Stars
Stars, the little twinkling lights in the night sky, are really Suns: giant glowing balls of gas held together by the force of gravity. Long ago dust and gas were compressed by gravity, forming the spheres that became stars. The dust was vaporised, and balls of gas remained. Stars are gas right through: they have no solid parts.Stars generate their own light and heat by nuclear fusion, the process in which hydrogen atoms join to form helium atoms at temperatures around 10 million degrees Celsius! Different stars have different brightnesses and colours. Generally the brightest are the nearest or largest. Colour is related to age and density. Stars like Aldebaran and Betelgeuse are "red giants" and are fairly old and relatively cool (as stars go). Others like Sirius a
VEGA
Vega (Alpha Lyrae) is a very bright star in the constellation Lyra. It is also known as the Harp Star and Fidis. Vega is the 5th brightest star in the sky and is pale blue. It is about 25 light years from Earth. Its spectral type is A0Va. A disk of dust surrounds Vega, from which planets might form. Vega, together with Deneb and Altair form the Summer Triangle.
Photograph courtesy NASA/Andrew Fruchter (STScI)
Neutron stars are ancient remnants of stars that have reached the end of their evolutionary journey through space and time.
These interesting objects are born from once-large stars that grew to four to eight times the size of our own sun before exploding in catastrophic supernovae. After such an explosion blows a star's outer layers into space, the core remains—but it no longer produces nuclear fusion. With no outward pressure from fusion to counterbalance gravity's inward pull, the star condenses and collapses in upon itself.
Despite their small diameters—about 12.5 miles (20 kilometers)—neutron stars boast nearly 1.5 times the mass of our sun, and are thus incredibly dense. Just a sugar cube of neutron star matter would weigh about one hundred million tons on Earth.
A neutron star's almost incomprehensible density causes protons and electrons to combine into neutrons—the process that gives such stars their name. The composition of their cores is unknown, but they may consist of a neutron superfluid or some unknown state of matter.
Neutron stars pack an extremely strong gravitational pull, much greater than Earth's. This gravitational strength is particularly impressive because of the stars' small size.
When they are formed, neutron stars rotate in space. As they compress and shrink, this spinning speeds up because of the conservation of angular momentum—the same principle that causes a spinning skater to speed up when she pulls in her arms.
Pulsing Lights
These stars gradually slow down over the eons, but those bodies that are still spinning rapidly may emit radiation that from Earth appears to blink on and off as the star spins, like the beam of light from a turning lighthouse. This "pulsing" appearance gives some neutron stars the name pulsars.
After spinning for several million years pulsars are drained of their energy and become normal neutron stars. Few of the known existing neutron stars are pulsars. Only about 1,000 pulsars are known to exist, though there may be hundreds of millions of old neutron stars in the galaxy.
The staggering pressures that exist at the core of neutron stars may be like those that existed at the time of the big bang, but these states cannot be simulated on Earth.nd Rigel are blue-white hot young stars. Then there are intermediate yellow stars like our Sun and Capella, which are middle-aged, "warm" stars. The blue-white star Rigel in Orion gives out 62,000 times more energy than the Sun. It is a young star (a few million years old) and is using its energy up at such a rate that it will not live long (10 million years or so). Compare this with our Sun which is already 4,600 million years old
These interesting objects are born from once-large stars that grew to four to eight times the size of our own sun before exploding in catastrophic supernovae. After such an explosion blows a star's outer layers into space, the core remains—but it no longer produces nuclear fusion. With no outward pressure from fusion to counterbalance gravity's inward pull, the star condenses and collapses in upon itself.
Despite their small diameters—about 12.5 miles (20 kilometers)—neutron stars boast nearly 1.5 times the mass of our sun, and are thus incredibly dense. Just a sugar cube of neutron star matter would weigh about one hundred million tons on Earth.
A neutron star's almost incomprehensible density causes protons and electrons to combine into neutrons—the process that gives such stars their name. The composition of their cores is unknown, but they may consist of a neutron superfluid or some unknown state of matter.
Neutron stars pack an extremely strong gravitational pull, much greater than Earth's. This gravitational strength is particularly impressive because of the stars' small size.
When they are formed, neutron stars rotate in space. As they compress and shrink, this spinning speeds up because of the conservation of angular momentum—the same principle that causes a spinning skater to speed up when she pulls in her arms.
Pulsing Lights
These stars gradually slow down over the eons, but those bodies that are still spinning rapidly may emit radiation that from Earth appears to blink on and off as the star spins, like the beam of light from a turning lighthouse. This "pulsing" appearance gives some neutron stars the name pulsars.
After spinning for several million years pulsars are drained of their energy and become normal neutron stars. Few of the known existing neutron stars are pulsars. Only about 1,000 pulsars are known to exist, though there may be hundreds of millions of old neutron stars in the galaxy.
The staggering pressures that exist at the core of neutron stars may be like those that existed at the time of the big bang, but these states cannot be simulated on Earth.nd Rigel are blue-white hot young stars. Then there are intermediate yellow stars like our Sun and Capella, which are middle-aged, "warm" stars. The blue-white star Rigel in Orion gives out 62,000 times more energy than the Sun. It is a young star (a few million years old) and is using its energy up at such a rate that it will not live long (10 million years or so). Compare this with our Sun which is already 4,600 million years old
Novae
From time to time a star may become visible where no star was previously seen. This is a "new star" or Nova. It is caused by the sudden brightening of a faint star - usually over a period of days or weeks. After reaching maximum brightness, a nova will generally fade over a period of months. Novae occur in binary (double) star systems in which a white dwarf star is very closely paired with a red giant star. The white dwarf has a strong gravitational field and attracts material from the red giant. "Runaway hydrogen burning" on the surface of the white dwarf then takes place, causing the brightening that we see as a nova.Supernovae
A Supernova is the explosion that signals the death of a star, and there are two types. Type I Supernovae seem to result from the incineration of white dwarf stars. Type II Supernovae mark the catastrophic collapse of very massive stars. In a Supernova explosion we are seeing the death of a star as it explodes. Not many Supernovae are bright enough to be seen with the naked eye but in 1987, Supernova 1987A was visible as a bright star in the Large Magellanic Cloud galaxy. The last one visible to the naked eye that occurred in our own Milky Way galaxy was in 1604.
No comments:
Post a Comment