Carbon is essential for life on Earth and it takes numerous forms but when a star gets really old and runs out of gas, carbon shows up. Stars begin their lives by fusing hydrogen nuclei and the good news is there’s lots of hydrogen to fuse. Fast forward many billions of years and the hydrogen party is about over but now there’s a bunch of helium, the byproduct of hydrogen fusion. Helium works too, but it takes more energy. Thanks to gravity the helium rich star’s core gets squeezed as the outward force of hydrogen fusion wanes. This gravity squeeze produces enough energy to get helium fusing and our star parties on.
The helium party however produces a bunch of oxygen and carbon and the carbon can get swept up into our star’s atmosphere. Over time the atmospheric carbon accumulates, and along with the star’s lower atmospheric temperature make for a nice red star, redder than typical red giant stars. Surrounding dust also helps diffuse light to make this star appear very red. We call them carbon stars and they’re beautiful.
But there’s more.
We know about red dwarf stars and what makes them tick, but dwarf carbon stars didn’t exist, couldn’t exist. That changed in the mid-1970s. Until then carbon stars were all thought to be giants. Astronomers in Arizona studied what they thought was a normal red giant carbon star in the constellation Taurus. Its name, a pretty inauspicious G77-61. Astronomers were studying this star to better understand carbon stars but noticed something peculiar. It was close, only 255 light years away, but it was very dim. So, they thought it had to be a red dwarf star. But its spectrum was different from red dwarf stars and more like red giant carbon stars.
When the astronomers mentioned this anomaly to other astronomers they were dismissed, told to go back and get their measurements right. You see, red dwarf stars fuse hydrogen into helium and have little carbon so this cannot be a dwarf carbon star…unless… Unless there’s another culprit in this little caper, and it appears there is a suspect. A white dwarf.
Many stars are born in pairs, so the theory of dwarf carbon star formation starts with two stars, one a brilliant blue star a few times the mass of our Sun, and a red dwarf. The blue star evolves like our Sun but faster, eventually running out of hydrogen, then fusing helium into oxygen and carbon. This star sheds mass, including carbon as it goes through typical gravity vs. fusion gyrations. Some carbon gets captured by the red dwarf and over time (billions of years) the red dwarf becomes carbon loaded.
It’s a dwarf carbon star now!
What’s in the Sky?
March 8; 2am = 3am: Spring forward, it’s daylight savings
March 11-25; an hour after sunset; west: Cone shaped zodiacal light rises from the horizon.