The Very First Stars of the Universe
Soon after the Big Bang, a class of stars was formed that weighed tens to hundreds of times the mass of the sun, burned extremely bright, and died away way too fast. These stars left behind extreme Supernovae that might have played an extremely crucial role in the evolution of later stars and the universe itself. Astronomers categorize these Monstrous stars as ‘Population-3’ stars. As these stars were large and currently leaves no trace of existence, they are of evident interest for astrophysicists.
Compared to the first generation of stars, the sun is a latecomer. However, it still contains ‘mostly’ hydrogen and helium, the purest by-product elements of the Big Bang. But, if we peer closely at the spectrum of the sun, we see traces of heavier elements and metals that might well have been ‘cooked’ at the heart of an extremely massive star long before the sun was a ‘twinkle’ at the giant molecular clouds.
Astronomers classify like to classify stars based on their metallicity (amount of elements heavier than hydrogen and helium) into 3 distinct groups:
i. Population-I stars: The population-I stars comprise of 2–3 percent of metals at their core. These stars are relatively new and are still forming today. Usually, the bright arms of spiral galaxies harbor them. i.e. Sun
ii. Population-II stars: These stars have a metal composition of less than 0.1 percent. They are usually dim and can be found at globular clusters and galactic bulges. i.e, Red Dwarf Stars.
iii. Population-III stars: These stars have no metal at its core whatsoever. These are the purest form of stars that evolved right after the big bang period. To make sense of our stellar models and their evolution, these stars have to exist. Yet, we don’t ever see them. However, it is likely that these stars have faded off long before and are currently non-existent.
As discussed before, these massive stars are extremely gigantic. This gigantic mass creates enormous pressure at the star’s core which in turn, increases the temperature. The temperature responds at the fourth of its power to luminosity which results, in a star burning extremely bright and extremely fast. This means that the star soon runs out of fuel and is eventually ‘dead’ within a few million years. A star that is 10 times the mass of the sun shines 10000 times brighter which means it only lives a fraction of the Sun’s lifespan.
So, how do we know that the first stars were so massive? That’s where something called Jean’s Instability kicks in. To form a star from a giant molecular cloud, we would need the cloud to cool down and collapse. Metals are especially useful to help this collapse run faster. However, the electrons from the metals quickly escape taking the energy from the collapsing cloud. Metals also perform a crucial task to shred the collapsing cloud into fragments, which in turn form multiple small stars. However, in the case of the first stars, there was no trace of metals in the collapsing clouds. As a result, when the clouds collapsed the heat was evenly regulated throughout the cloud which formed an entire star of its own, escaping the fragmentation process. As a result, these stars at least weighed from several hundred to a thousand solar masses.
Despite their quick demise, the first stars have left behind tremendous influence in the later development of the universe. These stars were the first to cook the heavier elements like Carbon, Oxygen, Neon, Silicon at their core. When they ended their lives in blistering, ultra-luminous supernovae, they pumped out the first heavy chunks. These chunks, billions of years later, successfully contributed to the formation of later stars, planets, and eventually, us, Homo Sapiens.
The stellar remnants often formed Black holes owing to their heavy, massive core. Stars that were 250 times massive than the sun, formed Black Holes without even exploding to a supernova. It is possible that the massive stars remained in colonies and once they collapsed down to black holes, they may well have merged to form larger ones. It is possible that some of these ‘large’ black holes, to form even larger ones and eventually give rise to the monstrous Super Massive Black Holes lurking at almost every galactic center. The SMBHs often produced Quasars, which itself was crucial to life formation.
The First stars may not be visible at all, but their influence dominates within every cell of our body. These stars remind us, that the black hole at the galactic center and the blood in our veins aren’t that separated after all.
