THE SPINS-UK SEMINAR SERIES
The SPINS-UK seminar series is a monthly series of online talks about neutron star science. We hope that this will be a great tool to bring together the national neutron star community and to learn more about each other's activities, bringing to light new collaborations and discussions!
The seminars are held on Wednesdays, from 1-2pm UK time roughly every 4 weeks, with breaks in the summer and winter holiday seasons. The inaugural talk took place on Wednesday 10th February 2021.
For information on how to access the seminars online, please contact Lucy Oswald at lucy.oswald@physics.ox.ac.uk.
We are inviting nominations and self-nominations for future speakers for this series. If you would like to propose a speaker to present a talk to the SPINS-UK community, please contact Lucy Oswald.
The seminars are held on Wednesdays, from 1-2pm UK time roughly every 4 weeks, with breaks in the summer and winter holiday seasons. The inaugural talk took place on Wednesday 10th February 2021.
For information on how to access the seminars online, please contact Lucy Oswald at lucy.oswald@physics.ox.ac.uk.
We are inviting nominations and self-nominations for future speakers for this series. If you would like to propose a speaker to present a talk to the SPINS-UK community, please contact Lucy Oswald.
UPCOMING TALKS
The seminar series will return in the autumn.
PREVIOUS TALKS
Inaugural talk - Dr Sam Lander
Date: Wednesday 10th February 2021
Time: 1pm UK time
Speaker: Dr Sam Lander, Lecturer in Physics at UEA
Time: 1pm UK time
Speaker: Dr Sam Lander, Lecturer in Physics at UEA
The early life of a neutron star's magnetic field
Neutron stars host the strongest magnetic fields in the Universe, but we still do not have a clear picture of what makes them so strong, nor why the field strengths of young neutron stars vary over roughly four orders of magnitude. This talk will provide an overview of ideas about how dynamo processes might generate highly intense magnetic fields, discussing potential problems with different candidate mechanisms and asking whether any other physics could drive field amplification. After dynamo action has ceased, we present models for the kind of steady state to which the young star’s magnetic field might relax. We conclude by showing how the birth physics of neutron stars could be constrained through measurements of their magnetic inclination angles.
Neutron stars host the strongest magnetic fields in the Universe, but we still do not have a clear picture of what makes them so strong, nor why the field strengths of young neutron stars vary over roughly four orders of magnitude. This talk will provide an overview of ideas about how dynamo processes might generate highly intense magnetic fields, discussing potential problems with different candidate mechanisms and asking whether any other physics could drive field amplification. After dynamo action has ceased, we present models for the kind of steady state to which the young star’s magnetic field might relax. We conclude by showing how the birth physics of neutron stars could be constrained through measurements of their magnetic inclination angles.
Dr Andrei Igoshev
Date: Wednesday 10th March 2021
Time: 1pm UK time
Speaker: Dr Andrei Igoshev, Postdoctoral Fellow at the University of Leeds
Time: 1pm UK time
Speaker: Dr Andrei Igoshev, Postdoctoral Fellow at the University of Leeds
Sleeping beasts: magnetic fields shape observational manifestations of neutron stars
Neutron stars (NSs) are seen as radio pulsars, magnetars and central compact objects. Magnetars and central compact objects are bright, young NSs seen close to the centra of supernova remnants. Magnetars are extremely magnetised neutron stars which shows a variety of observational phenomena associated to their magnetic fields, such as burst and giant flashes. Both magnetars and central compact objects are much hotter than it is excepted even for very young neutron stars. We perform first three-dimensional simulations of the magneto-thermal evolution using a spectral MHD code. Our results show that presence of strong toroidal magnetic field in magnetars is necessary to explain their quiescent thermal emission, in particular a formation of a single hot spot. Using our thermal maps we are able to explain light curves of 10 out of 19 magnetars in quiescence.
In the case of the central compact objects, we test the configuration of magnetic field formed as a result of stochastic dynamo. Such a magnetic field consists of multiple randomly orientated loops of magnetic field. The global dipolar field slowly formed as a result of the Hall and Ohmic evolution. In our simulations we see 5-7% pulsed fraction, formation of a few compact hot regions and difference of two times in temperature between hot and cold regions typical for observations of the central compact objects.
