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    Surprise! The Universe Has A Third Way To Form Black Holes

    Starts With A Bang

    The Universe is out there, waiting for you to discover it

    Opinions expressed by Forbes Contributors are their own. Ethan Siegel
    Ethan Siegel, Contributor

    Aaron Smith/TACC/UT-Austin

    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.

    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.

    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.

    Dana Berry, SkyWorks Digital, Inc.

    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.

    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, lead and uranium.

    Dana Berry/NASA

    Illustration of a black hole tearing apart and devouring a star. Supernova explosions or neutron star mergers (which create gamma ray bursts) should expel or kick a binary companion. The observations of black hole binaries hint at a third way.

    But in theory, there should be a third way: through direct collapse.

    J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University

    Distant, massive quasars show ultramassive black holes in their cores. It's very difficult to form them without a large seed, but a direct collapse black hole could solve that puzzle quite elegantly.

    If a massive enough gas cloud collapses under its own gravity, it should form a black hole directly, without any intervening star.

    X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI

    An ultra-distant quasar showing plenty of evidence for a supermassive black hole at its center. How that black hole got so massive so quickly is a topic of contentious scientific debate.

    This is one of the leading theories for how supermassive black holes begin, including at such early times in the ultra-distant Universe.

    L. Mayer et al. (2014), via

    Simulations of various gas-rich processes, such as galaxy mergers, indicate that the formation of direct collapse black holes should be possible. But none have ever been directly observed until now.

    If direct collapse is possible, we should see some massive stars with just the right properties disappearing with no explosion.

    NASA/ESA/C. Kochanek (OSU)

    The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation.

    For the first time, astronomers observed a 25 solar mass star just disappear.

    NASA/ESA/P. Jeffries (STScI)

    There was a brief brightening in the optical, corresponding to a 'failed supernova', but then the luminosity plummeted to zero, where it has remained.

    Direct collapse is the only explanation possible.

    LIGO, NSF, A. Simonnet (SSU)

    The 30-ish solar mass binary black holes first observed by LIGO are very difficult to form without direct collapse. Now that it's been observed, these black hole pairs are thought to be quite common.

    As many as 30% of massive stars should become black holes in this way, which is now verified for the first time.
    Mostly Mute Monday tells the astronomical story of an object, process or phenomenon in images, visuals and no more than 200 words.

    Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang! Check out his first book, Beyond The Galaxy, and look for his second, Treknology, this October!