Tuesday, October 31, 2017

NuSTAR Probes Black Hole Jet Mystery

This artist's concept shows a black hole with an accretion disk -- a flat structure of material orbiting the black hole - and a jet of hot gas, called plasma. Credit: NASA/JPL-Caltech.  › Larger view


Black holes are famous for being ravenous eaters, but they do not eat everything that falls toward them. A small portion of material gets shot back out in powerful jets of hot gas, called plasma, that can wreak havoc on their surroundings. Along the way, this plasma somehow gets energized enough to strongly radiate light, forming two bright columns along the black hole's axis of rotation. Scientists have long debated where and how this happens in the jet.

Astronomers have new clues to this mystery. Using NASA's NuSTAR space telescope and a fast camera called ULTRACAM on the William Herschel Observatory in La Palma, Spain, scientists have been able to measure the distance that particles in jets travel before they "turn on" and become bright sources of light. This distance is called the "acceleration zone." The study is published in the journal Nature Astronomy.

Scientists looked at two systems in the Milky Way called "X-ray binaries," each consisting of a black hole feeding off of a normal star. They studied these systems at different points during periods of outburst -- which is when the accretion disk -- a flat structure of material orbiting the black hole -- brightens because of material falling in.

One system, called V404 Cygni, had reached nearly peak brightness when scientists observed it in June 2015. At that time, it experienced the brightest outburst from an X-ray binary seen in the 21st century. The other, called GX 339-4,was less than 1 percent of its maximum expected brightness when it was observed. The star and black hole of GX 339-4 are much closer together than in the V404 Cygni system.

Despite their differences, the systems showed similar time delays - about one-tenth of a second -- between when NuSTAR first detected X-ray light and ULTRACAM detected flares in visible light slightly later. That delay is less than the blink of an eye, but significant for the physics of black hole jets.

"One possibility is that the physics of the jet is not determined by the size of the disc, but instead by the speed, temperature and other properties of particles at the jet's base," said Poshak Gandhi, lead author of the study and astronomer at the University of Southampton, United Kingdom.

The best theory scientists have to explain these results is that the X-ray light originates from material very close to the black hole. Strong magnetic fields propel some of this material to high speeds along the jet. This results in particles colliding near light-speed, energizing the plasma until it begins to emit the stream of optical radiation caught by ULTRACAM.

Where in the jet does this occur? The measured delay between optical and X-ray light explains this. By multiplying this amount of time by the speed of the particles, which is nearly the speed of light, scientists determine the maximum distance traveled.

This expanse of about 19,000 miles (30,000 kilometers) represents the inner acceleration zone in the jet, where plasma feels the strongest acceleration and "turns on" by emitting light. That's just under three times the diameter of Earth, but tiny in cosmic terms, especially considering the black hole in V404 Cygni weighs as much as 3 million Earths put together.

"Astronomers hope to refine models for jet powering mechanisms using the results of this study," said Daniel Stern, study co-author and astronomer based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Making these measurements wasn't easy. X-ray telescopes in space and optical telescopes on the ground have to look at the X-ray binaries at exactly the same time during outbursts for scientists to calculate the tiny delay between the telescopes' detections. Such coordination requires complex planning between the observatory teams. In fact, coordination between NuSTAR and ULTRACAM was only possible for about an hour during the 2015 outburst, but that was enough to calculate the groundbreaking results about the acceleration zone.

The results also appear to connect with scientists' understanding of supermassive black holes, much bigger than the ones in this study. In one supermassive system called BL Lacertae, weighing 200 million times the mass of our Sun, scientists have inferred time delays millions of times greater than what this study found. That means the size of the acceleration area of the jets is likely related to the mass of the black hole.

"We are excited because it looks as though we have found a characteristic yardstick related to the inner workings of jets, not only in stellar-mass black holes like V404 Cygni, but also in monster supermassive ones," Gandhi said.

The next steps are to confirm this measured delay in observations of other X-ray binaries, and to develop a theory that can tie together jets in black holes of all sizes.

"Global ground and space telescopes working together were key to this discovery. But this is only a peek, and much remains to be learned. The future is really bright for understanding the extreme physics of black holes," said Fiona Harrison, principal investigator of NuSTAR and professor of astronomy at Caltech in Pasadena.

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR's mission operations center is at UC Berkeley, and the official data archive is at NASA's High Energy Astrophysics Science Archive Research Center. ASI provides the mission's ground station and a mirror archive. Caltech manages JPL for NASA.


