Gaia, Theia, and a starving black hole: this week in space

Jessica Hall

Scientists put forth an interpretation of our planet’s collision history that they think does a better job accounting for the silicon and carbon content of our planet as a whole. Over four billion years ago, just shortly after our planet’s surface first cooled enough to solidify, the Mercury-sized planet Theia smashed obliquely into Earth, mingling mantles and sloshing molten rock out into space to form the moon. Theories vary on the relative force of the impact — I like the sloshing theory, but there’s also a paper saying the impact would’ve had to actually vaporize part of the planet’s mantle. But the mixing would explain why we find carbonates and silicates where we do, and also the very similar chemical composition of the Earth and its Moon.

The impact of Earth and Theia, as depicted by a NASA artist.

The good folks at the ESO found a black hole they think is “starving.” Debris falling into a black hole heats up enough to glow as it’s pulled in faster and faster. But black holes only light up their galaxies so long as they’ve got matter to eat; once they clear their surroundings, they sputter and dim — in this case, the black hole is just a tenth as bright as it used to be. Stranger still, there’s a ring of ingestable debris only 24 light-days away, but it isn’t falling in. It’s because there’s been some interruption to the black hole’s food supply. We think. The team doesn’t actually know, and needs a lot of telescope time to find out. But the leading theory among the group doing the observing is that this supermassive black hole is actually one of a binary pair, and that the other black hole is “interfering” with the influx of matter.

The ESA’s Gaia spacecraft made another great big three-dimensional map, and this one lays out the Milky Way in star-by-star detail. This is the kind of map that could be used with a shiny hologram projection widget to create a 3D, walk-through map of the galaxy. It catalogs more than a billion of the 100-400 billion stars and other objects making up our galaxy. It can also use parallax to watch the motion of the visible universe and comparing that with how it ought to be moving, and in this way, scientists hope to shed some light on dark matter too.

These days it seems like everything is about dark matter. If it’s got particle physics or astronomy in it, you can bet the scientists will be talking about dark matter too. And I think I know why. While I can’t speak for the larger scientific community, I have to say it seems like everyone else is just as sick as I am of not knowing what to make of the dark-matter-shaped hole in our theoretical framework. It’s making us look sloppy. Honestly, if we can’t make any better explanation than “there’s gotta be something there”, then it’s time to follow advice oft attributed to Lord Rutherford or Winston Churchill: “Gentlemen, we’ve run out of money. It is time to start thinking.”