The Orion Molecular Cloud Complex is a group of nebulae and stellar nurseries positioned some 1,500 light years away from Earth. This is a place where new stars are born, but also apparently where they meet an early end. New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile reveal a giant fireworks display in Orion Molecular Cloud 1 (OMC-1) that was caused by two young stars colliding.
The ALMA data was processed and released by scientists working with the National Radio Observatory (NRO). The NRO timeline for the explosion is a bit vague. It says the collision took place 500 years ago, but it takes light from OMC-1 1,500 years to reach us. I suppose the above image is a representation of the explosion 500 years after it occurred. If you tack on 1,500 years of light to reach us, that puts the actual event around 2,000 years ago.
Most stars form far enough apart that collisions are unlikely. However, OMC-1 is densely packed, and newly formed stars essentially drift at random. Over time, young stars slow down and fall toward the local center of gravity. In this case, two protostars ended up too close together and collided. The explosion launched material from the stars (and other nearby objects) outward at more than 150 kilometers per second (93 miles per second). This one event released more energy than our sun does in 10 million years.
The visible remains of a protostar collision are rather short lived by astronomical standards, and much of the debris isn’t in the visible spectrum from such a great distance. That’s why the radio frequency observations of ALMA were so revealing, but we were still lucky that ALMA managed to spot this one. You can see above the extent of the fireworks display, overlaid on a Hubble image of the relevant section of the Orion Molecular Cloud. The bright streamers represent the emissions of carbon monoxide gas as it’s propelled outward.
The short lifetime of the visible evidence of these collisions makes it hard to estimate how common they are, but astronomers suspect it’s a frequent occurrence in stellar nurseries like OMC-1. The first hints of this explosive event were uncovered in 2009 by the Submillimeter Array in Hawaii. That instrument lacked the power to reveal the true scale of the starburst formation. The same was true of infrared observations made with the Gemini-South telescope. Future study of the collision debris as it expands could help astronomers learn more about the conditions inside stellar nurseries like OMC-1.
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