Alpha Centauri

* A
* B
* Proxima (C)

## Kurzgesagt

### **First appearance**

The Largest Star in the Universe – Size Comparison

### **Latest appearance**

The Largest Star in the Universe – Size Comparison

## Kurzgesagt

### **First appearance**

The Largest Star in the Universe – Size Comparison

### **Latest appearance**

The Largest Star in the Universe – Size Comparison

## Kurzgesagt

### **First appearance**

The Largest Star in the Universe – Size Comparison

### **Latest appearance**

The Largest Star in the Universe – Size Comparison

## General Information

In the southern constellation of Centaurus, Alpha Centauri, also known as α Centauri, Alpha Cen, or α Cen, is a triple star system. Toliman (B), Proxima Centauri (C), and Rigil Kentaurus (Alpha Centauri A) are its three stars. At 4.2465 light-years (1.3020 pc), Proxima Centauri is the star nearest to the Sun.

Alpha Centauri AB is a binary star system made up of the Sun-like stars Alpha Centauri A and B (Class G and K, respectively). The two primary components appear as a single star with an apparent brightness of -0.27 to the unaided eye. Only Sirius and Canopus are brighter than it, making it the most luminous star in the constellation and additionally the third brightest star overall in the night sky.

Alpha Centauri B is substantially smaller and colder than Alpha Centauri A, with 0.9 solar mass with less than 0.5 solar brightness, while Alpha Centauri A has 1.5 times the luminosity and 1.1 times the mass of the Sun. The two have a 79-year orbital period around a shared center. The eccentricity of their elliptical orbit causes the distance between A and B to fluctuate between 35.6 astronomical units (AU), or roughly the distance between Pluto and the Sun, and 11.2 AU, or roughly the distance between Saturn and the Sun

Proxima Centauri, often known as Alpha Centauri C, is a very weak red dwarf star (Class M). At 4.24 ly (1.30 pc), slightly closer than Alpha Centauri AB, Proxima Centauri is the nearest star to the Sun even though it is not visible to the unaided eye. At the moment, both Proxima Centauri and Alpha Centauri AB are separated by around 13,000 AU (0.21 ly), which is almost 430 times the radius of that of Neptune's orbit.

As of 2022, Proxima d—a possible sub-Earth that orbits very near to Proxima Centauri—was revealed. Proxima b is an Earth-sized planet in the habitable zone that was identified in 2016. Proxima c is a mini-Neptune that was found 1.5 AU distant in 2019, however its existence is up for debate. Though not yet confirmed to be planetary in nature, Alpha Centauri A may include a candidate Neptune-sized planet in the habitable zone; it might also be a byproduct of the finding process.19] There are no known planets in Alpha Centauri B; the alleged 2012 discovery of planet Bb was subsequently shown to be false, and no other planet has been verified as of yet.

### History

When viewed with the unaided eye, Alpha Centauri AB, the brightest star in the southern constellation of Centaurus, seems to be a single star. Throughout the course of around 80 years, their apparent angular separation fluctuates between 2 and 22 arcseconds, although for the most part of the orbit, both may be clearly seen with binoculars or small telescopes. Only Sirius and Canopus are fainter than Alpha Centauri, a first-magnitude star with an apparent magnitude of −0.27 (when combining A and B magnitudes).

Ptolemy's star catalog, the Second-Century Almagest, has a listing for Alpha Centauri. He provided the ecliptic coordinates, yet there is disagreement among literature over whether 44° 10′ South or 41° 10′ South is the ecliptic latitude.45] (At 43.5° South at the moment, proper motion has caused the ecliptic latitude to drop by a little degree since Ptolemy's time.) When Alpha Centauri was first spotted by Ptolemy, it was visible from Alexandria, Egypt, at 31° N. However, because to precession, its declination has now changed to –60° 51′ South, meaning that it is no longer visible at that latitude.

Jean Richaud discovered that Alpha Centauri AB was a binary system in December 1689 while seeing a comet pass by from his Puducherry station. Acrux was the first binary star to be found before Alpha Centauri. Manuel John Johnson, viewing from Saint Helena, found Alpha Centauri AB's enormous proper motion, which he reported to Thomas Henderson at the Royal Observatory, Cape of Good Hope. Henderson later calculated the parallax of Alpha Centauri based on several precise positional measurements of the AB system made between April 1832 and May 1833.

Eventually, in 1834, John Herschel made the first observations using micrometry. Photographic plates have been used for measurements ever since the early 20th century. William Stephen Finsen estimated the approximate orbit elements by 1926, which are similar to those that are now recognized for this system. Visual observers may now use a binary star ephemeris to establish the relative locations of the stars because all future positions have become sufficiently accurate. Others, like as D. Pourbaix in 2002, have consistently improved the accuracy of newly released orbital elements.

In 1915, Robert T. A. Innes used blinking picture plates collected at various intervals during an appropriate motion study to find Proxima Centauri. These revealed substantial proper motion and parallax that were comparable to those of Alpha Centauri AB in terms of size and direction. This indicated that Proxima Centauri is a member of the Alpha Centauri system and is somewhat nearer Earth than Alpha Centauri AB. As a result, Innes came to the conclusion that Proxima Centauri was the star that was discovered closest to Earth.

### Properties

The two primary stars in the Alpha Centauri triple star system, Alpha Centauri A and Alpha Centauri B, combined make up a binary component. The mass center of a major binary system in relation to a companion star or stars in a multiple star system is indicated by the AB designation, or the older A×B.In The component of Proxima Centauri that is related to the central binary is denoted as AB-C, which represents the separation between the outlying companion and the center of mass. Proxima (C) and any of the Alpha Centauri A or B are comparable in distance, hence the AB binary system is frequently seen as an individual gravitational object.

Chromospheric activity, star rotation, and asteroseismic investigations all point to the Alpha Centauri system's age being comparable to or somewhat older than that of the Sun. According to astroseismic calculations, age estimates of 4.85±0.5 Gyr, 5.0±0.5 Gyr, 5.2 ± 1.9 Gyr, 6.4 Gyr, and 6.52±0.3 Gyr have been obtained for the Alpha Centauri stars, taking into account stringent observational limitations on solar characteristics. Chromospheric activity (Calcium H & K emission)-based age estimations for the stars produce 4.4 ± 2.1 Gyr, whereas gyrochronology-based age estimates yield 5.0±0.3 Gyr. Based on their mass and spectral properties, both stars appear to be somewhat older than the Sun—between 5 and 6 billion years—according to stellar evolution theory.