For more information on NuSTAR, visit: https://www.nasa.gov/nustar - http://www.nustar.caltech.edu/


News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
Elizabeth.landau@jpl.nasa.gov



Monday, October 30, 2017

BRITE space mission reveals the origins of fundamental structures in the wind of the supergiant star zeta Puppis

Artist’s impression of the hot massive supergiant Zeta Puppis. The rotation period of the star indicated by the new BRITE observations is 1.78 d, and its spin axis is inclined by (24 ± 9)° with respect to the line of sight. [Image credits: Tahina Ramiaramanantsoa] Hi-res image

Manifestations of bright spots at the surface of Zeta Puppis and corotating interaction regions (CIRs) in its wind. Bottom panels: Surface light variations of the star as observed by BRITE during one part of the observing campaign (Left), along with the surface map reconstructed from the light curve inversion algorithm (Right), revealing the locations of the dominant bright spots present during that part of the observing run. Top panels: Variations observed in the ionized Helium wind emission line (Left) compared to modelled line profile variations (Right) due to two arms of CIRs in the stellar wind driven by the two surface spots from the surface maps

Random variations at the surface of Zeta Puppis and clumps in its wind. Left panel: The random component of the surface light variations of star observed by BRITE during one night in February 2015 (Red = observations from the BRITE nanosats equipped with a red filter; Blue = observations from the BRITE nanosats equipped with a blue filter; Green = integrated residual intensity in the wind emission line). Main panel: The variations of the wind emission line due to the presence of wind clumps during that night. Right panel: Strong correlation between the amplitudes of the random surface variations and the clump-induced wind variations of Zeta Puppis.



ICRAR astronomer Paul Luckas has collaborated with a Canadian-led team of astronomers who have discovered observational evidence for how features at the surface of the massive southern supergiant star zeta Puppis induce the formation of fundamental structures in its wind.

We are the children of stars. But it is more precise to say that we are the children of massive stars. Indeed, in contrast to cool low-mass stars like the Sun, hot massive stars are scarce, possess extremely strong winds, and catastrophically end their lives as supernovae that stir up and enrich the interstellar medium with chemical elements involved in the creation of new stars and even planets like Earth. Thus, the research team’s breakthrough results on the hot massive supergiant star zeta Puppis are a significant step towards a better understanding of the true nature of hot massive stars which play a crucial role in the evolution of the Universe.

The research team used the network of nanosatellites of the BRIght Target Explorer (BRITE) space mission to monitor the visible brightness changes coming from the surface of zeta Puppis over about six months, and simultaneously monitored the behavior of the wind of the star from several ground-based professional and amateur observatories.

The observations revealed a 1.78-day periodicity both at the surface and in the wind of zeta Puppis. The behaviour of this periodic signal turns out to reflect the spinning of the star through the presence of slowly evolving bright spots tied to its surface, which are driving large-scale spiral-like structures dubbed corotating interaction regions (CIRs) in its wind. “Once we found that the variations in the brightness of zeta Puppis arise because bright spots on its surface are carried into and out of our view by the star’s rotation every 1.78 days, we employed an algorithm that used those brightness variations to make maps showing where the bright spots are on the star’s surface and how they change over time. Then by studying the light emitted at a specific wavelength by ionized helium from the star’s wind, we clearly saw some “S” patterns that are caused by arms of CIRs induced in the wind by the bright surface spots!”, explains Tahina Ramiaramanantsoa, PhD student at the Université de Montréal and member of the Centre de Recherche en Astrophysique du Québec (CRAQ), who led the investigation and the paper reporting on the results recently published in the Monthly Notices of the Royal Astronomical Society (MNRAS).

In addition to the 1.78-day periodicity, the research team also detected random changes on timescales of hours at the surface of zeta Puppis, strongly correlated with the behavior of small regions of higher density in the wind known as “clumps” that travel outward from the star. “These results are very exciting because we also find evidence, for the first time, of a direct link between surface variations and wind clumping, both random in nature”, comments investigating team member Anthony Moffat, professor emeritus at Université de Montréal, and Principal Investigator for the Canadian contribution to the BRITE mission.

The southern naked-eye bright star zeta Puppis is an evolved massive star currently at the stage of supergiant. It is often considered as the archetype of hot massive stars with strong stellar winds. Indeed, about sixty times more massive and seven times hotter than the Sun, zeta Puppis has a stellar wind about a billion times stronger than that of the Sun. In that sense, the solar wind that drives aurorae and shapes the tails of comets appears like a light breeze when compared to the gale-force wind from zeta Puppis.

Also, most massive stars occur in binary or multiple systems. However, zeta Puppis is particular because not only is it amongst the few massive stars known to be single, but also it is moving through space at a particularly fast velocity of about 60 km/s. Imagine an object about sixty times the mass of the Sun travelling about sixty times faster than a speeding bullet! “The existing theoretical scenarios that explain this high peculiar space velocity for zeta Puppis involve past interactions within a binary or a multiple system, and predicted a relatively short rotation period for the star. That prediction is now supported by these new observational results!”, exclaims investigating team member Dany Vanbeveren, professor at Vrije Universiteit Brussel.

