padova in Italy. “It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy centre.” [4]

A long-standing question is why only a small fraction of supermassive black holes at the centres of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly? These results reveal a previously unknown mechanism by which the black holes can be fed.

Yara Jaffé, an ESO fellow who contributed to the paper explains the significance: “These MUSE observations suggest a novel mechanism for gas to be funnelled towards the black hole’s neighbourhood. This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.

The current observations are part of a much more extensive study of many more jellyfish galaxies that is currently in progress.

This survey, when completed, will reveal how many, and which, gas-rich galaxies entering clusters go through a period of increased activity at their cores,” concludes Poggianti. “A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe. Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.



Notes

[1] To date, just over 400 candidate jellyfish galaxies have been found.


[2] The results were produced as part of the observational programme known as GASP (GAs Stripping Phenomena in galaxies with MUSE), which is an ESO Large Programme aimed at studying where, how and why gas can be removed from galaxies. GASP is obtaining deep, detailed MUSE data for 114 galaxies in various environments, specifically targeting jellyfish galaxies. Observations are currently in progress.

[3] It is well established that almost every, if not every, galaxy hosts a supermassive black hole at its centre, between a few million and a few billion times as massive as our Sun. When a black hole pulls in matter from its surroundings, it emits electromagnetic energy, giving rise to some of the most energetic of astrophysical phenomena: active galactic nuclei (AGN).

[4] The team also investigated the alternative explanation that the central AGN activity contributes to stripping gas from the galaxies, but considered it less likely. Inside the galaxy cluster, the jellyfish galaxies are located in a zone where the hot, dense gas of the intergalactic medium is particularly likely to create the galaxy’s long tentacles, reducing the possibility that they are created by AGN activity. There is therefore stronger evidence that ram pressure triggers the AGN and not vice versa.



More Information


This research was presented in a paper entitled “Ram Pressure Feeding Supermassive Black Holes” by B. Poggianti et al., to appear in the journal Nature on 17 August 2017.

The team is composed of B. Poggianti (INAF-Astronomical Observatory of Padova, Italy), Y. Jaffé (ESO, Chile), A. Moretti (INAF-Astronomical Observatory of Padova, Italy), M. Gullieuszik (INAF-Astronomical Observatory of Padova, Italy), M. Radovich (INAF-Astronomical Observatory of Padova, Italy), S. Tonnesen (Carnegie Observatory, USA), J. Fritz (Instituto de Radioastronomía y Astrofísica, Mexico), D. Bettoni (INAF-Astronomical Observatory of Padova, Italy), B. Vulcani (University of Melbourne, Australia; INAF-Astronomical Observatory of Padova, Italy), G. Fasano (INAF-Astronomical Observatory of Padova, Italy), C. Bellhouse (University of Birmingham, UK; ESO, Chile), G. Hau (ESO, Chile) and A. Omizzolo (Vatican Observatory, Vatican City State).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope 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”.



Links



Contacts

Bianca Poggianti
INAF-Astronomical Observatory of Padova
Padova, Italy
Tel: +39 340 7448663
Email: bianca.poggianti@oapd.inaf.it

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

Source: ESO/News

Tuesday, August 15, 2017

Hint of Relativity Effects in Stars Orbiting Supermassive Black Hole at Centre of Galaxy

Artist's impression of the orbits of stars close to the Galactic Centre 

Artist's impression of the effect of general relativity on the orbit of the S2 star at the Galactic Centre 

Image of the Galactic Centre



Videos

ESOcast 121 Light: Star orbiting supermassive black hole suggests Einstein is right (4K UHD)
ESOcast 121 Light: Star orbiting supermassive black hole suggests Einstein is right (4K UHD)

Orbits of three stars very close to the centre of the Milky Way
Orbits of three stars very close to the centre of the Milky Way



A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the centre of the Milky Way may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star S2 is deviating slightly from the path calculated using classical physics. This tantalising result is a prelude to much more precise measurements and tests of relativity that will be made using the GRAVITY instrument as star S2 passes very close to the black hole in 2018.

