Shedding light on the cosmic web

Snapshot of a supercomuter simulation showing part of the cosmic web, 11.5 billion years ago. The researchers created this and other models of the universe and directly compared them with quasar pair data in order to measure the small-scale ripples in the cosmic web. The cube is 24 million light-years on a side. © J. Oñorbe / MPIA

Schematic representation of the technique used to probe the small-scale structure of the cosmic web using light from a rare quasar pair. The spectra (bottom right) contain information about the hydrogen gas the light has encountered on its journey to Earth, as well as the distance of that gas. © J. Oñorbe / MPIA

Astronomers use the light of twin quasars to measure the structure of the universe

Astronomers believe that matter in intergalactic space is distributed in a vast network of interconnected filamentary structures known as the cosmic web. Nearly all the atoms in the Universe reside in this web, vestigial material left over from the Big Bang. A team led by researchers from the Max Planck Institute for Astronomy in Heidelberg have made the first measurements of small-scale fluctuations in the cosmic web just 2 billion years after the Big Bang. These measurements were enabled by a novel technique using pairs of quasars to probe the cosmic web along adjacent, closely separated lines of sight. They promise to help astronomers reconstruct an early chapter of cosmic history known as the epoch of reionization.

The most barren regions of the Universe are the far-flung corners of intergalactic space. In these vast expanses between the galaxies there are only a few atoms per cubic meter – a diffuse haze of hydrogen gas left over from the Big Bang. Viewed on the largest scales, this diffuse material nevertheless accounts for the majority of atoms in the Universe, and fills the cosmic web, its tangled strands spanning billions of light years.

Now, a team led by astronomers from the Max Planck Institute for Astronomy (MPIA) have made the first measurements of small-scale ripples in this primeval hydrogen gas. Although the regions of cosmic web they studied lie nearly 11 billion light years away, they were able to measure variations in its structure on scales a hundred thousand times smaller, comparable to the size of a single galaxy.

Intergalactic gas is so tenuous that it emits no light of its own. Instead astronomers study it indirectly by observing how it selectively absorbs the light coming from faraway sources known as quasars. Quasars constitute a brief hyperluminous phase of the galactic life-cycle, powered by the infall of matter onto a galaxy's central supermassive black hole.

Quasars act like cosmic lighthouses – bright, distant beacons that allow astronomers to study intergalactic atoms residing between the quasars location and Earth. But because these hyperluminous episodes last only a tiny fraction of a galaxy’s lifetime, quasars are correspondingly rare on the sky, and are typically separated by hundreds of millions of light years from each other.

In order to probe the cosmic web on much smaller length scales, the astronomers exploited a fortuitous cosmic coincidence: They identified exceedingly rare pairs of quasars right next to each other on the sky, and measured subtle differences in the absorption of intergalactic atoms measured along the two sightlines.

Alberto Rorai, a post-doctoral researcher at Cambridge university and the lead author of the study says: “One of the biggest challenges was developing the mathematical and statistical tools to quantify the tiny differences we measure in this new kind of data.”

Rorai developed these tools as part of the research for his doctoral degree at the MPIA, and applied his tools to spectra of quasars obtained with the largest telescopes in the world, including the 10 meter diameter Keck telescopes at the summit of Mauna Kea in Hawaii, as well as ESO's 8 meter diameter Very Large Telescope on Cerro Paranal, and the 6.5 meter diameter Magellan telescope at Las Campanas Observatory, both located in the Chilean Atacama Desert.

The astronomers compared their measurements to supercomputer models that simulate the formation of cosmic structures from the Big Bang to the present. “The input to our simulations are the laws of Physics and the output is an artificial Universe which can be directly compared to astronomical data. I was delighted to see that these new measurements agree with the well-established paradigm for how cosmic structures form,” says Jose Oñorbe, a post-doctoral researcher at the MPIA, who led the supercomputer simulation effort.

On a single laptop, these complex calculations would have required almost a thousand years to complete, but modern supercomputers enabled the researchers to carry them out in just a few weeks.

Joseph Hennawi, who leads the research group at MPIA responsible for the measurement, explains: “One reason why these small-scale fluctuations are so interesting is that they encode information about the temperature of gas in the cosmic web just a few billion years after the Big Bang.” According to the current level of knowledge, the universe had quite a mercurial youth: initially, about 400,000 years after the Big Bang, the universe had cooled down to such an extent that neutral hydrogen could arise. At that point, there were practically no heavenly bodies yet and therefore no light. It was not until few hundred million years later that this 'dark age' ended and a new era began, in which stars and quasars lit up and emitted energetic ultraviolet rays. The latter were so intense that they robbed atoms in the intergalactic space of their electrons - the gas was ionized again.

How and when reionization occurred is one of the biggest open questions in the field of cosmology, and these new measurements provide important clues that will help narrate this chapter of cosmic history.

Source:  Max Planck Institute for Astronomy

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Contact

Dr. Markus Pössel
Max Planck Institute for Astronomy, Heidelberg  
Phone:+49 6221 528-261  
Email:poessel@mpia.de
 
Dr. Joseph F. Hennawi
University of California at Santa Barbara  
Phone:+1 805 893-3503
Email:joe@physics.ucsb.edu

Dr. Jose Oñorbe
Max Planck Institute for Astronomy, Heidelberg  
Phone:+49 6221 528-370
Email:onorbe@mpia.de
 

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Original publication

A. Rorai et al.

Measurement of the Small-Scale Structure of the Intergalactic Medium Using Close Quasar Pairs
Science, 28 April 2017
 

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Related Articles 

 Black hole illuminates cosmic web

January 19, 2014

Cosmologists generally believe that matter in intergalactic space is distributed in a vast network of interconnected filamentary structures of gas known as the cosmic web. The vast majority of atoms in the Universe reside in this web as primordial hydrogen, vestigial matter left over from the Big Bang. Researchers from the University of California at Santa Cruz and the Max Planck Institute for Astronomy have now captured an image of these filamentary structures for the first time. To achieve this, they exploited the intense radiation generated by a supermassive black hole in a quasar.

