The Triangulum Galaxy – M33
The Triangulum Galaxy also known as M33 or NGC 598 or Pinwheel Galaxy that is about 3 million light-years away from Earth. While its mass is not well understood — one estimate puts it between 10 billion and 40 billion times the sun’s mass — what is known is it’s the third largest member of the Local Group, or the galaxies that are near the Milky Way. Triangulum also has a small satellite galaxy of its own, called the Pisces Dwarf Galaxy.
Overall, M33 has a diameter of about 60,000 light years and is estimated to contain 40 billion stars. For comparison, the Milky Way contains 400 billion stars and M31 about 1 trillion (1,000 billion).
M33 was probably discovered by Italian astronomer Giovanni Battista Hodierna before 1654. He listed it in his work regarding cometary orbits and admirable objects of the sky. Charles Messier independently re-discovered the galaxy on the night of August 25, 1764.
Among the galaxy”s most distinctive features are ionized hydrogen clouds, also called H-II regions, which are massive regions of starbirth.
Sprawling along loose spiral arms that wind toward the core, M33’s giant H-II regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars .
Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow.
The observations of Triangulum galaxy reveal that it is approaching the Milky Way Galaxy at about 62,000 mph (100,000 kph). Some astronomers believe that Triangulum is “gravitationally trapped” by the massive Andromeda Galaxy that is also hurtling toward our galaxy, the European Southern Observatory stated.
Among Triangulum’s most distinctive features is NGC 604, a region of starbirth so big that the Space Telescope Science Institute once described it as “monstrous.” Their 2003 estimate says that the gas cloud has more than 200 blue stars and that it is more than 1,300 light years across — or about 100 times bigger than the Orion Nebula.
Star Clusters and Nebulae in the Triangulum Galaxy (M33)
If NGC 604 were at the same distance from Earth as the Orion Nebula, it would be the brightest object in the night sky .
The young stars are extremely hot, at 72,000 degrees F (40,000 C), and the biggest ones are 120 times the mass of the sun. Radiation pumping out from the young stars floods into the gas in the region, making it fluoresce or glow.
“Within our Local Group, only the Tarantula Nebula in the Large Magellanic Cloud exceeds NGC 604 in the number of young stars even though the Tarantula Nebula is slightly smaller in size,” STScI stated.
Studying M33 in infrared light, NASA’s Wide-field Infrared Survey Explorer (WISE) revealed hotspots of activity within the galaxy in 2011 while also showing that the center of the galaxy doesn’t have much going on within it.
“Areas in the spiral arms that are hidden behind dust in visible light shine through brightly in infrared light, showing where clouds of cool gas are concentrated,” NASA wrote at the time.
“There isn’t a lot of star formation occurring near the center of M33. It would be difficult to deduce this lack of activity in the core by only looking a visible-light image, where the core appears to be the brightest feature.”
NASA added that the galaxy looks “surprisingly bigger” than an optical image would make it appear, because cold dust is visible further in space than what astronomers initially expected.