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Home , Pulsar

• Form from a 8-20 MSun

• Leftover 1.4 - 3 MSun core after

Neutron Star (tennis ball) and Chapter 11: Neutron Stars • Neutron Stars consist entirely Washington D.C. and Black Holes of (no )

Neutron Stars What’s holding it up? • About the size of a large city White dwarfs and neutron stars are held up by (5-10 miles), Several times the Degeneracy pressure mass of the • So they are incredibly dense! White Dwarfs and Neutron Stars are made of degenerate • One teaspoon of a neutron matter. star would weigh 100 million (tennis ball) and tons! Washington D.C. cannot be compressed….the neutrons are already as close as •Held up by degeneracy pressure: the energy possible. neutrons don’t like to be squished close together!

Pulsars: Stellar Beacons The ______Model of Pulsars

• Rotating neutron stars A pulsar is a ______• Strong emits a beam neutron star. radio waves along the magnetic poles

• These are not aligned with the axis of rotation.

• So the beam of radio waves A pulsar’s beam is like a lighthouse sweeps through the sky as the Neutron Star spins. Model of a Pulsar (a rotating Neutron Star) If the beam shines on Earth, then we see a ______of energy (radio waves) Neutron star’s magnetic field

1 The A massive star dies in a ______explosion. Most of the star is blasted into space.

The core that remains can be a neutron star. However… Neutron stars can not exist

with masses M > ___ Msun

If the core has more than 3 solar masses…

It will collapse completely to ______–

Inside the Crab , a Pulsar has been found => A !

Degenerate Matter Black Holes: Overview If a gets too heavy it will collapse… into a Neutron Star (this triggers a •A total victory for ______. second type of Supernova explosion) •Collapsed down to a single point. White dwarfs cannot be more •This would mean that they have ______massive than ____ Msun Similarly, Neutron stars cannot •Their is so strong, not even ____ be larger than about ___ M Sun can escape! They will collapse completely and turn into a ______!

Escape Velocity Why Are Black Holes Black?

Escape Velocity (vesc) is the speed required vesc On with more gravity than Earth, to escape ______’s pull. Vesc would be ______.

On Earth vesc ≈ 11.6 km/s. On a small body like an , Vesc would be so small you could ____ into If you launch a spaceship space. at v= 11.6 km/s or faster, it will escape the Earth A Black Hole is so massive that

Vesc = the ______. But vesc depends on the _____ of the or star… Not even can escape it, so it gives off no light!

2 Black Holes & Relativity Light Can be Bent by Gravity

• Einstein’s theory of says space is ______by mass • So a star like the Sun should _____ space, and light traveling past it will get thrown off course • This was confirmed during a solar eclipse in 1919

Event Horizon The Schwarzschild Radius

______can get If Vescape > c, then nothing can leave the star, not ____, out once it’s inside not ______. the event horizon We can calculate the radius of such a star: We have no way of V = c 2GM____ esc finding out what’s R = s 2 happening inside! c

M = mass G = gravitational constant

c = speed of R = Schwarzschild radius light s

If something is ______smaller than Rs it will turn into a black hole!

Black Holes: Don’t Jump Into One!

If you fall into a Black Hole, you will have a big problem:

Your feet will be pulled with more ______than your head.

You would experience “tidal forces” pushing & pulling

____ is also distorted near a black hole

3 Evidence for Black Holes How do we know they’re real? No light can escape a black hole, so black holes can not be observed directly. • Black holes: However, if a black – Kepler’s Laws, Newton’s Laws hole is part of a binary – disks , we can • Pulsars: measure its _____. – Observe radio jets – Strong magnetic fields If its mass > __ Msun then it’s a black hole!

Evidence for Black Holes: X-rays Evidence for Black Holes Matter falling into a black hole may form an . • Cygnus X-1 is a source of X rays As more matter falls on the disk, it heats up and emits ______. • It is a system, with an O type supergiant & a If X-rays are emitted outside the event horizon we can see “______” them.

The mass of the compact object is more than ___ Msun

This is too massive to be a white dwarf or neutron star.

This object must be a black hole. Artists’ drawings of Cygnus X-1: A black hole accretion disks

Supermassive Black Holes Life Cycles of Stars • Low-mass stars: Fade out, stay on • Stellar black holes come • Sun-like stars: White dwarf & planetary from the collapse of a star. • High-mass stars: Supernova -> SN remnant & dense core

• They have masses of – Core < 1.4 MSun = ______several Msun – 1.4 MSun < Core < 3 MSun = ______– Core > 3 MSun = ______• Bigger mass = bigger BH! Lifetime Mass • This happens in the center of most .

A devours a star, releasing X-rays

4 The “Milky Way”: A band of ____ and a ______

The band of light we see is Milky Way probably looks like really 100 billion stars Andromeda.

