Researchers from the University of Maryland have created the first high resolution image of a bubble in hot plasma expansion and ionized gas where stars are born.
The low resolution previous images they did not clearly show the bubble or reveal how it expanded into the surrounding gas.
The researchers used data collected by the SOFIA airborne telescope (Stratospheric Observatory for Infrared Astronomy) to analyze one of the star-forming regions brightest and most massive in the Milky Way.
Their analysis showed that a single expanding bubble of hot gas surrounds the Westerlund 2 star cluster and refuted previous studies suggesting that there may be two bubbles around Westerlund 2. The researchers also identified the source of the bubble and the energy that drives its expansion. Their results were published in The Astrophysical Journal.
When massive stars form, they emit much stronger ejections of protons, electrons and heavy metal atoms, compared to our sun, “Maitraiyee Tiwari, a postdoctoral associate in the UMD Department of Astronomy and lead author of the study, said in a statement. “These ejections are called stellar winds, and extreme stellar winds are capable of blowing and forming bubbles in the surrounding clouds of cold, dense gas. We observed such a bubble centered around the brightest star cluster in this region of the galaxy, and we were able to measure its radius, mass, and the speed at which it is expanding. “
The surfaces of these bubbles In expansion they are made of a dense gas of ionized carbon and form a kind of outer shell around the bubbles. New stars are believed to form within these layers. But like soup in a boiling cauldron, the bubbles that enclose these star clusters overlap and intermingle with surrounding gas clouds, making it difficult to distinguish the surfaces of individual bubbles.
Tiwari and his colleagues created a clearer picture of the bubble than surround Westerlund 2 measuring the radiation emitted by the cluster across the entire electromagnetic spectrum, from high-energy X-rays to low-energy radio waves. Previous studies, which only had radio wavelength and submillimeter data, had produced low-resolution images and did not show the bubble. Among the most important measurements was the far infrared wavelength emitted by a specific carbon ion in the shell.
By determining whether the carbon ions were moving towards or away from Earth and combining that information with measurements from the rest of the electromagnetic spectrum, Tiwari and Karim were able to create a 3D view of the expanding stellar wind bubble surrounding Westerlund 2.
In addition to find a single bubble stellar wind-driven around Westerlund 2, found evidence of new star formation in the region of this bubble’s layer. Their analysis also suggests that as the bubble expanded, it opened on one side, releasing hot plasma and slowing the expansion of the shell about a million years ago. But then, around 200,000 to 300,000 years ago, another bright star in Westerlund 2 evolved and its energy reinvigorated the expanding Westerlund 2 layer.
We saw that the expansion of the bubble around Westerlund 2 was accelerated again by the winds from another very massive star, and that started the process of expansion and star formation again, “Maitraiyee Tiwari said in a statement.” This suggests that the stars will continue to be born in this layer for a long time, but as this process progresses, the new stars will become less and less massive, “he concluded.