Biochemical and structural elucidation of the L-carnitine degradation pathway of the human pathogen .

is an opportunistic human pathogen which can use host-derived L-carnitine as sole carbon and energy source. Recently, an L-carnitine transporter (Aci1347) and a specific monooxygense (CntA/CntB) for the intracellular cleavage of L-carnitine have been characterized. Subsequent conversion of the resulting malic semialdehyde into the central metabolite L-malate was hypothesized.

Gravitational Waves from a Core g Mode in Supernovae as Probes of the High-Density Equation of State.

Using relativistic supernova simulations of massive progenitor stars with a quark-hadron equation of state (EOS) and a purely hadronic EOS, we identify a distinctive feature in the gravitational-wave signal that originates from a buoyancy-driven mode (g mode) below the proto-neutron star convection zone. The mode frequency lies in the range 200≲f≲800  Hz and decreases with time. As the mode lives in the core of the proto-neutron star, its frequency and power are highly sensitive to the EOS, in particular the sound speed around twice saturation density.

A metal-poor star with abundances from a pair-instability supernova.

The most massive and shortest-lived stars dominate the chemical evolution of the pre-galactic era. On the basis of numerical simulations, it has long been speculated that the mass of such first-generation stars was up to several hundred solar masses. The very massive first-generation stars with a mass range from 140 to 260 solar masses are predicted to enrich the early interstellar medium through pair-instability supernovae (PISNe).

Measurement of F(p, γ)Ne reaction suggests CNO breakout in first stars.

Proposed mechanisms for the production of calcium in the first stars (population III stars)-primordial stars that formed out of the matter of the Big Bang-are at odds with observations. Advanced nuclear burning and supernovae were thought to be the dominant source of the calcium production seen in all stars. Here we suggest a qualitatively different path to calcium production through breakout from the 'warm' carbon-nitrogen-oxygen (CNO) cycle through a direct experimental measurement of the F(p, γ)Ne breakout reaction down to a very low energy point of 186 kiloelectronvolts, reporting a key resonance at 225 kiloelectronvolts.

A wide star-black-hole binary system from radial-velocity measurements.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries.

Evidence from stable isotopes and Be for solar system formation triggered by a low-mass supernova.

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event.

Early solar system. Stellar origin of the ¹⁸²Hf cosmochronometer and the presolar history of solar system matter.

Among the short-lived radioactive nuclei inferred to be present in the early solar system via meteoritic analyses, there are several heavier than iron whose stellar origin has been poorly understood. In particular, the abundances inferred for (182)Hf (half-life = 8.9 million years) and (129)I (half-life = 15.

Effective helium burning rates and the production of the neutrino nuclei.

Effective values for the key helium burning reaction rates, triple-α and (12)C(α, γ)(16)O, are obtained by adjusting their strengths so as to obtain the best match with the solar abundance pattern of isotopes uniquely or predominately made in core-collapse supernovae. These effective rates are then used to determine the production of the neutrino isotopes. The use of effective rates considerably reduces the uncertainties in the production factors arising from uncertainties in the helium burning rates, and improves our ability to use the production of B11 to constrain the neutrino emission from supernovae.

New primary mechanisms for the synthesis of rare 9Be in early supernovae.

We present two new primary mechanisms for the synthesis of the rare nucleus (9)Be, both triggered by ν-induced production of (3)H followed by (4)He((3)H,γ)(7)Li in the He shells of core-collapse supernovae. For progenitors of ∼ 8M(⊙), (7)Li((3)H,n(0))(9)Be occurs during the rapid expansion of the shocked He shell. Alternatively, for ultra-metal-poor progenitors of ∼ 11-15 M(⊙), (7)Li(n,γ)(8)Li(n,γ)(9)Li(e(-)ν(e))(9)Be occurs with neutrons produced by (4)He(ν(e),e(+)n)(3)H, assuming a hard effective ν(e) spectrum from oscillations (which also leads to heavy element production through rapid neutron capture) and a weak explosion (so the (9)Be survives shock passage).

11B and constraints on neutrino oscillations and spectra from neutrino nucleosynthesis.

We study the sensitivity to variations in the triple-alpha and 12C(α,γ)16O reaction rates, of the yield of the neutrino-process isotopes 7Li, 11B, 19F, 138La, and 180Ta in core-collapse supernovae. Compared to solar abundances, less than 15% of 7Li, about 25%-80% of 19F, and about half of 138La is produced in these stars. Over a range of ±2σ for each helium-burning rate, 11B is overproduced and the yield varies by an amount larger than the variation caused by the effects of neutrino oscillations.

Pulsational pair instability as an explanation for the most luminous supernovae.

The extremely luminous supernova SN 2006gy (ref. 1) challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron-positron pairs.