We are talking about the diversity of the Solar System’s neighbors. Not all have beautiful and famous names, but each is interesting.
1. α Centauri system
The closest star system to us, known as α Centauri, is now at a distance of 4.34 light-years. It consists of three components. The yellow and orange dwarfs orbit a common center of mass in an elliptical orbit. The distance between them varies from 11 to 35 AU. With the naked eye, we see them as one luminary. Arab astronomers gave it the name Toliman.
Source: ESO/L. Calçada/N. Risinger
A red dwarf known as Proxima Centauri orbits this pair, taking approximately 550 thousand years to complete one revolution. Of the planets in this system, only the super-Earth Proxima b has been confirmed, and it is likely to always face its star.
Proxima d, which is similar in size to Mars, and an “exoplanet” in the habitable zone of the main component of the system, are still only candidates. Scientists currently doubt the existence of the cold “Neptune” Proxima c, but reject the possibility of any planets near the system’s orange star.
2. Barnard’s Star
Barnard’s Star is a red dwarf that is currently visible in the constellation Ophiuchus. Although it is only 5.96 light-years away, it is impossible to see it with the naked eye. The fact is that the mass of this object is only 14% of the solar mass, and its luminosity is 2500 times lower.
This star is called the “flying star”. As early as 1916, American astronomer Edward Barnard found that it has the largest known proper motion, changing its position against the background of other stars by 10.3 angular seconds per year. The reason for this is a combination of high speed relative to the Solar System and short distance.
Planets around Barnard’s Star have been discovered and “closed” many times during the 20th and 21st centuries. To date, the existence of four exoplanets has been confirmed, with masses several times less than the Earth’s.
3. Luhman 16
Surprisingly, people knew nothing about the existence of the third most distant star system from the Sun until 2013. It was then that the discovery of a pair of brown dwarfs at a distance of 6.5 light-years was officially announced in the WISE infrared sky survey data.
Source: NASA/JPL/Gemini Observatory/AURA/NSF
However, there is still some debate about whether brown dwarfs, including the pair discovered by Kevin Luhman, are stars or sub-stars. After all, not all of them have thermonuclear reactions.
Specifically, the components of the Luhman 16 pair have masses approximately 33 and 28 times that of Jupiter. This allows them to be classified as L and T, respectively. On the former, thermonuclear reactions may still be ongoing, but on the latter, they have most likely already stopped.
4. WISE 0855−0714
WISE 0855-0714 is another brown dwarf, this time “lonely”. Its distance is 7.43 light-years. Like the Luhman 16 pair, it is practically invisible even with powerful telescopes, so people learned about its existence thanks to an infrared survey of the sky carried out in 2009-2011.
The mass of WISE 0855-0714 is only three to ten times that of Jupiter, meaning that this object is on the borderline that separates brown dwarfs from orphan planets wandering alone in the galaxy. It belongs to the spectral class Y, so thermonuclear reactions do not occur on it, and it emits energy in the infrared spectrum solely due to the residual heat, of which it has very little left. At a temperature of 225-260 K (-48 to -13°C), WISE 0855-0714 is considered one of the coldest known brown dwarfs.
5. Wolf 359
The star Wolf 359 is located at a distance of 7.9 light-years. It is sometimes referred to as the CN Leo because it is visible in this zodiacal constellation. The red dwarf, which was first noticed by German astronomer Max Wolf, is one of the smallest and dimmest objects of this class. With a photospheric temperature of about 2800 K, it is close to sub-stars in terms of its parameters. However, thermonuclear reactions continue on it, as evidenced by flares that are much more powerful than those of the sun.
Despite this, astronomers suspect the existence of two planets in the vicinity of the star. However, the closer super-Earth has already been recognized as non-existent. But the reality of the small gas giant, which orbits Wolf 359 in just three days, is still under debate.
6. Lalande 21185
Lalande 21185 is another red dwarf named after the astronomer Joseph Jérôme Lefrançois de Lalande, who discovered it. It happened back in 1801, so it can be considered one of the first stars of this type known to humans.
Lalande 21185, located at a distance of 8.31 light-years from us, is considered large for its class. Its mass is 46% of the Sun’s, and its luminosity is about 50 times less than that of our star. This makes it easy to see through a small telescope or binoculars.