The physical origins of the bright surface spots and the random brightness variations discovered in zeta Puppis remain unknown at this point, and will be the subject of further investigations, probably requiring other types of observations. Actually, an existing theory is that, within the huge radiative envelopes of massive stars, there is probably a thin convective layer close to the stellar surface. This sub-surface convection zone could be the site for the generation of small- scale magnetic fields, which could occasionally breach through the stellar surface and produce magnetic bright spots. The formation of clumps at the very base of the wind could also be induced by waves randomly excited from that sub-surface convection layer or even from the deep convective core.

After several decades of puzzling over the potential link between the surface variability of very hot massive stars and their wind variability, these results are a significant breakthrough in massive star research, essentially owing to the BRITE nanosats and the large contribution by both professional and amateur astronomers around the world. “It is really exciting to know that small dedicated telescopes are able to play a significant role at the scientific front!”, says investigating team member Paul Luckas from the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia. Paul contributed a record breaking 257 high resolution spectra from his backyard observatory in Shenton Park over a 7 month period as part of a southern pro-am spectroscopy initiative.

Stay tuned!



Publication Detais 

BRITE-Constellation High-Precision Time-Dependent Photometry of the Early-O-Type Supergiant Z Puppies Unveils the Photospheric Drivers of its Small- and Large-Scale Wind Structures.’, to appear in Monthly Notices of the Royal Astronomical Society (MNRAS).
Click here for the research paper



More Information 

ICRAR 

The International Centre for Radio Astronomy Research, or ICRAR, is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

About the BRITE mission


BRITE (BRIght Target Explorer) Constellation is a network of five nanosatellites to investigate stellar structure and evolution of the brightest stars in the sky and their interaction with the local environment. Read more here and here



Contact Information


Tahina RAMIARAMANTSOA (Université de Montréal and Centre de Recherche en Astrophysique du Québec (CRAQ))
Email: tahina@astro.umontreal.ca


Sunday, October 29, 2017

Hubble Observes Exoplanet that Snows Sunscreen

Kepler-13Ab Artist's Concept
Artwork: NASA, ESA, and G. Bacon (STScI)
Science: NASA, ESA, and T. Beatty (Pennsylvania State University)

This is an artist’s impression of the gas giant planet Kepler-13Ab as compared in size to several of our solar system planets. The behemoth exoplanet is six times more massive than Jupiter. Kepler-13Ab is also one of the hottest known planets, with a dayside temperature of nearly 5,000 degrees Fahrenheit. It orbits very close to the star Kepler-13A, which lies at a distance of 1,730 light-years from Earth.  Credits: NASA, ESA, and A. Feild (STScI)



NASA's Hubble Space Telescope has found a blistering hot planet outside our solar system where it "snows" sunscreen. The problem is the sunscreen (titanium oxide) precipitation only happens on the planet's permanent nighttime side. Any possible visitors to the exoplanet, called Kepler-13Ab, would need to bottle up some of that sunscreen, because they won't find it on the sizzling hot, daytime side, which always faces its host star.

Hubble astronomers suggest that powerful winds carry the titanium oxide gas around to the colder nighttime side, where it condenses into crystalline flakes, forms clouds, and precipitates as snow. Kepler-13Ab's strong surface gravity — six times greater than Jupiter's — pulls the titanium oxide snow out of the upper atmosphere and traps it in the lower atmosphere.

Astronomers using Hubble didn't look for titanium oxide specifically. Instead, they observed that the giant planet's atmosphere is cooler at higher altitudes, which is contrary to what was expected. This finding led the researchers to conclude that a light-absorbing gaseous form of titanium oxide, commonly found in this class of star-hugging, gas giant planet known as a "hot Jupiter," has been removed from the dayside's atmosphere. 

The Hubble observations represent the first time astronomers have detected this precipitation process, called a "cold trap," on an exoplanet.

Without the titanium oxide gas to absorb incoming starlight on the daytime side, the atmospheric temperature grows colder with increasing altitude. Normally, titanium oxide in the atmospheres of hot Jupiters absorbs light and reradiates it as heat, making the atmosphere grow warmer at higher altitudes.

These kinds of observations provide insight into the complexity of weather and atmospheric composition on exoplanets, and may someday be applicable to analyzing Earth-size planets for habitability.

"In many ways, the atmospheric studies we're doing on hot Jupiters now are testbeds for how we're going to do atmospheric studies on terrestrial, Earth-like planets," said lead researcher Thomas Beatty of Pennsylvania State University in University Park. "Hot Jupiters provide us with the best views of what climates on other worlds are like. Understanding the atmospheres on these planets and how they work, which is not understood in detail, will help us when we study these smaller planets that are harder to see and have more complicated features in their atmospheres."

