<p>It is fundamentally a question of spectral lines.</p>
<p>Type I supernovae have no hydrogen lines, and type II have strong hydrogen lines. Type 1b have strong helium lines and no hydrogen lines, and type 1c have neither helium nor hydrogen lines. That’s why they aren’t designated as type II supernovae. The reason why type 1b and 1c supernovae have no hydrogen lines is because they’ve been stripped of the hydrogen of their outer envelope before core collapse (and in the case of 1c, their helium envelope as well).</p>
<p>They have this lack of hydrogen lines in common with type 1a supernovae, but distinctly lack silicon lines.</p>
<p>Naturally type 1b and 1c super novae will be smaller than a type II if they are imagined to have the same starting mass somehow pre-envelope loss, because there will be less material to collapse, and so less material to be thrown out.</p>

CC BY-SA 4.0
2021-11-15T07:50:53.317Z
And, of course, the basic spectroscopy-based naming scheme was devised and in use long before our understanding of the underlying physics.
Peter Erwin
CC BY-SA 4.0
2021-11-15T08:15:12.877Z
Did I read "...silicone..." correctly?
Stu Smith
CC BY-SA 4.0
2021-11-15T09:03:39.167Z
@StuSmith: Yes, but no.
planetmaker
CC BY-SA 4.0
2021-11-15T23:04:55.917Z
Haha thanks @planetmaker ! A silly little typo
Justin T
CC BY-SA 4.0
2021-11-15T05:03:04.650Z
2021-11-15T09:02:29.093Z
2021-11-15T09:02:29.093Z
Justin T
<p>What similarities do types Ib and Ic supernovae have in common with type 1a?</p>
<p>Are their spectra or their magnitudes more similar to accreting white dwarfs than the other supermassive, main sequence, exploding-at-the-ends-of-their-lives stars?</p>
<p>Are types 1a and 1b 'smaller' than type 2?</p>
<p>I am confused.....</p>

<observational-astronomy><supernova><classification><stellar-classification><explosion>
Why are type 1b and type 1c supernovae called type 1 rather than type 2; if they result from large exploding stars, rather than accreting dwarfs?
Kurt Hikes
# Why are type 1b and type 1c supernovae called type 1 rather than type 2; if they result from large exploding stars, rather than accreting dwarfs?

(Asked by: username_0 on 2021-11-15)

What similarities do types Ib and Ic supernovae have in common with type 1a?

Are their spectra or their magnitudes more similar to accreting white dwarfs than the other supermassive, main sequence, exploding-at-the-ends-of-their-lives stars?

Are types 1a and 1b 'smaller' than type 2?

I am confused.....

**Tags:** observational-astronomy, supernova, classification, stellar-classification, explosion

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## 1 answers

### Answer by username_1 on 2021-11-15. Score: 11

It is fundamentally a question of spectral lines.

Type I supernovae have no hydrogen lines, and type II have strong hydrogen lines. Type 1b have strong helium lines and no hydrogen lines, and type 1c have neither helium nor hydrogen lines. That’s why they aren’t designated as type II supernovae. The reason why type 1b and 1c supernovae have no hydrogen lines is because they’ve been stripped of the hydrogen of their outer envelope before core collapse (and in the case of 1c, their helium envelope as well).

They have this lack of hydrogen lines in common with type 1a supernovae, but distinctly lack silicon lines.

Naturally type 1b and 1c super novae will be smaller than a type II if they are imagined to have the same starting mass somehow pre-envelope loss, because there will be less material to collapse, and so less material to be thrown out.

> **Comments:**
> **username_2**: And, of course, the basic spectroscopy-based naming scheme was devised and in use long before our understanding of the underlying physics.  
> **username_3**: Did I read "...silicone..." correctly?  
> **username_4**: @StuSmith: Yes, but no.  
> **username_1**: Haha thanks @planetmaker ! A silly little typo  

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