Wednesday, April 26, 2017

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.”

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

Source: NASA/Sun

Tuesday, April 25, 2017

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.


Dr. Silke Britzen
Phone:+49 228 525-280
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Christian Fendt
Phone:+49 6221 528-387
Max-Planck-Institut für Astronomie, Heidelberg

Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
Max-Planck-Institut für Radioastronomie, Bonn

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)


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

Event Horizon Telescope (EHT)

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

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

Monday, April 24, 2017

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  

Sunday, April 23, 2017

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.


Saturday, April 22, 2017

Hubble celebrates 27 years with two close friends

A close galactic pair

PR Image heic1709b
A sea of galaxies 

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

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


Pan on NGC 4298 and NGC 4302
Pan on NGC 4298 and NGC 4302

Zoom-in on NGC 4298 and NGC 4302
Zoom-in on NGC 4298 and NGC 4302

Fulldome view of NGC 4298 and NGC 4302
Fulldome view of NGC 4298 and NGC 4302

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.

More Information

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



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

Friday, April 21, 2017

Hubble observes first multiple images of explosive distance indicator

Detailed look at a gravitationally lensed supernova

PR Image heic1710b
Hubble’s view on lensing galaxy 

PR Image heic1710c
Hubble’s view on lensed supernova

PR Image heic1710d
Palomar’s view on iPTF16geu

PR Image heic1710e
The SDSS view on iPTF16geu

Keck’s view on lensed supernova


Schematic of strong gravitational lensing
Schematic of strong gravitational lensing

Hubblecast 70: Peering around cosmic corners
Hubblecast 70: Peering around cosmic corners 

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.


[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.

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.



Ariel Goobar
Oskar Klein Centre at Stockholm University
Stockholm, Sweden
Tel: +46 8 5537 8659

Rahman Amanullah
Oskar Klein Centre at Stockholm University
Stockholm, Sweden
Tel: +46 8 5537 8848

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

 Source: ESA/Hubble/News

Blowing cosmic bubbles

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.

Thursday, April 20, 2017

Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life

Artist’s impression of the super-Earth exoplanet LHS 1140b

Location of the faint red star LHS 1140 in the constellation of Cetus (The Sea Monster)

PR Image eso1712c
 Artist’s impression of the newly-discovered rocky exoplanet, LHS 1140b 


Artist’s impression of a trip to the super-Earth exoplanet LHS 1140b
Artist’s impression of a trip to the super-Earth exoplanet LHS 1140b

Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

An exoplanet orbiting a red dwarf star 40 light-years from Earth may be the new holder of the title “best place to look for signs of life beyond the Solar System”. Using ESO’s HARPS instrument at La Silla, and other telescopes around the world, an international team of astronomers discovered a “super-Earth” orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth and has likely retained most of its atmosphere. This, along with the fact that it passes in front of its parent star as it orbits, makes it one of the most exciting future targets for atmospheric studies. The results will appear in the 20 April 2017 issue of the journal Nature.

The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster) [1]. Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.

This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.

"The present conditions of the red dwarf are particularly favourable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland [2].

For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere. When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them. In this case, the planet's large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.

The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made crucial follow-up observations which confirmed the presence of the super-Earth. HARPS also helped pin down the orbital period and allowed the exoplanet’s mass and density to be deduced [3].

The astronomers estimate the age of the planet to be at least five billion years. They also deduced that it has a diameter 1.4 times larger than the Earth — almost 18 000 kilometres. But with a mass around seven times greater than the Earth, and hence a much higher density, it implies that the exoplanet is probably made of rock with a dense iron core.

This super-Earth may be the best candidate yet for future observations to study and characterise its atmosphere, if one exists. Two of the European members of the team, Xavier Delfosse and Xavier Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: “The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries![4,5].

In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope will be able to assess exactly how much high-energy radiation is showered upon LHS 1140b, so that its capacity to support life can be further constrained.

Further into the future — when new telescopes like ESO’s Extremely Large Telescope are operating — it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.


[1] The habitable zone is defined by the range of orbits around a star, for which a planet possesses the appropriate temperature needed for liquid water to exist on the planet’s surface.

[2] Although the planet is located in the zone in which life as we know it could potentially exist, it probably did not enter this region until approximately forty million years after the formation of the red dwarf star. During this phase, the exoplanet would have been subjected to the active and volatile past of its host star. A young red dwarf can easily strip away the water from the atmosphere of a planet forming within its vicinity, leading to a runaway greenhouse effect similar to that on Venus.

[3] This effort enabled other transit events to be detected by MEarth so that the astronomers could nail down the detection of the exoplanet once and for all.

[4] The planet around Proxima Centauri (eso1629) is much closer to Earth, but it probably does not transit its star, making it very difficult to determine whether it holds an atmosphere.

[5] Unlike the TRAPPIST-1 system (eso1706), no other exoplanets around LHS 1140 have been found. Multi-planet systems are thought to be common around red dwarfs, so it is possible that additional exoplanets have gone undetected so far because they are too small.

More Information

This research was presented in a paper entitled “A temperate rocky super-Earth transiting a nearby cool star”, by J. A. Dittmann et al. to appear in the journal Nature on 20 April 2017.

