The article doesn't mention that a large number of these "Earths" are much closer to the center of the galaxy than we are, which it appears make it much less likely that life would form there. But even if those are eliminated, it might not be a billion, but certainly in the hundreds of millions.
The two main reasons are 1) the proximity to the black hole at the center of the galaxy would mean a lot of radiation, and 2) the larger number of supernovae closer to the system, would both be catastrophic to planets capable of sustaining life.
The article doesn't mention that a large number of these "Earths" are much closer to the center of the galaxy than we are, which it appears make it much less likely that life would form there. But even if those are eliminated, it might not be a billion, but certainly in the hundreds of millions.
That's quite interesting.
Do you mind elaborating why it is more unlikely to find life on planets closer to the centre of the galaxy?
The two main reasons are 1) the proximity to the black hole at the center of the galaxy would mean a lot of radiation, and 2) the larger number of supernovae closer to the system, would both be catastrophic to planets capable of sustaining life.
Here's some more about Galactic Habitable Zones.