Kavli Affiliate: Erin Kara
| First 5 Authors: Erin Kara, Javier García, , ,
| Summary:
X-rays are a critical wavelength for understanding supermassive black holes
(SMBHs). X-rays probe the inner accretion flow, closest to the event horizon,
where gas inspirals, releasing energy and driving black hole growth. This
region also governs the launching of outflows and jets that regulate galaxy
evolution and link SMBH growth to their host galaxies.
This review focuses on X-ray observations of SMBHs, through "standard
accretion" in persistent Active Galactic Nuclei (AGN) and in extreme transient
events, such as Tidal Disruption Events (TDEs), Changing-Look AGN (CLAGN), and
Quasi-Periodic Eruptions (QPEs). We describe the X-ray spectral and variability
properties of AGN, and the observational techniques that probe the inner
accretion flow. Through understanding the phenomenology and accretion physics
in standard, individual AGN, we can better search for more exotic phenomenon,
including binary SMBH mergers, or Extreme Mass Ratio Inspirals (EMRIs).
In this review, the reader will discover:
(1) X-ray variability on timescales from minutes to hours traces accretion
near the event horizon.
(2) X-rays can measure the black hole mass, spin and accretion flow geometry
and dynamics.
(3) In transients like TDEs, X-rays probe the newly formed accretion disk
that feeds the black hole.
(4) QPEs are posited to be EMRIs orbiting accreting SMBHs that would emit
low-frequency gravitational waves.
(5) Future X-ray, time-domain and multi-messenger surveys will revolutionize
our understanding of SMBH growth.
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