The spiralling signatures of planet formation

Artist's impression of the spiral structure in the disc around Elias 2-27

Credit: Institute of Astronomy - Amanda Smith & Farzana Meru

 

Simulation image of a protoplanetary disc with a planet that is ten times the mass of Jupiter and is at a distance of 425 astronomical units (i.e. 425 times the distance between the Sun and the Earth).  The interaction between the planet and the disc is causing the large scale spiral structures to form. Credit: Institute of Astronomy -  Farzana Meru

Simulation image of a protoplanetary disc that is so massive that the gravity within the disc causes the spiral structures to form.  The spirals extend out to approximately 300 astronomical units (i.e. 300 times the distance between the Sun and the Earth).  The disc has been inclined to show what a disc would look like if we look at it from a different angle, just like the Elias 2-27 disc. Credit: Institute of Astronomy -  Farzana Meru

A young star recently observed to be surrounded by spiralling gas and dust could be one of the first to show planet formation ‘in action’ via a mechanism once thought to be unlikely.

Astrophysicists at the University of Cambridge have used theoretical models to determine the origins of the striking large-scale spiral features surrounding a nearby star.

Young stars are surrounded by dense discs of gas and dust, and it is within these discs that planets are assembled. Obscured from our view, the precise details of just how planets form remain difficult to determine from the observations alone.

Last year, astronomers used the extremely sensitive Atacama Large Millimetre Array (ALMA) located in Chile to observe the young, one-million year old star Elias 2-27 (Pérez et al. 2016, Science 353, 1519). The observations were the first to directly resolve the disc around the young star, and showed something very surprising — rather than being a smooth disc, the image showed two prominent spiral arms, each extended to a length about ten times the distance between the Sun and Neptune in our own Solar System.

“These beautiful observations of Elias 2-27 immediately sparked much discussion amongst our research team about what could be causing the spiral arms” said Dr Farzana Meru, of the Institute of Astronomy. Meru and her colleagues set about using their theoretical models to investigate what might be happening around Elias 2-27.

However, this was not an easy task. The investigation involved running many computer simulations to solve the complex calculations of how the gas orbits in the disc and is heated by radiation from the central star. “The simulations we performed would take thousands of hours to run on your average laptop computer” said Dr John Ilee, a co-author on the study. “Fortunately, we were able to use a dedicated supercomputer and some clever tricks to speed up the calculations” added Ilee.

Meru and her collaborators showed two possibilities for the origin of the spiral structures.  The first is that the disc around Elias 2-27 may be so massive that its own gravity naturally causes spirals to form – a so-called ‘self gravitating’ disc.  However, Meru and her colleagues also discovered that the spirals could be formed another way – stirred up by a planet in the outer parts of the disc.

“At first, we were a little disappointed to discover that no single mechanism was able to produce the spiral structure” said Ilee, leaving the team with further questions.  “But we then found that the mass of the planet required to drive the spirals was huge – nearly 10 times the mass of Jupiter – and that it was very unlikely that the traditional method of planet formation would have been able to form such an object.”

This ‘traditional’ method of planet formation involves the slow, gradual collision and sticking of tiny dust particles within the disc.  Eventually, enough dust particles stick together to form pebbles, and then boulders, and, as the process continues, eventually planet sized objects form in a gradual process known as ‘core-accretion’.

“Given the young age of Elias 2-27, there simply hasn’t been enough time to create a planet of the required mass by core accretion” said Meru.  “The only way to make such a planet so quickly would be if regions of a self-gravitating disc collapse entirely, creating one or more planets in the process”.

It seems that, whatever the explanation for the spirals, Elias 2-27 could be a smoking gun for planet formation by a process once thought to be rare.

The research paper is published in The Astrophysical Journal Letters.

Source: Kavli Institute for the Physics and Mathematics of the Universe (KICC)

A matter of distance

NGC 7250 and TYC 3203-450-1

Credit: ESA/Hubble & NASA

In space, being outshone is an occupational hazard. This NASA/ESA Hubble Space Telescope image captures a galaxy named NGC 7250. Despite being remarkable in its own right — it has bright bursts of star formation and recorded supernova explosions— it blends into the background somewhat thanks to the gloriously bright star hogging the limelight next to it.

This bright object is a single and little-studied star named TYC 3203-450-1, located in the constellation of Lacerta (The Lizard), much closer than the much more distant galaxy. Only this way a normal star can outshine an entire galaxy, consisting of billions of stars. Astronomers studying distant objects call these stars “foreground stars” and they are often not very happy about them, as their bright light is contaminating the faint light from the more distant and interesting objects they actually want to study.

In this case TYC 3203-450-1 million times closer than NGC 7250 which lies over 45 million light-years away from us. Would the star be the same distance as NGC 7250, it would hardly be visible in this image.

Source: ESA/Hubble/Potw

'Iceball' Planet Discovered Through Microlensing

This artist's concept shows OGLE-2016-BLG-1195Lb, a planet discovered through a technique called microlensing. 

› Full image and caption

 

Scientists have discovered a new planet with the mass of Earth, orbiting its star at the same distance that we orbit our sun. The planet is likely far too cold to be habitable for life as we know it, however, because its star is so faint. But the discovery adds to scientists' understanding of the types of planetary systems that exist beyond our own. 

