Caty Pilachowski IU Astronomy Mini-University 2014
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Caty Pilachowski IU Astronomy Mini-University 2014 Monster Black Holes
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Monster Black Holes. Caty Pilachowski IU Astronomy Mini-University 2014. What is a black h ole , anyway?. A black hole is…. …an object whose gravity is so intense that light cannot escape. How Big Are Black Holes?. A black hole’s size depends on its mass…. - PowerPoint PPT Presentation
Transcript of Caty Pilachowski IU Astronomy Mini-University 2014
Caty PilachowskiIU AstronomyMini-University 2014
Monster Black Holes
What is a black hole, anyway?
A black hole is…. …an object whose gravity is so intense
that light cannot escape
How Big Are Black Holes?
A black hole’s size depends on its mass….
About 1 centimeter
About 3 kilometers
100 billion times smaller than a proton
• Strength of gravity changes rapidly with distance
• The closer you are, the stronger the gravity
Small black holes have strong “tides”
Strong Gravity! Spaghettification!
Black Hole
Safety! At larger
distances, a black hole’s gravity is exactly the same as if it were “normal” matter
Safe limit: hundreds or thousands of times the black hole’s diameter
Black holes are not intuitive!
from xkcd (www.xkcd.com)
Earth and Moon?
What would happen to the Moon if the Earth were suddenly to collapse into a Black Hole?
A
BC
A. Nothing – it would continue to orbit the Earth
B. The Moon would spiral into the Earth
C. The Moon would fly off into space
And the answer is….
The Moon would continue to orbit the Earth just as before…
A!
Black Hole
Historya
Escape Velocity
Isaac Newton, 1728A Treatise of the System of the World
A cannonball fired with enough velocity will orbit the EarthWith a high enough velocity, it will escape Earth entirely
Gravity Distance x Distance
Mass~
Dark Stars
• What happens if a star’s gravity is so strong that its escape velocity is faster than the speed of light?
• From the speed of light, Michell calculated that light could not escape from a star 500 x the Sun’s radius and the same density (125,000,000 solar masses!)
• The star would be dark!
John Michell, 18th century British scientist, Fellow of the Royal Society
Black Holes!
In the 1930s – Chandrasekhar, Oppenheimer, Snyder predict that massive stars can collapse into something denser – a black hole
J.A. Wheeler popularized the term “black hole”
Cygnus X-1: The FIRST Black Hole
Discovered in 1972A blue supergiant star orbits an invisible companionBright in x-raysHDE 226868, near Eta Cygni in Cygnus
Evidence for Black Holes
Effect of gravity on nearby objects – Mass!Accretion disks
Accretion disks emit x-rays as matter falls in But it’s hard to tell the difference between a black hole and a neutron star
Stellar Mass BHs
About 20 candidates known in the Milky Way Masses 4-12 times the mass of the Sun A few thousand light years away The galaxy contains many more yet to be discovered
The Monsters!
Sagittarius A*
1974 – A strong radio source was discovered in a radio- wavelength survey of the Galactic Center region
Sgr A* in X-rays
Strong X-ray emission from Sgr A* X-ray flares!
Sgr A* is not visible in visible or infrared light
But many stars surround Sgr A*
Stars Orbit Sgr A*
Even though Sgr A* is 26,000 light years away, we can see stars orbiting around it
Stars Orbit Sgr A*
The orbits of stars around Sgr A* tell us the mass of the central object
The mass of Sgr A* is 4,000,000 times the mass of the Sun
Other galaxies have black holes, too!
The giant elliptical galaxy M87 contains a massive black hole 3.5 BILLION solar masses!
All large galaxies contain central black holes Hubble has
examined many large galaxies and found super-massive black holes at their centers
How do Monster black holes form?
Does the galaxy make the
black hole?
-or-Does the black
hole make the galaxy?
Black Hole First
Dense clump of primordial gas
becomes a black hole
The black hole’s gravity attracts more
gas into a disk
The gas forms stars to make a galaxy
Galaxies First: IA single massive
star forms
The star collapses to form a few hundred
solar mass black hole
The black hole eats gas, stars, and other black holes to grow
A cluster of massive stars forms in a baby galaxy
The cluster collapses under gravity to form a massive black hole
The black hole grows
Galaxies First: II
Black Holes Grow with Galaxies
Black holes accrete gasBlack holes eat starsWhen galaxies merge, their central black holes also merge
NGC 5033 hosts TWO super-massive black holes!
The black holes will eventually merge into one
Black holes in the center of galaxies will eventually merge together
Merging Black Holes
Black Hole Eats
a Star• A star in the galaxy
RX J1242-11 came too close to its black hole
• The star was tidally shredded
• Strong x-ray flare
Artist’s Conception
BH Mass ~ 100 million suns
Accreting Gas
The Doomed CloudSmall gas cloud discovered in 2011Moving almost directly toward Sgr A* black hole (yellow )Velocity ~ several million km/hour!About 3 Earth-masses of gas (but is a star inside?)
The Cloud in 2013Closest approach to Sgr A* in early 2014, about 2200 x the black hole’s radiusAs the cloud approaches Sgr A*, gravity “spagettifies” the cloud
2014 Observations The leading edge of the cloud has whipped
around Sgr A* at 10,000,000 km/hour!Computer Simulation
We’re still not sure what it is…– An isolated cloud– A “wind bubble”
around a star
The Cloud’s Future… Current observations suggest the cloud
contains a star… Computer Simulation
Black Holes Affect Galaxy Evolution
High energy jets from feeding black holes may regulate star formation, gas accretion, and
galaxy growth!
Only a fraction of accreted material ends up in the black hole – most is shot back out in a jet!
Courtesy A. Feild / STScI / NASA
Summary
The End
