A team of astronomers has found … well, something near one of the Alpha Centauri stars that is consistent with a planet, possibly around the size of Neptune. However, to be very clear, it is not yet proven – it could be a cloud of dust or it could not even be real at all.
Call me “interested with caution.” But if it’s a planet, it would be very interesting.
Alpha Centauri is the closest star system to ours. It consists of three stars, a binary star made up of Alpha Centauri A and B, both orbited by Proxima Centauri, a faint red dwarf. Proxima probably has at least two planets and there is evidence for a third.
The binary is 4.37 light years away from us. Alpha Centauri A (or α Cen A) is slightly more massive, hotter, and brighter than the Sun, and the other (α Cen B) is less massive, colder, and weaker than the Sun.
Because they are close to us, it is easier to look for planets in their habitable areas, the distance from each star where there could be liquid water on the surface of the planet. For distant stars, this area appears so close to a star that it is difficult to see because of its brightness. With stars closer, it seems farther away and easier to notice. This makes α Cen a tempting target for direct imaging, literally taking an image of the stars and looking for an exoplanet in it.
In general, this method is best using infrared light (or IR), where the stars are weaker and the planets brighter, thus increasing the contrast. It worked well for quite a few exoplanets, but favors those that are far from their stars (where the star’s backlight is weaker), massive (making them brighter), and young (they are still hot when a few million years old). , so they give more IR light).
The direct image is not optimized to look for Earth-like planets in habitable areas that are colder, smaller, and much closer to their stars. However, new cameras and techniques could see these planets that might not bubble in heat boilers.
New Earths in the α Centauri region (or NEAR) is an experiment that uses these new methods to search for planets around the Alpha Centauri. It uses a very large 8.2 meter monster telescope in Chile, with a camera called VISIR: VLT Imager and Spectrometer for medium infrared. Most IR cameras look at shorter wavelengths, around 5 microns (the reddest light the human eye can see is about 0.8 microns). VISIR looks at 10 microns, where the colder planets emit light, making it possible to visualize more Earth-like planets.
This is what astronomers used to look at Alpha Centauri for 19 nights in May / June 2019. They received over 70 hours of useful observations and used a lot of techniques to reduce the brightness of the two stars, including setting them. behind a metal disk (called a coronagraph) to block the light from the inside of the star to reduce brightness, subtracting one star image from another to reduce a lot of light and more. Some of these methods are quite sophisticated and are needed to reduce the light of two of the brightest stars in the sky when viewed by one of the largest telescopes on Earth.
They found a lot of artifacts – light spots due to processing techniques or reflections inside the telescope – which makes it difficult to know exactly what is real and what is not. However, they found a light in a relatively clean part of the image where there should be no known detector artifacts and in the right place to be a planet. It is seen in several images, which increases the confidence that it is real. Previous observations made a few years ago rule out that it is a background star or a galaxy. Most fascinating to me, when all the images are combined, they form an elongated spot, consistent with the orbital motion of a planet around α Cen A in the 19 nights of observations!
However, and again I point this out, they can’t be sure it’s a planet, or even real. I will note that there was a brief downpour of excitement about the discovery of a possible planet orbiting α Cen a few years ago, but it was later withdrawn.
But if it is a planet, given its brightness, it matches a planet between 3 and 11 times the diameter of the Earth orbiting the star at about 165 million kilometers, 1.1 times the distance of the Sun Earth. It is right in the habitable area of the star (closer to the inner edge, but still). Previous observations indicate that there should not be a planet about 7 times the width of the Earth, so it is likely (again, if real) to be a planet around the size of Neptune or something.
They notice that it may not be a planet, but a cloud of dust. The sun, for example, has dust orbiting comets. It is weak, but it would look brighter in the middle of IR. They calculate that α Cen A would need about 60 times the amount of dust orbiting the Sun to explain the stain, which is a lot, but it has been seen that other similar stars have more, so it is not excluded.
So this is a planet orbiting α Cen A? Mayyyyyybe. In my opinion, the authors are appropriately cautious about this, do not make huge statements or draw conclusions. It seems that what they found is 1) real and b) could be a planet.
Clearly, more comments are needed. I would love to see some taken at a time when, if it is a planet, it would be on the other side of the star as it is seen from Earth due to its orbital motion. If they found him there (and nothing where they had seen him before) then I would be much more confident that he is real.
But as proof of the concept, this new camera and the methods they used are quite encouraging. We know that planets can exist around stars like the two in α Cen – our own Sun is proof of this, and we have found many planets orbiting stars in binaries – so there is no reason to believe that stars have no planets.
We need better evidence! But this is a very good start and I hope more comments will appear soon. I grew up in sci-fi, and the aliens in Alpha Centauri were so prevalent that it was almost cliché to use them (however, Zefram Cochrane). Of all the stars in the sky, I would be most excited to find planets there.