A Gravitational Shadow at the Dawn of the Universe ✛ ✎

Original: "Resolving the black hole sphere of influence in a hyper-luminous obscured quasar at redshift 4.6"

arXiv:2504.13409 · 2025-04-18 · arXiv non-exclusive · independent analysis · 2 min

For the first time, the mass of a supermassive black hole has been dynamically measured at a redshift greater than two, using the motion of gas within its sphere of influence.

Quasar W2246–0526 is a beacon lit when the universe was just 1.3 billion years old. Its light has traveled 12.8 billion years to reach us, yet even at such a distance, astronomers have spotted what had eluded them for decades: the gravitational shadow of a black hole. Here, shadow is not a metaphor but a precise image: a black hole with a mass of 6.3 billion Suns warps space so that the gas at the galaxy's center moves faster, as if caught in an invisible whirlpool.

To see this whirlpool, the ALMA telescope split the quasar's light into elliptical rings. In each ring, astronomers measured the spread of gas velocities, what they call velocity dispersion. At the outskirts, the gas flows calmly at 186 kilometers per second. Closer to the center, the dispersion rises to 300 kilometers per second. This profile is the imprint of the black hole's gravity, which dominates a region 2300 light-years across. This is its sphere of influence, and for the first time it has been resolved at such a vast distance.

The black hole in W2246–0526 has a mass equivalent to about 6.3 billion Suns, and its sphere of influence extends 2300 light-years, which is like the distance from the Sun to the nearest star multiplied by 500.

Previously, dynamical masses of black holes at redshifts greater than two had not been measured. In unobscured quasars, X-ray emission destroyed the [C ii] line, the main tracer of gas motion, and the sphere of influence was not resolved. W2246–0526 turned out to be an ideal target: a dense dusty envelope shields the X-rays, preserving the carbon line. Modeling showed that the black hole mass is 6.3±0.14×10⁹ M☉, and the galaxy within a radius of 1.31+0.34−0.39×10¹⁰ M☉. The Eddington ratio is 1.58±0.04, meaning the black hole is accreting matter faster than the limit that radiation pressure would seemingly impose.

This result is not just a record. It opens the way to statistically testing empirical mass estimation methods in the early universe. The agreement between the dynamical mass and the estimate from the Mg II line confirms that calibrations work for hyperluminous quasars. Now astronomers can target a sample of obscured quasars and gather statistics that will show whether black holes in the early universe are indeed overmassive relative to their galaxies. The answer to this question will change our understanding of the coevolution of galaxies and black holes.

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R_{\mathrm{SoI}} = \frac{G M_{\mathrm{BH}}}{\sigma^2}

The radius within which the black hole's gravity dominates over the galaxy's gravity; G is the gravitational constant, M_BH is the black hole mass, and σ is the velocity dispersion of stars or gas.

\sigma(r) = \sqrt{\frac{2}{3} \frac{G [M_{\mathrm{BH}} + M_{\mathrm{Host}}(<r)]}{r}}

The intrinsic velocity dispersion at radius r; M_Host(<r) is the galaxy mass within radius r.

Scientists

Stephen Hawking Jacob Bekenstein Fritz Zwicky John Archibald Wheeler Karl Schwarzschild Subrahmanyan Chandrasekhar

Concepts

intermediate mass black hole supermassive black hole schwarzschild radius neutron star mass limit obscured quasar schwarzschild metric spin parameter photon sphere surface gravity dark energy measurement radio loud quasar effective spin innermost stable circular orbit kerr metric gw190814 hubble tension Chandrasekhar limit black hole mass inner horizon

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A Gravitational Shadow at the Dawn of the Universe ✛ ✎