Pulsars, being even more massive than the Sun, are very dense neutron stars that are the size of a city. Like lighthouses for the universe, emit radio to gamma-ray waves when they rotate up to hundreds of times per second. This year has been quite busy for pulsar research at ICREA.

We found the most energetic pulsed photons from a pulsar to date, at TeV energies, and produced the most precise measurement of a pulsar nebula along several orders of magnitude in energy, with the MAGIC telescopes. We worked on detailed theoretical models for the latter emission. We witnessed the first pulsar discovered in another galaxy, as well as orbitally recurrent flaring in a pulsar binary, with Fermi-LAT. Transitional pulsars (which we discovered in 2013) are gamma-ray sources depending on the state they live, and we developed a propeller model that explains how.

In a series of five theoretical papers published in Monthly Notices of the Royal Astronomical Society this year, we examined synchro-curvature radiation as a mechanism for gamma-ray emission in pulsars. We found that a relatively simple model can reproduce the spectra of practically all gamma-ray pulsars detected by the Fermi-LAT satellite, and that significant correlations arise for the model parameters that can be used to predict the gamma-ray brightness. Fig. 1 below is the main result of this research.

Magnetars, among pulsars, usually possess very powerful magnetic fields. In 2013, we announced the discovery of a magnetar exceptionally close to the supermassive black hole at the center of the Galaxy. At a distance of 0.3 light years, this magnetar is by far the closest neutron star to a supermassive black hole ever discovered and is likely in its gravitational grip, see Fig. 2. We monitored the magnetar with X-ray satellites since, and this year we revealed that its brightness is dropping more slowly than any other previously observed, and its surface is hotter than expected. We considered starquakes and the bombardment of the surface of the magnetar by charged particles trapped in twisted bundles of magnetic fields above the surface as a way to provide heating, but the mystery still persists.

This commentary was written as an advice to the negotations for a climate agreement at the COP21 climate summit in Paris (30 November - 13 December 2015). It raised attention for a neglected issue, namely carbon rebound of climate strategies in the absence of an adequate climate treaty. Energy rebound denotes that saving energy through technological improvements or behavioral changes triggers indirect, additional energy use. Various mechanisms contribute to this: e.g., improvements in energy efficiency make associated energy services cheaper which increases their consumption; saving energy means often saving money which is then spent on other energy-using goods or services; and more energy-efficient technologies diffuse easily to new types of uses or sectors.

Unilateral national climate policies are not strict enough to control carbon rebound — a side effect of some energy conservation strategies that undercuts net carbon savings. I suggest that a global agreement on variable carbon pricing at the forthcoming climate summit in Paris would reap considerable rebound-related benefits.

Economy-wide studies indicate that overall carbon rebound is at least 50%, depending on the country (J. Dimitropoulos Energy Policy 35, 6354–6363; 2007). Despite this, the effects of rebound have been largely ignored by the Intergovernmental Panel on Climate Change and at United Nations climate meetings.

Technical standards do not control rebound effectively: they cover only a small subset of products. For example, when the European Union began phasing out incandescent light bulbs in 2009, light-emitting diodes became so widespread that any energy savings were reduced.

The most effective way to discourage rebound is through carbon pricing, a policy that underpins all potential energy saving decisions. Any rebound tendency would elicit a higher carbon price under a cap-and-trade permit scheme. A carbon tax would require frequent adjustment to achieve the same outcome. This would be difficult politically, especially in the form of nationally distinct taxes.