Where exactly is the Hertzsprung Gap?

[swampwiz]

There seem to be a lot of gaps in this figure, although some streamlined depictions of the figure show a void in the shape of a thin near-right rectangle with its sides as the hypotenuse on the bottom left being the main line, the major on the top being the supergiants, and the minor on the right being the giants. Is this it? I've tried doing an internet search, but nothing definitive has come up.

 

[anorlunda]

There seem to be a lot of gaps in this figure,

I think you forgot to post the figure. I don't see any figure.

 

[davenn]

There seem to be a lot of gaps in this figure,

I think you forgot to post the figure. I don't see any figure.

Presumably this one

@swampwiz which specific gaps are you referring to ?

 

[Vanadium 50]

Is this it? I've tried doing an internet search, but nothing definitive has come up.

Not even this? https://en.wikipedia.org/wiki/Hertzsprung_gap

 

[DaveC426913]

Here is a diagram with the HG labelled.

I am a little out of my league here, but I do believe the reason it is not obvious in typical diagrams is because they don't offer a time dimension that shows evolution of stars.

Main sequence stars pass through that gap to become red giants - but because they're unstable, they do so in a short period of time.

So, if we look into the heavens we don't see a lot of them due to that short duration. i.e. there's a gap.

The above diagram makes it a little more clear how stars age, and pass through the HG.

See caveat in sig line* and please correct me if I'm wrong.

[ EDIT ]
"Stars do exist in the Hertzsprung gap region, but because they move through this section of the Hertzsprung–Russell diagram very quickly in comparison to the lifetime of the star (thousands of years, compared to tens of billions of years for the lifetime of the star), that portion of the diagram is less densely populated."
https://en.wikipedia.org/wiki/Hertzsprung_gap

So yeah.

 

[swampwiz]

Presumably this one

View attachment 255826

@swampwiz which specific gaps are you referring to ?

Yes, this it the one to which I was referring. There are other depictions of this diagram but they don't seem to show any gap - or at least one prominent gap.

 

[swampwiz]

Not even this? https://en.wikipedia.org/wiki/Hertzsprung_gap

The figure for that article didn't have an annotation, and the gap was less prominent than the one to which I was referring, so I didn't reference it. And that one to which I was referring showed no gap between the main sequence and the giant branch, so it was all quite confusing.

 

[swampwiz]

Here is a diagram with the HG labelled.
View attachment 255827

I am a little out of my league here, but I do believe the reason it is not obvious in typical diagrams is because they don't offer a time dimension that shows evolution of stars.

Main sequence stars pass through that gap to become red giants - but because they're unstable, they do so in a short period of time.

So, if we look into the heavens we don't see a lot of them due to that short duration. i.e. there's a gap.

The above diagram makes it a little more clear how stars age, and pass through the HG.

See caveat in sig line* and please correct me if I'm wrong.

[ EDIT ]
"Stars do exist in the Hertzsprung gap region, but because they move through this section of the Hertzsprung–Russell diagram very quickly in comparison to the lifetime of the star (thousands of years, compared to tens of billions of years for the lifetime of the star), that portion of the diagram is less densely populated."
https://en.wikipedia.org/wiki/Hertzsprung_gap

So yeah.

I can grok the idea that stars follow a continuous path in the diagram, and that they spend a very small amount of time moving between the branches, resulting in very few stars being observed between them. in this sense, the "gap" is really an expression of this fact.

 

[Vanadium 50]

The figure for that article didn't have an annotation

Um...if you say so. That's not what I see.

 

[Bandersnatch]

There:

 

[alantheastronomer]

The figure for that article didn't have an annotation, and the gap was less prominent than the one to which I was referring, so I didn't reference it. And that one to which I was referring showed no gap between the main sequence and the giant branch, so it was all quite confusing.

It's not explicitly labeled, but it's between Procyon on the main sequence, and Pollux on the giant branch. Physically what's going on is that hydrogen burning in the core has finished leaving an inert helium core that begins to contract. The Hertzsprung gap is a reflection of the time it takes for hydrogen to start burning in a shell around that core. Once shell burning is initiated the star then appears on the giant branch.