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"Fabian, A C"
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Darwin
\"Charles Darwin can easily be considered one of the most influential scholars of his time. His thoughts, ideas, research and writings have had a far reaching impact and influence on modern thought in the arts, on society, and in science. With contributions from leading scholars, this collection of essays explores how Darwin's work grew out of the ideas of his time, and how its influence spread to contemporary thinking about creationism, the limits of human evolution and the diversification of living species and their conservation. A full account of the legacy of Darwin in contemporary scholarship and thought. With contributions from Janet Browne, Jim Secord, Rebecca Stott, Paul Seabright, Steve Jones, Sean Carroll, Craig Moritz and John Dupre;. This book derives from a highly successful series of public lectures, revised and illustrated for publication under the editorship of Professor William Brown and Professor Andrew Fabian of the University of Cambridge\"-- Provided by publisher.
BOOK
The Corona Contracts in a Black-Hole Transient
The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months1–3. When a black hole emerges from quiescence (that is, it ‘turns on’ after accreting material from its companion) it has a very hard (high-energy) X-ray spectrum produced by a hot corona4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk8,9 or by a reduction in the spatial extent of the corona10,11. Observations of X-ray reverberation lags in supermassive black-hole systems12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole14,15. Observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger16, leading to the suggestion that the accretion disk in the hard-X-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+07019,20. We find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. The timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron K emission line remains remarkably constant. This suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk.
Journal Article
Life
\"Life is a compelling addition to the Darwin College Lecture Series, in which eight distinguished authors each present an essay from their area of expertise devoted to the theme of 'life'. The book forges connections between art, science and the humanities in a vibrant and thought-provoking collection that exposes both conventional and unconventional views on the meaning of life, the enigmatic boundaries between the living and the dead, and what may or may not follow afterwards. This collection arises from the Darwin College Lecture Series of 2012 and includes contributions from eight distinguished scholars, all of whom are held in esteem not only for their research, but also for their ability to communicate their subject to popular audiences\"-- Provided by publisher.
Book
Star formation inside a galactic outflow
Star formation at a rate of more than 15 solar masses a year has been observed inside a massive outflow of gas from a nearby galaxy; this could also be happening inside other galactic outflows.
Star birth in gas flows
Massive, galactic-scale outflows of molecular gas with the physical conditions necessary to form stars have recently been observed and several models predict that star formation could ignite within the outflow itself. Roberto Maiolino
et al
. report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448 and at an inferred rate exceeding 15 times the mass of the Sun per year. This new mode of star formation might be occurring in other galactic outflows and could have implications for the morphological evolution of galaxies, while contributing to the population of high-velocity stars.
Recent observations have revealed massive galactic molecular outflows
1
,
2
,
3
that may have the physical conditions (high gas densities
4
,
5
,
6
) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself
7
,
8
,
9
,
10
,
11
. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies
12
, to the evolution in size and velocity dispersion of the spheroidal component of galaxies
11
,
13
, and would contribute to the population of high-velocity stars, which could even escape the galaxy
13
. Such star formation could provide
in situ
chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies
9
. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics
14
,
15
.
Journal Article
Broad line emission from iron K- and L-shell transitions in the active galaxy 1H 0707-495
L-line route to black holes
The emission line arising from a transition of an electron from the iron K shell to the ground state (the K line) is prominent in the reflection spectrum of the hard X-ray continuum irradiating dense accreting matter around a black hole. The corresponding iron L-line emission should be detectable when iron abundance is high. That's the theory, and now broad iron L-line emission has been observed, together with the broad K line in the narrow-line Seyfert galaxy 1H0707. There is a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the hole, a timescale comparable to the light-crossing time of the innermost radii around a supermassive black hole. This discovery opens a window on events close to the black hole event horizon in these objects.
Emission arising from a transition of an electron from the iron K shell to the ground state (the K line) is prominent in the reflection spectrum created by the hard X-ray continuum irradiating the dense accreting matter around a black hole. Here the presence of both iron K and L emission is reported in the spectrum of the active galaxy 1H 0707-495. There is a 'reverberation lag' with a timescale comparable to the light-crossing time of the innermost radii around a supermassive black hole.
Since the 1995 discovery of the broad iron K-line emission from the Seyfert galaxy MCG–6-30-15 (ref.
1
), broad iron K lines have been found in emission from several other Seyfert galaxies
2
, from accreting stellar-mass black holes
3
and even from accreting neutron stars
4
. The iron K line is prominent in the reflection spectrum
5
,
6
created by the hard-X-ray continuum irradiating dense accreting matter. Relativistic distortion
7
of the line makes it sensitive to the strong gravity and spin of the black hole
8
. The accompanying iron L-line emission should be detectable when the iron abundance is high. Here we report the presence of both iron K and iron L emission in the spectrum of the narrow-line Seyfert 1 galaxy
9
1H 0707-495. The bright iron L emission has enabled us to detect a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the black hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light minute, from the event horizon of a rapidly spinning, massive black hole.
