Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies (1112.1078v1)

Abstract: Observational work conducted over the last few decades indicates that all massive galaxies have supermassive black holes at their centres. Although the luminosities and brightness fluctuations of quasars in the early Universe suggest that some are powered by black holes with masses greater than 10 billion solar masses, the remnants of these objects have not been found in the nearby Universe. The giant elliptical galaxy Messier 87 hosts the hitherto most massive known black hole, which has a mass of 6.3 billion solar masses. Here we report that NGC 3842, the brightest galaxy in a cluster at a distance from Earth of 98 megaparsecs, has a central black hole with a mass of 9.7 billion solar masses, and that a black hole of comparable or greater mass is present in NGC 4889, the brightest galaxy in the Coma cluster (at a distance of 103 megaparsecs). These two black holes are significantly more massive than predicted by linearly extrapolating the widely-used correlations between black hole mass and the stellar velocity dispersion or bulge luminosity of the host galaxy. Although these correlations remain useful for predicting black hole masses in less massive elliptical galaxies, our measurements suggest that different evolutionary processes influence the growth of the largest galaxies and their black holes.

• The paper provides direct stellar kinematic measurements that reveal black hole masses far exceeding standard scaling predictions.
• Using Gemini North and Keck 2, researchers determined nearly 9.7×10^9 solar masses for NGC 3842 and approximately 2.1×10^10 for NGC 4889.
• The results imply that massive mergers or accretion in brightest cluster galaxies may require revised models of galaxy and black hole co-evolution.

Analysis of Supermassive Black Holes in Giant Elliptical Galaxies

The paper presents a detailed examination and direct measurement of the masses of supermassive black holes located at the centers of the giant elliptical galaxies, NGC 3842 and NGC 4889. These galaxies are unique as they reportedly host black holes with masses significantly larger than those expected by traditional empirical scaling relations, such as the black hole mass-bulge velocity dispersion (M-σ) and black hole mass-bulge luminosity (M-L) correlations. These findings challenge existing models of black hole and galaxy evolution, particularly in the context of the largest and most massive galaxies in the nearby universe.

The observational data supporting these findings were acquired through high-resolution two-dimensional stellar kinematics obtained using the Gemini North and Keck 2 telescopes. In NGC 3842, a black hole mass of approximately $9.7 \times 10^9$ solar masses was deduced, with a 68% confidence interval ranging from $7.2 \times 10^9$ to $12.7 \times 10^9$ solar masses. The associated velocity dispersion, peaking at 326 km/s at the galactic center, aligns with NGC 3842's status as the brightest cluster galaxy (BCG) of Abell 1367. Similarly, NGC 4889, the brightest galaxy in the Coma Cluster, also contains a black hole of comparable mass, with a best estimate at $2.1 \times 10^{10}$ solar masses. The broader implications of these measurements indicate that the black hole masses exceed those predicted by the standard M-σ and M-L correlations by up to a factor of ten.

The paper's findings suggest intriguing implications for our understanding of galaxy and black hole co-evolution. The assertion that different evolutionary processes may be at play in the largest galaxies suggests that massive mergers, accretion events, or other dynamic interactions might influence these scaling relations in unforeseen ways. Moreover, the distribution and kinematics of stars within these galaxies indicate variations in galactic structural development compared to less massive elliptical galaxies.

The significant discrepancy between measured and predicted black hole masses further implies that current models of black hole growth may be omitting crucial factors, especially in the field of BCGs. This misalignment may necessitate a revision of the scaling relationships at the upper mass range and add complexity to our understanding of massive black holes as relic quasars. Additionally, the intrinsic scatter observed in the M-σ relation at these scales indicates a potential breakdown or modification of the correlation, reinforcing the necessity for direct measurements, especially in such extreme cases.

Future studies building on these results could focus on more comprehensive surveys of the most massive galaxies using integral field spectrographs with advanced adaptive optics. By expanding the sample size and accessibility for direct black hole mass measurements, researchers may refine our comprehension of black hole and galaxy evolution profoundly. This could in turn inform simulations of galactic formation and dynamics, contributing critically to the broader astrophysical context of structure formation in the universe.