With space telescope and model, star’s birth pains revealed

Using a potent combination of observation and theory, astronomers are peeling away layers of cosmic dust to see the birth pains of sun-like stars.

“With the advent of high-powered telescopes like Hubble, we can start to look deep inside” obscuring cocoons of stardust to see the behavior of stars in their infancy, said Margaret Turnbull of UW–Madison, who with Barbara Whitney, also of UW–Madison, and Kenneth Wood of the Harvard-Smithsonian Center for Astrophysics reported their findings here today at a meeting of the American Astronomical Society.

When NASA's Hubble Space Telescope returned this image of HL Tauri several years ago, the complex nebulas around the young star puzzled astronomers. Now, a one-two punch of theory and observation may help solve the puzzle and give astronomers a way to look through the obscuring dust of the nebula to observe the behavior of newborn stars.

The findings are important because they promise astronomers a better feel for how powerful jets of dust and gas emanating from the poles of baby stars influence the dark clouds of stardust that surround them. It is that same cosmic dust that, as stars form, coalesces to build the planets and other objects that constitute solar systems.

The new insights were obtained with the aid of Hubble Space Telescope images of a star known as HL Tauri, and a sophisticated computer model that mimics the features of infant suns, said Turnbull, a UW–Madison undergraduate.

“HL Tauri is a lot like the sun,” she said. “We would expect solar systems like ours to look a lot like HL Tauri when they were young.”

Like other young sun-like stars, HL Tauri has powerful polar jets that sculpt vast cavities within their dust cocoons. It is the shapes of those cavities, apparently, that help explain the forms of the reflection nebulas created when starlight is reflected off the dust that surrounds a star.

“The problem with studying star formation is that you can’t see through the surrounding dust,” said Turnbull. “But the polar jets clear out cavities, and the nebula image we see depends on the shape of those cavities.”

Even the most powerful telescopes, including Hubble, cannot penetrate the thick clouds of stardust that envelope such nascent stars. Yet Hubble is capable of making detailed images of the reflection nebulas themselves.

And while scientists cannot see through the dust that veils infant stars, they know enough about star formation to build computer models that mimic their behavior.

“We can use these models to build the star in the computer,” explained Turnbull, “and when we match our model to what the Hubble Space Telescope sees, we can probe the most hidden parts of the stellar nursery.”

Motivated by recent Hubble and ground-based infrared observations of HL Tauri, located 450 light years from Earth in the constellation Taurus, the astronomers used their model to predict how reflection nebulas would appear for three different cavity shapes known to occur at different stages of star formation.

Matching results of their model with Hubble images of HL Tauri, the Wisconsin-Harvard-Smithsonian team was able to show that the star is very young and that its polar jets are carving bubble-shaped, bipolar cavities within its cocoon of dust.

Knowledge of how a star’s polar jets – features that can extend for several light years on either end of the star – influence the surrounding environment is important because the powerful streams of dust and gas help clear away the dense natal clouds and is a crucial ingredient in star formation.

While insightful, Turnbull said the new work needs to be supported and fleshed out on both the observational and theoretical fronts. She said the newly installed Near Infrared Camera on Hubble will soon provide more detailed images of HL Tauri and that those images will help further refine models of star-formation processes.

The work reported today was funded by grants from the Hubble Space Telescope Archival Research Program, NASA’s Long-Term Space Astrophysics Research Program, the Wisconsin Space Grant Consortium, and the Hilldale Scholarship Fund.