- 4004 - COSMIC DARK AGES - beginning of the universe? A gas cloud 13 billion light-years away may be the resting place of some of the earliest stars in the universe. Could this be the Cosmic Dark Ages?
-------------- 4004 - COSMIC DARK AGES - beginning of the universe?
- Astronomers may have just found the
remnants of some of the universe's very first stars. The chemical signatures of
these faraway, 13-plus-billion-year-old objects are remarkably different from
those of younger stars, like our sun. By studying them, scientists hope to shed
light on how stars, galaxies and even basic elements form.
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- In the earliest days of the universe, only
very simple elements such as hydrogen and helium were available. The first
stars ignited from these elements alone. Over time, their white-hot cores
gradually cooked simple atoms into heavier elements, such as carbon, oxygen,
magnesium and eventually metals.
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- Later generations of stars formed from
clouds of gas containing these heavier atoms, and today most of the stars
scientists observe are rich in metals like iron. (Our sun is about 98% hydrogen
and helium, but contains trace amounts of heavier elements like iron, neon and
carbon.)
-
- Nobody has observed the original
metal-deficient stars directly; most of them probably fizzled out or exploded
long ago. But scientists can still observe some of their dusty remains by
setting their sights billions of light years away.
-
- Using the “European Southern Observatory's
Very Large Telescope” (VLT), incoming light from nearby quasars, extremely
bright galactic cores formed by dust falling into a supermassive black hole,
revealed the cloud's secrets. Based on which wavelengths of light the gas clouds
absorbed, the team determined what elements the stellar remains were made of.
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- The clouds were extremely poor in iron and
other metallic elements, but rich in carbon, oxygen and magnesium, precisely
what would have been left over after the first stars ran out of fuel and
exploded. When the universe's first
stars emerged from the cosmic dark ages, they ballooned to 10,000 times the
mass of Earth's sun, new research suggests.
-
- The first stars in the cosmos may have
topped out at over 10,000 times the mass of the sun, roughly 1,000 times bigger
than the biggest stars alive today.
Nowadays, the biggest stars are 100 solar masses. But the early universe
was a far more exotic place, filled with mega-giant stars that lived fast and
died very, very young. And once these doomed giants died out, conditions were
never right for them to form again.
-
- More than 13 billion years ago, not long
after the Big Bang, the universe had no stars. There was nothing more than a
warm soup of neutral gas, almost entirely made up of hydrogen and helium. Over
hundreds of millions of years that neutral gas began to pile up into
increasingly dense balls of matter. This period is known as the “cosmic Dark
Ages”.
-
–
In the modern day
universe, dense balls of matter quickly collapse to form stars. But that’s
because the modern universe has something that the early universe lacked: a lot
of elements heavier than hydrogen and helium.
–
These elements
are very efficient at radiating energy away. This allows the dense clumps to
shrink very rapidly, collapsing to high enough densities to trigger “nuclear
fusion” the process that powers stars by combining lighter elements into
heavier ones.
-
- But the only way to get heavier elements is
through that same nuclear fusion process. Multiple generations of stars
forming, fusing, and dying enriched the cosmos to its present state.
-
- Without the ability to rapidly release
heat, the first generation of stars had to form under much different, and much
more difficult, conditions. To
understand this puzzle, a team of astrophysicists turned to sophisticated
computer simulations of the dark ages to understand what was going on back
then.
-
- The new work features all the usual
cosmological ingredients: dark matter to help grow galaxies, the evolution and
clumping of neutral gas, and radiation that can cool and sometimes reheat the
gas. But their work includes something that others have lacked: cold fronts,
fast-moving streams of chilled matter, that slam into already formed structures.
-
- The researchers found that a complex web of
interactions preceded the first star formation. Neutral gas began to collect
and clump together. Hydrogen and helium released a little bit of heat, which
allowed clumps of the neutral gas to slowly reach higher densities.
-
- But high-density clumps became very warm,
producing radiation that broke apart the
neutral gas and prevented it from fragmenting into many smaller clumps. That
means stars made from these clumps can become incredibly large.
-
- These back-and-forth interactions between
radiation and neutral gas led to massive pools of neutral gas, the beginnings
of the first galaxies. The gas deep within these proto-galaxies formed rapidly
spinning accretion disks, fast-flowing rings of matter that form around massive
objects, including black holes in the modern universe.
-
- Meanwhile, on the outer edges of the
proto-galaxies, cold fronts of gas rained down. The coldest, most massive
fronts penetrated the proto-galaxies all the way to the accretion disk.
-
- These cold fronts slammed into the disks,
rapidly increasing both their mass and density to a critical threshold, thereby
allowing the first stars to appear.
Those first stars weren’t just any normal fusion factories. They were
gigantic clumps of neutral gas igniting their fusion cores all at once,
skipping the stage where they fragment into small pieces. The resulting stellar
mass was huge.
-
- Those first stars would have been incredibly
bright and would have lived extremely short lives, less than a million years.
(Stars in the modern universe can live billions of years). After that, they
would have died in furious bursts of supernova explosions.
-
- Those explosions would have carried the
products of the internal fusion reactions, elements heavier than hydrogen and
helium, that then seeded the next round of star formation. But now contaminated
by heavier elements, the process couldn’t repeat itself, and those monsters
would never again appear on the cosmic scene.
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May 15, 2023 4004
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