Ram-pressure feeding of supermassive black holes

Nature 548, 7667 (2017). doi:10.1038/nature23462

Authors: Bianca M. Poggianti, Yara L. Jaffé, Alessia Moretti, Marco Gullieuszik, Mario Radovich, Stephanie Tonnesen, Jacopo Fritz, Daniela Bettoni, Benedetta Vulcani, Giovanni Fasano, Callum Bellhouse, George Hau & Alessandro Omizzolo

When a supermassive black hole at the centre of a galaxy accretes matter, it gives rise to a highly energetic phenomenon: an active galactic nucleus. Numerous physical processes have been proposed to account for the funnelling of gas towards the galactic centre to feed the black hole. There are also several physical processes that can remove gas from a galaxy, one of which is ram-pressure stripping by the hot gas that fills the space between galaxies in galaxy clusters. Here we report that six out of a sample of seven ‘jellyfish’ galaxies—galaxies with long ‘tentacles’ of material that extend for dozens of kiloparsecs beyond the galactic disks—host an active nucleus, and two of them also have galactic-scale ionization cones. The high incidence of nuclear activity among heavily stripped jellyfish galaxies may be due to ram pressure causing gas to flow towards the centre and triggering the activity, or to an enhancement of the stripping caused by energy injection from the active nucleus, or both. Our analysis of the galactic position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another possible mechanism for feeding the central supermassive black hole with gas.

Vigorous atmospheric motion in the red supergiant star Antares

Nature 548, 7667 (2017). doi:10.1038/nature23445

Authors: K. Ohnaka, G. Weigelt & K.-H. Hofmann

Red supergiant stars represent a late stage of the evolution of stars more massive than about nine solar masses, in which they develop complex, multi-component atmospheres. Bright spots have been detected in the atmosphere of red supergiants using interferometric imaging. Above the photosphere of a red supergiant, the molecular outer atmosphere extends up to about two stellar radii. Furthermore, the hot chromosphere (5,000 to 8,000 kelvin) and cool gas (less than 3,500 kelvin) of a red supergiant coexist at about three stellar radii. The dynamics of such complex atmospheres has been probed by ultraviolet and optical spectroscopy. The most direct approach, however, is to measure the velocity of gas at each position over the image of stars as in observations of the Sun. Here we report the mapping of the velocity field over the surface and atmosphere of the nearby red supergiant Antares. The two-dimensional velocity field map obtained from our near-infrared spectro-interferometric imaging reveals vigorous upwelling and downdrafting motions of several huge gas clumps at velocities ranging from about −20 to +20 kilometres per second in the atmosphere, which extends out to about 1.7 stellar radii. Convection alone cannot explain the observed turbulent motions and atmospheric extension, suggesting that an unidentified process is operating in the extended atmosphere.

Astronomy: A turbulent stellar atmosphere in full view

Nature 548, 7667 (2017). doi:10.1038/548288a

Authors: Gail H. Schaefer

The dynamic motion of gas in the outer atmosphere of a red supergiant star has been mapped, providing clues to the mysterious mechanism that causes massive stars to lose mass through stellar winds. See Letter p.310

Cosmic winds that form the long tentacles of jellyfish galaxies may also create the perfect conditions to sustain highly active supermassive black holes

Cloud cover? Cannot travel? Don’t fear! Watch the total solar eclipse online!

News Article Type: Homepage ArticlesPublished: Wednesday, August 16, 2017 - 12:37

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

While surveying the positions of over a billion stars, ESA's Gaia mission is also measuring their colour, a key diagnostic to study the physical properties of stars. A new image provides a preview of Gaia's first full-colour all-sky map, which will be unleashed in its highest resolution with the next data release in 2018.

Most of the water on Mars is at its poles, but ice near the equator may mean that the way the red planet is tilted has changed over the last few million years

Video Length: 3:20

Cassini is in the process of executing 22 daring ‘Grand Finale’ dives in the 1,200-mile gap between Saturn and its innermost ring, concluding with an epic final plunge into the gas giant’s upper atmosphere.

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Video Links: Cassini's Grand Finale - mp4YouTubeVimeo

Ten spacecraft, from ESA's Venus Express to NASA's Voyager-2, felt the effect of a solar eruption as it washed through the Solar System while three other satellites watched, providing a unique perspective on this space weather event.