Beatty's team selected Kepler-13Ab because it is one of the hottest of the known exoplanets, with a dayside temperature of nearly 5,000 degrees Fahrenheit. Past observations of other hot Jupiters have revealed that the upper atmospheres increase in temperature. Even at their much colder temperatures, most of our solar system's gas giants also exhibit this phenomenon. 

Kepler-13Ab is so close to its parent star that it is tidally locked. One side of the planet always faces the star; the other side is in permanent darkness. (Similarly, our moon is tidally locked to Earth; only one hemisphere is permanently visible from Earth.)

The observations confirm a theory from several years ago that this kind of precipitation could occur on massive, hot planets with powerful gravity.

"Presumably, this precipitation process is happening on most of the observed hot Jupiters, but those gas giants all have lower surface gravities than Kepler-13Ab," Beatty explained. "The titanium oxide snow doesn't fall far enough in those atmospheres, and then it gets swept back to the hotter dayside, revaporizes, and returns to a gaseous state."

The researchers used Hubble's Wide Field Camera 3 to conduct spectroscopic observations of the exoplanet's atmosphere in near-infrared light. Hubble made the observations as the distant world traveled behind its star, an event called a secondary eclipse. This type of eclipse yields information on the temperature of the constituents in the atmosphere of the exoplanet's dayside. 

"These observations of Kepler-13Ab are telling us how condensates and clouds form in the atmospheres of very hot Jupiters, and how gravity will affect the composition of an atmosphere," Beatty explained. "When looking at these planets, you need to know not only how hot they are but what their gravity is like."

The Kepler-13 system resides 1,730 light-years from Earth.

The team's results appeared in The Astronomical Journal



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Contact

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514

dweaver@stsci.edu / villard@stsci.edu

Thomas Beatty
Pennsylvania State University, University Park
814-863-7346

tbeatty@psu.edu


Source: HubbleSite/News

Saturday, October 28, 2017

Hubble discovers “wobbling galaxies”

Abell S1063, the final frontier

Hubble image of galaxy cluster MACS J1206 

Lensing cluster Abell 383

Brightest galaxy in Abell 2261

Galaxy cluster MACS J1720+35

 
Wide-field image of Abell S1063 (ground-based image)

Wide field view of MACS 1206 (ground-based image)



Videos

Pan across the galaxy cluster Abell S1063
Pan across the galaxy cluster Abell S1063

Pan across Abell 383
Pan across Abell 383

Pan across MACS 1206
Pan across MACS 1206



Observations may hint at nature of dark matter


Using the NASA/ESA Hubble Space Telescope, astronomers have discovered that the brightest galaxies within galaxy clusters “wobble” relative to the cluster’s centre of mass. This unexpected result is inconsistent with predictions made by the current standard model of dark matter. With further analysis it may provide insights into the nature of dark matter, perhaps even indicating that new physics is at work.

Dark matter constitutes just over 25 percent of all matter in the Universe but cannot be directly observed, making it one of the biggest mysteries in modern astronomy. Invisible halos of elusive dark matter enclose galaxies and galaxy clusters alike. The latter are massive groupings of up to a thousand galaxies immersed in hot intergalactic gas. Such clusters have very dense cores, each containing a massive galaxy called the “brightest cluster galaxy” (BCG).

The standard model of dark matter (cold dark matter model) predicts that once a galaxy cluster has returned to a “relaxed” state after experiencing the turbulence of a merging event, the BCG does not move from the cluster’s centre. It is held in place by the enormous gravitational influence of dark matter.
But now, a team of Swiss, French, and British astronomers have analysed ten galaxy clusters observed with the NASA/ESA Hubble Space Telescope, and found that their BCGs are not fixed at the centre as expected [1].

The Hubble data indicate that they are “wobbling” around the centre of mass of each cluster long after the galaxy cluster has returned to a relaxed state following a merger. In other words, the centre of the visible parts of each galaxy cluster and the centre of the total mass of the cluster — including its dark matter halo — are offset, by as much as 40 000 light-years.

“We found that the BCGs wobble around centre of the halos,” explains David Harvey, astronomer at EPFL, Switzerland, and lead author of the paper. “This indicates that, rather than a dense region in the centre of the galaxy cluster, as predicted by the cold dark matter model, there is a much shallower central density. This is a striking signal of exotic forms of dark matter right at the heart of galaxy clusters.”

The wobbling of the BCGs could only be analysed as the galaxy clusters studied also act as gravitational lenses. They are so massive that they warp spacetime enough to distort light from more distant objects behind them. This effect, called strong gravitational lensing, can be used to make a map of the dark matter associated with the cluster, enabling astronomers to work out the exact position of the centre of mass and then measure the offset of the BCG from this centre.

If this “wobbling” is not an unknown astrophysical phenomenon and in fact the result of the behaviour of dark matter, then it is inconsistent with the standard model of dark matter and can only be explained if dark matter particles can interact with each other — a strong contradiction to the current understanding of dark matter. This may indicate that new fundamental physics is required to solve the mystery of dark matter.

