How to calculate the distance of Andromeda galaxy from us?

The distance to deep space objects such as Andromeda galaxy is usually determined by "standard candlelight", and astronomers should loo

How to calculate the distance of Andromeda galaxy from us?

The distance to deep space objects such as Andromeda galaxy is usually determined by "standard candlelight", and astronomers should look for objects with known intrinsic luminosity (actual brightness). The apparent brightness of any luminous object (our visual brightness) decreases as the square of the distance between the celestial body and the observer decreases; Therefore, if we know the intrinsic luminosity of a celestial body, we can measure the luminosity and make a simple calculation to get the approximate distance of this celestial body. An example of this "standard candlelight" is the so-called Cepheid variable star. These young, massive and bright stars (brightness is about 1000 times that of the sun) have periodic luminosity changes.

It has been found that the period of Cepheid variable is related to its inherent brightness. Therefore, if we measure the frequency of the brightness change of a star, we can calculate its intrinsic brightness, and then calculate the distance to Cepheid variable. Another commonly used "standard candlelight" is a supernova called type Ia, which is caused by the collapse of a white dwarf star that takes mass from its companion star. Astronomers believe that all type Ia supernovae have roughly the same intrinsic luminosity peak (about-19.5). Similarly, because the intrinsic luminosity is known, the approximate distance to the supernova can be calculated by measuring the apparent luminosity. Because supernovae are surprisingly bright, they can be observed at a long distance, which is ideal for measuring celestial bodies (billions of light years) farther than Andromeda galaxy.

Edwin Hubble first determined the distance to Andromeda galaxy in the late 1920s (but it was not accurate). Hubble uses the calibration form of periodic photometric relationship first discovered by Henrietta Loewit around 19 1 1. Loewit studied Cepheid Variables in the more recent small magellanic cloud (SMC). These stars have a special property that their brightness changes regularly or periodically. The oscillation time of the brightness of a variable star from the brightest to the darkest and then to the brightest is called the period of the star. Cepheid variables get their name from the fact that they were found in Cepheus.

Loewit found that there is a linear relationship between the period of Cepheid variable and its apparent brightness. Because all these Cepheid variables are located in the small magellanic cloud, she concluded that their distances from the Earth are similar, so there should also be a linear relationship between their periods and their true brightness (brightness observed at a standard distance). If we can know the apparent brightness and true brightness of an object, it is easy to determine its distance. You can use inverse square law. Loewit speculated that if she could calculate the distance to Cepheid variable, she could calibrate her linear relationship to determine the distance to any Cepheid variable.

Later, Harold shapley calibrated Leuther's law, so it took Hubble about ten years to start using it. Hubble controls the new 100-inch Hooke telescope on Mount Wilson, California, which can be observed and studied by Levitt's law. For the first time, he was able to distinguish a star in the Andromeda galaxy. He was lucky to find some Cepheid variables in Andromeda. Hubble's most important work here is that it clearly shows for the first time that Andromeda galaxy is not a part of our galaxy, but a completely independent galaxy and an "island universe". Now we know that Andromeda galaxy is about 2.2 million light years away. Comparing the radius of the Milky Way galaxy around 50,000 light years, we will find how amazing Hubble's discovery was at that time.

relevant knowledge

Andromeda galaxy (IPA:/? Ann? Doctor? m？ d？ /,also known as messier 3 1, catalog number M3 1, NGC 224, which was called Andromeda Nebula in old literature and Quezon 2 1 in ancient China, is a spiral galaxy, about 2.5 million light years away from the Earth, and it is the closest galaxy to the Earth except Magellan Cloud (the companion galaxy of the Milky Way where the Earth is located). [3] Located in the direction of Andromeda, it is the farthest deep space object visible to the naked eye (3.4 magnitude). Andromeda galaxy is considered as the largest galaxy in this galaxy group, with a diameter of about 200,000 light-years and looks like the Milky Way. The members of this galaxy group are Andromeda, Milky Way, Triangle and about 50 small galaxies. However, according to improved measurement technology and recent research results, scientists now believe that there are many dark matter in the Milky Way, which may be the most mass in this group.

However, recent observations by Spitzer Space Telescope show that Andromeda galaxy has nearly one trillion (10 12) stars, far more than our own Milky Way. [5] In 2006, the mass of the Milky Way was re-estimated to be about 50% of the mass of Andromeda galaxy, which was 7.1×1kloc-0/m ☉. [2] Andromeda galaxy is easy to see with naked eyes in a moderately dark sky environment, but such a sky only exists in small towns and isolated areas. Andromeda galaxy is very small to the naked eye, because only a small area in the center has enough brightness, but the complete angular diameter of this galaxy is seven times that of the full moon.

Author: Nidi

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