P4_6 Orbiting a Black Hole

During the BBC's classic science fiction show Doctor Who, the Doctor and his assistant Rose land the TARDIS on a planet that is orbiting a black hole - an 'impossible situation' according to the Doctor. This paper calculates the minimum radius and required angular momentum of the closest stable circular orbit around a Schwarzschild black hole of comparable mass to the one at the centre of the Milky Way (named Sagittarius A*). The minimum radius is found to be 3.54x1010m while the angular momentum required to sustain this orbit is 2.04 x1010m2s-1kg-1

P4_7 Greatest Gravity

Earth is not of uniform density, but consists of many layers, causing acceleration due to free fall to be a non-linear function of radius. A model is constructed to evaluate at which radius the greatest gravitational acceleration is felt. This point was found to be at the meeting point of the lower mantle and the outer core, where the acceleration peaks at a = 10.8 ms-2

P4_5 The Relativistic Ionisation Speed Limit

The paper explores a possible speed limit to be enforced on relativistic vehicles so as to not expose pedestrians to ionising electromagnetic radiation; a result of Doppler shifted light from the vehicle’s headlights. A maximum speed limit of 2.89 × 108 ms-1, 0.96 times the speed of light, was established.Â

P4_1 Dead Sea Walking

The paper investigates the possibility of walking on the water of the Dead Sea under the assumption that salt can be added to the lake. The current salinity is not sufficient to enable a person to walk on the water. Theoretically, this feat would be achievable if the lake contained 9.71 × 1015 kg of salt. Practically, this amount of salt would not dissolve in the volume of water present in the Dead Sea

P4_2 Using the Forks: The Energy Yield of a Lightning Bolt

Lightning may be considered as a potential energy source if the yield is comparable to other renewable energy sources. The energy yield of one strike was evaluated to be 7.5×107 J, where approximately 50 strikes produce a yield equivalent to that of an average wind turbine in a year

P4_3 An Extra Minute

This paper presents a case study of a meteor impact which would result in the addition of one extra minute to the period of the Earth's spin. Initial conditions are set and the meteor mass needed to produce this effect is calculated to be 1.54x1019 kg. The effect of the collision on the period of the Earth's precession about the spin axis is also calculated and found to be 18 years shorter than the current 26000 year value

P4_8 The Solar Escapee

The paper investigates the circumstances in which a planet with an orbital radius of 1 AU from the Sun would escape the solar system due to the force supplied by the solar radiation pressure of the Sun. It is found that Earth, while fixing the mass, would require a radius above 3.06×1026 m before it would be ejected from the solar system. Alternatively a planet with the same density and orbit as Earth, but an unfixed mass, would require a radius below 2.76×10-7 m.Â

P4_4 The Solar Cell Efficiency of Superman

The paper investigates how efficiently Superman must absorb energy from the Sun's emission spectrum to be able to perform flight for 8 hours at a constant altitude. A solar cell efficiency of 656000% is calculated, which seemingly disobeys the law of conservation of energy assuming the model of Superman as a solar cell is reasonable

P4_9 Stealing Our Atmosphere

This paper investigates two scenarios; the first is the solar wind velocity required to compress Earth’s magnetopause to an altitude of 1500km and an unrealistic value of 1.6x108ms-1 is found. The second scenario is the time it would take the solar wind to erode all of the oxygen in the atmosphere if the Earth did not have a magnetic field and an approximate value of 1.97x109 years is calculated

Exploring the Angular Momentum -- Atomic Gas Content Connection with EAGLE and IllustrisTNG

We use the EAGLE (Evolution and Assembly of GaLaxies and their Environments) and IllustrisTNG (The Next Generation) cosmological simulations to investigate the properties of the baryonic specific angular momentum (j), baryonic mass (M) and atomic gas fraction ($f_{\rm{atm}}$) plane for nearby galaxies. We find EAGLE and TNG to be in excellent agreement with each other. These simulations are also consistent with the results obtained with xGASS (eXtended GALEX Arecibo SDSS Survey) for gas fractions greater than 0.01. This implies that the disagreements previously identified between xGASS and predictions from simple analytical disc stability arguments also holds true for EAGLE and TNG. For lower gas fraction (the regime currently unconstrained by observations), both simulations deviate from the plane but still maintain good agreement with each other. Despite the challenges posed by resolution limits at low gas fractions, our findings suggest a potential disconnect between angular momentum and gas fraction in the gas-poor regime, implying that not all gas-poor galaxies have low specific angular momentum.Comment: 12 pages, 10 figures. Accepted for publication in MNRA