"This 'iceball' planet is the lowest-mass planet ever found through microlensing," said Yossi Shvartzvald, a NASA postdoctoral fellow based at NASA's Jet Propulsion Laboratory, Pasadena, California, and lead author of a study published in the Astrophysical Journal Letters. 

Microlensing is a technique that facilitates the discovery of distant objects by using background stars as flashlights. When a star crosses precisely in front of a bright star in the background, the gravity of the foreground star focuses the light of the background star, making it appear brighter. A planet orbiting the foreground object may cause an additional blip in the star's brightness. In this case, the blip only lasted a few hours. This technique has found the most distant known exoplanets from Earth, and can detect low-mass planets that are substantially farther from their stars than Earth is from our sun. 

The newly discovered planet, called OGLE-2016-BLG-1195Lb, aids scientists in their quest to figure out the distribution of planets in our galaxy. An open question is whether there is a difference in the frequency of planets in the Milky Way's central bulge compared to its disk, the pancake-like region surrounding the bulge. OGLE-2016-BLG-1195Lb is located in the disk, as are two planets previously detected through microlensing by NASA's Spitzer Space Telescope.

"Although we only have a handful of planetary systems with well-determined distances that are this far outside our solar system, the lack of Spitzer detections in the bulge suggests that planets may be less common toward the center of our galaxy than in the disk," said Geoff Bryden, astronomer at JPL and co-author of the study.

For the new study, researchers were alerted to the initial microlensing event by the ground-based Optical Gravitational Lensing Experiment (OGLE) survey, managed by the University of Warsaw in Poland. Study authors used the Korea Microlensing Telescope Network (KMTNet), operated by the Korea Astronomy and Space Science Institute, and Spitzer, to track the event from Earth and space.

KMTNet consists of three wide-field telescopes: one in Chile, one in Australia, and one in South Africa. When scientists from the Spitzer team received the OGLE alert, they realized the potential for a planetary discovery. The microlensing event alert was only a couple of hours before Spitzer's targets for the week were to be finalized, but it made the cut.

With both KMTNet and Spitzer observing the event, scientists had two vantage points from which to study the objects involved, as though two eyes separated by a great distance were viewing it. Having data from these two perspectives allowed them to detect the planet with KMTNet and calculate the mass of the star and the planet using Spitzer data. 

"We are able to know details about this planet because of the synergy between KMTNet and Spitzer," said Andrew Gould, professor emeritus of astronomy at Ohio State University, Columbus, and study co-author. 

Although OGLE-2016-BLG-1195Lb is about the same mass as Earth, and the same distance from its host star as our planet is from our sun, the similarities may end there. 

OGLE-2016-BLG-1195Lb is nearly 13,000 light-years away and orbits a star so small, scientists aren't sure if it's a star at all. It could be a brown dwarf, a star-like object whose core is not hot enough to generate energy through nuclear fusion. This particular star is only 7.8 percent the mass of our sun, right on the border between being a star and not. 

Alternatively, it could be an ultra-cool dwarf star much like TRAPPIST-1, which Spitzer and ground-based telescopes recently revealed to host seven Earth-size planets. Those seven planets all huddle closely around TRAPPIST-1, even closer than Mercury orbits our sun, and they all have potential for liquid water. But OGLE-2016-BLG-1195Lb, at the sun-Earth distance from a very faint star, would be extremely cold -- likely even colder than Pluto is in our own solar system, such that any surface water would be frozen. A planet would need to orbit much closer to the tiny, faint star to receive enough light to maintain liquid water on its surface.

Ground-based telescopes available today are not able to find smaller planets than this one using the microlensing method. A highly sensitive space telescope would be needed to spot smaller bodies in microlensing events. NASA's upcoming Wide Field Infrared Survey Telescope (WFIRST), planned for launch in the mid-2020s, will have this capability. 

"One of the problems with estimating how many planets like this are out there is that we have reached the lower limit of planet masses that we can currently detect with microlensing," Shvartzvald said. "WFIRST will be able to change that." 

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 - http://www.nasa.gov/spitzer

News Media Contact

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

Source:  JPL-Caltech/News

NASA’s Cassini, Voyager Missions Suggest New Picture of Sun’s Interaction with Galaxy

New data from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions show that the heliosphere — the bubble of the sun’s magnetic influence that surrounds the inner solar system — may be much more compact and rounded than previously thought. The image on the left shows a compact model of the heliosphere, supported by this latest data, while the image on the right shows an alternate model with an extended tail. The main difference is the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. This tail is shown in the old model in light blue. Credits: Dialynas, et al. (left); NASA (right). Hi-res image

Many other stars show tails that trail behind them like a comet’s tail, supporting the idea that our solar system has one too. However, new evidence from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions suggest that the trailing end of our solar system may not be stretched out in a long tail. From top left and going counter clockwise, the stars shown are LLOrionis, BZ Cam and Mira. Credits: NASA/HST/R.Casalegno/GALEX. Hi-res image

New data from NASA’s Cassini mission, combined with measurements from the two Voyager spacecraft and NASA’s Interstellar Boundary Explorer, or IBEX, suggests that our sun and planets are surrounded by a giant, rounded system of magnetic field from the sun — calling into question the alternate view of the solar magnetic fields trailing behind the sun in the shape of a long comet tail.

The sun releases a constant outflow of magnetic solar material — called the solar wind — that fills the inner solar system, reaching far past the orbit of Neptune. This solar wind creates a bubble, some 23 billion miles across, called the heliosphere. Our entire solar system, including the heliosphere, moves through interstellar space. The prevalent picture of the heliosphere was one of comet-shaped structure, with a rounded head and an extended tail. But new data covering an entire 11-year solar activity cycle show that may not be the case: the heliosphere may be rounded on both ends, making its shape almost spherical. A paper on these results was published in Nature Astronomy on April 24, 2017.

