- 4502 - MILKY WAY'S - wrinkles with age? - The Milky Way's last major act of galactic cannibalism was surprisingly recent. We get wrinklier as we age For the Milky Way it is getting less wrinkly over time.
--------------------------------- 4502 - MILKY WAY'S - wrinkles with age?
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- New findings from the Gaia space telescope
indicate the Milky Way may have cannibalized a small galaxy not too long
ago. The last major collision between
our galaxy and another seems to have occurred billions of years later than
previously suspected.
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- The Milky Way has been long understood to
have grown via a series of violent collisions, which see smaller galaxies
ripped apart by the immense gravitational influence of our solar system's
spiral home.
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- These collisions distribute stars from the
devoured galaxy across the halo that surrounds the main disk of the Milky Way
and its distinctive spiral arms. These bouts of galactic cannibalism also send
"wrinkles" rippling through the Milky Way that affect different
"families" of stars, with different origins, in different ways.
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- With its ability to precisely pinpoint the
position and motion of over 100,000 stars local to the solar system within the
full catalog of stellar bodies in monitors, Gaia aims to retell the history of
the Milky Way by counting its wrinkles.
-
- By looking at how these wrinkles dissipate
over time, we can trace when the Milky Way experienced its last big crash, and,
it turns out this happened billions of years later than we thought.
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- These galactic wrinkles were only discovered
by Gaia in 2018; this marks the first time they have been extensively
researched to reveal the timing of the collision that created them. The halo of our galaxy is populated with
stars that have strange orbits, with many of these believed to be the
"leftovers" of galaxies the Milky Way once devoured.
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- Many of those stars are believed to be the
wreckage of the so-called "last major merger," referring to the last
time the Milky Way experienced a significant collision with another galaxy.
Scientists think this final major collision may have involved a massive dwarf
galaxy, and the event is known as the “Gaia-Sausage-Enceladus” (GSE) merger.
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- It is thought to have infused the Milky Way
with stars on orbits that bring them close to the Galactic Center. The GSE
event is thought to have happened between eight and 11 billion years ago when
the Milky Way was in its infancy.
-
- The Gaia observations of these strangely
orbiting stars, released as part of the space telescope's Data Release 3 in
2022, indicate these odd stellar bodies could have been deposited by a
different merger event.
-
- We can see how the shapes and number of
wrinkles change over time using these simulated mergers. This lets us pinpoint
the exact time when the simulation best matches what we see in real Gaia data
of the Milky Way today. By doing this,
we found that the wrinkles were likely caused by a dwarf galaxy colliding with
the Milky Way around 2.7 billion years ago. We named this event the “Virgo
Radial Merger."
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- For the wrinkles of stars to be as clear as
they appear in Gaia data, they must have joined us less than three billion
years ago — at least five billion years later than was previously thought. If
they'd joined us eight billion years ago, there would be so many wrinkles right
next to each other that we would no longer see them as separate features.
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- This result that a large portion of the
Milky Way only joined us within the last few billion years is a big change from
what astronomers thought up until now.
Many popular models and ideas about how the Milky Way grows would expect
a recent head-on collision with a dwarf galaxy of this mass to be very rare.
-
- They think that the Virgo Radial Merger
brought to our galaxy a family of other small dwarf galaxies and star clusters,
all of which would also have been devoured by the Milky Way at around the same
time.
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- This new research is the latest in a
treasure trove of results emerging from Gaia data that are rewriting the
history of the Milky Way. Such cosmic
revisionism has been made possible thanks to Gaia's unique ability to explore a
vast number of stars over Earth, allowing the space telescope to compile an
unrivaled map of the positions, distances and motions of around 1.5 billion
stars thus far.
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- Our picture of the Milky Way's past has
changed dramatically from even a decade ago, and our understanding of these
mergers will continue to change rapidly.
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-
June 19, 2024 MILKY WAY'S
- wrinkles with age? 4502
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--------------------- --- Wednesday, June 19,
2024
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