UBC astrophysicist Bill McCutcheon scans the night sky with radio
telescopes in search of celestial treasure. He and his colleagues
recently announced that they’d hit the jackpot with their discovery
of a hot star-forming region 5,000 light years away.
McCutcheon says the find is tantamount to a naked-eye astronomer,
previously aware of only the sun and faint stars, suddenly noticing
something new in the sky as bright as the moon.
Using the James Clerk Maxwell Telescope in Hawaii, the world’s
best high-frequency radio telescope, McCutcheon measured radiowave
emissions from carbon monoxide (CO) molecules deep in the Lagoon
Nebula. The CO emission line (registering a temperature of 130 Kelvin)
is the strongest measured in 20 years and the second strongest CO
line yet found in the sky.
The research group’s discovery, however, is invisible to the human
eye and high powered optical instruments like the Hubble telescope.
“These molecules we are detecting don’t emit light,” says Prof.
McCutcheon of the Dept. of Physics and Astronomy. “So in order to
study the earliest stages of star evolution, we analyze radio emissions
from various molecules.”
He explains that new stars begin to form when invisible clouds
of dust and hydrogen atoms are somehow compressed to the point where
hydrogen atoms turn to hydrogen molecules, undetectable at radio
wavelengths. However, this transformation also gives rise to carbon
monoxide molecules which do emit radio wavelengths and which act
as red flags to astronomers looking for newborn stars; generally
speaking, the hotter the CO signal, the more massive and hot the
newly forming star.
The star or stars forming in the Lagoon Nebula are buried in a
dense clump of gas weighing more than 30 times the mass of our sun
with a diameter of about one light year, or nearly 10 million million
kilometres.
McCutcheon says the young star, or “protostar,” scanned by the
Maxwell telescope probably won’t emerge from its cocoon and be a
visible point of light for another million years.
Based on their CO observations, McCutcheon and colleagues expect
this star-forming region to produce something much bigger than our
sun. The brightest and hottest stars can have temperatures up to
100,000 Kelvins at the surface while our sun measures just 6,000
Kelvins.
McCutcheon is part of an international collaboration which is mapping
a region of the Lagoon Nebula containing invisible dense cores of
hydrogen molecules. The region is shrouded in a visible glow from
energy emanating from the nearby hot star Herschel 36 and other
mature stars whose radiation excites the gas around them.
Says McCutcheon, “We knew stars had formed in this nebula and from
optical photos and infrared data we guessed that there had to be
a lot of energy stored in the region.”
For six, eight-hour nights, the researchers focused the Maxwell
telescope on the region and tuned it to receive high frequency radio
waves from CO molecules. Later analysis of the spectral data showed
that roughly halfway through the mapping exercise, CO readings climbed
four to six times the intensity level normally measured in our galaxy.
“We expected to detect carbon monoxide lines of maybe 20 to 30
Kelvins but detecting a line this hot was a total surprise,” says
McCutcheon. “The signal tells us that CO molecules embedded in the
hydrogen core are colliding with dust and radiating tremendous energy.”
Radio telescope data indicate that as the region collapses, narrow
jets of gas molecules are being expelled at rates of many tens of
kilometres a second. Eventually, as the gas cloud continues to collapse,
energy from radiation and the jets will disperse surrounding gas
and dust material leaving the newly formed star as a single point
of light.
Canada is a partner in funding the James Clerk Maxwell Telescope
along with Britain and the Netherlands. The team’s delicate mapping
exercise was made possible by the telescope’s large, 15-metre diametre,
its ability to operate at sub-millimetre wavelengths and a highly
sensitive receiver constructed in laboratories of the National Research
Council (NRC) of Canada. These three attributes enabled McCutcheon
and colleagues to map a large area of space with high resolution
in a relatively short period of time.
Individual researchers working with the telescope are supported
by grants from the Natural Sciences and Engineering Research Council
(NSERC). McCutcheon began the project 10 months ago with NRC scientist
Henry Matthews, and Glenn White and Nick Tothill from Queen Mary
and Westfield College, London University.
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