At the centre of the Milky Way, 26 000 light-years from Earth, lies the closest supermassive black hole, which has a mass four million times that of the Sun. This monster is surrounded by a small group of stars orbiting at high speed in the black hole’s very strong gravitational field. It is a perfect environment in which to test gravitational physics, and particularly Einstein’s general theory of relativity.

A team of German and Czech astronomers have now applied new analysis techniques to existing observations of the stars orbiting the black hole, accumulated using ESO’s Very Large Telescope (VLT) in Chile and others over the last twenty years [1]. They compare the measured star orbits to predictions made using classical Newtonian gravity as well as predictions from general relativity.

The team found suggestions of a small change in the motion of one of the stars, known as S2, that is consistent with the predictions of general relativity [2]. The change due to relativistic effects amounts to only a few percent in the shape of the orbit, as well as only about one sixth of a degree in the orientation of the orbit [3]. If confirmed, this would be the first time that a measurement of the strength of the general relativistic effects has been achieved for stars orbiting a supermassive black hole.

Marzieh Parsa, PhD student at the University of Cologne, Germany and lead author of the paper, is delighted: "The Galactic Centre really is the best laboratory to study the motion of stars in a relativistic environment. I was amazed how well we could apply the methods we developed with simulated stars to the high-precision data for the innermost high-velocity stars close to the supermassive black hole."

The high accuracy of the positional measurements, made possible by the VLT’s near-infrared adaptive optics instruments, was essential for the study [4]. These were vital not only during the star’s close approach to the black hole, but particularly during the time when S2 was further away from the black hole. The latter data allowed an accurate determination of the shape of the orbit.

"During the course of our analysis we realised that to determine relativistic effects for S2 one definitely needs to know the full orbit to very high precision," comments Andreas Eckart, team leader at the University of Cologne.

As well as more precise information about the orbit of the star S2, the new analysis also gives the mass of the black hole and its distance from Earth to a higher degree of accuracy [5].

Co-author Vladimir Karas from the Academy of Sciences in Prague, the Czech Republic, is excited about the future: "This opens up an avenue for more theory and experiments in this sector of science."

This analysis is a prelude to an exciting period for observations of the Galactic Centre by astronomers around the world. During 2018 the star S2 will make a very close approach to the supermassive black hole. This time the GRAVITY instrument, developed by a large international consortium led by the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany [6], and installed on the VLT Interferometer [7], will be available to help measure the orbit much more precisely than is currently possible. Not only is GRAVITY, which is already making high-precision measurements of the Galactic Centre, expected to reveal the general relativistic effects very clearly, but also it will allow astronomers to look for deviations from general relativity that might reveal new physics.



Notes

[1] Data from the near-infrared NACO camera now at VLT Unit Telescope 1 (Antu) and the near-infrared imaging spectrometer SINFONI at the Unit Telescope 4 (Yepun) were used for this study. Some additional published data obtained at the Keck Observatory were also used.

[2] S2 is a 15-solar-mass star on an elliptical orbit around the supermassive black hole. It has a period of about 15.6 years and gets as close as 17 light-hours to the black hole — or just 120 times the distance between the Sun and the Earth.

[3] A similar, but much smaller, effect is seen in the changing orbit of the planet Mercury in the Solar System. That measurement was one of the best early pieces of evidence in the late nineteenth century suggesting that Newton’s view of gravity was not the whole story and that a new approach and new insights were needed to understand gravity in the strong-field case. This ultimately led to Einstein publishing his general theory of relativity, based on curved spacetime, in 1915.

When the orbits of stars or planets are calculated using general relativity, rather than Newtonian gravity, they evolve differently. Predictions of the small changes to the shape and orientation of orbits with time are different in the two theories and can be compared to measurements to test the validity of general relativity.

[4] An adaptive optics system compensates for the image distortions produced by the turbulent atmosphere in real time and allows the telescope to be used at much angular resolution (image sharpness), in principle limited only by the mirror diameter and the wavelength of light used for the observations.

