New Largest Know Star in the Universe-Stephenson 2-18

a reply to: CraftyArrow

Stephenson 2-18 could possibly be a black-hole,

Don't black holes usually form an accretion disk? Never heard of an accretion sphere.


It seems to fit the spectral signature of a red giant quite well, and it's the largest of a "family" group. There is a good chance it will end up as a black hole, but there isn't much to indicate that it is one now.

originally posted by: Phage
a reply to: CraftyArrow

Stephenson 2-18 could possibly be a black-hole,

Don't black holes usually form an accretion disk? Never heard of an accretion sphere.


It seems to fit the spectral signature of a red giant quite well, and it's the largest of a "family" group. There is a good chance it will end up as a black hole, but there isn't much to indicate that it is one now.

It might have an accretion disk, I don't think there is any high-resolution infrared images of it. It might not be near any clusters. It could be a bright supernova in it's early stages.

It could possibly be something else, only because it's unusual.

a reply to: CraftyArrow

It could be a bright supernova in it's early stages.

But it has the spectrum of a red giant.

originally posted by: Phage
a reply to: CraftyArrow

It could be a bright supernova in it's early stages.

But it has the spectrum of a red giant.

I don't see the spectral type on simbad.
Maybe I'm not reading it right?

simbad.u-strasbg.fr...*+Stephenson+2+DFK+1&submit=SIMBAD+search

Don't see any Johnson-Cousins UBVRI. I guess that means it doesn't have any visible light. Probably because it's hidden behind gas and dust etc.

It does show the infrared. JHK is infared.

J 7.150 [0.026] C 2003yCat.2246....0C
H 4.698 [0.021] C 2003yCat.2246....0C
K 2.90 [0.19] D 2003yCat.2246....0C

We could say it has the same infra spectrum as a red galaxy, is it a galaxy? Maybe, Maybe Not.

Is it a red giant? Maybe, maybe not.

Not much info to go on.

a reply to: CraftyArrow

Spectral type M1.5Iab C

Simbad

We could say it has the same infra spectrum as a red galaxy, is it a galaxy?

No.

We re-evaluated a number of classification criteria proposed in the literature for this spectral range and found that we could use our spectra to derive spectral types and luminosity classes. We measured the radial velocity of five members of RSGC3, finding velocities similar to the average for members of Stephenson 2.

www.aanda.org...

a reply to: Phage

Yeah I saw the other Identifiers, they are just comparing the infrared... so it's still maybe or maybe not.

I'm not saying it is or isn't. : P