الوضع الليلي
4:6:27 
2023-08-21 
1191
An Australian astronomer has solved a 100-year-old mystery surrounding the nature of some "shape-shifting" galaxies, revealing in the process that our own Milky Way wasn't always in its now-famous spiral appearance.
Astronomer Alastair Graham has used old and new observations to show how galaxies evolve from one form to another, a process known as galaxy speciation.
The study shows that collisions and subsequent mergers between galaxies are a form of "natural selection" that drives cosmic evolution.
In the 1920s and 1930s, astronomer Edwin Hubble and others created a series of dissections of diverse galaxies, now known as the Hubble Sequence. Although it lacks evolutionary pathways, it is still widely used to classify galaxies based on their visible appearance.
Galaxies can contain billions of stars in an orderly fashion, follow circular orbits in a crowded disk, or move about randomly in a spherical or elliptical swarm.
These disks can host spiral patterns, with such spiral galaxies marking one end of the Hubble sequence.
In this sequence, lenticular galaxies, known as lenticular galaxies with a central spherical structure in a non-spiral disk, serve as a bridge between disk-dominated spiral galaxies such as our own Milky Way and elliptical galaxies such as M87.
In the new study, Professor Graham analyzed optical images from the Hubble Space Telescope and infrared images from the Spitzer Space Telescope of 100 nearby galaxies.
By comparing the masses of the stellar and central black hole, he discovered two types of lenticular galaxies: an old, dust-poor galaxy, and a young, dust-rich galaxy.
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