[5] The team finds a black hole mass of 4.2 × 106 times the mass of the Sun, and a distance from us of 8.2 kiloparsecs, corresponding to almost 27 000 light-years.

[6] The University of Cologne is part of the GRAVITY team (http://www.mpe.mpg.de/ir/gravity) and contributed the beam combiner spectrometers to the system.

[7] GRAVITY First Light was in early 2016 and it is already observing the Galactic Centre.



More Information

This research was presented in a paper entitled “Investigating the Relativistic Motion of the Stars Near the Black Hole in the Galactic Center”, by M. Parsa et al., to be published in the Astrophysical Journal.

The team is composed of Marzieh Parsa, Andreas Eckart (I.Physikalisches Institut of the University of Cologne, Germany; Max Planck Institute for Radio Astronomy, Bonn, Germany), Banafsheh Shahzamanian (I.Physikalisches Institut of the University of Cologne, Germany), Christian Straubmeier (I.Physikalisches Institut of the University of Cologne, Germany), Vladimir Karas (Astronomical Institute, Academy of Science, Prague, Czech Republic), Michal Zajacek (Max Planck Institute for Radio Astronomy, Bonn, Germany; I.Physikalisches Institut of the University of Cologne, Germany) and J. Anton Zensus (Max Planck Institute for Radio Astronomy, Bonn, Germany).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope 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”.



Links



Contacts

Marzieh Parsa
I. Physikalisches Institut, Universität zu Köln
Köln, Germany
Tel: +49(0)221/470-3495
Email: parsa@ph1.uni-koeln.de

Andreas Eckart
I. Physikalisches Institut, Universität zu Köln
Köln, Germany
Tel: +49(0)221/470-3546
Email: eckart@ph1.uni-koeln.de

Vladimir Karas
Astronomical Institute, Academy of Science
Prague, Czech Republic
Tel: +420-226 258 420
Email: vladimir.karas@cuni.cz

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

Source: ESO/News

Saturday, August 12, 2017

Small but significant

NGC 5949
Credit: ESA/Hubble & NASA


The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies.

With a mass of about a hundredth that of the Milky Way, NGC 5949 is a relatively bulky example of a dwarf galaxy. Its classification as a dwarf is due to its relatively small number of constituent stars, but the galaxy’s loosely-bound spiral arms also place it in the category of barred spirals. This structure is just visible in this image, which shows the galaxy as a bright yet ill-defined pinwheel. Despite its small proportions, NGC 5949’s proximity has meant that its light can be picked up by fairly small telescopes, something that facilitated its discovery by the astronomer William Herschel in 1801. 

Astronomers have run into several cosmological quandaries when it comes to dwarf galaxies like NGC 5949. For example, the distribution of dark matter within dwarfs is quite puzzling (the “cuspy halo” problem), and our simulations of the Universe predict that there should be many more dwarf galaxies than we see around us (the “missing satellites” problem).



Friday, August 11, 2017

IC 10: A Starburst Galaxy with the Prospect of Gravitational WavesA Quick Look at IC 10

IC 10
Credit: X-ray: NASA/CXC/UMass Lowell/S.Laycock et al.
Optical: Bill Snyder Astrophotography




animation




In 1887, American astronomer Lewis Swift discovered a glowing cloud, or nebula, that turned out to be a small galaxy about 2.2 billion light years from Earth. Today, it is known as the "starburst" galaxy IC 10, referring to the intense star formation activity occurring there.

More than a hundred years after Swift's discovery, astronomers are studying IC 10 with the most powerful telescopes of the 21st century. New observations with NASA's Chandra X-ray Observatory reveal many pairs of stars that may one day become sources of perhaps the most exciting cosmic phenomenon observed in recent years: gravitational waves.

By analyzing Chandra observations of IC 10 spanning a decade, astronomers found over a dozen black holes and neutron stars feeding off gas from young, massive stellar companions. Such double star systems are known as "X-ray binaries" because they emit large amounts of X-ray light. As a massive star orbits around its compact companion, either a black hole or neutron star, material can be pulled away from the giant star to form a disk of material around the compact object. Frictional forces heat the infalling material to millions of degrees, producing a bright X-ray source.

