MILKYWAY

Milky Way’s Giant Black Hole Awoke from Slumber 300 Years Ago

noreply@blogger.com (m4m) — Wed, 16 Dec 2009 03:08:00 +0000

I got a new news from nasa site, I had just visited the site. from the site I get information about black holes in the milkyway. Here's the news.

GREENBELT, Md. - Using NASA, Japanese, and European X-ray satellites, a team of Japanese astronomers has discovered that our galaxy’s central black hole let loose a powerful flare three centuries ago.

The finding helps resolve a long-standing mystery: why is the Milky Way’s black hole so quiescent? The black hole, known as Sagittarius A* (pronounced "A-star"), is a certified monster, containing about 4 million times the mass of our Sun. Yet the energy radiated from its surroundings is billions of times weaker than the radiation emitted from central black holes in other galaxies.

"We have wondered why the Milky Way’s black hole appears to be a slumbering giant," says team leader Tatsuya Inui of Kyoto University in Japan. "But now we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst."

The new study, which will appear in the Publications of the Astronomical Society of Japan, combines results from Japan’s Suzaku and ASCA X-ray satellites, NASA’s Chandra X-ray Observatory, and the European Space Agency’s XMM-Newton X-ray Observatory.

The observations, collected between 1994 and 2005, revealed that clouds of gas near the central black hole brightened and faded quickly in X-ray light as they responded to X-ray pulses emanating from just outside the black hole. When gas spirals inward toward the black hole, it heats up to millions of degrees and emits X-rays. As more and more matter piles up near the black hole, the greater the X-ray output.

These X-ray pulses take 300 years to traverse the distance between the central black hole and a large cloud known as Sagittarius B2, so the cloud responds to events that occurred 300 years earlier. When the X-rays reach the cloud, they collide with iron atoms, kicking out electrons that are close to the atomic nucleus. When electrons from farther out fill in these gaps, the iron atoms emit X-rays. But after the X-ray pulse passes through, the cloud fades to its normal brightness.

Amazingly, a region in Sagittarius B2 only 10 light-years across varied considerably in brightness in just 5 years. These brightenings are known as light echoes. By resolving the X-ray spectral line from iron, Suzaku’s observations were crucial for eliminating the possibility that subatomic particles caused the light echoes.

"By observing how this cloud lit up and faded over 10 years, we could trace back the black hole’s activity 300 years ago," says team member Katsuji Koyama of Kyoto University. "The black hole was a million times brighter three centuries ago. It must have unleashed an incredibly powerful flare."

This new study builds upon research by several groups who pioneered the light-echo technique. Last year, a team led by Michael Muno, who now works at the California Institute of Technology in Pasadena, Calif., used Chandra observations of X-ray light echoes to show that Sagittarius A* generated a powerful burst of X-rays about 50 years ago -- about a dozen years before astronomers had satellites that could detect X-rays from outer space. "The outburst three centuries ago was 10 times brighter than the one we detected," says Muno.

The galactic center is about 26,000 light-years from Earth, meaning we see events as they occurred 26,000 years ago. Astronomers still lack a detailed understanding of why Sagittarius A* varies so much in its activity. One possibility, says Koyama, is that a supernova a few centuries ago plowed up gas and swept it into the black hole, leading to a temporary feeding frenzy that awoke the black hole from its slumber and produced the giant flare.

Launched in 2005, Suzaku is the fifth in a series of Japanese satellites devoted to studying celestial X-ray sources and is managed by the Japan Aerospace Exploration Agency (JAXA). This mission is a collaborative effort between Japanese universities and institutions and NASA Goddard.

sources: http://www.nasa.gov/centers/goddard/news/topstory/2008/blackhole_slumber.html

Milky Way Galaxy

noreply@blogger.com (m4m) — Thu, 15 May 2008 10:28:00 +0000

Plasma Cosmology of the Universe has placed the Big Bang model. In 1966, the Plasma Universe was conceived by Hannes Alfven, a Swedish physicist. The model is consistent with Dirac's Theory of symmetry between matter and antimatter, and thousands of scientific observations and experiments. The gamma-ray bursts result when antimatter comets colliding with stars throughout the universe. The scientific discoveries conclude the Big Bang Model is the wrong and support Plasma Universe Model. See differences between the two models of the universe.

The Milky Way Galaxy is one of the hundreds of

billions

of galaxies in the universe. Scientists have observed the antimatter clouds coming from the centers of the Milky Way Galaxy and other galaxies as illustrated in picture of the Plasma Galaxy.

The Galaxy M83, shown on the right, is similar in size and shape to the Milky Way Galaxy and appears differently depending upon the wavelength used to view it.

Computer Models of the galaxies are almost indistinguishable from actual galaxies.

The Milky Way Galaxy is a spiral galaxies with galactic bulge in the center, a large circular disk where our solar system resides, and an encompassing halo.

The Bulge is a flattened spheroid, 3,000 light years high and 20,000 light years in diameter. In the center of the budge are two

black

holes. One is composed of condensed matter and the composed is condensed antimatter. The black holes have the mass of a billions of suns but maybe smaller than the sun. The Einstein-Rosen Bridge keeps the matter and antimatter black holes separated. The oscillations between the black holes at opposite ends of the wormhole force the black holes to become white holes that eject matter and antimatter in opposite directions forming the spiral arms of stars within the galactic disk. Scientists have observed hundreds of new stars are being churned out from the center of the

galaxy

.
The Disk has spiral arms, is 10,000 light years thick and 100,000 light years in diameter. One spiral arm is composed of matter and the other is antimatter. Each spiral arm contains billions of stars, planets, galactic dust and gas. There are a similar number of matter and antimatter

stars

. The sun is composed of matter and is located 28,000 light years from the center of the galaxy. When galactic antimatter enters our solar system, the antimatter is called comets.
The Halo is a diffuse spherical region that surrounds the Bulge and

