X-ray binaries (XRBs) are X-ray bright systems composed of a compact object (a black hole or a neutron star) and a companion star, typically referred to as the primary and the secondary star, respectively. Under the effect of the extreme gravity field around the compact object, matter is transferred from the secondary to the primary and finally accreted onto it. As this happens, the gravitational energy of matter is converted into radiation mainly in the X-ray band. Observing these systems with multi-wavelength telescopes provides scientists with the opportunity to study the behavior of matter in some of the most extreme environments in the Universe, such as neutron-star cores, and perform tests of General Relativity. In particular, the physical properties of the accretion flow around the compact object, e.g. its geometry, its temperature, and its chemical composition, can be probed with the analysis of X-ray spectra. Investigating the X-ray variability over short time-scales, i.e. from seconds to fractions of a millisecond, enables the discovery of periodic and quasi-periodic signals such as coherent pulsations (in the case of neutron stars) and quasi-periodic oscillations, whose nature is still debated. 

In this internship, we will use data from different X-ray telescopes, such as XMM-Newton, Chandra, and Swift to perform spectral and timing studies of an X-ray binary. The project will provide the student with the opportunity to learn how to reduce and analyze X-ray data, along with a theoretical background on accretion physics and compact objects.

The student will work as part of the MAGNESIA group at the ICE institute, a group focused on studying neutron-star physics through both an observational and theoretical perspective. They will also be welcome to join our activities, such as weekly group meetings and scientific projects, and benefit from the range of expertises of our team members.

Supermassive black holes of 10⁹ solar masses are found at the center of most massive galaxies. These galaxies and their black holes are thought to grow synchronously at the same time. Under this scenario, the supermassive black holes would have evolved from seed black holes of smaller mass formed in the early Universe. Detecting such seeds when the Universe was very young is extremely challenging but with the advent of cutting-edge observations we can now reach distant galaxies hosting black holes that are actively acretting matter: active galactic nuclei (AGN). Recently, a few AGN have been observed in dwarf galaxies when the Universe was much younger than it is today, 6,000 million years after the Big Bang. The black holes powering this distant AGN are found to be more massive than expected from a synchronized growth with their host galaxies (i.e., they are over-massive black holes), a result that challenges models of black hole-galaxy co-evolution (Mezcua, Siudek et al. 2023).

This TFM aims at identifying AGN in dwarf distant galaxies and estimating their black hole mass. The results can confirm if distant AGN dwarf galaxies host over-massive black holes or whether instead, they host black holes of smaller mass. The latter could represent the relics of the early Universe seed black holes from which supermassive black holes form. This project will have important implications for our understanding of the seed black hole formation. A basic knowledge of python is advisable.

Active galactic nuclei (AGN) are powered by massive black holes and play a key role in galaxy formation and evolution. From an observational point of view, the black hole mass correlates with the properties of the host galaxies, but the origin of this relationship is still largely unexplored and our understanding of the feedback process between black holes and galaxies is still incomplete.  Large-scale spectroscopic surveys provide a unique opportunity to study the co-evolution of black hole and host properties. However, the selection of AGN is still a challenging task. The standard selection methods based on emission line ratios result in incomplete and contaminated AGN samples. The goal of this TFM is to identify AGN based on an unsupervised machine learning method. The high-dimensional nature of galaxy spectra makes it challenging for humans to detect features associated with AGN, but not for advanced machine-learning algorithms. In this project, we aim at developing a new approach to identify AGN using the full information from the galaxy spectra and machine-learning techniques. Such an approach promises unbiased AGN selection and will be of interest for planning future AGN observing strategies. A good knowledge of python and basic knowledge of machine-learning methods is advisable.

Some of the most extreme astrophysical objects such as supernovae, accreting pulsars, X-ray binaries, compact object mergers (gravitational-wave sources), gamma-ray bursts, etc., are the products of binary stars. Understanding their evolution is therefore one major importance for modern astrophysics. However, the physical processes governing various phases of binary stellar evolution are not completely understood.

Traditionally, efforts to put constraints on binary evolution phases are based on comparing observations of a specific binary product (e.g., compact object mergers) with a set of synthetic populations (each with different physical assumptions). However, the degeneracies in the model parameters, and the limited observational handles (e.g., merger rates) are hindering these efforts.

Synthetic populations of multiple types of binary products, would put constraints on all phases of binary evolution (without focusing on those important for a specific type), addressing the degeneracy issue. In addition they would allow to exploit multiple observational results in the comparisons, addressing the limited constraining power of individual populations.

We will use binary population synthesis models (e.g., POSYDON) to produce synthetic populations of various types of binary products, under different sets of physical assumptions. Retaining the full evolution of the systems as a function of the age and metallicity, we will be able to populate galaxies in cosmological simulations, thus allowing us to compare realistic populations against observed ones for the current Universe, or their cosmic evolution.

The project is divided in 5 parts [indicative time noted]:

(a) Introduction to single/binary stellar evolution [~3 weeks]
(b) Introduction to the population synthesis method [~2 weeks]
(c) Running population synthesis codes and analyzing the output [~4 weeks]
(d) Study the binary star products at different ages/metallicities [~6 weeks]
(e) Report the findings (thesis writing) [~2 months]

The student will be trained in theoretical astrophysics, modern numerical techniques (including high-performance computing), scientific writing, and science communication through interaction with researchers from ICE (Spain), U. of Geneva (Switzerland), University of Crete (Greece), NorthWestern U. (USA).

The Laser Interferometer Space Antenna (LISA) is a future Large-class mission of the European Space Agency (ESA) to observe gravitational waves from space, covering the low-frequency band of the gravitational-wave spectrum, a band not accessible for the current ground-based observatories like LIGO and Virgo. One of the main sources of gravitational waves that LISA will observe is the capture and subsequent slow inspiral of a stellar-mass compact object (SCO; typically a stellar-mass black hole or a neutron star) into a supermassive black hole (SMBH) sitting at the center of a quiescent galaxy. Due to the large difference in mass between the SCO and the SMBH, these systems are usually called Extreme-Mass-Ratio Inspirals (EMRIs). The gravitational wave emission of EMRIs is long lasting. It has been estimated that during the last year before the SCO plunges into the SMBH, the system can emit of the order of 100000 gravitational wave cycles. During this emission, the trajectory of the SCO is very close to the SMBH horizon location, which means that the motion is highly relativistic, with strong precession of the periastron as well as of the orbital plane. In this way, during this long emission of gravitational waves, the SCO traces all the near-horizon geometry of the SMBH. This means that the gravitational waves emitted encode a map of the geometry of the SMBH that will allow us to understand the structure of Black Holes with LISA.  To that end, we need first to study the structure of the gravitational waveforms emitted, and from there to estimate the precision with which we will obtain the physical parameters of the EMRIs from the LISA data. The goal of this project is to use simplified models of the gravitational wave emission of EMRIs to estimate the precision in the measurement of the main EMRI parameters: Masses, spin, distance, etc.

LISA (the Laser Interferometer Space Antenna) is the future third L-class mission of the European Space Agency (ESA) to detect gravitational waves from space in the low-frequency band (between 10 micro-Hertz and 1 Hertz). LISA will detect gravitational waves generated by the coalescence of supermassive black hole binaries; by the capture and subsequent inspiral of stellar-mass black holes into supermassive black holes; by ultracompact binaries in our own galaxy; stellar-mass black hole binaries in the milli-Hertz regime; stochastic backgrounds; etc. In General Relativity, gravitational waves appear two have two independent polarizations, so that a general gravitational-wave emission can be written as a linear combination of these two polarizations, and similarly the response of LISA to it. However, in metric theories of gravity, gravitational waves may have up to six independent polarizations. The goal of this master thesis project is to study the response of LISA to the most general gravitational wave, or in other words, to gravitational waves that contain all possible six polarizations.