“Instead of a prolonged, comet-like tail, this rough bubble-shape of the heliosphere is due to the strong interstellar magnetic field — much stronger than what was anticipated in the past — combined with the fact that the ratio between particle pressure and magnetic pressure inside the heliosheath is high,” said Kostas Dialynas, a space scientist at the Academy of Athens in Greece and lead author on the study.

An instrument on Cassini, which has been exploring the Saturn system over a decade, has given scientists crucial new clues about the shape of the heliosphere’s trailing end, often called the heliotail. When charged particles from the inner solar system reach the boundary of the heliosphere, they sometimes undergo a series of charge exchanges with neutral gas atoms from the interstellar medium, dropping and regaining electrons as they travel through this vast boundary region. Some of these particles are pinged back in toward the inner solar system as fast-moving neutral atoms, which can be measured by Cassini.

“The Cassini instrument was designed to image the ions that are trapped in the magnetosphere of Saturn,” said Tom Krimigis, an instrument lead on NASA’s Voyager and Cassini missions based at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, and an author on the study. “We never thought that we would see what we’re seeing and be able to image the boundaries of the heliosphere.”

Because these particles move at a small fraction of the speed of light, their journeys from the sun to the edge of the heliosphere and back again take years. So when the number of particles coming from the sun changes — usually as a result of its 11-year activity cycle — it takes years before that’s reflected in the amount of neutral atoms shooting back into the solar system.

Cassini’s new measurements of these neutral atoms revealed something unexpected — the particles coming from the tail of the heliosphere reflect the changes in the solar cycle almost exactly as fast as those coming from the nose of the heliosphere.

“If the heliosphere’s ‘tail’ is stretched out like a comet, we’d expect that the patterns of the solar cycle would show up much later in the measured neutral atoms,” said Krimigis.

But because patterns from solar activity show just as quickly in tail particles as those from the nose, that implies the tail is about the same distance from us as the nose. This means that long, comet-like tail that scientists envisioned may not exist at all — instead, the heliosphere may be nearly round and symmetrical.

A rounded heliosphere could come from a combination of factors. Data from Voyager 1 show that the interstellar magnetic field beyond the heliosphere is stronger than scientists previously thought, meaning it could interact with the solar wind at the edges of the heliosphere and compact the heliosphere’s tail.

The structure of the heliosphere plays a big role in how particles from interstellar space — called cosmic rays — reach the inner solar system, where Earth and the other planets are.

“This data that Voyager 1 and 2, Cassini and IBEX provide to the scientific community is a windfall for studying the far reaches of the solar wind,” said Arik Posner, Voyager and IBEX program scientist at NASA Headquarters in Washington, D.C., who was not involved with this study. “As we continue to gather data from the edges of the heliosphere, this data will help us better understand the interstellar boundary that helps shield the Earth environment from harmful cosmic rays.”

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By Sarah Frazier
NASA’s Goddard Space Flight Center, Greenbelt, Md. 
Editor: Rob Garner   S

Source: NASA/Sun

Deep inside Galaxy M87

Schematic illustration of the turbulent mass injection process from the accretion disk of a supermassive black hole into a global helical magnetic field. © Axel. M. Quetz/MPIA Heidelberg

  

The origin of the jet from the close vicinity of the central black hole of an active galaxy

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the transformation of gravity into radiation.

Active black holes produce radiation via accretion of matter forming an accretion disk surrounding the central machine. A clear signpost of actively accreting massive black holes in the central cores of galaxies are enormous jets reaching out from the galaxies centers to scales of megaparsec and thus far beyond the optically visible galaxy.

M87, the central galaxy of the Virgo cluster, is at a distance of only 17 Mpc (corresponding to 50 million light years). It is the second closest active galactic nucleus (AGN), harboring an active black hole of six billion (6 x 10^9) solar masses in its centre. M87 was the first galaxy where a jet could be identified. It was found in optical observations at the Lick observatory almost 100 years ago ("a curious straight ray ... apparently connected with the nucleus by a thin line of matter", Heber Curtis, 1918).

The jet of M87 is one of the most thoroughly studied. It shows up across the electromagnetic spectrum from radio to X-ray wavelengths. M87 was also the first radio galaxy detected at highest gamma-ray energies in the TeV range.

Despite the wealth of observational material, the connection between the accreting black hole and the radiating jet is not known so far. The research team addressed this question by investigating interferometric radio observations of M87 with the VLBA network connecting radio telescopes across the United States from Hawaii to the Virgin Islands. The observations at 15 GHz (or 2 cm wavelength) provide an angular resolution of 0.6 mas (milli-arcseconds). At a distance of 17 Mpc this corresponds to 0.05 pc or 84 Schwarzschild radii only.

More than a hundred jets of active black holes have been studied thoroughly, but only M87 allows to explore the immediate vicinity of the central black hole.

The radio data were obtained within the MOJAVE (Monitoring of Jets in Active galactic nuclei with VLBA Experiments) project. “We re-analyzed these data providing us with an insight into the complex processes connecting the jet and the accretion disk of M87”, says Silke Britzen from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, the first author of the paper. “To our knowledge, this is the first time that processes related to the launching and loading of the jet can be investigated”. Fast turbulent processes involving magnetic reconnection phenomena, similar to those observed on much smaller scales on the surface of the Sun, provide the best explanation for the observed results (see Fig. 1).

“There are good reasons to think that the surface of the accretion disk behaves similar to the surface of the Sun - bubbling hot gas with ongoing magnetic activity such as reconnection and flares”, adds Christian Fendt from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, co-author in the team and an expert for jet-launching phenomena.

