- 4446
- OLDEST GALAXY - how to tell the ages? ? -
Scientists find one of the oldest stars in the universe in a galaxy
right next to ours. An ancient star
discovered in the Large Magellanic Cloud has revealed the chemical fingerprint
of the early universe. It hints that conditions were not the same everywhere
when the first stars forged the elements for life.
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------------------------- 4446 - OLDEST GALAXY - how to tell the ages? ?
- Scientists have identified one of the
oldest known stars outside the Milky Way. The discovered has uncovered a relic
from the early days of the universe in the Large Magellanic Cloud (LMC), a
satellite galaxy of the Milky Way, and
it's revealing the conditions from a time before the sun even existed.
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- The first stars born after the Big Bang
lived and died billions of years ago, so there are none left to tell the story
of the early universe. But traces of these stellar ancestors were preserved in
the second generation of stars that formed and still survive today.
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- The outer layers of these ancient stars
preserve the chemical composition of their natal gas cloud, and reveal the
composition of the first generation of stars that seeded those clouds with new chemicals. The composition of these stars offers a
window into the early production of elements when the stars formed billions of
years ago.
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- The earliest stars blazed to life billions
of years ago, soon after the Big Bang. They were behemoths made from the only
elements that existed in abundance at the time: about three-fourths hydrogen
and one-fourth helium. Those giants quickly burned through their nuclear fuel,
shedding their outer layers and then exploding as supernovas and polluting
their stellar neighborhood with new, heavier elements forged within their
cores.
-
- This stellar ash entered the mix when a
second generation of stars was born from the gas clouds enriched by the first.
This cycle continued, building ever-heavier elements and even seeding the
cosmos with the building blocks for life. This is the source of the oxygen we
breathe, the calcium in our bones, and the iron in our blood cells.
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- By measuring the amounts of these elements
in a star, astronomers can estimate its age. The less "ash" that has
accumulated, the older the star must be, while younger stars have built up a
lot of elements from many earlier generations.
-
- None of the first-generation stars has ever
been observed, but astronomers have spotted some ancient stars of the second
generation in our galaxy. These fossils are very rare. Fewer than 1 in 100,000
stars in our galaxy is from that second generation.
-
- From these relics, astronomers have learned
a lot about the early conditions in our galaxy. Now, they want to understand if
the Milky Way is typical or if those conditions were different in other
galaxies.
-
- To answer this question, astronomers turned
their sights to one of our nearest galactic neighbors, the “LMC”. Visible to
the naked eye from the Southern Hemisphere, the LMC is smaller than the Milky
Way and destined to merge with it in
about 2.4 billion years.
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- The team searched for old stars in the LMC
in data gathered by the European Space Agency's Gaia space telescope. They
followed up using the 6.5-meter Magellan telescope in Chile and identified 10
stars with about 100 times less iron than other LMC stars contain, meaning they
were very ancient.
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- One stood out. Known as “LMC-119”, it had
less of this cosmic pollution than any known star outside our galaxy. This
suggested it formed from gas enriched by just one supernova and was a sure sign
that LMC-119 is a second-generation star and very ancient. It is very likely at least 13 billion years
old. For comparison, the universe itself
is estimated to be 13.8 billion years old.
-
- Today, the LMC is about 160,000 light-years
away, but the authors estimated that it was about 6 million light-years distant
when its earliest stars formed. This
isolates the early LMC from ejecta from the first stars that formed in the
early Milky Way. This means that the LMC's ancient stars can tell astronomers
about infant conditions in another galaxy.
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- LMC-119 has much less carbon than ancient
stars in our galaxy do. This hints at a previously unknown difference in how
heavier elements built up in these two galaxies and suggests the environment in
our young galaxy was likely different from that of the LMC.
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- A new program to photograph one-quarter of
the southern sky is using the Blanco 4 meter telescope in Chile and equipment
designed to identify the most ancient fossil stars in the Milky Way and our
galactic neighbor. By uncovering these relics, astronomers hope to paint a
better picture of how stars have enriched the cosmos with the elements that
make up all that we see around us.
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April 27, 2023 OLDEST GALAXY
- how to tell the ages? ? 4446
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--------------------- --- Sunday, April 28, 2024
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