Disk

. Our galaxy has about 200 globular clusters containing between ten thousand to a million stars. The halo extends tens of thousands of light years beyond the edge of the disk.
The Whirlpool Galaxy is one of the most photogenic galaxies which shows the galactic budge and disk. The Space Telescope Science Institute, who is responsible for

operating

the Hubble Space Telescope as an international observatory, has a wealth of information and

pictures

of the Milky Way Galaxy and other galaxies in the universe.

from: http://www.matter-antimatter.com/milky_way_galaxy.htm

GALAXY

noreply@blogger.com (m4m) — Tue, 12 Feb 2008 07:13:00 +0000

Galaxy

"Milky Way in Sagittarius" photo by B.P. Snowder

If our solar system was the size of a coffee cup, the Milky Way Galaxy would be the size of the North American Continent.
Since ancient times people have speculated about the nature of the hazy band of light that stretches around the entire sky. It is widest and brightest in the summer sky, especially in Sagittarius. There is a long twisty dark lane through Cygnus known as the Great Rift. In autumn the path winds north past Cassiopeia and Perseus, in winter past Orion, and in Spring it reaches down to the Southern Cross.
Our galaxy appears to be in the shape of a big pancake with a bulge in the middle. Our solar system is embedded inside the pancake about half way between the edge and the middle. When we try to look out along the edges we see the combined light of billions of stars. Most of those stars are too far away to pick out individually but together they added up to a milky haze.
Our galaxy is about 100,000 light years across. The central bulge is about 16,000 light years thick. The thinner region where our solar system resides is about 3000 light years thick. Our solar system orbits around the core once every 200 million years. The total number of stars in the Milky Way is probably several hundred billion.
The core of our galaxy lies in the direction of Sagittarius. We have detected that stars in that region are circling the center at very high speed. The simplest explanation for why those stars can travel so fast without flying completely out of the galaxy is that there is a supermassive black hole in the core. The mass of the black hole is estimated at 2.7 million times the mass of the Sun.
The pancake and central bulge are only the obvious parts of the galaxy; the part that glows in the dark. There is also a part that we can't see with our eyes but can be detected by other means, directly and indirectly. We can directly measure light outside the range of human eyes, such as infrared and ultraviolet. We can also deduce where mass exists by its gravitational effect on other objects. We have concluded that the visible disk of the galaxy is surrounded by a huge sphere of material we call the halo.

"Map of the Milky Way" image by Richard Powell

One of the very visible populations in the halo is the globular clusters. These are the oldest objects made out of stars in the Universe. The globulars formed long before the birth of galaxies. When the galaxies came along, the globulars were caught by the gravity and have been orbiting around them ever since. There are about 200 globular clusters orbiting in the halo of the Milky Way.
The globular clusters were a key element in the research that revealed the size of the Milky Way galaxy. The astronomer who found the key was Harlow Shapley. From his measurements of the distance to globular clusters, Shapley could see that they were not evenly distributed around our solar system. They were instead distributed around a point 30,000 light years in the direction of Sagittarius, a point we now accept as the galactic core. At that time, (early 20th century), most astronomers still thought that the Milky Way was the whole of the Universe.

from : www.wwu.edu/depts/skywise/a101_milkyway.html

noreply@blogger.com (m4m) — Mon, 04 Feb 2008 09:31:00 +0000

Our Galaxy

The Universe is a vast expanse of space which contains all of the matter and energy in existence. The Universe contains all of the galaxies, stars, and planets. The exact size of the Universe is unknown. Scientists believe the Universe is still expanding outward. They believe this outward expansion is the result of a violent, powerful explosion that occurred about 13.7 billion years ago. This explosion is known as the Big Bang. By looking at an object's electromagnetic spectrum, scientists can determine if an object is moving away from Earth or towards Earth.

When distant objects, such as quasars (a distant energy source which gives off vast amounts of radiation, including radio waves and X-rays), are viewed from Earth, their spectrum (a band of colors which forms when visible light passes through a prism. The band ranges in color from violet, shorter wavelength, to red longer wavelength) is shifted towards red. Whenever there is a shift in a spectrum, it is called a Doppler Shift. If the shift is toward red, the light given off by the object is in longer wavelengths. When an object moves away from Earth, the light that it is giving off is seen in longer wavelengths. When an object moves toward Earth, the light that it is giving off is seen in shorter wavelengths. This causes a shift in the object's spectrum towards violet. The amount of shift in an object's spectrum is determined by how fast the object is moving. All of the distant galaxies have tremendous red shifts. Based on these data, scientists believe the Universe is still expanding outward.

Our Sun is a star in the Milky Way Galaxy. If you were looking down on the Milky Way, it would look like a large pinwheel rotating in space. Our Galaxy is a spiral galaxy that formed approximately 14 billion years ago. Contained in the Milky Way are stars, clouds of dust and gas called nebulae, planets, and asteroids. Stars, dust, and gas fan out from the center of the Galaxy in long spiraling arms.

The Milky Way

The Milky Way is approximately 100,000 light-years in diameter. Our solar system is 26,000 light-years from the center of the Galaxy. All objects in the Galaxy revolve around the Galaxy's center. It takes 250 million years for our Sun to pull us through one revolution around the center of the Milky Way. The stars we see over our head every night are also members of the Milky Way family.

The Big Bang

The Universe is believed to have been created about 13.7 billion years ago. At the point of this event all of the matter and energy of space was contained at one point. What existed prior to this event is completely unknown and is a matter of pure speculation. This occurrence was not a conventional explosion but rather an event filling all of space with all of the particles of the embryonic universe rushing away from each other. The Big Bang actually consisted of an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The galaxies were not all clumped together, but rather the Big Bang lay the foundations for the universe.