Video Length: 3:40

The cosmic ray detector known as CREAM is headed for the International Space Station, with a goal of measuring the highest energy possible for direct measurement of high-energy cosmic rays.

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Video Links: The Mystery of High-Energy Cosmic Rays - mp4YouTubeVimeo

A new experiment set for an Aug. 14 launch to the International Space Station will provide an unprecedented look at a rain of particles from deep space, called cosmic rays, that constantly showers our planet. The Cosmic Ray Energetics And Mass mission destined for the International Space Station (ISS-CREAM) is designed to measure the highest-energy particles of any detector yet flown in space.

CREAM was originally developed as a part of NASA's Balloon Program, during which it returned measurements from around 120,000 feet in seven flights between 2004 and 2016.

Meet Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM), an experiment designed to provide an unprecedented look at cosmic ray particles approaching energies of 1,000 trillion electron volts (1 PeV). ISS-CREAM detects these particles when they slam into the matter making up its instruments. They can distinguish electrons, protons and atomic nuclei as massive as iron as they crash through the detector stack.

"The CREAM balloon experiment achieved a total sky exposure of 191 days, a record for any balloon-borne astronomical experiment," said Eun-Suk Seo, a professor of physics at the University of Maryland in College Park and the experiment's principal investigator. "Operating on the space station will increase our exposure by over 10 times, taking us well beyond the traditional energy limits of direct measurements."

Technicians lower ISS-CREAM into a chamber that simulates the space environment during system-level testing at NASA's Goddard Space Flight Center in summer 2015.Credits: University of Maryland Cosmic Ray Physics Laboratory

Sporting new instruments, as well as refurbished versions of detectors originally used on balloon flights over Antarctica, the refrigerator-sized, 1.4-ton (1,300 kilogram) ISS-CREAM experiment will be delivered to the space station as part of the 12th SpaceX commercial resupply service mission. Once there, ISS-CREAM will be moved to the Exposed Facility platform extending from Kibo, the Japanese Experiment Module.

The ISS-CREAM payload was delivered to NASA's Kennedy Space Center in August 2015. The experiment is shown wrapped in plastic layers used to protect its sensitive electronics during shipment.Credits: University of Maryland Cosmic Ray Physics Laboratory

From this orbital perch, ISS-CREAM is expected to study the "cosmic rain" for three years — time needed to provide unparalleled direct measurements of rare high-energy cosmic rays.

At energies above about 1 billion electron volts, most cosmic rays come to us from beyond our solar system. Various lines of evidence, including observations from NASA's Fermi Gamma-ray Space Telescope, support the idea that shock waves from the expanding debris of stars that exploded as supernovas accelerate cosmic rays up to energies of 1,000 trillion electron volts (PeV). That's 10 million times the energy of medical proton beams used to treat cancer. ISS-CREAM data will allow scientists to examine how sources other than supernova remnants contribute to the population of cosmic rays.

Protons are the most common cosmic ray particles, but electrons, helium nuclei and the nuclei of heavier elements make up a small percentage. All are direct samples of matter from interstellar space. But because the particles are electrically charged, they interact with galactic magnetic fields, causing them to wander in their journey to Earth. This scrambles their paths and makes it impossible to trace cosmic ray particles back to their sources.

"An additional challenge is that the flux of particles striking any detector decreases steadily with higher energies," said ISS-CREAM co-investigator Jason Link, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So to better explore higher energies, we either need a much bigger detector or much more observing time. Operating on the space station provides us with this extra time."

Large ground-based systems study cosmic rays at energies greater than 1 PeV by making Earth's atmosphere the detector. When a cosmic ray strikes the nucleus of a gas molecule in the atmosphere, both explode in a shower of subatomic shrapnel that triggers a wider cascade of particle collisions. Some of these secondary particles reach detectors on the ground, providing information scientists can use to infer the properties of the original cosmic ray.

These secondaries also produce an interfering background that limited the effectiveness of CREAM's balloon operations. Removing that background is another advantage of relocating to orbit.

With decreasing numbers of particles at increasing energies, the cosmic ray spectrum vaguely resembles the profile of a human leg. At PeV energies, this decline abruptly steepens, forming a detail scientists call the "knee." ISS-CREAM is the first space mission capable of measuring the low flux of cosmic rays at energies approaching the knee.

