The closest neighboring galaxy to the Milky Way is Andromeda. It is significantly larger in the size of our galaxy and, according to various estimates, may have 2.5-5 times more stars than our Milky Way. It can be easily seen in the night sky from Earth. It is located in the constellation Andromeda, which is why it actually got its name.
The Andromeda Galaxy has attracted the attention of scientists for more than one century. The first written mention of this galaxy is contained in the "Catalog of Fixed Stars" by the Persian astronomer As-Sufi (946), who described it as "a small cloud". Interest in it is due not only to its close proximity to us, but also to some other interesting features, which we will talk about today.
Also known as Messier 31, or M31
It received this name from Charles Messier, the French astronomer, who included it in his famous catalog under the definition of M31. Messier cataloged many objects in the Northern Hemisphere, although not all of them were discovered by Messier.
In 1757, the scientist began searching for Halley's comet, but calculations showed that he was mistaken in the coordinates. However, at the same observation site, he discovered a nebula, the first object he cataloged as M1 (also known as the Crab Nebula). Interestingly, it was first observed by the English astronomer John Bevis back in 1731. The object, called M31, was included in the Messier catalog in 1767. By the end of the same year, a total of 38 items had been added to the catalog. By 1781, the number was already 103 objects, 40 of which were discovered personally by Messier.
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It got its name from the constellation Andromeda
You can see the constellation Andromeda in the night sky between the asterism Big Square and the star α Cassiopeia (the second lower corner if the observer sees the constellation Cassiopeia in the form of the letter W). According to ancient Greek myths, Princess Andromeda, the wife of the Greek hero Perseus, after death turned into a constellation. The constellation was first included in the catalog of the starry sky by Claudius Ptolemy "Almagest". Other stars of the constellation (Perseus, Cassiopeia, Cetus and Cepheus) also received their names after the characters in this myth.
The constellation Andromeda is also home to numerous other objects. It is located outside the galactic plane and does not contain clusters or nebulae of the Milky Way. However, it contains other visible galaxies. One of them is the Andromeda galaxy.
It's bigger than the Milky Way
Astronomy often uses the concept of a light year, which determines the distance to certain objects, but some astronomers prefer to use the term parsec. When it comes to very long distances, the term kiloparsec is used, equal to 1000 parsecs, as well as megaparsec - the equivalent of 1 million parsecs. The Milky Way spans about 100,000 light years, or 30 kiloparsecs. At first glance, this may seem like a very large distance, but in fact, compared to other galaxies, ours looks rather small.
The Andromeda galaxy has an approximate diameter of 220,000 light years, more than twice the size of the Milky Way. She is the largest galaxy in the local group. If the Andromeda galaxy were even brighter, then in the night sky it could look larger than the Moon, even though it is much, much further away. By the way, about the distance: the galaxy is located about 9.5 trillion kilometers from the Earth (the Moon, we recall, is only 384,000 kilometers).
Contains a trillion stars
According to rough estimates, the Milky Way may contain between 100 and 400 billion stars. But that's nothing compared to Andromeda, which can hold about one trillion. Thanks to the Hubble Space Telescope, scientists have learned about the presence of a very large and rare population of hot and bright stars among this trillion.
Hot, young stars tend to appear blue. However, the blue stars found in the Andromeda galaxy appear to be aging, more like the sun, stars that have burned out their inner layers and exposed their hot blue cores. They are scattered throughout the galactic center and are the brightest in the ultraviolet range.
Has a double core
Another interesting fact about the Andromeda galaxy is its double core. Observations have shown that in the central part of the galaxy there are two bright objects (P1 and P2), separated by a distance of only 5 light years. Each of them contains several million densely spaced young blue stars.
Astronomers later figured out that the two cores are not two separate clusters of stars, but rather one donut-shaped cluster and a supermassive black hole, whose mass exceeds 140 million times the mass of the Sun. The stars in the P1 cluster orbit very closely around the black hole, like planets around the sun, creating the effect of having a double core.