The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding. He discovered that a galaxys velocity is proportional to its distance. Galaxies that are twice as far from us move twice as fast. Another consequence is that the universe is expanding in every direction. This observation means that it has taken every galaxy the same amount of time to move from a common starting position to its current position. Just as the Big Bang provided for the foundation of the universe, Hubbles observations provided for the foundation of the Big Bang theory.

Since the Big Bang, the universe has been continuously expanding and, thus, there has been more and more distance between clusters of galaxies. This phenomenon of galaxies moving farther away from each other is known as the red shift. As light from distant galaxies approach earth there is an increase of space between earth and the galaxy, which leads to wavelengths being stretched.
In addition to the understanding of the velocity of galaxies emanating from a single point, there is further evidence for the Big Bang. In 1964, two astronomers, Arno Penzias and Robert Wilson, in an attempt to detect microwaves from outer space, inadvertently discovered a noise of extraterrestrial origin. The noise did not seem to emanate from one location but instead, it came from all directions at once. It became obvious that what they heard was radiation from the farthest reaches of the universe which had been left over from the Big Bang. This discovery of the radioactive aftermath of the initial explosion lent much credence to the Big Bang theory.

Even more recently, NASAs COBE satellite was able to detect cosmic microwaves eminating from the outer reaches of the universe. These microwaves were remarkably uniform which illustrated the homogenity of the early stages of the universe. However, the satillite also discovered that as the universe began to cool and was still expanding, small fluctuations began to exist due to temperature differences. These flucuatuations verified prior calculations of the possible cooling and development of the universe just fractions of a second after its creation. These fluctuations in the universe provided a more detailed description of the first moments after the Big Bang. They also helped to tell the story of the formation of galaxies which will be discussed in the next chapter.

The Big Bang theory provides a viable solution to one of the most pressing questions of all time. It is important to understand, however, that the theory itself is constantly being revised. As more observations are made and more research conducted, the Big Bang theory becomes more complete and our knowledge of the origins of the universe more substantial.

FROM schoolnet.gov.mt/.../The%20Universe.htm

The Milky Way Galaxy

noreply@blogger.com (m4m) — Sat, 02 Feb 2008 06:05:00 +0000

The Milky Way galaxy is the spiral galaxy we call home, as do roughly 100 billion other stars. It looks very much like other spiral galaxies when viewed from above. There are spiral arms and a bright central part. The Sun is far from the center of the Galaxy, halfway to the edge of the Galaxy along the Orion spiral arm.
The Sun is revolving around the center of the Galaxy at a speed of half a million miles per hour, yet it will still take 200 million years for it to go around once. Do you feel like you are moving at that speed through space? If you did, you would certainly need a seat belt! When we run, we feel the wind on our bodies because there are molecules which make up the air that push against our bodies. But there are very few molecules in the space between the stars. So there is nothing to push against our planet so that we "feel" like we are rushing around at half a million miles per hour.

galaxy like the Milky Way as viewed from the top, and the actual Milky Way as viewed in the infraredClick on top image for diagram (276K JPEG)Click on bottom image for diagram (204K JPEG)European Southern Observatory & NASA COBE Project

Like other spiral galaxies, the Milky Way has a bulge, a disk, and a halo. Although all are parts of the same galaxy, each contains different objects. The halo and central bulge contain old stars and the disk is filled with gas, dust, and young stars. Our Sun is itself a fairly young star at only 5 billion years old. The Milky Way galaxy is at least 5 billion years older than that.

from http://www.windows.ucar.edu/tour/link=/the_universe/Milkyway.html

GLOSSARY 2

noreply@blogger.com (m4m) — Fri, 01 Feb 2008 02:38:00 +0000

A ring One of three Saturnian rings visible from Earth. The A ring is farthest from the planet and is separated from the B ring by the Cassini division.

absolute brightness The apparent brightness a star would have if it were placed at a standard distance of 10 parsecs from Earth.

absolute magnitude The apparent magnitude a star would have if it were placed at a standard distance of 10 parsecs from Earth.

absorption line Dark line in an otherwise continuous bright spectrum, where light within one narrow frequency range has been removed.

acceleration The rate of change of velocity of a moving object.

accretion Gradual growth of bodies, such as stars or planets, by the accumulation of gas or other, smaller, bodies.

accretion disk Flat disk of matter spiraling down onto the surface of a neutron star or black hole. Often, the matter originated on the surface of a companion star in a binary system.

active galaxies The most energetic galaxies, which can emit hundreds or thousands of times more energy per second than the Milky Way.

active optics Collection of techniques now being used to increase the resolution of ground-based telescopes. Minute modifications are made to the overall configuration of an instrument as its temperature and orientation change, to maintain the best possible focus at all times.

active region Region of the photosphere of the Sun surrounding a sunspot group, which can erupt violently and unpredictably. During sunspot maximum, the number of active regions is also a maximum.

active Sun The unpredictable aspects of the Sun's behavior, such as sudden explosive outbursts of radiation in the form of prominences and flares.

adaptive optics Technique used to increase the resolution of a telescope by deforming the shape of the mirror's surface under computer control while a measurement is being taken, to undo the effects of atmospheric turbulence.

amino acids Organic molecules which form the basis for building the proteins that direct metabolism in living creatures.

amplitude The maximum deviation of a wave above or below the zero point.

angular momentum problem The fact that the Sun, which contains nearly all of the mass of the solar system, accounts for just 0.3 percent of the total angular momentum of the solar system. This is an aspect of the solar system that any acceptable formation theory must address.

angular resolution The ability of a telescope to distinguish between adjacent objects in the sky.