Milky Way

Milky Way Composite Photo Before the 1920’s, used a “______model” for the

Tried to estimate our location in the galaxy by counting stars in different ______

• ______in the center • Dark strip in the middle, from _____

Because some stars are ______by dust, the true shape of this group of stars was unclear.

Finding the Center Finding the Center

• Harlow Shapely studied Shapely plotted the ______of the globular star clusters. ______. He found that they are are not centered on the Sun…. • He theorized that they must …but are centered on a point about ______light years from orbit the true ______of the the . galaxy

A

5 The Milky Way Size: The Milky Way is roughly ______light years across, and about _____ light years thick.

Stars: The Milky Way is comprised of over ______stars!

Almost everything visible with the naked eye is inside the Milky Way

Parts of Our Galaxy Parts of Our Galaxy

Disk: The ____ Resides in the Disk

Nuclear Bulge: The dense ______region

Halo: Spherical region surrounding the disk where the ______live.

Milky Way Scales Lecture Questions: Tutorial: Page 123

• Work with a partner or two • Read directions and answer all questions carefully. Take time to understand it now! • Discuss each question and come to a consensus answer you all agree on before moving on to the next question. • How big is the Milky Way? • If you get stuck, ask another group for help. • Where are stars forming (or not forming)? • If you get really stuck, raise your hand and I will come around. • How much mass is in the Milky Way? • What’s going on at the center?

6 Milky Way: A Spiral Galaxy in the Milky Way Our galaxy seems to be ______: it has spiral arms • The Disk contains ___, so stars are still forming • These are dense concentrations of _____ and ____. there. (Population I stars) • Stars orbit the ______, pass through the The Halo has very little spiral arms as they go. ___, and no new stars are forming there. • Stars ______and pile up in the spiral arms, The halo of the galaxy like cars in a traffic jam. is populated by ___ stars. (Population II stars)

Measuring Distances Stellar Populations •To map the Milky Way Galaxy, we need to • Pop. I: Newer, disk & spiral arm stars, measure ______to stars. with _____ percentage heavy elements • Parallax only works for nearby stars (within • Pop. II: Older, bulge and halo stars, with about ____ light years) _____ percentage of heavy elements

• Heavy elements (metals): anything that • For more distant stars, we use Standard isn’t H, He, or Li Candles

Standard Candles Standard Candles • We can easily measure how bright a star appears (______magnitude) •If we knew how bright the star really was (its ______magnitude) then we could calculate its distance.

• We need a star whose absolute is always the same, wherever we observe it.

Car Headlights are standard candles: • Such a star is called a “standard candle” We use them to determine the car’s distance

7 Cepheid Variables Measuring Distances with Cepheids

. In 1908, Henrietta Leavitt discovered a new Cepheid stars change in brightness. standard candle using ______stars They pulsate in a very regular way. .These stars are called ______Large, bright Cepheids pulsate .They are named for δ Cephei, the _____, while small, dim Cepheids first example of such a star. pulsate ______.

If we observe the period of pulsation, we can figure out the & . Henrietta Leavitt If we compare this to the , we find the distance! Delta Cephei

The Structure of the Milky Way Mapping the Milky Way

By measuring the distances to various parts of the Milky Way Galaxy, we map out its structure The Sun is about ______out from the center

The Milky Way is a ______Galaxy

It has a straight structure at the center called a Bar

A modern map of the Milky Way (computer-generated diagram)

Measuring the Mass of the Milky Way Mass of the Milky Way

We use the Sun’s ______• The mass of the Milky Way is between ___ billion around the center of the Milky and MSun and ___ billion MSun Way • Stars & Gas we see in the Milky Way can only The greater the mass inside the orbit, the ______the Sun account for a fraction of the total mass. has move around the center. -What is it? - Why can’t we see it? This way we can measure the mass of the Milky Way.

Total mass: about ______MSun

8 The Center of Our Galaxy The Center of the Milky Way • The ______of stars in the Galactic Center is much greater than in the Sun’s neighborhood. • They appear to be orbiting a ______black hole at the center of the galaxy

Its mass is over

______MSun !

We now realize that our galaxy is only Chapter 13 one of billions of galaxies we can see.

These galaxies come in three main types:

Spiral, ______& ______Galaxies

Spiral Galaxies • Typically very bright, _____ in color • Look like ______(sometimes with ____)

M 100 NGC 300

9 Elliptical Galaxies … are ____, not flat like spirals

They are typically ___ in color.

Less gas and dust than spirals.

Irregular Galaxies • Lack any distinct shape • Are generally ______than spirals and ellipticals

Hubble Tuning Fork

______Galaxies (S): Classified according to spiral arms (a,b,c) and presence of a bar (“B”)

______Galaxies (E): Classified according to shape (E0-E9)

______Galaxies (Irr): Basically anything funky- looking!

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