The Columns: A Star Is Born

Steve Doty is one of a handful of scientists worldwide who have been charged with interpreting the data streaming in from the Herschel Space Observatory - data that reveal just how stars are made.
The Columns - A Star Is Born

Meet Steve Doty, obstetrician to the stars.

No, not those stars. The real ones. You know, like our sun.

“Stars are like people: They’re born, they live, and they die,” says Doty, who studies the first stage in that progression. To be precise, he is an astrophysicist who investigates how the massive balls of seething plasma we see twinkling in our night sky actually form in outer space. And as one of a select few scientists charged with interpreting the data on star formation being sent to Earth by the Herschel Space Observatory, a giant infrared telescope orbiting high above our planet, he’s in a unique position to unravel the mysteries of the starry birth process.

The basic problem that investigators like Doty face is a simple one: also like people, baby stars are hidden away in what Doty calls “a natural womb”–in this case, vast clouds of dust and gas. (The Orion Nebula, that fuzzy blob on Orion’s belt, is one such star-forming region.) The dust grains block visible light, preventing us from seeing the infant stars (scientists call them protostars) taking shape behind them and hiding the details of how a star is born. Fortunately, nature provides a solution. The light from a protostar can’t get past those dust grains, but it does heat them up. It also warms the various gas molecules in the star-forming clouds, such as carbon monoxide and water. And that heat is re-radiated as infrared energy that astronomers can see using special telescopes tuned to detect long wavelengths of light. By analyzing that light, astrophysicists can deduce the conditions that produced it: the chemical composition of the star-forming clouds, the amount of energy coming off the protostars, and more. “Just like we use ultrasound to image a fetus, we try to use long-wavelength light to image these stars,” Doty says.

The water vapor in Earth’s atmosphere absorbs most infrared energy, so the best results come from satellites orbiting far overhead. Herschel, which launched just last year, is both the latest and by far the most sensitive of these. A joint project of the European Space Agency and NASA, it is in fact the largest telescope ever placed in orbit–one and a half times larger even than the famous Hubble Space Telescope.

As a member of the Water In Star-forming Regions with Herschel (WISH) team, Doty works with scientists in Europe to analyze the reams of data that Herschel sends to Earth. (Water is one of the most abundant molecules in the universe, and the source of all life as we know it. As a result, astrophysicists want to know how much of the stuff is out there, and how it behaves.) He compares those data to the results he gets from the complex mathematical models that run on the computers in his lab–models that represent our current understanding of the physics behind star formation.

“We try to create a little mini-universe inside the computers using these models, and then we run the movie forward to see what happens,” Doty explains. If the models don’t agree with the data coming in from Herschel, then they need to be fixed. And every tweak brings us closer to understanding how the universe really works.

As one of the original six modeling experts on the WISH team, Doty also helped figure out where to point the telescope in the first place, and for how long–no trivial matter, given that every hour of Herschel’s time costs approximately $100,000. “We didn’t get everything right,” he says in retrospect, “but at least we weren’t stupidly wrong.”

Herschel is providing so much new information that Doty must travel to Europe every few months just to stay abreast of the latest developments, and he suspects it will take hundreds of scientists decades to make sense of it all. (He’ll be taking a group of Denison research students with him to Germany next summer in order to get a head start.) But Herschel has already confirmed a couple of hypotheses, and turned up a few surprises.

On the one hand, Herschel revealed that those dusty, gaseous, star-forming clouds contain every bit as much water as Doty’s models had predicted. The telescope also confirmed that the clouds are riddled with holes caused by powerful jets of matter and energy that stream from the protostars hidden within.

But Doty and his colleagues were surprised to see that some of the water in the clouds came in the form of a previously unknown, ionized vapor. And Doty says he was astonished to learn that much of the energy associated with those jets comes from the shock waves they create as they punch through the clouds at 400,000 miles an hour.

These discoveries have already led Doty to revise his models, and he looks forward to having Herschel shed even more light on the mysteries of star formation. For years, he felt as starved for data as a man trapped in the desert, desperately searching for a drop of water. “Then Herschel comes along,” he says, “and it’s like drinking from a firehose.”

Published November 2010