<p>Potentially, a short (less than a second) burst of gravitational waves (GWs) would be detected. Much depends on asymmetries in the core collapse, since a spherically symmetric collapse would not produce GWs (e.g. <a href="https://arxiv.org/abs/1801.01914" rel="nofollow noreferrer">Morozova et al. 2019</a>). However, theoretical models suggest that the GWs start at low frequency (tens of Hz) and are associated with the core bounce at the end of core collapse. After about half a second the frequencies rise to about 1kHz and are associated with oscillations of the proto-neutron star at the centre and then contunue to rise, but weaken in amplitude after that. Since LIGO is sensitive from about 20Hz to a few kHz, then only the initial phase that lasts a few tenths of a second would likely be detectable, but since GWs can travel through the star (and at the speed of light) without much hindrance they will indicate the moment of core collapse quite accurately.</p>
<p>The theoretical calculations referenced above suggest GW amplitudes of <span class="math-container">$h_{+}d \sim 10$</span>, where <span class="math-container">$h_{+}$</span> is the dimensionless GW strain and <span class="math-container">$d$</span> is the distance to the supernova in cm. Betelgeuse is at a distance of <span class="math-container">$\sim 6 \times 10^{20}$</span> cm (600 light years), so the strain at the detector would be <span class="math-container">$h_{+} \sim 2\times 10^{-20}$</span>. LIGO is sensitive to strains of above <span class="math-container">$10^{-23}$</span> in this frequency range, so there should be no problem (according to these models) in detecting such an event.</p>
<p>If they were produced with detectable strength, then they should be received <em>at the same time</em> as an anticipated neutrino burst. The difference would be that the neutrino burst should extend over about 10 s. That is because the dense centre of a supernova is opaque even to neutrinos (but not gravitational waves) for that period and so they &quot;leak out&quot; over that duration.</p>
<p>The electromagnetic signature of the supernova (i.e. a visible light increase) would be seen a few hours after that, since that is how long it takes for energy to be transferred to the envelope of the star.</p>
<p>NB: For all practical intents and purposes, over the distance to Betelgeuse, neutrinos, along with light and gravitational waves, travel at the same speed. i.e. The delay of the (<span class="math-container">$\sim  10$</span> MeV) neutrino burst due to their non-zero (<span class="math-container">$\
&lt; 1$</span> eV) mass would be negligible. If the Lorentz factor is <span class="math-container">$10^7$</span>, then the neutrino speed is the same as the speed of light to 1 part in <span class="math-container">$2\times 10^{14}$</span>, which means they take an extra 0.1 ms to arrive from Betelgeuse compared to light speed.</p>

CC BY-SA 4.0
2019-12-26T16:16:09.313Z
Newbie question: how is a spherical ly symmetrical collapse possible, it is rotating i assume? Can core collapse happen without any effect of the torque perturbing that symmetry?
Stian
CC BY-SA 4.0
2019-12-26T17:03:34.720Z
@StianYttervik That would be axially symmetric. Spherically symmetric collapse is unlikely - as you suggest.
ProfRob
CC BY-SA 4.0
2023-02-24T08:54:28.117Z
Axial symmetry does not prohibit the production of gravitational waves.
TimRias
CC BY-SA 4.0
2023-02-24T08:58:54.563Z
For strains of the order 10 kHz, LIGO's sensitivity extends to about 10 kHz.
TimRias
CC BY-SA 4.0
2023-02-24T14:48:24.030Z
@TimRias is there a sensitivity curve that extends to 10 kHz. All the ones I can see cut-out at about 5kHz and are already a factor of 5 less sensitive at that frequency.
ProfRob
CC BY-SA 4.0
2019-12-25T23:17:13.027Z
2023-02-24T16:15:09.997Z
2023-02-24T16:15:09.997Z
ProfRob
<p>Various issues in your question:</p>

