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"Sim, Stuart"
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Spherical symmetry in the kilonova AT2017gfo/GW170817
The mergers of neutron stars expel a heavy-element enriched fireball that can be observed as a kilonova
1
–
4
. The kilonova’s geometry is a key diagnostic of the merger and is dictated by the properties of ultra-dense matter and the energetics of the collapse to a black hole. Current hydrodynamical merger models typically show aspherical ejecta
5
–
7
. Previously, Sr
+
was identified in the spectrum
8
of the only well-studied kilonova
9
–
11
AT2017gfo
12
, associated with the gravitational wave event GW170817. Here we combine the strong Sr
+
P Cygni absorption-emission spectral feature and the blackbody nature of kilonova spectrum to determine that the kilonova is highly spherical at early epochs. Line shape analysis combined with the known inclination angle of the source
13
also show the same sphericity independently. We conclude that energy injection by radioactive decay is insufficient to make the ejecta spherical. A magnetar wind or jet from the black-hole disk could inject enough energy to induce a more spherical distribution in the overall ejecta; however, an additional process seems necessary to make the element distribution uniform.
Spectra taken after the kilonova associated with GW170817 show a high degree of spherical symmetry and a line shape is found that is consistent with a completely spherical expansion to within a few per cent.
Journal Article
Post-truth, scepticism & power
This book examines the concept of post-truth and the impact it is having on contemporary life, bringing out both its philosophical and political dimensions. Post-truth is contextualised within the philosophical discourse of truth, with particular reference to theories of scepticism and relativism, to explore whether it can take advantage of these to claim any intellectual credibility. Sim argues that post-truth cannot be defended on either sceptical or relativistic grounds ? even those provided by recent iconoclastic philosophical movements such as poststructuralism and postmodernism. The affinity between post-truth and conspiracy theory is emphasised, and the extent to which post-truth plays a role in religious doctrine is also considered. Post-truth is seen to constitute a threat to liberal democratic ideals and our Enlightenment heritage, raising the question of whether we are moving into a post-liberal age where the far right would hold power. To prevent this, post-truth urgently needs to be countered.
Book
Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs with mass ∼0.9M
Supernovae true to type
Type Ia supernovae are potentially invaluable as cosmological distance indicators, but if they are to provide a reliable measure of the expansion history of the Universe and nature of dark energy, more evidence that they are a largely homogeneous population will be required. A subclass of type Ia supernova, the 'sub-luminous 1991bg-like' objects, has proved problematic, as current models fail to predict their formation from the presumed supernova precursors, white dwarf stars. It had long been speculated that mergers of two white dwarfs should trigger such events, and now a new set of numerical simulations adds support to this idea. A merger of two equal-mass white dwarfs leads to a sub-luminous explosion if a single common-envelope phase is involved, and if the component stars are each about 0.9 solar masses in size.
Existing models of type Ia supernovae generally explain their observed properties, with the exception of the sub-luminous 1991bg-like supernovae. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event, but simulations so far have failed to produce an explosion. Here, a simulation of the merger of two equal-mass white dwarfs is presented that leads to a sub-luminous explosion; it requires a single common-envelope phase and component masses of about 0.9 solar masses.
Type Ia supernovae are thought to result from thermonuclear explosions of carbon–oxygen white dwarf stars
1
. Existing models
2
generally explain the observed properties, with the exception of the sub-luminous 1991bg-like supernovae
3
. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event
4
,
5
, but hitherto simulations have failed to produce an explosion
6
,
7
. Here we report a simulation of the merger of two equal-mass white dwarfs that leads to a sub-luminous explosion, although at the expense of requiring a single common-envelope phase, and component masses of ∼0.9
M
⊙
. The light curve is too broad, but the synthesized spectra, red colour and low expansion velocities are all close to what is observed for sub-luminous 1991bg-like events. Although the mass ratios can be slightly less than one and still produce a sub-luminous event, the masses have to be in the range 0.83
M
⊙
to 0.9
M
⊙
.
Journal Article
Introducing critical theory
The last few decades have seen an explosion in the production of critical theories, with deconstructionists, poststructuralists, postmodernists, second-wave feminists, new historicists, cultural materialists, postcolonialists, black critics and queer theorists, among a host of others, all vying for our attention. The world around us can look very different on the critical theory applied to it. This vast range of interpretations can leave one feeling confused and frustrated. This book provides a route through the tangled jungle of competing theories.
Book
Models for Type Ia Supernovae and Related Astrophysical Transients
We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we comment on some of the successes and shortcoming of these scenarios and highlight important outstanding issues.
Journal Article
Manifesto for silence
Silence has played a crucial role in human history in important areas of our existence such as religion and the arts. Yet we live in an increasingly noisy society in which silence is under perpetual assault from the 24/7 lifestyle. The business world cynically exploits noise as part of its marketing strategy; the military deploys noise as a weapon. Without question, noise is a political issue on a global scale.
eBook
Empires of belief
Is absolute belief making a comeback? Recently the public has accepted unquestioningly certain political, economic, and scientific theories, and for sceptical people, this is a deeply worrying trend. Stuart Sim outlines the history of scepticism in both Western and Islamic traditions from the Enlightenment to today. He argues that we need less belief and more doubt-an engaged scepticism that replaces dogmatism. Addressing contemporary debates surrounding terrorism and fundamentalism, Sims suggests that scepticism can play a greater role in public and political life.
eBook
The eighteenth-century novel and contemporary social issues
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This study introduces readers to the eighteenth-century novel through a consideration of contemporary social issues. Eighteenth-century authors grappled with very similar problems to the ones we face today such as: what motivates a fundamentalist terrorist? What are the justifiable limits of state power? What dangers lie in wait for us when we create life artificially?
The book discusses key authors from Aphra Behn in the late seventeenth century to James Hogg in the 1820s, covering the 'long' eighteenth century. It guides readers through the main genres of the period from Realism, Gothic romance and historical romance to proto-science fiction. It also introduces a range of debates around race relations, anti-social behaviour, family values and born-again theology as well as the power of the media, surveillance, political sovereignty and fundamentalist terrorism. Each novel is shown to be directly relevant to some of the most urgent moral issues of our own time.
Key Features
Relates the novels of the eighteenth century to current social and political debatesAccessibly and engagingly written for non-specialistsCovers the key authors and texts of the period including Robinson Crusoe, Gulliver's Travels, Pamela, Northanger Abbey, Tristram Shandy and Frankenstein
eBook