In addition to formation by supernovae and neutron star mergers, it should be possible for black holes to form via direct collapse. For the first time, we caught one red-handed, not just in simulations as shown here. Image credit: Aaron Smith/TACC/UT-Austin.

Surprise! The Universe has a third way to form black holes

It isn’t just supernovae or merging neutron stars. In fact, it’s the quietest way of all!

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae.” -Scott Adams

When a massive enough star runs out of fuel in its core and collapses, the resulting Type II supernova will produce a black hole.

Cassiopeia A in X-ray light from the Chandra X-ray Observatory. It is conceivable that there is a black hole remnant at the core of this object, although the evidence is not indisputable. Image credit: NASA / CXC.

Supernovae that aren’t quite massive enough will produce neutron stars instead, which themselves will make black holes if they either accrete more matter or collide with another neutron star.

Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. About 3–5% of the mass gets expelled in such a collision; the rest becomes a single black hole. Image credit: Dana Berry, SkyWorks Digital, Inc.

These two processes both enrich the Universe with heavy elements: supernovae with elements like iron, silicon, sulphur and phosphorous, while neutron star collisions create gold, mercury…