Bangladeshi scientist leads cosmic study offering clearer look at black holes

In September 2020, preeminent American science biweekly – Science News – named 10 scientists in the world – all under 40 years of age – whom it considered the most promising in their respective fields of scientific works. Bangladeshi scientist Tonima Tasnim Ananna, then only 29 years of age, made it to the Science News’ – ‘10 Scientists to Watch’ – list being the youngest of the lot.

Science News, now in its 100th year of publication, praised her feat saying: “Tonima Tasnim Ananna is bringing the heaviest black holes out of hiding. She has drawn the most complete picture yet of black holes across the universe — where they are, how they grow and how they affect their environments.”

Two years later, Tonima and her team at the United States’ Dartmouth College have now advanced mankind’s knowledge about black holes and lights emitted therefrom, which have long mystified researchers.

Supermassive black holes are believed to reside at the center of nearly all large galaxies. The space objects devour galactic gas, dust and stars. By knowing how fast a black hole is feeding, its mass, and the amount of radiation nearby, researchers can determine when some black holes underwent their biggest growth spurts. That information, in turn, can tell them about the history of the universe.

When new images captured by Nasa’s James Webb Space Telescope help scientists understand some of the most powerful forces in the universe, Ananna and her team’s latest study is clarifying the mystery of supermassive black holes in the rapid growth stage, known as active galactic nuclei or AGN.

“The light signatures from these objects have mystified researchers for over a half-century,” says Tonima Tasnim Ananna, currently a Postdoctoral Research Associate in Professor Ryan Hickox’s group at Dartmouth College. She is the lead author of a new paper on the special family of black holes, published last month in the Astrophysical Journal (ApJ), run by the American Astronomical Society.

Light coming from near supermassive black holes can have different colors with varied levels of brightness and spectral signatures. Until recently, researchers believed that the differences depended on viewing angle and how much a black hole was obscured by its “torus,” a doughnut-shaped ring of gas and dust that usually surrounds active galactic nuclei.

But Ananna, Ryan Hickox and their other team members challenged this model and they have found that the black holes look differently because they are actually in separate stages of the life cycle.

According to a Dartmouth College news report, the team’s study found that the amount of dust and gas surrounding a supermassive black hole is directly related to how actively it is growing. When a black hole is feeding at a high rate, the energy blows away dust and gas. As a result, it is more likely to be unobscured and appear brighter.

The research provides some of the strongest evidence yet that there are fundamental differences between supermassive black holes with different light signatures, and that these differences cannot be explained only by whether the observation is taking place through or around an AGN’s torus.

“This provides support for the idea that the torus structures around black holes are not all the same,” the Dartmouth College report quoted Hickox, the study co-author, as saying. “There is a relationship between the structure and how it is growing.”

Taking the study to larger distances of the Universe
In an email interview with Dhaka Tribune, Ananna says, their research will open up pathways to better understand where do the supermassive black holes come from, eventually giving us more knowledge about the universe as a whole.

“This result is the current snapshot of the Universe, but as we look at greater distances, we look further back in time, and we want to understand how black holes have evolved over time, so my team’s next steps will be to expand our study to larger distances of the Universe,” explained Ananna, a graduate from Bryn Mawr College who obtained her master’s and doctorate degrees from Yale University.

Talking about Nasa’s James Webb Space Telescope (JWST), Ananna says: “The Hubble Telescope was launched in 1990, and provided us with images of galaxies with unprecedented clarity. This spurred the astronomical community into action to build a telescope that could provide even greater clarity and see even further back in time, and thus, the JWST was proposed. This telescope has been in the making for the last two decades. In fact, when I was an intern in Nasa’s Space Telescope Science Institute (STScI) in 2011, the gold-plated mirrors were already built and assembled, and I got to see them and meet Dr. Jane Rigby, the Goddard Space Flight Center Astrophysicist who presented the JWST images to President Biden this July.”

“She has been working on this telescope for about 15 years, and a lot of people have spent an entire career building this telescope. There are many risk factors associated with a launch like this, so it is truly amazing that all their hard work has paid off.”
Ananna further states: “The JWST is an infrared telescope, whereas the Hubble Space Telescope is an optical telescope. These are two distinct parts of the electromagnetic spectrum. We can see optical light using our eyes. We can feel infrared as heat, and we see the effect of ultraviolet rays on our skin. Each wavelength shows a different aspect of the Universe to us.”

“The advantage of infrared light over optical light in observing the Universe is that infrared wavelengths are bigger, so it can penetrate a lot of dust and gas, giving us a clearer view of hidden things that would be difficult to detect using optical light – such as the majority of supermassive black holes. The topic of my research is supermassive black holes, so I am excited to start looking into data from the JWST.”

Besides providing amazing images, according to Ananna, the JWST will lead to many scientific breakthroughs. She thinks: “So the next decade would be a very exciting time for infrared Astrophysics, and for communicating science to the general public!”

At an early age Ananna realized there were other worlds
When Ananna was a 5-year-old in Dhaka, Bangladesh, her mother told her about the Pathfinder spacecraft landing on Mars. Her mother was a homemaker, she says, but was curious about science and encouraged Ananna’s curiosity, too.

“That’s when I realized there were other worlds,” she says. “That’s when I wanted to study astronomy.”

There were not a lot of opportunities to study space in Bangladesh, so she came to the United States for undergrad, attending Bryn Mawr College in Pennsylvania. She chose an all-women’s school not known for a lot of drinking to reassure her parents that she was not “going abroad to party.” Although Ananna intended to keep her head down and study, she was surprised by the social opportunities she found. “The women at Bryn Mawr were fiercely feminist, articulate, opinionated and independent,” she says. “It really helped me grow a lot.” Traveling for internships at Nasa and CERN, the European particle physics laboratory near Geneva, and a year at the University of Cambridge, boosted her confidence. (She did end up going to some parties — “no alcohol for me, though.”)

Now, Ananna is giving back. She co founded Wi-STEM (pronounced “wisdom”), a mentorship network for girls and young women who are interested in science. She and four other Bangladeshi scientists who studied in the United States mentor a group of 20 female high school and college students in Bangladesh, helping them find paths to pursue science.