annular eclipse annular eclipse Solar eclipse occurring at a time when the Moon is far enough away from the Earth that it fails to cover the disk of the Sun completely, leaving a ring of sunlight visible around its edge.

aphelion The point on the elliptical path of an object in orbit about the Sun that is most distant from the Sun

Apollo asteroid See Earth-crossing asteroid.

apparent brightness The brightness that a star appears to have, as measured by an observer on Earth.

apparent magnitude The apparent brightness of a star, expressed using the magnitude scale.

arc degree Unit of angular measure. There are 360 arc degrees in one complete circle.

association Small grouping of (typically 100 or less) stars, spanning up to a few tens of parsecs across, usually rich in very young stars.

asteroid One of thousands of very small members of the solar system orbiting the Sun between the orbits of Mars and Jupiter. Asteroids are often referred to as "minor planets."

asteroid belt Region of the solar system, between the orbits of Mars and Jupiter, in which most asteroids are found.

asthenosphere Layer of Earth's interior, just below the lithosphere, over which the surface plates slide.

astronomical unit (A.U.) The average distance of Earth from the Sun. Precise radar measurements yield a value for the A.U. of 149,603,500 km.

astronomy Branch of science dedicated to the study of everything in the universe that lies above Earth's atmosphere.

asymptotic giant branch Path on the H-R diagram corresponding to the changes that a star undergoes after helium burning ceases in the core. At this stage, the carbon core shrinks and drives the expansion of the envelope, and the star becomes a swollen red giant for a second time.
atmosphere Layer of gas confined close to a planet's surface by the force of gravity.

atom Building block of matter, composed of positively charged protons and neutral neutrons in the nucleus, surrounded by negatively charged electrons.

aurora Event which occurs when atmospheric molecules are excited by incoming charged particles from the solar wind, then emit energy as they fall back to their ground states. Aurorae generally occur at high latitudes, near the north and south magnetic poles.

autumnal equinox Date on which the Sun crosses the celestial equator moving southward, occurring on or near September 22.

FROM

http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/GLOSSARY/GLOSS_A.HTM

B
B ring One of three Saturnian rings visible from Earth. The B ring is the brightest of the three, and lies just within the Cassini division, closer to the planet than the A ring.

barred-spiral galaxy Spiral galaxy in which a bar of material passes through the center of the galaxy, with the spiral arms beginning near the ends of the bar.

baseline The distance between two observing locations used for the purposes of triangulation measurements. The larger the baseline, the better the resolution attainable.

belt Dark, low-pressure region in the atmosphere of a jovian planet where gas flows downward.

Big Bang Event that cosmologists consider the beginning of the universe, in which all matter and radiation in the entire universe came into being.

binary-star system A system which consists of two stars in orbit about their common center of mass, held together by their mutual gravitational attraction. Most stars are found in binary-star systems.

blackbody curve The characteristic way in which the intensity of radiation emitted by a hot object depends on frequency. The frequency at which the emitted intensity is highest is an indication of the temperature of the radiating object. Also referred to as the Planck curve.

black dwarf The end-point of the evolution of an isolated, low-mass star. After the white dwarf stage, the star cools to the point where it is a dark clinker in interstellar space.

black hole A region of space where the pull of gravity is so great that nothing-not even light-can escape. A possible outcome of the evolution of a very massive star.

blue giant Large, hot, bright star at the upper left end of the main sequence on the Hertzsprung–Russell diagram. Its name comes from its color and size.

blue shift Motion-induced changed in the observed wavelength from a source that is moving toward us. Relative approaching motion between the object and the observer causes the wavelength to appear shorter (and hence bluer) than if there were no motion at all.

blue supergiant The very largest of the large, hot, bright stars at the uppermost left end of the main sequence on the Hertzsprung–Russell diagram.

Bohr model First theory of the hydrogen atom to explain the observed spectral lines. This model rests on three ideas: that there is a state of lowest energy for the electron, that there is a maximum energy, beyond which the electron is no longer bound to the nucleus, and that within these two energies the electron can only exist in certain energy levels.

brown dwarf Remnant of a fragment of collapsing gas and dust that did not contain enough mass to initiate core nuclear fusion. Such objects are frozen somewhere along their pre-main-sequence contraction phase, continually cooling into compact dark objects. Because of their small sizes and low temperatures they are extremely difficult to detect observationally.

brown oval Feature of Jupiter's atmosphere that appears only at latitudes near 20 degrees N, this structure is a long-lived hole in the clouds that allows us to look down into Jupiter's lower atmosphere.

FROM

http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/GLOSSARY/GLOSS_B.HTM

C
C ring One of three Saturnian rings visible from Earth. The C ring lies closest to the planet and is relatively thin compared to the A and B rings.

carbon-detonation supernova See type-I supernova.

Cassegrain telescope A type of reflecting telescope in which incoming light hits the primary mirror and is then reflected upward toward the prime focus, where a secondary mirror reflects the light back down through a small hole in the main mirror, into a detector or eyepiece.

Cassini Division A relatively empty gap in Saturn's ring system between the A and B rings, discovered in 1675 by Giovanni Cassini. It is now known to contain a number of thin ringlets.

catastrophic theory A theory that invokes statistically unlikely accidental events to account for observations.

celestial&151;coordinates Pair of quantities—right ascension and declination—similar to longitude and latitude on Earth, used to pinpoint locations of objects on the celestial sphere.

celestial equator The projection of the Earth's equator onto the celestial sphere.

celestial sphere Imaginary sphere surrounding the Earth, to which all objects in the sky were once considered to be attached.

center of mass The "average" position in space of a collection of massive bodies, taking their masses into account. In an isolated system this point moves with constant velocity, according to Newtonian mechanics.