Will collide with our galaxy
An intergalactic collapse awaits us. At the moment, the Andromeda galaxy is moving towards the Milky Way at a speed of 400,000 kilometers per hour. At this speed, the globe can be circled in just 6 minutes. Astronomers predict that the Milky Way and Andromeda will collide in about 3.75 billion years. What will happen to the Earth after this?
Experts believe that, despite such a large-scale event, the Earth will still survive. Together with the rest of the solar system. Scientists assume that our planet will hardly be affected by this intergalactic collapse, since both galaxies have a lot of free space. Nevertheless, it will be very interesting to observe the event from Earth (if, of course, life is still preserved on it by that time). Both galaxies will be attracted to each other until the black holes at their centers eventually merge into one. Once this happens, our solar system will become part of a completely different galaxy - elliptical. If the Sun does not swallow the Earth in about 5 billion years, then every night on it will be very bright, thanks to the presence of many new stars. Instead of a streak of light from the Milky Waywe will see a more spheroidal light source.
Has an absolute value of 3.4
In astronomy, the luminosity of an astronomical object is characterized by an absolute value. It allows us to determine the brightness of any object, regardless of its distance from us.
The Andromeda Galaxy has an absolute magnitude of 3.4, which makes it the brightest object in the Messier catalog. On a moonless night, the galaxy is visible even to the naked eye. True, it should be noted that only the central part of the galaxy will be visible to the naked eye. It will look like a faint star. If you look at it through binoculars, it will look like a small elliptical cloud. When observed through a large telescope, it can look up to six times the size of the Moon.
It's full of black holes
There were once 9 known black holes in the Andromeda galaxy, but the actual number rose to 35 in 2013. Astronomers have observed 26 new black hole candidates, making the galaxy one of the most populous of its kind. Most of these new black holes are 5-10 times the mass of our Sun. Seven black holes are located about 1000 light-years from the galactic center.
Astronomers are confident that in the future they will be able to find even more such objects in this galaxy. For example, in 2017, two more new black holes were discovered. At the same time, it was noted that both objects are in the most dangerous proximity ever documented. They are separated by a distance of only 0.01 light years, which is approximately equal to a couple of hundred distances from the Earth to the Sun. Experts estimate that these black holes could collide with each other in less than 350 years, merging into one supermassive black hole.
Contains 450 globular clusters
Globular clusters are densely packed clusters of old stars closely related by gravity. They can contain hundreds of thousands and even millions of stars. Globular clusters help determine the age of the universe, and also often help determine where the center of a galaxy is. Astronomers have discovered at least 200 globular clusters in the Milky Way, and about 450 in Andromeda.
The number of globular clusters in Andromeda may be much larger, but the distant borders of this galaxy are still poorly understood. If the globular clusters of the Andromeda galaxy had a similar size to the clusters of the Milky Way, then their real number could be somewhere between 700 and 2800.
The Andromeda Galaxy was once considered a nebula
Nebulae are huge clusters of gas, dust, hydrogen, helium and plasma in which new stars are born. Galaxies that are very distant from us have often been mistaken for these massive clusters. In 1924, astronomer Edwin Hubble announced that the Andromeda spiral nebula is actually a galaxy and that the Milky Way is not the only galaxy in the universe.
Hubble discovered a number of stars belonging to the Andromeda galaxy, including several Cepheids. The latter are a class of pulsating variable stars with a fairly accurate period-luminosity relationship. He determined how far away these stars are, which helped him calculate the distance at which the Andromeda galaxy was from us. It was 860,000 light years, which is more than 8 times the distance to the most distant stars in the Milky Way. This helped to prove that Andromeda is exactly a galaxy, and not a nebula, as it was originally proposed. Later, Hubble confirmed the existence of several dozen other galaxies.
Nikolay Khizhnyak