While close to the disk surface the small-scale magnetic structures dominate the mass loading of the jet, over long distances only the global helical magnetic field structure survives and governs the jet motion.

In the future, observations at higher frequencies and thus better resolution in the framework of the Event Horizon Telescope (EHT) project will allow to approach supermassive black holes even further. “There are only two targets which give us a chance to image the event horizon showing up as a shadow in the radio observations”, concludes Andreas Eckart from Cologne University. “The central black holes of M87 and our galaxy, the Milky Way, are very different in activity and mass, but also in distance. In both objects, however, the black hole subtends a similar angle on the sky and thus they cover similar portions of the image by a dark shadow.” Vladimir Karas (Astronomical Institute of the Czech Academy of Sciences) emphasizes that the new observational evidence for M87 can be seen as basis for follow-up work, both observational and theoretical. The immediate vicinity of the black hole is surrounded by a very interesting region called ergosphere, which however stays below the resolution limit of current telescopes.

The observations within the EHT project providing the highest angular resolution in astronomy just took place in the first two weeks of April 2017. The results from these observations could help to further refine the model presented in the paper and, more generally, our understanding of the connection between jets and supermassive black holes.

Hubble Space Telescope observations of the M87 jet with an inlay (schematic illustration) showing the central region where the jet is launched in turbulent processes and guided by a large-scale magnetic field. © J. A. Biretta et al., Hubble Heritage Team (STScI /AURA), NASA; Axel. M. Quetz/MPIA, S. Britzen/MPIfR

The research team comprises Silke Britzen, Christian Fendt, Andreas Eckart, and Vladimir Karas.

The Schwarzschild radius is defined as the radius of a sphere such that, if all its mass was compressed within that radius, the escape velocity from the surface of the sphere would equal the speed of light. The radius is named after Karl Schwarzschild who, in 1916, obtained the first exact solution to Einstein’s field equations for a non-rotating, spherically symmetric object.

The event horizon, in general relativity, is a boundary in spacetime beyond which events cannot affect an outside observer. The Schwarzschild radius is the radius of the event horizon surrounding a non-rotating black hole. Sgr A*'s Schwarzschild radius is 10 micro arcseconds. For M87, because of ist larger distance from Earth the event horizon appears to be smaller, between 4-7 micro arcseconds on the sky. However, the visible event horizon, affected by lensing in its own gravitational potential, is predicted to be larger. The shadow diameter is expected to be about 1 to 5 times the Schwarzschild radius.

The VLBA observations discussed here allow us to investigate the jet of M87 from about 30 Schwarzschild radii distance from the black hole to 3500 Schwarzschild radii. The VLBA (Very Long Baseline Array) of radio telescopes includes 10 radio telescopes of 25 m diameter each in the United States – from Hawaii to Virgin Islands.

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Contact

Dr. Silke Britzen
Phone:+49 228 525-280
Email: sbritzen@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Christian Fendt
Phone:+49 6221 528-387
Email: fendt@mpia-hd.mpg.de
Max-Planck-Institut für Astronomie, Heidelberg

Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
Email: njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

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Original Paper

A new view on the M87-jet origin: Turbulent loading leading to large-scale episodic wiggling

S. Britzen, C. Fendt, A. Eckart, and V. Karas et al., 2017, Astronomy & Astrophysics (April 2017), 10.1051/0004-6361/201629469 (DOI)

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Links

Radio Astronomy / VLBI
Research Department "Radio Astronomy. VLBI" at MPIfR Bonn Event Horizon Telescope
MPIfR web page for the EHT observations in April 2017

EHT
Event Horizon Telescope (EHT)

MOJAVE
Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE)

VLBA
Very Long Baseline Array (VLBA)

The Galactic Center Black Hole Laboratory
A. Eckart et al., in: "Equations of Motion in Relativistic Gravity", D. Puetzfeld et. al. (eds.), Fundamental theories of Physics 179, pages 759-781, Springer 2015

“Do Black Holes Exist? - The Physics and Philosophy of Black Holes”
641. WE-Heraeus-Seminar, Physikzentrum Bad Honnef/Germany, April 24-28, 2017

Source:  Max Planck Institute for Radio Astronomy

The onset of an extra-solar system - feeding a baby star with a dusty hamburger

Figure 1: Jet and disk in the HH 212 protostellar system: (a) A composite image for the jet in different molecules, produced by combining the images from the Very Large Telescope (McCaughrean et al. 2002) and ALMA (Lee et al. 2015). Orange image around the center shows the dusty envelope+disk at submillimeter wavelength obtained with ALMA at 200 AU resolution. (b) A zoom-in to the very center for the dusty disk at 8 AU resolution. Asterisks mark the possible position of the central protostar. A dark lane is seen in the equator, causing the disk to appear as a "hamburger". A size scale of our solar system is shown in the lower right corner for size comparison. (c) An accretion disk model that can reproduce the observed dust emission in the disk.  Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.

An international research team, led by Chin-Fei Lee in Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), has made a new high-fidelity image with the Atacama Large Millimeter/submillimeter Array (ALMA), catching a protostar (baby star) being fed with a dusty "Hamburger", which is a dusty accretion disk. This new image not only confirms the formation of an accretion disk around a very young protostar, but also reveals the vertical structure of the disk for the first time in the earliest phase of star formation. It not only poses a big challenge on some current theories of disk formation, but also potentially brings us key insights on the processes of grain growth and settling that are important to planet formation.

"It is so amazing to see such a detailed structure of a very young accretion disk. For many years, astronomers have been searching for accretion disks in the earliest phase of star formation, in order to determine their structure, how they are formed, and how the accretion process takes place. Now using the ALMA with its full power of resolution, we not only detect an accretion disk but also resolve it, especially its vertical structure, in great detail", says Chin-Fei Lee at ASIAA.

