These seminars have been going on for 10 years now. We gather at the patio of the institute to eat pizza after the seminar as a nice way of ending the week. Since the last few months, the seminars are a hybrid event and we're happy to see you every Friday at 12 pm online.
Nuclear Physics from Neutron Star Mergers
David Tsang (University of Bath)
Neutron stars are the universe’s best natural laboratories to study dense nuclear matter. At high densities and low temperatures inaccessible in terrestrial collider experiments, neutron stars host the most extreme matter in the universe. Different regions of neutron stars will probe different physics, with some observables dominated by the poorly understood physics at supranuclear densities, while others can be used to constrain properties of nucleonic matter, such as the nuclear symmetry energy. I will discuss our latest work on Resonant Shattering Flares, multimessenger signatures which can be used as a powerful constraint on nuclear physics. Studying the spectrum of asteroseismic modes in a neutron stars can provide probes at different densities, and hence of different physics.
The ngVLA, its science cases, and the current role of Mexico
Alfonso Trejo Cruz, Instituto de Radioastronomía y Astrofísica (IRyA-UNAM)
The ngVLA, led by the National Radio Astronomy Observatory (NRAO), will be the largest radio interferometer ever built in the northern hemisphere. With more than 200 antennas distributed across the US, Canada, and Mexico, the array will reach spatial resolutions and sensitivities without precedents. The ngVLA will open a new window on the universe through ultra-sensitive imaging of spectral lines and continuum emission with milliarcsecond resolution. We will summarise the main science goals, from the initial conditions of planetary systems to understanding the origin and evolution of black holes. For Galactic science, synergies between ongoing efforts with the current VLA and the ngVLA will be provided, in particular for AGB stars. In the second part of the talk, we will describe the current ngVLA efforts being pursued in Mexico. The MID Array of the ngVLA will provide some of the longest baselines of the new observatory, with a large fraction of those enabled by the antennas in Northern Mexico. We will discuss the work to select the final MID sites in Mexico, including synthetic observations to characterise the array performance. We’ll finalise with the observatory designs that Mexico is leading, such as antenna base foundations, antenna site layouts, and antenna supporting buildings. Finally, we outline the next steps in the coming 2 years, including workshops and conferences.
I will give a very general review on our group's research on neutron stars in a cauldron of boiling multi-band observations and theoretical simulations. I will then report on two recent results: the first related to a new creepy class of periodic radio bursters, and the second to a few super cold rotating jack-o'-lanterns... and how those are changing our understanding of these wicked stellar zombies.
Current flow in pulsar magnetospheres and the role of twist
Kostas Gourgouliatos, University of Patras (Greece)
He will discuss some properties of the axisymmetric force-free pulsar magnetosphere focusing on the inner edge of the current sheet, the so-called Y-point. While it is usually postulated that it is located at the intersection of the equator with the light-cylinder, we propose that it is energetically favourable to be located within the light-cylinder. Should this be the case, the spin-down dipole magnetic field is likely to be an overestimate of the star's actual field. Furthermore, he will discuss the impact of currents flowing within the closed field lines: in this case, the spin-down power is higher than the one corresponding to the dipole field and for sufficiently high twists the field adopts the structure of a split monopole.
B-field Orion Protostellar Survey: Magnetized Envelopes in Orion
Bo Huang (Institute of Space Sciences, ICE-CSIC)
B-field Orion Protostellar Survey (BOPS) used ALMA to observe 870 um dust polarization toward 61 young low-mass protostars in the Orion molecular clouds. Its main objective is to investigate the role of B-fields from 400 to several thousands au scales, corresponding to the size of molecular envelopes about the youngest (predominately Class 0) protostars. This survey uniformly probe the B-field structure within the envelopes surrounding the protostars to help remove biases based on resolution and different environments. Both the polarization and outflow were successfully detected emission in 56 sources. In 16 of them the polarization is likely produced by self-scattering, most of these are Class 0, suggesting that grain growth appears to be significant in disks in earlier protostellar phases. For the rest sources, the dust polarization traces the magnetic field, whose morphology can be approximately classified into three categories: standard-hourglass, inverted-hourglass, and spiral-like morphology. Two-fifth of the sources exhibit a mean magnetic field direction approximately perpendicular to the outflow from several hundreds to thousands au scales, but for the rest of protostars, this relative orientation appears to be random, probably due to the complex set of morphologies observed. Furthermore, the protostars are classified into three types based on the velocity gradient traced by C17O (3--2): PerpType (gradient perpendicular to outflow), RandType (gradient randomly aligned with outflow), and UnresType (unresolved gradient, less than 1 km/s/arcsec). In PerpType, field lines are preferentially perpendicular to the outflow, and along the collapsing direction, most of them are inverted-hourglass, suggesting that magnetic field have been overwhelmed by gravity. The spiral-like magnetic fields are associated with sources with large velocity gradients, indicating that the rotation motions is strong enough to twist significantly the field lines. All the sources with a standard-hourglass field morphology show no significant velocity gradient probably due to the strong magnetic braking.
