This image from Wikipedia shows that main sequence stars above 1.5 solar masses have a convective core and a radiative envelope. The surface of our sun grainy because of convection cells right below the photosphere. But massive main sequence stars wouldn't have this, since they don't have convective envelopes, right? So what would their surface look like?
$\begingroup$
$\endgroup$
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
We do have some images of stars with a radiative envelope. Altair has a mass of 1.86 solar masses. We do have an image of it: 
There aren't any convective granules visible in this image, but the resolution is probably too low to show them, if there are any. One difference that can be analyzed is the magnetic field of the star. However, there are many ways magnetic fields can be generated in massive stars. This Article states that Core dynamo processes, sub-surface convective layers, fossil fields, or failed fossil fields can create the magnetic field. The absence of a magnetic field would indicate less solar activity, including no starspots, faculae, or mass ejections. However, it is shown that massive stars can have a magnetic field, even thought it might be weaker than other stars'.
Massive stars would probably lack the solar granules as shown here: 
But sub-surface magnetic fields detailed in the article above (caused by an iron peak) can cause some granules. Granules are created by the tops of convection zones, but the absence of these would cause MS stars above 1.5 solar masses to lack these, except those caused by the iron peak.
In conclusion, stars with a radiative envelope would lack convective granules, starspots, faculae, and coronal mass ejections, although those are still possible with sub-surface convection.
Something else to be considered is that radiation is more efficient than convection, so the luminosity of these radiative stars would be higher than a similar convective star of the same mass.
