NASA's Hubble Space Telescope solved the long-term mystery behind the source of a magellanic stream spread half-way across the Milky Way revealing most of the gas was stripped from the Small Magellanic Cloud about 2 billion years ago.
Scientists have long pondered over the source of the Magellanic Stream. It is a ribbon of gas stretching nearly halfway around the Milky Way. The stream, which was discovered by radio telescopes in the early 1970s, is headed by the Large and Small Magellanic Clouds and two dwarf galaxies orbiting the Milky Way.
In a new finding, NASA's Hubble Space Telescope revealed that most of the gas was stripped from the Small Magellanic Cloud about 2 billion years ago and another region of the stream originated more recently from the Large Magellanic Cloud.
The discovery was made using Hubble's Cosmic Origins Spectrograph that measured the amount of heavy elements like sulfur and oxygen along six locations in the Magellanic Stream. The measurements were made by observing how these elements absorbed ultraviolet light. Researchers also examined faraway quasars that emit light passing through the gas stream. Quasars are cores of active galaxies.
Andrew J. Fox of the Space Telescope Science Institute in Baltimore and his team found a low amount of oxygen and sulfur in most locations that matched the level of these elements in the Small Magellanic Cloud. The researchers were surprised to find a much higher level of sulfur in a region of the stream closer to the Magellanic Clouds.
"We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," said Fox in a press statement. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently. Only Hubble can measure these abundances. These abundances can only be measured in ultraviolet light, which Earth's atmosphere absorbs, and so the observations can only be done from a telescope in space."
Researchers found that unlike other satellite galaxies in the Milky Way, the Large and Small Magellanic Clouds have managed to retain most of their gas and continue to form stars owing to their massive size when compared to other satellite galaxies. However, as these clouds near the Milky Way, they've begun feeling the effect of its gravity, and also the galaxy's own gases have pushed the other gases out leading to the formation of a stream or ribbon of gas.
Researchers suspect that this stream of gas will ultimately fall onto the Milky Way's disc and fuel the formation of stars. Fox revealed that this process is generally how new stars form in a galaxy.
Further studies need to be conducted on the origin of this gas so that researchers can better understand the formation of stars.
"We want to understand how galaxies like the Milky Way strip the gas from small galaxies that fall into them and then use it to form new stars," Fox explained. "This seems like it's an episodic process. It's not a smooth process where a slow stream of gas comes in continuously. Instead, once in a while a large gas cloud falls in. We have a way of testing that here, where two galaxies are coming in. We've shown which of them is producing the gas that ultimately will fall into the Milky Way."
The latest findings were revealed in two papers published in the recent issue of The Astrophysical Journal.
