Astrophysicist detects star's birth 5,000 light-years away

by Charles Ker
Staff writer

Astrophysicist Bill McCutcheon scans the night sky with radio telescopes in search of celestial treasure. Recently, he and his colleagues announced that they'd hit the jackpot with their discovery of a hot star-forming region 5,000 light-years away.

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 degrees Kelvin) is the strongest measured in 20 years and the second strongest CO line yet found in the sky.

McCutcheon says the find is tantamount to an astronomer, previously aware with the naked eye of only the sun and faint stars, suddenly noticing something new in the sky as bright as the moon.

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 degrees Kelvin at the surface while our sun measures just 6,000 degrees Kelvin.

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 international team's delicate mapping exercise was made possible by the telescope's large, 15-metre diameter, 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.