Supernovae are the most powerful of all known stellar explosions, and they can be detected all the way to the very edge of the visible Universe. Indeed, for one brief shining moment, the fireworks display performed by these exploding stars can out-dazzle their entire host galaxy. Type II, or core-collapse supernovae, herald the final, fatal grand finale of a massive star that has finished burning its necessary supply of fuel by way of the process of nuclear fusion–thus creating heavier and heavier atomic elements out of lighter ones. However, the bitter, brilliant end must come at last when the star contains a core of iron that cannot be used as fuel. In April 2018, astronomers using NASA’s Hubble Space Telescope (HST), announced that they had photographed within the fading afterglow of a supernova blast, the very first image of a surviving companion to a supernova. Their discovery is the most compelling evidence to date that some supernovae originate in binary (double-star) systems. But the stellar companion of the dead star was no innocent bystander to the blast–in fact, it was the culprit behind it.
The story began almost two decades ago when astronomers observed a supernova blast 40 million light-years away in a galaxy dubbed NGC 7424, situated in the southern constellation Grus (the Crane). Within the dim, lingering light of the fading afterglow of that once-brilliant blast, NASA’s HST managed to obtain the very first image of the surviving companion to a star that has gone supernova. The image captured by the astronomers unveils the stellar survivor. This discovery suggests that some supernovae originate in binary star systems. 바카라사이트
“We know that the majority of massive stars are in binary pairs. Many of these binary pairs will interact and transfer gas from one star to the other when their orbits bring them close together,” Dr. Stuart Ryder explained in an April 26, 2018 Space Telescope Science Institute (STSI) Press Release. Dr. Ryder is from the Australian Astronomical Observatory (AAO) in Sydney, Australia. The STSI is in Baltimore, Maryland.
The guilty stellar companion of the dead massive progenitor star had sucked up almost all of the hydrogen from its doomed companion’s stellar envelope. A star’s envelope is the region that transports energy from the stellar core to its atmosphere. Millions of years before the primary star perished in the fiery fury of a supernova conflagration, the companion star’s vampire-like behavior had created an instability in the doomed primary star. This instabilty made the victimized star episodically blow off a cocoon and shells of hydrogen gas before it finally met its catastrophic fate.
The supernova blast, dubbed SN 2001ig, is a rare type of beast inhabiting the supernova zoo. SN 2001ig is categorized as a Type IIb stripped-envelope supernova. This type of stellar explosion, that heralds the final farewell performance of a doomed star, is considered to be somewhat unusual because most–if not all–of its hydrogen is already gone before the fatal fireworks have begun. This rare type of stellar explosion was first identified in 1987 by team member Dr. Alex Filippenko of the University of California, Berkeley.
Type IIb Supernovae
All of the various classes of Type II (core-collapse) supernovae result from the rapid collapse and horrific explosion of a massive star. However, the progenitor star must sport at least 8 times, but no more than 40 to 50 times, the mass of our Sun. Otherwise the star cannot experience this type of explosive end.
Type II blasts differ from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed inhabiting the spiral arms of galaxies and in H II regions. However, they are not found in elliptical galaxies, which do not possess spiral arms.
Stars manufacture energy by way of the process of nuclear fusion. Unlike our relatively small Sun, stars that are larger and heavier contain enough mass to fuse atomic elements all the way up to iron. Stars manage to perform this feat of atomic metamorphosis as the result of ever-increasing temperatures and pressures. The degeneracy pressure of electrons, along with the energy created by fusion reactions, wage war against the merciless pull of squeezing gravity. This continuous battle prevents the star from collapsing, and the still-“living” star is able to maintain stellar equilibrium. The star continues to fuse progressively heavier and heavier atomic elements out of lighter ones, commencing with the lightest atomic element–hydrogen–and then continuing on and on to fuse all of the atomic elements up to nickel and iron. Nuclear fusion of iron and nickel cannot manufacture net energy output. For this reason, no additional fusion of atomic elements can occur, leaving the nickel-iron core inert. Since there is no longer energy production to create outward pressure, equilibrium in broken, and the doomed star must meet its final violent fate. Within only seconds, the dying star’s outer core reaches a breathtaking internal velocity of as much as 21% of the speed of light, while the temperature of the inner core screams upward to as much as 100 million Kelvin.
Type II supernovae usually completely wreck the massive progenitor star, blowing it to pieces and launching its brilliant rainbow of varicolored gaseous layers out into the space between stars. The most massive stars of all collapse and explode into stellar mass black holes. However, massive stars, that are not quite that massive, leave behind in their wreckage a dense, Chicago-sized object dubbed a neutron star. A baby neutron star is a rapidly spinning pulsar, that emits regular beams of light that are often likened to a lighthouse beacon. Neutron stars usually reside within the heart of a multicolored supernova remnant.
There are several categories of Type II supernova explosions, which are categorized according to their resulting light curves. A light curve is a graph of luminosity versus time in the aftermath of the explosion. Type IIb supernovae like SN 2001ig display only a weak hydrogen line in their initial spectrum–which is the reason why they are classified as Type II. However, as time passes, the hydrogen emission becomes undetectable, and there is also a second peak in the light curve that has a spectrum similar to a Type Ib supernova. The progenitor could have been a massive star that launched most of its outer layers into interstellar space. Alternatively, the progenitor could have been a star that lost most of its hydrogen envelope because of interactions with a vampire-like companion in a binary system–leaving behind, in its funeral pyre, a core that consists almost entirely of helium. As the ejecta of a Type IIb expands, the hydrogen layer rapidly becomes increasingly transparent and reveals the deeper gaseous layers. The IIb class of core-collapse supernovae was first introduced –as a theoretical concept–by Dr. Stanford E. Woosley et al. back in 1987. The class was soon applied to a duo of other supernovae: SN 1987 and SN 1993.
