Related papers: Cometary outbursts in the Oort cloud
We consider $\gamma$-ray emission from heavy nuclei that are accelerated in the shocks of stellar winds and are excited in interactions with the ambient matter in the Orion complex. We show that the recent detection of $\gamma$-ray lines in…
Recent observations have detected molecular outflows in a few nearby starburst nuclei. We discuss the physical processes at work in such an environment in order to outline a scenario that can explain the observed parameters of the…
This text was originally written to accompany a series of lectures that I gave at the `35th Saas-Fee advanced course' in Switzerland and at the Institute for Astronomy of the University of Hawaii. It reviews my current understanding of the…
Odd radio circles (ORCs) are mysterious rings of faint, diffuse emission recently discovered in radio surveys, some of which may be associated with galaxies in relatively dense environments. We propose such ORCs to be synchrotron emission…
Hot temperature minerals have been detected in a large number of comets and were also identified in the samples of Comet Wild 2 that were returned by the Stardust mission. Meanwhile, observations of the distribution of hot minerals in young…
Recent satellite data have revealed a surprising correlation between galactic cosmic ray (GCR) intensity and the fraction of the Earth covered by clouds. If this correlation were to be established by a causal mechanism, it could provide a…
The first radio surveys of the sky discovered that some large clusters of galaxies contained powerful sources of synchrotron emission. Optical images showed that long linear filaments with bizarre emission-line spectra permeated the…
The Sun was born in a clustered environment with 10,000 other stars. Being an isolated star today, the Sun must have left the nest. We do not directly know when that happened, how violent the ejection was, or how far the Solar siblings have…
Dust jets, i.e. fuzzy collimated streams of cometary material arising from the nucleus, have been observed in-situ on all comets since the Giotto mission flew by comet 1P/Halley in 1986. Yet their formation mechanism remains unknown.…
Exocomets scattered by planets have been invoked to explain observations in multiple contexts, including the frequently found near- and mid-infrared excess around nearby stars arising from exozodiacal dust. Here we investigate how the…
The primary radiation generated in the central continuum-forming region of Active Galactic Nuclei can be reprocessed by very dense, small-scale clouds that are optically-thin to Thomson scattering. In spite of the extreme conditions…
The chemical influence of luminosity outbursts on the environments of young solar-type stars is explored. Species are categorised into several types according to their response to the outburst. The first and second types imply chemical…
The BN/KL region in the Orion molecular cloud is an archetype in the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars, but it is difficult to study because of overlying…
Planets in close orbits around their host stars are subject to strong irradiation. High-energy irradiation, originating from the stellar corona and chromosphere, is mainly responsible for the evaporation of exoplanetary atmospheres. We have…
The radiative cooling timescales at the centers of hot atmospheres surrounding elliptical galaxies, groups, and clusters are much shorter than their ages. Therefore, hot atmospheres are expected to cool and to form stars. Cold gas and star…
To date, at least three comets -- 2I/Borisov, C/2016 R2 (PanSTARRS), and C/2009 P1 (Garradd) -- have been observed to have unusually high CO concentrations compared to water. We attempt to explain these observations by modeling the effect…
We have investigated the effect of stellar encounters on the formation and disruption of the Oort cloud using the classical impulse approximation. We calculate the evolution of a planetesimal disk into a spherical Oort cloud due to the…
We used the Very Large Array to carry out a multi-epoch radio continuum monitoring of the Orion Nebula Cluster and Orion Molecular Cloud. Our observations reveal the presence of 19 sources. With the exception of the sources BN and C the…
Anisotropic outgassing from comets exerts a torque sufficient to rapidly change the angular momentum of the nucleus, potentially leading to rotational instability. Here, we use empirical measures of spin changes in a sample of comets to…
Comets are believed to be born in the outer Solar System where the temperature is assumed to have never exceeded T ~ 100 K. Surprisingly, observations and samples of cometary dust particles returned to Earth showed that they are in fact…