Black Holes The Science Behind The Science Fiction Eliot Quataert (Berkeley Astronomy Dept) Eliot Quataert (Berkeley Astronomy Dept)

Science Fiction “Infinite Space, Infinite Terror” “A Journey That Begins Where Everything Ends”

A Muse for Popular Culture The giant Schilling vortex has become the black hole of popular culture, sucking in all images and sound and allowing only soundbites about The Great Pitcher’s courage and legacy to escape. Angry Yankee’s Fan “Suddenly, through forces not yet fully understood, Darren Belsky’s apartment became the center of a new black hole” The Far Side Gary Larson

What is a black hole? Do BHs exist in Nature? –YES! How do we find them? What do they look like?

First, Something Simpler: Stars Pressure Balances Gravity The Sun From

Eluding Gravity’s Grasp Earth: V esc = 27,000 miles/hour (11 km/s) Sun: V esc = 1.4 million miles/hour (600 km/s) Mass M Radius R Escape Velocity Speed Needed To Escape An Object’s Gravitational Pull

“Dark Stars” Rev. John Michell (1783) & Pierre-Simon Laplace (1796)  Speed of light  1 billion miles/hour (3x10 5 km/s) What if a star were so small, escape speed > speed of light? A star we couldn’t see! Earth mass: R  1 inch Solar mass: R  2 miles V esc = speed of light 

1915: General Relativity, Einstein’s Theory of Gravity 1916: Schwarzschild’s Discovery of BHs in GR BHs only understood & accepted in the 1960s (Term “Black Hole” coined by John Wheeler in 1967) Karl Schwarzschild Albert Einstein

If an object is small enough, gravity overwhelms pressure and the object collapses. Gravity is so strong that nothing, not even light, can escape. “Radius” of a BH  2 miles for a solar mass  1 inch for an Earth mass NOT a solid surface All Mass at the Center (GR not valid there) Black Holes in GR

Dispelling the Myths … BHs are not cosmic vacuum cleaners: only inside the horizon is matter pulled inexorably inward Far away from a BH, gravity is no different than for any other object with the same mass If a BH were to replace the sun, the orbits of planets, asteroids, moons, etc., would be unchanged (though it would get really really cold).

How do we find BHs in Nature? “It’s black, and it looks like a hole. I’d say it’s a black hole.” Sidney Harris

Where are BHs Found? Centers of GalaxiesBinary Stars 1 BIG BH per galaxy million-billion x mass of sun formation not fully understood millions of ‘little’ BHs per galaxy ~ 10 x mass of sun formed by collapse of a massive star

Shedding Light on BHs: X-ray Binaries If two stars orbit close enough to each other, mass gets pulled from one and falls (accretes) onto the other. The smaller the target object, the faster the gas moves and the hotter it gets. very hot Gas falling into a BH gets very hot and emits lots of radiation in X-rays Accretion is how we “see” a black hole Matsuda

How do we know it’s a BH? Nature is tricky: couldn’t it be another “small star” like a neutron star or a white dwarf? Measure mass of “X-ray star” by motion of its companion (a star like the sun)

How do we know it’s a BH? Nature is tricky: couldn’t it be another “small star” like a neutron star or a white dwarf? Measure mass of “X-ray star” by motion of its companion (a star like the sun) Mass > 3 solar Mass > 3 solar masses  BH! masses  BH! Roughly a dozen BHs found this way (tip of the iceberg) Chandrasekhar

Where are BHs Found? Centers of GalaxiesBinary Stars 1 BIG BH per galaxy million-billion x mass of sun unclear how they form millions of ‘little’ BHs per galaxy ~ 10 x mass of sun formed by collapse of a massive star

The Milky Way Galaxy: ~ 100,000 light-years across M sun Black Hole Scale: Size of Solar System: 0.01 light-years Typical Distance btw. Stars: 1 light-year Central Black Hole Mass: 4 million M sun Also ~ millions of 10 M sun BHs

Stars in the Central Light-Year of the Galaxy Keep Zooming In …

Evidence for a Big BH at the center of our Galaxy 10 light-days  size of solar system Genzel et al; also Ghez et al. Motion of stars at the center of the Milky Way over the past decade

Evidence for a Big BH at the center of our Galaxy 10 light-days  size of solar system Genzel et al; also Ghez et al. BH in our Galaxy weighs in at 4 MILLION SOLAR MASSES Velocities & Orbits of Stars  Mass

Light From Gas Falling Into the Black Hole X-ray Image Infrared Image BH Analogy: Solar Flare

Many Varieties of Massive BHs Many Varieties of Massive BHs Our Galaxy Brightness of Central Black Hole

“Active Galactic Nuclei” The BH can outshine all of the stars in its host galaxy! The BH ejects beams (“jets”) of matter & energy far outside its host galaxy into the surrounding universe radio image

The Moral of the Story … Physicists said that Black Holes could exist –the ultimate victory of gravity over all other forces Astronomers find that BHs do exist – 1 Big BH per galaxy (~ million-billion solar masses) – millions of little BHs per galaxy ( ~ solar mass) BHs are responsible for the most dramatic and energetic phenomena in the universe –BHs are “seen” via the light produced by infalling gas & via the gravitational pull that they exert on nearby objects