Cepheid variable Star whose luminosity varies in a characteristic way, with a rapid rise in brightness followed by a slower decline. The period of a Cepheid variable star is related to its luminosity, so a determination of this period can be used to obtain an estimate of the star's distance.

chaotic rotation Unpredictable tumbling motion that non-spherical bodies in eccentric orbits, such as Saturn's satellite Hyperion, can exhibit. No amount of observation of an object rotating chaotically will ever show a well-defined period.

Electronic device used for data acquisition, composed of many tiny pixels, each of which records a buildup of charge to measure the amount of light striking it.

chromatic aberration The tendency for a lens to focus red and blue light differently, causing images to become blurred.

chromosphere The Sun's lower atmosphere, lying just above the visible photosphere.

closed universe Geometry that the universe as a whole would have if the density of matter is above the critical value. A closed universe is finite in extent, and has no edge, like the surface of a sphere. It has enough mass to stop the present expansion, and will eventually collapse.

cold dark matter Class of dark-matter candidates made up of very heavy particles, such as supersymmetric relics.

collecting area The total area of a telescope that is capable of capturing incoming radiation. The larger the telescope, the greater its collecting area, and the fainter the objects it can detect.

color index A convenient method of quantifying a star's color by comparing its apparent brightness as measured through different filters. If the star's radiation is well described by a black-body spectrum, the ratio of its blue intensity (B) to its visual intensity (V) is a measure of the object's surface temperature.

color-magnitude diagram A way of plotting stellar properties, in which absolute magnitude is plotted against color index.

coma An effect occurring during the formation of an off-axis image in a telescope. Stars whose light enters the telescope at a large angle acquire comet-like tails on their images. The brightest part of a comet, often referred to as the "head."

comet A small body, composed mainly of ice and dust, in an elliptical orbit about the Sun. As it comes close to the Sun, some of its material is vaporized to form a gaseous head and extended tail.

comparative planetology The systematic study of the similarities and differences among the planets, with the goal of obtaining deeper insight into how the solar system formed and has evolved in time.

condensation nuclei Dust grains in the interstellar medium which act as seeds around which other material can coagulate. The presence of dust was very important in causing matter to clump during the formation of the solar system.

condensation theory Currently favored model of solar system formation which combines features of the old nebular theory with new information about interstellar dust grains, which acted as condensation nuclei.

conservation of mass and energy A fundamental law of modern physics which states that the sum of mass and energy must always remain constant in any physical process. In fusion reactions, the lost mass is converted into energy, primarily in the form of electromagnetic radiation.

constellation A human grouping of stars in the night sky into a recognizable pattern.

contact binary A binary star system in which both stars have expanded to fill their Roche lobes and the surfaces of the two stars merge. The binary system now consists of two nuclear burning stellar cores surrounded by a continuous common envelope.

continuous spectrum Spectrum in which the radiation is distributed over all frequencies, not just a few specific frequency ranges. A prime example is the black-body radiation emitted by a hot, dense body.

convection Churning motion resulting from the constant upwelling of warm fluid and the concurrent downward flow of cooler material to take its place.

convection zone Region of the Sun's interior, lying just below the surface, where the material of the Sun is in constant convective motion. This region extends into the solar interior to a depth of about 200,000 km.

Copernican revolution The realization toward the end of the sixteenth century that Earth is not at the center of the universe.

core The central region of Earth, surrounded by the mantle. The central region of the Sun.

core-collapse supernova See type-II supernova.

core hydrogen burning The energy burning stage for main sequence stars, in which the helium is produced by hydrogen fusion in the central region of the star. A typical star spends up to 90% of its lifetime in hydrostatic equilibrium brought about by the balance between gravity and the energy generated by core hydrogen burning.
corona One of numerous large, roughly circular regions on the surface of Venus, thought to have been caused by upwelling mantle material causing the planet's crust to bulge outward.

corona The tenuous outer atmosphere of the Sun, which lies just above the chromosphere, and at great distances turns into the solar wind.

coronal hole Vast regions of the Sun's atmosphere where the density of matter is about 10 times lower than average. The gas there streams freely into space at high speeds, escaping the Sun completely.

cosmic distance scale Collection of indirect distance-measurement techniques that astronomers use to measure the scale of the universe.

cosmic evolution The collection of the seven major phases of the history of the universe, namely galactic, stellar, planetary, chemical, biological, cultural, and future evolution.

cosmic microwave background The almost perfectly isotropic radio signal that is the electro-magnetic remnant of the Big Bang.

cosmological principle Two assumptions which make up the basis of cosmology, namely that the universe is homogeneous and isotropic on sufficiently large scales.

cosmological redshift The component of the redshift of an object which is due only to the Hubble flow of the universe.

cosmology The study of the structure and evolution of the entire universe.

crater Bowl-shaped depression on the surface of a planet or moon, resulting from a collision with interplanetary debris.

critical density The cosmic density corresponding to the dividing line between a universe that recollapses and one that expands forever.

critical universe Geometry that the universe would have if the density of matter is exactly the critical density. The universe is infinite in extent, and has zero curvature. The expansion will continue forever, but approach an expansion speed of zero.

crust Layer of the Earth which contains the solid continents and the seafloor.

