WHAT IS THIEN HA?
A galaxy is a huge collection of stars, gas, and dust held together by gravity. Galaxies can be very large, up to a trillion stars, or very small, just a few million stars.
Galaxies come in a wide variety of shapes, from massive star clouds to intricate spirals with distinct star-filled arms. Their sizes range from a few thousand light-years to more than 100,000 light-years. Our Sun is just one of billions of stars in the Milky Way galaxy, and our own galaxy is just one of hundreds of billions.
The Milky Way is part of a cluster of galaxies called Local group of galaxies, including the Andromeda Galaxy (Andromeda, M 31) and about 45 other galaxies, including the Large Magellanic Clouds and the Small Magellanic Clouds. Groups of galaxies are bound together by gravity, and it is this fundamental force that binds groups of galaxies together to form a supercluster. The Local Group is part of The Virgo Supercluster (Virgo).
Yes: there is an M-7 Contributions: Descubre Foundation, Calar Alto Observatory, OAUV, DSA, V. Peris (OAUV), JL Lamadrid (CEFCA), J. Harvey (SSRO), S. Mazlin (SSRO), I. Rodriguez (PTeam), OL (PTeam), J. Rabbit (PixInsight).
THIEN HOA CLASSIFICATION
There are four main types of galaxies: spiral, elliptical, lenticular, and amorphous, as described below. Astronomer Edwin Hubble classifies galaxies based on their distinct shapes. For elliptical galaxies, he added the letter “E” in front of it and a number from 0 to 7 to indicate how much the shape of the galaxy deviated from the standard sphere (the zero corresponds to the shape of the ellipse). ). The lens galaxy has the number S0. Spiral galaxies fall into two groups: horizontal spirals are prefixed with “SB”, while spirals without horizontal bands are simply “S”. Hubble’s classification scale expansion divides amorphous galaxies into two categories: “Irr I” – those that show signs of structure, and “Irr II” – which appear to have no structure.
Edwin Hubble’s classification of spiral and elliptical galaxies. Source: Wikipedia
Spiral galaxies make up about a third of the galaxies in the near universe. The old stars in their center are surrounded by spiral arms (or arms) filled with bright young stars. These galaxies are rich in star-forming regions, as they contain large amounts of gas and dust. Banded spiral galaxies, such as the galaxy NGC 6217 in the image below, have a star-filled horizontal band running through the central region.
Image: Spiral galaxy NGC 6217. Source: NASA, ESA and the Hubble SM4 ERO team
Elliptical galaxy (elliptical galaxy)
Elliptical galaxies often look like large “blobs” made up of old red and yellow stars. Unlike spiral galaxies, they contain almost no star-forming nebulae. The largest known elliptical galaxy has a spherical shape. In the image below, a powerful jet of gas is ejected from the supermassive black hole at the center of the massive elliptical galaxy M87.
Elliptical galaxy M 87. Source: NASA
Lenticular galaxies typically have a large, nearly spherical central region containing old stars and are surrounded by a disk of gas and stars, giving them the appearance of a lens. Lenticular galaxies also have disks of gas and stars like spiral galaxies, but without the spiral arms, young stars, and star-forming nebulae that glow and are filled with dust.
Lenticular galaxy NGC 2787. Source: ESA/Hubble
Amorphous galaxies do not have a clear shape. They usually contain a lot of gas,
dust with hot blue stars, but no specific structure. Some of them
they show signs of structure, such as the central bar, which often contains very large pink star-forming nebulae. NGC 2366 (pictured below) is a dwarf galaxy with a nova region 10 times larger than the star-forming region of the Milky Way, although this galaxy is much smaller than ours.
Amorphous dwarf galaxy NGC 2366. Source: NRAO
Active Galaxy (Active Galaxy)
Observations deep in the universe reveal that some galaxies emit large amounts of radiation from their central regions. They are active galaxies. A supermassive black hole sits at the center of every galaxy, engulfing a rotating disc of gas and dust, constantly falling inside. This released a huge amount of high-energy radiation and also created two powerful jets of matter that shot out from either side of the black hole. Most, if not all, galaxies have a central black hole, but in most cases they are inactive, so the matter in the galaxy is kept in a stable orbit and spins around them.
There are four main types of active galaxies: Blazars, Seyfert galaxies, quasars and radio galaxies. They seem to have their own characteristics, but it is thought that the difference in appearance is probably due to the intensity of the activity and the angle from which they are observed. The most distant objects ever discovered are super bright quasars.
The luminous quasar PG 0052+251 is located in the center of a spiral galaxy, about 1.4 billion light-years from Earth. Image source: ESA
Galaxies are deep objects, most at a distance of millions of light-years from Earth, which creates interesting and interesting challenges for amateur astronomers. Unlike stars, galaxies are spread out and their surface luminosity is relatively low. Only a few galaxies are visible to the naked eye under the night sky, and you’ll need at least a pair of binoculars and preferably a large telescope to see most of the rest.
You’ll quickly understand why they’re often mistaken for nebulae – their great distance from Earth makes them appear like faint specks in amateur telescopes, hence their nickname ‘faint fuzzies’. Some of the brightest galaxies may show undetectable structures, such as traces of spiral arms or trails of dust.
The Andromeda Galaxy (Andromeda, M 31) is the brightest galaxy in the Northern Hemisphere sky. Located at a distance of 2.5 million light-years from Earth, it is one of the most distant objects visible to the naked eye.. Source: Pinterest