The Big Crunch
If there is enough matter in the Universe eventually gravitational forces will stop its expansion. When this happens gravity will cause the universe to reverse its direction and begin to collapse under its own weight. This phase of the Universe’s life is known as the Big Crunch. Eventually all of the matter in the Universe will collapse into a super dense state and possibly even collapse into an unimaginably massive black hole. Some theorize that the Universe could collapse into the same state that it began as and then blow up in another Big Bang. In this way the Universe would last forever but would continually go through these phases of expansion and contraction, Big Bang and Big Crunch and so on…
Gamma Ray Bursts – The Most Powerful Objects in the Universe?
In the 1960’s, the United States launched some satellites to look for very high energy light, called Gamma Rays. Gamma Rays are produced whenever a nuclear bomb explodes. The satellites found many bursts of Gamma Rays, but they were not coming from explosions on Earth. They were coming from outer space.
Modern satellites have found thousands of these Gamma Ray Bursts. They happen about once a day and come from all over the sky, as the map shows. There are two types of bursts. Some are short, lasting less than 2 seconds. Others are longer, bursting for as long as 1000 seconds. We now think that all Gamma Ray Bursts come from the creation of black holes in distant galaxies. The two types of bursts come from two different ways to make a black hole.
Short Gamma Ray Bursts come from two neutron stars orbiting each other. They slowly lose energy and merge together to form a black hole. The gamma rays come from debris falling into the black hole.
Long Gamma Ray Bursts come from the deaths of very massive stars. At the end of their lives, these stars collapse and explode as a type of supernova. The gamma rays shoot out along jets from these powerful explosions.
Neutron Stars are the end point of a massive star’s life. When a really massive star runs out of nuclear fuel in its core the core begins to collapse under gravity. When the core collapses the entire star collapses. The surface of the star falls down unti l it hits the now incredibly dense core. It then bounces off the core and blows apart in a supernova. All that remains is the collapsed core, a Neutron Star or sometimes a Black Ho le, if the star was really massive.
A typical neutron star is the size of a small city, only 10 Kilometers in diameter but it may have the mass of as many as three suns. It is quite dense. One spoonful of neutron star material on Earth would weigh as much as all the cars on Earth put togeth er.
Some neutron stars spin very rapidly and have very strong magnetic fields. If the magnetic poles are not lined up with the star’s rotation axis then the magnetic field spins around very fast. Charged particles can get caught up in the magnetic fields and beem away radiation like a lighthouse lamp. This type of neutron star is called a pulsar. Pulsars are detected by their rapidly repeating radio signals beemed at Earth from those charged particles trapped in the magnetic field. When they were first discov ered it was thought that they were radio signals from “Little Green Men” from outer space. Weird.
Spiral galaxies may remind you of a pinwheel. They are rotating disks of mostly hydrogen gas, dust and stars. Through a telescope or binoculars, the bright nucleus of the galaxy may be visible but the spiral arms are dimmer and difficult to see.
Spiral galaxies are complex objects and have several components: a disk, a bulge, and a halo. The disk contains gas, dust, and young stars in its spiral arms. The dense bulge in the center of the disk contains mostly old stars and no gas or dust. The halo is the home of a very few, scattered stars and globular clusters. The halo is also the home of dark matter in spiral galaxies.
Spirals are subdivided based on the appearance of the arms and the central region. Sa types have a large, bright central region and tightly wound arms, while Sc types have a smaller central region and loosely wound arms. Sb types are somewhere in between. Spiral galaxies can also have bar-like structures through them. These galaxies are classified as SB.
Galaxies like to live together in groups called clusters. There are not many of spirals in a cluster usually, but they are more common than ellipticals in the regions between clusters.
|What’s in a Name:||Arabic for “head of the demon”|
|Claim to Fame:||Represents Medusa’s eye in Perseus. A special variable
star that “winks” every 3 days.
|Type of Star:||Blue-white Main Sequence Star, and a yellow Subgiant|
|How Far Away:||105 light years away|
|How Bright:||Almost 100,000 times brighter than the Sun!|
|Where to View:||In the constellation Perseus the Hero|
|When to View:||November through March
Sirius B – Bizarre White Dwarf Companion of Sirius A