Miquel Colom i Bernadich (Max-Planck-Institut für Radioastronomie)
Radio pulsars are highly magnetised, fast-rotating neutron stars born from the collapse of massive stars at the end of their life cycle. Pulsar timing is the technique of modelling a pulsar’s rotation down to every single revolution and comparing it with the times of arrival of radio pulses as recorded by telescopes on Earth. When found in binary systems, this technique is used to track the orbital motion of pulsars in their system. This allows us to investigate a wide range of fundamental physics and astrophysics, such as light propagation physics, alternative theories of gravity, equation of state models of neutron stars and binary evolution. The MeerKAT radio telescope in South Africa is currently the most sensitive facility in the Southern Hemisphere, constituting a great leap forward in the search for and study of pulsars in the Southern Sky. In this talk, he highlights recent science results from pulsar observations with MeerKAT and showcase some of the currently ongoing science projects, such as the TRAPUM pulsar surveys and the RelBin pulsar timing programme.
Closing down the observation gap on millisecond to second timescale relativistic X-ray and radio transients
Sujay Mate, Tata Institute of Fundamental Research (TIFR), Mumbai
Over the past few decades, transient astronomy has boomed with discovery of different types of transient phenomena (e.g. Gamma-ray Bursts — GRBs, Fast Radio Burst — FRBs, compact binary coalescence in gravitational waves — CBCs). Most of these transients are highly relativistic events and key to understanding them is to do multi-wavelength and multi-messenger observations. In this talk, I will present our efforts to build instrumentation to detect milliseconds to second timescale relativistic transient phenomena at X-ray and radio wavelengths. I will present the proposed Indian mission Daksha that aims to detect GRBs and electromagnetic counterparts of GW events. Once launched, Daksha will be one of the most sensitive X-ray/gamma-ray telescope. In particular, I will talk about the prospects of measuring hard X-ray polarisation of GRBs using Daksha, which is a key to understanding emission mechanisms and geometry of GRB jets. For this analysis, we have carried out detailed simulations and have developed a pipeline to measure the polarisation. We estimate that Daksha will have Minimum Detectable Polarisation of 30% for a GRB with fluence 10^-4 erg/cm^2. With this sensitivity, Daksha will be able to measure polarisation of at least five GRBs per year. Towards the end, I will briefly talk about the CHIME/Slow search, that involves our novel efforts to detect radio transients at seconds timescale with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. This parameter space is as-yet unexplored and could harbour interesting transients such as "slower" duration or extremely scattered FRBs, radio counterparts of GRBs or binary neutron star mergers, flaring stars, magnetized white dwarfs and radio emission from X-ray binaries.
Supporting a culture of public engagement at ICE-CSIC
Jorge Rivero, Institute of Space Sciences (ICE-CSIC)
Astronomy allows us to study the far reaches of the universe but also gives us a different perspective on our planet, showing us its fragility and fostering a sense of global citizenship. In this sense, astronomy is in a unique position to engage citizens on scientific topics, make them reflect on their place in the universe, and encourage their critical thinking. Several studies show that citizens consider that professional scientists are best qualified to explain the impact of scientific and technological developments on society. And even though astronomers are quite involved in public engagement in comparison with scientists in other fields, they often rely on individual endeavours with approaches with little engagement and/or lacking goals for deeper interaction beyond one-off events. In this respect it is important to work together with the institution's communication professionals in our common journey to share the wonders of the universe with society while we establish a culture of public engagement at the institution. In this talk, he will present his thoughts on why public engagement is important, why researchers should get involved and work together with science communication professionals as well as showcase the opportunities we offer through ICE-CSIC's Communication and Outreach Office to participate in communication and public engagement activities.
The MagMAR project: First Results
Paulo Cortes, National Radio Astronomy Observatory (NRAO)
The process governing the formation of high-mass stars, those exceeding eight solar masses, remains enigmatic, despite their pivotal role in regulating chemical, radiative, and energetic feedback within our galaxy. Of all the pertinent parameters influencing high-mass star formation, the magnetic field stands as a predominantly uncharted territory, its presence inevitable yet exploration limited. Endeavoring to bridge this knowledge gap, the MagMAR project leverages the unparalleled mapping capabilities of ALMA. In this presentation, he will introduce the MagMAR project and showcase its initial results.
He will show that deceleration (and not acceleration) is the correct interpretation for current measurements of cosmic expansion. The concept of cosmic acceleration, q, that we commonly used is based in the comoving distance. This is a 3D space-like coordinate, which corresponds to distance between events that can not be observed and are not causally related. For a correct interpretation cosmic expansion should be measured using the distance between (4D null) causal events. This is implemented here using a new definition, q_E, for cosmic acceleration. We present a comparison of the two alternative definitions, q_E and q, against data from supernovae (SN) and radial galaxy/QSO clustering (BAO). The standard q analysis reproduces some known tension between SN and BAO, but this tension disappears for q_E, indicating that this definition better fits observations. Data clearly shows that cosmic expansion is decelerating so that cosmic events are trapped inside an Event Horizon, like in the interior of a Black Hole (BH). Rather than a new form of dark energy or modified Gravity, this corresponds to a boundary force that causes friction, i.e. an attractive force, similar to a rubber band that prevents further expansion.