The team is composed of Jason A. Dittmann (Harvard Smithsonian Center for Astrophysics, USA), Jonathan M. Irwin (Harvard Smithsonian Center for Astrophysics, USA), David Charbonneau (Harvard Smithsonian Center for Astrophysics, USA), Xavier Bonfils (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, France), Nicola Astudillo-Defru (Observatoire de Genève, Switzerland), Raphaëlle D. Haywood (Harvard Smithsonian Center for Astrophysics, USA), Zachory K. Berta-Thompson (University of Colorado, USA), Elisabeth R. Newton (MIT, USA), Joseph E. Rodriguez (Harvard Smithsonian Center for Astrophysics, USA), Jennifer G. Winters (Harvard Smithsonian Center for Astrophysics, USA), Thiam-Guan Tan (Perth Exoplanet Survey Telescope, Australia), José-Manuel Almenara (Institut de Planétologie et d'Astrophysique de Grenoble - Université Grenoble-Alpes/CNRS, France; Observatoire de Genève, Switzerland), François Bouchy (Aix Marseille Université, France), Xavier Delfosse (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes / CNRS, France), Thierry Forveille (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, France), Christophe Lovis (Observatoire de Genève, Switzerland), Felipe Murgas (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes / CNRS, France; IAC, Spain), Francesco Pepe (Observatoire de Genève, Switzerland), Nuno C. Santos (Instituto de Astrofísica e Ciências do Espaço and Universidade do Porto, Portugal), Stephane Udry (Observatoire de Genève, Switzerland), Anaël Wünsche (CNRS/IPAG, France), Gilbert A. Esquerdo (Harvard Smithsonian Center for Astrophysics, USA), David W. Latham (Harvard Smithsonian Center for Astrophysics, USA) and Courtney D. Dressing (Caltech, USA).

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



Jason Dittmann
Harvard-Smithsonian Center for Astrophysics
Cambridge, USA

Nicola Astudillo-Defru
Geneva Observatory - Université of Geneva
Geneva, Switzerland

Xavier Bonfils
Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS
Grenoble, France

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

Megan Watzke
Harvard-Smithsonian Center for Astrophysics
Cambridge, USA
Tel: +1 617-496-7998

Source: ESO

Wednesday, April 19, 2017

NGC 4696: The Arrhythmic Beating of a Black Hole Heart A Tour of NGC 4696

NGC 4696
Credit: X-ray: NASA/CXC/MPE/J.Sanders et al.; 
Optical: NASA/STScI; Radio: NSF/NRAO/VLA

At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.

New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.

In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data from the NSF's Karl G. Jansky Very Large Array (blue) that shows high-energy particles produced by the black hole-powered jets. Visible light data from the Hubble Space Telescope (green) show galaxies in the cluster as well as galaxies and stars outside the cluster.

Cavity processing scale: This image shows a larger field of view than the main composite image above and is about 122,000 light years across. This image has also been rotated slightly clockwise to the main composite image above.

Astronomers employed special processing to the X-ray data (shown above) to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

The researchers estimate that these black hole bursts, or "beats", have occurred every five to ten million years. Besides the vastly differing time scales, these beats also differ from typical human heartbeats in not occurring at particularly regular intervals.

Curved processing scale: This image also shows a larger field of view than the main composite image and is about 550,000 light years across. This image has also been rotated slightly clockwise to the main composite image.

A different type of processing of the X-ray data (shown above) reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate. (Note that both images showing the labeled cavities and this image are rotated slightly clockwise to the main composite.)
The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies. The pitch of the sound in Centaurus is extremely deep, corresponding to a discordant sound about 56 octaves below the notes near middle C. This corresponds to a slightly higher (by about one octave) pitch than the sound in Perseus. Alternative explanations for these curved features include the effects of turbulence or magnetic fields.

The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova explosions. The authors of the study of the Centaurus cluster created a map showing the density of elements heavier than hydrogen and helium. The brighter colors in the map show regions with the highest density of heavy elements and the darker colors show regions with a lower density of heavy elements. Therefore, regions with the highest density of heavy elements are located to the right of the black hole. A lower density of heavy elements near the black hole is consistent with the idea that enriched gas has been lifted out of the cluster's center by bursting activity associated with the black hole. The energy produced by the black hole is also able to prevent the huge reservoir of hot gas from cooling. This has prevented large numbers of stars from forming in the gas.