"In the earliest phase of star formation, there are theoretical difficulties in producing such a disk, because magnetic fields can slow down the rotation of collapsing material, preventing such a disk from forming around a very young protostar. This new finding implies that the retarding effect of magnetic fields in disk formation may not be as efficient as we thought before," says Zhi-Yun Li at University of Virginia.

HH 212 is a nearby protostellar system in Orion at a distance of about 1300 ly. The central protostar is very young with an age of only ~40,000 yrs (which is about 10 millionth of the age of Our Sun) and a mass of ~0.2 Msun. It drives a powerful bipolar jet and thus must accrete material efficiently. Previous search at a resolution of 200 AU only found a flattened envelope spiraling toward the center and a hint of a small dusty disk near the protostar. Now with ALMA at a resolution of 8 AU, which is 25 times higher, we not only detect but also spatially resolve the dusty disk at submillimeter wavelength.

The disk is nearly edge-on and has a radius of about 60 AU. Interestingly, it shows a prominent equatorial dark lane sandwiched between two brighter features, due to relatively low temperature and high optical depth near the disk midplane. For the first time, this dark lane is seen at submillimeter wavelength, producing a "hamburger"-shaped appearance that is reminiscent of the scattered-light image of an edge-on disk in optical and near infrared. The structure of the dark lane clearly implies that the disk is flared, as expected in an accretion disk model.

Our observations open up an exciting possibility of directly detecting and characterizing small disks around the youngest protostars through high-resolution imaging with ALMA, which provides strong constraints on theories of disk formation. Our observations of the vertical structure can also yield key insights on the processes of grain growth and settling that are important to planet formation in the earliest phase.

Paper and research team 

This research was presented in a paper "First Detection of Equatorial Dark Dust Lane in a Protostellar Disk at Submillimeter Wavelength," by Lee et al. to appear in the journal Science Advances.

The team is composed of Chin-Fei Lee (ASIAA, Taiwan; National Taiwan University, Taiwan), Zhi-Yun Li (University of Virginia, USA), Paul T.P. Ho (ASIAA, Taiwan; East Asia Observatory), Naomi Hirano (ASIAA, Taiwan), Qizhou Zhang (Harvard-Smithsonian Center for Astrophysics, USA), and Hsien Shang (ASIAA, Taiwan).

The figure above shows an artist's impression of an accretion disk feeding the central protostar and a jet coming out from the protostar. Credit: Yin-Chih Tsai/ASIAA  

Source: Atacama Large Millimeter/submillimeter Array (ALMA)

Using the Pleiades as guinea-pigs for new photometric method

Target pixel mask of Alcyone from Kepler image. The four squared-in pixels are used for the registration of the brightness of the star. 

The white pixels are useless due to saturation.

Tim White as lead author and several other researchers related to SAC have a paper out in Monthly Notices of the Royal Astronomical Observatory, titled 'Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades'. The astronomers will never be content! They strive to observe the faintest stars possible, and this means that some of the brighter stars are actually too bright to observe with modern equipment. A workaround to this has now been developed by an international group of astronomers led by Tim White of Stellar Astrophysics Centre, Aarhus University and the method has been tested successfully on the seven brightest stars in the open cluster named the Pleiades or the Seven Sisters.

Aiming a beam of light from a bright star at a point on a CCD detector will cause several of the central pixels of the star's image to be saturated, and the construction of the CCD will cause long ghost images of saturated pixels in various directions out from the center of the image. Saturation means a loss of precision in the measurement of the total brightness of the star. The solution is simple: the star is bright enough that you can skip all the saturated pixels, selecting a set of unsaturated positions on the CCD hit by enough light that you can still make a reliable measurement of the brightness variations that are of interest if you want to do asteroseismology, observing the regular short time variations or if you want to see if an exoplanet passes in front of the star causing the intensity to drop shortly.

This new method has been named halo photometry. It is simple and fast and it has been used by the authors for observing the seven brightest named stars in the open cluster using data from the extended K2 mission by the NASA Kepler satellite.

The Pleiades with the light curves of the seven brightest stars inserted. Maia is obviously the odd sister out.

The seven stars are closely of the same age and six of the show regular B-star pulsations. This is interesting for determining the values of some of the poorly understood processes in the core of these stars. The seventh star, Maia is different. It is not variable in any way comparable to the other bright stars in the cluster, but it does vary with a regular period of 10 days. Previous studies have shown that Maia belongs to a class of stars with a deficiency of both He and Hg, and the authors conclude that the variability is due to a large spot on the surface of the star of different chemical composition. This means that Maia itself does definitely not belong to the controversial group af stars named Maia variables, and the authors implore for the sanity of future astronomers that this designation should not be used anymore!

No signs of exoplanets were detected during the study.

Ole J. Knudsen

 

Source: Stellar Astrophysics Centre - Aarhus University

Hubble celebrates 27 years with two close friends

PR Image heic1709a

A close galactic pair

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A sea of galaxies 

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Wide-field image of NGC 4298 and NGC 4302 (ground-based image) 

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Annotated wide-field image of NGC 4298 and NGC 4302 (ground-based image)

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Videos

PR Video heic1709a

Pan on NGC 4298 and NGC 4302

PR Video heic1709b

Zoom-in on NGC 4298 and NGC 4302

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Fulldome view of NGC 4298 and NGC 4302

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This stunning cosmic pairing of the two very different looking spiral galaxies NGC 4302 and NGC 4298 was imaged by the NASA/ESA Hubble Space Telescope. The image brilliantly captures their warm stellar glow and brown, mottled patterns of dust. As a perfect demonstration of Hubble’s capabilities, this spectacular view has been released as part of the telescope’s 27th anniversary celebrations.