Neutron stars (NSs) are seen as radio pulsars, magnetars and central compact objects. Magnetars and central compact objects are bright, young NSs seen close to the centra of supernova remnants. Magnetars are extremely magnetised neutron stars which shows a variety of observational phenomena associated to their magnetic fields, such as burst and giant flashes. Both magnetars and central compact objects are much hotter than it is excepted even for very young neutron stars. We perform first three-dimensional simulations of the magneto-thermal evolution using a spectral MHD code. Our results show that presence of strong toroidal magnetic field in magnetars is necessary to explain their quiescent thermal emission, in particular a formation of a single hot spot. Using our thermal maps we are able to explain light curves of 10 out of 19 magnetars in quiescence.
In the case of the central compact objects, we test the configuration of magnetic field formed as a result of stochastic dynamo. Such a magnetic field consists of multiple randomly orientated loops of magnetic field. The global dipolar field slowly formed as a result of the Hall and Ohmic evolution. In our simulations we see 5-7% pulsed fraction, formation of a few compact hot regions and difference of two times in temperature between hot and cold regions typical for observations of the central compact objects.
Dr Manisha Caleb
Date: Wednesday 7th April 2021
Time: 1pm UK time
Speaker: Dr Manisha Caleb, Postdoctoral Researcher at the University of Manchester
Time: 1pm UK time
Speaker: Dr Manisha Caleb, Postdoctoral Researcher at the University of Manchester
Fast radio bursts and their possible links to neutron stars
Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since the pioneering discovery in 2007. The FRB class encompasses a number of microsecond-millisecond duration pulses occurring at Galactic to cosmological distances with energies spanning over 5 orders of magnitude. While most FRBs have been observed as singular events, a small fraction of them have been observed to repeat over various timescales leading to an apparent dichotomy in the population. Though ~50 progenitor model theories have been proposed with the majority involving neutron stars, no consensus has emerged for their origin(s). However, with the discovery of an FRB-like pulse from the Galactic magnetar SGR J1935+2154, magnetar engine models appear to be the current leading favourite. In this talk, I will present an overview of the field of FRBs and the recent results from the MeerTRAP project at the MeerKAT radio telescope.
Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since the pioneering discovery in 2007. The FRB class encompasses a number of microsecond-millisecond duration pulses occurring at Galactic to cosmological distances with energies spanning over 5 orders of magnitude. While most FRBs have been observed as singular events, a small fraction of them have been observed to repeat over various timescales leading to an apparent dichotomy in the population. Though ~50 progenitor model theories have been proposed with the majority involving neutron stars, no consensus has emerged for their origin(s). However, with the discovery of an FRB-like pulse from the Galactic magnetar SGR J1935+2154, magnetar engine models appear to be the current leading favourite. In this talk, I will present an overview of the field of FRBs and the recent results from the MeerTRAP project at the MeerKAT radio telescope.
Dr Diego Altamirano
Date: Wednesday 5th May 2021
Time: 1pm UK time
Speaker: Dr Diego Altamirano, Principal Research Fellow at the Astronomy Group, School of Physics and Astronomy, University of Southampton
Time: 1pm UK time
Speaker: Dr Diego Altamirano, Principal Research Fellow at the Astronomy Group, School of Physics and Astronomy, University of Southampton
Marginally stable burning as a potential tool to constrain the EoS of NSs
Understanding the physics of thermonuclear burning of H/He on the neutron star surface is a fascinating area of research. In this talk I will first briefly review our current theoretical understanding of the different (thermonuclear) burning regimes we observe, and then focus on the so-called "marginally stable burning", a regime that occurs at the transition between stable and unstable burning. I will review the recent observational results and the current state of theoretical simulations that describe this regime. Finally, I will highlight and discuss why the observation of marginally stable burning has the potential to put constraints on the Equation of State of Neutron Stars.
Understanding the physics of thermonuclear burning of H/He on the neutron star surface is a fascinating area of research. In this talk I will first briefly review our current theoretical understanding of the different (thermonuclear) burning regimes we observe, and then focus on the so-called "marginally stable burning", a regime that occurs at the transition between stable and unstable burning. I will review the recent observational results and the current state of theoretical simulations that describe this regime. Finally, I will highlight and discuss why the observation of marginally stable burning has the potential to put constraints on the Equation of State of Neutron Stars.
