Unusual black hole found at universe’s dawn presents dusty mystery to astronomers

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The astronomers spotted the object in question in the study from when the universe was just around 660 million years old. File. NASA via AP.

When the James Webb Space Telescope looks deep into the Universe, some of the objects it finds appear as small, red dots. Astronomers call them little red dots (LRDs), and they have become one of the telescope’s more intriguing discoveries.

Now, an international team of astronomers has found an unusual object that may help explain what at least some of these red dots actually are: unusually young and rapidly growing black holes surrounded by an enormous amount of dense gas.

The astronomers spotted the object in question in the study from when the universe was just around 660 million years old. Put another way, the light from this object has travelled for more than 13 billion years before reaching the earth, which the Webb telescope orbits.

The researchers’ observations suggest that almost all the light coming from the object is produced by a supermassive black hole. They were published in Nature on August 12 .

Astronomers have generally thought that the red colour of LRDs is due to dust. This is because dust absorbs blue light more readily than red light, so more red light reaches the observer.

However, the team found the object to be telling a different story. Specifically, they found that its colour could instead be explained by a colossal cocoon of gas surrounding the black hole.

The team first spotted the object in images taken by the Webb telescope because it was exceptionally red in colour. It appeared in some of the telescope’s infrared filters but virtually disappeared at shorter wavelengths.

The researchers then used one of Webb’s instruments to split its light into its spectrum — its various wavelengths. And this spectrum contained something extraordinary: a very large Balmer break. This is a gap in the spectrum that occurs because hydrogen is absorbing light at those wavelengths. Astronomers are used to seeing this break in light coming from stars, but it is still not so big.

The Balmer break in the light from the object suggested that the light was passing through a large and turbulent quantity of hydrogen gas.

According to the astronomers’ model, it would have to have around 100 billion particles per cubic centimetre, extend to several million kilometres around the black hole, and move at hundreds of kilometres per second.

(Aside: Even air at sea level on the earth contains around 25 billion particles per cubic centimetre — meaning the hydrogen cocoon is around 250 million times less dense than ordinary air! The cocoon is still exceptional because of the fact that this relatively thin gas is still spread across a large distance while also being concentrated around a violent black hole, and being dense enough to distort the light passing through it.)

The black hole is actively feeding on matter. As material falls towards it, it forms a hot, bright accretion disk and releases enormous amounts of radiation.