Hydrogen-rich supernovae (SNe II) are produced by the final explosion of massive stars (>8 Msun). They retain a significant fraction of hydrogen at the moment of the explosion, and hence their spectra show prominent Balmer lines. Recently, SNe II have been proposed as metallicity indicators, making them relevant in the cosmic context. More precisely, theoretical models predict that the strength of metal lines around 50 days post-explosion is related to the metallicity of the SN progenitor [1]. Thus, SN II metal-line pseudo-equivalent-widths (pEWs) generally become stronger when metallicity increases. This project aims to explore this correlation and test the parameter space obtained from the models. The student will work with observations and models, astronomical tools and python codes. The sample used for the project comprises spectra from the literature and new observations, plus theoretical models developed by Dr Luc Dessart.

Type Ia supernovae (SNIa) are one of the most precise distance indicators to distant galaxies, once their peak brightness is standardized using luminosity-width and -color empirical relations. However, there is a family of subluminous SNIa, also known as 1991bg-like SNIa [1], that are not standardizable and therefore are not useful for cosmology [2]. The most accepted picture is that these objects are physically different to ‘normal’ SNIa, but it is not known in detail whether the difference comes from the explosion mechanism, or from another progenitor scenario (subChandra explosions), or even other effects (asymmetries, viewing angle…). The goal of this master thesis is to define the main peculiarities of 91bg-like SNIa compared to ‘normal’ SNIa, from a sample of 91bg-like SNIa with unpublished photometric and spectroscopic observations. The student will have to develop analysis and visualization tools in python, and learn how to use the light-curve fitter SNooPy [3] to obtain the main observational properties.

The Pound-Drever-Hall (PDH) is a laser frequency stabilization technique used as an essential part in all gravitational wave detectors. The basic idea behind its standard implementation is to use a Fabry-Perot cavity to measure the laser frequency noise to then feed back this measurement into the laser to suppress frequency fluctuations. The Gravitational Astronomy group at the Institut de Ciències de l’Espai (ICE-CSIC) has provided the Data and Diagnostics Subsystems of LISA Pathfinder, a precursor mission launched in December 2015, which has successfully measured
the residual acceleration of two free-falling test masses in space down to the 5 x 10-15 m/s2/√Hz in the milliHertz band.

A particular interesting challenge arising in LISA and other fundamental physics space missions is the high stability control of temperature in the very low-frequency range (below the milliHertz). Our group is currently developing the techniques with potential impact in these future missions. For that purpose, we are investigating temperature sensing by means of phase locking to optomechanical resonators. The candidate will work in the implementation of the Pound-Drever-Hall technique that will be used to stabilize the frequency of the laser to the resonator, acting as an optical cavity. The student will work in an optical experiment and will implement the control loop scheme to suppress the laser frequency noise.

Gravitational waves are a prediction of Einstein’s General Relativity recently detected by the on-ground laser interferometers LIGO. LISA (Laser Interferometer Space Antenna) is an ESA mission with expected launch in 2034 aiming to detect gravitational radiation by putting three satellites in heliocentric orbit separated 2.5 million km one from each other, forming a triangle. The Gravitational Astronomy group at the Institut de Ciències de l’Espai (ICE-CSIC) has provided the Data and Diagnostics Subsystems of LISA Pathfinder, a precursor mission launched in December 2015 that successfully proved the key technologies to reach the purest free-fall in space to the date, i.e. down to the sub-femto-g. Our group led the analysis of the magnetic diagnostics onboard. A particular interesting mphenomenon to study in this context is the effect of magnetic induced kicks in the free falling test mass. An effect with interest for LISA and other future gravitational wave detectors. The student will work on the analysis of the LISA Pathfinder data and characterize the observed magnetic induced kicks in the in-flight times series. He/she will study these effects analytically and numerically by means of FEM models.

Space instrumentation requires precise phases of analysis and testing of the functionality and performance of developed technology. Most of these require at some point performance tests at different and stable temperature environment’s in vacuum. Depending on the instrument circumstances, this can turn out to be a complicated or tedious task, since vacuum chambers are of limited size (in order to host the device-under-test (DUT) and the testing equipment) and are keen to high temperature gradients. Being so, instrumentation for vacuum requires of special design parameters. For this thesis, we propose the development of a heater-cooling + sensors system, using a PID control loop to achieve thermal stabilities in the mK range (or higher). For this, the student will study and analyze existing actuators and sensors, and implement PID control using software-based tools. In addition, the thermal control system will be put into test inside a vacuum chamber, for which thermal shields will need to be designed.

