Institute of Astronomy

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The diversity of quasars unified by accretion and orientation

Astronomy News - 10 September 2014 - 1:00am

The diversity of quasars unified by accretion and orientation

Nature 513, 7517 (2014). doi:10.1038/nature13712

Authors: Yue Shen & Luis C. Ho

Quasars are rapidly accreting supermassive black holes at the centres of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine. These properties, however, are not random, but form well-defined trends. The dominant trend is known as ‘Eigenvector 1’, in which many properties correlate with the strength of optical iron and [O iii] emission. The main physical driver of Eigenvector 1 has long been suspected to be the quasar luminosity normalized by the mass of the hole (the ‘Eddington ratio’), which is an important parameter of the black hole accretion process. But a definitive proof has been missing. Here we report an analysis of archival data that reveals that the Eddington ratio indeed drives Eigenvector 1. We also find that orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a flattened, disk-like geometry for the fast-moving clouds close to the black hole. Our results show that most of the diversity of quasar phenomenology can be unified using two simple quantities: Eddington ratio and orientation.

Astrophysics: Quasar complexity simplified

Astronomy News - 10 September 2014 - 1:00am

Astrophysics: Quasar complexity simplified

Nature 513, 7517 (2014). doi:10.1038/513181a

Authors: Michael S. Brotherton

An analysis of a sample comprising some 20,000 mass-accreting supermassive black holes, known as quasars, shows that most of the diverse properties of these cosmic beacons are explained by only two quantities. See Letter p.210

Hubble Finds Companion Star Hidden for 21 Years in a Supernova's Glare

Astronomy News - 9 September 2014 - 6:00pm

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For over two decades astronomers have been patiently monitoring the fading glow of a supernova in a nearby galaxy. They've been looking for a suspected companion star that pulled off almost all of the hydrogen from the doomed star that exploded. At last Hubble's ultraviolet-light sensitivity pulled out the blue glow of the star from the cluttered starlight in the disk of the galaxy. This observation confirms the theory that the supernova originated in a double-star system where one star fueled the mass-loss from the aging primary star. The surviving star's brightness and estimated mass provide insight into the conditions that preceded the 1993 explosion.

Hubble Finds Supernova Companion Star after Two Decades of Searching

Astronomy News - 9 September 2014 - 5:00pm
Using NASA’s Hubble Space Telescope, astronomers have discovered a companion star to a rare type of supernova.

No easy parking spot for first-ever comet landing

Astronomy News - 9 September 2014 - 4:25pm
High-res images from the European Space Agency's Rosetta spacecraft show its target comet is covered in cliffs – great for science but scary for landing






Scientists Find Evidence of ‘Diving’ Tectonic Plates on Jupiter’s Moon Europa

Astronomy News - 8 September 2014 - 5:00pm
Scientists have found evidence of plate tectonics on Jupiter’s moon Europa. This indicates the first sign of this type of surface-shifting geological activity on a world other than Earth.

Europa's icy plate tectonics may support life

Astronomy News - 8 September 2014 - 1:18pm
Jupiter's moon Europa may be the first world other than Earth to sport plate tectonics, only above its ocean instead of below






AUDIO: Meteorite strikes Nicaragua

Astronomy News - 8 September 2014 - 12:15pm
A meteorite that landed near the Nicaraguan capital Managua on Sunday could have come from the 2014 RC asteroid which was passing the earth at the time, experts have said.

Meteorite lands in Nicaragua capital

Astronomy News - 8 September 2014 - 10:19am
A small meteorite which may have broken off an asteroid caused a 12m-wide crater near Managua's international airport, Nicaraguan officials say.

Plate tectonics found on Europa

Astronomy News - 7 September 2014 - 1:00am

Plate tectonics found on Europa

Nature 513, 7517 (2014). http://www.nature.com/doifinder/10.1038/513153a

Author: Alexandra Witze

Discovery buoys bid for mission to Jovian moon.

Rosetta Comet is Darker than Charcoal

Astronomy News - 5 September 2014 - 8:48pm
A NASA instrument onboard Europe's Rosetta spacecraft has shown that the core of Comet 67P/Churyumov-Gerasimenko is unusually dark--darker than charcoal-black--when viewed at ultraviolet wavelengths.

Small Asteroid to Safely Pass Close … to Earth Sunday

Astronomy News - 5 September 2014 - 8:11am
A small asteroid, designated 2014 RC, will safely pass very close to Earth on Sunday, Sept. 7, 2014. At the time of closest approach, based on current calculations to be about 2:18 p.m. EDT (11:18 a.m. PDT / 18:18 UTC), the asteroid will be roughly over New Zealand.

NASA Instrument aboard European Spacecraft Returns First Science Results

Astronomy News - 4 September 2014 - 5:00pm
A NASA instrument aboard the European Space Agency’s (ESA's) Rosetta orbiter has successfully made its first delivery of science data from comet 67P/Churyumov-Gerasimenko.

Chameleons and holograms: Dark energy hunt gets weird

Astronomy News - 3 September 2014 - 6:00pm
Three ingenious experiments are duking it out to solve the mystery of whether dark energy exists and how it might be accelerating the universe's growth






Cosmic Forecast: Dark Clouds Will Give Way to Sunshine

Astronomy News - 3 September 2014 - 11:00am
Lupus 4, a spider-shaped blob of gas and dust, blots out background stars like a dark cloud on a moonless night in this intriguing new image. Although gloomy for now, dense pockets of material within clouds such as Lupus 4 are where new stars form and where they will later burst into radiant life. The Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile captured this new picture.

Heavenly homes

Astronomy News - 3 September 2014 - 1:00am

Heavenly homes

Nature 513, 7516 (2014). doi:10.1038/513006a

The discovery of our Galaxy’s place in the Universe adds detail to our address.

Cosmology: Meet the Laniakea supercluster

Astronomy News - 3 September 2014 - 1:00am

Cosmology: Meet the Laniakea supercluster

Nature 513, 7516 (2014). doi:10.1038/513041a

Authors: Elmo Tempel

An analysis of a three-dimensional map of galaxies and their velocities reveals the hitherto unknown edges of the large system of galaxies in which we live — dubbed the Laniakea supercluster. See Letter p.71

The Laniakea supercluster of galaxies

Astronomy News - 3 September 2014 - 1:00am

The Laniakea supercluster of galaxies

Nature 513, 7516 (2014). doi:10.1038/nature13674

Authors: R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède

Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called ‘superclusters’, although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter. Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as water does at watershed divides, and we trace the surface of divergent points that surrounds us. Within the volume enclosed by this surface, the motions of galaxies are inward after removal of the mean cosmic expansion and long range flows. We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea.

Rosetta set for 'capture' manoeuvres

Astronomy News - 2 September 2014 - 6:38pm
The Rosetta probe is about to begin the manoeuvres that will take it properly into orbit around Comet 67P/Churyumov-Gerasimenko.