Solar Twins – How Are Stars Born?
How is a star born? Or better said, how are the stars born? Yes, because the stars are never born alone but in a real stellar nursery that gives life to real clusters. But why?
Surely because when the universe optimizes, as it does naturally, it tends to use as little energy as possible to reach the final result, but objectively the “guilty” one is gravity. When in these immense clouds of gas and dust, the gravity of a grain begins to be felt (in a way not yet completely clear to astronomers), here a chain reaction is triggered, causing the gas to precipitate to a certain point (of the cloud) and growing over millions of years; it has a mass that guarantees temperatures and pressures that support the reactions of nuclear fusion. Here, in a few lines I explained what gravity does in millions of years, a star was born: but what about the others?
The others are probably born thanks to an effect of “resonance” created by the first-born star whose gravity influences the cloud that collapses the gas at a point and so on … But what triggers the birth of the first of the sisters? It is not known with certainty, probably shock waves caused by supernovae exploded nearby or the “collision” and “crossing” of two gas clouds (in this case, the most accredited one, tends to explain why the stars that compose a cluster almost always have the same age and composition). Even our Sun was born in a group and therefore had sisters, but where did they go?
Yes, they are scattered around the galaxy because the stars still have their own motion and their “direction” and immediately after the formation they tend to move away from each other, so much so that in little less than 5 billion years the companions of the Our Sun will surely have traveled the Milky Way like crazy splinters.
An example could be HD164595, a star in Hercules placed at 94 light years from us, not visible to the naked eye but that has age, composition, temperature and metallicity (equal to 91%) practically identical to the Sun, among other things was discovered a planet that orbits it (it has a mass comparable to that of Neptune and orbits in just 40 days).
Or HIP 102152 in Capricorn (at 250 light years) that has virtually identical temperature, composition and metallicity (98%) but is older than 3.6 billion years.
The “twins of the Sun” known today are about a dozen placed at distances ranging from 45 light years of 18 Scorpii to 2940 YBP 1194: obvious that this is not a star born with our Sun, but was probably born from a cloud very similar to what it has given, it is appropriate to say, light our star. But why look for twin stars of the Sun?
Simply because, to date, it is the only one that possesses life that revolutions around and then hopes in the “twin star = same conditions” but it is not at all said. As already mentioned, each nebula has a different composition and therefore the stars that will originate will all necessarily have that type of imprint, a sort of cosmic identity card that will allow us, perhaps, when, to rediscover the Sun’s roaming sisters. ESO image it is possible to see a comparison between the age of 2 twins of the Sun, 18 Scorpii and HIP 102152: as you can see although they are similar in composition and temperature, the first is 1.5 billion years younger while the second 3.6 billion older.