The Ins and Outs of Black Holes

Presented by:

Sarah Silva and Phil Plait (SSU)

with

Simon Steel and Erika Reinfeld (CfA)

January 26, 2007

Our Agenda

Presentation: Black Holes: The Other Side of Infinity

News: From the January 2007 meeting of the AAS/AAPT

Q&A: Burning questions can be emailed to Phil at phil@universe.sonoma.edu

Learn More: Featured resources for the Museum Alliance

*6 toggles mute on and off

8 most commonly asked questions about black holes

1. What is a black hole?2. How do black holes form?3. Where are black holes located?4. How do black holes affect things near them?5. What happens when you fall into a black hole?6. Can black holes be used to travel through

spacetime?7. What can we learn from black holes?8. If black holes are black, how can we find them?

Section 1

The Formation of Black HolesIn 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.

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) Schwarzschild BH

Masses of Black Holes

• Primordial – can be any size, including very small If >1014 g (mountain), 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, producing a long gamma-ray burst

– 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.

Gamma-Ray Bursts to measure the universe

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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 4261800 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.

Artist’s Illustration

Radio Lobe Galaxy

Radio lobes

Jet

Accretion Disk

Artist’s Illustration

Two Views of an Active Galaxy

View at an angle to jetView at 90 from Jet

Radio Lobe Galaxy Seyfert Galaxy

Black Holes as Galaxy shapers

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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’ observations 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),

• Every few hundred thousand years, a star wanders too close to the Milky Way’s supermassive 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

Inside a Black Hole 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:If black holes are black, how can we find them?

What can we learn from black holes?

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.

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 supermassive 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?

Make your own black hole!

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More About This Resource

• 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/

Everything You Ever Wanted To Know But Were Afraid To

Ask (…until now…)

• Before we jump into the full portfolio of resources available on the Museum Alliance portal, we want to give YOU a chance to contribute to the conversation.

• Presenters are standing by…

• Feeling shy? Email phil@universe.sonoma.edu

• Feeling loud? Check your “mute” button (*6)

Featured Black Hole Resources on the Museum Alliance Portal

Black Holes: The Edge of Infinity

Universe > Multimedia > Planetarium Shows

GLAST Black Hole Resource Area

Universe > Professional Development > Resources

Featured Black Hole Resources on the Museum Alliance Portal

Inside Einstein’s Universe: Hands-on Activities

Universe > Education/Programs > Demos, Docent Activities,…

IEU Annotated Animations

Universe > Multimedia > Videos

Featured Black Hole Resources on the Museum Alliance Portal

Hubble Space Telescope Black Hole Kiosk Software

Universe > Models/Exhibits > Kiosk Software

Coming in 2009: A 2,500 square foot traveling exhibit about black holes

Smithsonian Astrophysical Observatory

Thanks for joining us!

phil@universe.sonoma.edusarah@universe.sonoma.edu

sjsteel@cfa.harvard.edu

ereinfeld@cfa.harvard.edu

In association with NASA’s Science Mission Directorate and the Astrophysics Missions