Co-author Frederic Courbin, also at EPFL, concludes: “We’re looking forward to larger surveys — such as the Euclid survey — that will extend our dataset. Then we can determine whether the wobbling of BGCs is the result of a novel astrophysical phenomenon or new fundamental physics. Both of which would be exciting!”



Notes

[1] The study was performed using archive data from Hubble. The observations were originally made for the CLASH and LoCuSS surveys.



More Information

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

This research was presented in a paper entitled “A detection of wobbling Brightest Cluster Galaxies within massive galaxy clusters” by Harvey et al., which appeared in the Monthly Notices of the Royal Astronomical Society.

The international team of astronomers in this study consists of David Harvey (Laboratoire d’Astrophysique EPFL, Switzerland), F. Courbin (Laboratoire d’Astrophysique EPFL, Switzerland), J.P. Kneib (Laboratoire d’Astrophysique EPFL, Switzerland; CNRS, France), and Ian G. McCarthy (Liverpool John Moores University, UK).

Image credit: NASA, ESA, J. Lotz (STScI), M. Postman (STScI), J. Richard (CRAL) and J.-P. Kneib (LAM), T. Lauer (NOAO), S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State), C. McCully (Rutgers University) and the CLASH Team



Links



Contacts

David Harvey
Laboratoire d’Astrophysique EPFL
Versoix, Switzerland
Tel: +41 22 37 92277

Frederic Courbin
Laboratoire d’Astrophysique EPFL
Versoix, Switzerland
Tel: +41 22 37 92418

Jean-Paul Kneib
Laboratoire d’Astrophysique - EPFL
Versoix, Switzerland
Tel: +41 79 733 21 11

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


Optical/Infrared Telescopes Follow Gravitational Waves to Treasure

Figure 1: Three-color false-color composite images showing the time evolution of the optical and near-infrared counterpart of GW170817 made using data from the Subaru Telescope (z-band, blue) and IRSF (H-band, green; Ks-band, red). Figure without the labels is linked here. Credit: NAOJ/Nagoya University

Figure 2: Artist's impression of the GW170817 kilonova
Credit: NAOJ

Astronomers have tracked down the source of a gravitational wave and discovered the first observed kilonova: a nuclear furnace 100 million times brighter than the Sun producing thousands of times the entire mass of the Earth in heavy elements such as precious metals.

On August 17, 2017 the LIGO-Virgo collaboration alerted more than 90 astronomy teams around the world, that they had detected a signal (GW170817) consistent with the inspiral and merger of two neutron stars. Dr. Raffaele Flaminio (NAOJ and CNRS/LAPP), a scientist from the Virgo and KAGRA collaborations, explains that "Thanks to the combination of the data from the LIGO detectors in the US and the Virgo detector in Europe, this was the best ever localized gravitational wave source."

J-GEM (Japanese collaboration of Gravitational wave Electro-Magnetic follow-up) is a research project to search for optical counterparts of gravitational wave sources because optical observations give us different information than gravitational wave observations. Indeed multi-messenger astronomy, observing the same phenomenon with both gravitational waves and normal light, is needed to paint the full picture of the phenomenon. 

Neutron star mergers are expected to have strong optical and infrared light emissions, so J-GEM sprang in to action. Using a network of telescopes around the world, including the Subaru Telescope in Hawai'i and the 1.4-m IRSF telescope in South Africa (run by Nagoya University and Kagoshima University), they observed the source located 130 million light-years away in the constellation Hydra, trying to discern its true nature. As they watched the object change day by day, they realized that they were observing the first ever confirmed kilonova. 

Astronomers have long searched for sites in the Universe where the heavy elements were produced by rapid neutron capture (r-process) reactions. One possible candidate was kilonova explosions which are predicted to produce 10,000 times the mass of the Earth in rare earth elements and precious metals.

The time evolution of the color and brightness of the object at the origin of the gravitational waves were too rapid to be a supernova, but matched the simulations of a kilonova made by the ATERUI supercomputer at the National Astronomical Observatory of Japan.

"We were so excited to see the rapid brightness evolution revealed day by day through observations at facilities operated by Japanese institutes distributed all over the world." said Dr. Yousuke Utsumi (Hiroshima University), a scientist in the J-GEM collaboration.

Movie: The optical and near-infrared counterpart of GW170817 capture by HSC mounted on the Subaru Telescope. (Credit: NAOJ)

Two papers on this research will be published in Publications of the Astronomical Society of Japan (PASJ) on October 16, 2017 (Utsumi et al., "J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817", and Tanaka et al., "Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817"). Another paper is also submitted to PASJ (Tominaga et al., "Subaru Hyper Suprime-Cam survey for an optical counterpart of GW170817").



