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NASA’s IXPE Reveals Insights into New Binary Black Hole System Swift J1727.8-1613
NASA’s Imaging X-ray Polarimetry Explorer (IXPE) has provided astronomers with a deeper understanding of the structures surrounding black holes, particularly the swirling accretion disks and the dynamic plasma regions known as coronas.
In the summer of 2023, astronomers identified a stellar-mass black hole within the binary system Swift J1727.8-1613 during a notable brightening event. This occurrence saw the black hole temporarily surpass almost all other X-ray sources in brightness. IXPE is the first spacecraft of its kind to observe the black hole through the stages of this X-ray outburst, capturing crucial data from inception to cessation.
This discovery has sparked a series of important studies in scientific journals, including The Astrophysical Journal Letters, The Astrophysical Journal, and Astronomy & Astrophysics. Researchers assert that these results enhance our understanding of the behavior and evolution of black hole X-ray binary systems.
Astrophysicist Alexandra Veledina from the University of Turku, Finland, noted the remarkable speed of the outburst’s evolution. “The system peaked just days after we first detected it. By that point, IXPE and various other telescopes were gathering critical information. Witnessing the entire cycle from eruption to quiescence was truly thrilling,” she remarked.
Swift J1727 displayed a brightness that eclipsed that of the Crab Nebula, a standard reference for measuring X-ray brightness, until late 2023. Such bright outbursts are common in binary star systems, but the proximity of Swift J1727, located a mere 8,800 light-years away, makes it particularly significant for observation. The binary system honors the Swift Gamma-ray Burst Mission, which initially identified the outburst on August 24, 2023, using its Burst Alert Telescope, leading to the recognition of the black hole.
Typically, X-ray binary systems consist of two closely situated stars in different life stages. When the older star depletes its nuclear fuel, it can undergo a supernova explosion, leaving behind either a neutron star, white dwarf, or black hole. In the case of Swift J1727, the black hole’s intense gravitational pull strips material from its companion star. This material reaches temperatures exceeding 1.8 million degrees Fahrenheit, generating a significant output of X-rays. The resulting mass forms an accretion disk, which may also include a superheated corona. Additionally, matter can escape from the binary system as relativistic jets from the black hole’s poles.
IXPE has been pivotal in studying these phenomena, specializing in X-ray polarization, a light property that aids in mapping the structures surrounding such intense energy sources. This capability allows scientists to infer the workings of black holes even when direct observation is impossible due to their gravitational pull.
“Since light can’t escape from within a black hole’s gravity, we rely on observing the surrounding activity to understand their processes,” Veledina explained. “IXPE plays a vital role in this exploration.”
Two studies utilizing IXPE data, spearheaded by Veledina and Adam Ingram from Newcastle University, concentrated on the initial phases of Swift J1727’s remarkable outburst. During the brief period of heightened luminosity, the corona emerged as the predominant source of detected X-ray radiation.
“IXPE documented the polarization of X-ray radiation aligned with the estimated direction of the black hole jet, indicating the hot plasma is concentrated in the plane of the accretion disk,” noted Veledina. This finding aligns with previous results observed in the well-studied black hole binary Cygnus X-1, confirming the consistency of geometric structures among short-lived eruptive systems.
The research group also tracked changes in polarization values throughout the peak of Swift J1727’s outburst, revealing that the conclusions corresponded with observations spanning other bands of electromagnetic radiation.
Further investigations led by Jiří Svoboda and Jakub Podgorný from the Czech Academy of Sciences focused on the X-ray polarization characteristics during the latter stages of the outburst and the subsequent return to a highly energetic state after several months. Podgorný’s work with IXPE data and black hole simulations earned him a prestigious national award for his doctoral thesis in the natural sciences.
The polarization findings suggested a stability in the corona’s geometry despite the system’s evolution and a marked decrease in X-ray brightness during later energy states.
This series of studies marks a significant advance in understanding the evolving structures of accretion disks, coronas, and related features surrounding black holes. Moreover, they demonstrate IXPE’s potential in linking different elements within black hole systems and collaborating with other observatories to monitor sudden cosmic changes effectively.
“While additional observations of matter surrounding black holes in binary systems are essential, the successful initial observation campaign of Swift J1727.8–1613 represents an exciting start to this new chapter of exploration,” stated Michal Dovčiak, co-author and leader of the IXPE working group focused on stellar-mass black holes at the Czech Academy of Sciences.
More information:
Alexandra Veledina et al., “Discovery of X-Ray Polarization from the Black Hole Transient Swift J1727.8−1613,” The Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/ad0781
Adam Ingram et al., “Tracking the X-Ray Polarization of the Black Hole Transient Swift J1727.8–1613 during a State Transition,” The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad3faf
J. Podgorný et al., “Recovery of the X-ray polarization of Swift J1727.8−1613 after the soft-to-hard spectral transition,” Astronomy & Astrophysics (2024). DOI: 10.1051/0004-6361/202450566
Jiří Svoboda et al., “Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State,” The Astrophysical Journal Letters (2024). DOI: 10.3847/2041-8213/ad402e
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