<p>Gravitational waves cannot be part of dark energy, because -- just like electromagnetic waves -- their energy density dilutes as the universe expands: both due to the simple expansion of space <em>and</em> due to the cosmological redshifting that the expansion produces.</p>

<p><a href="https://en.wikipedia.org/wiki/Dark_energy" rel="nofollow noreferrer">Dark energy</a>, on the other hand, has an energy density that remains <em>constant</em> as the universe expands (truly constant if it's the cosmological constant, very close to constant if it's something stranger like quintessence), so it can't be made up of GWs.</p>

<p>GWs probably don't contribute much to the energy density we attribute to dark <em>matter</em>, either, since dark matter is diluted by the cosmological expansion but <em>not</em> by redshift. So if the energy density attributed to DM ten billion years ago were due to GWs, then it would be significantly lower than the DM energy density we measure today. (Also, current cosmological observations indicate significant dark matter was present very early in the universe, <em>before</em> the star formation that was necessary to create binary black holes in the first place.)</p>

<p>The GW energy from a binary-black-hole merger <em>is</em> enormous, yes; but those are very rare events. The current estimate from LIGO observations is about 50 or 100 such mergers per year per cubic gigaparsec, which translates into a rate of less than one per million years per galaxy. <a href="https://arxiv.org/abs/1710.05837" rel="nofollow noreferrer">This paper by the LIGO and Virgo Collaborations</a> has estimates of the current GW energy density in units of the current energy density of the universe (their Figure 1): </p>

<p><a href="https://i.sstatic.net/xxpt1.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/xxpt1.png" alt="enter image description here"></a></p>

<p>The green curve shows the estimated energy density from binary-black-hole mergers as a function of the frequency of the GWs; the red curve shows the contribution from binary-neutron-star mergers. The combined peak is always less than <span class="math-container">$10^{-8}$</span> of the critical energy density, so even summing up over frequencies, we have an energy density much smaller than that due to ordinary matter (<span class="math-container">$\Omega \sim 5$</span>%), so it's probably safe to ignore its effects. </p>

CC BY-SA 4.0
2019-03-26T02:10:46.380Z
Sounds, tyvm for the detailed answer.
ShloEmi
CC BY-SA 4.0
2019-03-26T07:51:21.863Z
What I wanted to say in my comment to Q is that ultimately GW are due to mass, is kind of gravity redistribution. So basically is accounted for by the mass. (Independently of the fraction of mass energy it represent, it seems to me a release of gravitational energy, so it would not cause expansion any way). Does this make sense?
Alchimista
CC BY-SA 4.0
2019-03-25T13:43:45.600Z
2019-03-25T13:58:26.030Z
2019-03-25T13:58:26.030Z
Peter Erwin
<p>Do the current models of the universe consider the energy release of gravitational waves?</p>

<p>E.g. iirc, the last black hole merger detected had a gravitational wave energy equal to ~3 solar masses (hope I'm not mistaken in this fact).</p>

<p>Same for other mergers, and supernovae: the energy related to their gravitational waves should sum up to something.</p>

CC BY-SA 4.0
2019-03-21T08:34:26.993Z
Interesting. But I suspect it is already accounted for  by the baryonic term of mass.
Alchimista
CC BY-SA 4.0
2019-03-23T15:15:38.693Z
Might, but i'm almost sure this is pure energy, not barionic one.
ShloEmi
CC BY-SA 4.0
2019-03-23T15:54:23.497Z
In a merger, mass is involved.  I have just made a drastic assumption, like "no mass no grav. waves".  Like a kind of potential inherent to the baryonic mass present in the universe
Alchimista
CC BY-SA 4.0
2019-03-24T11:49:00.803Z
Well, regarding pure energy (lol) it’s all an illusion, matter is energy and vice-versa, so I might be wrong, just curious if it was counted.
ShloEmi
CC BY-SA 4.0
2019-03-24T11:50:21.537Z
You could try Physics SE.
Alchimista
CC BY-SA 4.0
2019-03-24T11:52:39.950Z
TY, but I don't think it's physics question, because it's related to the big-scale of astro-physics == Astronomy.
ShloEmi
CC BY-SA 4.0
2019-03-24T11:56:41.157Z
Is totally physics! Google also for "Feynmann rings on a rod gravitational waves" or so, as for he speaks about doing work with GW. Wheter thet energy is coming from, its origin could be mentioned.
Alchimista
CC BY-SA 4.0
2019-03-24T13:32:06.790Z
TY again  @Alchimista , can please give a direct reference?
ShloEmi
CC BY-SA 4.0
2019-03-24T17:12:02.653Z
https://en.m.wikipedia.org/wiki/Sticky_bead_argument  dig around
Alchimista
CC BY-SA 4.0
2019-03-26T02:24:00.183Z
Thats a big article to dig, ty
ShloEmi
<black-hole><supermassive-black-hole><gravitational-waves><dark-energy>
Are gravitational waves part of dark energy?
ShloEmi
# Are gravitational waves part of dark energy?

