Today was Gaia DR2. My day started at 05:00 for the press release, and ended at 18:00 with the champagne toast we lifted to the entire Gaia DPAC, who have actually changed the world. Amazing things happened during the day, way too much to report on in this forum. So I will just tell you what I was paying close attention to today.
Ana Bonaca (Harvard) and Adrian Price-Whelan (Princeton) looked to see if they could see the long, cold stellar stream GD-1. They found it, and it is in the data at immense signal-to-noise. It is still subtle though, reminding us that finding brand-new streams in the data will still be a challenging project. Their map of the stream confirms the gaps we thought we saw many years ago, and there might even be hints of kinematic distortions at the edges of those gaps. If any of that turns out to be real, we might be able to directly measure substructure in the stream.
Megan Bedell (Flatiron) did the match between Gaia and Kepler and made basic visualizations. These already revealed something interesting: Although there are very few planets around blue subdwarfs (and no, I have no idea what they are, but blue stars below the main sequence), the fraction of blue subdwarfs that host planets looks like it is way too high. What could this mean? Perhaps even more interesting: The planet orbital periods are too short for the planets to have survived the stellar evolution up the red-giant branch and back down again, so there is an astrophysical mystery there too.
In the Gaia DR2 press conference, the team attributed complexity in the white-dwarf color-magnitude diagram (and check it out, it is beautiful!) to different compositions (or maybe surface compositions) of the white dwarfs in the different stripes or modes in the diagram. Kareem El-Badry (Berkeley) did some digging in the white-dwarf world and finds that this is not a good explanation for the differences, or at least not a complete explanation. He thinks there must be some complexity to the mass distribution of white dwarfs, unless the cooling models have serious issues. And he also thinks that the diagram is not showing lots of white-dwarf–white-dwarf binaries, but also not showing zero of them!
There were some reporters at the event. I thought this story by Lee Billings (Scientific American) captured a lot of the spirit of the day!