In the constellation Carina, 20,000 light years from Earth, a dusty nebula is bubbling like a boiling cauldron, and inside the bubbles, new stars are being born.
One of these bubbles surrounds the Westerlund 2 star cluster within the nebula. Astronomers have used the SOFIA telescope to capture a high-resolution image of the bubble – an expanding region of hot ionized gas or plasma. The image revealed that new stars are forming in the shell of the bubble.
The study, conducted by researchers at the University of Maryland, refuted previous research suggesting that the star cluster was surrounded by two bubbles, not one, and found the source of the bubble’s expansion.
“When massive stars form, they emit ejections of protons, electrons and heavy metal atoms that are much stronger than our Sun,” said Dr Maitraiyee Tiwari, postdoctoral associate in the Department of Astronomy at the UMD.
âThese ejections are called stellar winds, and the extreme stellar winds are able to blow and bubble 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 expands.
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Previous images of the Westerlund 2 star cluster had been taken using waves in the radio and submillimeter (far infrared and microwave) regions of the electromagnetic spectrum. The team captured the new high-resolution image of the cluster using light of all wavelengths, from low-energy radio waves to high-energy x-rays. By combining all of this data, the team was able to see how stellar winds were pushing the bubble to expand.
The researchers also found that around a million years ago, the bubble burst. On one side, it had burst outward, spitting out plasma. As a result, the expansion had slowed down. However, around 200,000 to 300,000 years ago, a new star had evolved in the cluster and its stellar winds gave new life to the bubble.
âWe saw that the expansion of the bubble surrounding Westerlund 2 was re-accelerated by winds from another very massive star, and it started the process of expansion and star formation all over again,â Tiwari said. “This suggests that stars will continue to be born in this shell for a long time, but as this process continues, the new stars will become less and less massive.”
Reader’s Q&A: How many stars are in the Milky Way?
Question from: Sophie Wyatt
Astronomers cannot be sure of this number, as not all stars in the Milky Way are visible from Earth, as some of them are too far away, too faint, or obscured by gas or dust. However, various estimates are available: some based on the shape and size of our Galaxy, others based on the probable mass of our Galaxy. These estimates generally range from 100 to 400 billion stars. For comparison, 100 billion is roughly the number of people who have ever lived on Earth.