Cosmic compact objects

Are the most extreme objects in the Universe, accumulating enormous amount of mass in a small space. They are formed as e result of supernovae explosions of the largest stars. The explosion is so powerful that the core of the star collapses inward, creating a black hole or neutron star. Neutron stars are made of atomic nuclei so crushed that this kind of matter cannot be obtained in Earth laboratories. On the other hand, black holes are regions of space-time where the compressed elementary particles are no longer able to create any gravitationally stable formation defined by the known laws of matter. Therefore, black holes are constantly collapsing stars, interacting with their surroundings only through the enormous force of gravity. Dead stars roam the cosmos. If on their way, they encounter areas of gas, they naturally initiate the phenomenon of accretion - i.e. the gravitational fall of gas onto a compact object.

Accretion

Of gas onto compact object, either onto black hole or neutron star, is one of the most powerful way of energy production in the Universe, which is than converted into electromagnetic flux. Therefore, astrophysicists, aiming to understand the nature of compact objects of various masses, they constantly monitor the radiation of matter, which disappears on our eyes, feeding black holes.

Therefore, there is a great importance to find common mechanism responsible for X-ray fingerprints of accreting compact objects – those with huge BH mass as active galactic nuclei (AGN) and those with stellar mass black holes or neutron stars. Over many years of X-ray observations we can formulate characteristic features, which are as fingerprints of accreting compact object.

Fingerprints

1st fingerprint - double peak continuum emission, where soft energy component is related to the disk emission and hard energy component describes the emission from the hot region (inner accretion flow or hot corona), observed in AGN by: Vasudevan & Fabian (2009) and Jin et al. (2012); in ULXs by Stobbart et al. (2006) and Gladstone et al. (2009); and in XRBs by: Ebisawa et al. (1994) and Zdziarski et al. (2002).

2nd fingerprint - soft X-ray excess at ~1keV, observed in AGN by: Pounds et al. (1987) and Magdziarz et al. (1998); in ULXs by: Goad et al. (2006) and Pintore & Zampieri (2012); and in XRBs by: Gierliński et al. (1999) and Zhang et al. (2000).

3rd fingerprint - iron Kα emission line produced by external illumination, observed in AGN by: Tanaka et al. (1995) and Iwasawa et al. (1999); in ULXs by: Strohmayer & Mushotzky (2003) and Mondal et al. (2021a); and in XRBs by: Miniutti, G. et al. (2004) and Miller et al. (2004).

4th fingerprint - narrow absorption lines originating from ionized winds, observed in AGN by: Kaspi et al. (2001) and Behar et al. (2003); in ULXs by: Pinto et al. (2016); and in XRBs by: Lee et al. (2002) and Miller et al. (2008).

5th fingerprint - soft X-ray lag as a tracer of the mass of compact object observed in AGN by: Fabian et al. (2009), De Marco et al. (2011) and Kara et al. (2013); in ULXs by: Heil & Vaughan (2010) and De Marco et al. (2013a); and in XRBs by: Uttley et al. (2011).

We explore

All these fingerprints in the context of developing new codes for computing advanced theoretical models of emission, collecting and analyzing X-ray data from currently working satellites, and finally making predictions of signal detected by future X-ray missions as ATHENA (European Space Agency, ESA mission) and ARCUS (NASA mission).

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