- 3876 - MILKY WAY GALAXY - how did it form? Although the night sky may seem unchanging, the universe is a dynamic place. Galaxies like M31 and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history.
----------- 3876
- MILKY WAY
GALAXY - how did it form?
-
- The influx
of stars into the galaxy next door to the Milky Way was revealed by intricate
patterns in their motion today and reflects a violent event in our galaxy’s
past. Andromeda, the galaxy next door to
our own, grew by merging with another galaxy. The event triggered a mass
migration of stars into the galaxy.
-
- This event
suggests that the migration of stars to Andromeda and the galaxy's growth history
is very similar to that of the Milky Way. That means the findings have
implications for our understanding of both galaxies.
-
- The
evidence came in the form of observations of the individual motions of almost
7,500 stars in the inner halo of Andromeda. This showed these stars had begun
their lives as part of another galaxy that merged with Andromeda around 2
billion years ago.
-
- The
majority of the stars in the Milky Way's halo are also believed to have
originated in another galaxy finding a new galactic home during a massive
merger event thought to have occurred between 8 to 10 billion years ago.
-
- To trace
stellar migration in the galaxy astronomers used DESI due to the fact that it is the most
powerful multi-object survey spectrograph in the world, capable of measuring
the spectra of more than 100,000 galaxies in a single night.
-
- It's
amazing that we can look out at the sky and read billions of years of another
galaxy's history as written in the motions of its stars — each star tells part
of the story.
-
- Earth's
journey through the Milky Way may have had a profound impact on our planet's
geology. New research indicates that every 200 million years, when Earth passes
through its galaxy's spiral arms, the planet is pummeled with high-energy
comets, and this bombardment may thicken Earth's continental crust.
-
- The dense
clouds of gas in the spiral arms interact with comets at the edge of the solar
system, sending them hurtling toward Earth.
The geologists reached their conclusion by examining zircon crystals
from two of Earth's oldest continents and regions, where the planet's earliest
continental history is preserved: the North American Craton, in Greenland, and
the Pilbara Craton, in Western Australia.
-
- The decay
of uranium in zircon crystals in these regions has been used to create a
geological timeline spanning 1 billion years, from 2.8 billion to 3.8 billion
years ago, during the Archean eon. This timeline could help geologists discover
how Earth became the only planet known to have continents and active plate
tectonics.
-
- Isotopes of
the element hafnium in zircon enable scientists to spot periods in Earth's
history that experienced an influx of juvenile magma, magma containing elements
that have never reached the surface before, a sign of crust production.
-
- Therefore,
Earth's journey around the Galactic Center helps shape the planet's
geology. Not only does the solar system
travel around the Galactic Center, but the spiral arms that radiate from it
also turn, at a different rate.
-
- The sun
orbits the Galactic Center at around 536,000 mph , while the spiral arms turn
at approximately 47,000 mph. This means the sun and the solar system, as well
as many of the Milky Way's other stars, move in and out of the spiral arms,
much like fans doing "the wave" at a stadium.
-
- When the
solar system moves into the spiral arms, icy planetesimals in the Oort cloud at
its outer edge (around 4.6 trillion miles from the sun) interact with dense
gas clouds of the whip-like arms, sending icy material hurtling toward the
inner solar system and our planet.
-
- These
objects arrive with more energy than the asteroids that regularly pelt Earth.
Most of those space rocks come from the main asteroid belt between Mars and
Jupiter , a region that is much closer to Earth than the Oort cloud is.
-
- The
influence of impacts on rock formation and increased crustal generation was
also apparent in spherule beds, which are deposits of small spheres created by
ejected material that cools, condenses and falls back to Earth after impacts.
-
- Spherule
beds were also correlated with Earth's passage into the Milky Way's dense
spiral arms between around 3.3 billion and 3.5 billion years ago, when the planet
was just over 1 billion years old.
