I had never seen such a map before (I suppose some previous version of it, even with a rough spatial binning, existed?) but I like it
Quote from: eeergo on 04/25/2018 12:52 pmI had never seen such a map before (I suppose some previous version of it, even with a rough spatial binning, existed?) but I like it I've not seen anything like that before either, and it was the thing that most surprised me: spatial galactic radial velocity differences.
It makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).
Astronomy professor Helmi lead author of one of six papers describing the quality of the Gaia data
The data shows, for example, two satellite galaxies with a very similar trajectory. This suggests they share a common origin. The trajectories of satellite galaxies are also governed by how the mass of the Milky Way is distributed, especially in the halo. ‘We can now estimate the mass distribution in the halo of the Milky Way more accurately, and this is where dark matter dominates and dictates the motion of stars, globular clusters and satellite galaxies. This means we should be able to probe much more directly the nature of dark matter and test whether the law of Gravity needs modification.
Quote from: eeergo on 04/25/2018 01:18 pmIt makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre). As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...--- Tony
Where's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.
Quote from: jebbo on 04/25/2018 03:30 pmQuote from: eeergo on 04/25/2018 01:18 pmIt makes sense these "counter-currents" are located as shown, since it has been known for a long time the Sun lies in the periphery of a galactic arm (in fact, one of the first science-related trivia I remember from when I was a child was this one nugget!).I'm not at all sure this is related to the spiral structure. The colours are Vr (i.e. radial velocity relative to the galactic centre). As all the stars are orbiting the centre in roughly circular orbits, this spatial distributiuon is surprising - at least to me, but I must admit to not knowing much about galaxies ...--- TonyWhere's the map from? I can't find it on the ESA site and I'd like to see some explanation about it.
SETI with Gaia: The observational signatures of nearly complete Dyson spheresErik Zackrisson, Andreas J. Korn, Ansgar Wehrhahn, Johannes Reiter(Submitted on 23 Apr 2018)A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M ⊙ ). This scenario can be further tested through upcoming Gaia data releases.
Interesting paper:https://arxiv.org/abs/1804.08351QuoteSETI with Gaia: The observational signatures of nearly complete Dyson spheresErik Zackrisson, Andreas J. Korn, Ansgar Wehrhahn, Johannes Reiter(Submitted on 23 Apr 2018)A star enshrouded in a Dyson sphere with high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson-sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson-sphere candidates in the sample of stars common to Gaia Data Release 1 and RAVE Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M ⊙ ). This scenario can be further tested through upcoming Gaia data releases.