Fig 1. Protostar FIR 3 (HOPS 370) with outflow that may have
triggered the formation of younger protostar FIR 4 (HOPS 108, location
marked with red dot), in the Orion star-forming region. (au =
astronomical unit, the distance from the Earth to the Sun, about 93
million miles.) Credit: Osorio et al., NRAO/AUI/NSF.
Fig 2. Protostar FIR 3 (HOPS 370) with outflow that may have
triggered the formation of younger protostar FIR 4 (HOPS 108), in the
Orion star-forming region. Pullouts are individual VLA images of each
protostar. (au = astronomical unit, the distance from the Earth to the
Sun, about 93 million miles.) Credit: Osorio et al., NRAO/AUI/NSF.
Astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) have found new evidence suggesting that a jet of fast-moving material ejected from one young star may have triggered the formation of another, younger protostar.
“The orientation of the jet, the speed of its material, and the
distance all are right for this scenario,” said Mayra Osorio, of the
Astrophysical Institute of Andalucia (IAA-CSIC) in Spain. Osorio is the
lead author of a paper reporting the findings in the Astrophysical Journal.
The scientists studied a giant cloud of gas some 1,400 light-years
from Earth in the constellation Orion, where numerous new stars are
being formed. The region has been studied before, but Osorio and her
colleagues carried out a series of VLA observations at different radio
frequencies that revealed new details.
Images of the pair show that the younger protostar, called HOPS
(Herschel Orion Protostar Survey) 108, lies in the path of the outflow
from the older, called HOPS 370. This alignment led Yoshito Shimajiri
and collaborators to suggest in 2008 that the shock of the fast-moving
material hitting a clump of gas had triggered the clump’s collapse into a
protostar.
“We found knots of material within this outflow and were able to
measure their speeds,” said Ana K. Diaz-Rodriguez also of IAA-CSIC.
The new measurements gave important support to the idea that the
older star’s outflow had triggered the younger’s star’s formation
process.
The scientists suggest that the jet from HOPS 370 (also known as FIR
3) began to hit the clump of gas about 100,000 years ago, starting the
process of collapse that eventually led to the formation of HOPS 108
(also known as FIR 4). Four other young stars in the region also could
be the result of similar interactions, but the researchers found
evidence for shocks only in the case of HOPS 108.
While the evidence for this triggering scenario is strong, one fact
appears to contradict it. The younger star seems to be moving rapidly in
a way that indicates it should have been formed elsewhere, apart from
the region impacted by the older star’s outflow.
“This motion, however, might be an illusion possibly created by an
outflow from the newer star itself,” explained Osorio. “We want to
continue to observe it over a period of time to resolve this question,”
she added.
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