- 3880 - GALAXY FORMATION - unwound history - 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.
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3880 - GALAXY
FORMATION - unwound history
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- Galaxies
fill a lot of roles in the universe. The most obvious one is star formation
factories. Without that activity, the cosmos would be a very different place.
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- NGC 4303 is
a beautiful spiral galaxy located more than 50 million light-years away, in the
Virgo Cluster of galaxies. Astronomers rank it as a weakly barred spiral. It
also looks like it may have a ring structure within its spiral arms. The arms
sparkle with star formation, making it a starburst galaxy. There’s has an
active nucleus there likely hiding a supermassive black hole.
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- This galaxy
is classified as a “late-type spiral”. That means it turned gas into stars more
slowly in the past and still has a lot left today. It appears very rich in neutral hydrogen.
That’s the building block of stars.
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- The galaxy
has a massive collection of stars at its heart. In addition, it sports older
star clusters. These all indicate starforming activity in the ancient past.
There’s also ample evidence of more recent star-birth activity across the
entire galaxy. Bright nebulae highlight places where newborn stars are forming.
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- Astronomers
used the “Multi-Unit Spectroscopic Explorer” -MUSE- instrument at the Very Large Telescope to
study existing stars in the galaxy. It can image the galaxy in one observation.
At the same time, it measures the intensity of light coming from various
regions. In doing so, it provides a fascinating “3D” look at the galaxy and its
components.
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- MUSE is a
second-generation instrument in development for ESO´s Very Large Telescope
(VLT). It is an extremely powerful and
innovative 3D spectrograph with a wide field of view, providing simultaneous
spectra of numerous adjacent regions in the sky.
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- The
“Atacama Large Millimeter Array” provided a different view using millimeter
waves (close to radio waves). It specifically observes the clouds of hydrogen
in the galaxy. The idea is to compare the amount of gas available for star
formation to the populations of stars already formed. By using two different
instruments, astronomers get a better idea of what triggers star birth.
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- The
creation of supermassive stars can gobble up the available gas. That leaves
very little to form smaller stars. In other places, the deaths of supermassive
stars in supernova explosions send out shock waves. Those can trigger the
process of star birth in nearby molecular clouds.
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- This study
of NGC 4303 is part of a larger effort called the “Physics at High Angular
Resolution in Nearby Galaxies”' (PHANGS) project. It uses ground-based
telescopes, as well as space-based observatories, to make detailed observations
of neighboring galaxies.
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- PHANGS is
joined by a number of other projects doing similar studies of galaxy evolution
and star birth at different wavelengths. These include MUSTANG—the “Multi-scale
Star Formation across Nascent Galaxies” project, which looks at the lifecycle
of clouds and starforming regions.
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Astronomers have discovered new evidence that 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.
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- 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.
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- 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.
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- Scientists
have long predicted that large galaxies like the Milky Way and Andromeda have
grown to their current sizes via collisions and mergers throughout their
history, but the patterns in the motions of stars that could confirm this have
been elusive.
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- The
majority of the stars in the Milky Way's halo are 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. Looking at relics
of a previous merger and stellar migration event in Andromeda could help
astronomers hunt for similar artifacts in our own galaxy.
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- To trace
stellar migration in the galaxy, the team turned to 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.
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- In only a
few hours of observing time, DESI was able to surpass more than a decade of
spectroscopy with much larger telescopes.
The team will now continue to use the team-up between DESI and the
Mayall Telescope to investigate stars located closer to the edge of Andromeda.
They hope this will further reveal the galaxy's structure and the immigration
history of its stars.
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February 17, 2023 GALAXY
FORMATION - unwound history 3880
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--- Monday, February 20, 2023 ---------------------------
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