<p>The rate is evolving with time (and consequently with redshift). According to a paper in 2005 by Evan Scannapieco &amp; Lars Bildsten (<a href="https://arxiv.org/abs/astro-ph/0507456" rel="nofollow noreferrer">https://arxiv.org/abs/astro-ph/0507456</a>), the rate of SNe Ia is 1 to 3.5×10<sup>4</sup> per yr per Mpc<sup>3</sup> at z=2, which is the peak rate. </p>

<p>You can very roughly consider it as 1 to 3.5 events in a galaxy in 10,000 years.
Considering there are so many galaxies in our observable universe, you can still observe some in each year. With more powerful telescopes and strategies, there will more and more SNe Ia be observed. They are dimmer, but more. Probably, more than once per day.</p>

CC BY-SA 4.0
2024-02-17T18:22:13.290Z
I don't understand how you got your inferred supernova rates within a galaxy. They look 2 orders of magnitude too small to me.
ProfRob
CC BY-SA 4.0
2024-02-25T17:02:47.800Z
You are confused by the units. The rate is per cubic Mpc, not per galaxy. Look instead at Fig 1, which suggests a minimum rate of 0.3 per century in a galaxy with as many stars as the Milky Way.
ProfRob
CC BY-SA 4.0
2020-01-23T01:06:06.747Z
2020-01-23T01:47:24.720Z
2020-01-23T01:47:24.720Z
Yuan-Chuan Zou
<p>I have a much different answer. I'm taking a course in Astrophysics and the instructors took the approach of using the amount of iron in our galaxy to calculate the number of SN since galaxy was formed. They found how many SN it would take to produce that much iron. According to their calculations you need about 1 SN every 50 years from the Milky Way.</p>

CC BY-SA 4.0
2020-01-23T20:11:27.380Z
I don't think that's "much different" from the other answers. Can you show the calculation?
pela
CC BY-SA 4.0
2020-01-23T21:06:04.067Z
This is indeed a valid and more direct cross-check of results for the Milky Way (since we have not been able to observe enough Type Ia supernovae in the MW to count directly). However, could you give a reference for the calculation and be clear whether this results applies to Type Ia supernovae (which is what the question is asking about) or all supernovae. Another point is that this presumably then is an average rate over the lifetime of the Galaxy? If so, the current rate is likely to be significantly lower.
ProfRob
CC BY-SA 4.0
2020-01-24T18:46:34.653Z
The course is a series of video lectures.  they are located here: https://courses.edx.org/courses/course-v1:ANUx+ANU-ASTRO1x+2T2016/courseware/58c9d12675784e03af620827fcea5bad/04691a84185b4c48b8ae121a7e0cd764/3?activate_block_id=block-v1%3AANUx%2BANU-ASTRO1x%2B2T2016%2Btype%40vertical%2Bblock%4002bcea3bb1db424bac4fb4e9cdeb8a23. This links takes you to the video before the one of interest. So scroll to the top of page and select the next lecture.
Natsfan
CC BY-SA 4.0
2020-01-24T18:54:04.410Z
The calculation is for type II sn which they state accounts for 1/3 of all the iron, and yes they use the lifetime of the universe.
Natsfan
CC BY-SA 4.0
2020-01-25T17:57:00.803Z
So @jmh, it isn't an answer to this question.
ProfRob
CC BY-SA 4.0
2020-01-25T22:55:19.160Z
what isn't an answer. My answer is an answer but it may be wrong.
Natsfan
CC BY-SA 4.0
2020-12-15T22:31:11.550Z
It isn;t an answer to "How often do type Ia supernovae typically occur in a galaxy ?"
ProfRob
CC BY-SA 4.0
2020-01-23T19:35:26.503Z
2020-01-23T19:35:26.503Z
Natsfan
<p>There is a lot of scope to provide a very detailed answer here. The rate depends on what sort of a galaxy you are considering and when, what its star formation rate is (or was) and what its total stellar mass is.</p>

<p>A good reference is the Annual Review of Astrophysics article by <a href="https://arxiv.org/abs/1312.0628" rel="noreferrer">Maoz et al. (2019)</a>. This says that for a Sbc galaxy like the Milky Way, the <em>specific rate</em> ( the rate per unit of stellar mass in the galaxy) of type Ia supernovae is <span class="math-container">$10^{-13}$</span> per year per solar mass of stars. For a Milky Way stellar mass of <span class="math-container">$\sim 6\times 10^{10} M_\odot$</span>, this means a rate of 0.006 per year, or one type Ia SNe every <span class="math-container">$\sim 200$</span> years.</p>

<p>In the local universe this rate scales as about <span class="math-container">$M^{-0.5}$</span>, where <span class="math-container">$M$</span> is the galaxy mass (valid over about 5 orders of magnitude for <span class="math-container">$M&gt;10^7 M_\odot$</span>; <a href="https://arxiv.org/abs/1810.00011" rel="noreferrer">Brown et al. 2018</a>). So the specific rate of type Ia supernovae is larger in smaller galaxies.</p>

