Composition, structure and size of our galaxy

2024 Author: Miguel Ramacey | [email protected]. Last modified: 2023-12-17 06:11

The Milky Way is a striped spiral galaxy. Our galaxy is between 100,000 and 180,000 light years in diameter. It is estimated by scientists to contain 100-400 billion stars. There are probably at least 100 billion planets in the Milky Way. The solar system lies within the disk, 26,490 light-years from the Galactic center, on the inner edge of the Orion Arm, one of the spiral concentrations of gas and dust. Stars in the innermost 10,000 light years form a bulge and one or more rods. The galactic center is an intense radio source known as Sagittarius A, which is likely a 4.100 million solar mass supermassive black hole.

Velocity and radiation

Stars and gases over a wide range of distances from the orbit of the Galactic Center move at a speed of about 220 kilometers per second. A constant rotational speed is contrary to the laws of Keplerian dynamics and suggests that most ofThe mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been called "dark matter". The rotation period is about 240 million years at the position of the Sun. The Milky Way is moving at a speed of about 600 km per second relative to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the universe itself and likely formed shortly after the Big Bang Dark Ages.

Appearance

The center of the Milky Way is visible from Earth as a hazy band of white light, about 30° wide, arched by the night sky. All individual stars in the night sky visible to the naked eye are part of the Milky Way. The light comes from an accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and Koalsak, are areas where interstellar dust blocks light from distant stars. The region of the sky that the Milky Way hides is called the Zone of Avoidance.

Brightness

The Milky Way has a relatively low surface brightness. Its visibility can be greatly reduced by backgrounds such as light or moonlight. For the Milky Way to be visible, the sky must be darker than usual. It should be visible if the magnitude limit is approximately +5.1 or higher, and shows more detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but very visible from rural areas whenThe moon is below the horizon. "New World Atlas of Artificial Night Sky Brightness" reveals that more than one-third of the world's population cannot see the Milky Way from their homes due to air pollution.

Size of the Milky Way galaxy

The Milky Way is the second largest galaxy in the Local Group, with its stellar disk about 100,000 litas (30 kpc) in diameter and about 1000 litas (0.3 kpc) average thick. The ring-shaped string of stars wrapped around the Milky Way may belong to the galaxy itself, oscillating above and below the galactic plane. If so, this would indicate a diameter of 150,000-180,000 light-years (46-55 kpc).

Mass

Estimates of the mass of the Milky Way vary depending on the method and data used. At the lower end of the estimation range, the mass of the Milky Way is 5.8 × 1011 solar masses (M☉), somewhat less than the mass of the Andromeda galaxy. Measurements using a very long base array in 2009 showed speeds as high as 254 km/s (570,000 mph) for stars on the outer edge of the Milky Way. Since the orbital velocity depends on the total mass in the orbital radius, this suggests that the Milky Way is more massive, roughly equal to the mass of the Andromeda Galaxy at 7×1011 M☉ within 160,000 liters (49 kpc) of its center. In 2010, a measurement of the radial velocity of halo stars showed that the mass contained within 80 kiloparsecs is 7×1011 M☉. According to a study published in 2014, the mass of the entire Milky Wayestimated at 8.5×1011 M☉, which is about half the mass of the Andromeda Galaxy.

Dark matter

Most of the Milky Way is dark matter, an unknown and invisible form of it, which gravitationally interacts with ordinary matter. The dark matter halo is distributed relatively evenly over a distance greater than one hundred kilometers (kpc) from the Galactic Center. Mathematical models of the Milky Way suggest that the mass of dark matter is 1-1.5×1012 M☉. Recent studies show a mass range of 4.5×1012 M☉ and a dimension of 8×1011 M☉.

Interstellar gas

The total mass of all stars in the Milky Way is estimated to be between 4.6×1010 M☉ and 6.43×1010 M☉. In addition to the stars, there is also an interstellar gas containing 90% hydrogen and 10% helium, with two-thirds of the hydrogen in atomic form and the remaining third in the form of molecular hydrogen. The mass of this gas is equal to 10% or 15% of the total mass of the stars in the galaxy. Interstellar dust makes up another 1% of the total mass.

The structure and size of our galaxy

The Milky Way contains between 200 and 400 billion stars and at least 100 billion planets. The exact figure depends on the number of very low mass stars that are difficult to detect, especially at distances greater than 300 litas from the Sun. In comparison, the neighboring Andromeda Galaxy contains approximately three trillion stars, and therefore exceeds the size of our galaxy. Milky Waymay also contain perhaps ten billion white dwarfs, billionth neutron stars, and one hundred million black holes. Filling the space between stars is a disk of gas and dust called the interstellar medium. This disk is at least comparable in radius to the stars, while the thickness of the gaseous layer ranges from hundreds of light years for cooler gas to thousands of light years for warmer gas.

The Milky Way consists of a rod-shaped core region surrounded by a disk of gas, dust and stars. The mass distribution in the Milky Way closely resembles Hubble's Sbc type, representing spiral galaxies with relatively free-spanning arms. Astronomers first began to suspect that the Milky Way is a closed spiral galaxy, rather than an ordinary spiral galaxy, in the 1960s. Their suspicions were confirmed by Spitzer Space Telescope observations in 2005, in which the Milky Way's central barrier was larger than previously thought.

Conceptions about the size of our galaxy may vary. The disk of stars in the Milky Way does not have a sharp edge beyond which there are no stars. Rather, the concentration of stars decreases with distance from the center of the Milky Way. For reasons that are not clear, beyond a radius of about 40,000 litas from the center, the number of stars per cubic parsec falls much faster. The surrounding galactic disk is a spherical galactic halo of stars and globular clusters that extends further outward but is limited in size by orbitstwo satellites of the Milky Way - the Large and Small Magellanic Clouds, the nearest of which is located at a distance of about 180,000 litas from the Galactic Center. At or beyond this distance, the orbits of most halo objects will be destroyed by the Magellanic Clouds. Therefore, such objects are likely to be ejected from the vicinity of the Milky Way.

Star systems and independent planets

A question about the size of the Milky Way is a question about how big galaxies are in general. Both gravitational microlensing and planetary transit observations indicate that there are at least as many starbound planets as there are stars in the Milky Way. And microlensing measurements indicate that there are more independent planets not tied to host stars than stars themselves. According to the Meiling Way, there is at least one planet per star, resulting in an estimated 100-400 billion.

In order to understand the structure and size of our galaxy, scientists often conduct various analyzes of this kind, constantly updating and revising outdated data. For example, another analysis of Kepler data in January 2013 found that there are at least 17 billion Earth-sized exoplanets in the Milky Way. On November 4, 2013, astronomers reported, based on data from the Kepler space mission, that within the limits of stars and red dwarfs suitable for the Sun in the Milky Way region, up to 40billion Earth-sized planets, 11 billion of these estimated planets may orbit sun-like stars. According to a 2016 study, the closest such planet could be 4.2 light years away. Such Earth-sized planets may be more numerous than gas giants. In addition to exoplanets, "exocomets", comets outside the solar system, have also been detected and may be common in the Milky Way. The sizes of stars and galaxies may vary.