Cosmic Archaeology

Listen 00:08:46

Trying to learn about the early history of the galaxy, NASA has used Hubble Space Telescope to find the oldest galactic ‘bones’ yet found – white dwarf stars in the galaxy’s central bulge. White Dwarfs are the cooling remnants of formerly energetic stars that are now dying. Our sun will become a White Dwarf star some 10 billion years form now. White Dwarfs are about the size of Earth but 200,000 times denser. A teaspoon of white dwarf material would weigh about 15 tons. Their tiny stature makes them so dim that it would be as challenging as looking for the glow of a pocket flashlight located on the moon. This group was found down near the core of our galaxy where the earliest stars would’ve formed and the oldest stars would be found. These as remnants of the earliest stars are some 12 billion years old.

As they continue to cool, ultimately becoming dark embers of once-mighty stars, astronomers can analyze them just as old bones would be analyzed to learn about early conditions in the galaxy and about how the galaxy developed over time.
More massive stars, up to three times our sun’s mass, turn into red supergiants, eventually lose the balance struggle catastrophically and explode as supernovas. This leaves a rapidly expanding shell of gas and if the core survives THAT explosion, the core left over has become a massive glob of neutron stars. The spinning ones are called pulsars because as they spin, their released energy sweeps through space so fast it seems as if the pulse. Some flash – actually sweep – at astonishing rates, thousands of times per second – millisecond pulsars!

Bigger than three times our sun’s mass, the core continues to collapse to an unbelievably tiny size yet it retains all the mass of the full size core. This drives the escape velocity beyond the speed of light and we end up with – yes, a black hole!

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