<p>The rate also decays after a galaxy is formed, or after a burst of star formation as something like <span class="math-container">$t^{-1}$</span>.</p>

CC BY-SA 4.0
2020-01-22T04:38:44.193Z
This answer hurt my brain with all the math and astronomy going on here, especially when contemplating that we have actually calculated this sort of thing and can use it to calculate subsequent events. I like it.
Doktor J
CC BY-SA 4.0
2020-01-22T23:53:59.750Z
Interestingly, nasa.gov says "Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way."
Victor Stone
CC BY-SA 4.0
2020-01-23T00:03:16.523Z
@VictorStone the rate of type Ia supernovae must of course be smaller than the rate of (all) supernovae And is probably smaller than the rate of core collapse (type II) supernovae.
ProfRob
CC BY-SA 4.0
2024-02-25T14:15:23.510Z
"supernova rate per star mass per galaxy mass" is a strange choice to leave as that... why not to simplify for the reader and multiply by galaxy mass to get supernova rate scaling as sqrt of galaxy mass?
Noone AtAll
CC BY-SA 4.0
2024-02-25T16:46:32.943Z
@NooneAtAll I have not used the words or the units you have put in quotes.
ProfRob
CC BY-SA 4.0
2024-02-27T17:38:32.910Z
@ProfRob 1)"the specific rate (the rate per unit of stellar mass in the galaxy)" 2)"this rate scales as $M^{-0.5}$, where M is the galaxy mass"
Noone AtAll
CC BY-SA 4.0
2024-02-27T17:48:28.237Z
to calculate reasonable for noobies measure "number of supernovas per year in a specific galaxy" from your answer, one has to multiply rate by galaxy mass. EXCEPT rate itself is also a function of mass, so reader has to double check what to multiply/devide by, find that it's to divide by sqrt of same galaxy mass and carry on. Why not to make life easier for the reader?
Noone AtAll
CC BY-SA 4.0
2024-02-28T10:42:17.203Z
@NooneAtAll One could do that, but you would be conflating two pieces of work that have measured the stellar mass of galaxies in different ways. and using different assumptions. The second piece of work also does not give absolute specific supernova rates and is not  only considering Sbc galaxies. All work on supernova rates uses the rate per unit stellar mass as the quantity of interest.
ProfRob
CC BY-SA 4.0
2020-01-21T20:24:46.537Z
2020-01-23T00:04:48.107Z
2020-01-23T00:04:48.107Z
ProfRob
<p>Type Ia supernova are used as <a href="https://en.wikipedia.org/wiki/Cosmic_distance_ladder" rel="noreferrer">standard candles</a>. But they also are transient events. This means that to determine the distance of a galaxy using supernovae, you have to wait for one to occur. How often do type Ia supernovae typically occur in a galaxy ?</p>

CC BY-SA 4.0
2020-01-21T18:49:58.503Z
Some things really.....    https://en.wikipedia.org/wiki/History_of_supernova_observation
Carl Witthoft
CC BY-SA 4.0
2020-01-21T19:48:12.340Z
Don't think the Wikipedia article answers the OP's question, it seems to mostly discuss very local supernovae. I read it as asking for the supernova rate in galaxies generally (which is a function of redshift, metallicity and galaxy type) rather than in the Milky Way specifically
astrosnapper
<supernova>
How often do Type Ia supernovae occur?
usernumber
# How often do Type Ia supernovae occur?

(Asked by: username_0 on 2020-01-21)

Type Ia supernova are used as [standard candles](https://en.wikipedia.org/wiki/Cosmic_distance_ladder). But they also are transient events. This means that to determine the distance of a galaxy using supernovae, you have to wait for one to occur. How often do type Ia supernovae typically occur in a galaxy ?

**Tags:** supernova
> **Comments:**
> **username_1**: Some things really.....    https://en.wikipedia.org/wiki/History_of_supernova_observation  
> **username_2**: Don't think the Wikipedia article answers the OP's question, it seems to mostly discuss very local supernovae. I read it as asking for the supernova rate in galaxies generally (which is a function of redshift, metallicity and galaxy type) rather than in the Milky Way specifically  

---

## 3 answers

### Answer by username_4 on 2020-01-21. Score: 31 | Accepted answer

There is a lot of scope to provide a very detailed answer here. The rate depends on what sort of a galaxy you are considering and when, what its star formation rate is (or was) and what its total stellar mass is.

A good reference is the Annual Review of Astrophysics article by [Maoz et al. (2019)](https://arxiv.org/abs/1312.0628). This says that for a Sbc galaxy like the Milky Way, the *specific rate* ( the rate per unit of stellar mass in the galaxy) of type Ia supernovae is $10^{-13}$ per year per solar mass of stars. For a Milky Way stellar mass of $\sim 6\times 10^{10} M\_\odot$, this means a rate of 0.006 per year, or one type Ia SNe every $\sim 200$ years.

