- 4202 -
MILKY WAY GALAXY
- is it still a spiral? The Milky Way wasn't always a spiral and
astronomers may finally know why it 'shape-shifted'. A century-old mystery of how galaxies change
shapes has been solved by considering 'survival of the fittest' collisions
between cosmic titans.
--------------------- 4202 - MILKY WAY GALAXY - is it still a spiral
- A 100-year-old
mystery surrounding the "shape-shifting" nature of some galaxies has
been solved, revealing in the process that our Milky Way galaxy did not always
possess its familiar spiral appearance.
-
- The evolution of
galaxies from one shape to another takes place is a process known as “galactic
speciation” . The research shows that clashes and subsequent mergers between
galaxies are a form of "natural selection" that drives the process of
cosmic evolution.
-
- The Milky Way's history of cosmic violence is the survival of the fittest out there. "Astronomy now has a new anatomy sequence and finally an
evolutionary sequence in which galaxy speciation is seen to occur through the inevitable marriage of galaxies ordained by gravity.
-
- Galaxies come in
an array of shapes. Some, like the Milky Way, are composed of arms of
well-ordered stars revolving in a spiral shape around a central concentration
or "bulge" of stellar bodies. Other galaxies like Messier 87 (M87)
are composed of an ellipse of billions of stars chaotically buzzing around a
disordered central concentration.
-
- Since the 1920s,
astronomers have classified galaxies based on a sequence of varying galaxy
anatomy called the "Hubble sequence." Spiral galaxies like ours sit
at one end of this sequence, while elliptical galaxies like M87 sit at the
other. Bridging the gap between the two are elongated sphere-shaped galaxies,
lacking spiral arms, called “lenticular galaxies”.
-
- To understand our
evolutionary paths on the Hubble sequence astronomers looked at 100 galaxies
near to the Milky Way in optical light images collected by the Hubble Space
Telescope and compared them to infrared images from the Spitzer Space
Telescope. This allowed him to compare the mass of all the stars in each galaxy
to the mass of their central supermassive black holes.
-
- This revealed the
existence of two different types of bridging lenticular galaxies: One version
that is old and lacks dust, and the other that is young and rich in dust.
-
- When dust-poor
galaxies accrete gas, dust, and other matter, the disk that surrounds their
central region is disrupted, with said disruption creating a spiral pattern
radiating out from their hearts. This creates spiral arms, which are over-dense
rotating regions that create gas clumps as they turn, triggering collapse and
star formation.
-
- The dust-rich
lenticular galaxies are created when spiral galaxies collide and merge. This is
indicated by the fact that spiral galaxies have a small central spheroid with
extending spiral arms of stars, gas and dust. Young and dusty lenticular
galaxies have notably more prominent spheroids and black holes than spiral
galaxies and dust-poor lenticular galaxies.
-
- The surprising
result of this is the conclusion that spiral galaxies like the Milky Way
actually lie between dust-rich and dust-poor lenticular galaxies on the Hubble
sequence. The lenticular galaxies are not the single bridging population they
were long portrayed.
-
- The history of the
Milky Way is believed to be punctuated with a series of
"cannibalistic" events in which it devoured smaller surrounding
satellite galaxies to grow. In addition
to this, our galaxy's cosmic "acquisitions" also included it
accreting other material and gradually transforming from a dust-poor lenticular
galaxy to the spiral galaxy we know today.
-
- Our galaxy is set
for a dramatic merger with its closest large galactic neighbor, the Andromeda
galaxy, in between 4 billion and 6 billion years. This collision and merger
will see the spiral arm pattern of both galaxies erased and the new research
indicates that the daughter galaxy created by this union is likely to be a
dust-rich lenticular galaxy still possessing a disk, albeit without a spiral
structure carved through it.
-
- Should the Milky
Way-Andromeda daughter galaxy encounter a third, dust-rich lenticular galaxy
and merge with it, then the disk-like aspects of both galaxies will also be
wiped clean. This would create an elliptical-shaped galaxy without the ability
to harbor cold gas and dust clouds.
-
- Just as this new
galaxy will carry the story of its evolution for astronomers in the far-future,
the dust-poor lenticular galaxies could serve as fossil records of the
processes that transformed old and common disk-dominated galaxies in the early
universe.
-
- This could help
explain the discovery by the James Webb Space Telescope (JWST) of a massive
spheroid-dominated galaxy just 700 million years after the Big Bang. The new
research could indicate that the merging of elliptical galaxies is a process
that could explain the existence of some of the universe's most massive
galaxies, which sit at the heart of clusters of over 1,000 galaxies.
-
-
October 28, 2023 MILKY
WAY GALAXY - is
it still a spiral? 4202
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Sunday, October 29, 2023 ---------------------------------
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