When the massive companion star runs out of fuel, it will undergo a catastrophic collapse that will produce a supernova explosion, and leave behind a black hole or neutron star. The end result is two compact objects: either a pair of black holes, a pair of neutron stars, or a black hole and neutron star. If the separation between the compact objects becomes small enough as time passes, they will produce gravitational waves. Over time, the size of their orbit will shrink until they merge. LIGO has found three examples of black hole pairs merging in this way in the past two years.

Starburst galaxies like IC 10 are excellent places to search for X-ray binaries because they are churning out stars rapidly. Many of these newly born stars will be pairs of young and massive stars. The most massive of the pair will evolve more quickly and leave behind a black hole or a neutron star partnered with the remaining massive star. If the separation of the stars is small enough, an X-ray binary system will be produced.

This new composite image of IC 10 combines X-ray data from Chandra (blue) with an optical image (red, green, blue) taken by amateur astronomer Bill Snyder from the Heavens Mirror Observatory in Sierra Nevada, California. The X-ray sources detected by Chandra appear as a darker blue than the stars detected in optical light.

The young stars in IC 10 appear to be just the right age to give a maximum amount of interaction between the massive stars and their compact companions, producing the most X-ray sources. If the systems were younger, then the massive stars would not have had time to go supernova and produce a neutron star or black hole, or the orbit of the massive star and the compact object would not have had time to shrink enough for mass transfer to begin. If the star system were much older, then both compact objects would probably have already formed. In this case transfer of matter between the compact objects is unlikely, preventing the formation of an X-ray emitting disk.

Chandra detected 110 X-ray sources in IC 10. Of these, over forty are also seen in optical light and 16 of these contain "blue supergiants", which are the type of young, massive, hot stars described earlier. Most of the other sources are X-ray binaries containing less massive stars. Several of the objects show strong variability in their X-ray output, indicative of violent interactions between the compact stars and their companions.

A pair of papers describing these results were published in the February 10th, 2017 issue of The Astrophysical Journal and is available online here and here. The authors of the study are Silas Laycock from the UMass Lowell's Center for Space Science and Technology (UML); Rigel Capallo, a graduate student at UML; Dimitris Christodoulou from UML; Benjamin Williams from the University of Washington in Seattle; Breanna Binder from the California State Polytechnic University in Pomona; and, Andrea Prestwich from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

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 IC 10:


Category: Neutron Stars/X-ray Binaries, Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 00h 20m 23.2s | Dec 59° 17´ 34.7"
Constellation: Cassiopeia
Observation Date: 6 pointings between December 2009 and September 2010
Observation Time: 24 hours 19.5 min
Obs. ID: 11081-11086
Instrument: ACIS
References: Laycock S. et al., 2017, ApJ, 836, 50; arXiv:1611.08611. Laycock S. et al., 2017, ApJ [in press]; arXiv:1701.03803
Color Code: X-ray (Blue); Optical (Red, Green, Blue)
Distance Estimate: About 2.2 billion light years


Thursday, August 10, 2017

Four Earth-Sized Planets Found Orbiting the Nearest Sun-Like Star

This illustration compares the four planets detected around the nearby star Tau Ceti (top) and the inner planets of our solar system (bottom). Credit:  F. FENG, University of Hertfordshire, United Kingdom



Maunakea, Hawaii – A new study by an international team of astronomers reveals that Tau Ceti, the nearest Sun-like star about 12 light years away from the Sun, has four Earth-sized planets orbiting it.

These planets have masses as low as 1.7 Earth mass, making them among the smallest planets ever detected around the nearest Sun-like stars. Two of them are Super-Earths located in the habitable zone of the star and thus could support liquid surface water.

The data were obtained by using the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory in Chile, combined with the High-Resolution Echelle Spectrometer (HIRES) at the W. M. Keck Observatory on Maunakea, Hawaii.