Dr Matt Middleton
Date: Wednesday 2nd June 2021
Time: 1pm UK time
Speaker: Dr Matt Middleton, Associate Professor, School of Physics and Astronomy, University of Southampton
Time: 1pm UK time
Speaker: Dr Matt Middleton, Associate Professor, School of Physics and Astronomy, University of Southampton
Neutron star ULXs - magnetars or X-ray lighthouses?
Although it was long suspected that neutron stars and stellar mass black holes could be powering the extreme apparent X-ray luminosities of ultraluminous X-ray sources (ULXs), it wasn’t until 2014 -- when the first X-ray pulsations from a ULX were discovered -- that this paradigm was put beyond doubt. The mechanisms by which an accreting neutron star can appear at more than a hundred times its Eddington limit are well established in theory but depend sensitively on the dipole field strength and the accretion rate, both of which can be hard to infer. In this talk I will discuss some of the phenomenology of these enigmatic sources, the open questions still facing the field (such as the true nature of the population demographic) and how we can hope to obtain the answers.
Although it was long suspected that neutron stars and stellar mass black holes could be powering the extreme apparent X-ray luminosities of ultraluminous X-ray sources (ULXs), it wasn’t until 2014 -- when the first X-ray pulsations from a ULX were discovered -- that this paradigm was put beyond doubt. The mechanisms by which an accreting neutron star can appear at more than a hundred times its Eddington limit are well established in theory but depend sensitively on the dipole field strength and the accretion rate, both of which can be hard to infer. In this talk I will discuss some of the phenomenology of these enigmatic sources, the open questions still facing the field (such as the true nature of the population demographic) and how we can hope to obtain the answers.
Prof Nils Andersson
Date: Wednesday 30th June 2021
Time: 1pm UK time
Speaker: Prof Nils Andersson, Professor of Applied Mathematics, Head of General Relativity Group, University of Southampton
Time: 1pm UK time
Speaker: Prof Nils Andersson, Professor of Applied Mathematics, Head of General Relativity Group, University of Southampton
Neutron stars with mountains
A spinning neutron star will radiate continuous gravitational waves if it is deformed away from axial symmetry. Such signals are expected to be weak but this is (to some extent) compensated for by long integration times (as the detectability improves as the square-root to the observation time). While there have been many efforts to find signals from rotating neutron stars (both from targeted sources and through all-sky searches), the best we have at the moment are observational upper limits on the signal strength. In this talk, I will consider these results in the context of our theoretical understanding. I will argue that observations of both millisecond radio pulsars and accreting neutron stars in low-mass X-ray binaries hint at a gravitational-wave contribution to the spin evolution. I will summarise recent progress in the modelling of the neutron star "mountains" and discuss what has to be done if we want to make (further) progress on this problem.
A spinning neutron star will radiate continuous gravitational waves if it is deformed away from axial symmetry. Such signals are expected to be weak but this is (to some extent) compensated for by long integration times (as the detectability improves as the square-root to the observation time). While there have been many efforts to find signals from rotating neutron stars (both from targeted sources and through all-sky searches), the best we have at the moment are observational upper limits on the signal strength. In this talk, I will consider these results in the context of our theoretical understanding. I will argue that observations of both millisecond radio pulsars and accreting neutron stars in low-mass X-ray binaries hint at a gravitational-wave contribution to the spin evolution. I will summarise recent progress in the modelling of the neutron star "mountains" and discuss what has to be done if we want to make (further) progress on this problem.
Dr Arnau Rios Huguet
Date: Wednesday 22nd September 2021
Time: 1pm UK time
Speaker: Dr Arnau Rios Huguet, Ramón y Cajal Fellow, University of Barcelona and Visiting Professor, University of Surrey
Time: 1pm UK time
Speaker: Dr Arnau Rios Huguet, Ramón y Cajal Fellow, University of Barcelona and Visiting Professor, University of Surrey
The Quantum Many-Body Physics of Neutron Stars
This talk will be concerned with the interior properties of neutron stars. I will discuss the techniques that are necessary to understand the structure of the dense matter in the neutron-star crust and core, with an emphasis on recent theoretical developments that aim at providing predictions with quantifiable uncertainties. I will illustrate recent advances across the quantum many-body theory domain, some of which may impact our understanding of the equation of state and the pairing dynamics of neutron stars.
