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Tag Archives: VLT

From an ESO press release, October 26, 2016:

An international team of astronomers has discovered glowing gas clouds surrounding distant quasars, active galaxies less than two billion years after the Big Bang. This new survey by ESO’s Very Large Telescope indicates that halos around quasars are far more common than expected. The properties of the halos in this surprising find are also in striking disagreement with currently accepted theories of galaxy formation in the early Universe.

Bright halos around distant quasars

Credit: ESO/Borisova et al.

The study involved 19 quasars, selected from among the brightest that are observable with the telescope’s MUSE instrument. Previous studies have shown that around 10% of all quasars examined were surrounded by halos, made from gas known as the intergalactic medium. These halos extend up to 300,000 light-years away from the centers of the quasars. This new study, however, has thrown up a surprise, with the detection of large halos around all 19 quasars observed – far more than the two halos that were expected statistically.

The newly detected halos also revealed another surprise: they consist of relatively cold intergalactic gas – approximately 10,000 degrees Celsius. This revelation is in strong disagreement with currently accepted models of the structure and formation of galaxies, which suggest that gas in such close proximity to galaxies should have temperatures upwards of a million degrees.

Links: full ESO press release, including video animations.

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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.