Links


Friday, October 27, 2017

Cosmic archaeology

Credit: ESA/Hubble & NASA


This NASA/ESA Hubble Space Telescope image is chock-full of galaxies — each glowing speck is a different galaxy, bar the bright flash in the middle of the image which is actually a star lying within our own galaxy that just happened to be in the way. At the centre of the image lies something especially interesting, the centre of the massive galaxy cluster called WHL J24.3324-8.477, including the brightest galaxy of the cluster.

The Universe contains structures on various scales — planets collect around stars, stars collect into galaxies, galaxies collect into groups, and galaxy groups collect into clusters. Galaxy clusters contain hundreds to thousands of galaxies bound together by gravity. Dark matter and dark energy play key roles in the formation and evolution of these clusters, so studying massive galaxy clusters can help scientists to unravel the mysteries of these elusive phenomena.

This infrared image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study. Such research will tell us more about our cosmic origins.



Thursday, October 26, 2017

Astronomers Detect Comets Outside our Solar System

An artist's conception of a view from within the Exocomet system KIC 3542116
Credit: Danielle Futselaar


AUSTIN — Astronomers from The University of Texas at Austin, working with scientists from other institutions and amateur astronomers, have spotted the dusty tails of six exocomets — comets outside our solar system — orbiting a faint star 800 light years from Earth.

These cosmic balls of ice and dust, which were about the size of Halley’s comet and traveled about 100,000 miles per hour before they ultimately vaporized, are some of the smallest objects yet found outside our own solar system.

The discovery by Andrew Vanderburg, NASA Sagan Fellow at UT Austin, and the team marks the first time that an object as small as a comet has been inferred using transit photometry, a technique by which astronomers observe a star’s light for telltale dips in intensity. Such dips signal potential transits, or crossings of planets or other objects in front of a star, which momentarily block a small fraction of its light.

“It’s just thrilling to find these comets,” Vanderburg says. “No one has ever seen anything quite like these transits before. These are some of the first glimpses at the population of comets outside our own solar system.”

The researchers were able to pick out the comet’s tail, or trail of gas and dust, which blocked about one-tenth of 1 percent of the star’s light as the comet streaked by.

“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris,” says Saul Rappaport, professor emeritus of physics in MIT’s Kavli Institute for Astrophysics and Space Research. “It’s pretty impressive to be able to see something so small, so far away.”

The team have published their results this week in the Monthly Notices of the Royal Astronomical Society. Rappaport is the paper’s lead author. Other authors include Vanderburg, Adam Kraus, and Aaron Rizzuto of The University of Texas at Austin; astronomers from NASA Ames Research Center and Northeastern University; and amateur astronomers including Thomas Jacobs of Bellevue, Washington.

“Where few have traveled”

The detection was made using data from NASA’s Kepler Space Telescope, a stellar observatory that was launched into space in 2009. For four years, the spacecraft monitored about 200,000 stars for dips in starlight caused by transiting exoplanets.

To date, the mission has identified and confirmed more than 2,400 exoplanets, mostly orbiting  anonymous stars in the constellation Cygnus, with the help of  automated algorithms that quickly sift through Kepler’s data, looking for characteristic dips in starlight.

The smallest exoplanets detected thus far measure about one-third the size of the Earth. Comets, in comparison, span just several football fields, or a small city at their largest, making them incredibly difficult to spot.

However, on March 18, Jacobs, an amateur astronomer who has made it his hobby to comb through Kepler’s data, was able to pick out several curious light patterns amid the noise.

Jacobs, who works as an employment consultant for people with intellectual disabilities by day, is a member of the Planet Hunters — a citizen scientist project first established by Yale University to enlist amateur astronomers in the search for exoplanets. Members were given access to Kepler’s data (which are now public) in hopes that they might spot something of interest that a computer might miss.

In January, Jacobs set out to scan the entire four years of Kepler’s data taken during the main mission, comprising over 200,000 stars, each with individual light curves, or graphs of light intensity tracked over time. Jacobs spent five months sifting by eye through the data, often before and after his day job, and through the weekends.

“Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance,” Jacobs says. “For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.”

“Something we’ve seen before”

Jacobs’ goal was to look for anything out of the ordinary that computer algorithms may have passed over. In particular, he was searching for single transits — dips in starlight that happen only once, meaning they are not periodic like planets orbiting a star multiple times.

In his search, he spotted three such single transits around KIC 3542116, a faint star located 800 light years from Earth (the other three transits were found later by the team). He flagged the events and alerted Rappaport and Vanderburg, with whom he had collaborated in the past to interpret his findings.

“We sat on this for a month, because we didn’t know what it was — planet transits don’t look like this,” Rappaport recalls. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before.’”