“HIRES is one of only a few spectrometers in the world that have routinely delivered the level of radial velocity precision needed for this kind of work,” said co-author Dr. Steve Vogt, professor of astronomy and astrophysics at University of California, Santa Cruz. “And it is one of only two instruments in the world, the other being HARPS, that has been able to deliver this precision level for over a decade. It is a very unique facility in the exoplanet discovery field.”

The four planets were detected by observing the wobbles in the movement of Tau Ceti. This wobble, known as the Doppler effect, happens when a planet’s gravity slightly tugs at its host star as it orbits.

Measuring Tau Ceti’s wobbles required techniques sensitive enough to detect variations in its movement as small as 30 centimeters per second. The smaller the planet, the weaker its gravitational pull on its host star, and the harder it is to detect the star’s wobble.

"We are getting tantalizingly close to the 10 centimeters per second limit required for detecting Earth analogs,” said Dr. Fabo Feng from the University of Hertfordshire in the United Kingdom and lead author of the study. “Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth’s habitability through comparison with these analogs."

The outer two planets around Tau Ceti are likely to be candidate habitable worlds, although a massive debris disc around the star probably reduces their habitability due to intensive bombardment by asteroids and comets.

The same team also investigated Tau Ceti four years ago in 2013, when Dr. Mikko Tuomi led an effort in developing data analysis techniques and used the star as a benchmark case.

"We came up with an ingenious way of telling the difference between signals caused by planets and those caused by a star's activity. We realized that we could see how a star's activity differed at different wavelengths, then used that information to separate this activity from signals of planets," said Dr. Tuomi.

"We have painstakingly improved the sensitivity of our techniques and could rule out two of the signals our team identified in 2013 as planets. But no matter how we look at the star, there seems to be at least four rocky planets orbiting it," Dr. Tuomi added. "We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable, planets in the system."

Sun-like stars are thought to be the best targets for searching for habitable Earth-sized planets due to their similarity to the Sun. Unlike more common smaller stars such as the red dwarf stars Proxima Centauri and Trappist-1, they are not so faint that planets would be tidally locked, showing the same side to the star at all times.

Tau Ceti is very similar to the Sun in its size and brightness, and they both host multi-planet systems. If the outer two planets are found to be habitable, Tau Ceti could be an optimal target for interstellar colonization, as seen in science fiction.

"Such weak signals of planets almost the size of the Earth cannot be seen without using advanced statistical and modeling approaches. We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals," said Dr. Feng.


  About HIRES

The High-Resolution Echelle Spectrometer (HIRES) produces spectra of single objects at very high spectral resolution, yet covering a wide wavelength range. It does this by separating the light into many "stripes" of spectra stacked across a mosaic of three large CCD detectors. HIRES is famous for finding planets orbiting other stars. Astronomers also use HIRES to study distant galaxies and quasars, finding clues to the Big Bang.



Authors
  • Fabo Feng, Mikko Tuomi, Hugh Jones - University of Hertfordshire, UK 
  • John Barnes - The Open University, UK 
  • Guillem Anglada-Escude - Queen Mary University ofLondon, UK 
  • Steve Vogt - University of California at Santa Cruz, USA 
  • Paul Butler - Carnegie Institute of Washington, USA



About W. M. Keck Observatory


The W. M. Keck Observatory operates the most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California, and NASA.



Media Contact:

Mari-Ela Chock, Communications Officer
W. M. Keck Observatory
(808) 554-0567
mchock@keck.hawaii.edu


Wednesday, August 09, 2017

From the Residencia to the Milky Way

Credit: ESO/B. Tafreshi (twanight.org)


This image captures the route from the Residencia — the guesthouse for visitors to ESO's Paranal Observatory— to the breathtaking heart of the Milky Way, which covers the entire night sky.