A paper describing these results was published in the March 21st 2016 issue of the Monthly Notices of the Royal Astronomical Society and is available online. The first author is Jeremy Sanders from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

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

Fast Facts for NGC 4696:

Scale: Image is about 2.2 arcmin across (about 93,000 light years)
Category: Black Holes, Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 12h 48m 48.90s | Dec -41° 18′ 44.40
Constellation: Centaurus
Observation Date: 15 pointings between May 2000 and June 2014
Observation Time: 216 hours 29 min (9 days 29 min)
Obs. ID: 504, 505, 4190, 4191, 4954, 4955, 5310, 16223-16225, 16534, 16607-16610
Instrument: ACIS
References: Sanders, J. et al., 2016, MNRAS, 457, 82; arXiv:1601.01489
Color Code: X-ray (Red); Optical (Green); Radio (Blue)
Distance Estimate: About 145 million light years

Monday, April 17, 2017

Investigates 'DeeDee,' a Distant, Dim Member of Our Solar System

Figure 1. ALMA image of the planetary body 2014 UZ224, more informally known as DeeDee. At three times the distance of Pluto from the Sun, DeeDee is the second most distant confirmed TNO with a confirmed orbit in our solar system.  Credit: NRAO/AUI/NSF

Figure 2. Size comparisons of objects in our solar system, including the recently discovered planetary body 'DeeDee.'  
Credit: Alexandra Angelich (NRAO/AUI/NSF)  

Figure 3. Orbits of objects in our solar system, showing the current location of the planetary body 'DeeDee'.  
Credit: Alexandra Angelich (NRAO/AUI/NSF)

Figure 4. Artist concept of the planetary body 2014 UZ224, more informally known as DeeDee. ALMA was able to observe the faint millimeter-wavelength "glow" emitted by the object, confirming it is roughly 635 kilometers across. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.  Credit: Alexandra Angelich (NRAO/AUI/NSF) 

Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have revealed extraordinary details about a recently discovered far-flung member of our solar system, the planetary body 2014 UZ224, more informally known as DeeDee.

At about three times the current distance of Pluto from the Sun, DeeDee is the second most distant known trans-Neptunian object (TNO) with a confirmed orbit, surpassed only by the dwarf planet Eris. Astronomers estimate that there are tens-of-thousands of these icy bodies in the outer solar system beyond the orbit of Neptune.

The new ALMA data reveal, for the first time, that DeeDee is roughly 635 kilometers across, or about two-thirds the diameter of the dwarf planet Ceres, the largest member of our asteroid belt. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.

"Far beyond Pluto is a region surprisingly rich with planetary bodies. Some are quite small but others have sizes to rival Pluto, and could possibly be much larger," said David Gerdes, a scientist with the University of Michigan and lead author on a paper appearing in the Astrophysical Journal Letters

"Because these objects are so distant and dim, it's incredibly difficult to even detect them, let alone study them in any detail. ALMA, however, has unique capabilities that enabled us to learn exciting details about these distant worlds."

Currently, DeeDee is about 92 astronomical units (AU) from the Sun. An astronomical unit is the average distance from the Earth to the Sun, or about 150 million kilometers. At this tremendous distance, it takes DeeDee more than 1,100 years to complete one orbit. Light from DeeDee takes nearly 13 hours to reach Earth.

Gerdes and his team announced the discovery of DeeDee in the fall of 2016. They found it using the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile as part of ongoing observations for the Dark Energy Survey, an optical survey of about 12 percent of the sky that seeks to understand the as-yet mysterious force that is accelerating the expansion of the universe.

he Dark Energy Survey produces vast troves of astronomical images, which give astronomers the opportunity to also search for distant solar system objects. The initial search, which includes nearly 15,000 images, identified more than 1.1 billion candidate objects. The vast majority of these turned out to be background stars and even more distant galaxies. A small fraction, however, were observed to move slowly across the sky over successive observations, the telltale sign of a TNO.

One such object was identified on 12 separate images. The astronomers informally dubbed it DeeDee, which is short for Distant Dwarf.

The optical data from the Blanco telescope enabled the astronomers to measure DeeDee's distance and orbital properties, but they were unable to determine its size or other physical characteristics. It was possible that DeeDee was a relatively small member of our solar system, yet reflective enough to be detected from Earth. Or, it could be uncommonly large and dark, reflecting only a tiny portion of the feeble sunlight that reaches it; both scenarios would produce identical optical data.

Since ALMA observes the cold, dark universe, it is able to detect the heat - in the form of millimeter-wavelength light - emitted naturally by cold objects in space. The heat signature from a distant solar system object would be directly proportional to its size.

"We calculated that this object would be incredibly cold, only about 30 degrees Kelvin, just a little above absolute zero," said Gerdes.

While the reflected visible light from DeeDee is only about as bright as a candle seen halfway the distance to the moon, ALMA was able to quickly home in on the planetary body’s heat signature and measure its brightness in millimeter-wavelength light.

This allowed astronomers to determine that it reflects only about 13 percent of the sunlight that hits it. That is about the same reflectivity of the dry dirt found on a baseball infield.

By comparing these ALMA observations to the earlier optical data, the astronomers had the information necessary to calculate the object's size. "ALMA picked it up fairly easily," said Gerdes. 

"We were then able to resolve the ambiguity we had with the optical data alone."

Objects like DeeDee are cosmic leftovers from the formation of the solar system. Their orbits and physical properties reveal important details about the formation of planets, including Earth.

This discovery is also exciting because it shows that it is possible to detect very distant, slowly moving objects in our own solar system. The researchers note that these same techniques could be used to detect the hypothesized "Planet Nine" that may reside far beyond DeeDee and Eris.

"There are still new worlds to discover in our own cosmic backyard," concludes Gerdes. "The solar system is a rich and complicated place."