Observations from the Green Bank Telescope (GBT) have revealed that a giant intergalactic gas stream flowing from neighbor galaxies around our Milky Way is much longer and older than previously thought. The Magellanic Stream flows from the Milky Way’s two largest satellite galaxies, the Magellanic Clouds, and stretches over 100 degrees across the sky. The stream was discovered more than 30 years ago and subsequent observations added tantalizing suggestions that there was more. However, the earlier picture showed gaps that left unanswered whether this other gas was part of the same system. The new GBT observations show that the stream is continuous across the gap and 40 percent longer than previously known with certainty.

UVa’s David Nidever, Steven Majewski and their colleagues Butler Burton (NRAO) and Lou Nigra (U. Wisconsin) observed the Magellanic Stream for more than 100 hours with the GBT. They then combined their GBT data with that from earlier studies with other radio telescopes, including the Arecibo telescope in Puerto Rico, the Parkes telescope in Australia, and the Westerbork telescope in the Netherlands. The result shows a much more complete map of the Magellanic Stream.

One consequence of the added length of the gas stream is that it must be older. The new estimate of the age of the stream is 2.5 billion years. The revised size and age of the Magellanic Stream also provides a new potential explanation for how the flow got started. The new age of the stream puts its beginning at about the time when the two Magellanic Clouds may have passed close to each other, triggering massive bursts of star formation. The strong stellar winds and supernova explosions from that burst of star formation could have blown out the gas and started it flowing toward the Milky Way. Earlier explanations for the stream’s cause required the Magellanic Clouds to pass much closer to the Milky Way, but recent orbital simulations have cast some doubt on the effectiveness of such mechanisms.

Nidever and his colleagues presented their findings to the American Astronomical Society’s meeting in Washington, DC and submitted their work for publication in The Astrophysical Journal.

The above all-sky image shows the Milky Way and Magellanic Clouds in optical light (blue and white), and the hydrogen gas of the Magellanic Stream in red. Brown indicates dust clouds in the Milky Way disk.

CREDIT: Nidever, et al., NRAO/AUI/NSF, Meilinger, Leiden-Argentine-Bonn Survey, Parkes Observatory, Westerbork Observatory, and Arecibo Observatory.