When Dead Stars Collide

Before the first stars were born, the Universe was an expanse of featureless darkness–devoid of light and life. The first generation of stars to shatter this swath of blackness, with their fierce stellar fires, were not like the stars we see today, because they were not born the same way. The first stars were giants, that formed directly from the lightest of all atomic gases–mostly hydrogen, with a smaller amount of helium, both of which formed in the wildly expanding fireball of the Universe’s mysterious Big Bang birth almost 14 billion years ago. The first stars are responsible for changing the Universe from what it was then, to what it now is. This is because they created, in their nuclear-fusing hearts, all of the atomic elements heavier than helium, thus “polluting” the Cosmos with the atomic elements that made planets, moons, and people possible. In June 2018, scientists at the California Institute of Technology (Caltech) in Pasadena, announced that they have found, for the first time, that colliding and merging duos of dense neutron stars are responsible for creating most of the heavy atomic elements present in small dwarf galaxies, shedding new light on yet another mystery of star-birth.

Heavy atomic elements, such as gold and silver, are called “metals” by astronomers, and they are of critical importance for planet formation, as well as the emergence of life itself. By observing these relatively tiny dwarf galaxies, the scientists hope to learn more about the primary sources of “metals” for the entire Universe.

The origin of most of the heaviest atomic elements listed in the familiar Periodic Table, including 95% of all the gold present on Earth, has been a subject of debate among astronomers for decades. However, it is now understood that the heavy “metals” are created when the nuclei of atoms within stars snare elementary particles called neutrons. In the case of most elderly stars, including those inhabiting the dwarf galaxies observed in this study, the process happens very rapidly–and, as a result, is termed an r-process, where the r signifies “rapid.”

There are currently two proposed potential sites where the r-process is theorized to take place. The first possible site is a rare form of supernova called a magnetorotational supernova, which is a type of stellar explosion that can create large magnetic fields. The second proposed site involves two neutron stars that collide and then merge. In August 2017, the National Science Foundation (NSF)-funded Interferometry Gravitational-wave Observatory (LIGO), along with other ground-based telescopes, spotted just such a neutron star collision that was in the midst of creating a treasure trove composed of the heaviest atomic elements. However, observing only one event is not sufficient to tell astronomers where most of these heavy “metals” are created within galaxies. 바카라사이트

Stellar Generations

Astronomers classify stars as either Population I (metal-rich) or Population II (metal-poor). However, even the most metal-poor stars belonging to Population II contain small amounts of metals. This means that these metal-poor ancient stars are composed of more than only the pristine hydrogen and helium gas that was produced in the Big Bang (Big Bang Nucleosynthesis). For this reason, there had to exist an earlier population of stars to manufacture these heavy metals.

Therefore, astronomers were forced to propose the existence of a third stellar population–the very ancient Population III stars that were composed entirely of ancient primordial gas that had been churned out in the Big Bang. Big Bang Nucleosynthesis produced only hydrogen, helium, and trace quantities of lithium or beryllium. The first stars produced the first batch of metals that “polluted” younger generations of stars. Population III stars served as the source of the small amount of metals observed in the metal-poor Population II stars.

The more massive the star, the shorter its hydrogen burning “life.” Massive stars burn their necessary supply of nuclear-fusing hydrogen fuel in their cores much more rapidly than smaller stars, thus manufacturing increasingly heavier and heavier atomic elements out of lighter ones. The end comes when the massive star finally has managed to fuse for itself a core of iron that cannot be used for fuel. At this terrible grand finale of a massive star’s “life”, it collapses and then blows itself to smithereens in a fatal supernova blast. In contrast, relatively small stars like our Sun–which is a metal-rich Population I star–blissfully burn their hydrogen fuel for about 10 billion years. More massive stars, however, “live” for mere millions, as opposed to billions, of years and do not die quietly. When small stars like our Sun reach the end of the stellar road they first become swollen Red Giant stars that eventually puff off their outer gaseous layers. The relic core of a small Sun-like star becomes a dense dead stellar corpse, called a white dwarf, that is surrounded by a beautiful, multicolored, sparkling shroud of what was once the dead progenitor star’s outer gases.

Therefore, massive stars, like Population III stars–as well as younger generations of massive stars–do not die in peace. They go out with a bang. When a massive star dies, it explodes as a supernova–a brilliant fatal blast that causes the erstwhile star to either leave a relic neutron star behind, or a stellar mass black hole. The core-collapse (Type II) supernova blasts out into space a good-bye gift to the Universe–its freshly forged batch of metals. These metals will ultimately be incorporated into Populations I and II stars–with all of their beautiful life-sustaining possibilities. We are here because the stars are here.

Stellar Burn-Out

Neutron stars are both the smallest and densest of known stellar objects. Usually, a neutron star will sport a radius of about 6.2 miles and a mass that ranges between 1.4 and 3 times that of our Sun. They are the end-product of a supernova that has compressed the core of the massive progenitor star to the density of an atomic nucleus. Once born, neutron stars can no longer generate heat, and they cool off as time goes by–but, it is still possible for them to evolve further as a result of collisions or accretion.

Most models indicate that neutron stars are almost entirely made up of neutrons, which are subatomic particles with no net electrical charge and with a slightly larger mass than protons. Protons and neutrons form the nuclei of atoms. Electrons and protons present in normal atomic matter combine to create neutrons at the conditions of neutron stars.



Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *