Rice astronomer Patrick Hartigan displays a target from an experiment to re-create the physics of stellar jets on a small scale. Powerful lasers blasted a tiny plug of titanium inside the gold-coated cone, shooting the atomized material into a ball of foam-covered plastic. The experiment re-created some of the fluid dynamics that occur on a huge scale when newborn stars spew columns of high-speed gas and dust. Photo: Jeff Fitlow/Rice University |
When it comes to big-budget action movies, Rice
University astronomer Patrick Hartigan
prefers Hubble to Hollywood.
Using Hubble Space Telescope images collected over 14 years, Hartigan has
created time-lapse movies that offer astronomers their first glimpse of the
dynamic behavior of stellar jets, huge torrents of gas, and particles that spew
from the poles of newborn stars.
An analysis of the movies that was published in The Astrophysical Journal is forcing astronomers to rethink some of
the processes that occur during the latter stages of star birth. And in an
effort to learn even more, Hartigan and colleagues are using powerful lasers to
recreate a small-scale version of the solar-system-sized jets in a laboratory
in upstate New York.
“The Hubble’s given us spectacular images,” says Hartigan,
professor of physics and astronomy at Rice. “In the nebulae where stars
are born, for instance, we can see beautiful filaments and detailed structure.
We know these images are frozen snapshots in time, but we would need to watch
for hundreds of thousands of years to see how things actually play out.”
Hartigan says stellar jets are different because they move very quickly.
Stellar jets blast out into space from the poles of newly formed stars at about
600,000 miles an hour. Astronomers first noticed them about 50 years ago, and
they believe the sun probably had stellar jets when it formed about 4.5 billion
years ago.
Hartigan began using Hubble to collect still frames of stellar jets in 1994.
The jets emerge from each pole of a young star, and Hartigan used Hubble to
revisit the jets from three stars in 1994, 1998, and 2008. All three stars are
about 1,350 light years from Earth. Two are near the Orion Nebula, and the
third is in the southern sky in the constellation Vela.
By lacing the images together and using a computer to fill in what occurred
between still frames, Hartigan and his collaborators created time-lapse movies.
The movies clearly showed something that wasn’t obvious in any of the still
images; clouds of dust and gas within the jets move at different speeds.
“The bulk motion of the jet is about 300 km/sec,” Hartigan says.
“That’s really fast, but it’s kind of like watching a stock car race; if
all the cars are going the same speed, it’s fairly boring. The interesting
stuff happens when things are jumbling around, blowing past one another or
slamming into slower moving parts and causing shockwaves.”
Understanding what happens in those huge collisions is another challenge.
The phenomena didn’t look like anything that Hartigan and his astronomer
colleagues had seen. But when he showed them to colleagues who were familiar
with the physics of nuclear explosions, they immediately saw patterns in the
shockwaves that looked familiar.
“The fluid dynamicists immediately picked up on an aspect of the
physics that astronomers typically overlook, and that led to a different
interpretation for some of the features we were seeing,” Hartigan explains.
“The scientists from each discipline bring their own unique perspectives
to the project, and having that range of expertise has proved invaluable for
learning about this critical phase of stellar evolution.”
Motivated by the results from Hubble, Hartigan and colleagues are conducting
experiments at the Omega Laser Facility in Rochester, New York,
to recreate small-scale versions of the solar-system-sized features captured in
the movies.