The site shown here is Cerro Paranal, home to ESO's Very Large Telescope (VLT), a telescope comprising four 8.2-metre Unit Telescopes. The VLT can also act as an interferometer in the form of the appropriately-named VLT Interferometer, or VLTI, by gathering additional light from four smaller Auxiliary Telescopes, which can be independently moved around and placed in different configurations. One of these Auxiliary Telescopes is shown in this image, gazing at the sky with its dome wide open.

The road from the observatory to the Residencia appears as a shining thread, weaving amongst the rocky outcrops and hills of the desert environment. The yellow glow is caused by dim security lights — the street lighting is kept to a minimum in order to avoid unnecessary light pollution.

Source: ESO/images

Monday, August 07, 2017

Hubble Detects Exoplanet with Glowing Water Atmosphere

Artist's View of WASP-121b
Illustration: NASA, ESA, and G. Bacon (STScI)
Credits: Science: NASA, ESA, and T. Evans (University of Exeter)

Comparison of WASP-121b Stratosphere with Brown Dwarf Atmosphere
Credits: Illustration: NASA, ESA, and A. Feild (STScI)




Scientists have discovered the strongest evidence to date for a stratosphere on a planet outside our solar system, or exoplanet. A stratosphere is a layer of atmosphere in which temperature increases with higher altitudes.

"This result is exciting because it shows that a common trait of most of the atmospheres in our solar system — a warm stratosphere — also can be found in exoplanet atmospheres," said Mark Marley, study co-author based at NASA's Ames Research Center in California's Silicon Valley. "We can now compare processes in exoplanet atmospheres with the same processes that happen under different sets of conditions in our own solar system."

Reporting in the journal Nature, scientists used data from NASA's Hubble Space Telescope to study WASP-121b, a type of exoplanet called a "hot Jupiter." Its mass is 1.2 times that of Jupiter, and its radius is about 1.9 times Jupiter's — making it puffier. But while Jupiter revolves around our sun once every 12 years, WASP-121b has an orbital period of just 1.3 days. This exoplanet is so close to its star that if it got any closer, the star's gravity would start ripping it apart. It also means that the top of the planet's atmosphere is heated to a blazing 4,600 degrees Fahrenheit (2,500 degrees Celsius), hot enough to boil some metals. The WASP-121 system is estimated to be about 900 light-years from Earth — a long way, but close by galactic standards.

Previous research found possible signs of a stratosphere on the exoplanet WASP-33b as well as some other hot Jupiters. The new study presents the best evidence yet because of the signature of hot water molecules that researchers observed for the first time.

"Theoretical models have suggested stratospheres may define a distinct class of ultra-hot planets, with important implications for their atmospheric physics and chemistry," said Tom Evans, lead author and research fellow at the University of Exeter, United Kingdom. "Our observations support this picture."

To study the stratosphere of WASP-121b, scientists analyzed how different molecules in the atmosphere react to particular wavelengths of light, using Hubble's capabilities for spectroscopy. Water vapor in the planet's atmosphere, for example, behaves in predictable ways in response to certain wavelengths of light, depending on the temperature of the water.

Starlight is able to penetrate deep into a planet's atmosphere, where it raises the temperature of the gas there. This gas then radiates its heat into space as infrared light. However, if there is cooler water vapor at the top of the atmosphere, the water molecules will prevent certain wavelengths of this light from escaping to space. But if the water molecules at the top of the atmosphere have a higher temperature, they will glow at the same wavelengths.

"The emission of light from water means the temperature is increasing with height," said Tiffany Kataria, study co-author based at NASA's Jet Propulsion Laboratory, Pasadena, California. "We’re excited to explore at what longitudes this behavior persists with upcoming Hubble observations."

The phenomenon is similar to what happens with fireworks, which get their colors from chemicals emitting light. When metallic substances are heated and vaporized, their electrons move into higher energy states. Depending on the material, these electrons will emit light at specific wavelengths as they lose energy: sodium produces orange-yellow and strontium produces red in this process, for example. The water molecules in the atmosphere of WASP-121b similarly give off radiation as they lose energy, but in the form of infrared light, which the human eye is unable to detect.