(Asked by: username_0 on 2019-03-21)

Do the current models of the universe consider the energy release of gravitational waves?

E.g. iirc, the last black hole merger detected had a gravitational wave energy equal to ~3 solar masses (hope I'm not mistaken in this fact).

Same for other mergers, and supernovae: the energy related to their gravitational waves should sum up to something.

**Tags:** black-hole, supermassive-black-hole, gravitational-waves, dark-energy
> **Comments:**
> **username_1**: Interesting. But I suspect it is already accounted for  by the baryonic term of mass.  
> **username_0**: Might, but i'm almost sure this is pure energy, not barionic one.  
> **username_1**: In a merger, mass is involved.  I have just made a drastic assumption, like "no mass no grav. waves".  Like a kind of potential inherent to the baryonic mass present in the universe  
> **username_0**: Well, regarding pure energy (lol) it’s all an illusion, matter is energy and vice-versa, so I might be wrong, just curious if it was counted.  
> **username_1**: You could try Physics SE.  
> **username_0**: TY, but I don't think it's physics question, because it's related to the big-scale of astro-physics == Astronomy.  
> **username_1**: Is totally physics! Google also for "Feynmann rings on a rod gravitational waves" or so, as for he speaks about doing work with GW. Wheter thet energy is coming from, its origin could be mentioned.  
> **username_0**: TY again  @Alchimista , can please give a direct reference?  
> **username_1**: https://en.m.wikipedia.org/wiki/Sticky_bead_argument  dig around  
> **username_0**: Thats a big article to dig, ty  

---

## 1 answers

### Answer by username_2 on 2019-03-25. Score: 1 | Accepted answer

Gravitational waves cannot be part of dark energy, because -- just like electromagnetic waves -- their energy density dilutes as the universe expands: both due to the simple expansion of space *and* due to the cosmological redshifting that the expansion produces.

[Dark energy](https://en.wikipedia.org/wiki/Dark_energy), on the other hand, has an energy density that remains *constant* as the universe expands (truly constant if it's the cosmological constant, very close to constant if it's something stranger like quintessence), so it can't be made up of GWs.

GWs probably don't contribute much to the energy density we attribute to dark *matter*, either, since dark matter is diluted by the cosmological expansion but *not* by redshift. So if the energy density attributed to DM ten billion years ago were due to GWs, then it would be significantly lower than the DM energy density we measure today. (Also, current cosmological observations indicate significant dark matter was present very early in the universe, *before* the star formation that was necessary to create binary black holes in the first place.)

The GW energy from a binary-black-hole merger *is* enormous, yes; but those are very rare events. The current estimate from LIGO observations is about 50 or 100 such mergers per year per cubic gigaparsec, which translates into a rate of less than one per million years per galaxy. [This paper by the LIGO and Virgo Collaborations](https://arxiv.org/abs/1710.05837) has estimates of the current GW energy density in units of the current energy density of the universe (their Figure 1):

[![enter image description here](https://i.sstatic.net/xxpt1.png)](https://i.sstatic.net/xxpt1.png)

The green curve shows the estimated energy density from binary-black-hole mergers as a function of the frequency of the GWs; the red curve shows the contribution from binary-neutron-star mergers. The combined peak is always less than $10^{-8}$ of the critical energy density, so even summing up over frequencies, we have an energy density much smaller than that due to ordinary matter ($\Omega \sim 5$%), so it's probably safe to ignore its effects.

> **Comments:**
> **username_0**: Sounds, tyvm for the detailed answer.  
> **username_1**: What I wanted to say in my comment to Q is that ultimately GW are due to mass, is kind of gravity redistribution. So basically is accounted for by the mass. (Independently of the fraction of mass energy it represent, it seems to me a release of gravitational energy, so it would not cause expansion any way). Does this make sense?  

---

