Proxima Centauri

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Coordinates: 14h 29m 42.9487s, −62° 40′ 46.141′′′

Proxima Centauri or Alpha Centauri C (from Latin proximus, -a, -um: "next to" or "close to") is a dwarf star Red light of 11th apparent magnitude located approximately 4.22 light-years (1,295 parsecs) from Earth, in the constellation of Centaurus and possibly belonging to the Alpha Centauri system. Discovered in 1915 by Robert Innes, director of the Union Observatory in South Africa, it is the closest star to the Sun, although its luminous intensity is too weak to be observed without astronomical instruments. Its distance from the stars that make up the Alpha Centauri binary system is 15,000 ± 700 AU (0.237 ± 0.011 light-years). Proxima Centauri may be part of a triple star system with Alpha Centauri A and B, but this extreme has not been confirmed.

Due to the proximity of this star, its angular diameter of 1.02 ± 0.08 milliarcseconds can be measured directly; from it it follows that its real diameter is one seventh of the solar diameter. The mass of Proxima Centauri is about one eighth that of the Sun, and its density is about 40 times greater. Although it has a very low average luminosity, Proxima Centauri is a flare star that undergoes spectacular random increases in brightness due to magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The "fuel" mixture in Proxima Centauri's core through convection and the star's relatively low rate of energy production suggest it will be a main sequence star for another four billion years, or nearly 300 times the current age of the universe.

The star is known to harbor two planets, Proxima Centauri b, discovered in 2016 and Proxima Centauri c, discovered in 2019. However, for years the search for other stellar objects orbiting Proxima Centauri had been fruitless, ruling out the presence of brown dwarfs and supermassive planets. Studies of its radial velocity have also accurately ruled out the presence of super-Earths within the habitable zone of the star. Detection of smaller objects will require the use of new instruments, such as the James Webb Space Telescope. Since Proxima Centauri is a red dwarf and a flare star, it is disputed whether a planet orbiting this star could support life. However, due to the star's proximity to Earth, it has been proposed as a destination for interstellar travel.

Observation

In 1915 astronomer Robert Innes, director of the Union Observatory in Johannesburg, South Africa, discovered that Proxima Centauri shared the same proper motion as Alpha Centauri. Innes further suggested the name Proxima Centauri for the star. In 1917, at the Royal Cape Observatory in Cape Town, the Dutch astronomer Joan Voûte measured the distance using trigonometric parallax and determined that Proxima Centauri's distance from the Sun was 4.22 light-years. Proxima Centauri was soon seen to be very dim, one of the dimmest stars known at the time. The first precise determination of the parallax of Proxima Centauri was made by the American astronomer Harold l. Alden in 1928, who confirmed the above results with a parallax of 0.783 ± 0.005 seconds of arc.

In 1951, Harlow Shapley announced that Proxima Centauri was a flaring star. Examinations of previously taken series of photographs showed that the star exhibited variations in luminosity of around 8%, making this star the most active of the flare stars discovered to date.

The proximity of the star allows detailed observation of its flare activity. In 1980, the Einstein Observatory produced a detailed X-ray energy curve of a Proxima Centauri stellar flare. Other observations of the flares were made with the Exosat and ROSAT satellites, while smaller X-ray emissions, similar to solar flares, were observed by the Japanese ASCA satellite in 1995. Proxima Centauri has since been the subject of study by most. X-ray observatories, including XMM-Newton and Chandra.

Due to Proxima Centauri's southward declination, it can only be seen south of 27°N latitude. Red dwarfs like Proxima Centauri are too dim to be seen with the naked eye; even from Alpha Centauri A and B, Proxima Centauri would only be observable as a 5th magnitude star. It has an apparent magnitude of 11, so a telescope with an aperture of at least 8 cm is needed to be observed, even under ideal viewing conditions.

Features

Relative sizes of the Sun (Sun), Alfa Centauri A and B and Proxima Centauri

Proxima Centauri is a red dwarf — which implies that it is on the main sequence in the Hertzsprung–Russell diagram — of spectral type is M5.5. It is also classified as a "late M-type dwarf", which means that it is located towards the extreme of lower mass and temperature within this type of star. Its absolute magnitude, or its visual magnitude from a distance of 10 parsecs, is +15.5.

Cataloged as a flaring star with the variable name V645 Centauri, it shows random variations in luminosity due in part to its magnetic activity. It has a mass equivalent to one eighth of the solar mass and is therefore a very low luminosity star. Its total luminosity across the electromagnetic spectrum is equal to 0.17% of that of the Sun, but when observed at visible light wavelengths, to which the eye is most sensitive, its luminosity drops to about 0.0056% of the solar luminosity, since more than 85% of its energy is radiated in wavelengths corresponding to the infrared.

Since Proxima Centauri is the closest star to the solar system, it follows that there are no red dwarfs that can be seen with the naked eye. Even from nearby Alpha Centauri A and B, it would barely look like a magnitude 5 star.