Since its launch on 24 April 1990, Hubble has been nothing short of a revolution in astronomy. The first orbiting facility of its kind, for 27 years the telescope has been exploring the wonders of the cosmos. Astronomers and the public alike have witnessed what no other humans in history have before. In addition to revealing the beauty of the cosmos, Hubble has proved itself to be a treasure chest of scientific data that astronomers can access.

ESA and NASA celebrate Hubble’s birthday each year with a spectacular image. This year’s anniversary image features a pair of spiral galaxies known as NGC 4302 — seen edge-on — and NGC 4298, both located 55 million light-years away in the northern constellation of Coma Berenices (Berenice’s Hair). The pair, discovered by astronomer William Herschel in 1784, form part of the Virgo Cluster, a gravitationally bound collection of nearly 2000 individual galaxies.

The edge-on NGC 4302 is a bit smaller than our own Milky Way Galaxy. The tilted NGC 4298 is even smaller: only half the size of its companion.

At their closest points, the galaxies are separated from each other in projection by only around 7000 light-years. Given this very close arrangement, astronomers are intrigued by the galaxies’ apparent lack of any significant gravitational interaction; only a faint bridge of neutral hydrogen gas — not visible in this image — appears to stretch between them. The long tidal tails and deformations in their structure that are typical of galaxies lying so close to each other are missing completely.

Astronomers have found very faint tails of gas streaming from the two galaxies, pointing in roughly the same direction — away from the centre of the Virgo Cluster. They have proposed that the galactic double is a recent arrival to the cluster, and is currently falling in towards the cluster centre and the galaxy Messier 87 lurking there — one of the most massive galaxies known. On their travels, the two galaxies are encountering hot gas — the intracluster medium — that acts like a strong wind, stripping layers of gas and dust from the galaxies to form the streaming tails.

Even in its 27th year of operation, Hubble continues to provide truly spectacular images of the cosmos, and even as the launch date of its companion — the NASA/ESA/CSA James Webb Space Telescope — draws closer, Hubble does not slow down. Instead, the telescope keeps raising the bar, showing it still has plenty of observing left to do for many more years to come. In fact, astronomers are looking forward to have Hubble and James Webb operational at the same time and use their combined capabilities to explore the Universe.

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More Information

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

Image credit: NASA, ESA

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Links

• Images of Hubble
• Hubblesite release
• 26th anniversary image: Bubble Nebula
• 25th anniversary image: Westerlund 2

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Contacts

Mathias Jäger

ESA/Hubble, Public Information Officer

Garching bei München, Germany

Tel: +49 176 62397500

Email: mjaeger@partner.eso.org

Source: ESA/Hubble/News

Hubble observes first multiple images of explosive distance indicator

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Detailed look at a gravitationally lensed supernova

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Hubble’s view on lensing galaxy 

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Hubble’s view on lensed supernova

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Palomar’s view on iPTF16geu

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The SDSS view on iPTF16geu

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Keck’s view on lensed supernova

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Videos

PR Video heic1710a

Schematic of strong gravitational lensing

PR Video heic1710b

Hubblecast 70: Peering around cosmic corners 

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Lensed supernova will give insight into the expansion of the Universe

A Swedish-led team of astronomers used the NASA/ESA Hubble Space Telescope to analyse the multiple images of a gravitationally lensed type Ia supernova for the first time. The four images of the exploding star will be used to measure the expansion of the Universe. This can be done without any theoretical assumptions about the cosmological model, giving further clues about how fast the Universe is really expanding. The results are published in the journal Science.

An international team, led by astronomers from the Stockholm University, Sweden, has discovered a distant type Ia supernova, called iPTF16geu [1] — it took the light 4.3 billion years to travel to Earth [2]. The light from this particular supernova was bent and magnified by the effect of gravitational lensing so that it was split into four separate images on the sky [3]. The four images lie on a circle with a radius of only about 3000 light-years around the lensing foreground galaxy, making it one of the smallest extragalactic gravitational lenses discovered so far. Its appearance resembles the famous Refsdal supernova, which astronomers detected in 2015 (heic1525). Refsdal, however, was a core-collapse supernova.

Type Ia supernovae always have the same intrinsic brightness, so by measuring how bright they appear astronomers can determine how far away they are. They are therefore known as standard candles. These supernovae have been used for decades to measure distances across the Universe, and were also used to discover its accelerated expansion and infer the existence of dark energy. Now the supernova iPTF16geu allows scientists to explore new territory, testing the theories of the warping of spacetime on smaller extragalactic scales than ever before.

“Resolving, for the first time, multiple images of a strongly lensed standard candle supernova is a major breakthrough. We can measure the light-focusing power of gravity more accurately than ever before, and probe physical scales that may have seemed out of reach until now,” says Ariel Goobar, Professor at the Oskar Klein Centre at Stockholm University and lead author of the study.

The critical importance of the object meant that the team instigated follow-up observations of the supernova less than two months after its discovery. This involved some of the world’s leading telescopes in addition to Hubble: the Keck telescope on Mauna Kea, Hawaii, and ESO’s Very Large Telescope in Chile. Using the data gathered, the team calculated the magnification power of the lens to be a factor of 52. Because of the standard candle nature of iPTF16geu, this is the first time this measurement could be made without any prior assumptions about the form of the lens or cosmological parameters.

Currently the team is in the process of accurately measuring how long it took for the light to reach us from each of the four images of the supernova. The differences in the times of arrival can then be used to calculate the Hubble constant — the expansion rate of the Universe — with high precision [4]. This is particularly crucial in light of the recent discrepancy between the measurements of its value in the local and the early Universe (heic1702).

