Indianapolis, IN - If
you had a time machine that could take you anywhere in the past, what
time would you choose? Most people would probably pick the era of the
dinosaurs in hopes of spotting a T. rex. But many astronomers would
choose the period, four and a half billion years ago, that our solar
system formed.
In lieu of a working time machine, we learn about the birth of our Sun
and its planets by studying young stars in our galaxy. New work suggests
that our Sun was both active and "feisty" in its infancy, growing in
fits and starts while burping out bursts of X-rays.
"By studying TW Hydrae, we can watch what happened to our Sun when it
was a toddler," said Nancy Brickhouse of the Harvard-Smithsonian Center
for Astrophysics (CfA). She presented the findings today in a press
conference at a meeting of the American Astronomical Society.
Brickhouse and her colleagues reached this conclusion by studying the
young star TW Hydrae, located about 190 light-years from Earth in the
southern constellation Hydra the Water Snake. TW Hydrae is an orange,
type K star weighing about 80 percent as much as our Sun. It is about 10
million years old, and is still accreting gas from a surrounding disk
of material. That same disk might contain newborn planets.
In order to grow, the star "eats" gas from the disk. However, the disk
doesn't extend all the way to the star's surface, so the star can't dine
from it directly. Instead, infalling gas gets funneled along magnetic
field lines to the star's poles.
Fortunately, we are looking almost directly down on one of the star's
poles. As a result, we can study the accretion process in detail.
"We're looking right where the action is," said team member Andrea Dupree of the CfA.
Infalling material smashes into the star, creating a shock wave and
heating the accreting gas to temperatures greater than 5 million degrees
Fahrenheit. The gas glows with high-energy X-rays. As it continues
moving inward, the gas cools and its glow shifts to optical wavelengths
of light. To study the process, Brickhouse and her team combined
observations from NASA's Chandra X-ray Observatory with those from
ground-based optical telescopes.
"By gathering data in multiple wavelengths we followed the gas all the
way down. We traced the whole accretion process for the first time,"
explained Brickhouse.
They found that accretion was clumpy and episodic in building a star. At
one point the amount of material landing on the star changed by a
factor of five over the course of a few days.
"The accretion process changes from night to night. Things are happening all the time," stated Dupree.
Some of the infalling material is pushed away in a stellar wind much
like the solar wind that fills our solar system. Some gets channeled
into giant loops and stellar prominences.
Astronomers have known that young stars are much more magnetically
active than our middle-aged Sun, but now they can actually probe the
interplay between the star's magnetic fields and the protoplanetary
disk.
"The very process of accretion is driving magnetic activity on TW Hydrae," added Brickhouse.
Headquartered in Cambridge, Mass., the
Harvard-Smithsonian Center for Astrophysics (CfA) is a joint
collaboration between the Smithsonian Astrophysical Observatory and the
Harvard College Observatory. CfA scientists, organized into six research
divisions, study the origin, evolution and ultimate fate of the
universe.
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
