Chapter 10 – part 3 - Neutron stars and Black Holes Neutron stars

Neutron stars and black holes LEARNING GOALS Describe the properties of neutron stars and explain how they form. Explain the nature and origin of pulsars and account for their characteristic radiation. List and explain some of the observable properties of neutron-star binary systems. Describe how black holes are formed, and discuss their effects on matter and radiation in their vicinity. Discuss the difficulties in observing black holes, and explain some of the ways in which a black hole might be detected.

Neutron Star: extremely compact and dense solid sphere, made of neutrons, about 20 km across, density over kg/m 3 spins rapidly

Pulsar Radiation is believed to come from spinning neutron stars. About 1500 of these objects are known. They are created in the core collapse that causes the Type II Supernovae. The exterior of the star is blown off, and only the neutron star remains. This graph shows the intensity of radio emission from the first pulsar, discovered by Jocelyn Bell.

Pulsar Model: the “lighthouse” model, showing “hot spots” that sweep by our direction as the neutron star rotates.

Gamma Ray Pulsars emit mostly high energy radiation

An Isolated Neutron Star has been seen by the Hubble!

M1 – the Crab Nebula is from a supernova seen in year A.D The remnant is 1800 pc away and the diameter is currently 2 pc.

The Crab Nebula contains a pulsar: The Crab Pulsar is due to a spinning neutron star that rotates 30 times per second.

Crab Pulsar can be seen in visible pictures, first OFF, then ON

The Crab Pulsar also blinks ON and OFF in X-rays. The Chandra observatory has seen some detail in the accretion disk of the Crab pulsar.

7 images of Crab pulsar, from Nov to April 2001

Movie using those 7 images of the accretion disk

X-Ray Bursters are due to nuclear explosions on the surface of an accreting neutron star.

A Millisecond Pulsar rotates very rapidly, after millions of years of spinning up due to accretion of incoming material.

Cluster X-Ray Binaries

Neutron stars and black holes LEARNING GOALS Describe the properties of neutron stars and explain how they form. *** They are extremely dense, small (20 km), and spin rapidly. *** *** They are formed from the remnant core of Type II supernovae.*** Explain the nature and origin of pulsars and account for their characteristic radiation. *** Pulsars are due to spinning neutron stars which are accreting gas at magnetic poles. The spin of the star causes the hot region to sweep by our direction like the light from a lighthouse. *** List and explain some of the observable properties of neutron-star binary systems. *** Accretion disks are seen, and the stars may be spiraling in toward each other. These are good tests of theoretical predictions. ***

Chapter 10 – part 3 - Neutron stars and Black Holes Black holes

Neutron stars and black holes LEARNING GOALS Describe the properties of neutron stars and explain how they form. Explain the nature and origin of pulsars and account for their characteristic radiation. List and explain some of the observable properties of neutron-star binary systems. Describe how black holes are formed, and discuss their effects on matter and radiation in their vicinity. Discuss the difficulties in observing black holes, and explain some of the ways in which a black hole might be detected.

Gamma-Ray Bursts have been observed and they are very short duration, which means that they come from relatively small objects (smaller than a star).

Gamma-Ray Bursts come from all directions in the sky, which means they originate from distant objects – most likely from outside the galaxy (the Milky Way).

Gamma-Ray Burst Counterparts are seen in visible (galaxies)

Gamma-Ray Burst Models involve compact objects

Curved Space is due to massive objects.

Some 2-dimensional models of “curved space” On a sphere, the “straightest line” is a great circle. On a cylinder, a “line” can be a circle, which is closed, or a helix, which is open and infinite in length. On a more complex surface, we use the idea of a “geodesic” to describe the “straightest curve” that is possible on that surface. Massive objects “cause” the “surface” representing “space” to become “curved” (i.e., not flat like a sheet).

The first test of General Relativity was during an eclipse. Light from a distant star was deviated by the Sun.

General Relativity also explains the precession of the perihelion of Mercury

A Robot falling into a black hole would disappear forever from the view of the rest of the universe.

While approaching the black hole, there would be a Gravitational Red Shift of the radiation emitted by any falling object.

Cygnus X-1 is a possible black hole. The website for the Chandra Observatory has more pictures of possible black holes. chandra.harvard.edu (link) (link)

Black Holes probably have accretion disks.

The Chandra Observatory has taken X-ray pictures of the center of the Milky Way Galaxy (our galaxy).

These X-ray pictures of the center of the Milky Way Galaxy are a mosaic of many smaller pictures.

The X-ray pictures of the center of the Milky Way show lots of white dwarfs, neutron stars and ….

We believe that there is a massive black hole in the center of the Milky Way galaxy, with an accretion disk. This is a close-up image of the center of the Milky Way galaxy using X-rays, taken by the Chandra X-ray Observatory. ESO has made a movie of this.

Intermediate-Mass Black Holes (500 M sun ) may have been seen in another galaxy(M82).

Neutron stars and black holes LEARNING GOALS Describe how black holes are formed, and discuss their effects on matter and radiation in their vicinity. *** Black holes probably form during supernova explosions, when the collapse of the core continues past the density of neutron stars. They have a huge amount of mass, and will attract nearby mass just like any other large mass. But any mass (or light!) falling past the event horizon is lost forever, and will never escape. *** Discuss the difficulties in observing black holes, and explain some of the ways in which a black hole might be detected. *** Black holes are completely invisible, because light cannot escape. However, the accretion disk will be very hot, and will radiate large amounts of X-rays, UV, visible light, radio, etc. ***

Exam # 4 – Thur. Dec. 2 The exam will cover only Ch. 9 and 10 and have about 45 questions. I have a new homepage: If you didn’t do a paper on the first movie, your paper on the second movie is due NOW. Late papers will lose 2 points (out of 10) per day that they are late. Turn them in to the box outside my office at 532 Currens (top floor).

Final exam Tues. Dec. 14 at 3 p.m. The exam will cover Ch and have about 60 questions. We will cover Ch. 11 on galaxies. See my homepage: for the study guide for Ch. 11 (next week).