The Astrophysics of Compact Objects

The new generation of X-ray satellites has boosted X-ray astronomy to unprecedented levels in the last decade. The future will bring marvellous spectroscopic capabilities to study even extreme physical phenomena, like gravity around black-holes. Even before the planned high throughput missions, smaller scale missions, like Symbol-X, will extend imaging to higher energy (10-80 keV), widening the horizons of X-ray astronomy.

At INAF-Padova X-ray astronomy focuses on compact objects, especially black holes in ultraluminous X-ray sources, isolated neutron stars and white dwarfs in accreting and hydrogen burning systems. We investigate the basic physical parameters (mass, radius, spin, surface magnetic field) and the evolution and fate of these systems.

Ultraluminous X-ray sources (ULXs) are extragalactic, non-nuclear X-ray sources that appear to belong to a given galaxy, so that the distance is known, but are extremely luminous. As a matter of fact the luminosity of ULXs is orders of magnitude above the Eddington limit for a few solar masses. The object powering the X-ray luminosity may be a black hole of ~100 solar masses. We are leading a national project, funded by a PRIN-INAF grant, aimed at tackling the most challenging questions on these puzzling sources. The planned activity in this area will concentrate on the measurement of the orbital period of ULX binary systems, the investigation of the correlation between the X-ray spectral and timing properties of ULXs, the comparison of theoretical models of ULX binary systems with observations and the exploration of alternative scenarios for the formation of their compact remnants.

Our research on X-ray dim isolated neutron stars has led to the first identification of the seventh member of this class of objects. We have shown evidence of a periodicity in the X-ray flux and an absorption feature in the X-ray spectrum, yielding an estimate of the surface magnetic field consistent with that of magnetars. Recently we reported the very first detection of a candidate optical counterpart for this object. In the future, we plan to compare the light curves and spectra of this unique class of objects with theoretical models.

We also study the extremely hot white dwarfs in post-outburst novae. The amazing recurrent nova RS Ophiuchi was observed and monitored at all wavelengths by all facilities in the world during its 2006 outburst. We obtained the first high resolution X-ray spectra of both the white dwarf and the nova wind, with the first emission lines spectra of the ejecta. This research is continuing with new observations of other classical novae. One important aim is to understand their X-ray variability and periodic oscillations. Thanks to these observations, we are beginning to gain insight also in the influence of white dwarf rotation and magnetic field in the nova outburst and secular evolution.

We are also engaged in X-ray population studies in nearby galaxies. Our aim is to follow the possible path of supersoft X-ray sources towards SN Ia evolution. In order to address issues such as: "Does hydrogen burning continue at extremely high rates on secular time scales, or do strong winds from the binary systems prevent accumulation of sufficient mass for the supernova?", we observe the frequency and evolution of close binary supersoft X-ray sources in external galaxies. We also monitor the sources for several years, as we recently did on Andromeda.

The Astrophysics of Compact Objects -PAST STUDIES

News – MEDIA INAF

Il notiziario online dell'Istituto Nazionale di Astrofisica
  • La mappa del campo magnetico realizzata da un team di astronomi nei dintorni del buco nero nel sistema binario V404 Cygni presenta valori dell’intensità del campo magnetico fino a quattrocento volte inferiore a quelli attesi. Piergiorgio Casella (Inaf): «È un risultato senza precedenti, che apre la strada ad una comprensione maggiore di ciò che avviene attorno a questi oggetti misteriosi»

  • Due articoli firmati dall’astronomo svizzero André Maeder, entrambi pubblicati su ApJ, presentano un modello cosmologico che ambisce a spiegare ciò che osserviamo senza dover ricorrere a energia e materia oscure. È plausibile? Lo abbiamo chiesto a un cosmologo dell’Inaf, Carlo Burigana

  • Usando le antenne di Alma, un gruppo di ricercatori ha scoperto due galassie che si sarebbero formate quando l'universo aveva appena il 5 per cento dell'età attuale. Secondo i dati raccolti, i due oggetti lontanissimi erano avvolti da un’immensa struttura: un alone di materia oscura

  • Lo spettrografo di terza generazione installato al Very Large Telescope dell'Eso ha condotto con successo le sue prime osservazioni. Filippo Zerbi (Inaf): «Espresso è uno strumento fuori dal comune e fuori dal comune è stata la sfida decennale per concepirlo, realizzarlo e infine portarlo pienamente funzionale al telescopio»

  • Ipotizzate nel 2014, le “strongly interacting massive particles” sono entrate a far parte della lista di particelle candidate a spiegare la dark matter. Ne ha parlato in questi giorni a Cape Town, al 29esimo Texas Symposium on Relativistic Astrophysics, uno degli scienziati che le hanno proposte, Hitoshi Murayama

  • Lo scienziato australiano Tobias Westmeier ha prodotto la mappa più dettagliata mai ottenuta delle nubi di idrogeno neutro ad alta velocità. Il risultato, pubblicato su Monthly Notices of the Royal Astronomical Society, migliora in sensibilità e risoluzione le mappe precedenti, e potrebbe fornire nuovi indizi sull'origine di queste nubi e sulle condizioni fisiche al loro interno

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