In a typical planetary transit, the resulting light curve resembles a “U,” with a sharp dip, then an equally sharp rise, as a result of a planet first blocking a little, then a lot, then a little of the light as it moves across the star. However, the light curves that Jacobs identified appeared asymmetric, with a sharp dip, followed by a more gradual rise.

Rappaport realized that the asymmetry in the light curves resembled disintegrating planets, with long trails of debris that would continue to block a bit of light as the planet moves away from the star. However, such disintegrating planets orbit their star, transiting repeatedly. In contrast, Jacobs had observed no such periodic pattern in the transits he identified.

“We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end,” Rappaport says.

In other words, instead of orbiting around and around the star, the objects must have transited, then ultimately flown too close to the star, and vaporized.

“The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet,” Rappaport says.

The researchers calculated that each comet blocked about one-tenth of 1 percent of the star’s light. To do this for several months before disappearing, the comet likely disintegrated entirely, creating a dust trail thick enough to block out that amount of starlight.

Vanderburg says the fact that these six exocomets appear to have transited very close to their star in the past four years raises some intriguing questions, the answers to which could reveal some truths about our own solar system.

“Why are there so many comets in the inner parts of these solar systems?” Vanderburg says. “Is this an extreme bombardment era in these systems? That was a really important part of our own solar system formation and may have brought water to Earth. Maybe studying exocomets and figuring out why they are found around this type of star … could give us some insight into how bombardment happens in other solar systems.”

The researchers say that in the future, the MIT-led mission TESS (Transiting Exoplanet Survey Satellite) will continue the type of research done by Kepler.

Apart from contributing to the fields of astrophysics and astronomy, Rappaport says, the new detection speaks to the perseverance and discernment of citizen scientists.

“I could name 10 types of things these people have found in the Kepler data that algorithms could not find, because of the pattern-recognition capability in the human eye,” Rappaport says. “You could now write a computer algorithm to find this kind of comet shape. But they were missed in earlier searches. They were deep enough but didn’t have the right shape that was programmed into algorithms. I think it’s fair to say this would never have been found by any algorithm.”

This research made use of data collected by the Kepler mission, funded by the NASA Science Mission directorate. This work was performed in part under contract with the California Institute of Technology/Jet Propulsion Laboratory funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Original release text courtesy of MIT News.





Media Contact:

Rebecca Johnson
Communications Mgr. McDonald Observatory
The University of Texas at Austin
512-475-6763

Science Contact: 

Dr. Andrew Vanderburg, NASA Sagan Fellow 
The University of Texas at Austin
Department of Astronomy
512-471-6493


Wednesday, October 25, 2017

Revealing Galactic Secrets

Revealing the galactic secrets of NGC 1316

The galaxy pair NGC 1316 and 1317 in the constellation of Fornax

PR Image eso1734c
Wide-field view of the sky around the galaxies NGC 1316 and 1317

Annotated view of the sky surrounding NGC 1316



Videos
 
ESOcast 134 Light: Revealing Galactic Secrets (4K UHD)
ESOcast 134 Light: Revealing Galactic Secrets (4K UHD)

Zooming in on the galaxy NGC 1316
Zooming in on the galaxy NGC 1316

Panning across the galaxy NGC 1316
Panning across the galaxy NGC 1316



Countless galaxies vie for attention in this monster image of the Fornax Galaxy Cluster, some appearing only as pinpricks of light while others dominate the foreground. One of these is the lenticular galaxy NGC 1316. The turbulent past of this much-studied galaxy has left it with a delicate structure of loops, arcs and rings that astronomers have now imaged in greater detail than ever before with the VLT Survey Telescope. This astonishingly deep image also reveals a myriad of dim objects along with faint intracluster light.

Captured using the exceptional sky-surveying abilities of the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile, this deep view reveals the secrets of the luminous members of the Fornax Cluster, one of the richest and closest galaxy clusters to the Milky Way. This 2.3-gigapixel image is one of the largest images ever released by ESO.

Perhaps the most fascinating member of the cluster is NGC 1316, a galaxy that has experienced a dynamic history, being formed by the merger of multiple smaller galaxies. The gravitational distortions of the galaxy’s adventurous past have left their mark on its lenticular structure [1]. Large ripples, loops and arcs embedded in the starry outer envelope were first observed in the 1970s, and they remain an active field of study for contemporary astronomers, who use the latest telescope technology to observe the finer details of NGC 1316’s unusual structure through a combination of imaging and modelling.

The mergers that formed NGC 1316 led to an influx of gas, which fuels an exotic astrophysical object at its centre: a supermassive black hole with a mass roughly 150 million times that of the Sun. As it accretes mass from its surroundings, this cosmic monster produces immensely powerful jets of high-energy particles , that in turn give rise to the characteristic lobes of emission seen at radio wavelengths, making NGC 1316 the fourth-brightest radio source in the sky [2].