Journal Article
BASS XXXVII: The Role of Radiative Feedback in the Growth and Obscuration Properties of Nearby Supermassive Black Holes
We study the relation between obscuration and supermassive black hole (SMBH) accretion using a large sample of hard X-ray selected active galactic nuclei (AGNs). We find a strong decrease in the fraction of obscured sources above the Eddington limit for dusty gas ( logλEdd≳−2 ) confirming earlier results, and consistent with the radiation-regulated unification model. This also explains the difference in the Eddington ratio distribution functions (ERDFs) of type 1 and type 2 AGNs obtained by a recent study. The break in the ERDF of nearby AGNs is at logλEdd*=−1.34±0.07 . This corresponds to the λ Edd where AGNs transition from having most of their sky covered by obscuring material to being mostly devoid of absorbing material. A similar trend is observed for the luminosity function, which implies that most of the SMBH growth in the local universe happens when the AGN is covered by a large reservoir of gas and dust. These results could be explained with a radiation-regulated growth model, in which AGNs move in the N H–λ Edd plane during their life cycle. The growth episode starts with the AGN mostly unobscured and accreting at low λ Edd. As the SMBH is further fueled, λ Edd, N H and the covering factor increase, leading the AGN to be preferentially observed as obscured. Once λ Edd reaches the Eddington limit for dusty gas, the covering factor and N H rapidly decrease, leading the AGN to be typically observed as unobscured. As the remaining fuel is depleted, the SMBH goes back into a quiescent phase.
Journal Article
Local crystallization inside the polymer electrolyte for lithium metal batteries observed by operando nanofocus WAXS
The development of next-generation lithium-based batteries is accompanied by the intention to suppress the formation of dendritic lithium on the electrode, and is dominated by the picture that dendrites start to grow at the electrodes. Shifting from liquid to solid-state electrolytes, a high transference number is a quantity that promises the restraint of such parasitic side reactions. In this study, nanofocus X-ray wide-angle scattering is used to detect possible lithium-based crystallites in the polymer-based electrolyte. We perform
operando
scanning nanofocus wide-angle X-ray scattering on a composite gel-type polymer consisting of poly(vinylidene fluoride-co-hexafluoropropylene) and the single-ion conducting polymer poly((trifluoromethane) sulfonimide lithium styrene) in a lithium symmetric cell. We observe the occurrence and kinetics of lithium carbonate crystallites inside the electrolyte over a depth of 16 µm during three half-cycles. Furthermore, we prove the existence of lithium hydroxide crystallites near the lithium electrode and their absence in the bulk. Importantly, we identify the growth of pure metallic lithium inside the electrolyte as a sign of lithium dendrite growth happening inside the polymer-based electrolyte and not at the electrodes. Thus, nanofocus wide-angle X-ray scattering visualizes local structure changes such as dendrite formation inside the polymer-based electrolyte despite an unchanged electrochemical performance.
Polymer electrolytes are promising candidates as separators in lithium metal batteries. Here, authors reveal the existence of local lithium-based crystallites inside the polymer electrolyte in a lithium symmetric cell. A combination of unique operando wide-angle X-ray scattering with a nano-sized beam and complementary spectroscopic techniques identifies these crystallites as lithium carbonate, lithium hydroxide, and even metallic lithium. It is shown that these crystallites lower the ionic conductivity and the transference number.
Journal Article
The role of black holes in galaxy formation and evolution
Galaxies and black holes
The massive black holes found at the centre of most galaxies, including our own, release prodigious amounts of energy that power spectacular phenomena such as quasars and active galactic nuclei. If just a tiny fraction of that energy were absorbed into the host galaxy it could stop star formation in its tracks by heating and ejecting the ambient gas. The latest of our 'IYA 2009' reviews, marking the International Year of Astronomy and collected together on
http://www.nature.com/astro09
, tackles one of the central questions in galaxy evolution — the degree to which black hole activity has limited star formation in large elliptical galaxies. These contain much less cool gas and fewer young stars than spiral galaxies, a contrast that could relate to how the central black hole interacts with its surroundings.
Virtually all massive galaxies host central black holes, the growth of which releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. However, a tiny fraction of this energy could halt star formation by heating and ejecting ambient gas; a central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies.
Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solar masses. The growth of these black holes releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejecting ambient gas. A central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies.
Journal Article
BASS. XLII. The Relation between the Covering Factor of Dusty Gas and the Eddington Ratio in Nearby Active Galactic Nuclei
Accreting supermassive black holes (SMBHs) located at the centers of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-ray. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z ≲ 0.1) hard X-ray (14–195 keV) selected nonblazar active galactic nuclei (AGN) and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings that showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density–Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs.
Journal Article
Magnetic support of the optical emission line filaments in NGC 1275
The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster, is surrounded by a well-known giant nebulosity of emission-line filaments
1
,
2
, which are plausibly in excess of 10
8
years old
3
. The filaments are dragged out from the centre of the galaxy by radio-emitting ‘bubbles’ rising buoyantly in the hot intracluster gas
4
, before later falling back. They act as markers of the feedback process by which energy is transferred from the central massive black hole to the surrounding gas. The mechanism by which the filaments are stabilized against tidal shear and dissipation into the surrounding extremely hot (4 × 10
7
K) gas has been unclear. Here we report observations that resolve thread-like structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc wide. We conclude that magnetic fields in the threads, in pressure balance with the surrounding gas, stabilize the filaments, so allowing a large mass of cold gas to accumulate and delay star formation.
Journal Article