<ul>
<li><p>Betelgeuse is currently undergoing a "low-state" period, which is the combined effect of two periodic variations (See for instance <a href="http://www.astronomerstelegram.org/?read=13365" rel="noreferrer">http://www.astronomerstelegram.org/?read=13365</a>). Hence, there is no clear evidence right now that it will blow up as a core-collapse supernova, say, wihtin the next months.</p></li>
<li><p>We are able to know if a core-collapse supernova occurs before optical light reaches us thanks to the detection of neutrinos. This was the case for the famous SN1987A in the Magellanic Clouds (<a href="https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions" rel="noreferrer">https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions</a>, 2-3 hours before optical light)</p></li>
<li><p>LIGO is already operational (<a href="https://en.wikipedia.org/wiki/LIGO" rel="noreferrer">https://en.wikipedia.org/wiki/LIGO</a>)</p></li>
<li><p>As far as I can tell, the merging of two neutron stars or two black holes releases more energy and produces a stronger gravitational wave that a "simple" collapse of a massive star (but this is a non-documented opinion). But Betelegeuse being a lot closer than the current detected sources of Gravitational Waves, this might be an interesting target indeed (although, see first point...)</p></li>
</ul>

CC BY-SA 4.0
2019-12-26T16:05:49.170Z
Since Betelgeuse is about 700 light years away, it conceivably *could* have gone supernova well before LIGO became operational (or was even imagined), say 350 years ago? And we won't know until 700 years after it "actually" happened. (Ignoring relativistic concerns about simultaneity. I'm positing a useful reference frame that includes both the Sun and Betelgeuse close to relative rest.)
Ross Presser
CC BY-SA 4.0
2019-12-26T20:47:56.563Z
It would be a little better to be clear that we don't have a telescopic observation of first light from SN1987A to compare with the neutrino observations, so the delay you quote is very much an informed guess.
dmckee --- ex-moderator kitten
CC BY-SA 4.0
2019-12-26T21:35:50.417Z
I'd be a *little* bit cautious about saying that the current dimming is due to the confluence of "two periodic variations", largely because of the uncertainty in the long-term behavior - although yes, I agree with downplaying the pre-supernova hypothesis.
HDE 226868
CC BY-SA 4.0
2019-12-27T00:35:05.493Z
@HDE226868: The telegram cited by this answer seems to well document the two periodic variations by citing 25 years of data. That seems a lot more convincing than any other explanation so far.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-12-27T00:39:06.537Z
@AtmosphericPrisonEscape I'm certainly not arguing with that; I'm just saying that phrasing like "appears to be" rather than "is" would probably be more exact; though it's the most convincing, we don't know for sure.
HDE 226868
CC BY-SA 4.0
2019-12-27T06:20:28.763Z
@RossPresser If Betelgeuse is exactly 700 light years away and went supernova exactly 350 years ago, we will detect the gravitational waves from it in exactly 350 years because gravitational waves travel at the speed of light.
CJ Dennis
CC BY-SA 4.0
2019-12-27T16:04:52.847Z
@CJDennis Exactly. I wrote my comment because this answer had written "LIGO is already operational" as if it were a rebuttal of the part of OP's original question that (before editing) read "Assuming that Betelgeuse did not go supernova before LIGO became operational."
Ross Presser
CC BY-SA 4.0
2019-12-27T22:03:54.953Z
@RossPresser I think it's safe to say that all events detected by LIGO happened before it was built since building commenced 25 years ago and there are no objects we know of within 25 light years that could cause a detectable event.
CJ Dennis
CC BY-SA 4.0
2019-12-25T22:44:32.807Z
2019-12-25T22:44:32.807Z
onekiloparsec
<p>What observations can be expected from the <a href="https://en.wikipedia.org/wiki/LIGO" rel="nofollow noreferrer">LIGO</a><sup>†</sup>  gravitational wave observatory if and when Betelgeuse goes supernova?</p>
<p>Would we know that Betelgeuse has gone supernova before we see it light up our night sky?</p>
<p><sup>†</sup>or any other current or soon-to-be completed gravitational wave obervatories.</p>