FROM

http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/GLOSSARY/GLOSS_C.HTM

Glossary

noreply@blogger.com (m4m) — Fri, 01 Feb 2008 02:17:00 +0000

Glossary

(note that this glossary is pertaining to both sections "Observation" and "Theory". For a list of definitions pertinent to celestial mechanics, see too the tutorial "Celestial Mechanics Definitions List")

Asteroid : minor planet mostly found in the asteroid belt, located between Mars and Jupiter. Asteroids originated as planetesimals, these building blocks of the solar system. Such planetesimals collided, yielding the asteroids. Asteroids are found too in orbits outside the asteroid belt. "Minor planet" is an alternative term for "asteroid"

Astronomy : science studying stars and the Universe

Astrophysics :modern aspect of astronomy. Astrophysics is studying deep-sky object on the point of their composition and dynamics

Big Bang: now well-accepted conception of the beginnings of the Universe. Our Universe originated as a minute point seen as a quantum singularity. Expanding swiftly in all directions, such an event created all the particles of matter, then the atoms, then the large-scale structures of the Universe. Universe is still expanding today

Comet : icy body orbit of which brings its more or less close to the Sun. In the process, the comet develops a tail. The term "comet" comes from the Latin "comata", f. "long-haired"

Constellation: stars which are looking close to each other in the night sky. Since the oldest Antiquity such groups of stars have been given names and significances

Copernicus :Polish scientist of the 16th century who displaced the center of the solar system from the Earth to the Sun, bringing the first important revolution in the view of our Universe

Cosmology : reflexion about the Universe at large and its origins

Dark Energy: recently discovered part of the energy-mass budget of the Universe. An anti-gravity of sort, dark energy began to overwhelm matter about 7 billion years ago. Since that time, Universe expansion pace is progressively accelerating. Dark energy represents 75 percent of the Universe's energy-mass budget

Dark Matter : recently discovered concept which designates an unseen part of the Universe. Although still unknown in its composition, dark matter accounts for 25 percent of the mass budget of the Universe

Dust clouds :vast zones of interstellar gas and dust, found inside galaxies. Dust clouds are the zones were stars are forming

Einstein: German scientist whose theory (the Relativity) is describing the Universe. Relativity surpassed the old Newtonian vision of the Universe. The main base to Einstein theory is that space is bent by matter

Exoplanets : term designating a planet orbiting a star other than Sun

Galaxy : ensemble of stars. Galaxies are large-scale structures in the Universe. They comprise stars and gas clouds. Most of them have a supermassive black hole at their center

Galaxy Cluster : most of galaxies are found grouped into clusters. Such clusters in turn are grouped into superclusters. Both these large-scale structures are now understood like embedded in a filamentary network of gas and matter encompassing the whole Universe

Heliosphere: the heliosphere is the domain of the Sun among the interstellar medium. It is, alike the Earth's magnetosphere, a comet-shaped region, with a bow shock in front of it, and a comet tail-shaped form in the trailing direction. The heliosphere is shielding the solar system from what is found in the interstellar medium

Inflation: refinement to the Big Bang theory of the Universe. This theory describes how the Universe endured a rapid and enormous increase in size at its very beginnings. The inflation theory is useful as it clarifies numerous characteristics of the Universe

Infrared : part of the electromagnetic spectrum found beyond the visible red color. It is this part of the spectrum that coming science will focus on as dusty places where important objects of the early Universe are forming are best studied in this wavelength

Kuiper Belt : recently discovered region of the solar system, beyond the orbit of Neptune, where icy planetesimals, leftovers of the formation of the solar system, are found

Light-Year : unit of measure conveniently used in astronomy to qualify the important distances existing in the Universe. 1 light-year is 5.9 trillion miles (9,463 billion km)

Magnitude: unit of measure of how bright a star is appearing. Each class of magnitude represents a star brightness 2.512 fainter than the previous. Classes starts at 0 with negative classes for brighter stars

Milky Way : the Milky Way is our Galaxy. As the Sun is located inside it, we can not see it from the outside. The Milky Way, in the sense of the faintly glowing strip seen in the night sky, is a glimpse of our Galaxy. It's our Galaxy seen edge on

Milky Way Galaxy
(see at Milky Way)

Minor Planet
equivalent of Asteroid

Moon : accessory object to a planet. A moon, or satellite, is an object smaller than the planet and orbiting around it. On the other hand, absolutely, Moon is the name for Earth's only moon

NEO :asteroid orbit of which may represent a hazard to Earth. As NEO stands for "Near-Earth Object", the category may encompass comets too. Strictly a grazing asteroid is a NEA (Near-Earth Asteroid)

Newton :English scientist of the 17th century who built a comprehensive view of the solar system working on previous studies

Oort Cloud :vast zone of leftovers of the solar system formation which stretches to about 1 or 2 light-years from the Sun

Orbit :path which a celestial body is following around another

Planetology :science studying planets of the solar system, as exoplanets

Protoplanetary Disk : disk of gas and material which forms in the equatorial plane of a star during the formation process of the latter. Such a protoplanetary disk may further evolves into planets

Quantum Theory : quantum theory is to the particles world what Einstein's Relativity is to the Universe. The main base of quantum theory is that particles behavior may be described in terms of likelihood only

Quasars : very active galaxies found in the early Universe. Such galaxies are thought to be harbouring supermassive black holes which are outshining them. Such objects might be the proof that galaxies and black holes are developing interacting. "Quasar" stands for "quasi-stellar object"

Redshift : unit of measure mostly used for the farthest objects of the Universe. As the American scientist Hubble demonstrated, all galaxies in the Universe are seen receding from each other, and the further they are from an observer, the faster they seem to recede from him. As when a faraway celestial body is receding from an observer its wavelengths become longer, that is is shifted to the red part of the spectrum, the redshift allows to know of how the wavelength is shifting, hence how quickly the galaxy is receding, hence how far it is

Reflector : astronomical instrument working on the principle of a primary optical device reflecting the incoming light

Refractor : astronomical instrument working on the principle of a primary optical device refracting the incoming light

Satellite : equivalent of moon

Solar system : ensemble composed of the Sun and its nine planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto in this order). The asteroid belt composed of asteroids is part of the solar system too

