- 4144 - MILKY WAY
- birth of spiral galaxies? - The
Milky Way wasn't always a spiral. A
century-old mystery of how galaxies change shapes has been solved by
considering 'survival of the fittest' collisions between cosmic titans. 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.
-------------- 4144 - MILKY WAY - birth of spiral galaxies? -
- How does the evolution of galaxies from one
shape to another takes place, 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.
-
- This means that the Milky Way's history of
cosmic violence is not unique to our home galaxy. Nor is it over. Astronomy now
has a new anatomy sequence and finally an evolutionary sequence in which galaxy
speciation is seen to occur through the inevitable marriage.
-
- 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”.
-
- 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 them 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,
this 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 more prominent spheroids and black holes than
spiral galaxies and dust-poor lenticular galaxies.
-
- The surprising upshot 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 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. 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 milky Way galaxy is set for a dramatic
merger with its closest large galactic neighbor, the Andromeda galaxy, in
between 4 billion and 6 billion years from now. 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, 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,
too, 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.
-
-
September 7, 2023 MILKY WAY -
birth of spiral galaxies?
4144
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