Characterization of exoplanets requires high instrumental precision as well as combining measurements from very different sources in a common framework. In addition to this, numerous instrumental and astrophysical degeneracies exist so interpreting this high quality data requires holistic and unbiased techniques to combine all the data consistently. Although we can simulate most of the complexity of the observations, these degeneracies are often difficult to predict a priori, creating all sorts of false negative and false positive detections of exoplanet features.

To account for this, and to accommodate the increasing complexity of astronomical datasets, we will implement data and model driven machine learning techniques. Instead of predicting all the cross dependencies a priori, we will use deep neural networks to identify exoplanetary features in time-series (true Doppler signals, true transit signals) and on spectroscopic observations such as the ones that are being obtained from ground based and space based observatories. This project will work with both synthetic and real observations from ground and space based observatories. Detailed knowledge of machine learning is not required, but good coding skills (especially in Python, which is the main coding language for machine learning techniques) are strongly recommended.

HydroGNSS is the second ESA Scout mission, a satellite that will provide measurements of key hydrological climate variables, including soil moisture, freeze–thaw state over permafrost, inundation and wetlands, and above-ground biomass, using a technique called Global Navigation Satellite System (GNSS) reflectometry. HydroGNSS funding has now been secured, and it shall be launched in 2024. ICE CSIC/IEEC is part of the proposing and developing team, in charge of --among other aspects-- developing, implementing and validating the operator that will retrieve Earth surface flooding conditions from the electromagnetic measurements.

HydroGNSS will have the unique capability to measure and download to Earth GNSS-R measurements at much higher sampling rate and preserving the information embedded in the phase of the electromagnetic field. These aspects open the door to new retrieval techniques, at much higher spatial resolution. The Earth Observation group at ICE-CSIC/IEEC has developed an initial algorithm that uses phase information to detect flooding. This algorithm or its evolution will become the operational level-2 operator, this is, the official mission algorithm for inverting the electromagnetic records into geophysically meaningful variables. The student will contribute towards the validation of the flood detection algorithm using existing GNSS-R data from already orbiting satellites and other sources of information.

The Radio Occultations and Heavy Precipitation aboard PAZ satellite (ROHP-PAZ) is an experiment that had the objective to test, for the first time, the capability of the Global Navigation Satellite System (GNSS) Polarimetric Radio Occultation (PRO) technique to sense precipitation. Led by the Institut de Ciències de l’Espai (ICE-CSIC,IEEC) and on orbit since February 2018, the results of the analyses of first years of data have demonstrated that PRO are not only able to sense rain, but also to provide information of the vertical cloud structures.

With the objective to continue with the validation of the PRO technique and exploit its applications, the aim of this project is to analyze the numerous coincident measurements between the ROHP-PAZ observations and radars and radiometers. The NASA’s Global Precipitation Measurement (GPM) core satellite (CO) flies a precipitation radar that provides detailed information about rain and, partially, of its associated cloud structure. A significant number of coincidences have been identified between our ROHP-PAZ observations and GPM-CO, which are complemented by the numerous microwave radiometers also aboard GPM-CO and from other satellite platforms.

This project will consist on analyzing the coincidences and infer relationships between the different observations, with the objective to characterize the vertical structure of the ROHP-PAZ observations.

The Institute of Space Sciences is developing a radio-interferometer in the 10.7 GHz – 12.7 GHz range. The current development of the instrument requires the characterization of the current hardware in terms of phase delay measurements and its noise characteristics in a controlled environment.

The interferometer will be set up in our laboratory. A known signal will be injected into the different antenna ports and will be used as a calibration signal. Using post-processing techniques, the complex cross-correlation (visibility functions) obtained with the interferometer will be computed, and its stability and noise characterized. These measurements will yield the ultimate precision of the achievable phase delays. Phase closures shall be applied to the measured visibilities to determine the stability of the instrument itself. This is an experimental project.