Star : celestial body working on the base of nuclear fusion

Sun : central star to the solar system. Sun is our star

Supernova : form attained by some stars at the end of their life. Various processes have the dying star collapsing and expelling its outside material in a gigantic explosion. Nebulae like the Crab Nebula are the remaining form of a supernovae event. Plural form of "supernova" is "supernovae"

Telescope : in English, term used to designate any optical instrument used for the purpose of astronomical observation

Universe : ensemble of all what composes our space surroundings

FROM http://stars5.netfirms.com/glossa.htm

Glossary

noreply@blogger.com (m4m) — Fri, 01 Feb 2008 02:04:00 +0000

Astronomy Picture of the Day's Glossary

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Cepheid: A pulsating variable star. This type of star undergoes a rhythmic pulsation as indicated by its regular pattern of changing brightness as a function of time. The period of pulsation has been demonstrated to be directly related to a Cepheid's intrinsic brightness making observations of these stars one of the most powerful tools for determining distance known to modern day astronomy. The existence of this period-luminosity relationship was a point of contention during the 1920 Curtis-Shapley debate.

coma: A spherical cloud of material surrounding the head of a comet. This material is mostly gas that the Sun has caused to boil off the comet's icy nucleus. This gas shines both by reflected sunlight and light emitted by excited molecules. A cometary coma can extend up to a million miles from the nucleus.

comet: A chunk of frozen gasses, ice, and rocky debris that orbits the Sun. A comet nucleus is about the size of a mountain on earth. When a comet nears the Sun, heat vaporizes the icy material producing a cloud of gaseous material surrounding the nucleus, called a coma. As the nucleus begins to disintegrate, it also produces a trail of dust or dust tail in its orbital path and a gas or ion tail pointing away from the Sun. Comet comas can extend up to a million miles from the nucleus and comet tails can be millions of miles long. There are thought to be literally trillions of comets in our solar system out past Neptune and Pluto, but only once per decade or so does one become near and bright enough to see easily without binoculars or a telescope.

dust grains: Not the dust one finds around the house, which is typically fine bits of fabric, dirt, or dead skin cells. Rather interstellar dust grains are much smaller clumps, on the order of a fraction of a micron across, irregularly shaped, and composed of carbon and/or silicates. Dust is most evident by its absorption, causing large dark patches in regions of our Milky Way Galaxy and dark bands across other galaxies. The exact nature and origin of interstellar dust grains is unknown, but they are clearly associated with young stars.

emission nebula: A type of nebula that shines by emitting light when electrons recombine with protons to form hydrogen atoms. The electron frequently approaches the proton in steps emitting energy as light as it gets pulled in. In one of the most common "steps," the recombining electron emits a photon of red light. Since many atoms in the nebula do this all at once, the nebula appears red in color. This type of nebula is created when energetic ultraviolet light from a hot star shines on a cloud of hydrogen gas, stripping away electrons from the atoms (ionization). The free electrons can then begin the process of recombination. Plural of nebula: nebulae.

fusion: A process where nuclei collide so fast they stick together and emit a great deal of energy. In the center of most stars, hydrogen fuses together to form helium. Fusion is so powerful it supports the star's enormous mass from collapsing in on itself, and heats the star so high it glows as the bright object we see today. Scientists here on earth are trying to make nuclear fusion in the laboratory a useful energy source.

galaxy: A system of about 100 billion stars. Our Sun is a member of the Milky Way Galaxy, which is sometimes just designated by capitalization: Galaxy. There are billions of galaxies in the observable universe. Exactly when and how galaxies formed in the Universe is a topic of current astronomical research.

H II region: A region of hot gas surrounding a young star or stars that is mostly ionized. The energetic light from these young stars ionizes the existing gas. This region typically appears red as it glows with the photons emitted when electrons recombine with hydrogen protons.

helium: The second lightest and second most abundant element. The typical helium atom consists of a nucleus of two protons and two neutrons surrounded by two electrons. Helium was first discovered in our Sun. Roughly 25 percent of our Sun is helium.

hydrogen: The lightest and most abundant element. A hydrogen atom consists of one proton and one electron. A hydrogen nucleus is just a single proton. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth.

infrared: Light that is so red humans cannot see it. A band of the electromagnetic spectrum between the visible and the microwave. Photons of infrared light are less energetic than photons of visible light.

Messier, Charles: While hunting for comets in the skies above France, 18th century astronomer Charles Messier made a list of the positions of about 100 fuzzy, diffuse looking objects which appeared at fixed positions in the sky. Although these objects looked like comets, Messier knew that since they did not move with respect to the background stars they could not be the undiscovered comets he was searching for. These objects are now well known to modern astronomers to be among the brightest and most striking gaseous nebulae, star clusters, and galaxies. Objects on Messier's list are still referred to by their "Messier number". For example the Andromeda Galaxy, the 31st object on the list, is known as M31.

neutrino: A small particle that has no charge and is thought to have very little mass. Neutrinos are created in energetic collisions between nuclear particles. The universe is filled with them but they rarely collide with anything.

neutron star: The imploded core of a massive star produced by a supernova explosion. (typical mass of 1.4 times the mass of the sun, radius of about 5 miles, density of a neutron.) According to astronomer and author Frank Shu, "A sugarcube of neutron-star stuff on Earth would weigh as much as all of humanity! This illustrates again how much of humanity is empty space." Neutron stars can be observed as pulsars.

planet: A spherical ball of rock and/or gas that orbits a star. The Earth is a planet. Our solar system has nine planets. These planets are, in order of increasing average distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

QSO - Quasi Stellar Object, also Quasar: QSOs are objects that, at first glance, appear as normal stars. Upon closer inspection, however, QSOs have very large redshifts (i.e. the light they emit is strongly displaced toward the red end of the spectrum). Although their exact nature is controversial, they are commonly considered to be extremely distant, unusually bright nuclei of galaxies. If so, then the light we see from them would have been emitted when the universe was a fraction of its present age.

