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Adapted from a press release of the Max Planck Institute for Extraterrestrial Physics, November 24, 2014:

Astronomers at the Max Planck Institute for Extraterrestrial Physics recently presented new observations of the gas cloud G2 in the Galactic Centre, which was originally discovered in 2011. These data are in remarkably good agreement with an on-going tidal disruption. As a complete surprise came the discovery that the orbit of G2 matches that of another gas cloud detected a decade ago, suggesting that G2 might actually be part of a much more extensive gas streamer. This would also match some of the proposed scenarios that try to explain the presence of G2. One such model is that G2 is originating from the wind from a massive star.

The gas cloud G2 is on a highly eccentric orbit around the Galactic Center. Observations in 2013 have shown that part of the gas cloud is already past its closest approach to the black hole, at a distance of roughly 20 light hours (a bit more than 20 billion kilometres).

The new, deep infrared observations with the SINFONI instrument at the VLT track the ongoing tidal disruption of the gas cloud by the powerful gravitational field. While the shape and path of the gas cloud agrees well with predictions from the models, so far there has been no significant enhanced high-energy emission, as one might have expected from the associated shock front.

Copyright and credit: Max Planck Institute for Extraterrestrial Physics

Copyright and credit: Max Planck Institute for Extraterrestrial Physics

However, a closer look into the data set led to a surprise. A decade ago, another gas cloud – now call G1 – was observed in the central region of our galaxy and it has a similar orbit. The researchers postulate that G1 and G2 might be clumps of the same gas streamer. G1 and G2 could be clumps in the wind ejected from of one of the massive disk stars in the vicinity. This could help to explain the missing X-ray emission from the gas cloud near the black hole (although the non-detection of such emission is not yet understood).

Links: MPE press release, including figures and detailed captions.


In Chapter 15 (the opening photo, p. 382, and Figure 15-15d, p. 395), we discuss the prospective effect of a gas cloud called G2 (“G” for “gas”) that was heading for the center of the Milky Way, perhaps dropping material in to the supermassive black hole known as Sagittarius A* (pronounced A-star) and causing it to flare brightly in x-rays and radio waves, at least. But the prediction for its closest approach is about now, mid-2014, and no brightening has apparently happened. It is still possible that there could be dramatic flaring in the future, but that could be years or decades off.

Credit: ESO

Credit: ESO

Scientists at the Max-Planck Institute for Extraterrestrial Physics in Germany base it on their observations with the European Space Agency’s Very Large Telescope. They suggest that “G2 may be a bright knot in a much more extensive gas streamer.”

Daryl Haggard, who has recently moved to Amherst College from Northwestern University, is lead author of a report of Chandra X-ray Observatory monitoring of “Sgr A*/G2” through six observations in the first half of 2014, including the predicted time of the closest encounter.

These articles describing the situation is available free online, and the main results are discussed by correspondent Ron Cowen in The New York Times for July 22, 2014.

Links: NY Times article by Cowan; the original ApJ article by Oliver Pfuhl, Stefan Gillessen, and a dozen others; Daryl Haggard’s report, from The Astronomer’s Telegram.