sign in sign up
<<
Home , Neutron star, Pulsar, Supermassive black hole

• Form from a 8-20 MSun

• Leftover 1.4-3 MSun core after

Neutron Star (tennis ball) and Chapter 14: Neutron Stars • Neutron Stars consist entirely Washington D.C. and 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 of the • So they are incredibly dense! White Dwarfs and Neutron Stars are made of degenerate • One teaspoon of a neutron

y . g star would weigh 100 million (tennis ball) and r e

Washington D.C. n e

tons! cannot be n o

r compressed….the (or t c

e neutrons) are already as close l •Held up by degeneracy pressure: the E as possible. neutrons don’t like to be squished close together!

Pulsars: Stellar Beacons The Lighthouse Model of

• Spinning neutron stars A is a rotating • 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 , then we see a Pulse of (radio waves) Neutron star’s magnetic field

1 The A massive star dies in a Supernova 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 M > 3 Msun

If the core has more than 3 solar masses…

It will collapse completely to single point –

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 infinite massive than 1.4 Msun Similarly, Neutron stars cannot •Their gravity is so strong, not even be larger than about 3 M Sun can escape! They will collapse completely and turn into a black hole!

Escape Velocity Why Are Black Holes Black?

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

On Earth vesc ≈ 11.6 km/s. On a small body like an , Vesc would be so small you could jump 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 mass of the or star… Not even light 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 curved by mass • So a star like the Sun should bend space, and light traveling past it will get thrown off course • This was confirmed during a solar eclipse in 1919

Event Horizon The

Nothing can get out If Vescape > c, then nothing can leave the star, not light, once it’s inside the not matter. We can calculate the radius of such a star: We have no way of V = c 2_G__M_ 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 compressed 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 gravity than your head.

You would experience “tidal forces” pushing & pulling

Time 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 mass. – Observe radio jets – Strong magnetic fields If its mass > 3 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 . • X-1 is a source of X rays As more matter falls on the disk, it heats up and emits X-rays. • It is a system, with an O type supergiant & a compact If X-rays are emitted outside the event horizon we can see object them.

The mass of the compact object is more than 20 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 from • Sun-like stars: White dwarf & planetary the collapse of a star. • High-mass stars: Supernova -> SN remnant & dense core • They have masses of several – Core < 1.4 MSun = W.D. Msun – 1.4 MSun < Core < 3 MSun = Neutron Star • Bigger mass = bigger BH! – Core > 3 MSun = Black Hole Lifetime • This happens in the center of Mass most .

A devours a star, releasing X-rays

4 Lecture- The Tutorial: Page 121

• Work with a partner or two • Read directions and answer all questions carefully. Take time to understand it now! • Come to a consensus answer you all agree on before moving on to the next question. • If you get stuck, ask another group for help. • If you get really stuck, raise your hand and I will come around.

“Milky Way”: A band of light 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 “grindstone model” for the galaxy

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

• Bulge in the center • Dark strip in the middle, from dust

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

5 Finding the Center Finding the Center

• Harlow Shapely studied Shapely plotted the locations of the globular star clusters. globular clusters. He found that they are are not centered on the Sun…. • He theorized that they must …but are centered on a point about 25,000 light years from the the true center of the . galaxy

A

The Milky Way Size: The Milky Way is roughly 100,000 light years across, and about 1,000 light years thick.

Stars: The Milky Way is comprised of over 100 billion stars!

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

Top View Parts of Our Galaxy Parts of Our Galaxy

100,000 Disk: The Sun Resides in the light years Disk 1,000 light years Nuclear Bulge: The dense central region

Halo: Spherical region surrounding the disk where the globular clusters live.

Side View

6 Milky Way Scales Lecture 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. • If you get stuck, ask another group for help. • If you get really stuck, raise your hand and I will come around.

7