Constellation knowledge: structural composition of Andromeda galaxy

Compared with most people, "Andromeda galaxy" is still a strange term. We usually only hear about the solar system and the Milky Way, but we don't know anything about the Andromeda galaxy, let alone its structure! It doesn't matter if you don't know. Constellation knowledge will now answer questions about the structure of Andromeda galaxy. Let's have a look!

Galactic structure

According to the shape seen in visible light, Andromeda galaxy is classified as spiral galaxy under the extended expansion classification system of de Vaucouleurs-Sandage. However, in the data of the 2MASS survey, the core ball of M3 1 is box-shaped, which implies that M3 1 is actually a rod-spinning galaxy, and we observe this galaxy almost in the direction of the long axis. Andromeda galaxy is also a LINRER galaxy (low free nuclear radiation region), and it is a very common active galactic nucleus in classification.

The inclination of the galaxy relative to the earth is estimated to be 77 (90 when viewed directly from the side), and the cross section of the galaxy is shaped like the letter S, not a plane. One possible reason for this shape distortion is the interaction between M3 1 and satellite galaxies gravity. Spectroscopic observations provide detailed measurements of the rotational speed of galaxies at different radii from the core. In the area near the core, the rotational speed reaches a peak of 225 km/s (140 mph); It begins to descend at the radius of 1 300 light years, and reaches a minimum of 50km/s (3 1 mile/hour) at 7000 light years. Then, the speed rises steadily, reaching a peak of 250 km/s (155 mph) at a radius of 33,000 light years. Beyond this distance, the speed slowly drops to 200 km/s (124 mph) at 80,000 light years. These velocity measurements show that the mass concentrated in the core is about 6 × 109M☉, and the total mass linearly increases to a radius of 45,000 light years, and then gradually slows down with the increase of the radius.

The spiral arm of Andromeda galaxy extends a series of ionized hydrogen regions, which Budd described as "a string of pearls". They look closely intertwined, but they are far apart in our galaxy. The corrected galaxy map clearly shows that there are spiral arms rotating clockwise around spiral galaxies. About 1, 600 light years away from the core, there are two continuous spiral arms dragging outward, and the nearest distance between them is about 1, 3000 light years away. The spiral pattern may be due to the interaction with M32. These substitutions can be observed through the neutral hydrogen clouds of stars.

1998, the image from the Infrared Space Observatory of the European Space Agency shows that the overall image of Andromeda galaxy may turn into a ring galaxy. The gas and dust in the Andromeda galaxy form several overlapping rings, the most prominent of which is located within a radius of 32,000 light years from the core. This ring is made of cold dust, so it is invisible in visible light images.

More detailed observation shows that there is a smaller dust ring inside, which is believed to be caused by the interaction with M32 two million years ago. Simulation shows that this smaller galaxy passes through the disk of Andromeda galaxy along the polar axis. The collision stripped more than half the mass from the smaller M32 and created a ring structure in the Andromeda galaxy.

The study of M3 1 extended halo shows that the stars in the universe are also poor in metals, and become poorer with the increase of distance. These evidences show that the two galaxies follow similar evolutionary routes. In the past 65.438+0.2 billion years, they may have swallowed 654.38+0-200 low-mass galaxies. The stars in the extended halo of M3 1 may be close to one third of the distance between the two galaxies.