The formation of relatively close (about 10 astronomical units, au) stellar binaries may inhibit or reduce significantly planet forma1on, because the circumstellar disk are expected to have a small radius ( about 1 au), and the circumbinary disk may not be stable and dense enough for planet forma1on. We have obtained with ALMA very high angular resolu1on and high fidelity images of the molecular gas around a well know very young binary system. ALMA (Atacama Large Millimeter Arrays) is the most powerful radio facility at millimeter wavelengths. The project will consist in analyzing the images to better understand how the accretion proceeds from the observed spiral filaments toward the 1ny circumstellar disk around the two young stars. Ultimately, we want to see whether the accre1on prices is high enough to allow planet formation at au scales.

Stellar activity poses a major limitation to the extraction of planetary signals from radial velocities and transits. An evolving and rotating inhomogeneous star surface hampers the detection of small planets in temperate orbits and also atmospheric characterization of exoplanets using transit spectroscopy. Our ability to account for these effects is closely related to improving our understanding of stellar activity as a function of time and wavelength. This project will develop methodology to retrieve planetary signals from data affected by activity. One of the main tools will be the StarSim code, which is capable of accurately simulating stellar variability effects. Among other sources, proprietary data from the CARMENES radial velocity spectrometer will be analyzed.

The Cosmology and Extragalactic Astronomy groups at ICE-IFAE-PIC have a long expertise on generating mock galaxy catalogs for several large extra-galactic surveys ongoing or being in which we actively collaborate such as PAU, DES or Euclid. In order to fully exploit and interpret the observed data from galaxy surveys it is essential to produce mock galaxy catalogues since they can help in a variety of ways. They are useful to design and calibrate galaxy surveys. They can help to study selection effects, to calibrate errors and explore systematic effects, to test new techniques to measure cosmological parameters or to calibrate cluster finders and photometric redshift estimators.

Accurately reproducing observed distributions in simulations is mandatory to achieve successful scientific analysis. In this Master thesis project we propose to apply in a novel way a method to estimate a continuous transformation that maps one N-dimensional probability density function distribution to another. This method will allow not only to reproduce the observed distributions but also to maintain the correlations between the observables. We will apply and validate this methodology using MICE and/or Euclid simulations.

Although general relativity is the simplest approach to gravity, it is not the only one. Higher order extensions of Einstein gravity play important roles in various areas such as cosmology, the early universe or quantum gravity. An alternative, known as scalar-tensor theories, goes back to the early 1960s and is the work of physicists Robert Dicke and Carl Brans, so that usually it gets the name of Brans-Dicke theory. Another family of modifications of general relativity, which appeared later but are no less famous are the f(R)-theories, where terms in higher powers of the Ricci scalar, R, as well as other suitable functions of it (as the exponential one) are introduced, has also become very popular. The new theories may have important implications in early-time cosmology, both for inflationary models and for the alternative bounce models. All this has given rise to a wide research field.

According to observations, the expansion of the universe is accelerating, but at a very gentle pace. The only way to account for this in general relativity is to include a cosmological constant, an extra value in the equations that has an incredibly small, but non-zero, value. That feature of the cosmological constant troubles most physicists because it seems incredibly unnatural. If dark energy had almost any other value, the expansion of the cosmos would have torn apart the cosmos long ago, leaving it unable to support life (including anyone who could observe it), and yet it is not perfectly zero, either. An alternative to model this behavior is to modify general relativity and use, e.g., f(R) theories. Some of them are able to connect the present accelerated expansion of the universe with the one that gave rise to inflation in its earlier history. They may be also able to describe the different intermediate epochs of the universe evolution thus providing a unified perspective of the whole universe history.

The detection of gravitational waves (GWs) gave great impulse to the possibility of observing strong and quantum gravity effects in Black Hole (BH) systems. At the moment we can only affirm that the Schwarzschild solution is not wrong if compared to the data, but a number of future experiments is promising to reach much higher levels of sensitivity and probe different frequency ranges and larger redshifts. For the first time over the last century, possible anomalies pointing at new physics and giving insights on the nature of the gravitational interaction and BHs may be detected. Various alternative descriptions of BHs have been developed with the aim of solving some of the most puzzling issues of gravitation, central singularity and information loss paradox and the related no-hair theorem among the others.