CC BY-SA 4.0
2019-12-26T01:47:27.410Z
I made some small edits to your (really interesting) question, feel free to roll back or edit further, thanks!
uhoh
CC BY-SA 4.0
2019-12-26T18:14:20.233Z
The question mentions specific gravitational wave observatories. Do you require answers to take into account what the observatories are (or will be) capable of measuring, or are you looking for what could theoretically be measured, if the instruments were capable of measuring it? For instance, LIGO and VIRGO are tuned for stellar mass neutron star/black hole merger events, and may be unlikely to detect any gravitational waves from a supernova.
asgallant
CC BY-SA 4.0
2019-12-26T21:30:28.683Z
@asgallant The papers I have looked at suggest that a SN at the distance of Betelgeuse would be *easily* detected by LIGO.
ProfRob
<observational-astronomy><supernova><gravitational-waves>
What observations can be expected on LIGO if any when Betelgeuse goes supernova?
Lord Loh.
# What observations can be expected on LIGO if any when Betelgeuse goes supernova?

(Asked by: username_0 on 2019-12-25)

What observations can be expected from the [LIGO](https://en.wikipedia.org/wiki/LIGO)† gravitational wave observatory if and when Betelgeuse goes supernova?

Would we know that Betelgeuse has gone supernova before we see it light up our night sky?

†or any other current or soon-to-be completed gravitational wave obervatories.

**Tags:** observational-astronomy, supernova, gravitational-waves

> **Comments:**
> **username_1**: I made some small edits to your (really interesting) question, feel free to roll back or edit further, thanks!  
> **username_2**: The question mentions specific gravitational wave observatories. Do you require answers to take into account what the observatories are (or will be) capable of measuring, or are you looking for what could theoretically be measured, if the instruments were capable of measuring it? For instance, LIGO and VIRGO are tuned for stellar mass neutron star/black hole merger events, and may be unlikely to detect any gravitational waves from a supernova.  
> **username_3**: @username_2 The papers I have looked at suggest that a SN at the distance of Betelgeuse would be *easily* detected by LIGO.  

---

## 2 answers

### Answer by username_3 on 2019-12-25. Score: 32

Potentially, a short (less than a second) burst of gravitational waves (GWs) would be detected. Much depends on asymmetries in the core collapse, since a spherically symmetric collapse would not produce GWs (e.g. [Morozova et al. 2019](https://arxiv.org/abs/1801.01914)). However, theoretical models suggest that the GWs start at low frequency (tens of Hz) and are associated with the core bounce at the end of core collapse. After about half a second the frequencies rise to about 1kHz and are associated with oscillations of the proto-neutron star at the centre and then contunue to rise, but weaken in amplitude after that. Since LIGO is sensitive from about 20Hz to a few kHz, then only the initial phase that lasts a few tenths of a second would likely be detectable, but since GWs can travel through the star (and at the speed of light) without much hindrance they will indicate the moment of core collapse quite accurately.

The theoretical calculations referenced above suggest GW amplitudes of $h\_{+}d \sim 10$, where $h\_{+}$ is the dimensionless GW strain and $d$ is the distance to the supernova in cm. Betelgeuse is at a distance of $\sim 6 \times 10^{20}$ cm (600 light years), so the strain at the detector would be $h\_{+} \sim 2\times 10^{-20}$. LIGO is sensitive to strains of above $10^{-23}$ in this frequency range, so there should be no problem (according to these models) in detecting such an event.

If they were produced with detectable strength, then they should be received *at the same time* as an anticipated neutrino burst. The difference would be that the neutrino burst should extend over about 10 s. That is because the dense centre of a supernova is opaque even to neutrinos (but not gravitational waves) for that period and so they "leak out" over that duration.

The electromagnetic signature of the supernova (i.e. a visible light increase) would be seen a few hours after that, since that is how long it takes for energy to be transferred to the envelope of the star.

