The nearest neighbor to the Milky Way galaxy is Andromeda. It is much larger in the size of our galaxy and according to various estimates it can have 2.5-5 times more stars than our Milky Way. It can easily be seen in the night sky from Earth. It is located in the constellation Andromeda, thanks to which 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 conditioned not only by its close neighborhood with us, but also by some other interesting features, which we will now talk about.
Also known as Messier 31, or M31
This name she received from Charles Messier, a French astronomer who brought her to his famous catalog under the definition of M31. Messier cataloged many objects of the Northern Hemisphere, although not all of them were discovered by Messier.
In 1757, the scientist began to search for Halley’s comet, but calculations showed that he was mistaken in coordinates. Nevertheless, at the same place of observation, he discovered a nebula – the first object that he introduced into his catalog called M1 (also known as the Crab Nebula). Interestingly, the first to observe her was the English astronomer John Bevis back in 1731. The object called M31 fell into the Messier catalog in 1767. By the end of the same year a total of 38 objects were added to the catalog. By 1781, the number was already 103 objects, 40 of which were personally discovered by Messier.
Received its name thanks to the constellation Andromeda
To see the constellation of Andromeda in the night sky, it is possible between asterism the Large square and the star of 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, turned into a constellation after death. The constellation was first included in the catalog of the starry sky of Claudius Ptolemy “Almagest”. Other stars of the constellation (Perseus, Cassiopeia, Keith and Cepheus) also received their names in honor of the characters of this myth.
The constellation of Andromeda is also home to many 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
In astronomy, the term light-year is often used to determine the distance to certain objects, but some astronomers prefer to use the term parsec. When it comes to very large distances, the term kiloparsec is used, equal to 1000 parsecs, and also a megaparsec – the equivalent of 1 million parsecs. The Milky Way stretches for about 100,000 light years, or 30 kiloparsecs. At first glance this may seem like a very long distance, but in fact, against the background of other galaxies, our looks are rather small.
The approximate diameter of the Andromeda galaxy is 220,000 light-years, which is more than twice the size of the Milky Way. It is the largest galaxy in the local group. If Andromeda’s galaxy was even brighter, then in the night sky it could look larger than the Moon, even though it is much, much farther. By the way, about the distance: the galaxy is located about 9.5 trillion kilometers from the Earth (the moon, recall, is only 384,000 kilometers).
Contains trillion stars
According to rough estimates, the Milky Way can contain from 100 to 400 billion stars. But this is nothing compared to Andromeda, which can contain about one trillion. Thanks to the Hubble Space Telescope, scientists learned about the presence of a very large and rare population of hot and bright stars among this trillion.
Hot, young stars tend to look blue. However, the blue stars found in the Andromeda galaxy look more aging, more like the Sun, stars that burnt their inner layers and exposed their hot blue nuclei. They are scattered all over the center of the galaxy and in the ultraviolet range are the brightest.
Has a double core
Another interesting fact about the Andromeda galaxy is its double core. Observations showed 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 located young blue stars.
Later, astronomers found out that the two cores are not two separate clusters of stars, but rather one cluster in the form of a donut and a supermassive black hole whose mass exceeds 140 million solar masses. The stars in the P1 cluster are drawn very closely around the black hole, like planets around the Sun, thereby creating the effect of having a double core.
Will collide with our galaxy
We are waiting for intergalactic collapse. At the moment, the Andromeda galaxy is moving toward the Milky Way at a speed of 400,000 kilometers per hour. At this speed, the globe can be flown in just 6 minutes. Astronomers predict that in about 3.75 billion years there will be a clash of the Milky Way and Andromeda. 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 suggest that our planet will not suffer much from this intergalactic collapse, since both galaxies have a lot of free space. Nevertheless, from Earth, watching the event will be very interesting (if, of course, life by that time on it still exists). Both galaxies will be attracted to each other as long as the black holes in their centers eventually merge into one. As soon as this happens, our solar system will become part of a completely different galaxy – elliptical. If the Sun does not absorb the Earth in about 5 billion years, then every night it will be very bright, thanks to the presence of many new stars. Instead of a strip of light from the Milky Way,
Has an absolute value of 3.4
In astronomy, the absolute value is the luminosity of an astronomical object. It allows us to determine the brightness of any object, regardless of its distance to us.
The Andromeda Galaxy has an absolute value of 3.4, which allows it to be the most striking object of 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 dim star. If you look at it with binoculars, it will look like a small elliptical cloud. If you follow it in a large telescope, it can look up to six times the size of the moon.
It is full of black holes
Once in the Andromeda galaxy there were 9 known black holes, but the actual number of them increased to 35 in 2013. Astronomers have monitored 26 new candidates for black holes, which made the galaxy one of the most densely populated with similar objects. Most of these new black holes have a mass that is 5-10 times greater than the mass of our Sun. The seven black holes are located about 1000 light-years from the galactic center.
Astronomers are sure that in the future they will be able to detect even more such objects in this galaxy. For example, in 2017, two new black holes were discovered. At the same time it was noted that both objects are in the most dangerous of ever documented proximity. 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. According to experts, these black holes can collide with each other in less than 350 years, merging into one supermassive black hole.
Contains 450 globular clusters
The globular clusters are densely packed clusters of old stars closely connected by gravity. They can be hundreds of thousands and even millions of stars. Ball globes help determine the age of the universe, and also often help determine where the center of the galaxy lies. In the Milky Way, astronomers have detected at least 200 globular clusters, in Andromeda – about 450.
The number of globular clusters in Andromeda can be much greater, however, the long-range boundaries of this galaxy still remain poorly understood. If the globular clusters of the Andromeda galaxy had the same dimensions of the Milky Way clusters, then their real number could be something between 700 and 2800.
Once the Andromeda galaxy was considered a nebula
Nebulae are huge accumulations of gas, dust, hydrogen, helium and plasma, in which new stars are born. Very distant from us galaxies are often mistaken for these massive clusters. In 1924, astronomer Edwin Hubble announced that Andromeda’s spiral nebula is actually a galaxy and 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 represent a class of pulsating variable stars with a fairly accurate period-luminosity dependence. He determined how far away these stars are, which helped him calculate the distance on which the Andromeda galaxy was located from us. It was 860,000 light years, which is more than 8 times the distance to the most distant stars of 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.