How do supermassive black holes grow? Does this change over cosmic time?

« Back to Science Goals

One of the main themes in extragalactic astronomy continues to be the exploration of the dawn of the modern Universe, when the first galaxies formed. A crucial ingredient of galaxy formation and evolution are Supermassive Black Holes (SMBHs). The most efficient way to study SMBHs at large redshifts is with X-rays, since these wavelengths penetrate the surrounding absorbing gas and dust. While future observatories like JWST, ALMA and 30m–class ground-based telescopes will observe the starlight from galaxies out to the highest redshifts, IXO will play a crucial role by detecting the accretion power from their embedded SMBHs (10⁷–10⁹ solar masses), even when obscured.

To find and study growing SMBH at large z, which are rare objects, requires a combination of large effective area (3 m² at 1 keV), good angular resolution (5 arcsec) and large field of view (18 arcmin). These capabilities allow IXO to reach Chandra´s limiting sensitivity 20 times faster, enabling the first full characterization of the population of accreting SMBHs at z ~ 7, and constraints at z = 8–10, deep into the cosmic "dark age."

IXO will measure X-ray spectral slopes and luminosities, which in turn provide constraints on accretion rates, thus assessing directly SMBH growth at large redshifts. Constraints of Fe Kα lines and other spectral features are generally too weak at present to provide useful physical insights (e.g., black hole spin), but will be measured routinely with IXO´s large throughput.

For more information, refer to IXO Astro 2010 Decadal White Papers:

1. Fundamental Accretion and Ejection Astrophysics, J. Miller et al.
2. Stellar-Mass Black Holes and Their Progenitors, J. Miller et al.
3. The Growth of Supermassive Black Holes Over Cosmic Time, K. Nandra et al.