This talk will be concerned with the interior properties of neutron stars. I will discuss the techniques that are necessary to understand the structure of the dense matter in the neutron-star crust and core, with an emphasis on recent theoretical developments that aim at providing predictions with quantifiable uncertainties. I will illustrate recent advances across the quantum many-body theory domain, some of which may impact our understanding of the equation of state and the pairing dynamics of neutron stars.
Dr Bettina Posselt
Date: Wednesday 20th October 2021
Time: 1pm UK time
Speaker: Dr Bettina Posselt, Postdoctoral Researcher at the University of Oxford and Affiliate Associate Research Professor at Pennsylvania State University
Time: 1pm UK time
Speaker: Dr Bettina Posselt, Postdoctoral Researcher at the University of Oxford and Affiliate Associate Research Professor at Pennsylvania State University
Taking the temperature of a neutron star
Thermal emission from a neutron star can be used to (i) study the details of its surface properties such as the surface composition and the spatial temperature and magnetic field distribution, (ii) obtain an indirect view into the deeper layers of the compact objects by constraining cooling and heating processes, and (iii) assess effects of the magnetosphere, for example through the impact of accelerated particles that create hot spots.
Measuring the exact temperature of a neutron star (or a hot spot on the neutron star surface) is subject to many model assumptions and currently almost impossible to achieve. However, relative temperature measurements and statistical temperature studies have been crucial to identify different neutron star populations, constrain their evolution and the equation of state in their interiors.
In my talk, I will provide an overview on why and how we measure temperatures of neutron stars, and which open questions and future challenges are related to this endeavour. As one example of current studies, I will present the latest constraints on the cooling of the youngest known neutron star with detected thermal X-ray emission - the 300 year young Central Compact Object in the Cassiopeia A supernova remnant.
Thermal emission from a neutron star can be used to (i) study the details of its surface properties such as the surface composition and the spatial temperature and magnetic field distribution, (ii) obtain an indirect view into the deeper layers of the compact objects by constraining cooling and heating processes, and (iii) assess effects of the magnetosphere, for example through the impact of accelerated particles that create hot spots.
Measuring the exact temperature of a neutron star (or a hot spot on the neutron star surface) is subject to many model assumptions and currently almost impossible to achieve. However, relative temperature measurements and statistical temperature studies have been crucial to identify different neutron star populations, constrain their evolution and the equation of state in their interiors.
In my talk, I will provide an overview on why and how we measure temperatures of neutron stars, and which open questions and future challenges are related to this endeavour. As one example of current studies, I will present the latest constraints on the cooling of the youngest known neutron star with detected thermal X-ray emission - the 300 year young Central Compact Object in the Cassiopeia A supernova remnant.
Dr Fabian Jankowski
Date: Wednesday 9th February 2022
Time: 1pm UK time
Speaker: Dr Fabian Jankowski, Postdoctoral Researcher at the Jodrell Bank Centre for Astrophysics, University of Manchester
Time: 1pm UK time
Speaker: Dr Fabian Jankowski, Postdoctoral Researcher at the Jodrell Bank Centre for Astrophysics, University of Manchester
The broadband emission of neutron stars
Pulsars are one of the manifestations of neutron stars, and they are observable across the electromagnetic spectrum from radio to gamma-rays. This provides us with the primary observational tool to measure their rotation, radiative and environmental parameters and perform some of the most stringent tests of fundamental physics. However, the inherent emission physics that make pulsars shine remain far from fully understood. Emission theories are further challenged by the presence of a wide variety of complex phenomena observed in pulsars, especially at the single-pulse level. Fortunately, the recent commissioning of wide-band instrumentation at several facilities has significantly broadened our view. In this talk, I will summarise a selection of recent results that shed light on the broadband radiative properties of young and canonical pulsars, rotating radio transients (RRATs), and radio-loud magnetars.
Pulsars are one of the manifestations of neutron stars, and they are observable across the electromagnetic spectrum from radio to gamma-rays. This provides us with the primary observational tool to measure their rotation, radiative and environmental parameters and perform some of the most stringent tests of fundamental physics. However, the inherent emission physics that make pulsars shine remain far from fully understood. Emission theories are further challenged by the presence of a wide variety of complex phenomena observed in pulsars, especially at the single-pulse level. Fortunately, the recent commissioning of wide-band instrumentation at several facilities has significantly broadened our view. In this talk, I will summarise a selection of recent results that shed light on the broadband radiative properties of young and canonical pulsars, rotating radio transients (RRATs), and radio-loud magnetars.
