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Most items in the heavens are inconceivably large. The sun, a fairly ordinary star has a diameter of 1,391,000 kilometers (864,327 miles). Even a tiny planetoid like the moon has a diameter of 3,474 km (2,159 miles). However a few noteworthy items in the heavens are so small that we can think of them in human terms—like neutron stars, which are the size of a town or small city with a diameter of only 20 or 30 kilometers (about ten to 15 miles miles). But even though they are the size of a small asteroid or Manhattan Island, neutron stars are hardly inconsequential. These dinky stars can have more mass than the entire glorious sun (which itself is 332,946 times more massive than the Earth and everything on it). A 1.27 cubic centimeter block of such material (approximately the size of a half an inch sugar cube) would weigh approximately the same as all of the human inhabitants of Earth (give or take).
Neutron stars are left-over fragments of supernovae explosions. When a star 4 to 8 times more massive than our sun burns through all available fuel, its outer layers blow apart in a supernova which spreads glittering matter across great swaths of space. The dense remaining portion of the stellar core undergoes a titanic battle between electron degeneracy pressure and gravity. If the fragment has more than 1.44 stellar masses, gravity wins and the electrons and protons of its constituent matter are crushed into super dense neutrons. Such explosions are tremendously dynamic and bright. In 1054 AD, Sung dynasty astronomers recorded such an explosion which outshone the moon. Contemporary astronomers have determined that the 1054 AD supernova created the Crab Nebula, an oval shaped mass of hydrogen, carbon, oxygen, nitrogen, neon, sulfur, and iron.
In the center of the Crab Nebula is a spinning neutron star which is emitting jets of particles at a tremendous velocity from its magnetic poles. These jets produce very powerful beams of electromagnetic radiation (which varies in intensity and wavelength according to elaborate nuclear & stellar physics, much of which is not yet understood). The forces which create neutron stars often leave the stars spinning and pulsing with energy in such a way that they become pulsars. These pulsars are useful for studying gravity, general relativity, and the behavior of matter at nuclear densities (albeit indirectly). They also make accurate time measurement devices and useful beacons. It is strange to think that stars so prominent for vast distances and so useful to astronomers actually have such minimal volume.
A day ago an international team of stellar physicists announced that the sun’s surface is covered with thousands of searing hot plasma super tornadoes each of which is the size of a large continent on Earth. Using a combination of a space telescope and a ground telescope, researchers discovered that each of these plasma vortexes spins at velocities up to 14,500 kilometers (9,000 miles) an hour.
The mystery of why the corona of the sun is 300 times hotter than the star’s surface has long vexed scientists. The surface of the sun is a balmy 5,526 degrees Celsius (9,980 Fahrenheit), while temperatures in the corona peaks 2 million degrees Celsius (3.5 million Fahrenheit). The discovery of these giant fast-moving storms provides a new mechanism by which heat is transferred through the sun’s atmosphere and ejected into the corona. Energy locked in the powerful magnetic vortexes is effectively self-insulated and does not heat the solar photosphere and chromosphere as much as the corona (where the storms widen and dissipate).
Sven Wedemeyer-Böhm, a Norwegian scientist working on the team was quick to stress that the tornadoes are likely one of several complicated energy transfer mechanisms by which heat reaches the solar corona. However it seems that there are more than 11,000 of these huge plasma tornadoes on the solar surface at any given time.
The brightest star in the night sky is Sirius. Only 8.6 million light years from Earth, Sirius A is 25 times more luminous than the sun. Because of its brightness, the star was well known in ancient times—it was named Sopdet in Ancient Egypt and it was the basis of the Egyptian calendar. After a 70-day absence from the skies Sirius (or Sopdet) first became visible just before sunrise near the Summer solstice—just prior to the annual Nile floods. Greek and Roman astronomers philosophized and speculated about Sirius, (which they called “the dog star” because of its closeness to the constellation Canis Majoris). Arabs knew the star as Aschere “the leader”. Polynesians used it as a principle focus of their astonishing oceanic navigation. Over countless millennia, Sirius has worked its way deep into human consciousness as one of the immutable landmarks of the night sky.
So imagine the shock when it was discovered that Sirius is not alone. The bright star we know is actually Sirius A, a star with twice the mass of the sun. In 1844 the German astronomer Friedrich Bessel hypothesized a tiny companion for Sirius based on the irregular proper motion of Sirius. Then, in 1862, as the American Civil war was being fought an American astronomer in Chicago first observed the tiny companion, Sirius B (thereafter affectionately known as “the Pup”). Sirius B has nearly the same mass as the sun (.98 solar mass) but it is only 12,000 kilometers (7,500 mi) in diameter—nearly the same distance around as Earth.
Today Sirius B is the closest white dwarf star to planet Earth. However it has not always been so, Sirius B began its life as a luminous blue B-type main sequence star with a mass five times that of the sun. About 124 million years ago—as the dinosaurs grazed on the first magnolias—Sirius B fused its way through the hydrogen and helium in its mass. As Sirius B began to fuse together larger elements like oxygen and carbon it expanded into a red giant star with a diameter 10 to 100 times that of the sun. Then Sirius B ran out of nuclear fuel. Without the heat generated by nuclear fusion to support it, the star underwent gravitational collapse and shrank into a hyper dense white dwarf star. These tiny stars are extremely dense and hot when they are formed, but since they generate no new energy their heat and radiance gradually radiate away over billions of years until the stars are completely black and dead.
Although Sirius B is largely composed of a carbon-oxygen mixture, its core is overlaid by an envelope of lighter elements. Hydrogen, being lightest, forms the outermost layer (which is why the little star currently appears uniformly white).
Eta Carinae is a star system 8,000 light years from the solar system. It contains a luminous blue hypergiant star which probably has about 100 times the mass of the sun and shines 4 million times more brightly. For those of you keeping tally, that gives the star approximately the same mass as 33 million earths!
Eta Carinae was originally cataloged by Edmond Halley in 1677 (hence its stylish Latin name) as a comparatively dim 4th magnitude star, however astronomers noticed that its brightness varied greatly over the decades. In 1827 it began to become significantly more luminous and by 1843 it was the second brightest star in the night sky (after Sirius, our next door stellar neighbor which is only 8.6 light years away). The star then dimmed down to the eighth magnitude—becoming invisible to the naked eye. Today it is believed that this strange occurrence was a supernova impostor event in which the star nearly exploded. Looking at Eta Carinae now through the Hubble telescope reveals two huge hemispheres of material ejected from the star. Scientists have named this cloud the Homunculus nebula and it is nearly a light year in diameter.
Stars as massive as Eta Carinae are very rare. At this stage of galactic development there are perhaps a dozen in a galaxy the size of the Milky Way (which contains 200 billion to 400 billion stars). Eta Carinae is probably fated to die in a hypernova explosion (an immense supernova event). A similar impostor event to Eta Carinae’s 1843 flare-up was witnessed on SN 2006jc, a star within galaxy UGC 4904 (perhaps you now appreciate the Latin and Arabic names of familiar nearby astronomical objects). SN 2006jc went hypernova two years after its impostor nova event. It is very possible that Eta Carinae no longer exists but was destroyed a long time ago. The light we see now is eight thousand years old. Who knows what happened since then?
When Eta Carinae goes hypernova it will destroy star systems nearby. Additionally, a massive gamma ray burst will shoot from both of its poles as its center collapses into a black hole. Any living, earth-like world caught in such a beam would be sterilized completely–although we are mercifully not currently in Eta Carinae’s polar vector…