In the local universe this rate scales as about $M^{-0.5}$, where $M$ is the galaxy mass (valid over about 5 orders of magnitude for $M>10^7 M\_\odot$; [Brown et al. 2018](https://arxiv.org/abs/1810.00011)). So the specific rate of type Ia supernovae is larger in smaller galaxies.

The rate also decays after a galaxy is formed, or after a burst of star formation as something like $t^{-1}$.

> **Comments:**
> **username_7**: This answer hurt my brain with all the math and astronomy going on here, especially when contemplating that we have actually calculated this sort of thing and can use it to calculate subsequent events. I like it.  
> **username_8**: Interestingly, nasa.gov says "Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way."  
> **username_4**: @VictorStone the rate of type Ia supernovae must of course be smaller than the rate of (all) supernovae And is probably smaller than the rate of core collapse (type II) supernovae.  
> **username_9**: "supernova rate per star mass per galaxy mass" is a strange choice to leave as that... why not to simplify for the reader and multiply by galaxy mass to get supernova rate scaling as sqrt of galaxy mass?  
> **username_4**: @NooneAtAll I have not used the words or the units you have put in quotes.  
> **username_9**: @ProfRob 1)"the specific rate (the rate per unit of stellar mass in the galaxy)" 2)"this rate scales as $M^{-0.5}$, where M is the galaxy mass"  
> **username_9**: to calculate reasonable for noobies measure "number of supernovas per year in a specific galaxy" from your answer, one has to multiply rate by galaxy mass. EXCEPT rate itself is also a function of mass, so reader has to double check what to multiply/devide by, find that it's to divide by sqrt of same galaxy mass and carry on. Why not to make life easier for the reader?  
> **username_4**: @NooneAtAll One could do that, but you would be conflating two pieces of work that have measured the stellar mass of galaxies in different ways. and using different assumptions. The second piece of work also does not give absolute specific supernova rates and is not  only considering Sbc galaxies. All work on supernova rates uses the rate per unit stellar mass as the quantity of interest.  

---

### Answer by username_3 on 2020-01-23. Score: 3

The rate is evolving with time (and consequently with redshift). According to a paper in 2005 by Evan Scannapieco & Lars Bildsten (<https://arxiv.org/abs/astro-ph/0507456>), the rate of SNe Ia is 1 to 3.5×104 per yr per Mpc3 at z=2, which is the peak rate.

You can very roughly consider it as 1 to 3.5 events in a galaxy in 10,000 years.
Considering there are so many galaxies in our observable universe, you can still observe some in each year. With more powerful telescopes and strategies, there will more and more SNe Ia be observed. They are dimmer, but more. Probably, more than once per day.

> **Comments:**
> **username_4**: I don't understand how you got your inferred supernova rates within a galaxy. They look 2 orders of magnitude too small to me.  
> **username_4**: You are confused by the units. The rate is per cubic Mpc, not per galaxy. Look instead at Fig 1, which suggests a minimum rate of 0.3 per century in a galaxy with as many stars as the Milky Way.  

---

### Answer by username_5 on 2020-01-23. Score: -1

I have a much different answer. I'm taking a course in Astrophysics and the instructors took the approach of using the amount of iron in our galaxy to calculate the number of SN since galaxy was formed. They found how many SN it would take to produce that much iron. According to their calculations you need about 1 SN every 50 years from the Milky Way.

> **Comments:**
> **username_6**: I don't think that's "much different" from the other answers. Can you show the calculation?  
> **username_4**: This is indeed a valid and more direct cross-check of results for the Milky Way (since we have not been able to observe enough Type Ia supernovae in the MW to count directly). However, could you give a reference for the calculation and be clear whether this results applies to Type Ia supernovae (which is what the question is asking about) or all supernovae. Another point is that this presumably then is an average rate over the lifetime of the Galaxy? If so, the current rate is likely to be significantly lower.  
> **username_5**: The course is a series of video lectures.  they are located here: https://courses.edx.org/courses/course-v1:ANUx+ANU-ASTRO1x+2T2016/courseware/58c9d12675784e03af620827fcea5bad/04691a84185b4c48b8ae121a7e0cd764/3?activate_block_id=block-v1%3AANUx%2BANU-ASTRO1x%2B2T2016%2Btype%40vertical%2Bblock%4002bcea3bb1db424bac4fb4e9cdeb8a23. This links takes you to the video before the one of interest. So scroll to the top of page and select the next lecture.  
> **username_5**: The calculation is for type II sn which they state accounts for 1/3 of all the iron, and yes they use the lifetime of the universe.  
> **username_4**: So @jmh, it isn't an answer to this question.  
> **username_5**: what isn't an answer. My answer is an answer but it may be wrong.  
> **username_4**: It isn;t an answer to "How often do type Ia supernovae typically occur in a galaxy ?"  

---