Dr Geraint Pratten
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Date: Wednesday 9th March 2022
Time: 1pm UK time Speaker: Dr Geraint Pratten, Postdoctoral Research Associate at the University of Birmingham |
Gravitational-wave asteroseismology with fundamental modes from compact binary inspirals
Gravitational waves (GWs) from binary neutron stars encode unique information about ultra-dense matter through characteristic signatures associated with a variety of phenomena including tidal effects during the inspiral. The main tidal signature depends predominantly on the equation of state (EoS)-related tidal deformability parameter Λ, but at late times is also characterised by the frequency of the star’s fundamental oscillation mode (f-mode). In this talk I will detail the impact of dynamical tides on the equation of state inferred from future GW observations and highlight prospects for measuring the fundamental mode in future GW detector networks.
Gravitational waves (GWs) from binary neutron stars encode unique information about ultra-dense matter through characteristic signatures associated with a variety of phenomena including tidal effects during the inspiral. The main tidal signature depends predominantly on the equation of state (EoS)-related tidal deformability parameter Λ, but at late times is also characterised by the frequency of the star’s fundamental oscillation mode (f-mode). In this talk I will detail the impact of dynamical tides on the equation of state inferred from future GW observations and highlight prospects for measuring the fundamental mode in future GW detector networks.
Dr Toby Wood
Date: Wednesday 6th April 2022
Time: 1pm UK time
Speaker: Dr Toby Wood, Lecturer in Applied Mathematics, Newcastle University
Time: 1pm UK time
Speaker: Dr Toby Wood, Lecturer in Applied Mathematics, Newcastle University
Superconductivity in neutron stars
In the core of a neutron star, neutrons and protons condense into a superfluid and a superconductor, respectively. The rotational and magnetic evolution of the core is fundamentally changed by the quantisation of vorticity and magnetic flux in these quantum fluids. We will show that coupling between the fluids can produce novel types of superconductivity, beyond the standard type-I and type-II regimes. Time permitting, we will also describe the ingredients needed for a fully dynamical microscale model of the core.
In the core of a neutron star, neutrons and protons condense into a superfluid and a superconductor, respectively. The rotational and magnetic evolution of the core is fundamentally changed by the quantisation of vorticity and magnetic flux in these quantum fluids. We will show that coupling between the fluids can produce novel types of superconductivity, beyond the standard type-I and type-II regimes. Time permitting, we will also describe the ingredients needed for a fully dynamical microscale model of the core.
Prof Aris Karastergiou
Date: Wednesday 11th May 2022
Time: 1pm UK time
Speaker: Prof Aris Karastergiou, Associate Professor and Senior Research Fellow, University of Oxford
Time: 1pm UK time
Speaker: Prof Aris Karastergiou, Associate Professor and Senior Research Fellow, University of Oxford
What are observations of radio pulsars telling us about the emission mechanism and the pulsar population?
I recently gave a version of this talk to a group of Indian and South-African graduate students and some of their supervisors. It is a simple description of some of the key observables of radio pulsars, and how we use them to derive an understanding of the pulsar population. It is worth returning to some of the fundamental questions about the radio pulsar population, such as the birth rate and birth properties, and the evolution of the magnetic field strength and structure, and see what answers we are getting from the latest data. Despite the SPINS-UK audience probably having deeper expertise than my original target audience, there is always some value in showing what the highest quality radio pulsar data are telling us about pulsar emission and the pulsar population.
I recently gave a version of this talk to a group of Indian and South-African graduate students and some of their supervisors. It is a simple description of some of the key observables of radio pulsars, and how we use them to derive an understanding of the pulsar population. It is worth returning to some of the fundamental questions about the radio pulsar population, such as the birth rate and birth properties, and the evolution of the magnetic field strength and structure, and see what answers we are getting from the latest data. Despite the SPINS-UK audience probably having deeper expertise than my original target audience, there is always some value in showing what the highest quality radio pulsar data are telling us about pulsar emission and the pulsar population.
