BLACK HOLES:The Other Side of Infinity Presented by: Sarah Silva And Phil Plait (SSU NASA)
8 most commonly asked questions about black holes • What is a black hole? • How do black holes form? • Where are black holes located? • How do black holes affect things near them? • What happens when you fall into a black hole? • Can black holes be used to travel through spacetime? • What can we learn from black holes? • If black holes are black, how can we find them?
Section 1 The Formation of Black Holes In this section, we will address the fundamental questions: What is a black hole? How do black holes form?Where are black holes located?
First comes first • What is a black hole? • Not just a vacuum cleaner • If you take an object and squeeze it down in size, or take an object and pile mass onto it, its gravity (and escape velocity) will go up.
Schwarzschild BH Black Hole Structure • Schwarzschild radius defines the event horizon • Rsch = 2GM/c2 • Not even light can escape, once it has crossed the event horizon • Cosmic censorship prevails (you cannot see inside the event horizon)
Masses of Black Holes • Primordial – can be any size, including very small If >1014 g, they would still exist - could have masses smaller than that of the Sun • “Stellar-mass” black holes – must be at least 3 Mo ~1034 g – many examples are known • Intermediate black holes – range from 100 to 1000 Mo - located in normal galaxies – many seen • Massive black holes – about 106 Mo – such as in the center of the Milky Way – many seen • Supermassive black holes (SMBHs) – about 109-10 Mo - located in Active Galactic Nuclei, often accompanied by jets – many seen
How do black holes form? • Stellar-mass black holes • Supernova: an exploding star. When a star with about 25 times the mass of the Sun ends its life, it explodes. • called a “stellar-mass black hole,” or a “regular” black hole • Stellar-mass black holes also form when two orbiting neutron stars – ultra-dense stellar cores left over from one kind of supernova – merge to produce a short gamma-ray burst.
News! • GRBs
How do black holes form? • Supermassive black holes • lurk in the centers of galaxies, and are huge • millions or even billions of times the mass of the Sun! • Most likely formed at the same time as their parent galaxies, but exactly how is not known for sure. • Astronomers think there is a supermassive black hole in the center of nearly every large galaxy, including our own Milky Way.
Monstrous black holes • At the heart of every galaxy lies a black hole, millions to billions times the mass of our Sun HST/NGC 4261 800 light years
Target Object of the Day • Normal galaxy • A system of gas, stars, and dust bounded together by their mutual gravity. VS. • Active galaxy • An galaxy with an intensely bright nucleus. At the center is a supermassive black hole that is feeding.
News! • Relationship between black hole and galaxy formation
Radio Lobe Galaxy Radio lobes Jet Accretion Disk
Two Views of an Active Galaxy View at 90o from Jet View at an angle to jet Radio Lobe Galaxy Seyfert Galaxy
News! • Jets
Where are black holes located? • Let’s think…. • They form from exploded stars… • We have one at the center of the Milky Way…. • The nearest one discovered is still 1600 light years away • Black holes are everywhere!
Evidence • This shows ten years worth of Prof. Ghez’ data at 2.2 microns of the stars orbiting around a 4 million solar mass black hole at the center of the Milky Way. • It also shows the star’s orbits extrapolated into the future Note: Stars S0-2 and S0-16 provide the best data
Section 2 The gravity of the situation (around black holes) In this section, we will address the fundamental questions: How do black holes affect things near them? What happens when you fall into a black hole?
How do black holes affect things near them? • Are we in danger of being gobbled up by a black hole? • The gravity from a black hole is only dangerous when you’re very close to it. • If the Sun were to become a black hole (don’t worry, it’s way too lightweight to ever do that), what size would it have to be? (remember activity 1) • Every few hundred thousand years, a star wanders too close to the black hole and gets torn apart. This produces a blast of X-rays that can be visible for decades!
How do black holes affect things near them? • Stars in the inner parts of a galaxy orbit the galactic center faster when the galaxy’s central supermassive black hole is more massive. • Astronomers conclude that the total mass of the inner region of a galaxy is proportional to the (relatively very small) mass of its central black hole! • It’s as if the formation of that black hole somehow affected the formation of the billions of normal stars around it.
What happens when you fall into a black hole? If you fall into a black hole You’re doomed. Sure, once you fall in you can never get back out, but it turns out you’ll probably be dead before you get there.
Section 3 Travel Inside the Black Hole at the Center of the Milky Way In this section, we will address the fundamental question: Can black holes be used to travel through spacetime?
Can black holes be used to travel through spacetime? • In reality, this probably won’t work. • While wormholes appear to be possible mathematically, they would be violently unstable, or need to be made of theoretical forms of matter which may not occur in nature.
Section 4 The Search for Black Holes In this section, we will address the fundamental questions: What can we learn from black holes? If black holes are black, how can we find them?
What can we learn from black holes? • As matter falls into a black hole, it heats up and emits X-rays. • Current data indicate we may be missing as many as 80% of the black holes. • Unanswered questions: • What happens at the very edge of a black hole? • Where light cannot escape? • Where space and time swap places? • Where even Einstein’s General Relativity is stretched to the breaking point?
If black holes are black, how can we find them? • Binary star systems • measure the orbit of the normal star and determine the mass of the black hole • X-ray signatures • The first black hole, Cygnus X-1, was identified using data from the first X-ray satellite, Uhuru, in 1972 • NASA’s Chandra Observatory has found indications of black holes in practically every galaxy that it has studied in detail.
Resources • This presentation has been adapted from the Beyond the Event Horizon Black Hole education unit: http://glast.sonoma.edu/teachers/blackholes/bhguide06.pdf • Many more black hole resources for every age: http://glast.sonoma.edu/teachers/blackholes/
The show content • The Search for Black Holes • The Formation of Stellar-Mass Black Holes • Supermassive Black Holes • Travel Inside the Black Hole at the Center of the Milky Way
BLACK HOLES for educators • Section 1 - The Formation of Black Holes • Activity 1 - Aluminum Foil, Balloons, and Black Holes • Activity 2 - Building Perspectives with Active Galaxies • Section 2 - The gravity of the situation (around black holes) • Activity 3 - Black Hole Space Warp • Section 3 - Travel Inside the Black Hole at the Center of the Milky Way • Activity 4 - Science Fiction or Fact • Section 4 - The Search for Black Holes • Activity 5 – The Past, Present, and Future of Black Holes