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International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld

Supermassive black holes and powerful telescopes: new Professor Joe Hennawi

Meet the newest Full Professor at the Leiden Observatory: Joe Hennawi. All the way from Santa Barbara, California, Hennawi will strengthen the astronomy institute. In Leiden, he will use his recent ERC Advanced Grant to study how supermassive black holes come into existence.

An observatory with a great atmosphere

Previously a long-term visitor at the Leiden Observatory, Hennawi just started his official position as a Leiden Professor on 1 June 2021. ‘I am delighted to be here,’ he says. ‘Leiden Observatory is one of the top astronomical research institutes in the world. The atmosphere here is intellectually stimulating and very collegial.’

Originally from California, Hennawi is also a professor in his home state. Here, he works in the department of Physics at the University of California, Santa Barbara (UCSB). On departing for Europe, Hennawi said:  ‘My parents are still in California and were sad to see me go. However, I’ll be visiting them regularly since I’m still on the faculty at UCSB.’

Unraveling the secrets of supermassive black holes

Part of Hennawi’s motivation for coming to Leiden was his European Research Council (ERC) Advanced grant, which provides him with 2.5 million euro’s to fund his research in Leiden for the next five years. His research is all about distant astronomical objects known as quasars. Hennawi: ‘Quasars are located in the center of a massive galaxy. They consist of a supermassive black hole surrounded by a gaseous accretion disk. As the material of the disk falls onto this supermassive black hole, energy is released. During these phases of black hole growth quasars shine nearly a thousand times brighter that than the galaxy they reside in!’

Hennawi’s research group studies these quasars using the most powerful telescopes on earth and in space to address fundamental questions about the Universe’s history. The main goal? ‘Trying to understand how these supermassive black holes came into existence’, Hennawi says.

An artist’s impression of the second most distant quasar ever found. It was discovered by the international Gemini Observatory and Cerro Tololo Inter-American Observatory (CTIO), Programmes of NSF’s NOIRLab. In honour of its discovery from Maunakea, a sacred mountain revered in Hawaii, the quasar J1007+2115 was given the indigenous Hawaiian name Pōniuāʻena, meaning 'unseen spinning source of creation, surrounded with brilliance'. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld

A telescope upgrade that will trigger new discoveries

The biggest upcoming development will be the launch of the James Webb Space Telescope (JWST) in October of this year, which is the successor to the well-known Hubble Space Telescope. ‘JWST will observe objects in the distant Universe with unprecedented sensitivity,’ says Hennawi. ‘It will likely usher in many important new astronomical discoveries.’

Testing a 60-year-old theory

In fact, Hennawi will be one of the first astronomers to use the powerful new JWST to observe the most distant quasars in the Universe. According to Hennawi, the biggest challenge in understanding how supermassive black holes grow, arises from the fact that the process is believed to occur over tens of millions of years. ‘That’s far longer than humans have even existed on Earth, so we can never directly measure this process from beginning to end.’ Similar to how anthropologists indirectly piece together human evolution, astronomers therefore employ indirect methods to understand how black holes grow. 

Hennawi and his colleagues have recently proposed a new experiment to use JWST to directly measure how long quasars have been shining, which is critical for testing theories of how they formed. Hennawi: ‘The first quasar was discovered in 1963 by the Dutch astronomer Maarten Schmidt. Astronomers back then argued that they must shine for 50 million years. Now, 60 years later, JWST will allow us to test this idea directly.’

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