can you see
can you see
If the core has a mass between 1.4 and 3 solar masses, the neutrons will bump up against each other to form a degenerate gas in a neutron star about the size of small city. The neutrons prevent further collapse of the core. Nothing can prevent the highest mass cores (greater than 3 solar masses) from collapsing to a point. On the way to total collapse, it may momentarily create a neutron star and the resulting supernova rebound explosion and powerful
bursts of gamma-rays in bipolar jets (possibly the source of some of the ``gamma-ray burst'' objects). Gravity finally wins. Nothing holds it up. The gravity around the collapsed core becomes so great that Newton's law of gravity becomes inadequate and the gravity must be described by the more powerful theory of General Relativity developed by Albert Einstein. This will be discussed further below.
The supercompact point mass is called a black hole because the escape velocity around the point mass is greater than the speed of light. Since the speed of light is the fastest that any radiation or any other information can travel, the region is totally black. The distance at which the escape velocity equals the speed of light is called the event horizon because no information of events occurring inside the event horizon can get to the outside. The radius of the event horizon in kilometers = 3 × core mass in solar masses.
wow
Stars initially begin their lives near other stars in a cluster. After a few orbits around the galactic center, gravitational tugs from other stars in the galaxy cause the stars in the cluster to wander away from their cluster and live their lives alone or with perhaps one or two companions.
Stars initially begin their lives near other stars in a cluster. After a few orbits around the galactic center, gravitational tugs from other stars in the galaxy cause the stars in the cluster to wander away from their cluster and live their lives alone or with perhaps one or two companions.
The figure below illustrates the inter-dependence of measurable quantities with the derived values that have been discussed so far. In the left triangular relationship, the apparent brightness, distance, and luminosity are tied together such that if you know any two of the sides, you can derive the third side. For example, if you measure a glowing object's apparent brightness (how bright it appears from your location) and its distance (with trigonometric parallax), then you can derive the glowing object's luminosity. Or if you measure a glowing object's apparent brightness and you know the object's luminosity without knowing its distance, you can derive the distance (using the inverse square law). In the right triangular relationship, the luminosity, temperature, and size of the glowing object are tied together. If you measure the object's temperature and know its luminosity, you can derive the object's size. Or if you measure the glowing object's size and its temperature, you can derive the glowing object's luminosity---its electromagnetic energy output.\n\napparent brightness, distance, luminosity triangle + luminosity, temperature, size triangle\n\nFinally, note that a small, hot object can have the same luminosity as a large, cool object. So if the luminosity remains the same, an increase in the size (surface area) of the object must result in a DEcrease in the temperature to compensate.\n\n
Hydrostatic equilibrium: gravity compression is balanced by pressure outward. | Greater gravity compresses the gas, making it denser and hotter, so the outward pressure increases. |
In any given layer of a star, there is a balance between the thermal pressure (outward) and the weight of the material above pressing downward (inward). This balance is called hydrostatic equilibrium. A star is like a balloon. In a balloon the gas inside the balloon pushes outward and the elastic material supplies just enough inward compression to balance the gas pressure. In a star the star's internal gravity supplies the inward compression. Gravity compresses the star into the most compact shape possible: a sphere. Stars are round because gravity attracts everything in an object to the center. Hydrostatic equilibrium also explains why the Earth's atmosphere does not collapse to a very thin layer on the ground and how the tires on your car or bicyle are able to support the weight of your vehicle.
Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star.
To understand this paragraph you need to make yourself familar with the Hertzsprung-Russel diagram. Look up an image of these diagrams that are used to classify stars according to two criteria. What are the criteria? You should also remember that colour is related to temperature.
Despite what you might think, space is not a perfect vacuum. The space between the stars is filled with a tenuous range of material that provides the building blocks of stars. This material is gas and dust and collectively is known as the interstellar medium (ISM). The ISM gas is predominantly hydrogen whilst the dust is about 1% by mass and includes carbon compounds and silicates. Dust is responsible for the interstellar reddening and extinction of starlight. The more of the ISM a star's light travels through on its way to an observer on Earth the more it gets scattered and absorbed, decreasing the star's apparent brightness and reddening its appearance.
22 items | 46 visits
These pages help describe the formation of, the aging and fate of stars found in our universe.
Updated on Dec 14, 09
Created on Sep 21, 07
Category: Schools & Education
URL: