by Ann » Sun Aug 07, 2011 6:42 am
Greg Parker, thank you for photographing one blue and one red star to bring out their colors!
Blue Algol is one of the sky's most mythological stars, the eye of the demon, which has long been known to change in brightness. We now know that Algol is a binary, consisting of one big but dim red star and one smaller but much brighter blue star. Originally the now-red star was bright and blue, but then it ran out of fuel, expanded, cooled and turned red (really orange). It expanded so much that it filled its so-called Roche lobe (ask neufer to explain), its outer layers got very close to the compact blue component, and the blue component started siphoning off gas from the orange primary. Now the blue component has robbed its red "sibling" of so much gas that the red star has shrunk and become really dim, whereas the blue component has beefed up. We see this binary pair almost edge-on. When the red component passes in front of the bright blue star, Algol dips noticeably in brightness!
Red Rho Persei is what the orange component of Algol may once have been. It is a very cool, very big and quite bright star: no Betelgeuse, but quite bright nevertheless. It is about 400 times brighter than the Sun in visual light, and perhaps tens of thousands of times brighter in total energy output (because most of the energy produced by cool Rho Per is infrared light). And it is just barely possible that the blue component of Algol will once become as big, bright and cool as Rho Persei, although I find that slightly doubtful.
Rho Per is intrinsically brighter than Algol, but it looks dimmer, because it is more than three times farther away.
Well, what a fascinating stellar duo (or trio) you photographed for us, Greg!
Ann
Greg Parker, thank you for photographing one blue and one red star to bring out their colors! :D
Blue Algol is one of the sky's most mythological stars, the eye of the demon, which has long been known to change in brightness. We now know that Algol is a binary, consisting of one big but dim red star and one smaller but much brighter blue star. Originally the now-red star was bright and blue, but then it ran out of fuel, expanded, cooled and turned red (really orange). It expanded so much that it filled its so-called Roche lobe (ask neufer to explain), its outer layers got very close to the compact blue component, and the blue component started siphoning off gas from the orange primary. Now the blue component has robbed its red "sibling" of so much gas that the red star has shrunk and become really dim, whereas the blue component has beefed up. We see this binary pair almost edge-on. When the red component passes in front of the bright blue star, Algol dips noticeably in brightness!
Red Rho Persei is what the orange component of Algol may once have been. It is a very cool, very big and quite bright star: no Betelgeuse, but quite bright nevertheless. It is about 400 times brighter than the Sun in visual light, and perhaps tens of thousands of times brighter in total energy output (because most of the energy produced by cool Rho Per is infrared light). And it is just barely possible that the blue component of Algol will once become as big, bright and cool as Rho Persei, although I find that slightly doubtful.
Rho Per is intrinsically brighter than Algol, but it looks dimmer, because it is more than three times farther away.
Well, what a fascinating stellar duo (or trio) you photographed for us, Greg! :D
Ann