mollwollfumble said:
And most especially the disordered patch of white dwarf stars from earlier diagrams has resolved itself into two evolutionary lines, one each for hydrogen and helium dwarfs. And there are other white dwarfs in a region whose existance is totally unexplained.
For more on the white dwarfs, including elimination of unresolved binaries above the main collection, and the two separate evolutionary lines, see
https://arxiv.org/pdf/1805.05849.pdf
This paper also gives mass loss inherent in going from a main sequence star to a white dwarf. Masses in solar masses
Initial_mass, White_dwarf_mass
1, 0.5
1.5, 0.6
3, 0.75
5, 0.85
6.5, 1.0
This remains something of a mystery to me. How does a bog standard star like our Sun lose half of its mass without going supernova?
For more on white dwarfs from Gaia see https://arxiv.org/pdf/1805.04070.pdf, “Hundreds of new extremely low-mass (ELM) white dwarfs”. These ELM white dwarfs have a mass below 0.3 solar masses (see above table) and so cannot be explained using current physics. The best guess is that they were generated by extra mass loss due to close binary progenitors. Alternative hypotheses include the merger of the inner binary in a triple star system, supernova stripping, and mass ejection caused by a massive planet.
Other recent discoveries using data from Gaia include the following. The Gaia Data Release 2 (DR2) was made public at noon (CEST) on 25 April 2018 All of the following were published May 2018.
- Nine more open star clusters
- Another low mass “cannonball” (ie. very fast) star
- “An Efficient Color-Based Selection of Red Giant Stars”, uses distances from Gaia to improve the colour selection method for separating red giant stars from red dwarf stars – if visible at large distances they have to be red giants and this allows calibration of the colour selection method.
- Three new cepheid variables – Gaia data here is not accurate enough to be of any use, but will be useful a year from now.
- The young σ Orionis open cluster is a cornerstone for studying X-ray emission, discs, jets, accretion, photometric variability, magnetism, abundances, and mass function of OB-type, Herbig Ae/Be and T Tauri stars, brown dwarfs, and objects beyond the deuterium burning mass limit. The distances and velocities of virtually all these very young stars has now been found using the Gaia data DR2.
- Analysis of distance and velocity structure of the new stars in the Orion complex, which spans the entire constellation of Orion.
- Anisotropy of the Milky Way’s stellar halo
- Discovery of the most ultra-luminous quasar. SO SMSS J215728.21-360215.1 with magnitude z= 16.9 and W4= 7.42 at redshift 4.75. It is the QSO with the highest unlensed UV-optical luminosity currently known in the Universe. https://arxiv.org/pdf/1805.04317
- Gaia and the Galactic Center Origin of Hypervelocity Stars. Stars with >450 km s−1 radial velocities, above Galactic escape velocity originate from the Galactic center.
- Validating wide stellar binaries. We selected our binaries by matching data for the five dimensions of phase space: positions, proper motions, and parallaxes. Eliminating chance coincidences.
- Rotation of the Andromeda galaxy and its satellite M33.
- The galactic disc in 6-D phase space.
- The search for new quasars. 50 or so new quasars found in Gaia data.
- Distances for Galactic Luminous Blue Variables. Two key results are that the instability strip may not be as clearly defined as previously thought, and that there exists a population of LBVs at relatively low luminosities.
etc.