-
- New data
from the star-mapping Gaia satellite are helping scientists unlock the mystery
of our Milky Way galaxy's spiral arms.
Since the 1950s, astronomers have known that our galaxy, the Milky Way,
looks like a spiral, with several dense streams of stars and dust emanating
from the galactic center, winding through the galactic disc and dissolving
around its edges. However, scientists have struggled to understand how many of
these streams there are and what created them.
-
- The
European Space Agency's (ESA) Gaia mission has been mapping the Milky Way since
2014, measuring the precise positions and distances from Earth of nearly two
billion stars. The first two batches of data have revolutionized the study of
our galaxy. In addition to the fixed positions, the spacecraft also measures
how fast stars move in three-dimensional space, allowing astronomers to model
the evolution of the Milky Way in the past as well as into the future.
-
- Astronomers
derive the distance of the stars from a measure called the parallax. And this parallax measurement is 20% better
with the latest release. Parallax is a
star's apparent movement against the background of more distant stars as Earth
revolves around the sun.
-
- By
measuring the change in the angle between the star and Earth from two opposite
points in the planet’s orbit, astronomers can calculate the distance of the
star using simple trigonometry.
-
- The Milky
Way is known to have two main spiral arms, the Perseus arm and the
Scutum-Centaurus arm. Our galaxy also possesses two less pronounced arms, or
spurs, called the Sagittarius and the Local Arm (which passes close to the
sun).
-
- Scientists
can predict the future motions of stars in the Milky Way from Gaia data. Young stars are especially valuable when
studying the spiral arms because with their dense concentration of dust and
gas, are believed to be where the majority of stars form.
- Astronomers
are also still speculating about the origin of those arms and their longevity.
Some earlier theories proposed that the shape of the arms is somehow fixed and
spins around the galactic center over a long period of time while individual
stars, orbiting at their own velocities, move in and out of this shape.
-
- This
so-called “density wave theory”, however, is being disputed by the latest
findings enabled by the Gaia mission. Many scientists now think that the spiral
arms might not be fixed at all. Instead, they might form temporarily, as a
result of the rotation of the galactic disc, and later dissolve and reform
again in a different configuration.
-
- To find
which theory is correct astronomers looked at open clusters, groups of
thousands of young stars born from the same cloud of gas and dust. Due to their
young age, these stars are still close to their birth place, that is within the
spiral arms. If the newer theories were correct, the amount of younger open
clusters in the spiral arms would be higher than the amount of older open
clusters. And that's exactly what the data showed.
-
- The spiral
structure appears to contain the younger population of stars but disappears if
you look at the older stars. We see that
the rotation rate of the shape is more or less similar to the rotation rate of
the stars and varies with the radius to the galactic center.
-
- The shape
and the stars can't be decoupled, and that means we don't have a global shape,
which would be the spiral arms, and then the stars moving in and out of them as
the density wave theory suggests. The
spiral arms may exist for about 80 to 100 million years, a small fraction of
time in the 13-billion-year life of our galaxy.
-
- Why those
spiral arms in the Milky Way exist in the first place? While some theories
expect this swirl of stellar streams may have been born after another, smaller
galaxy crashed into the Milky Way, others believe it came to existence
naturally as a result of the rotation of the galactic disc.
-
- We expect
that we would see different signatures in the motion of the stars if the spiral
arms were caused by an external impact.
-
- The next
batch of Gaia data, the full Data Release 3, is expected to be made available
to scientists worldwide in about mid-2022. Gaia, one of the most productive
missions in history (measured by the number of scientific papers it produces),
will continue scanning the sky until 2025.
-
- The vast
catalogues of stellar positions, motions and velocities Gaia creates will keep
astronomers busy for decades to come.
-
February
14, 2023 MILLKY WAY
GALAXY - how did it form? 3876
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to
whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies
or Index of all reviews
--- to:
------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
---------------------
--- Wednesday, February 15, 2023 ---------------------------
-
No comments:
Post a Comment