The Herschel Space Telescope, now approaching its final days, has helped astronomers spot one of the earliest stages of star formation.
Astronomers have found stars in the earliest stage of formation 1,600 light-years away, inside the bright nebulae of the Orion constellation, reports a recent study published in the Astrophysical Journal.
The discovery came as part of the Herschel Orion Protostar Survey. HOPS is studying hundreds of forming stars at multiple wavelengths with the aim of following stars from their infancy to adulthood.
Astronomers know that protostars begin their lives as dense clumps of gas. Not yet dense enough to shine by fusing hydrogen, protostellar cores glow from the heat of gravitational collapse. The Spitzer Space Telescope spots the infrared light emitted by older, hotter protostars and had already identified several before the Herschel Space Telescope took a look. Herschel, which is running low on coolant these days, observes at even longer far-infrared and sub-millimetre wavelengths, so the instrument is ideal for finding protostars’ faint younger siblings.
Still, it was happenstance that led the HOPS team to the elusive baby stars, says Tom Megeath (University of Toledo), the HOPS project leader. He was confirming Herschel detections of Spitzer-discovered protostars when he saw something unexpected.
“In the first Herschel image I looked at, sure enough, there was the protostar – but there was another object right next to it,” Megeath explains. “That second object hadn't shown up in the shorter-wavelength images taken with the Spitzer telescope.”
HOPS observations turned up 55 new candidate protostars, which were either very faint or undetected in the Spitzer survey. The team analyzed the objects to confirm they were actually protostars instead of, say, distant galaxies, which can mimic a protostar’s faint, red appearance.
Of these, the team claims 11 candidates can be reliably identified as extremely young protostars in the very earliest stage of formation, known as Class 0. Combining Herschel and Spitzer data, the team finds an additional 7 sources that were previously known, bringing the total number of newborn stars in the area up to 18. These protostars are swaddled in some of the densest gas envelopes found in Orion, says the team, so they’re probably accreting gas very quickly.
The newborn stage of stellar infancy lasts just 25,000 years, says Amelia Stutz (Max Planck Institute for Astronomy, Germany), the study’s lead author. That’s a blink of the eye in cosmic terms. Her team arrived at this estimate by counting up the stars in the area and comparing the number of new protostars to those that are more evolved. For comparison, a fully formed “adult” star lives roughly 10 billion years.
These findings might help astronomers learn more about the mysterious, enshrouded phase of star formation. “We don’t know exactly what the conditions in such star-forming cores are like, or how those conditions influence the forming star,” Stutz says.
As Herschel’s imminent shutdown approaches, the team is squeezing in some follow-up observations to look at the protostars in more detail. Even after Herschel’s coolant runs out and the instrument goes into hibernation, Stutz hopes to continue using other long-wavelength facilities, such as the Institute for Radio Astronomy in the Millimeter Range (IRAM) and Atacama Large Millimeter/submillimeter Array (ALMA).
“Further observations and detailed studies will reveal key aspects of these very young sources,” Stutz says.
Guest blogger Phil Unsworth studied astrophysics at the University Of Hertfordshire before writing for Astronomy Now. He was born in and still lives near Sheffield, England.