The formation of stars begins with the collapse and fragmentation of molecular clouds into very dense clumps. These clumps initially contain ~0.01 solar masses of material, but increase in mass as surrounding material is accumulated through accretion. The temperature of the material also increases while the area
over which it is spread decreases as gravitational contraction
continues, forming a more stellar-like object in the process. During
this time, and up until hydrogen burning begins and it joins the main sequence, the object is known as a protostar.
This stage of stellar evolution may last for between 100,000 and 10 million years depending on the size of the star being formed. If the final result is a protostar with more than 0.08 solar
masses, it will go on to begin hydrogen burning and will join the main
sequence as a normal star. For protostars with masses less than this,
temperatures are not sufficient for hydrogen burning to begin and they
become brown dwarf stars.
Protostars are enshrouded in gas and dust and are not detectable at visible wavelengths. To study this very early stage of stellar evolution, astronomers must use infrared or microwave wavelengths.
Protostars are also known as Young Stellar Objects (YSOs).
This Is Why Hubble Can’t See The Very First Galaxies
“By observing dark, empty patches of sky, it reveals ancient galaxies without nearby interference.
When distant galaxy clusters are present, these massive gravitational clumps behave as natural magnifying lenses.
The most distant observed galaxies have their light bent, distorted, and amplified along the journey.
Hubble discovered the current cosmic record-holder, GN-z11, via lensing.
Its light arrives from 407 million years after the Big Bang: 3% of the Universe’s current age.”
No astronomical observatory has revolutionized our view of the Universe quite like NASA’s Hubble Space Telescope. With the various servicing missions and instrument upgrades that have taken place over its lifetime, Hubble has pushed back the cosmic frontier of the first stars and galaxies to limits never before known. Yet there must be galaxies before them; some of the most distant Hubble galaxies have stars in them that push back the time of the first galaxies to just 250 million years after the Big Bang. Yet Hubble is physically incapable of seeing that far. Three factors: cosmic redshift, warm temperatures, and light-blocking gas, prevent us from going much beyond what we’ve already seen. In fact, we’re remarkably lucky to have gotten as distant as we have.
