What is the biggest black hole as seen from Earth?

And what are our prospects for observing its event horizon?

“Never look down to test the ground before taking your next step; only he who keeps his eye fixed on the far horizon will find the right road.”
–Dag Hammarskjold

If you collapse a large enough mass into a small enough volume, you’ll create a black hole.

*The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. Image credit: Nicole Rager Fuller for the NSF.*

Every object has a gravitational field, and without enough speed, you can’t leave it; you can’t reach escape velocity.

*The first-stage separation of the Apollo 11 rocket. The multi-stage design allowed the Saturn V rocket to reach escape velocity, if desired, with its final stage. Image credit: NASA.*

For black holes, where escape velocity is bigger than the speed of light at the event horizon, nothing can escape, not even light.

Black holes may still emit light from outside the event horizon, as accelerated matter either falls in or is funneled into jets, but nothing inside the event horizon can ever escape. Image credit: ESO/L. Calçada, of an illustration of the quasar SDSS J1106–1939.

Black holes are formed from the collapse of incredibly massive objects: ultramassive stars imploding in supernovae at the end of their lives.

But common, stellar mass black holes, at 1–100 times the Sun’s mass, are surpassed by rarer, supermassive ones.

*The core of galaxy NGC 4261, like the core of a great many galaxies, show signs of a supermassive black hole in both infrared and X-ray observations. Image credit: NASA / Hubble and ESA.*

Almost every galaxy has one, including our Milky Way.

*The largest flare ever observed from the supermassive black hole at our galaxy’s center. Image credit NASA/CXC/Stanford/I. Zhuravleva et al.*

At 4 million solar masses, our black hole is only 26,000 light years away.

Other, larger, more distant galaxies, like Messier 87, have even larger black holes, reaching into the billions of solar masses.

Three views of the center of Messier 87 and its central, 6.6 billion solar mass black hole. Images credit: Top, optical, Hubble Space Telescope / NASA / Wikisky, via Wikimedia Commons user Friendlystar; lower left, radio, NRAO / Very Large Array (VLA); lower right, X-ray, NASA / Chandra X-ray telescope.

Later this decade, an array of radio telescopes — the Event Horizon Telescope — comes online.

*The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at* *https://www.as.arizona.edu/event-horizon-telescope*.

With a resolution of 10 micro-arc-seconds (μas), it should see the Milky Way’s supermassive black hole’s event horizon.

*The expected view of the Milky Way’s supermassive black hole through the Event Horizon Telescope. It should be the only one directly visible. Image credit: S. Doeleman et al., via* *http://www.eventhorizontelescope.org/docs/Doeleman_event_horizon_CGT_CFP.pdf*.

With an angular diameter of 37 μas, no other black hole appears larger from Earth.

Mostly Mute Monday tells the story of a single astronomical phenomenon or object primarily in visuals, with no more than 200 words of text.

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