Lalande 21185 is a BY Draconis variable. This means that its surface is covered with large spots that greatly affect its brightness. Also, this star is sometimes described as flare-prone, but this has not been confirmed to date.
The existence of planets in Lalande 21185 has been reported many times. But each time their existence was denied. Now it is believed that the star has three planets. These are gas giants about the same size as Jupiter and orbit with periods ranging from 12 days to 7 years.
7. Sirius
Sirius, or α Canis Majoris, is the brightest star in the Earth’s sky. It is a system of two stars at a distance of 8.6 light-years. They both belong to spectral class A, but that’s where their similarities end.
Source: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)
The central star of the system is about twice as massive as the Sun, but its luminosity is 25 times higher. Sirius B circles it in an elliptical orbit with a rotation period of just under 50 years. The mass of this object is approximately the same as that of our star, but its radius is not much larger than the Earth’s.
Sirius B is a typical white dwarf. It was once a star, even more massive than the main component of the system, but it quickly used up all its fusion fuel, turned into a red giant, and then shed its outer shells to become the star we know today.
8. Luyten 726-8
Another red dwarf at a distance of 8.7 light-years from us is Luyten 726-8. It is also named after the scientist Willem Jacob Luyten, who was the first to discover this object in 1948. It is a double system of two small red stars orbiting each other in a strong elliptical orbit. The distance between them varies from 2.2 to 8.8 AU.
Both stars are variable and belong to the UV Ceti type, named after an alternative designation for one of them. The variability of this class of stars is determined by the powerful flares that occur on their surface. It is known that in 1952, one of the system’s components increased its brightness 75 times within 20 seconds.
9. Ross 154
Ross 154 is a star 9.69 light-years away in the constellation Sagittarius. This red dwarf is also named after the discoverer. The mass of this luminary is 17% of the Sun’s, and its radius is five times smaller than our own. The star is quite young, as its age is less than a billion years.
Ross 154 is also a UV Ceti variable type, meaning that powerful outbursts occur on its surface. Their frequency is approximately two days. It is also a source of X-rays.
10. Ross 248
The tenth most distant star from the Sun is also a red dwarf, known by its designation in the catalog of American astronomer Frank Elmore Ross. It is 10.3 light years away from us and is located in the constellation Andromeda.
Ross 248 belongs to variable stars, not the flaring ones (like UV Ceti), but the ones that are covered with spots, like BY Draconis. No signs of planets or brown dwarfs have been detected near it.
In 33 thousand years, this luminary will become the closest star system to us. In another three thousand years, Ross 248 will approach us at a distance of three light-years and begin to move away. Almost at the same time, the Voyager 2 spacecraft will fly by at a distance of 1.7 light-years.
11. Epsilon Eridani
At a distance of 10.5 light-years from us is the star ε Eridani, a young orange dwarf with a mass of 82% of the sun’s and a luminosity about three times lower than our own. It also has its name, Ran, in honor of the sea giant from Norse mythology. It is a fairly young star, which is why the flow of charged particles from its surface (stellar wind) is about 30 times stronger than that of the Sun.
The ε Eridani system is quite complex. There is an asteroid belt at a distance of 1.5-2 AU from the central body. Behind it, about 3 AU from the star, the gas giant Aegir, named after the mythological man Ran, orbits. Its mass is about 20% greater than that of Jupiter.
Further, at a distance of 8 to 20 AU from Ran, the second asteroid belt begins. And 40 AU away, approximately where Pluto is located in the Solar System, there is another planet whose existence has not yet been confirmed. It is believed to be a small “exoplanet”, perhaps ten times smaller than Jupiter. Just beyond its orbit is another wide disk, this time of gas and dust.
12. Lacaille 9352
Finally, the twelfth most distant star system from us is Lacaille 9352. This is another red dwarf named after the astronomer Nicolas-Louis de Lacaille. For its class, it is quite large – its diameter is 47% of the solar diameter.
The existence of two planets in the system has been confirmed – super-Earths too hot for life. The first is almost four times larger than the Earth and orbits the star in nine days. The second one takes 21 days to do so, and its mass is seven times that of the Earth.
There are also signs of a third super-Earth. If it does exist, it has a mass eight times that of our planet and orbits a star with a period of 50 days. In this case, it may well be suitable for life.
This article was published in Universe Space Tech magazine, issue #1 (189), 2023. You can buy this issue in the electronic version in our store.
