Black holes
The signal, from two merging black holes 3 billion light-years away, is the most distant observation yet.
Theoretical physicists contemplate the seemingly impossible situation of a point in space-time where gravity goes to infinity.
New simulations suggests life could exist in universes very different from our own.
This month's featured images include an awe-inspiring view of the Milky Way and a vibrant shot of a Martian canyon colorfully adorned by minerals.
Scientists detect billion-year-old gravitational message.
A physicist presents a solution to present-day cosmic mysteries.