Lasers point way to astronomical phenomena
BOSTON, Mass. — Large lasers and Z-pinch generators in laboratories
are recreating conditions relevant to astrophysical phenomena of the universe
such as supernovae, black holes, molecular clouds like the Eagle Nebula,
and the creation of new planets.
Laboratory physicist Bruce Remington will discuss this and other findings
this weekend in a presentation entitled: "Laboratory Astrophysics
Using High-Power Lasers," during the "Visualizing and Looking
Beyond Earth" track of the annual meeting of the American Association
for the
Advancement of Science in Boston.
"Modern laser and magnetic pinch facilities offer new opportunities
for pursuing experimental science under extreme conditions of temperature
and density," Remington said. "The potential of this new experimental
capability is phenomenal when it comes to applications in astrophysics
and planetary physics."
An understanding of supernovae, the cataclysmic death of a massive star,
relies on an understanding of macroscopic matter under extreme conditions.
Recreating aspects of the dynamics and energetics of supernova explosions
has already been achieved on lasers and z-pinch facilities in laboratory
experiments, thereby providing direct measurements under relevant and
controlled conditions.
Remington said the next generation "mega lasers" — the
National Ignition Facility at the Lab and the Laser Mega Joule in France
— may be used to experimentally address questions of thermonuclear
ignition and rare nuclear reaction measurements that are common occurrences
in supernovae.
Supernova remnants (SNRs) are the vestiges of supernovae explosions. These
remnants evolve for centuries, producing glowing filamentary structures
in the galaxy and are widely believed to produce most of the cosmic rays
that irradiate the Earth. Lab experiments can help improve the understanding
of several of the mechanisms present in SNRs and can test aspects of the
computational models developed to interpret their behavior. Experiments
on high-energy density facilities can address uncertainties in remnant
evolution such as the radiative hydrodynamics of SNRs. In the future,
experiments may be able to address issues of collisionless shocks and
particle acceleration (the first step in cosmic ray generation).
Galactic and extragalactic jets present some of the most visually captivating
images encountered in modern astronomy. Using lasers and pulsed power
facilities, Remington said scientists have already demonstrated how high
Mach number hydrodynamic jets and radiatively collapsing jets evolve and
interact.
Cold, dense molecular clouds illuminated by bright, young nearby massive
starts serve as the stellar incubators of the universe. The radiation
on the cloud creates high pressure at the surface by ablation and ram
pressure from the stellar wind. Such systems are thought to be "cosmic
nurseries" where active star formation takes place. Through lab experiments
with large lasers and pulsed power facilities, scientists can recreate
the dominant ablation-front hydrodynamics of radiatively driven molecular
clouds, the best known example being the Eagle Nebula.
"With driven molecular clouds, the possibility to form an integrated
program of theory, modeling, test-bed laboratory experiments, and astronomical
observations is very real," Remington said. "Such an integrated
program would have been undreamed of just a decade ago."
Scientists have moved one step closer to understanding the immediate vicinity
of black holes, where matter is relentlessly swept down a singular gravitational
abyss. Astronomers use high-resolution spectroscopy of the X-ray emissions
from heated matter as it is tugged down the black hole to conditions close
to the black hole. Laboratory scientists have demonstrated on Z-pinch
facilities that scaled versions of these accretion disk conditions can
be recreated for close-up scrutiny.
As for new planets, experimental techniques are being developed on pulsed
power facilities, lasers, gas guns and diamond anvil cells to probe the
properties of matter under the relevant extreme conditions of pressure
and compression. These laboratory conditions reproduce those of the interiors
of terrestrial and giant gas planets, brown dwarfs, low mass stars and
the envelopes of white dwarfs Gamma-ray bursts — which are detected
at a rate of more than one per day from random directions in the sky —
have typical burst durations of a few seconds, but exhibit fluctuations
as short as a millisecond. Laboratory experiments using ultra-intense,
short-pulse lasers offer the most promising means for accessing the relativistic
plasma dynamics and directed flow of gamma-ray bursts"Lab experiments
and computer simulations are helping to identify and understand some of
the dominant physics that are taking place in the vast universe that,
until now, we’ve only been able to observe from afar from an astronomical
viewpoint," Remington said.