White Dwarfs Neutron Stars and Black Holes

White Dwarfs Neutron Stars and Black Holes

Solar Mass Star: Comparative Sizes Red Giant vs Sun Red Giants can be as big as the Earth’s orbit around the Sun Sun vs White Dwarf White Dwarfs are about the size of Earth White Dwarf vs Neutron Star Neutron Stars are about the size of a small city, like Las Cruces Neutron Star vs Black Hole Solar mass Black Holes are about the size of a university campus, like NMSU

White Dwarfs WDs are the hot core remnants of dying low mass (<8 Msun) stars. When they first form the outer layers of the star can be seen in a planetary nebula The WD is made of oxygen and carbon locked into a degenerate gas. The density is about 106 g (million times that of water). A young unknown student in India named Chadrashekar realized that WDs with larger masses were smaller. But, his calculations showed that at 1.4 times Msun, the locked together oxygen and carbon could no longer support the star! It had to collapse. He was laughed at, but he was right. (bigger mass -> smaller size)

Equation of State--- relationship between size and density There is a vast region of density of matter where matter is unstable. There exists no physics nor form of matter to support itself from gravity. Some Examples No Equation of State Exists in the Universe! Earth 1/10 Earth WD NS Las Cruces 1 million times water! 100 trillion times water! Thus, no objects exist with densities between a few million and 10 trillion times that of water (1g/cc).

A Neutron Star is Born So What Happens? During SN explosion, if the core mass is greater than 1.4 Msun, then the core must totally collapse. All the atomic nuclei in all the atoms mash together into one big nucleus, made of neutrons and electrons and other forms of exotic matter. CRAB NEBULA: a supernova that blew 950 yrs ago. It has a NS in its center. How do we know?

Neutron stars are the lighthouses of the Universe. The magnetic fields of the stars also collapse and become very very concentrated. The star is now spinning very very fast (between 30 up to 1 million times per second!). With all that energy and spinning, surface electrons get stripped out and beam gamma-ray, X-ray, UV, and optical radiation along the star’s poles.

Crab Nebula Pulsar pulses every 0.033 seconds time Neutron Star! Called a PULSAR

But what happens when the density of the collapsing core exceeds 100 trillion times the density of water? STRANGE THINGS HAPPEN- YOU HAVE ENTERED THE TWILIGHT ZONE

Light has no mass, but it follows the force of gravity!!! WHY? Einstein’s THEORY OF GENERAL RELATIVITY. Ol’ Albert realized that mass places a stress on both time and space. Thus, light is only following the local space time curvature… and this can cause some… strange… effectS …

Mass really “warps” space and time. Think of space as a two dimensional sheet. A lot of mass in a small area forms a very deep and narrow funnel. The more space is warped, the slower time flows. Deep in the funnel time passes slowly, away from the funnel it passes “normally”. time normal time slowed The motions of much smaller masses in the proximity of a massive object is governed by the shape of space. It just so happens that Newton’s Law of Gravity describes these motions perfectly well, but only in regions that are not deep in the funnel. But note that Einstein says these motions are a consequence of space-time warps due to masses.

Black Hole When the a large mass is confined to a small size, the funnel becomes infinitely deep! The density is so high (greater than 100 trillion times water) that … no form of matter can support itself against the crush of its own space time warp! 2GM The “size” of a black hole! Rs = c2 1. Photon Sphere: 1.5Rs distance where light can go into circular orbit! 2. Event Horizon: Rs distance where escape speed equals speed of light! 3. Singularity: ? Mathematical point at center… we don’t know what it is, but it is where the point of the funnel comes to a head… if it does? 1 2 3 Rs = radius of event horizon is the “size of black hole. Depends upon mass and the speed of light.

The shape of space around a black hole results in what we call the “bending”’ of light. The bending of light can lead to some strange effects!! If the Earth were squeezed to the size of a pea, it would collapse into a black hole! If this pea sized, Earth mass black hole passed between you and a background object, the light paths would be bent and you would see some pretty bizarre features!

What would it look like if a Earth mass black hole passed in front of Albert?

The space time around a star is identical to the space time around a black hole, until you get close to the event horizon. WHAT WE SEE WHEN YOU ARE FALLING IN WHAT YOU SEE FALLING IN Redshifted (turn red) until redshifted to infinity (you disappear from view) Time slows until it stops when you reach the event horizon Squeezed and stretched Looking back out to the universe and all time passes by in an instant! PAIN What you see is totally different than what we see time slows Event horizon

Most black holes are found because they are eating their companion stars! Like Neutron Stars, there are intense magnetic fields that channels some of the matter into jets.

In some galaxies, black holes lurk in their centers. These BHs have devoured so much matter, which makes them grow! Some BHs have masses of several million Msun! And the jets these babies make…. Astronomical Maniacs!!!!! More later. Size of the Milky Way! This image (and a spectrum) is smoking gun evidence, the material is orbiting very very fast and computations show that the radius is less than Event Horizon size for this object!

Cheating Space… travel through a black hole and wormhole to Vega!

White Dwarfs Neutron Stars and Black Holes