"The origin of the knee and other features remain longstanding mysteries," Seo said. "Many scenarios have been proposed to explain them, but we don't know which is correct."

Astronomers don't think supernova remnants are capable of powering cosmic rays beyond the PeV range, so the knee may be shaped in part by the drop-off of their cosmic rays in this region.

"High-energy cosmic rays carry a great deal of information about our interstellar neighborhood and our galaxy, but we haven't been able to read these messages very clearly," said co-investigator John Mitchell at Goddard. "ISS-CREAM represents one significant step in this direction."

ISS-CREAM detects cosmic ray particles when they slam into the matter making up its instruments. First, a silicon charge detector measures the electrical charge of incoming particles, then layers of carbon provide targets that encourage impacts, producing cascades of particles that stream into electrical and optical detectors below while a calorimeter determines their energy. Two scintillator-based detector systems provide the ability to discern between singly charged electrons and protons. All told, ISS-CREAM can distinguish electrons, protons and atomic nuclei as massive as iron as they crash through the instruments.

ISS-CREAM will join two other cosmic ray experiments already working on the space station. The Alpha Magnetic Spectrometer (AMS-02), led by an international collaboration sponsored by the U.S. Department of Energy, is mapping cosmic rays up to a trillion electron volts, and the Japan-led Calorimetric Electron Telescope (CALET), also located on the Kibo Exposed Facility, is dedicated to studying cosmic ray electrons.

Overall management of ISS-CREAM and integration for its space station application was provided by NASA’s Wallops Flight Facility on Virginia’s Eastern Shore. ISS-CREAM was developed as part of an international collaboration led by the University of Maryland at College Park, which includes teams from NASA Goddard, Penn State University in University Park, Pennsylvania, and Northern Kentucky University in Highland Heights, as well as collaborating institutions in the Republic of Korea, Mexico and France.

By Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

News Article Type: Homepage ArticlesPublished: Friday, August 11, 2017 - 15:17

Cassini is on its final five full orbits of Saturn, getting close enough to directly "taste" its gases.

No large population of unbound or wide-orbit Jupiter-mass planets

Nature 548, 7666 (2017). doi:10.1038/nature23276

Authors: Przemek Mróz, Andrzej Udalski, Jan Skowron, Radosław Poleski, Szymon Kozłowski, Michał K. Szymański, Igor Soszyński, Łukasz Wyrzykowski, Paweł Pietrukowicz, Krzysztof Ulaczyk, Dorota Skowron & Michał Pawlak

Planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes. Unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form. A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions as well as wide-field surveys, but these studies are incomplete for objects below five Jupiter masses. Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis of 474 microlensing events found an excess of ten very short events (1–2 days)—more than known stellar populations would suggest—indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet-formation theories and surveys of young clusters. Here we analyse a sample of microlensing events six times larger than that of ref. 11 discovered during the years 2010–15. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1–2 days) microlensing events, we found no excess of events with timescales in this range, with a 95 per cent upper limit on the frequency of Jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than half a day), which may indicate the existence of Earth-mass and super-Earth-mass free-floating planets, as predicted by planet-formation theories.

Turning point: Galactic groundbreaker

Nature 548, 7666 (2017). doi:10.1038/nj7666-251a

Author: Virginia Gewin

Brazilian astrophysicist bridges fields to gain cosmological insights.

Citizen scientists chase total solar eclipse

Nature 548, 7666 (2017). http://www.nature.com/doifinder/10.1038/nature.2017.22415

Author: Rachael Lallensack

Non-scientists are being recruited to collect data on everything from the Sun’s outer atmosphere to animal behaviour.

Mysteries of Sun's corona on view during upcoming eclipse

Nature 548, 7666 (2017). http://www.nature.com/doifinder/10.1038/548146a

Author: Alexandra Witze

From ground, sky and space, researchers are ready to test latest technologies on the Great American Eclipse.

Cosmic map reveals a not-so-lumpy Universe

Nature 548, 7666 (2017). http://www.nature.com/doifinder/10.1038/nature.2017.22413

Author: Davide Castelvecchi

Odd results could still be consistent with the ‘standard model’ of cosmology.

Lunar rock shows the moon’s magnetic field lasted a billion years longer than we thought, which may help us understand how planets keep their protective fields

The moon has bright coils of dust we can’t study without getting up close. A NASA proposal would send two satellites tied together to dangle over the surface