Dr David Tsang
Date: Wednesday 8th June 2022
Time: 1pm UK time
Speaker: Dr David Tsang, Lecturer at the University of Bath
Time: 1pm UK time
Speaker: Dr David Tsang, Lecturer at the University of Bath
Resonant Shattering Flares: Nuclear Physics Constraints from Multi-messenger Neutron Star Mergers
Neutron stars are ideal laboratories for testing nuclear physics – with access to high-density low-temperature regimes inaccessible with terrestrial collider experiments. Indeed, neutron star mergers can provide powerful constraints on equation of state and nuclear physics parameters. Resonant Shattering Flares – Gamma-Ray Flares induced by tidal resonance during binary inspiral – can occur when the surface magnetic fields are sufficiently strong, and depend on the properties of neutron star at the crust-core interface, near nuclear saturation density. I will highlight our recent work showing how combining the gravitational-wave chirp and the gamma-ray signal of an RSF allows for the crust-core interface mode frequency to be determined to high precision, as well as how this puts strong constraints on nuclear symmetry energy parameters. We show that the constraints on these nuclear physics parameters from a single multimessenger RSF detection will be comparable to current terrestrial collider experiments.
Neutron stars are ideal laboratories for testing nuclear physics – with access to high-density low-temperature regimes inaccessible with terrestrial collider experiments. Indeed, neutron star mergers can provide powerful constraints on equation of state and nuclear physics parameters. Resonant Shattering Flares – Gamma-Ray Flares induced by tidal resonance during binary inspiral – can occur when the surface magnetic fields are sufficiently strong, and depend on the properties of neutron star at the crust-core interface, near nuclear saturation density. I will highlight our recent work showing how combining the gravitational-wave chirp and the gamma-ray signal of an RSF allows for the crust-core interface mode frequency to be determined to high precision, as well as how this puts strong constraints on nuclear symmetry energy parameters. We show that the constraints on these nuclear physics parameters from a single multimessenger RSF detection will be comparable to current terrestrial collider experiments.
Dr Jakob van den Eijnden
Date: Wednesday 6th July 2022
Time: 1pm UK time
Speaker: Dr Jakob van den Eijnden, Junior Research Fellow at St Hilda's College, University of Oxford
Time: 1pm UK time
Speaker: Dr Jakob van den Eijnden, Junior Research Fellow at St Hilda's College, University of Oxford
Jets and shocks in and around neutron star high-mass X-ray binaries
With upgraded observatories and the advent of SKA pathfinders, radio telescopes now allow us to probe the properties of X-ray binaries down to unprecedented sensitivities. In addition, their excellent ability to detect large-scale, diffuse emission enables deeper studies of interactions between X-ray binary and its surroundings, driven by outflows such as the jet or the stellar wind. These developments are particularly relevant for the study of neutron stars orbited by massive donor stars, which make up roughly half of all known X-ray binaries; due to their radio faintness, these systems have long escaped detection. In this talk, I will highlight what the new and upgraded radio observatories have revealed about this very common type of X-ray binary. Firstly, I will discuss the launch of relativistic jets by the strongly-magnetized neutron stars and the implications for jet formation models. Secondly, I will turn to the study of the interaction between the binary and its surroundings, through the discovery of a radio bow shock around Vela X-1. Finally, I will discuss the unexpected radio brightness of persistent high-mass X-ray binaries and explore possible explanations, in particular the presence of relativistic particle acceleration in shocks between the jet and the massive stellar wind.
With upgraded observatories and the advent of SKA pathfinders, radio telescopes now allow us to probe the properties of X-ray binaries down to unprecedented sensitivities. In addition, their excellent ability to detect large-scale, diffuse emission enables deeper studies of interactions between X-ray binary and its surroundings, driven by outflows such as the jet or the stellar wind. These developments are particularly relevant for the study of neutron stars orbited by massive donor stars, which make up roughly half of all known X-ray binaries; due to their radio faintness, these systems have long escaped detection. In this talk, I will highlight what the new and upgraded radio observatories have revealed about this very common type of X-ray binary. Firstly, I will discuss the launch of relativistic jets by the strongly-magnetized neutron stars and the implications for jet formation models. Secondly, I will turn to the study of the interaction between the binary and its surroundings, through the discovery of a radio bow shock around Vela X-1. Finally, I will discuss the unexpected radio brightness of persistent high-mass X-ray binaries and explore possible explanations, in particular the presence of relativistic particle acceleration in shocks between the jet and the massive stellar wind.
