Description: Vega is arguably one of the prettiest stars in the night sky. It is one of the brightest stars in the sky. A paper just published suggests that it may have a planet orbiting it. If so, it would be very interesting. On the one hand, very few planets have been found around stars like it. On the other hand, it will be incredibly hot, the second hottest planet ever discovered, hotter than some stars.
Vega radiates a bright blue glow, like a dazzling sapphire marking the position of Lyra in the northern starry sky. It is one of the brightest stars in the night sky, due to the fact that it is so close to us, only 25 light-years away, and self-illuminating, which releases more than 40 times the energy of the sun.
A paper that has just been published suggests that it is possible — just possible — to have a planet of its own. If that were the case, it would be interesting, and not just because we could send Judy Foster to explore. First, very few planets like it have been found around stars. Second, it will be outrageously hot, probably the second hottest planet has been discovered, hotter than some stars.
Vega is a so-called A-type star with a mass and about twice the size of the Sun. It is very young, about 700 million years old (the sun is 4.6 billion years old), and rotates very fast. In fact, it rotates so fast that it becomes somewhat flattened, and the equatorial diameter is about 10% longer than the distance between the poles. Coincidentally, we are in a position almost opposite its poles, in the same straight line as its axis of rotation. This is important, and I'll elaborate on that later.
Vega, one of the brightest stars in the sky, emits a distinctive bright blue glow that is recognizable to the naked eye.
The astronomers who published the paper studied more than 1,500 spectral maps of Vega over a decade. A spectrometer can measure an object's corresponding brightness based on its wavelength (color) and can tell you a lot of information about the star including its temperature, mass, spin, chemical composition, age, and even in some cases whether it has a planet or not.
Much of their work is focused on observing the star itself, investigating its surface activity such as sunspots. But the same spectrum can also be used to find planets. It's not wrong to say that planets move around stars, but it's more accurate to say that they all move around the center of their mass, which astronomers call the center of mass. Planets orbit larger and stars have smaller orbits, and the proportion of orbital size is commensurate with the ratio of their mass.
The motion of stars is sometimes detected by spectrometers because their spectra produce periodic Doppler shifts. This method is called the reflection velocity method, and it works best when planets are massive and stars are less massive because the motion of stars can be relatively maximized. Vega is a massive star, so this method is more difficult to use.
In addition, Doppler shifts also occur as stars move closer to or farther away from us, so this effect is maximized when we look at the orbits of planets from the side. As I mentioned earlier, we observe Vega at an angle very close to its axis of rotation, so this effect is minimized. This is very frustrating.
However, by looking at all the data, they found a faint signal. It occurs periodically every 2.43 days. By calculating that the probability of them finding a false positive is 1%, it means that there is a 99% chance that it is not a false positive. However, because the signal is too weak, they cannot determine its authenticity.
The illustration shows a giant gaseous planet orbiting a star larger and hotter than the Sun at great close range. Due to the intense light and heat of the star, the planet is losing its atmosphere. Editor: NASA/JPL-Caltech
But if true, then it could come from a Vega planet. Its mass is at least 20 times that of Earth, and it is more likely. This would make it a giant gaseous planet, and very close to Vega to reach higher orbital velocities. Being close to a star with a temperature of 10,000°C means that the planet's own temperature drops to nearly 3,000°C! This is hotter than many red dwarfs, and only planet KELT-9b is hotter than it, at about 3800°C. If it were a giant gaseous planet, its heat would cause it to expand significantly, even if it was as massive as Neptune or Jupiter.
Note that it is important to be clear that it may not be a planet. For stars like Vega, this type of analysis is tricky, and the team is also very careful to point out that they can't get definitive results yet. Even if it were true, it would be great. Only a handful of planets with the same or greater mass as Vega have been discovered, so each planet we find contributes to our in-depth understanding of it.
In addition, we know that Vega is surrounded by a huge dust disk. It has a sharp inner rim that is more than 10 billion kilometers long and extends outward for about 30 billion kilometers. It may have come from a collision between asteroids, and its inner rim may have been cut by the gravitational pull of a nearby large planet sweeping through the dust. So, this is already direct evidence that there is already some planetary system around Vega.
It's not easy to affirm or deny the existence of the planet, which requires a lot of observations using equipment specifically designed to find planetary signals. I'd love it to really exist, but it depends on where the data points us. Hopefully it will point us to the planets.
Anyway, it makes me want to revisit the movie "Time-Lapse Contact" again.
* I'm going to talk about first author Spencer Hurt, who is still just a college undergraduate! He is currently studying in the Department of Astrophysics and Planetary Sciences at the University of Colorado. When I was still in college astronomy I could have picked up a telescope and pointed it at Vega, but the job might have been beyond my reach, lol. So I was quite impressed with him.
BY: Phil Plait
FY: Rose in the palm of your hand
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