620 ly away, a planet 3x the mass & 2x the diameter of Jupiter orbits so close to its star that temps reach 4600 K. That's ~1000 K higher than most stars! This heat allowed astronomers to, for the 1st time, find atomic iron & titanium in its atmosphere.
space.com/41501-iron-and…
space.com/41501-iron-and…
(GIF from video in the link above, which was uploaded by Vanderbilt University)
Titanium has been detected in atmospheres of exoplanets, but bc they aren't as hot, never in its atomic form. Exoplanets with temps over 2000 K are called "Ultrahot Jupiters", this one is by far the hottest. Detecting atomic Titanium and Iron are a really big deal.
No, we won't find life on this scorching planet dubbed KELT-9b, but learning about exoplanets and their compositions can help us get a better picture of how planets form, why they gave the masses they do, etc. It helps complete the story of the birth of star systems.
Now, back to that insane tempetature: This planet, with temperatures reaching 4600 K, is (as mentioned above) hotter than most stars. But wait, what are the most common stars, and what are their temperatures?
You might think the most common star is Sun-like, but our Sun, ~5800 K, is rather rare. The most common stars are red dwarfs, only 0.08 to 0.5x the mass of the Sun. These stars are much less massive, and thus only reach temperatures of 2500 K to 4000 K.
But their small masses also mean that they burn fuel at a far lower rate than more massive stars. The least massive stars have a lifetime of trillions of years, far longer than the age of the Universe!
The Sun has a lifetime of about 10 billion years, so about 5 billion left in our hydrogen fusing friend. (And we're about to learn a whole lot more about this star thanks to the Parker Solar Probe!! 🛰🌞)
By contrast, the most massive stars with ~100x the mass of the Sun, will burn out their fuel in a few million years. Again, the age of the Universe is ~13.8 billion years, so a few million isn't even a grain of sand on the cosmic lifetime scale.
So clearly, the least massive stars outlive the most massive ones, which is one reason why they're the most common: the most massive stars burn their fuel out too quick to stick around long enough!
This is because luminosity goes like the mass^4, so a small increase in mass -> large increase in luminosity. And the lifetime of a star is (very roughly) proportional to its mass divided by its luminosity, so a little change in mass makes a huge difference.
Because we said L ~ M^4, and lifetime (in solar lifetimes) goes like M/L which is M/M^4, meaning the lifetime of a star goes like 1/M^3; that is, it goes like the *inverse* of its mass cubed!
(Disclaimer: this is a very rough estimate; things change when you're dealing with really massive or really light stars, but it's a good way to show just how much mass makes a difference in the lifetime of a star)
But massive stars are also far more difficult to make, so not only is it easier to make stars that are less massive, but they also by far outlive those that are very massive! This is why red dwarfs are the most common stars.
And this scorching hot planet is nearly 1000 K hotter than most stars bc of its proximity to its host star. That doesn't make it a star---to be a star, an object must be massive enough to ignite hydrogen fusion---but it makes it one darn hot planet. The Universe is awesome 😎