In Earth's stratosphere, ozone gas traps ultraviolet radiation from the sun, which raises the temperature of this layer of atmosphere. Other solar system bodies have stratospheres, too; methane is responsible for heating in the stratospheres of Jupiter and Saturn's moon Titan, for example.

In solar system planets, the change in temperature within a stratosphere is typically around 100 degrees Fahrenheit (about 56 degrees Celsius). On WASP-121b, the temperature in the stratosphere rises by 1,000 degrees (560 degrees Celsius). Scientists do not yet know what chemicals are causing the temperature increase in WASP-121b's atmosphere. Vanadium oxide and titanium oxide are candidates, as they are commonly seen in brown dwarfs, "failed stars" that have some commonalities with exoplanets. Such compounds are expected to be present only on the hottest of hot Jupiters, as high temperatures are needed to keep them in a gaseous state.

"This super-hot exoplanet is going to be a benchmark for our atmospheric models, and it will be a great observational target moving into the Webb era," said Hannah Wakeford, study co-author who worked on this research while at NASA's Goddard Space Flight Center, Greenbelt, Maryland.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. The California Institute of Technology (Caltech) manages the Jet Propulsion Laboratory (JPL) for NASA.



Links

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Contacts
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, California
818-354-6425

elizabeth.landau@jpl.nasa.gov
 
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514

villard@stsci.edu


Source: HubbleSite

Sunday, August 06, 2017

Spot the cluster

Credit: ESO
Acknowledgements: Flickr user hdahle70



This image from the Wide-Field Imager on the MPG/ESO 2.2-metre telescope shows the starry skies around a galaxy cluster named PLCKESZ G286.6-31.3. The cluster itself is difficult to spot initially, but shows up as a subtle clustering of yellowish galaxies near the centre of the frame.

PLCKESZ G286.6-31.3 houses up to 1000 galaxies, in addition to large quantities of hot gas and dark matter. As such, the cluster has a total mass of 530 trillion (530 000 000 000 000) times the mass of the Sun.

When viewed from Earth, PLCKESZ G286.6-31.3 is seen through the outer fringes of the Large Magellanic Cloud (LMC) — one of the Milky Way’s satellite galaxies. The LMC hosts over 700 star clusters, in addition to hundreds of thousands of giant and supergiant stars. The majority of the cosmic objects captured in this image are stars and star clusters located inside the LMC .

The MPG/ESO 2.2-metre telescope has been in operation at ESO’s La Silla Observatory since 1984. The telescope has been utilised for a variety of cutting-edge scientific studies, including ground-breaking research into gamma-ray bursts, the most powerful explosions in the Universe. The 67-million-pixel Wide Field Imager (WFI) — mounted on the telescope’s Cassegrain focus — has been obtaining detailed views of faint, distant objects since 1999.

The data to create this image was selected from the ESO archive as part of the Hidden Treasures competition.




Source: ESO/Images

Saturday, August 05, 2017

The Hockey Stick Galaxy

 Credit: ESA/Hubble & NASA


The star of this Hubble Picture of the Week is a galaxy known as NGC 4656, located in the constellation of Canes Venatici (The Hunting Dogs). However, it also has a somewhat more interesting and intriguing name: the Hockey Stick Galaxy! The reason for this is a little unclear from this partial view, which shows the bright central region, but the galaxy is actually shaped like an elongated, warped stick, stretching out through space until it curls around at one end to form a striking imitation of a celestial hockey stick.

This unusual shape is thought to be due to an interaction between NGC 4656 and a couple of near neighbours, NGC 4631 (otherwise known as The Whale Galaxy) and NGC 4627 (a small elliptical). Galactic interactions can completely reshape a celestial object, shifting and warping its constituent gas, stars, and dust into bizarre and beautiful configurations. The NASA/ESA Hubble Space Telescope has spied a large number of interacting galaxies over the years, from the cosmic rose of Arp 273 to the egg-penguin duo of Arp 142 and the pinwheel swirls of Arp 240. More Hubble images of interacting galaxies can be seen here.