20
years
Length of the 19th
century Eta Carinae
eruption
10
solar masses
Material shed
during the
eruption
Reflected glow
lights up past
Visible echoes make sense
of explosion from long ago
By Nadia Drake
Scientists are closer to understanding
an enormous two-decade-long eruption
that transformed one of the galaxy’s most
massive stars into a fireball millions of
times brighter than the sun.
From 1838 to 1858, astronomers
watched the giant star Eta Carinae erupt,
shedding more than 10 solar masses of
material and producing an oddly shaped,
double-lobed cloud 7,500 light-years
from Earth. Scientists have thought a
dense stellar wind fueled the outburst
and considered it the prototype for
“supernova impostors,” or shorter-lived
eruptions that don’t quite destroy a star.
But new observations suggest that an
explosion may have caused Eta Carinae’s
Great Eruption, says study coauthor
Armin Rest, an astrophysicist at the Space
Telescope Science Institute in Baltimore.
While scientists already knew much
about the star (now recognized as a binary
star system), Rest says they lacked infor-
After analyzing light echoes left over from an outburst of the binary star system Eta Carinae seen more than 150 years ago, scientists suggest an explosion rather than an energetic stellar wind created the spectacle.
mation about the outburst, originally
observed without modern technology.
So Rest’s team sifted through dust
clouds forming a sort of net that bounces
the eruption’s original light back to
Earth in what’s known as light echoes.
These echoes act like time capsules
that preserve the energy spectrum of
the light as it appeared in the mid-1800s.
“It is like a science fiction dream to be
able to travel in time to ... analyze the Big
Eruption with 21st century instrumentation,” says Augusto Damineli, an astrophysicist at the University of São Paulo.
The spectrum didn’t match predictions
of accepted stellar wind theory, Rest and
colleagues report in the Feb. 16 Nature.
The temperature indicated by the light
echoes was about 2,000 degrees Celsius
cooler than anticipated, suggesting that
something other than windblown star
stuff, such as a mini-explosion or an
interaction between Eta Carinae and its
companion, played a role in the eruption.
Neutrino speed blamed on cable
Evidence mounts against faster-than-light finding in Italy
By Devin Powell
Faulty wiring has been proposed as the
glitch that caused a European physics experiment to clock particles flying
faster than light.
Scientists at Italy’s OPERA experi-
ment reported in September that nearly
weightless particles called neutrinos
were apparently traveling from the CERN
laboratory on the Swiss-French bor-
der to an underground detector in Italy,
730 kilometers away, faster than the
speed of light in a vacuum. The apparent
violation of Einstein’s theory of special
relativity immediately produced a cho-
rus of theorists offering reasons why neu-
trinos simply could not be going that fast
(SN: 11/5/11, p. 10).
www.sciencenews.org
April 7, 2012 | SCIENCE NEWS | 9
