Scientists discover a colossal black hole, possibly the largest ever, with the mass of 36 billion suns.

Astronomers have discovered an ultramassive black hole, weighing an incredible 36 billion times the mass of our Sun, at the heart of a galaxy nicknamed the "Cosmic Horseshoe." This black hole, one of the largest ever detected, is located about 5 billion light-years away and is challenging our understanding of how these cosmic behemoths grow and evolve.

The Discovery and the Cosmic Horseshoe 🔭

The discovery was made by a team of researchers using a new method that combines two different astronomical techniques: gravitational lensing and stellar kinematics. Gravitational lensing occurs when a massive object, like a galaxy, bends and magnifies the light from a more distant object behind it. In the case of the Cosmic Horseshoe, the foreground galaxy is so massive it warps light from a background galaxy into a striking horseshoe-shaped ring.

Stellar kinematics involves measuring the speed and movement of stars within a galaxy. By analyzing how the stars in the Cosmic Horseshoe galaxy were zipping around its center—at speeds of nearly $400$ km/s—and how the black hole's gravity was altering the path of light, the scientists were able to make a direct and highly accurate measurement of its mass. This is a significant breakthrough because most previous measurements of similarly large black holes were indirect and had much larger uncertainties.

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An Ultramassive, Dormant Giant 😴

This newly discovered black hole is classified as ultramassive, a term used for black holes exceeding 5 billion solar masses. It's also a "dormant" black hole, meaning it isn't actively consuming material and blasting out energy as a quasar. Its detection relied solely on its immense gravitational pull and the effect it has on its surroundings. This new method of detection allows astronomers to find and measure the mass of "silent" black holes across the universe, even when they're not visible in the traditional sense.

The host galaxy, LRG 3-757, is a type of "fossil group," a galaxy that has absorbed all of its nearby companion galaxies. The researchers believe that the ultramassive black hole at its center likely formed from the merger of all the smaller supermassive black holes that were once at the core of those swallowed galaxies. This suggests that we may be witnessing the "end state" of both galaxy and black hole formation in this system.

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Impact on Our Understanding of the Universe 🤔

The existence of such a massive black hole within the Cosmic Horseshoe is particularly intriguing because it doesn't fit neatly into the established relationship between a supermassive black hole's mass and the velocity dispersion of stars in its host galaxy. This finding suggests that the relationship between black holes and their host galaxies may be more complex at the highest mass scales, and that different processes—such as galaxy mergers and powerful jets from active black holes in the past—might have played a role in their co-evolution.

The research team plans to apply their new method to data from the European Space Agency's Euclid telescope to find more ultramassive black holes. These future discoveries will help to refine our understanding of this relationship and shed light on why some galaxies, like the Cosmic Horseshoe, have stopped forming new stars.