Looking Up: A ‘super bubble’ grows in another galaxy
Astronomers call the large, almost circular object in the upper half of the picture a "Super Bubble." It is an outward expanding balloon of energy caused by a series of supernova explosions.
This one is called N51D. The interesting fact is that it is not in our own galaxy. It lies in the Large Magellanic Cloud – a separate galaxy lying about 160,000 light years away.
If you have ever been able to view the skies of the Southern Hemisphere, in South America, Australia, or Africa for instance, the sight of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) is unforgettable. They loom above you in the dark, night sky like someone has mistakenly placed a couple of very large, earth bound clouds way up in space.
They are named after the great explorer Ferdinand Magellan. He was the Portuguese sea captain who first navigated the world. While they were named after him he was not the first to discover them.
As one of the stories goes his small fleet was making its way south off the coast of Brazil one night. He was asleep below in his cabin when the sailors on deck saw the Magellanic Clouds up in the night sky. They were frightened and woke him up to see them.
While he sailed that trip under the flag of Spain Magellan was a Portuguese seaman, and was familiar with the discoveries of the great Portuguese voyages under their king, Henry the Navigator. So when he looked up on the deck that night he knew that these strange clouds were regular features of the Southern Hemisphere. They hung in the skies along the coast of Africa, and had been previously reported by Portuguese sailors.
So he calmed his men that night. The sighting of the Clouds was recorded in the voyage's records, and Magellan's name was forever associated with them after that.
What are they? The Clouds are 2 separate, smaller galaxies being absorbed (eaten) by our own galaxy. As gravity pulls them into the Milky Way they are undergoing a major upheaval. Giant nebulas in the LMC are mass producing new stars as regions experience cooling, and collapse under the influence of gravitational pull from the Milky Way.
This, in turn, produces large amounts of very hot, bright, new stars. Many of these are Type O and Type A giants that are short lived. The largest collapse on themselves when they run out of the nuclear energy powering their cores, and this results in incredible explosions called "Supernovas".
That brings us to our "Super Bubble". In its central region a series of supernovas has created the bubble shape, and the energy released by the explosions is pushing outward.
It develops that the LMC is a particularly good place to observe these "Super Bubbles". While they exist in our own galaxy, the accumulation of dust along our line of sight across the disk of the Milky Way prevents us from seeing many of them.
The LMC has at least 20 Super Bubbles, and we have a clear line of sight to study them.
In fact, this very bubble (N51D) was the site of the first discovery of a special type of feature, associated with the birth of young stars, never seen outside our own galaxy. Its an energized jet of material coming out of a new born star that is colliding with nearby clouds of material called a Herbig-Haro object.
So that night on the deck of their boat Magellan and his crew were looking up at galaxies beyond our own, wracked with star birth because of their impending collision with our much larger galactic world.
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Ted Wolfe is a member of the Everglades Astronomical Society. Organized in 1981 it serves the Naples community providing information in all aspects of amateur astronomy. Its goals include educating the general public, school children, and other groups to the wonders of the universe. The Society meets at 7 p.m. every second Tuesday of the month at the Norris Center (public invited). Regular viewing visits to a special, dark sky site in the Everglades are held each month, allowing the general public to observe the night sky through telescopes, under pristine conditions. For more information visit the website at: http://naples.net/clubs/eas.