Given the parallax of 772.3 ± 2.4 milliarcseconds as measured by the Hipparcos satellite (and the more precise parallax determined by the Hubble Space Telescope of 768.7 ± 0.3 milliarcseconds), Proxima Centauri It is almost certainly located at a distance of 4.2 light years from Earth, or what amounts to the same thing, it is 270,000 times further away than the Sun. Nearby are Alpha Centauri A and B (a 0.21 light-years), the Sun, Barnard's Star (6.6 light-years) and Ross 154 (8.1 light-years). Viewed from Earth, Proxima Centauri is separated 2.2° from Alpha Centauri, which is equivalent to 4 times the angular diameter of the full moon.

Proxima Centauri has a relatively large proper motion, moving about 3.85 arcseconds per year on the sky.

In 2002 the Very Large Telescope (VLT) used optical interferometry to measure the angular diameter of Proxima Centauri, which was found to be 1.02 ± 0.08 milliarcseconds. As the distance at which it is located is well known, the radius of Proxima Centauri could be calculated, obtaining the value of 1/7 of the solar radius or 1.5 times that of Jupiter.

Due to its relatively low mass, the interior of the star is completely convective, which means that energy is transferred to the exterior by the physical motion of the plasma and not by radiation. Convection is associated with the generation and storage of a magnetic field. The magnetic energy of this field comes to the surface through solar flares that increase the luminosity of the star at times. These flares have enough energy to radiate X-rays, and in fact their luminosity in that range is equivalent to that of the Sun. However, the star's activity is relatively low compared to other stars of the same type, and the activity appears to vary over a period of about 442 days. Due to the nuclear fuel mixing processes that occur in its core and its relatively low rate of energy production, Proxima will remain on the main sequence for 4 × 10¹² years (about 300 times the current age of the universe).

Possible substellar companions

**Maximum mass of the accompanying object**
Orbital period (days)	Separation (UA)	Maximum mass (M)_Jup)
50	0.13	3.7
600	0.69	8.3
3000	1,00	22

The search for substellar companions orbiting Proxima Centauri has been unsuccessful to date, ruling out the presence of brown dwarfs and supermassive planets. Precision measurements of their radial velocity have also ruled out the presence of "super-Earths" within the habitable zone of the star. Detection of minor objects will require the use of new equipment; For this reason, Proxima Centauri, along with Alpha Centauri A and B, is among the targets of NASA's "Group 1" in the mission called Space Interferometry Mission (SIM). In theory, SIM will be able to detect planets as small as three times the mass of Earth. Since Proxima Centauri is a flaming red dwarf, there is controversy as to whether a planet orbiting it could support life.

The presence of a massive planet around Proxima Centauri would cause the star to move along its orbit. If the orbital plane is tilted with respect to the line of sight from Earth, such displacement would produce changes in radial velocity, which have not been detected so far. This significantly constrains the maximum mass of the possible accompanying object.

Earth-like planet in the habitable zone

Proxima Centauri b, was announced on August 24, 2016.

The data reveals that the planet is at least 1.3 times the mass of Earth and revolves around Proxima Centauri every 11.2 days at a distance of about seven million kilometers. This distance is 5% of that between the Earth and the Sun, which suggests that it could be a boiling planet; however, Proxima Centauri is a cooler and smaller star than the Sun, which means that the planet is in the habitable zone even though it is closer to its star. The composition of the planet still remains to be clarified, if it were a rocky planet like Earth and being in the habitable zone, we would be facing a planet that could harbor life, although the periodic flares of the sun that surrounds it do little. likely.

Proxima Centauri d was announced on February 10, 2022. It would be a rocky planet, orbiting 4 million km from the star and completing its orbit in five days.

The Alpha Centauri Star System

Next Centauri orbital movement around Alpha Centauri. The position of Proxima Centauri in the future in millennia is also represented.

Ever since its discovery, Proxima Centauri was suggested to be a true component of the Alpha Centauri star system. At a distance of just 0.21 light-years or 15,000 ± 700 AU, Proxima Centauri can orbit Alpha Centauri with an orbital period of 500,000 years or more. For this reason, it is also called Alpha Centauri C. Modern estimates, taking into account the small divergence between the relative velocities of the stars, suggest that the chance that the observed alignment is just a coincidence is about one in a million.

The most recent work, which combines data from the Hipparcos satellite with observations made from Earth, is consistent with the hypothesis that the three stars are linked to each other. In this case, Proxima Centauri would currently be near the apoaster (maximum separation from the inner pair AB). However, more precise measurements of radial velocity are needed to confirm this conclusion.

In a 2017 paper, Pierre Kervella and colleagues showed that, based on new high-precision radial velocity measurements, Proxima Centauri and Alpha Centauri are gravitationally linked with a high degree of confidence. The orbital period of Proxima Centauri is approximately 550,000 years old, with an eccentricity of 0.5 ± 0.08. Proxima Centauri approaches 4,300 AU from Alpha Centauri in the periastro, while in the apoastro it moves away to about 13,000 AU.

Interstellar travel

It has been suggested that Proxima Centauri is the most logical destination for a first interstellar journey, but as a flaring star, it may not be very hospitable. Still, assuming a travel speed of 40 km/s (versus 10.7 km/s for Apollo 10), it would take humans roughly 32,000 years to get there. At the current speed that the Parker probe has achieved, the journey could be reduced to about 8,000 years.