As usual in physics, a lot of information can be extracted through scattering experiments. Within this framework the quasi-normal modes (QNMs) and greybody factors play a fundamental role. The first are the dissipation modes of a perturbed BH and they seem to be deeply related to the nature of the BH itself. This is why they are considered as the characteristic oscillation modes of the BH. Furthermore, they are seen to dominate the ringdown gravitational waveforms at late time so that they are among the preferred candidates to host possible deviations from the general relativistic description. On the other side, the greybody factors encode the deviation of Hawking radiation from the pure black-body one, or in other words, the percentage of Hawking radiation which could reach us after scattering through the potential barrier surrounding the BH. Again, these quantities are intimately connected to the parameters describing the BH.

Therefore, a deep investigation of QNMs and greybody factors in different physical situations (such as possible exotic compact objects) and with different tools (both purely theoretical and numerical) offers a rich playground to test the quantum nature of gravity, no-hair theorems and alternative theories of gravity among other things.

Photometric studies of stars are a crucial tool to understand the variability of stellar radiation, provide insights on magnetohydrodynamical processes occurring in the stars, and for detecting exoplanetary transiting between us and their host stars. Variations of stellar luminosities show up in stellar light curves and can reveal both noisy fluctuations in stellar radiation and transiting exoplanets. Thanks to time series of photometric data we can measure the period of rotation for a star. This problem may appear easy, but it is in fact quite complex because every measure of rotational period relies on features appearing on stellar surface like stellar spots or faculae. The occurrence of these features is currently not understood and it is difficult to predict, and so it is their life time. We therefore need to employ new analysis techniques so to analyze time series and extract useful informations on stellar photometry.

We will analyze data from the Nasa Kepler mission, that observed several thousands of stars. We will concentrate on some M dwarfs from the Kepler catalogue, some sun-like stars, and we will also analyze solar data. We will use a new time series analysis technique base on multifractal modelling of data. This multifractal technique allows identifying time scales with a model-free approach, and provides information the noisy beheaviour of data sets. We will compare our results with previous findings, and depict the time evolution of noise in these different kind of stars.

• Get familiar with the multifractal technique, both numerically and
  mathematically (3 weeks)
• Find and download the data (3 weeks)
• Run the analysis (2.5 months)
• Write up our findings (2 months)

Compact stars, and more particularly neutron stars, are a unique laboratory for testing matter under extreme conditions. Over the past years a particular effort has been invested in studying different scenarios for the dense phases of matter in the core of neutron stars, from quarks to hadrons at high densities. The final aim is to understand neutron star observables, such as the mass, radius, magnetic fields or rotation, in terms of a plausible scenario for its interior.

For this purpose, theoretical approaches based on effective field theories for hadronic and quark matter have been developed in our group. The master thesis proposed aims at following the study of the interior of neutron stars by applying the previously developed theoretical frameworks to obtain the equation of state and transport properties of dense matter in the core of neutron stars. With these ingredients, we will be able to address the mass and radius of neutron stars as well as the dynamical properties of neutron stars, going from rotation to the effect of magnetic fields onto neutron stars.

The transport of water and organics to our planet occurred from sequestration of these volatile phases at an early stage of the formation of planetary embryos. The study of chondritic meteorites can be complemented with the interpretation of modern dynamic studies of the mixing of primordial materials available in proto-planetary disks.

Eclipsing binary stars are fundamental laboratories in stellar astrophysics because they can provide the masses and radii of stars with a precision of a few percent, which can be later used to compare the predictions of stellar theoretical models. Our research group has a lot of experience on the analysis of eclipsing binary stars. Currently, we are conducting photometric and spectroscopic observations to revise the parameters of several systems and to derive the properties of some new ones that have been found using TESS data. Besides, we are measuring eclipse timings from TESS and ground-based data. These eclipse timings can be used with several purposes: to investigate the presence of third bodies in the system (planets or stars), to test General Relativity, or to infer the internal properties of the component stars. In this project, we expect the student to make use of these data to study the properties of such systems.