Zombie Star!


White Dwarf stars are the bizarre relics of smaller stars like our own Sun that have perished after having consumed their necessary supplies of nuclear fuel. First the small Sun-like star swells to hideous proportions, to become a monstrous, bloated Red Giant star, that ultimately puffs its outer gaseous layers into interstellar Space, leaving behind only the ghostlike White Dwarf–its former core. But something else happens when the small Sun-like star dwells in a binary system with a “still-living” sister star, in which case strange and ghastly things can occur. As the Dwarf sips up material from its sister star–and victim–it can reach critical mass and blow itself to pieces in a Type Ia supernova blast, leaving absolutely nothing, nothing, nothing at all behind. However, in August 2014, a team of astronomers using NASA’s venerable Hubble Space Telescope (HST), announced that they have–for the first time–detected a star system that later produced a bizarre “zombie star” after an unusually weak supernova explosion of this type.

Examining archived HST images taken before the supernova blast, the astronomers say that they have spotted the blue sister companion star of the ghastly White Dwarf. The White Dwarf had slowly, relentlessly sipped up fuel from its blue stellar sister, eventually triggering a runaway nuclear reaction in the dead star, resulting in a weak supernova explosion.

This particular supernova belongs to a recently identified class of stellar blast termed Type Iax. These exploding small stars are less energetic and considerably dimmer than normal Type Ia supernovae, which also ignite as the result of exploding White Dwarfs in doomed binary systems. At first, astronomers thought these weaker stellar explosions were unique Type Ia supernovae. However, so far, they have not detected more than 30 of these faint runts of the supernova litter, which occur at one-fifth the rate of normal Type Ia supernovae. 바카라사이트

“Astronomers have been searching for decades for the progenitors of Type Ia’sType Ia’s are important because they’re used to measure vast cosmic distances and the expansion of the Universe. But we have very few constraints on how any White Dwarf explodes. The similarities between Type Iax’s and normal Type Ia’s make understanding Type Iax progenitors important, especially because no Type Ia progenitor has been conclusively identified. This discovery shows us one way that you can get a White Dwarf explosion,” explained Dr. Saurabh Jha in a n August 6, 2014 HUBBLESITE Press Release. Dr. Jha is of Rutgers University in Piscataway, New Jersey.

The team’s study appears in the August 7, 2014 edition of the journal Nature.

Supernovae Runts

When a large, massive star has finally burned up its necessary supply of hydrogen fuel, it may “die” a violent, fiery, explosive supernova death. Supernovae are the most powerful stellar blasts known, and they are visible all the way to the very edge of the visible Universe. The visible Universe is that relatively small region of the unimaginably vast Cosmos that we are able to observe–the rest of it resides beyond the reach of our visibility, because the light emanating from those objects dwelling in those very, very remote regions has not had sufficient time to reach us since the Big Bang birth of the Universe almost 14 billion years ago. The speed of light sets something of a cosmological speed limit. No known signal in the Universe can travel faster than light.

When a heavy, large star perishes in a supernova conflagration, it usually leaves behind a small relic as testimony to its former stellar existence–an extremely weird, very dense stellar corpse termed a neutron star, or an even more bizarre entity called a stellar mass black hole.

All stars, both heavy and light, “live” out the best years of their stellar “lives” on the hydrogen-burning main-sequence. Stars must maintain a very delicate balance between two warring forces–gravity and radiation pressure–from the time they are born until they die. The radiation pressure of a star on the main sequence pushes all of its material outward and away from the star, and it keeps this seething, fiery, roiling ball of gas blissfully bouncy against the heartless squeeze of its own powerful gravity that tries to crush it–pulling all of its material in. A star’s radiation pressure is the result of nuclear fusion, which begins with the burning of hydrogen into helium. Helium is the second-lightest atomic element in the Universe. This process, termed stellar nucleosynthesis, keeps fusing heavier atomic elements out of lighter one. Literally all of the atomic elements heavier than helium (metals, in astronomical terminology) were manufactured in the nuclear-fusing cores of our Universe’s multitude of dazzling stars–or in their explosive supernovae “deaths”, which produce the heaviest atomic elements of all, such as gold and uranium.

When a very massive main-sequence star, weighing a hefty eight solar masses– or even more–has succeeded in fusing its entire necessary supply of hydrogen fuel, it is doomed. The heavy star, at this tragic point, cannot hold its own against the relentless crush of its own weight, and gravity wins this very ancient war–and the massive star goes supernova.

Supernovae usually blast the elderly star to shreds, violently tossing its incandescent, multicolored layers of beautiful gases out into interstellar Space. This violent event occurs when the iron heart of the heavy star attains the truly impressive weight of 1.4 solar-masses. This triggers the doomed star’s ultimate end, which is characterized by that brilliant stellar blast, its grand finale.

Supernovae are usually divided into two main classes–although it is really much more complicated than this. The first of the two primary classes, Type II supernovae, ignite when the heart of a massive star weighing in at 8 to 100 times solar-mass, runs out of its necessary supply of hydrogen fuel and collapses into an unimaginably dense chunk in the smallest fraction of a second–tossing luminous radiation out into the Space between stars. The second class, termed Type Ia supernovae, are triggered when a White Dwarf star has perished after sipping up too much mass from a sister companion star–or, alternatively, after two White Dwarfs collide into each other.

White Dwarfs are the ghostly remains of smaller stars, like our own Sun. Stars that are like our Sun perish much more peacefully than their more massive stellar kin. When a small Sun-like star has at last burned its necessary supply of hydrogen fuel, it has reached the end of the road. White Dwarfs are normally surrounded by glimmering, incandescent, multicolored, and famously beautiful shells of gases (planetary nebulae). This is the fate of stars like our Sun–at least when they are solitary stars. When these small stars dwell in a close binary system with a sister star–that is still on the hydrogen-burning main sequence–it is a party waiting to happen. The fireworks begin when the White Dwarf sips up material from its main-sequence sister star, gulping down more and more and more of its material, until it can swallow no more–and it goes critical. The White Dwarf pays for its sinister feast by going supernova–just like the big guys–and blasting itself to smithereens. This results in a Type Ia supernova.

 


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