redshift: When the light an object emits is displaced toward the red end of the spectrum it is said to be redshifted. In general, photons of light that are emitted at a source at one energy and detected by an observer at a lower energy are redshifted. Often, the redshift of an object can be measured by examining atomic absorption or emission lines in its spectrum. Redshifts can be caused by the motion of a source away from an observer. For distant objects, redshifts can be caused by the expansion of the Universe.

reflection nebula: A type of nebula that shines by reflected light. Bright stars near reflection nebulae emit light into the region that is reflected by the large amount of dust there. The size of the dust grains causes blue light to be reflected more efficiently than red light, so these reflection nebulae frequently appear blue in color. Plural of nebula: nebulae.

solar wind: The wind from the Sun. More specifically, particles, usually electrons and protons, continually streaming away from the corona of the Sun. The solar wind is extremely sparse, containing only a few fast moving particles per cubic centimeter at the Earth. The exact geometry and extent of the solar wind is not well known.

star: A ball of mostly hydrogen and helium gas that shines extremely brightly. Our Sun is a star. A star is so massive that its core is extremely dense and hot. At the high stellar core temperatures, atoms move so fast that they sometimes stick to other atoms when they collide with them, forming more massive atoms and releasing a great amount of energy. This process is known as nuclear fusion. Scientists have not yet been able to use nuclear fusion as a power source here on earth, but they are trying!

supernova: The death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradual fading. At peak light output, supernova explosions can outshine a galaxy. The outer layers of the exploding star are blasted out in a radioactive cloud. This expanding cloud, visible long after the initial explosion fades from view, forms a supernova remnant .

ultraviolet: Light that is so blue humans cannot see it. A band of the electromagnetic spectrum between the visible and the X-ray. Photons of ultraviolet light are more energetic than photons of visible light.

white dwarf: A star that is the remnant core of a star that has completed fusion in its core. The sun will become a white dwarf. White dwarfs are typically composed primarily of carbon, have about the radius of the earth, and do not significantly evolve further.

X-ray: Light that is so blue humans cannot see it. A band of the spectrum between the ultraviolet and the gamma-ray. Photons of X-ray light are more energetic than photons in the ultraviolet but less energetic than photons in the gamma-ray. X-radiation can go through human skin tissue but is stopped by dense bones. This property thus makes X-rays valuable in medicine.

from http://bjp.org.cn/apod/glossary.htm

Massive Gas Cloud Speeding Toward Collision With Milky Way

noreply@blogger.com (m4m) — Wed, 30 Jan 2008 12:43:00 +0000

A giant cloud of hydrogen gas is speeding toward a collision with our Milky Way Galaxy, and when it hits -- in less than 40 million years -- it may set off a spectacular burst of stellar fireworks.

"The leading edge of this cloud is already interacting with gas from our Galaxy," said Felix J. Lockman, of the National Radio Astronomy Observatory (NRAO), leader of a team of astronomers who used the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) to study the object. The scientists presented their findings to the American Astronomical Society's meeting in Austin, Texas.

The cloud, called Smith's Cloud, after the astronomer who discovered it in 1963, contains enough hydrogen to make a million stars like the Sun. Eleven thousand light-years long and 2,500 light-years wide, it is only 8,000 light-years from our Galaxy's disk. It is careening toward our Galaxy at more than 150 miles per second, aimed to strike the Milky Way's disk at an angle of about 45 degrees.

"This is most likely a gas cloud left over from the formation of the Milky Way or gas stripped from a neighbor galaxy. When it hits, it could set off a tremendous burst of star formation. Many of those stars will be very massive, rushing through their lives quickly and exploding as supernovae. Over a few million years, it'll look like a celestial New Year's celebration, with huge firecrackers going off in that region of the Galaxy," Lockman said.

When Smith's Cloud was first discovered, and for decades after, the available images did not have enough detail to show whether the cloud was part of the Milky Way, something being blown out of the Milky Way, or something falling in.

Lockman and his colleagues used the GBT to make an extremely detailed study of hydrogen in Smith's Cloud. Their observations included nearly 40,000 individual pointings of the giant telescope to cover the cloud with unprecedented sensitivity and resolution. Smith's Cloud is about 15 degrees long in the sky, 30 times the width of the full moon.

"If you could see this cloud with your eyes, it would be a very impressive sight in the night sky," Lockman said. "From tip to tail it would cover almost as much sky as the Orion constellation. But as far as we know it is made entirely of gas -- no one has found a single star in it."

The detailed GBT study dramatically changed the astronomers' understanding of the cloud. Its velocity shows that it is falling into the Milky Way, not leaving it, and the new data show that it is plowing up Milky Way gas before it as it falls.

"Its shape, somewhat similar to that of a comet, indicates that it's already hitting gas in our Galaxy's outskirts," Lockman said. "It is also feeling a tidal force from the gravity of the Milky Way and may be in the process of being torn apart. Our Galaxy will get a rain of gas from this cloud, then in about 20 to 40 million years, the cloud's core will smash into the Milky Way's plane," Lockman explained.

The cloud will likely strike a region somewhat farther from the Galactic center than our Solar System and about 90 degrees ahead of us in the Milky Way disk. The collision may trigger a period of rapid star formation fueled by the new gas and the shock from the collision. Some theories say that the ring of bright stars near the Sun, called Gould's Belt, was created by just such a collision event.

Lockman worked with Robert A. Benjamin and A.J. Heroux of the University of Wisconsin-Whitewater and Glen I. Langston of NRAO.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

from ;http://www.nrao.edu/pr/2008/smithscloud/

milkywai galaxi

noreply@blogger.com (m4m) — Thu, 24 Jan 2008 02:55:00 +0000