Meet CR7– A completely new type of black hole

Astronomers have found a strange source of powerful radiation that is likely an unusual type of black hole born in the early universe, according to a new report in the journal Monthly Notices of the Royal Astronomical Society.

Using observations from the Hubble telescope, the study team discovered evidence  for a “direct-collapse black hole,” a type of object that had been solely theoretical until now.

“It’s a cosmic miracle,” study author Volker Bromm, an astronomer at The University of Texas at Austin, said in a news release. “It’s the only time in the history of the universe when conditions are just right” for them to form.”

Finding an Elusive Black Hole

Scientists have said these kinds of black holes eventually become the supermassive black holes found in the middle of many, if not all, galaxies.

When an immense star reaches the end of its lifetime, it can collapse inward on itself to create a black hole. These dense balls of matter then grow by feasting on surrounding gas and dust, but this sequence can take time. With some supermassive black holes existing only 750 million years after the Big Bang, researchers have had a difficult time explaining how such a massive black hole could develop over such a short time, especially when forming stars in the early galaxy tended to blow away cosmic dust and gas.

“Star formation is the enemy of forming massive black holes” in early galaxies, Bromm said. “Stars produce feedback that blows away the surrounding gas cloud.”

In 2003, researchers speculated that clouds of gas and dust in the early universe were so hot they didn’t break down into several clumps of thousands of stars. Rather, such clouds probably produced just a single substantial star at the center, approximately 1 million times bigger than standard stars.

In the pursuit of confirming this theory, the study team focused on a galaxy identified by the Hubble telescope called CR7, seen to us as it was 1 billion years after the Big Bang. Follow-up observations showed extremely strange features in the light signature coming from CR7. In particular a hydrogen line in the spectrum, referred to as “Lyman-alpha,” was many times more brilliant than expected. The scientists said they were surprised to see the spectrum also exhibited an unusually bright helium line.

To stay superhot and lead to a rapid death, the gas in the middle of this sequence would need to be nearly all hydrogen and helium, without “heavier” elements to cool it down. Because heavy elements are generated in the hearts of stars and then spit out during a supernova, such “direct-collapse black holes” could only establish in the early universe, the scientists said.

Observations of CR7 showed no signs of elements besides helium and hydrogen. Simulations ran by the study team confirmed a star cluster scenario for CR7 “spectacularly failed,” while the direct collapse black hole model performed well.

Bromm said the study is about more than just one early galaxy.

“With CR7, we had one intriguing observation,” he said. “We are trying to explain it, and to predict what future observations will find. We are trying to provide a comprehensive theoretical framework.”

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Image credit: Aaron Smith/TACC/UT-Austin

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