Supernova Destroys Star Rho Cas
A Last Silent yet Bright Explosion Spews Star-Stuff Deep into Space
10,000 light years away, the yellow hypergiant star, Rho Cassiopeiae ("Rho Cas" a type F8-G2 Ia0 star,) has a fantastic chance of already having blown itself apart.
Time = Distance
According to Dr. Garik Israelian, a member of the team examining Rho Cas, using the Utrecht Echelle Spectrograph on the William Herschel Telescope: “given the large distance it is possible that Rho [Cas] has already exploded and become a black hole or a neutron star.”
A light year is distance not time. Most are comfortable using “year” with respect to time, but in celestial cases a light year is the distance light travels, in a vacuum, in one year or 9.461 x 10 to 12th-power kilometers (5.9 trillion miles.) Rho Cas is 59.1 quadrillion miles away from Earth (59.1 with 15 zeros after it.) It is a long way away and even with light traveling at 298,000 km/sec (186,000 m/sec) it still takes the light 10,000 years to get here.
In essence, the star’s deathand destruction may well have happened thousands of years ago but still it may take years for us to see the final explosion.
Evidence
Rho Cas (F8-G2 Ia0) belongs to a rare class of post red hypergiant stars, called yellow hypergiants. Neither cool like red hypergiant Yad al-Jauza (aka Betelgeuse, 14 solar masses at 5,000 degrees K) nor hot like blue hypergiant Suhail Hadar (aka Zeta Puppis, 59 solar masses at 42,000+ degrees K); Rho Cas (20-40 solar masses at 7,000-5,000 degrees K) is only 1 of an extremely small sample of these stars in our galaxy.
One of the brightest hypergiants in our Milky Way; Rho Cas has been exemplifying the classic characteristics of a pending progenitor for a Type 1b or II supernova.* During a complete pulsation cycle in 2003-2004, observations were made that saw Rho Cas brighten from 4.6 to 3.4 magnitude. After the 2000-2001 outburst, emissions decreased to as low as 5.4. In essence it was nearly invisible to the naked eye (6.0 being the assumed lowest unaided visual limit on the modified Hipparchus scale.)
Messers. Gorlova et al. studies data from 3 compression/expansion cycles of Rho Cas (1979–1981, 1987-1989and 2000–2004) which indicated increased variability during the cycles.
Location
As we look up at the star tonight we still see Rho Cas shinning at an apparent magnitude of 4.5. While this type of hypergiant Ia0 is at the top of the Hertzsprung-Russell absolute magnitude chart (about -9.0 in our case) the dispersal of light over 10,000 light years reduces the effect by 465,661 times (2.5 to the 13.5 power.)
Even with this loss of brightness we can still easily see her. Find the constellation Cassiopeia in the Northern sky. It looks like the letter “W” lying on its side pointing to the east and down. Then draw a line from the left tip to the right tip of the "W." Extend the line a little and you will see two vertical stars. One slightly above the right tip of the "W" and one slightly below the right tip of the "W." The extended line will nearly bisect these two stars and go throw another star. That middle star, the one between the other two stars on the right of the “W” is Rho Cas!
* The uncertainty arises due to the large amount of atmospheric shell that was expelled in the 2000 outburst (argument for Type 1b SN), but the remaining relatively high H spectral lines observed in 2003 argue for Type II. With high Ca, K & Mg lines it appears Type 1b may be in store after she expels more atmosphere.
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- Dr. Israelian, Garik. 31 January 2003 “The William Herschel Telescope Finds The Best Candidate for a Supernova Explosion”. Isaac Newton Group of Telescopes. 30 July 2007
- Drs. Nadya Gorlova, Alex Lobel, Adam Burgasser, George Rieke, Ilya Ilyin, and John R. Stauffe. “On the CO Near-Infrared Band and the Line-splitting Phenomenon in the Yellow Hypergiant Cassiopeiae”. The Astrophysical Journal, 651:1130-1150, July 7 2006, reprinted November 10 2006. Section 2 Observations and Data Reduction subsection 2.2 Optical Spectroscopy p. 7. The American Astronomical Society 2006
- Ibid. Gorlova, “5.1. Comparing CO with Peculiar Atomic Lines” p. 16-18.