NB: For all practical intents and purposes, over the distance to Betelgeuse, neutrinos, along with light and gravitational waves, travel at the same speed. i.e. The delay of the ($\sim 10$ MeV) neutrino burst due to their non-zero ($\
< 1$ eV) mass would be negligible. If the Lorentz factor is $10^7$, then the neutrino speed is the same as the speed of light to 1 part in $2\times 10^{14}$, which means they take an extra 0.1 ms to arrive from Betelgeuse compared to light speed.

> **Comments:**
> **username_4**: Newbie question: how is a spherical ly symmetrical collapse possible, it is rotating i assume? Can core collapse happen without any effect of the torque perturbing that symmetry?  
> **username_3**: @StianYttervik That would be axially symmetric. Spherically symmetric collapse is unlikely - as you suggest.  
> **username_5**: Axial symmetry does not prohibit the production of gravitational waves.  
> **username_5**: For strains of the order 10 kHz, LIGO's sensitivity extends to about 10 kHz.  
> **username_3**: @username_5 is there a sensitivity curve that extends to 10 kHz. All the ones I can see cut-out at about 5kHz and are already a factor of 5 less sensitive at that frequency.  

---

### Answer by username_6 on 2019-12-25. Score: 7

Various issues in your question:

* Betelgeuse is currently undergoing a "low-state" period, which is the combined effect of two periodic variations (See for instance <http://www.astronomerstelegram.org/?read=13365>). Hence, there is no clear evidence right now that it will blow up as a core-collapse supernova, say, wihtin the next months.
* We are able to know if a core-collapse supernova occurs before optical light reaches us thanks to the detection of neutrinos. This was the case for the famous SN1987A in the Magellanic Clouds (<https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions>, 2-3 hours before optical light)
* LIGO is already operational (<https://en.wikipedia.org/wiki/LIGO>)
* As far as I can tell, the merging of two neutron stars or two black holes releases more energy and produces a stronger gravitational wave that a "simple" collapse of a massive star (but this is a non-documented opinion). But Betelegeuse being a lot closer than the current detected sources of Gravitational Waves, this might be an interesting target indeed (although, see first point...)

> **Comments:**
> **username_7**: Since Betelgeuse is about 700 light years away, it conceivably *could* have gone supernova well before LIGO became operational (or was even imagined), say 350 years ago? And we won't know until 700 years after it "actually" happened. (Ignoring relativistic concerns about simultaneity. I'm positing a useful reference frame that includes both the Sun and Betelgeuse close to relative rest.)  
> **username_8**: It would be a little better to be clear that we don't have a telescopic observation of first light from SN1987A to compare with the neutrino observations, so the delay you quote is very much an informed guess.  
> **username_9**: I'd be a *little* bit cautious about saying that the current dimming is due to the confluence of "two periodic variations", largely because of the uncertainty in the long-term behavior - although yes, I agree with downplaying the pre-supernova hypothesis.  
> **username_10**: @username_9: The telegram cited by this answer seems to well document the two periodic variations by citing 25 years of data. That seems a lot more convincing than any other explanation so far.  
> **username_9**: @username_10 I'm certainly not arguing with that; I'm just saying that phrasing like "appears to be" rather than "is" would probably be more exact; though it's the most convincing, we don't know for sure.  
> **username_11**: @username_7 If Betelgeuse is exactly 700 light years away and went supernova exactly 350 years ago, we will detect the gravitational waves from it in exactly 350 years because gravitational waves travel at the speed of light.  
> **username_7**: @username_11 Exactly. I wrote my comment because this answer had written "LIGO is already operational" as if it were a rebuttal of the part of OP's original question that (before editing) read "Assuming that Betelgeuse did not go supernova before LIGO became operational."  
> **username_11**: @username_7 I think it's safe to say that all events detected by LIGO happened before it was built since building commenced 25 years ago and there are no objects we know of within 25 light years that could cause a detectable event.  

---