NGC 1316 has also been host to four recorded type Ia supernovae, which are vitally important astrophysical events for astronomers. Since type Ia supernovae have a very clearly defined brightness [3], they can be used to measure the distance to the host galaxy; in this case, 60 million light-years. These “standard candles” are much sought-after by astronomers, as they are an excellent tool to reliably measure the distance to remote objects. In fact, they played a key role in the groundbreaking discovery that our Universe is expanding at an accelerating rate.

This image was taken by the VST at ESO’s Paranal Observatory as part of the Fornax Deep Survey, a project to provide a deep, multi-imaging survey of the Fornax Cluster. The team, led by Enrichetta Iodice (INAF – Osservatorio di Capodimonte, Naples, Italy), have previously observed this area with the VST and revealed a faint bridge of light between NGC 1399 and the smaller galaxy NGC 1387 (eso1612) . The VST was specifically designed to conduct large-scale surveys of the sky. With its huge corrected field of view and specially designed 256-megapixel camera, OmegaCAM, the VST can produce deep images of large areas of sky quickly, leaving the much larger telescopes — like ESO’s Very Large Telescope (VLT) — to explore the details of individual objects.



Notes


[1] Lenticular or “lens-shaped” galaxies are an intermediate form between diffuse elliptical galaxies and the better-known spiral galaxies such as the Milky Way.


[2] As this radio source is the brightest in the constellation of Fornax it is also known as Fornax A.


[3] Type Ia Supernovae occur when an accreting white dwarf in a binary star system slowly gains mass from its companion until it reaches a limit that triggers the nuclear fusion of carbon. In a brief period of time, a chain reaction is initiated that eventually ends in a huge release of energy: a supernova explosion. The supernova always occurs at a specific mass, known as the Chandrasekhar limit, and produces an almost identical explosion each time. The similarity of type Ia supernovae allow astronomers to use the cataclysmic events to measure distance.



More Information


This research was presented in the paper “The Fornax Deep Survey with VST. II. Fornax A: A Two-phase Assembly Caught in the Act”, by E. Iodice et al., in the Astrophysical Journal.

The team is composed of E. Iodice (INAF – Astronomical Observatory of Capodimonte, Italy), M. Spavone (Astronomical Observatory of Capodimonte, Italy), M. Capaccioli (University of Naples, Italy), R. F. Peletier (Kapteyn Astronomical Institute, University of Groningen, The Netherlands), T. Richtler (Universidad de Concepción, Chile), M. Hilker (ESO, Garching, Germany), S. Mieske (ESO, Chile), L. Limatola (INAF – Astronomical Observatory of Capodimonte, Italy), A. Grado (INAF – Astronomical Observatory of Capodimonte, Italy), N.R. Napolitano (INAF – Astronomical Observatory of Capodimonte, Italy), M. Cantiello (INAF – Astronomical Observatory of Teramo, Italy), R. D’Abrusco (Smithsonian Astrophysical Observatory/Chandra X-ray Center, US), M. Paolillo (University of Naples, Italy), A. Venhola (University of Oulu, Finland), T. Lisker (Zentrum für Astronomie der Universität Heidelberg, Germany), G. Van de Ven (Max Planck Institute for Astronomy, Germany), J. Falcon-Barroso (Instituto de Astrofísica de Canarias, Spain) and P. Schipani (Astronomical Observatory of Capodimonte, Italy).

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 and by Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.



Links



Contacts

Enrichetta Iodice
INAF – Osservatorio Astronomico di Capodimonte
Napoli, Italy
Tel: +39 0815575546
Email: iodice@na.astro.it

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

Friday, October 20, 2017

A glimpse of the future

Credit: ESA/Hubble & NASA



This image, captured by the NASA/ESA Hubble Space Telescope, shows what happens when two galaxies become one. The twisted cosmic knot seen here is NGC 2623 — or Arp 243 — and is located about 250 million light-years away in the constellation of Cancer (The Crab).

NGC 2623 gained its unusual and distinctive shape as the result of a major collision and subsequent merger between two separate galaxies. This violent encounter caused clouds of gas within the two galaxies to become compressed and stirred up, in turn triggering a sharp spike of star formation. This active star formation is marked by speckled patches of bright blue; these can be seen clustered both in the centre and along the trails of dust and gas forming NGC 2623’s sweeping curves (known as tidal tails). These tails extend for roughly 50 000 light-years from end to end. Many young, hot, newborn stars form in bright stellar clusters — at least 170 such clusters are known to exist within NGC 2623.

NGC 2623 is in a late stage of merging. It is thought that the Milky Way will eventually resemble NGC 2623 when it collides with our neighbouring galaxy, the Andromeda Galaxy, in four billion years time.

In contrast to the image of NGC 2623 released in 2009 (heic0912), this new version contains data from recent narrow-band and infrared observations that make more features of the galaxy visible.


 Source: ESA/Hubble/Potw