As important as lensed supernovae are for cosmology, it is extremely difficult to find them. Not only does their discovery rely on a very particular and precise alignment of objects in the sky, but they are also only visible for a short time. “The discovery of iPTF16geu is truly like finding a somewhat weird needle in a haystack,” remarks Rahman Amanullah, co-author and research scientist at Stockholm University. “It reveals to us a bit more about the Universe, but mostly triggers a wealth of new scientific questions.”

Studying more similarly lensed supernovae will help shape our understanding of just how fast the Universe is expanding. The chances of finding such supernovae will improve with the installation of new survey telescopes in the near future.

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Notes

[1] iPTF16geu was initially observed by the iPTF (intermediate Palomar Transient Factory) collaboration with the Palomar Observatory. This is a fully automated, wide-field survey delivering a systematic exploration of the optical transient sky. 

[2] This corresponds to a redshift of 0.4. The lensing galaxy has a redshift of 0.2.

[3] Gravitational lensing is a phenomenon that was first predicted by Albert Einstein in 1912. It occurs when a massive object lying between a distant light source and the observer bends and magnifies the light from the source behind it. This allows astronomers to see objects that would otherwise be to faint to see.

[4] For each image of the supernova, the light is not bent in the same way. This results in slightly different travel times. The maximum time delay between the four images is predicted to be less than 35 hours.

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More Information

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

This research was presented in a paper entitled “iPTF16geu: A multiply-imaged gravitationally lensed Type Ia supernova” by Goobar et al., which appeared in the journal Science.

The international team of astronomers in this study consists of A. Goobar (The Oskar Klein Centre, Sweden), R. Amanullah (The Oskar Klein Centre, Sweden), S. R. Kulkarni (Cahill Center for Astrophysics, USA), P. E. Nugent (University of California, USA; Lawrence Berkeley National Laboratory, USA), J. Johansson (Weizmann Institute of Science, Israel), C. Steidel (Cahill Center for Astrophysics, USA), D. Law (Space Telescope Science Institute, USA), E. Mörtsell (The Oskar Klein Centre, Sweden), R. Quimby (San Diego State University, USA; Kavli IPMU (WPI), Japan), N. Blagorodnova (Cahill Center for Astrophysics, USA), A. Brandeker (Stockholm University, Sweden), Y. Cao (eScience Institute and Department of Astronomy, USA), A. Cooray (University of California, USA), R. Ferretti (The Oskar Klein Centre, Sweden), C. Fremling (The Oskar Klein Centre, Sweden), L. Hangard (The Oskar Klein Centre, Sweden), M. Kasliwal (Cahill Center for Astrophysics, USA), T. Kupfer (Cahill Center for Astrophysics, USA), R. Lunnan (Cahill Center for Astrophysics, USA; Stockholm University, Sweden), F. Masci (Infrared Processing and Analysis Center, USA), A. A. Miller (Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), USA; The Adler Planetarium, USA) H. Nayyeri (University of California, USA), J. D. Neill (Cahill Center for Astrophysics, USA), E. O. Ofek (Weizmann Institute of Science, Israel), S. Papadogiannakis (The Oskar Klein Centre, Sweden), T. Petrushevska (The Oskar Klein Centre, Sweden), V. Ravi (Cahill Center for Astrophysics, USA), J. Sollerman (The Oskar Klein Centre, Sweden), M. Sullivan (University of Southampton, UK), F. Taddia (The Oskar Klein Centre, Sweden), R. Walters (Cahill Center for Astrophysics, USA), D. Wilson (University of California, USA), L. Yan (Cahill Center for Astrophysics, USA), O. Yaron (Weizmann Institute of Science, Israel).

Image credit: NASA, ESA, Sloan Digital Sky Survey, W. M. Keck Observatory, Palomar Observatory/California Institute of Technology.

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Links

• Images of Hubble
• Science paper
• Caltech press release
• Berkeley press release

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Contacts

Ariel Goobar
Oskar Klein Centre at Stockholm University
Stockholm, Sweden
Tel: +46 8 5537 8659
Email: ariel@fysik.su.se

Rahman Amanullah
Oskar Klein Centre at Stockholm University
Stockholm, Sweden
Tel: +46 8 5537 8848
Email: rahman@fysik.su.se

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

 Source: ESA/Hubble/News

Blowing cosmic bubbles

Sh2-308

Credit: ESA/Hubble & NASA

This entrancing image shows a few of the tenuous threads that comprise Sh2-308, a faint and wispy shell of gas located 5200 light-years away in the constellation of Canis Major (The Great Dog).

Sh2-308 is a large bubble-like structure wrapped around an extremely large, bright type of star known as a Wolf-Rayet Star — this particular star is called EZ Canis Majoris. These type of stars are among the brightest and most massive stars in the Universe, tens of times more massive than our own Sun, and they represent the extremes of stellar evolution. Thick winds continually poured off the progenitors of such stars, flooding their surroundings and draining the outer layers of the Wolf-Rayet stars. The fast wind of a Wolf-Rayet star therefore sweeps up the surrounding material to form bubbles of gas.

EZ Canis Majoris is responsible for creating the bubble of Sh2-308 — the star threw off its outer layers to create the strands visible here. The intense and ongoing radiation from the star pushes the bubble out further and further, blowing it bigger and bigger. Currently the edges of Sh2-308 are some 60 light-years apart!

Beautiful as these cosmic bubbles are, they are fleeting. The same stars that form them will also cause their death, eclipsing and subsuming them in violent supernova explosions.

Source: ESA/Hubble/Potw